Structured oxidation catalysts - Patent Application 20050239643

Title:

Structured oxidation catalysts

Document Type and Number:

United States Patent Application 20050239643

Kind Code:

Abstract:

Structured catalysts useful for oxidizing alkanes, alkenes and combinations of alkanes and alkenes are described. The structure catalysts comprise one or more mixed metal oxide catalysts having a three dimensional structure that is self-supporting and that facilitates movement of gas phase reactants and products and one or more mixed metal oxide catalysts deposited on a three dimensional form of continuous unitary structures having openings that facilitates movement of gas phase reactants and products.

Inventors:

Benderly, Abraham (Elkins Park, PA, US)
Gaffney, Anne Mae (West Chester, PA, US)
Han, Scott (Lawrenceville, NJ, US)
Maroldo, Stephen Gerard (Ambler, PA, US)

Plaque It!

Sponsored by:
Flash of Genius

Application Number:

11/112225

Publication Date:

10/27/2005

Filing Date:

04/22/2005

View Patent Images:

Images are available in PDF form when logged in. To view PDFs, Login or Create Account (Free!)

Export Citation:

Click for automatic bibliography generation

Primary Class:

502/312

International Classes:

(IPC1-7): B01J023/00

Attorney, Agent or Firm:

ROHM AND HAAS COMPANY;PATENT DEPARTMENT (100 INDEPENDENCE MALL WEST, PHILADELPHIA, PA, 19106-2399, US)

Claims:

1. A structured catalyst comprising: one or more mixed metal oxide catalysts, each catalyst sequentially deposited as essential elements, in random order, the relative amounts of elements satisfying the expression
MoV_aNb_bX_cZ_dO_n wherein X is at least one element selected from the group consisting of Te and Sb, Z is at least one element selected from the group consisting of W, Cr, Ta, Ti, Zr, Hf, Mn, Re, Fe, Ru, Co, Rh, Ni, Pd, Pt, Ag, Zn, B, Al, Ga, In, Ge, Sn, Si, Pb, P, Bi, Y, Ce, rare earth elements and alkaline earth elements, 0.1≦a≦1.0, 0.01≦b≦1.0, 0.01≦c≦1.0, 0≦d≦1.0 and n is determined by the oxidation states of the other elements; wherein the one or more metal oxide catalysts are self-supporting and further comprise a three dimensional structure having openings that facilitates movement of gas phase reactants and products.

2. The structured catalyst according to claim 1, wherein the one or more mixed metal catalysts are deposited by chemical vapor deposition, physical vapor deposition and combinations thereof, resulting in a porous catalyst.

3. A structured catalyst comprising: one or more mixed metal oxide catalysts, each catalyst satisfying the expression
MoV_aNb_bX_cZ_dO_n wherein X is at least one element selected from the group consisting of Te and Sb, Z is at least one element selected from the group consisting of W, Cr, Ta, Ti, Zr, Hf, Mn, Re, Fe, Ru, Co, Rh, Ni, Pd, Pt, Ag, Zn, B, Al, Ga, In, Ge, Sn, Si, Pb, P, Bi, Y, Ce, rare earth elements and alkaline earth elements, 0.1≦a≦1.0, 0.01≦b≦1.0, 0.01≦c≦1.0, 0≦d≦1.0 and n is determined by the oxidation states of the other elements, in contact with a three dimensional form of continuous unitary structures having openings that facilitate movement of gas phase reactants and products; wherein the three dimensional form of continuously unitary structures comprise ceramic foams and ceramic monoliths selected from the group consisting of cordierite, alumina, zirconia, silica, aluminosilicate zeolites, phosphosilicate zeolites, other zeolites and combinations thereof, and wherein the one or more mixed metal oxide catalysts are deposited on the ceramic foams and ceramic monoliths by methods selected from the group consisting of impregnation, wash coating, slurry dip-coating, chemical vapor deposition, physical vapor deposition, precipitation and combinations thereof.

4. The structured catalysts according to claims 1 or 3, wherein the structured catalysts are fabricated in the form of a microreactor or arrays of microreactors having mechanically produced openings selected from the group consisting of pores, cells, channels, and other narrow passages.

5. A modified structured catalyst comprising: one or more mixed metal oxide catalysts, each catalyst sequentially deposited as essential elements, in random order, the relative amounts of elements satisfying the expression
MoV_aNb_bX_cZ_dO_n wherein X is at least one element selected from the group consisting of Te and Sb, Z is at least one element selected from the group consisting of W, Cr, Ta, Ti, Zr, Hf, Mn, Re, Fe, Ru, Co, Rh, Ni, Pd, Pt, Ag, Zn, B, Al, Ga, In, Ge, Sn, Si, Pb, P, Bi, Y, Ce, rare earth elements and alkaline earth elements, 0.1≦a≦1.0, 0.01≦b≦1.0, 0.01≦c≦1.0, 0≦d≦1.0 and n is determined by the oxidation states of the other elements; wherein the modified catalyst is self-supporting and further comprises a three dimensional structure having openings that facilitates movement of gas phase reactants and products; and wherein at least one catalyst is modified using one or more chemical treatments, one or more physical treatments and one or more combinations of chemical and physical treatments.

6. The modified structured catalysts of claim 5 wherein one or more modified mixed metal catalysts are deposited on a three dimensional form of continuously unitary structures comprising ceramic foams and ceramic monoliths, selected from the group consisting of cordierite, alumina, zirconia, silica, aluminosilicate zeolites, phosphosilicate zeolites, other zeolites and combinations thereof, by methods selected from the group consisting of impregnation, wash coating, slurry dip-coating, chemical vapor deposition, physical vapor deposition, precipitation and combinations thereof.

7. A process for improving one or more performance characteristics of one or more mixed metal oxide catalysts, comprising the steps of: a) depositing one or more metal oxide catalysts as a self-supporting structured catalyst or on a three dimensional form of continuous unitary structures having openings that facilitate movement of gas phase reactants and products; and optionally b) treating the structured catalyst with one or more chemical treatments, one or more physical treatments and one or more combinations of chemical and physical treatments.

8. A process for preparing a structured catalyst comprising the step of depositing one or more mixed metal oxide catalysts, each catalyst deposited as essential elements in random order satisfying the expression
MoV_aNb_bX_cZ_dO_n wherein X is at least one element selected from the group consisting of Te and Sb, Z is at least one element selected from the group consisting of W, Cr, Ta, Ti, Zr, Hf, Mn, Re, Fe, Ru, Co, Rh, Ni, Pd, Pt, Ag, Zn, B, Al, Ga, In, Ge, Sn, Si, Pb, P, Bi, Y, Ce rare earth elements and alkaline earth elements, 0.1≦a≦1.0, 0.01≦b≦1.0, 0.01≦c≦1.0, 0≦d≦1.0 and n is determined by the oxidation states of the other elements, wherein the structured catalyst produced is self-supporting and facilitates movement of gas phase reactants and products or by depositing the one or more mixed metal oxide catalysts on a three dimensional form of continuous unitary structures having openings that facilitate movement of gas phase reactants and products.

9. A process for producing C₂-C₈oxygenates, including C₂-C₈unsaturated carboxylic acids, which comprises the step of contacting a corresponding alkane, alkene or a mixture of corresponding alkane and alkene to a vapor phase catalytic oxidation reaction with a structured catalyst comprising one or more mixed metal oxide catalysts; wherein yield and selectivity of the oxygenates, including unsaturated carboxylic acids, is improved using the structured catalyst as compared to the one or more corresponding unmodified mixed metal oxide catalysts.

10. A process for producing C₂-C₈oxygenates, including C₂-C₈unsaturated carboxylic acids, which comprises the steps of: a) modifying a structured catalyst comprising one or more mixed metal oxides using one or more chemical treatments, one or more physical treatments and one or more combinations of chemical and physical treatments; and b) contacting a corresponding alkane, alkene or a mixture of corresponding alkane and alkene to a vapor phase catalytic oxidation reaction with the modified structured catalyst; wherein yield and selectivity of the oxygenates, including unsaturated carboxylic acids, is improved using the one or more modified structured catalysts as compared to the one or more corresponding unmodified structured catalysts.

Description:

The present invention relates to the preparation and use of structured catalysts for catalytically converting alkanes, alkenes and mixtures thereof to their corresponding oxygenates, including unsaturated carboxylic acids and esters thereof, by vapor phase oxidation. In particular, the invention is directed to preparation of such catalysts in three-dimensional forms that provide improved thermal stability, improved thermal integration and improved mass transfer coupled with reduced pressure drop during specific catalytic conversions of alkanes, alkenes and mixtures thereof. In addition, the invention includes one or more chemical and/or physical modifications of structured catalysts, which in turns improves their efficiency and selectivity for converting alkanes, alkenes and mixtures thereof to their corresponding oxygenates. The invention is further directed to methods for preparing structured catalysts and to vapor phase catalytic processes using the structured catalysts, including catalytic oxidations of alkanes, alkenes and mixtures thereof.

The selective partial oxidation of alkenes to unsaturated carboxylic acids and their corresponding esters is an important commercial process. However, the selective and efficient partial oxidation/dehydrogenation of alkanes to products including olefins, unsaturated carboxylic acids and esters of unsaturated carboxylic acids using conventional fixed bed reactors have significant disadvantages, including high pressure drop in the catalyst bed, inadequate mass transfer during catalysis, and thermal instability of the catalyst; all which contribute to the resulting non-uniform access of reactants to the catalyst, non-uniformity of the catalytic surface and non-optimal local process conditions. An unsatisfactory product distribution results as a consequence.

International Patent Publication No. WO 99/55459 discloses a exhaust gas catalytic converter comprising a monolithic catalyst in the form of a honeycomb having a plurality of parallel channels defined by the honeycomb walls. The catalyst has different zones along the length of the channels, each zone defined by their coating or lack of a coating, and the zone extend for a length of the channel in which there is the same coating and architecture. Moreover, soluble components in the coating compositions are fixed in their respective zones. Unfortunately, there are a number of limitations associated with such layered catalyst composites. One inherent limitation of the catalysts is that they are designed for three way conversions (TWC), namely three different types of catalytic conversions, the reduction of nitrogen oxides to nitrogen, the oxidation of carbon monoxide to carbon dioxide and the oxidation of hydrocarbons. In addition to the inherent non-optimal distributions of different products, there are other limitations including pressure drop in the catalyst bed and inadequate mass transfer during catalysis. The latter issue is particularly of concern when the catalyst comprises mixed metal oxides and when the catalytic conversion include multiple conversions, such as the conversion of alkanes to their corresponding oxygenates. One impediment to the provision of a commercially viable process for such catalytic oxidations is the identification of an optimal structured catalyst, structured catalysts or structured catalyst system, processed and/or prepared in three-dimensional forms that provide improved thermal stability, improved thermal integration and improved mass transfer coupled with reduced pressure drop during specific catalytic conversions of alkanes, alkenes and mixtures thereof. Such structured catalysts would provide improved alkane/alkene conversions and product selectivities, which in turn provides increased yields of corresponding unsaturated products.

The inventors have discovered structured catalysts useful for converting alkanes, alkenes and mixtures thereof to their corresponding oxygenates. The structured catalysts, prepared from both mixed metal oxide catalysts and modified mixed metal oxide catalysts are processed in to three-dimensional forms that provide improved thermal stability, improved thermal integration and improved mass transfer coupled with reduced pressure drop during specific catalytic conversions of alkanes, alkenes and mixtures thereof. Inventors have further discovered that one or more chemical, physical and combinations of chemical and physical modifications to the structured catalysts results in unexpected improvements in alkane/alkene conversions, product selectivities and yields of oxygenates as compared to corresponding unmodified structured catalysts.

Accordingly, there is provided a structured catalyst comprising: one or more mixed metal oxide catalysts, each catalyst sequentially deposited as essential elements, in random order, the relative amounts of elements satisfying the expression
MoV _aNb _bX _cZ _dO _n
wherein X is at least one element selected from the group consisting of Te and Sb, Z is at least one element selected from the group consisting of W, Cr, Ta, Ti, Zr, Hf, Mn, Re, Fe, Ru, Co, Rh, Ni, Pd, Pt, Ag, Zn, B, Al, Ga, In, Ge, Sn, Si, Pb, P, Bi, Y, Ce, rare earth elements and alkaline earth elements, 0.1≦a≦1.0, 0.01≦b≦1.0, 0.01≦c≦1.0, 0≦d≦1.0 and n is determined by the oxidation states of the other elements; wherein the one or more metal oxide catalysts are self-supported and further comprise a three dimensional structure having openings that facilitates movement of gas phase reactants and products. The structured catalyst is useful for oxidizing alkanes, alkenes and combinations of alkanes and alkenes.

There is also provided a structured catalyst useful for oxidizing alkanes, alkenes and combinations of alkanes and alkenes comprising: one or more mixed metal oxide catalysts in contact with a three dimensional form of continuous unitary structures having openings that facilitates movement of gas phase reactants and products.

According to one embodiment, the structured catalysts are in the form of three-dimensional structures selected from the group consisting of ceramic foams and ceramic monoliths comprising ceramics including cordierite, alumina, zirconia, silica, aluminosilicate zeolites, phosphosilicate zeolites PSZ, and other zeolites, wherein the catalyst or catalysts are present on or inside walls of the openings. The ceramic acts as a support and the catalyst or catalysts are deposited on the surface by coating or are deposited inside the support by methods including impregnation, wash coating, slurry dip-coating, chemical vapor deposition (CVD), physical vapor deposition (PVD) and precipitation. Ceramic foams are prepared by chemical vapor deposition (CVD) and physical vapor deposition (PVD). The foam structures comprise specific numbers of pores per inch. The monoliths comprise specific numbers of cells per inch. The structured catalysts permit high space velocities of reactants and products with a corresponding minimized pressure drop. According to a separate embodiments, the structured catalysts are in the form of three-dimensional structures selected from the group consisting of metallic foams and metallic monoliths, extruded catalysts, membrane catalysts having permeable walls between openings, catalysts arranged in arrays, catalysts having openings including grooves, channels and other passages created by techniques including corrugation, stacking staggering and superimposing, fibrous catalysts, woven catalysts, mesh catalysts, non-woven catalysts, multi-layered catalysts joined together by a thermally conductive connection and coated with an oxidation barrier, perforated ceramic and metallic disks, microreactor catalysts wherein the catalysts is fabricated as a microreactor, structured composite catalysts containing combinations of three-dimensional structures, and modified structured catalysts wherein the structured catalysts undergoes one or more chemical, physical or combinations of chemical and physical treatments modifying the structured catalyst as compared to the unmodified structured catalysts.

The present invention also provides a process for improving one or more performance characteristics of one or more mixed metal oxide catalysts comprising the step of: preparing one or more metal oxide catalysts as a self supporting structured catalyst that facilitates movement of gas phase reactants and products or depositing one or more mixed metal oxide catalysts on a three dimensional form of continuous unitary structures having openings that facilitates movement of gas phase reactants and products; wherein catalyst performance characteristics of the structured catalyst is improved as compared to corresponding performance characteristics of the one or more unstructured (unmodified) mixed metal oxide catalysts. According to one embodiment, the structured catalyst unexpectedly provides improved selectivities and yields of oxygenates including unsaturated carboxylic acids from their corresponding alkanes, alkenes and combinations of corresponding alkanes and alkenes at constant alkane/alkene conversion as compared to corresponding unstructured mixed metal oxide catalysts.

The present invention also provides a process for improving one or more performance characteristics of one or more mixed metal oxide catalysts, comprising the steps of:

- a) preparing one or more metal oxide catalysts into a structured catalyst that facilitates movement of gas phase reactants and products or depositing one or more mixed metal oxide catalyst on a three dimensional form of continuous unitary structures having openings that facilitates movement of gas phase reactants and products; and
- b) treating the structured catalyst with one or more chemical treatments, one or more physical treatments and one or more combinations of chemical and physical treatments;
  wherein catalyst performance characteristics of the modified structured catalysts is improved as compared to corresponding performance characteristics of the one or more unmodified structured catalyst. According to one embodiment, the modified structured catalyst unexpectedly provides improved selectivities and yields of oxygenates including unsaturated carboxylic acids from their corresponding alkanes, alkenes and corresponding combinations of alkanes and alkenes at constant alkane/alkene conversion as compared to the corresponding unmodified structured catalyst.

The invention also provides a process for preparing a structured catalyst comprising the step of: preparing a three dimensional form of continuous unitary structures having openings that is self supporting and facilitates movement of gas phase reactants and products by sequentially depositing a catalyst composition comprising one or more mixed metal oxides, in random order, as essential elements. According to one embodiment, the structured catalysts are in the form of three-dimensional structures selected from the group consisting of ceramic foams and ceramic monoliths comprising ceramics including cordierite, alumina, zirconia, silica, aluminosilicate zeolites, phosphosilicate zeolites PSZ, and other zeolites, wherein the catalyst or catalysts are present on or inside walls of the openings. The ceramic acts as a support and the catalyst or catalysts are deposited on the surface by coating or are deposited inside the support by methods including impregnation, wash coating, slurry dip-coating, chemical vapor deposition (CVD), physical vapor deposition (PVD) and precipitation. Ceramic foams are prepared by chemical vapor deposition (CVD) and physical vapor deposition (PVD). The foam structures comprise specific numbers of pores per inch. The monoliths comprise specific numbers of cells per inch. The structured catalysts permit high space velocities of reactants and products with a corresponding minimized pressure drop. According to a separate embodiments, the structured catalysts are in the form of three-dimensional structures selected from the group consisting of metallic foams and metallic monoliths, extruded catalysts, membrane catalysts having permeable walls between openings, catalysts arranged in arrays, catalysts having openings including grooves, channels and other passages created by techniques including corrugation, stacking staggering and superimposing, fibrous catalysts, woven catalysts, mesh catalysts, non-woven catalysts, multi-layered catalysts joined together by a thermally conductive connection and coated with an oxidation barrier, perforated ceramic and metallic disks, microreactor catalysts wherein the catalysts is fabricated as a microreactor, structured composite catalysts containing combinations of three-dimensional structures, and modified structured catalysts wherein the structured catalysts undergoes one or more chemical, physical or combinations of chemical and physical treatments modifying the structured catalyst as compared to the unmodified structured catalysts.

The invention also provides a process for preparing one or more structured catalysts, comprising the steps of:

- a) providing a catalyst support;
- b) sequentially depositing on the catalyst support a catalyst composition comprising, in random order, as essential elements, at least one layer comprising Mo, at least one layer comprising V, at least one layer comprising Te, and at least one layer comprising X, wherein X is at least one element selected from the group consisting of Nb, Ta, W, Ti, Al, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pd, Pt, Sb, Bi, B, In and Ce, to form a loaded support, said sequential vapor deposition providing relative amounts of said elements such that, after a calcination of said loaded support, the relative amounts of the elements satisfy the expression
  Mo _aV _bTe _cX _d
- wherein a, b, c and d are the relative atomic amounts of the essential elements Mo, V, Te and X, respectively, and, when a=1, b=0.01 to 1.0, c=0.01 to 1.0 and d=0.01 to 1.0; and
- c) calcining said loaded support.

The present invention also provides a process for producing C2-C8 oxygenates, including C2-C8 unsaturated carboxylic acids, which comprises the step of contacting a corresponding alkane, alkene or a mixture of corresponding alkane and alkene to a vapor phase catalytic oxidation reaction with one or more structured catalysts comprising one or more mixed metal oxides; wherein yield and selectivity of the oxygenates, including unsaturated carboxylic acids, is improved using the one or more structured catalysts as compared to the one or more corresponding unmodified mixed metal oxide catalysts.

The present invention also provides a process for producing C2-C8 oxygenates, including C2-C8 unsaturated carboxylic acids, which comprises the steps of:

- a) modifying one or more structured catalysts comprising one or more mixed metal oxides using one or more chemical treatments, one or more physical treatments and one or more combinations of chemical and physical treatments; and
- b) contacting a corresponding alkane, alkene or a mixture of corresponding alkane and alkene to a vapor phase catalytic oxidation reaction with one or more the modified structured catalysts comprising one or more mixed metal oxides; wherein yield and selectivity of the oxygenates, including unsaturated carboxylic acids, is improved using the one or more modified structured catalysts as compared to the one or more corresponding unmodified structured catalysts.

The invention also provides a process for preparing unsaturated carboxylic acids from corresponding alkanes, alkenes, or corresponding alkanes and alkenes, the process comprising the step of:

- passing a gaseous alkane, alkene or alkane and alkene, and molecular oxygen to a reactor, the reactor including one or more structured catalysts, including modified structured catalysts, cumulatively effective at converting the gaseous alkane, alkene, or alkane and alkene to its corresponding gaseous unsaturated carboxylic acid; wherein the reactor is operated at a temperature of from 100° C. to 600° C. According to one embodiment, one or more structured catalysts comprising one or more mixed metal oxides, including modified mixed metal oxides, are used and a conventional reactor is used with the alkane or alkane and alkene having a reactor residence time of greater than 100 milliseconds. According to a separate embodiment, a short contact time reactor is used with the alkane or alkane and alkene having a reactor residence time of no greater than 100 milliseconds.

The structured catalyst comprises one or more modified mixed metal oxide catalysts having the empirical formula:
MoV _aNb _bX _cZ _dO _n
wherein X is at least one element selected from the group consisting of Te and Sb, Z is at least one element selected from the group consisting of W, Cr, Ta, Ti, Zr, Hf, Mn, Re, Fe, Ru, Co, Rh, Ni, Pd, Pt, Ag, Zn, B, Al, Ga, In, Ge, Sn, Pb, P, Bi, Y, rare earth elements and alkaline earth elements, 0.1≦a≦1.0, 0.01≦b≦1.0, 0.01≦c≦1.0, 0≦d≦1.0; n is determined by the oxidation states of the other elements According to one embodiment, the structured catalyst comprises one or more modified mixed metal oxide catalysts having the empirical formula:
M _eMoV _aNb _bX _cZ _dO _n
wherein M _eis at least one or more chemical modifying agents, X is at least one element selected from the group consisting of Te and Sb, Z is at least one element selected from the group consisting of W, Cr, Ta, Ti, Zr, Hf, Mn, Re, Fe, Ru, Co, Rh, Ni, Pd, Pt, Ag, Zn, B, Al, Ga, In, Ge, Sn, Pb, P, Bi, Y, rare earth elements and alkaline earth elements, 0.1≦a≦1.0, 0.01≦b≦1.0, 0.01≦c≦1.0, 0≦d≦1.0 and n, e are determined by the oxidation states of the other elements.

As used herein, the term “structured catalyst” refers to any catalyst, including mixed metal oxide catalysts, prepared and or fabricated in to in a three dimensional form of continuous unitary structures having openings that facilitate movement of gas phase reactants and products. The term “modified structured catalyst” which is equivalent to “treated structured catalysts” which is also equivalent to “post-treated structured catalysts” refers to any chemical, physical and combinations of chemical and physical modification or modifications of one or more structured catalysts as compared to corresponding structured catalysts having undergone no such modification or modifications (also referred to as unmodified structured catalysts, equivalently referred to as untreated structured catalysts). Modifications to structured catalysts include, but are not limited to, any differences in the modified structured catalysts as compared to corresponding unmodified structured catalysts. Suitable modifications to structured catalysts include, for example, structural changes, spectral changes (including position and intensity of characteristic X-ray diffraction lines, peaks and patterns), spectroscopic changes, chemical changes, physical changes, compositional changes, changes in physical properties, changes in catalytic properties, changes in performance characteristics in conversions of organic molecules, changes in yields of organic products from corresponding reactants, changes in catalyst activity, changes in catalyst selectivity and combinations thereof. This includes one or more chemical modifying agents, one or more physical processes and combinations of one or more chemical modifying agents and one or more physical processes.

As used herein, the term “modified catalyst” which is equivalent to “treated catalysts” which is also equivalent to “post-treated catalysts” refers to any chemical, physical and combinations of chemical and physical modification or modifications of one or more prepared catalysts as compared to corresponding catalysts having undergone no such modification or modifications (also referred to as unmodified catalysts, equivalently referred to as untreated catalysts). The term is described and defined in co-pending U.S. Provisional Application Ser. No. 60/523,297. This includes one or more chemical modifying agents (e.g. a reducing agent such as an amine), one or more physical processes (e.g. mechanical grinding at cryogenic temperatures also referred to as “cryo-grinding”) and combinations of one or more chemical modifying agents and one or more physical processes. The term “cryo” in front of any treatment term refers to any treatment that occurs with cooling, under freezing temperatures, at cryogenic temperatures and any use of cryogenic fluids. Suitable cryogenic fluids include, but are not limited to for example, any conventional cryogens and other coolants such as chilled water, ice, compressible organic solvents such as freons, liquid carbon dioxide, liquid nitrogen, liquid helium and combinations thereof. Suitable chemical and physical modification of prepared (untreated) catalysts results in unexpected improvements in treated catalyst efficiency and selectivity in alkane, alkene or alkane and alkene oxidations as compared to corresponding untreated catalysts and improved yields of oxygenated products using modified catalysts using modified catalysts as compared to unmodified catalysts. The term prepared catalysts refers to unmodified catalysts. The prepared catalysts are obtained from commercial sources or are prepared by conventional preparative methods, including methods described herein. The term “treated catalysts” and “modified catalysts” does not refer to or include regenerated, reconditioned and recycled catalysts. The term conditioning refers to conventional heating of prepared metal oxide catalysts with gases including hydrogen, nitrogen, oxygen and selected combinations thereof.

As used herein, the term “cumulatively converting” refers producing a desired product stream from one or more specific reactants using one or more modified catalysts and modified catalyst systems of the invention under specific reaction conditions. As an illustrative example, cumulatively converting an alkane to its corresponding unsaturated carboxylic acid means that the modified catalyst(s) utilized will produce a product stream comprising the unsaturated carboxylic acid corresponding to the added alkane when acting on a feed stream(s) comprising the alkane and molecular oxygen under the designated reaction conditions.

As used herein, mixed metal oxide catalyst refers to a catalyst comprising more than one metal oxide. The term “catalytic system” refers to two or more catalysts. For example, platinum metal and indium oxide impregnated on an alumina support defines both a catalytic system and a mixed metal oxide catalyst. Yet another example of both is palladium metal, vanadium oxide and magnesium oxide impregnated on silica.

Accordingly, structured catalysts of the present invention are utilized for oxidizing alkanes, alkenes and combinations of alkanes and alkenes. Any structured catalyst of this type that is prepared and or fabricated into a three dimensional form of continuous unitary structures having openings that facilitate movement of gas phase reactants and products is useful in accordance with the invention. The openings are physical features that facilitates movement of gas phase reactants and products during catalytic conversions of carbon containing molecules. One advantage of structured catalysts is that they permit high space velocities of reactants and products with a corresponding minimized pressure drop as compared to unmodified catalysts and catalysts having random orientations of catalysts particles.

Suitable structured catalysts include, but are not limited to for example, monolithic catalysts comprising continuous unitary structures including many openings selected from pores, cells, channels, and other narrow passages, membrane catalysts having wall structures that are permeable in addition to openings; arranged catalysts comprising unitary structures ordered in arrays and other patterns; and composite structures prepared and or fabricated from combinations thereof. In monolithic catalysts, the openings are uniform and are oriented in a regular patterns, including straight, angular, zig-zag patterns and irregular patterns. The cross-section of the monolithic catalysts openings reveals ordered patterns, including but not limited to honeycomb structures. Catalysts are dispersed uniformly over the global repeating structure of the monolith, are deposited within the layer of materials that comprise the walls of the openings structure. Monoliths comprise both ceramics, including both metal oxide and non-metal oxide ceramics, and metals. In membrane catalysts the wall structures comprises uniform and non-uniform arrangements of features providing wall permeability. Catalysts are dispersed uniformly on the wall structures or in the wall structures. Arranged catalysts are oriented in directions of the flow of reactants and products, including perpendicular to the direction of reactant/product flow.

Suitable monolithic catalysts of the invention comprise structured catalysts that are prepared to have three dimensional structures and are self-supported and structured catalysts including one or more catalysts and a catalytic support. Suitable examples of the former monolithic catalysts include, but are not limited to for example, ceramic foams prepared from CVD or PVD of metal oxides resulting in a self-supported structured catalyst comprising one or more mixed metal oxides and one or more mixed metal oxides foams or monoliths fabricated in the form of a microreactor or arrays of microreactors having mechanically produced openings (referred to as cells) selected from pores, cells, channels, and other narrow passages. The foams structures include from 30 to 150 openings per inch. The monolithic structures include from 200 to 800 cells per inch. Suitable examples of the latter monolithic catalysts include, but are not limited to for example, ceramic foams and ceramic monoliths comprising ceramic supports including, but not limited to for example, cordierite, alumina, zirconia, silica, aluminosilicate zeolites, phosphosilicate zeolites PSZ, and other zeolites, wherein the catalyst or catalysts are present on or inside walls of the openings. The catalyst or catalysts are deposited on the surface of the support or are deposited inside the support. The catalyst or catalysts are deposited on the surface by coating or are deposited inside the support by methods including, but not limited to for example, impregnation, wash coating, slurry dip-coating, chemical vapor deposition (CVD), physical vapor deposition (PVD) and precipitation. Other suitable examples of the latter monolithic catalysts include, but are not limited to for example, metallic foams and metallic monoliths, extruded catalysts wherein the extrudate has a regular structure, catalysts having openings including grooves, channels and other passages created by techniques including corrugation, stacking staggering and superimposing, perforated ceramic and metallic disks, microreactor catalysts wherein the catalysts is fabricated as a microreactor, structured composite catalysts containing combinations of three-dimensional structures, and modified structured catalysts wherein the structured catalysts undergoes one or more chemical, physical or combinations of chemical and physical treatments modifying the structured catalyst as compared to the unmodified structured catalysts.

Suitable membrane catalysts of the invention comprise permeable wall structures in addition to openings formed from the wall structures. Radial mass transport occurs by diffusion through the openings of the wall structures. As a consequence, mass fluxes through the wall structures are often small. Suitable examples of membrane catalysts include, but are not limited to for example, organic membrane having the catalyst or catalysts deposited on or incorporating within the catalyst, inorganic membrane catalysts, including dense membrane catalysts incorporating metals, non-metals and metal oxides, and porous membrane catalysts, both types having the catalyst or catalysts deposited on or incorporating within the catalyst.

Suitable arranged catalysts of the invention comprise unitary structures arranged in arrays and oriented with respect to the direction of reactant/product flow. The arranged structured catalysts provide relatively fast mass transport over the reaction zone, typically oriented perpendicular to the direction of reactant/product flow. Suitable examples of arranged catalysts include, but are not limited to for example, particulate catalysts arranged in arrays, extruded catalysts arranged in arrays, fibrous catalysts, woven catalysts, mesh catalysts, non-woven catalysts, and multi-layered catalysts joined together by a thermally conductive connection and coated with an oxidation barrier.

The structured catalysts of the invention are prepared by conventional methods well known in the art. Methods for making structured catalysts are described by X. Xu and J. A. Moulijn in Chapter 21, pp. 599-615 in “Structured Catalysts and Reactors”, edited by A. Cybulski and J. A. Moulijn, Marcel Dekker, New York (1998). Methods for making catalytic foams are described in U.S. Pat. Nos. 6,103,149; 6,040,266; 5,780,157; 5,283,109; and 5,154,970. Suitable structured catalysts fabricated as a microreactor and structured catalysts having mechanically produced microfeatures are described in International Publication No. WO 03/106386.

Modified structured catalysts are obtained by treating one or more metal oxides with one or more chemical, physical and combinations of chemical and physical treatments or are obtained by preparing structured catalysts from one or more modified mixed metal oxide catalysts.

Chemical treatments, resulting in treated/modified catalysts, include one or more chemical modifying agents. Suitable chemical modifying agents include, but are not limited to for example, oxidizing agents selected from hydrogen peroxide, nitrogen, nitric acid, nitric oxide, nitrogen dioxide, nitrogen trioxide, persulfate; reducing agents selected from amines, pyridine, hydrazine, quinoline, metal hydrides, sodium borohydride, C1-C4 alcohols, methanol, ethanol, sulfites, thiosulfites, aminothiols; combinations of oxidizing agents and reducing agents; acids selected from HCl, HNO3, H2SO4; organic acids, organic diacids, acetic acid, oxalic acid, combinations of C1-C4 alcohols and C1-C4 organic acids, oxalic acid and methanol; inorganic bases selected from NH3, NH4OH, H2NNH2, HONH2, NaOH, Ca(OH)2, CaO, Na2CO3, NaHCO3, organic bases selected from ethanol amine, diethanolamine, triethanolamine; pH adjustments; peroxides selected from inorganic peroxides, H2O2, organic peroxides, tBu2O2; chelating agents, ethylenediamine, ethylenediaminetetraacetic acid (EDTA); electrolysis including electrolytic reduction; treatment with high energy radiation including ultraviolet and X-ray radiation; and combinations thereof.

Physical treatments, resulting in treated/modified catalysts, include one or more physical processes. Suitable physical processes include, but are not limited to for example, cooling, cryogenic cooling, pressure cooling, compacting under pressure, high pressure die pressing, thermolyzing (also referred to as polymer burn off), mechanical grinding at cryogenic temperatures, high shear grinding at cryogenic temperatures, cryo-milling, cryo-densifying, cryo-stressing, cryo-fracturing, cryo-pelletizing, deforming, wash coating, molding, forming, shaping, casting, machining, laminating, drawing, extruding, lobalizing, impregnating, forming spheres (spherolizing or jetting), slurrying, cryo-slurrying, preparing shelled catalysts (shelling), multi-coating, electrolyzing, electrodepositing, compositing, foaming, cryo-fluidizing, cryo-spraying, thermal spraying, plasma spraying, vapor depositing, adsorbing, ablating, vitrifying, sintering, cryo-sintering, fusing, fuming, crystallizing, any altering of catalyst crystal structure, polycrystallizing, recrystallizing, any surface treating of the catalyst, any altering of catalyst surface structure, any altering of catalysts porosity, any altering of catalyst surface area, any altering of catalyst density, any altering of bulk catalysts structure, reducing the particle size of the primary catalyst particles in combination with cooling or thermolyzing the catalyst, and any combinations of chemical and physical treatments, including but not limited to solvent extraction, Soxhlet extraction, batch solvent extraction, continuous flow solvent extraction, extraction in supercritical solvents, contacting the catalyst with one or more leaching agents including solvents, altering catalyst pH, any chemical treatments used in modifying catalyst surface structure, mechanical grinding in supercritical solvents, chemisorbing one or more chemical agents, ultrasonification using one or more solvents selected from organic solvents such as alcohols and amines ultrasonification, and any physical treatments employing solvents under supercritical conditions. According to a separate embodiment, modified catalysts include one or more further chemical and/or physical treatments of already modified catalysts.

Any one or more metal oxide catalysts are usefully modified and used to prepare both structured catalysts and modified structured catalysts utilized in catalytic conversions of molecules containing carbon in accordance with the invention. According to one embodiment, the structured catalysts comprise both unmodified and modified mixed metal oxide catalysts useful for catalytically converting alkanes, alkenes and combinations of alkanes and alkenes to their corresponding oxygenates. The modified structured catalysts are prepared using one or more chemical, physical and combined chemical and physical treatments to provide modified structured catalysts.

According to one embodiment of the invention, suitable prepared catalysts used and modified in accordance with the invention are one or more mixed metal oxide catalysts having a catalyst having the empirical formula
MoV _aNb _bX _cZ _dO _n
wherein X is at least one element selected from the group consisting of Te and Sb, Z is at least one element selected from the group consisting of W, Cr, Ta, Ti, Zr, Hf, Mn, Re, Fe, Ru, Co, Rh, Ni, Pd, Pt, Ag, Zn, B, Al, Ga, In, Ge, Sn, Pb, P, Bi, Y, rare earth elements and alkaline earth elements, 0.1≦a≦1.0, 0.01≦b≦1.0, 0.01≦c≦1.0, 0≦d≦1.0 and n is determined by the oxidation states of the other elements. Preparation of the mixed metal oxide (MMO) catalysts is described in U.S. Pat. Nos. 6,383,978; 6,641,996; 6,518,216; 6,403,525; 6,407,031; 6,407,280; and 6,589,907; U.S. Publication Application No. 20030004379; U.S. Provisional Application Ser. Nos. 60/235,977; 60/235,979; 60/235,981; 60/235,984; 60/235,983; 60/236,000; 60/236,073; 60/236,129; 60/236,143; 60/236,605; 60/236,250; 60/236,260; 60/236,262; 60/236,263; 60/283,245; and 60/286,218; and EP Patent Nos. EP 1 080 784; EP 1 192 982; EP 1 192 983; EP 1 192 984; EP 1 192 986; EP 1 192 987; EP 1 192 988; EP 1 192 982; EP 1 249 274; and EP 1 270 068. The synthesis of such MMO (mixed metal oxide) catalysts is accomplished by several methods well known by those having skill in the art. A precursor slurry of mixed metal salts is first prepared by conventional methods and methods described above that include, but are not limited to for example, rotary evaporation, drying under reduced pressure, hydrothermal methods, co-precipitation, solid-state synthesis, impregnation, incipient wetness, sol gel processing and combinations thereof. After the precursor slurry is prepared it is dried according to conventional drying methods including, but not limited to for example, drying in ovens, spray drying and freeze drying. The dried precursor is then calcined to obtain prepared MMO catalysts using well known techniques and techniques described above to those having skill in the art including, but not limited to for example, flow calcinations, static calcinations, rotary calcinations and fluid-bed calcinations. In some cases the prepared MMO catalysts are further milled to improve their catalytic activity.

It is noted that promoted mixed metal oxides having the empirical formulae Mo _jV _mTe _nNb _yZ _zO _oor W _jV _mTe _nNb _yZ _zO _o, wherein Z, j, m, n, y, z and o are as previously defined, are particularly suitable for use in connection with the present invention. Additional suitable embodiments are either of the aforesaid empirical formulae, wherein Z is Pd. Suitable solvents for the precursor solution include water; alcohols including, but not limited to, methanol, ethanol, propanol, and diols, etc.; as well as other polar solvents known in the art. Generally, water is preferred. The water is any water suitable for use in chemical syntheses including, without limitation, distilled water and de-ionized water. The amount of water present is preferably an amount sufficient to keep the elements substantially in solution long enough to avoid or minimize compositional and/or phase segregation during the preparation steps. Accordingly, the amount of water will vary according to the amounts and solubilities of the materials combined. Preferably, though lower concentrations of water are possible for forming a slurry, as stated above, the amount of water is sufficient to ensure an aqueous solution is formed, at the time of mixing.

According to a separate embodiment of the invention, suitable prepared mixed metal oxide catalysts used and modified in accordance with the invention are one or more promoted mixed metal oxide catalysts having the empirical formula
J _jM _mN _nY _yZ _zO _o
wherein J is at least one element selected from the group consisting of Mo and W, M is at least one element selected from the group consisting of V and Ce, N is at least one element selected from the group consisting of Te, Sb and Se, Y is at least one element selected from the group consisting of Nb, Ta, Ti, Al, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Sb, Bi, B, In, As, Ge, Sn, Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, and Z is selected from the group consisting of Ni, Pd, Cu, Ag and Au; and wherein, when j=1, m=0.01 to 1.0, n=0.01 to 1.0, y=0.01 to 1.0, z=0.001 to 0.1 and o is dependent on the oxidation state of the other elements. Preparation of the mixed metal catalysts is described in U.S. Pat. Nos. 6,383,978; 6,641,996; 6,518,216; 6,403,525; 6,407,031; 6,407,280; and 6,589,907; U.S. Provisional Application Ser. Nos. 60/235,977; 60/235,979; 60/235,981; 60/235,984; 60/235,983; 60/236,000; 60/236,073; 60/236,129; 60/236,143; 60/236,605; 60/236,250; 60/236,260; 60/236,262; 60/236,263; 60/283,245; and 60/286,218; and EP Patent Nos. EP 1 080 784; EP 1 192 982; EP 1 192 983; EP 1 192 984; EP 1 192 986; EP 1 192 987; EP 1 192 988; EP 1 192 982; and EP 1 249 274.

According to a separate embodiment of the invention, suitable prepared catalysts modified and used in accordance with the invention are one or more mixed metal oxide catalysts having the empirical formula
A _aD _bE _cX _dO _e
wherein A is at least one element selected from the group consisting of Mo and W, D is at least one element selected from the group consisting of V and Ce, E is at least one element selected from the group consisting of Te, Sb and Se, and X is at least one element selected from the group consisting of Nb, Ta, Ti, Al, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Sb, Bi, B, In, As, Ge, Sn, Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu; and a=1, b=0.01 to 1.0, c=0.01 to 1.0, d=0.01 to 1.0, and e is dependent on the oxidation state of the other elements. The catalyst composition is treated to exhibit peaks at X-ray diffraction angles (2θ) of 22.1°, 27.1°, 28.2°, 36.2°, 45.2°, and 50.0°, with a relative increase in a diffraction peak at the diffraction angle (2θ) of 27.1 degrees when compared with an untreated catalyst of like empirical formula.

In this regard, in addition to the above noted peak at 27.1 degrees, the preferred mixed metal oxide exhibits the following five main diffraction peaks at specific diffraction angles (2θ) in the X-ray diffraction pattern of the treated mixed metal oxide (as measured using Cu—Kα radiation as the source):



X-ray lattice plane
Diffraction angle 2θ	Spacing medium	Relative
(±0.3°)	(Å)	intensity

22.1°	4.02	100
28.2°	3.16	20˜150
36.2°	2.48	5˜60
45.2°	2.00	2˜40
50.0°	1.82	2˜40

The intensity of the X-ray diffraction peaks may vary upon the measuring of each crystal. However, the intensity, relative to the peak intensity at 22.10 being 100, is usually within the above ranges. Generally, the peak intensities at 2θ=22.1° and 28.2° are distinctly observed. However, so long as the above five diffraction peaks are observable, the basic crystal structure is the same even if other peaks are observed in addition to the five diffraction peaks (e.g. at 27.1 degrees), and such a structure is useful for the present invention. Preparation of the mixed metal catalysts is described in U.S. Patent Application Publication No. 20020183547 and European Patent Publication No. EP 1 249 274.

Other suitable prepared catalysts modified using the invention include those described in U.S. Pat. No. 5,380,933 discloses a method for producing an unsaturated carboxylic acid comprising subjecting an alkane to a vapor phase catalytic oxidation reaction in the presence of a catalyst containing a mixed metal oxide comprising, as essential components, Mo, V, Te, O and X, wherein X is at least one element selected from the group consisting of niobium, tantalum, tungsten, titanium, aluminum, zirconium, chromium, manganese, iron, ruthenium, cobalt, rhodium, nickel, palladium, platinum, antimony, bismuth, boron, indium and cerium; and wherein the proportions of the respective essential components, based on the total amount of the essential components, exclusive of oxygen, satisfy the following relationships: 0.25<r(Mo)<0.98, 0.003<r(V)<0.5, 0.003<r(Te)<0.5 and 0.003<r(X)<0.5, wherein r(Mo), r(V), r(Te) and r(X) are the molar fractions of Mo, V, Te and X, respectively, based on the total amount of the essential components exclusive of oxygen.

Yet other suitable examples of prepared catalysts modified using the invention include those described in Published International Application No. WO 00/29106 discloses a catalyst for selective oxidation of propane to oxygenated products including acrylic acid, acrolein and acetic acid, said catalyst system containing a catalyst composition comprising
Mo _aV _bGa _cPd _dNb _eX _f
wherein X is at least one element selected from La, Te, Ge, Zn, Si, In and W,

- a is 1,
- b is 0.01 to 0.9,
- c is >0 to 0.2,
- d is 0.0000001 to 0.2,
- e is >0 to 0.2, and
- f is 0.0 to 0.5; and
  wherein the numerical values of a, b, c, d, e and f represent the relative gram-atom ratios of the elements Mo, V, Ga, Pd, Nb and X, respectively, in the catalyst and the elements are present in combination with oxygen.

Yet other suitable examples of prepared catalysts modified using the invention include those described in Japanese Laid-Open Patent Application Publication No. 2000-037623 and European Published Patent Application No. 0 630 879 B1. Other suitable catalysts for a variety of vapor phase oxidation reactions are described fully in U.S. Pat. Nos. 6,383,978, 6,403,525, 6,407,031, 6,407,280, 6,461,996, 6,472,552, 6,504,053, 6,589,907 and 6,624,111.

By way of an illustrative example, when a mixed metal oxide of the formula Mo _aV _bTe _cNb _dO _e(wherein the element A is Mo, the element D is V, the element E is Te and the element X is Nb) is to be prepared, an aqueous solution of niobium oxalate and a solution of aqueous nitric acid may be added to an aqueous solution or slurry of ammonium heptamolybdate, ammonium metavanadate and telluric acid, so that the atomic ratio of the respective metal elements would be in the prescribed proportions. In one specific illustration, it is further contemplated that a 5% aqueous nitric acid is mixed with niobium oxalate solution in a ratio of 1:10 to 1.25:1 parts by volume acid solution to oxalate solution, and more preferably 1:5 to 1:1 parts by volume acid solution to oxalate solution.

For example, when a promoted mixed metal oxide of the formula Mo _jV _mTe _nNb _yAu _zO _fwherein the element J is Mo, the element M is V, the element N is Te, the element Y is Nb, and the element Z is Au, is to be prepared, an aqueous solution of niobium oxalate may be added to an aqueous solution or slurry of ammonium heptamolybdate, ammonium metavanadate, telluric acid and ammonium tetrachloroaurate, so that the atomic ratio of the respective metal elements would be in the prescribed proportions.

A unmodified mixed metal oxide (promoted or not), thus obtained, exhibits excellent catalytic activities by itself. However, the unmodified mixed metal oxide is converted to a catalyst having higher activities by one or more chemical, physical and combinations of chemical and physical treatments.

Modified metal oxide catalysts are obtained by treating chemical, physical and combinations of chemical and physical treatments of suitable prepared metal oxide catalyst. Optionally, the modified catalysts are further modified by conventional processing techniques well known to persons having skill in this art.

Chemical treatments, resulting in treated/modified catalysts, include one or more chemical modifying agents. Suitable chemical modifying agents include, but are not limited to for example, oxidizing agents selected from hydrogen peroxide, nitrogen, nitric acid, nitric oxide, nitrogen dioxide, nitrogen trioxide, persulfate; reducing agents selected from amines, pyridine, hydrazine, quinoline, metal hydrides, sodium borohydride, C1-C4 alcohols, methanol, ethanol, sulfites, thiosulfites, aminothiols; combinations of oxidizing agents and reducing agents; acids selected from HCl, HNO3, H2SO4; organic acids, organic diacids, acetic acid, oxalic acid, combinations of C1-C4 alcohols and C1-C4 organic acids, oxalic acid and methanol; inorganic bases selected from NH3, NH4OH, H ₂NNH2, HONH2, NaOH, Ca(OH) ₂, CaO, Na2CO3, NaHCO3, organic bases selected from ethanol amine, diethanolamine, triethanolamine; pH adjustments; peroxides selected from inorganic peroxides, H ₂O ₂, organic peroxides, tBu2O2; chelating agents, ethylenediamine, ethylenediaminetetraacetic acid (EDTA); electrolysis including electrolytic reduction; treatment with high energy radiation including ultraviolet and X-ray radiation; and combinations thereof.

According to one embodiment, modified catalysts are further modified by one or more physical treatments including, but not limited to for example, heating, drying, cooling, freeze, pressure cooling, thermal die pressing, high pressure die pressing, thermal and high pressure die pressing, thermal high shear milling and grinding, thermal de-polymerizing, thermolyzing (also referred to as polymer burn off), mechanical grinding at cryogenic temperatures, mechanical grinding at elevated temperatures, thermal milling, cryo-milling, thermal shearing, cryo-shearing, cryo-densifying, densification, coagulation, flocculation, sedimenting, lyophilizing, agglomerating, reducing particle size of primary particles, increasing surface area of primary particles, thermal and cryo-compacting, thermal and cryo-compressing, thermal and cryo-stressing, cryo-fracturing, shear loading, thermal and cryo-shear loading, drawing, thermal and cryo-drawing, thermal and cryo-centrifuging, thermal and cryo-granulating, thermal and cryo-spray drying, atomizing, thermal and cryo-dry pressing, cryo-pressing, heat pressing, dry compacting, cryo-compacting, heat compacting, isocompacting, thermal and cryo-isocompacting, thermal and cryo-pelletizing, thermal and cryo-roll pressing, thermal and cryo-deforming, jiggering, thermal and cryo-molding, thermal and cryo-forming, thermal and cryo-shaping, thermal and cryo-casting, thermal and cryo-machining, thermal and cryo-laminating, thermal and cryo-tape casting, fiber drawing, thermal and cryo-fiber drawing, thermal and cryo-fiber extruding, thermal and cryo-extruding, thermal and cryo-lobalizing, thermal and cryo-impregnating, forming sphere forming (spherolizing or jetting), slurrying, cryo-slurrying, preparing shelled catalysts (shelling), multi-coating, electrolyzing, electrodepositing, compositing, rolling, roll forming, foaming, cementing, fluidizing, cryo-spraying, thermal spraying, plasma spraying, vapor depositing, adsorbing, ablating, firing, vitrifying, sintering, cryo-sintering, pre-shaping before extruding, thermal and cryo-pre-shaping before extruding, lobalizing, fusing, thermal fusing, fuming, coking, colloidalizing, crystallizing, thermal and cryo-crystallizing, any altering of crystal structure, polycrystallizing, recrystallizing, any surface treating, any altering of surface structure, any altering of porosity, any altering of density, any altering of bulk structure, altering catalyst pH, any chemical treatments used in modifying catalyst surface structure, mechanical grinding in supercritical solvents, chemisorbing one or more chemical agents, ultrasonification using one or more solvents selected from organic solvents, aqueous solvents and combinations of organic and aqueous solvents including, but limited to for example, acids, alcohols, chelating agents and amines ultrasonification, and any physical treatments employing solvents under supercritical conditions and any combinations thereof.

Other suitable treatments involve combinations of one or more chemical modifying agents and one or more physical processes, resulting in treated/modified catalysts. Suitable examples include, but are not limited to for example, solvent extraction using a Soxhlet extractor, extraction using a Parr bomb, solvent extraction using microwave radiation, batch solvent extraction, continuous flow solvent extraction, leaching, altering pH, any surface treatments, grinding in supercritical solvents, extraction in supercritical solvents, chemisorption, ultrasonification using one or more solvents selected from organic solvents such as alcohols and amines; and combinations thereof.

According to one embodiment of the invention, a structured mixed metal oxide catalyst is prepared by employment of a deposition technique selected from chemical vapor deposition (CVD) or physical vapor deposition (PVD). In other words, the layers of catalyst precursor materials are applied to the support by PVD or CVD, in each case under reduced pressure, i.e. at less than 10 mbar, preferably less than 1 mbar. Possible PVD methods are vapor deposition, sputtering and anodic or cathodic arc coating. Possible CVD methods are thermal- or plasma-supported gas-phase deposition. Plasma-supported methods, such as sputtering or arc coating are preferred, sputtering being particularly preferred.

In arc coating, the coating material is removed by means of an electric arc, which leads to a high degree of ionization of the coating material in the process gas atmosphere. The support to be coated can be provided with a bias voltage, which is generally negative and leads to intensive ion bombardment during coating.

In sputtering, the materials to be coated are applied in solid form as a target to the cathode of the plasma system, sputtered under reduced pressure (preferably from 5×10 ⁻⁴to 1×10 ⁻¹mbar) in a process gas atmosphere and deposited on the support. The process gas usually comprises a noble gas, such as argon.

Various versions of the sputtering method, such as magnetron sputtering, DC or RF sputtering, bias sputtering or reactive sputtering and combinations thereof are suitable for the production of the presently contemplated layers. In magnetron sputtering, the target to be puttered is present in an external magnetic field which concentrates the plasma in the region of the target and hence increases the sputtering rate. In DC or RF sputtering, the sputtering plasma is excited in a conventional manner by DC or RF generators. In bias sputtering, a generally negative bias voltage which leads to intensive bombardment of the support with ions during coating is applied to the support to be coated.

In reactive sputtering, reactive gases, such as hydrogen, hydrocarbons, oxygen or nitrogen are mixed in the desired amount with the process gas at a suitable time. As a result, the relevant metal oxide, nitride, carbide, carbide oxide, carbide nitride, oxide nitride or carbide oxide nitride layers can be deposited directly by sputtering a metal, for example, in the presence of hydrocarbons, oxygen and/or nitrogen, in the process gas.

The desired layer thickness, chemical composition and microstructure may be obtained, as described below, by way of controlling the deposition parameters such as process gas pressure, process gas composition, sputtering power, sputtering mode, substrate temperature and deposition time.

PVD/CVD methods allow the layer thickness to be changed in a manner which is very reproducible and, as a result of the deposition parameters (e.g., deposition rate, deposition time), simple. The layer thickness can be readily chosen from a few atomic layers to about 100 mμ. For supported catalysts, catalyst layer thicknesses are preferably from 5 nm to 50 mμ, in particular from 10 nm to 20 mμ, very particularly from 10 nm to 10 mμ, and most particularly from 10 nm to 100 nm.

PVD/CVD technologies, in particular sputtering technology, offer very considerable freedom with regard to the chemical composition of the deposited catalyst precursor layers. The spectrum of layers which can be produced ranges from two- or three- to multi-component materials. Multi-component materials are usually prepared by introducing a suitable target into the coating unit and by subsequently sputtering the target in a noble gas plasma, preferably argon. Suitable targets are homogeneous metal targets or homogeneous alloy targets, which are prepared in a known manner by melting processes or by powder metallurgy methods, or inhomogeneous mosaic targets, which are prepared by joining together smaller pieces having different chemical compositions or by placing or sticking small, disk-like material pieces on homogeneous targets. Alternatively, metallic alloys can be prepared by simultaneously puttering two or more targets of different compositions. The supports to e coated are arranged so that they are exposed in an advantageous manner to the flow of material produced by the sputtering of the various targets. In an advantageous arrangement, the supports to be coated are passed periodically through the simultaneously burning sputtering plasmas, a layer whose composition is periodically modulated through the layer depth being applied to the supports. The modulation period may be adjusted within wide limits by the sputtering power of the individual targets and by the speed of the periodic movement of the supports. In particular, by setting a very small modulation period, it is also possible to achieve a very thorough mixing of the individual layers and hence deposition of a homogeneous alloy.

The preparation of mixed oxide, nitride or carbide systems can be carried out either by sputtering of corresponding oxide, nitride or carbide targets, or by the reactive sputtering of metal targets in corresponding reactive gas plasmas. By appropriately controlling the reactive gas flow during the reactive sputtering, it is also possible to achieve partial oxidation, nitride formation or carbide formation in the alloy layer. For example, in alloys of noble and non-noble metals, selective oxidation of the non-noble metal component can be achieved by skillful adjustment of the oxygen gas flow.

Another commonly used PVD method is the sequential PVD deposition of different metals, such as Te, Nb, V, Mo, etc. in vacuum conditions (base pressure <1×10 ⁻⁶Torr). The metal sources are made by melting individual metal powders into different crucibles. The PVD system is typically equipped with multiple pockets that house multiple crucibles containing different metals. During PVD, an individual metal source is heated by electron beam, and the deposition rate is typically monitored using a quartz crystal balance that is located near the substrate.

With the stated deposition methods, it is also possible to produce thin gradient layers whose composition is varied in a defined manner with increasing layer depth. The variation of the composition can be controlled in a simple manner by the corresponding deposition parameters (for example, sputtering power, in the case of simultaneous sputtering, reactive gas flow, etc.). Moreover, non-periodic layer systems, e.g., layer systems comprising different metallic alloys or composite layers consisting of metallic and oxide layers, are also possible.

The microstructure (e.g., phase distribution, crystallite shape and size, crystallographic orientation) and the porosity of the layers can be controlled within wide limits by the choice of suitable deposition parameters. For example, DC magnetron sputtering of a metallic target at a pressure of from 4×10 ⁻³to 8×10 ⁻³mbar leads to very dense and hence pore-free layers, whereas a column-like morphology with increasing porosity is observed at a sputtering pressure above 1×10 ⁻²mbar. In addition to the sputtering pressure, the substrate temperature and any applied bias voltage have a considerable effect on the microstructure.

Examples of suitable supports are moldings of glass, quartz glass, ceramic, titanium dioxide, zirconium dioxide, alumina, aluminosilicates, borates, steatite, magnesium silicate, silica, silicates, metal, carbon (e.g., graphite), or mixtures thereof. The support may be porous or non-porous. Suitable moldings include, for example, strans, pellets, wagon wheels, stars, monolith, spheres, chips, rings or extrudates. Spheres, pellets and strands are particularly preferred.

In order to achieve uniform coating of the supports, it is advantageous to keep the supports in random motion during deposition or by the use of suitable mechanical apparatus having good flow mechanical properties. Suitable mechanical apparatus includes, e.g., periodically moved cages, drums, shells or channel in which the supports are caused to make random movements. The mechanical apparatus must, of course, have suitable openings to permit the passage of the deposition material or access by any plasma required.

In one particularly preferred aspect of the present invention, the ceramic support structure is an open or closed cell ceramic foam or monolith. More preferably, the ceramic is made from a material selected from the group consisting of cordierite, alumina, zirconia, partially stabilized zirconia (PSZ), niobium, and mixtures thereof. Of course, other like materials may also be employed. The foam structure preferably has 30 to 150 pores per inch. The monoliths may have 200 to 800 cells per inch.

These forms for the support permit high space velocities with a relatively minimal pressure drop. The skilled artisan will be familiar with such configurations and the manner of making the same, in view of teachings such as “Structured Catalysts and Reactors, A. Cybulski and J. A. Moulijn (Eds.), Marcel Dekker, Inc., 1998, p. 599-615 (Ch. 21): X. Xu and J. A. Moulijn, “Transformation of a Structured Carrier into Structured Catalyst”.

Structures including a fibrous or fabric support may also be employed. For instance, ceramic oxide fabric catalyst supports, fibrous ceramic composite catalysts, or a combination, provide other attractive supported structures, which are easily formed and are readily scaled to fit commercial reactors. These types of structures, which may or may not be self-supporting, preferably will resist thermal shock under the reaction conditions of interest and will generally avoid hot-spot induced circumstances, such as a meltdown. These structures may be formed into any of a variety of three-dimensional configurations, and may employ one or more different fiber diameters, may be woven, unwoven or a mixture thereof, or even braided or otherwise aggregated into a suitable configuration, mesh or otherwise.

It will be appreciated as to the support structures disclosed herein that plural layers may be employed, with each layer having the same or different structure, composition, orientation, or other characteristic relative to a previous layer. For instance, a catalyst bed may contain a stack or layers of fabric disks formed from ceramic oxide fabric supported catalysts or the fibrous ceramic composite catalysts. Individual layers may or may not be self-supporting. Preferably, however, the combination embodied in the overall structure is generally self-supporting. When employed herein, ceramic oxide fibers may be comprised of alumina, silica, boria, cordierite, magnesia, zirconia, or a combination of any of these oxides.

It will be appreciated that the supports of the present invention, though discussed above in the context of preferred groups of materials may be selected from any of a number of different materials, such as (without limitation) a ceramic selected from the group consisting of cordierite, alumina, zirconia, partially stabilized zirconia (PSZ), niobium, silica, boria, magnesia, titania and mixtures thereof. The groups discussed herein are thus not intended as limiting.

In another embodiment, multi-layer structures may include a stack of a plurality of perforated plates (e.g., thin, circular perforated metal disks), preferably joined together by a thermally conductive connection. The plates may be coated with an oxidation barrier, to thereby serve as thermal shock resistant catalyst supports for active catalyst materials. By way of illustration, recognizing that the teachings are applicable to other material systems or configurations, the catalyst preparation for this aspect includes fabricating a stack of thin, circular perforated metal disks and joining them together by a thermally conductive connection. The multi-disk structure is scaled at a high temperature for sufficient time to grow an alumina layer. The multi-layer structure is impregnated with the active catalyst precursor material, dried and calcined to the result in a monolith catalyst. In one example, the multi-layer structure is scaled, or pretreated, by heating in air or oxygen at 900° C. to 1200° C., for a period of time ranging from about 10-100 hours, to form a thin, tightly adhering oxide surface layer which protects the underlying support alloy from further oxidation during high temperature use. The surface layer also preferably functions as a diffusion barrier to the supported metal catalyst, thus preventing alloying of the catalyst metal with the alloy of the catalyst support. For example, the protective surface layer may be composed predominantly of alpha-alumina, but also contain a small amount of yttrium oxide. After pretreatment, the multi-layer support structure is coated with a catalyst metal, or catalyst precursor material.

The supported catalysts as described herein may be further performance tuned as desired, and may be varied in their stacking, layering, or other integration characteristics in the reactor system in such a manner to improve reaction productivity. For example, in one aspect, it may be beneficial to initially provide an oxidative dehydrogenation active catalyst (supported as described herein or unsupported) upstream in the reactor system for the conversion of an alkane to alkylene (e.g., propane to propylene) in the cases of pure, mixed and/or recycle streams. These forms might then be followed by supported or unsupported selective oxidation catalysts towards acid production.

The present mixed metal oxide catalyst (or combination of catalyst and support) can be prepared in a suitable manner such as that illustrated in the following discussion. Turning now in more specific detail to the first aspect of the present invention, the mixed metal oxide is prepared by introducing a metal and/or series of metals into a catalyst precursor admixture, such as by deposition. As discussed herein, the step of deposition is accomplished by employment of a deposition technique selected from chemical vapor deposition or physical deposition.

Generally, the metal compounds contain elements Mo, V, Te and X, as previously defined.

Once obtained, the catalyst precursor may be calcined into its desired supported form or into another suitable form. The calcination may be conducted in an oxygen-containing atmosphere or in the substantial absence of oxygen, e.g., in an inert atmosphere or in vacuo. The inert atmosphere may be any material which is substantially inert, i.e., does not react or interact with, the catalyst precursor. Suitable examples include, without limitation, nitrogen, argon, xenon, helium or mixtures thereof. Preferably, the inert atmosphere is argon or nitrogen. The inert atmosphere may flow over the surface of the catalyst precursor or may not flow thereover (a static environment). When the inert atmosphere does low over the surface of the catalyst precursor, the flow rate can vary over a wide range, e.g., at a space velocity of from 1 to 500 hr ⁻¹.

The calcination is usually performed at a temperature of from 350° C. to 850° C., preferably from 400° C. to 700° C., more preferably from 500° C. to 640° C. The calcination is performed for an amount of time suitable to form the aforementioned catalyst. Typically, the calcination is performed for from 0.5 to 30 hours, preferably from 1 to 25 hours, more preferably for from 1 to 15 hours, to obtain the desired mixed metal oxide.

In a preferred mode of operation, the catalyst precursor is calcined in two stages. In the first stage, the catalyst precursor is calcined in an oxidizing environment (e.g. air) at a temperature of from 275° C. to 400° C., preferably from 275° C. to 325° C. for from 15 minutes to 8 hours, preferably for from 1 to 3 hours. In the second stage, the material from the first stage is calcined in a non-oxidizing environment (e.g., an inert atmosphere) at a temperature of from 500° C. to 700° C., preferably for from 550° C. to 650° C., for 15 minutes to 8 hours, preferably for from 1 to 3 hours. Optionally, a reducing gas, such as, for example, ammonia or hydrogen, may be added during the second stage calcination.

In a particularly preferred mode of operation, the catalyst precursor in the first stage is placed in the desired oxidizing atmosphere at room temperature and then raised to the first stage calcination temperature and held there for the desired first stage calcination time. The atmosphere is then replaced with the desired non-oxidizing atmosphere for the second stage calcination, the temperature is raised to the desired second stage calcination temperature and held there for the desired second stage calcination time.

Although any type of heating mechanism, e.g., a furnace, may be utilized during the calcination, it is preferred to conduct the calcination under a flow of the designated gaseous environment. Therefore, it is advantageous to conduct the calcination in a bed with continuous flow of the desired gas(es) through the bed of solid catalyst precursor particles.

With calcination, a catalyst is formed having the formula Mo _aV _bTe _cX _dO _ewherein Mo is molybdenum; V is vanadium; Te is tellurium; X is as previously defined; O is oxygen; a, b, c and d are as previously defined; and e is the relative atomic amount of oxygen present in the catalyst and is dependent on the oxidation state of the other elements

The oxide obtained by the above-mentioned method may be used as a final catalyst, but it may further be subjected to heat treatment usually at a temperature of from 200° to 700° C. for from 0.1 to 10 hours.

The resulting modified mixed metal oxide (promoted or not) may be used by itself as a solid catalyst. The modified catalysts are also combined with one or more suitable carriers, such as, without limitation, silica, alumina, titania, aluminosilicate, diatomaceous earth or zirconia, according to art-disclosed techniques. Further, it may be processed to a suitable shape or particle size using art disclosed techniques, depending upon the scale or system of the reactor.

Alternatively, the metal components of the modified catalysts are supported on materials such as alumina, silica, silica-alumina, zirconia, titania, etc. by conventional incipient wetness techniques. In one typical method, solutions containing the metals are contacted with the dry support such that the support is wetted; then, the resultant wetted material is dried, for example, at a temperature from room temperature to 200° C. followed by calcination as described above. In another method, metal solutions are contacted with the support, typically in volume ratios of greater than 3:1 (metal solution:support), and the solution agitated such that the metal ions are ion-exchanged onto the support. The metal-containing support is then dried and calcined as detailed above.

According to a separate embodiment, modified catalysts are also prepared using one or more promoters. The starting materials for the above promoted mixed metal oxide are not limited to those described above. A wide range of materials including, for example, oxides, nitrates, halides or oxyhalides, alkoxides, acetylacetonates, and organometallic compounds may be used. For example, ammonium heptamolybdate may be utilized for the source of molybdenum in the catalyst. However, compounds such as MoO ₃, MoO ₂, MoCl ₅, MoOCl ₄, Mo(OC ₂H ₅) ₅, molybdenum acetylacetonate, phosphomolybdic acid and silicomolybdic acid may also be utilized instead of ammonium heptamolybdate. Similarly, ammonium metavanadate may be utilized for the source of vanadium in the catalyst. However, compounds such as V ₂O ₅, V ₂O ₃, VOCl ₃, VCl ₄, VO(OC ₂H ₅) ₃, vanadium acetylacetonate and vanadyl acetylacetonate may also be utilized instead of ammonium metavanadate. The tellurium source may include telluric acid, TeCl ₄, Te(OC ₂H ₅) ₅, Te(OCH(CH ₃) ₂) ₄and TeO ₂. The niobium source may include ammonium niobium oxalate, Nb ₂O ₅, NbCl ₅, niobic acid or Nb(OC ₂H ₅) ₅as well as the more conventional niobium oxalate.

In addition, with reference to the promoter elements for the promoted catalyst, the nickel source may include nickel(II) acetate tetrahydrate, Ni(NO ₃) ₂, nickel(II) oxalate, NiO, Ni(OH) ₂, NiCl ₂, NiBr ₂, nickel(II) acetylacetonate, nickel(II) sulfate, NiS or nickel metal. The palladium source may include Pd(NO ₃) ₂, palladium(II) acetate, palladium oxalate, PdO, Pd(OH) ₂, PdCl ₂, palladium acetylacetonate or palladium metal. The copper source may be copper acetate, copper acetate monohydrate, copper acetate hydrate, copper acetylacetonate, copper bromide, copper carbonate, copper chloride, copper chloride dihydrate, copper fluoride, copper formate hydrate, copper gluconate, copper hydroxide, copper iodide, copper methoxide, copper nitrate, copper nitrate hydrate, copper oxide, copper tartrate hydrate or a solution of copper in an aqueous inorganic acid, e.g., nitric acid. The silver source may be silver acetate, silver acetylacetonate, silver benzoate, silver bromide, silver carbonate, silver chloride, silver citrate hydrate, silver fluoride, silver iodide, silver lactate, silver nitrate, silver nitrite, silver oxide, silver phosphate or a solution of silver in an aqueous inorganic acid, e.g., nitric acid. The gold source may be ammonium tetrachloroaurate, gold bromide, old chloride, gold cyanide, gold hydroxide, gold iodide, gold oxide, gold richloride acid and gold sulfide.

Modified catalysts of the invention have different chemical, physical and performance characteristics in catalytic reactions of carbon based molecules as compared to unmodified catalysts. According to one embodiment, the treated catalyst exhibits changes in X-ray lines, peak positions and intensity of such lines and peaks as compared with corresponding X-ray diffraction data for corresponding unmodified catalysts. Such difference indicate structural differences between the modified and unmodified catalysts and are born out in the catalytic activity and selectivity. For example, compared with an untreated catalyst composition, a treated catalyst composition of the present invention exhibits an X-ray diffraction pattern having a relative increase in a diffraction peak at a diffraction angle (2θ) of 27.1 degrees when compared with an untreated catalyst, which may exhibit no peak at all at 27.1 degrees.

The relative difference between peak intensities of treated versus untreated compositions may be greater than 5%, more preferably greater than 10%, and still more preferably greater than 20% of the intensity of the untreated catalyst composition at the diffraction angle (2θ) of 27.1 degrees. Without intending to be bound by theory, it is believed that at least two phases (A and B) are present in the resulting mixed metal oxide catalyst and the treatment of the catalyst precursor with a source of NO _xresults in an increase in phase B relative to phase A in the resulting catalyst. The increase in phase B is believed to contribute to improved performance of the catalyst in terms of selectivity, reactivity and yield.

Modified catalysts of the invention have improved performance characteristics as compared to unmodified catalysts in catalytic processes comprising any carbon containing molecule. According to one embodiment of the invention, the modified catalysts have improved performance characteristics as compared to unmodified catalysts in processes for preparing dehydrogenated products and oxygenated products from alkanes and oxygen, alkenes and oxygen and combination of alkanes, alkenes and oxygen. The reactions are typically carried out in conventional reactors with the alkanes catalytically converted at conventional residence times (>100 milliseconds) in conventional reactors. According to a separate embodiment the reactions are carried out at short contact times (≦100 milliseconds) in a short contact time reactor. Suitable alkanes include alkanes having straight or branched chains. Examples of suitable alkanes are C ₂-C ₂₅alkanes, including C ₂-C ₈alkanes such as propane, butane, isobutane, pentane, isopentane, hexane and heptane. Particularly preferred alkanes are propane and isobutane.

Modified catalysts of the invention convert alkanes, alkenes or alkanes and alkenes to their corresponding alkenes and oxygenates including saturated carboxylic acids, unsaturated carboxylic acids, esters thereof, and higher analogue unsaturated carboxylic acids and esters thereof. The modified catalyst and catalytic systems are designed to provide specific alkenes, oxygenates and combinations thereof. Alkanes are catalytically converted to one or more products in a single pass, including corresponding alkenes. Any unreacted alkane, alkene or intermediate is recycled to catalytically convert it to its corresponding oxygenate. According to one embodiment, alkenes produced from dehydrogenation of corresponding alkanes using catalyst systems of the invention are deliberately produced as in-process chemical intermediates and not isolated before selective partial oxidation to oxygenated products. For example, when catalytically converting an alkane to its corresponding ethylenically unsaturated carboxylic acid, any unreacted alkene produced is recovered or recycled to catalytically convert it to its corresponding ethylenically unsaturated carboxylic acid product stream.

According to a separate embodiment, alkanes, alkenes or alkanes and alkenes are also catalytically converted to its corresponding oxygenates through two or more catalytic zones. For example, an alkane is catalytically converted to its corresponding saturated carboxylic acid in a first catalytic zone or layer of a mixed catalyst bed. The saturated carboxylic acid, in the presence of an additional formaldehyde stream, to its corresponding higher analogue ethylenically unsaturated carboxylic acid in a second catalytic zone or layer of a mixed bed catalyst. In a specific example, propane is catalytically converted to propionic acid and the propionic acid in the presence of formaldehyde is catalytically converted to methacrylic acid.

As used herein, the term “higher analogue unsaturated carboxylic acid” and “ester of a higher analogue unsaturated carboxylic acid” refer to products having at least one additional carbon atom in the final product as compared to the alkane or alkene reactants. For example given above, propane (C ₃alkane) is converted to propionic acid (C ₃saturated carboxylic acid), which in the presence of formaldehyde is converted to its corresponding higher analogue (C ₄) carboxylic acid, methacrylic acid using catalysts of the invention.

Suitable alkenes used in the invention include alkenes having straight or branched chains. Examples of suitable alkenes include C ₂-C ₂, alkenes, preferably C ₂-C ₈alkenes such as propene (propylene), 1-butene (butylene), 2-methylpropene (isobutylene), 1-pentene and 1-hexene. Particularly preferred alkenes are propylene and isobutylene.

Suitable aldehydes used in the invention include for example formaldehyde, ethanal, propanal and butanal.

Modified catalysts and catalyst systems of the invention convert alkanes, alkenes or alkanes and alkenes to their corresponding oxygenates including saturated carboxylic acids having straight or branched chains. Examples include C ₂-C ₈saturated carboxylic acids such as propionic acid, butanoic acid, isobutyric acid, pentanoic acid and hexanoic acid. According to one embodiment, saturated carboxylic acids produced from corresponding alkanes using catalyst systems of the invention are deliberately produced as in-process chemical intermediates and not isolated before selective partial oxidation to oxygenated products including unsaturated carboxylic acids, esters of unsaturated carboxylic acids, and higher esters of unsaturated carboxylic acids. According to a separate embodiment, any saturated carboxylic acid produced is converted using catalysts of the invention to its corresponding product stream including an ethylenically unsaturated carboxylic acid, esters thereof, a higher analogue unsaturated carboxylic acid or esters thereof.

Modified catalysts and catalyst systems of the invention also convert alkanes to their corresponding ethylenically unsaturated carboxylic acids and higher analogues having straight or branched chains. Examples include C ₂-C ₈ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, butenoic acid, pentenoic acid, hexenoic acid, maleic acid, and crotonic acid. Higher analogue ethylenically unsaturated carboxylic acids are prepared from corresponding alkanes and aldehydes. For example, methacrylic acid is prepared from propane and formaldehyde. According to a separate embodiment, the corresponding acid anhydrides are also produced when preparing ethylenically unsaturated carboxylic acids from their respective alkanes. The modified catalysts of the invention are usefully employed to convert propane to arcylic acid and its higher unsaturated carboxylic acid methacrylic acid and to convert isobutane to methacrylic acid.

The modified catalysts and catalyst systems of the invention are also advantageously utilized converting alkanes to their corresponding esters of unsaturated carboxylic acids and higher analogues. Specifically, these esters include, but are not limited to, butyl acrylate from butyl alcohol and propane, β-hydroxyethyl acrylate from ethylene glycol and propane, methyl methacrylate from methanol and isobutane, butyl methacrylate from butyl alcohol and isobutane, β-hydroxyethyl methacrylate from ethylene glycol and isobutane, and methyl methacrylate from propane, formaldehyde and methanol.

In addition to these esters, other esters are formed through this invention by varying the type of alcohol introduced into the reactor and/or the alkane, alkene or alkane and alkene introduced into the reactor.

Suitable alcohols include monohydric alcohols, dihydric alcohols and polyhydric alcohols. Of the monohydric alcohols reference may be made, without limitation, to C ₁-C ₂₀alcohols, preferably C ₁-C ₆alcohols, most preferably C ₁-C ₄alcohols. The monohydric alcohols may be aromatic, aliphatic or alicyclic; straight or branched chain; saturated or unsaturated; and primary, secondary or tertiary. Particularly preferred monohydric alcohols include methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol, isobutyl alcohol and tertiary butyl alcohol. Of the dihydric alcohols reference may be made, without limitation, to C ₂-C ₆diols, preferably C ₂-C ₄diols. The dihydric alcohols may be aliphatic or alicyclic; straight or branched chain; and primary, secondary or tertiary. Particularly preferred dihydric alcohols include ethylene glycol (1,2-ethanediol), propylene glycol (1,2-propanediol), trimethylene glycol (1,3-propanediol), 1,2-butanediol and 2,3-butanediol. Of the polyhydric alcohols reference will only be made to glycerol (1,2,3-propanetriol).

The unsaturated carboxylic acid corresponding to the added alkane is the α,β-unsaturated carboxylic acid having the same number of carbon atoms as the starting alkane and the same carbon chain structure as the starting alkane, e.g., acrylic acid is the unsaturated carboxylic acid corresponding to propane and methacrylic acid is the unsaturated carboxylic acid corresponding to isobutane.

Similarly, the unsaturated carboxylic acid corresponding to an alkene is the α,β-unsaturated carboxylic acid having the same number of carbon atoms as the alkene and the same carbon chain structure as the alkene, e.g., acrylic acid is the unsaturated carboxylic acid corresponding to propene and methacrylic acid is the unsaturated carboxylic acid corresponding to isobutene.

Likewise, the unsaturated carboxylic acid corresponding to an unsaturated aldehyde is the α,β-unsaturated carboxylic acid having the same number of carbon atoms as the unsaturated aldehyde and the same carbon chain structure as the unsaturated aldehyde, e.g., acrylic acid is the unsaturated carboxylic acid corresponding to acrolein and methacrylic acid is the unsaturated carboxylic acid corresponding to methacrolein.

The alkene corresponding to the added alkane is the alkene having the same number of carbon atoms as the starting alkane and the same carbon chain structure as the starting alkane, e.g., propene is the alkene corresponding to propane and isobutene is the alkene corresponding to isobutane. (For alkenes having four or more carbon atoms, the double bond is in the 2-position of the carbon-carbon chain of the alkene.)

The unsaturated aldehyde corresponding to the added alkane is the α,β-unsaturated aldehyde having the same number of carbon atoms as the starting alkane and the same carbon chain structure as the starting alkane, e.g., acrolein is the unsaturated aldehyde corresponding to propane and methacrolein is the unsaturated carboxylic acid corresponding to isobutane.

Similarly, the unsaturated aldehyde corresponding to an alkene is the α,β-unsaturated carboxylic acid having the same number of carbon atoms as the alkene and the same carbon chain structure as the alkene, e.g., acrolein is the unsaturated aldehyde corresponding to propene and methacrolein is the unsaturated aldehyde corresponding to isobutene.

The modified catalysts are processed in to three-dimensional forms or are supported on three-dimensional support structures.

The support structure is three-dimensional, i.e. the support has dimensions along an x, y and z orthogonal axes of a Cartesian coordinate system, and affords a relatively high surface area per unit volume. Though lower and higher amounts are possible, in one embodiment, the support structure exhibits a surface area of 0.01 to 50 m ²/g, preferably 0.1 to 10 m ²/g.

Preferably, the support structure will have a porous structure and exhibit a pore volume percent ranging from 1 to 95%, more preferably 5 to 80%, and still more preferably 10 to 50%. Thus, the support structure permits relatively high feed velocities with insubstantial pressure drop.

Further, the support structure is sufficiently strong so that it does not fracture under the weight of the catalyst, which can range up to almost 100% of the weight of the combination of the catalyst and the support structure. More preferably, however, the support structure is at least 60% of the weight of the combination. Still more preferably, it is 70 to 99.99% of the weight of the combination. Even still more preferably, the support structure is 90 to 99.9% of the weight of the combination.

The exact physical form of the support structure is not particularly important so long as it meets the above noted general criteria. Examples of suitable physical forms of modified catalysts and supported modified catalysts include foam, honeycomb, lattice, mesh, monolith, woven fiber, non-woven fiber, gauze, perforated substrates (e.g., foil), particle compacts, fibrous mat and mixtures thereof. For these supports it will be appreciated that typically one or more open cells will be included in the structure. The cell size may vary as desired, as may the cell density, cell surface area, open frontal area and other corresponding dimensions. By way of example, one such structure has an open frontal area of at least 75%. The cell shape may also vary and may include polygonal shapes, circles, ellipses, as well as others.

The support structure may be fabricated from a material that is inert to the reaction environment of the catalytic reaction. Suitable materials include ceramics and their isomorphs such as silica, alumina (including α-, β- and γ-isomorphs), silica-alumina, aluminosilicate, zirconia, titania, boria, mullite, lithium aluminum silicate, oxide-bonded silicon carbide, metal alloy monoliths, Fricker type metal alloys, FeCrAl alloys and mixtures thereof. (Alternatively, the catalyst may be prepared so as to define the support structure itself, e.g., by “green” compacting or another suitable technique.)

The modified catalysts may be applied to the support structure using any suitable art-disclosed technique. For instance, the catalyst may be vapor deposited (e.g., by sputtering, plasma deposition or some other form of vapor deposition). The catalyst may be impregnated or coated thereon (e.g., by wash coating a support with a solution, slurry, suspension or dispersion of catalyst). The support may be coated with a catalyst powder (i.e. powder coating). (Alternatively, where the support structure is the catalyst itself, a “green” body of catalyst may be compacted to yield the desired structure.)

Modified catalysts of the invention include promoters, modifiers and oxidants. Promoters are usefully employed to oxidatively dehydrogenate alkanes to their corresponding alkenes. According to one embodiment the modified catalysts also incorporate finely dispersed metal particles including alloys (microns to nanometers) having high surface area. Alternatively, the modified catalyst is in the form of a fine gauze, including nanometer sized wires. The catalyst is impregnated on the support using techniques selected from metal sputtering, chemical vapor deposition, chemical and/or electrochemical reduction of the metal oxide.

Modifiers are usefully employed to partially oxidize alkanes to their corresponding saturated carboxylic acids and unsaturated carboxylic acids. Typical modifiers are metal oxide and MMO catalysts in the form of binary, ternary, quaternary or higher order mixed metal oxides. The modifier may preferably be present in an amount of from 0.0001 to 10 wt % of the catalyst composition (promoter plus reducible metal oxide), more preferably from 0.001 to 5 wt % of the catalyst composition, and still more preferably from 0.01 to 2 wt % of the catalyst composition.

Oxidants are usefully employed to partially oxidize alkanes, alkenes and alkanes and alkenes to their corresponding alkenes, saturated carboxylic acids and unsaturated carboxylic acids. Typically they are also metal oxide catalysts and MMO catalysts in the form of binary, ternary, quaternary or higher order mixed metal oxides. The promoter is typically present in an amount of from 0.0001 to 10 wt % of the catalyst composition (promoter plus reducible metal oxide), more preferably from 0.001 to 5 wt % of the catalyst composition, and still more preferably from 0.01 to 2 wt % of the catalyst composition. The modified catalyst is present alone or deposited, including impregnated, on the support in the form of finely dispersed metal oxide particles (microns to nanometers) having high surface area. The catalytic system component comprises metal oxides and metal oxides used in combination with promoters in contact with a metal oxide supported.

The unmodified catalysts are prepared in steps. In a first step, a slurry or solution may be formed by admixing metal compounds, preferably at least one of which contains oxygen, and at least one solvent in appropriate amounts to form the slurry or solution. Preferably, a solution is formed at this stage of the catalyst preparation. Generally, the metal compounds contain the elements required for the particular catalyst, as previously defined.

Suitable solvents include water, alcohols including, but not limited to, methanol, ethanol, propanol, and diols, etc., as well as other polar solvents known in the art. Generally, water is preferred. The water is any water suitable for use in chemical syntheses including, without limitation, distilled water and de-ionized water. The amount of water present is preferably an amount sufficient to keep the elements substantially in solution long enough to avoid or minimize compositional and/or phase segregation during the preparation steps. Accordingly, the amount of water will vary according to the amounts and solubilities of the materials combined. However, as stated above, the amount of water is preferably sufficient to ensure an aqueous solution is formed at the time of mixing.

For example, when a mixed metal oxide of the formula Mo _aV _bTe _cNb _dO _eis to be prepared, an aqueous solution of telluric acid, an aqueous solution of niobium oxalate and a solution or slurry of ammonium paramolybdate may be sequentially added to an aqueous solution containing a predetermined amount of ammonium metavanadate, so that the atomic ratio of the respective metal elements would be in the prescribed proportions.

Once the aqueous slurry or solution (preferably a solution) is formed, the water is removed by any suitable method, known in the art, to form a catalyst precursor. Such methods include, without limitation, vacuum drying, freeze drying, spray drying, rotary evaporation and air drying. Vacuum drying is generally performed at pressures ranging from 10 mmHg to 500 mmHg. Freeze drying typically entails freezing the slurry or solution, using, for instance, liquid nitrogen, and drying the frozen slurry or solution under vacuum. Spray drying is generally performed under an inert atmosphere such as nitrogen or argon, with an inlet temperature ranging from 125° C. to 200° C. and an outlet temperature ranging from 75° C. to 150° C. Rotary evaporation is generally performed at a bath temperature of from 25° C. to 90° C. and at a pressure of from 10 mmHg to 760 mmHg, preferably at a bath temperature of from 400 to 90° C. and at a pressure of from 10 mmHg to 350 mmHg, more preferably at a bath temperature of from 40° C. to 60° C. and at a pressure of from 10 mmHg to 40 mmHg. Air drying may be effected at temperatures ranging from 25° C. to 90° C. Rotary evaporation or air drying are generally employed.

Once obtained, the catalyst precursor is calcined. The calcination is usually conducted in an oxidizing atmosphere, but it is also possible to conduct the calcination in a non-oxidizing atmosphere, e.g., in an inert atmosphere or in vacuo. The inert atmosphere may be any material which is substantially inert, i.e., does not react or interact with, the catalyst precursor. Suitable examples include, without limitation, nitrogen, argon, xenon, helium or mixtures thereof. Preferably, the inert atmosphere is argon or nitrogen. The inert atmosphere may flow over the surface of the catalyst precursor or may not flow thereover (a static environment). When the inert atmosphere does flow over the surface of the catalyst precursor, the flow rate can vary over a wide range, e.g., at a space velocity of from 1 to 500 hr ⁻¹.

The calcination is usually performed at a temperature of from 350° C. to 1000° C., including from 400° C. to 900° C., and including from 500° C. to 800° C. The calcination is performed for an amount of time suitable to form the aforementioned catalyst. Typically, the calcination is performed for from 0.5 to 30 hours, preferably from 1 to 25 hours, more preferably for from 1 to 15 hours, to obtain the desired mixed metal oxide.

In one mode of operation, the catalyst precursor is calcined in two stages. In the first stage, the catalyst precursor is calcined in an oxidizing atmosphere (e.g., air) at a temperature of from 200° C. to 400° C., including from 275° C. to 325° C. for from 15 minutes to 8 hours, including from 1 to 3 hours. In the second stage, the material from the first stage is calcined in a non-oxidizing environment (e.g., an inert atmosphere) at a temperature of from 500° C. to 900° C., including from 550° C. to 800° C., for from 15 minutes to 8 hours, including from 1 to 3 hours.

Optionally, a reducing gas, such as, for example, ammonia or hydrogen, is added during the second stage calcination.

In a separate mode of operation, the catalyst precursor in the first stage is placed in the desired oxidizing atmosphere at room temperature and then raised to the first stage calcination temperature and held there for the desired first stage calcination time. The atmosphere is then replaced with the desired non-oxidizing atmosphere for the second stage calcination, the temperature is raised to the desired second stage calcination temperature and held there for the desired second stage calcination time.

With calcination, a mixed metal oxide catalyst is formed having a stoichiometric or non-stoichiometric amounts of the respective elements.

The invention provides also process for preparing modified mixed metal oxide catalysts that convert alkanes to their corresponding alkenes and oxygenates comprising the steps of

- mixing salts of metals selected from the group consisting of Mo, Te, V, Ta and Nb at temperatures above the melting point of the highest melting salt to form a miscible molten salt; and
- calcining the mixture of salts in the presence of oxygen to provide a mixed metal oxide catalyst, optionally using a metal halide salt or a metal oxyhalide salt as solvent.

The starting materials for the above mixed metal oxide are not limited to those described above. A wide range of materials including, for example, oxides, nitrates, halides or oxyhalides, alkoxides, acetylacetonates and organometallic compounds may be used. For example, ammonium heptamolybdate may be utilized for the source of molybdenum in the catalyst. However, compounds such as MoO ₃, MoO ₂, MoCl ₅, MoOCl ₄, Mo(OC ₂H ₅) ₅, molybdenum acetylacetonate, phosphomolybdic acid and silicomolybdic acid may also be utilized instead of ammonium heptamolybdate. Similarly, ammonium metavanadate may be utilized for the source of vanadium in the catalyst. However, compounds such as V ₂O ₅, V ₂O ₃, VOCl ₃, VCl ₄, VO(OC ₂H ₅) ₃, vanadium acetylacetonate and vanadyl acetylacetonate may also be utilized instead of ammonium metavanadate. The tellurium source may include telluric acid, TeCl ₄, Te(OC ₂H ₅) ₅, Te(OCH(CH ₃) ₂) ₄and TeO ₂. The niobium source may include ammonium niobium oxalate, Nb ₂₀₅, NbCl ₅, niobic acid or Nb(OC ₂H ₅) ₅as well as the more conventional niobium oxalate.

Use of low-melting salts opens up a new approach to preparing mixed metal oxide cata