Title:

Nonwoven composites and related products and processes

Document Type and Number:

United States Patent Application 20050042151

Kind Code:

Abstract:

The present invention in certain embodiments is directed to a catalytic substrate suitable for use in a number of applications, including as a substrate in a catalytic converter or a particulate filter. Another aspect of the present invention is a filtering substrate suitable for use in a number of applications, including as a substrate in a particulate filter, such as a diesel particulate filter (DPF), or diesel particulate trap (DPT). The invention also provides an improved substrate for removing and/or eliminating pollutants from the exhaust of combustion engines. The catalytic substrate and filtering substrate provide, in certain embodiments, improvements in removing pollutants from an exhaust gas. The improvements include one or more of the following: faster light-off period, depth filtration of PM, less backpressure, lower probability of clogging, ability to be placed in multiple locations in the exhaust system including the manifold or the head itself, high probability of catalytic reaction, high conversion ratios of NOx, HC, and CO, a faster burnoff of PM, minimization of catalyst material use, and the like.

Inventors:

Alward, Gordon S. (Palm Desert, CA, US)
Dichiara Jr., Robert A. (Carlsbad, CA, US)

Plaque It!

CROSS-REFERENCE TO RELATED APPLICATIONS

This application includes material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction of the patent disclosure, as it appears in the United States Patent and Trademark Office files or records, but otherwise reserves all rights. This application is a continuation-in-part of U.S. patent application Ser. No. 10/281,179, filed Oct. 28, 2002, which is herein incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

This invention relates to substrates useful for catalyzing particular reactions and for filtering particulate matter, and to embodiments related thereto, such as but not limited to the treatment of emissions from internal combustion engines, and more specifically to catalyst/substrate combinations useful in emissions control and related processes and to related products and methods of manufacture. It is believed that embodiments of the invention described herein materially enhances the quality of the environment of mankind by contributing to the restoration or maintenance of one or more basic life-sustaining natural elements, including air, water, and/or soil. The invention and embodiments thereof are more fully described below in the Brief Summary of the Invention and Detailed Description sections.

Exhaust, Industry, and Pollution

Engines produce much of the power and mechanical work used across the globe. The internal combustion engine is perhaps the most widespread device, as it is more efficient than an external combustion engine, such as those that existed on old-fashioned trains and steamboats. With internal combustion engines, combustion of the fuel takes place internally. Such engines produce motion and power used for any number of purposes. Examples include motor vehicles, locomotives, marine applications, recreational vehicles, tractors, construction equipment, generators, power plants, manufacturing facilities, and industrial equipment. Fuels used to power internal combustion engines include, but are not limited to gasoline, compressed gas, diesel, ethanol, and vegetable oil. Inherent inefficiencies in engine mechanics and the fuels used to power the them result in emissions of various pollutants. Thus, while they are a great innovation and convenience, the millions of engines used throughout the world today represent a substantial source of air pollution.

There are two main types of pollutants produced by internal combustion engines: particulate and nonparticulate. Particulate pollution is generally small solids and liquid particles. Examples include carbonaceous soot and ash, dust, and other related particles. Nonparticulate pollutants include gases and small molecules, such as carbon monoxide, nitrogen oxides, sulfur oxides, unburned hydrocarbons, and volatile organic compounds. Particulate pollutants can be filtered from the exhaust and, in certain situations, further burned off. Nonparticulate pollutants are converted to nonpollutants. Both kinds of pollutants can also be produced from non-engine sources, such as “off-gas” chemical reactions and evaporative emissions.

Air pollution can cause serious health problems for people and the environment. Ground-level ozone and airborne particles are the two pollutants that pose one of the greatest threats to human health in this country. Ozone (O₃), can irritate the respiratory system, causing coughing, irritation in the throat, and/or a burning sensation in the respiratory airways. Ozone contributes to the formation of smog. Ozone can also reduce lung function, causing feelings of chest tightness, wheezing and shortness of breath, and can aggravate asthma. Particle pollution, is composed of microscopic solids or liquid droplets that are small enough to get deep into the lungs and cause serious health problems. When exposed to these small particles, people may experience nose and throat irritation, lung damage and bronchitis, and can increase their risk of heart or lung disease. Short-term effects of air pollutants include irritation to the eyes, nose, and throat. Upper respiratory infections such as bronchitis and pneumonia may also result. Other symptoms can include headaches, nausea, and allergic reactions. Long-term health effects can include chronic respiratory disease, lung cancer, heart disease, and even damage to the brain, nerves, liver, or kidneys. Continual exposure to air pollution affects the lungs of growing children and may aggravate or complicate medical conditions in the elderly.

Medical conditions arising from air pollution can be very expensive. Healthcare costs, lost productivity in the workplace, and human welfare impacts cost billions of dollars each year. Understanding the health effects of pollution and finding means to ameliorate, prevent, or eliminate pollution would not only enhance the overall respiratory health of the population but would also decrease the substantial burden and cost borne by the healthcare system.

For all of these reasons, governments, environmental agencies, and various industries have committed to reducing the level of air pollution emitted from various sources. Government agencies are the principal bodies setting emissions standards and implementing regulations. In the European Union (EU), regulations stem from European Community legislation; individual countries enforce the regulations. For instance, most EU states have taxes on sources that produce excessive air pollution. A recent development was the Kyoto Protocol, which called for worldwide reductions in greenhouse gases. Many nations, including the EU, ratified the protocol. The EU, Japan, and U.S. have enacted some of the most stringent standards worldwide, but many other countries, including Argentina, Brazil, Mexico, Korea, Thailand, India, Singapore, and Australia, have all enacted regulations on air pollution. In the U.S., there are many different groups that affect regulations in certain geographies, such as: state environmental agencies (e.g., California Air Resources Board (CARB)), national parks, forest agencies, and the Mine Safety and Health Administration. Some states and metropolitan areas that have failed national ambient air quality standards (NAAQS) have been designated as “non-attainment areas” and implement standards of their own. CARB has historically been one of the strictest agencies regulating air pollution in the U.S. The chief U.S. regulatory agency, however, is the Environmental Protection Agency (EPA). It was created by the Nixon administration in the 1970 amendments to the Clean Air Act (CAA) of 1963. The Clean Air Act is the comprehensive Federal law that regulates air emissions from area, stationary, and mobile sources. (See, e.g., 42 U.S.C. SS 7401 et seq. (1970) of the Clean Air Act). The Clean Air Act has had five major amendments, the most recent of which was in 1990. The 1990 amendments to the Clean Air Act in large part were intended to meet unaddressed or insufficiently addressed problems such as acid rain, ground-level ozone, stratospheric ozone depletion, and air toxics. These amendments required the EPA to issue 175 new regulations, including automotive emissions, gasoline reformation, uses of ozone depleting chemicals, etc.

Following the Clean Air Act legislation, the EPA set regulations for pollutants that are or could be harmful to people. This set of “criteria pollutants” includes: (1) ozone (O₃); (2) lead (Pb); (3) nitrogen dioxide (NO₂); (4) carbon monoxide (CO); (5) particulate matter (PM); and (6) sulfur dioxide (SO₂). Each criteria pollutant is described in turn.

Ground-level ozone (a primary constituent of smog) continues to be a pollution problem in the U.S. Ozone is not emitted directly into the air but is formed by the reaction of volatile organic compounds (VOCs) or reactive organic gases (ROGs) and nitrogen oxides (NOx) in the presence of heat and sunlight. VOCs/ROGs are emitted from a various sources including burning fuels, and from solvents, petroleum processing, and pesticides, which come from sources such as motor vehicles, chemical plants, refineries, factories, consumer and commercial products, and other industrial sources. Nitrogen oxides are emitted from motor vehicles, power plants, and other sources of combustion. Ozone and the precursor pollutants that cause ozone also can be carried miles from their original sources by wind. In 1997, the EPA revised the national ambient air quality standards for ozone by replacing the 1-hour ozone 0.12 parts per million (ppm) standard with a new 8-hour 0.08 ppm standard.

Nitrogen dioxide (NO₂) is a reactive gas that can be formed by the oxidation of nitric oxide (NO). Nitrogen oxides (NOx), the term used to describe NO, NO₂, and other oxides of nitrogen, play a major role in the formation of ozone and smog. The major sources of man-made NOx emissions include high-temperature combustion processes, such as those occurring in automobiles, heavy construction equipment, and power plants. Home heaters and gas stoves also produce substantial amounts of NO₂.

Carbon monoxide (CO) is a colorless, odorless, and poisonous gas that can be formed by incomplete combustion of carbon in fuels. Motor vehicle exhaust contributes about 60% of CO emissions in the U.S. In cities, as much as 95% of CO emissions may come from automobile exhaust. Other sources of CO emissions include industrial processes, non-transportation fuel combustion, and natural sources such as wildfires.

Particulate matter (PM) is a term used for a mixture of solid particles and liquid droplets found in the air. Some particles are large or dark enough to be seen as soot or smoke. Others are so small they can be detected only with an electron microscope. These particles, which come in a wide range of sizes (“fine” particles are less than 2.5 micrometers in diameter and coarser particles are larger than 2.5 micrometers), originate from many different stationary and mobile sources as well as from natural sources. Fine particles (PM-2.5) result from fuel combustion from motor vehicles, power generation, and industrial facilities, as well as from residential fireplaces and wood stoves. Coarse particles (PM-10) are generally emitted from sources such as vehicles traveling on unpaved roads, materials handling equipment, and crushing and grinding operations, as well as windblown dust. Some particles are emitted directly from their sources, such as smokestacks and cars. In other cases, gases such as sulfur oxide, SO₂, NOx, and VOC interact with other compounds in the air to form fine particles. Their chemical and physical compositions vary depending on location, time of year, and weather. In 1997, the EPA added two new PM-2.5 standards, set at 15 micrograms per cubic meter (μGA) and 65 μg/m³, respectively, for the annual and 24-hour standards.

Sulfur dioxide can be formed when fuel containing sulfur (such as coal and oil) is burned, for example, during metal smelting and other industrial processes.

The last criteria pollutant, lead, was historically produced from use of leaded fuel in automobiles. As a result of regulatory efforts to reduce the content of Pb in gasoline, the contribution from the transportation sector has declined over the past decade. Today, metals processing is the major source of Pb emissions to the atmosphere.

The Clean Air Act requires to EPA and states to develop plans to meet national ambient air quality standards for these six criteria pollutants. Outside of the six is a separate list of 188 “toxic air pollutants.” Examples of toxic air pollutants include benzene, found in gasoline; perchloroethylene, emitted from some dry cleaning facilities; and methylene chloride, used as a solvent and paint stripper by a number of industries. Some air toxics are released from natural sources, but most originate from anthropogenic sources, including both mobile sources (e.g., cars, trucks, and buses) and stationary sources (e.g., factories, refineries, and power plants). The CAA required the EPA to have a two-phased program for these 188 pollutants. The first phase consists of identifying the sources of toxic pollutants and developing technology-based standards to significantly reduce them. The EPA determined a list of over 900 stationary sources, which resulted in new air toxics emissions standards, affecting many industrial sources, including: chemical plants, oil refineries, aerospace manufacturers, and steel mills, as well as smaller sources, such as dry cleaners, commercial sterilizers, secondary lead smelters, and chromium electroplating facilities. The second phase consists of strategies and programs for evaluating the remaining risks and ensuring that the overall program has achieved substantial reductions; this phase is still in progress.

Internal combustion engines are directly affected by these regulations since they emit criteria pollutants. These engines run on two fuel. The most common types of fuel used are: gasoline and diesel. Each type of fuel contains complex mixtures of hydrocarbon compounds as well as traces of many other materials, including sulfur. Even when burned completely, these fuels produce pollutants. Moreover, because no engine is capable of “perfect” combustion, some fuel is incompletely oxidized and therefore produces additional pollutants. Other types of fuel can also be used, for example, ethanol mixtures, vegetable oils, and other fuels known in the art.

In gasoline engines, in order to reduce emissions, modern car engines carefully control the amount of fuel they burn. They try to keep the air-to-fuel ratio very close to the stoichiometric point, which is the calculated ideal ratio of air to fuel. Theoretically, at this ratio, all of the fuel will be burned using all of the oxygen in the air. The fuel mixture actually varies from the ideal ratio quite a bit during driving. Sometimes the mixture can be lean (e.g., an air-to-fuel ratio higher than the typical value of 14.7), and other times the mixture can be rich (e.g., an air-to-fuel ratio lower than 14.7). These deviations result in various air emissions.

Significant emissions of a gasoline car engine include: nitrogen gas (N₂) (air is 78% N₂); carbon dioxide (CO₂), a combustion product; and water vapor (H₂O), another combustion product. These emissions are mostly benign to humans (although excess levels of atmospheric CO₂are believed to contribute to global warming). Gasoline engines, however, also produce carbon monoxide, nitrogen oxides, and unburned hydrocarbons, all of which are included in the EPA's criteria pollutants (unburned hydrocarbons form part of the ozone formation mechanism, along with NOx).

Diesel engines also contribute to the criteria pollutants. These engines use hydrocarbon fractions that auto-ignite when compressed sufficiently in the presence of oxygen. In general, diesel combusting within a cylinder produce greater amounts of particulate matter and the pollutants nitrogen and sulfur oxides (NO_xand SO_xrespectively) than does gasoline. Even so, diesel mixtures are generally lean, with relatively abundant amounts of oxygen present. Consequently, the combustion of smaller hydrocarbons is usually more complete, producing less carbon monoxide than gasoline. Longer chain hydrocarbons are more difficult to burn completely and can result in the formation of particulate residues such as carbon “soot.”

Despite these drawbacks, fossil fuels are relatively abundant, easy to handle, and economical. Thus, these fuels will continue to represent a significant source of mechanical power and pollution for years to come. Moreover, the pervasiveness of the internal combustion engine indicates how fossil fuels will continue to be a necessary source of energy.

There are at least three markets of internal combustion engines that produce air significant pollution: 1) mobile, on-road engines, equipment, and vehicles 2) mobile, non-road engines, equipment, and vehicles and 3) stationary or “point” sources. In each of these markets, government agencies and other organizations have dictated restrictions on levels of air pollution. These restrictions have become increasingly stringent as the number of internal combustion engines in use proliferates and more is learned about the harm caused by air pollution. The ever-tightening regulations have required industries to continuously research, develop, and invest in new emissions control technologies, from fuel formulations to engine redesign, to after treatment devices. These technologies vary in both effectiveness and cost but have become essential in order for companies to comply with regulations. No single emissions control technology has been able to remove all relevant pollutants, so multiple technologies often have to be used together in order to enable a particular type of vehicle or equipment to meet regulatory emission limits. These markets, their regulations, and the technologies on which they rely are described in the following paragraphs. The technologies, including their benefits and drawbacks, are described in more detail following this section. While the sections focus on U.S. engines, equipment, and vehicles, other geographies have similar products and regulations. For instance, the EU has similar market sizes but focuses more on selective catalytic reduction than exhaust gas recirculation as a diesel emission control technology, uses catalytic converters in a greater percentage of its small, off-road engines, and has a much larger percentage of diesel engines in light duty vehicles. Other geographies have their own characteristic differences from the U.S., but essentially use the same types of equipment and restrict the same types of air pollutants.

The mobile, on-road engines, equipment, and vehicles include, but are not limited to, passenger cars, pickup trucks, minivans, sport-utility vehicles (SUVs), buses, delivery trucks, semi-trucks, passenger vans, and two or three-wheeled motorcycles designed for on-road use. These markets historically have lead the way in emissions control and continue to do so today by following regulations that dictate lower levels of air pollutants.

The car and truck markets are divided by weights. Those under 8,500 pounds Gross Vehicle Weight Rating (GVWR) are considered light duty vehicles. Vehicles between 8,500 and 10,000 lbs GVWR that are designed for passenger transport are considered medium duty vehicles. Vehicles over 8,500 lbs GVWR that are not designed for personal use are labeled as heavy-duty vehicles.

Passenger cars and light-duty vehicles were previously regulated by vehicle weight and fuel type but will be regulated in one group in future standards. Less than 1% of ˜17 million new passenger cars and light-duty vehicles produced in the United States use diesel engines. Passenger cars and light-duty vehicles includes those made by manufacturers such as Ford, General Motors (GM), DaimlerChrysler, BMW, Honda, Hyundai, Daewoo, First Automobile Group, Toyota, Nissan, SAIC-Chevy and Subaru.

Regulations on passenger cars and light-duty vehicles have existed for decades but have recently become much more stringent. The Tier 2 standards, phasing in from model year (MY) 2004-2009, require original equipment manufacturers (OEMs) to certify their fleet into certain “bins” of standards and to maintain a corporate average for NOx emissions. Vehicles under 6,000 lbs GVWR must be fully compliant by 2007, those from 6,000-8,500 lbs and MDVs must be compliant by 2009. Pollutants included in the standards include: NOx, formaldehyde (HCHO), CO, PM, and non-methane organic gases. California has historically had tighter regulations than the EPA, and other states, including New Jersey, New York, Vermont, Maine, and Massachusetts, have joined in California's even lower emissions levels for new and used vehicles. Manufacturers who do not meet the standards are essentially prohibited from producing their vehicles in these markets, and are fined for ones discovered on the market. In the aftermarket, states regulate cars and light duty vehicles' emissions through inspection and maintenance (I/M) programs. These programs are often created from state implementation plans (SEPs) required in national ambient air quality (NAAQ) non-attainment areas. Meeting both new vehicle and aftermarket standards requires the use of emission control technologies, often in parallel.

Historically, three-way catalytic converters have had widespread use in cars and light-duty vehicles. Recent improvements in these converters (such as increased substrate porosity, an optimized washcoat, reduced catalyst loading, etc), have yielded incremental improvements in emissions control. To meet the newest set of U.S. regulations, manufacturers will likely increase catalyst loading or the number of substrates per vehicle. Cars in use that do not meet inspection/maintenance standards have to replace the faulty technology or purchase additional devices. Other emission control devices include, but are not limited to, advanced injection systems (such as injection timing, injection pressure, rate shaping, common rail injection, and electronic controls), changed combustion chamber design (such as higher compression ratios, piston geometry, and injector location), variable valve timing, catalytic converters, and filters.

Heavy-duty vehicles (HDV) include both private and commercial trucks and buses over 8,500 lbs GVWR. The vast majority of these engines run on diesel fuel; over 300,000 are produced each year in the U.S. Manufacturers and engine suppliers include, but are not limited to, Cummins, Caterpillar, Detroit Diesel, GM, Mack/Volvo, International/Navistar, Sterling, Western Star, Kenworth, and Peterbilt. Other companies offering other emission control technologies for the aftermarket include, but are not limited to, Donaldson, Engelhard, Johnson Matthey, Lubrizol, Fleetguard, Cleaire, Clean Air Partners, and Engine Control Systems.

Heavy-duty trucks are facing rigorous emissions-reducing standards for PM, NOx, CO, and non-methane hydrocarbons (NMHC). The PM standard takes effect in 2007, while NOx and NMHC standards phase-in from 2007-2010. Similar to light duty vehicles, California, along with certain other states and metropolitan areas, has often enacted tighter emissions standards than the EPA. For vehicles that do not meet standards, the manufacturers are prohibited from selling them. Non-compliance penalties for NOx range up to $12,000 per vehicle, based on size and compliance effort. While other industries, such as locomotive, marine, agriculture, and construction use highly similar engines to those in heavy-duty vehicles, the HDV market has faced the tightest emission standards. Meanwhile, some states and metropolitan areas (such as California, New York City, and Seattle) require additional retrofits or offer incentives for retrofits to further bring down pollution levels. These areas have certified technologies that meet the approved levels and qualifications. Examples include Donaldson's diesel oxidation catalyst muffler and diesel particulate filter, Cleaire's diesel oxidation catalyst and diesel particulate filter, and Johnson Matthey's continuously regenerating technology particulate filter.

Emissions control technologies used to meet these standards and for retrofits include, but are not limited to, advanced injection systems (injection timing, injection pressure, rate shaping, common rail injection, electronic controls), exhaust gas recirculation, changes in combustion chamber design (higher compression ratios, piston geometry, and injector location), advanced turbocharging, ACERT, diesel particulate filters, NOx adsorbers, selective catalytic reduction, conventional catalytic converters, catalytic exhaust mufflers, and diesel oxidation catalysts. Meeting the 2007 standards has initiated new research and development on many of these emission control technologies. There has been tremendous cost and effort put into determining an emissions control solution for 2007 HDVs.

Motorcycles are another type of mobile, on-road vehicle and include both two and three-wheeled motorcycles designed for on-road use. Motorcycles primarily use gasoline fuel. Manufacturers include, but are not limited to: Harley Davidson, BMW, Honda, Kawasaki, Triumph, Tianjin Gangtian, Lifan Motorcycle, and Yamaha. Regulations for on-road motorcycles were adopted in 1978 and then left unrevised through 2003, when new standards following those in California were agreed upon. Pollutants monitored in the new standards include HC, NOx, and CO.

Emissions control technologies for motorcycles include, but are not limited to, conversion of 2-stroke engines to 4-stroke, advanced injection systems (injection timing, injection pressure, rate shaping, common rail injection, and electronic controls), pulse air systems, changed combustion chamber design (higher compression ratios, piston geometry, and injector location), and use of catalytic converters. Limitations in motorcycles' emissions control technologies are different than those in light or heavy-duty vehicles. Motorcycles focus more on the appearance, placement, and heat of aftertreatment devices, as there are fewer places to “hide” the device and the passenger is in much closer proximity to the exothermic oxidation reaction.

The mobile, non-road engines, equipment, and vehicles category includes, but is not limited to, engines for agriculture, construction, mining, lawn and garden, personal watercraft, boats, commercial ships, locomotives, aircraft, snowmobiles, off-road motorcycles, and ATVs.

Small engines emit significant levels of air pollution for their size; they are the largest single contributor to nonroad HC inventories. Small engine equipment includes, but is not limited to, leaf blowers, trimmers, brush cutters, chainsaws, lawn mowers, engine riding mowers, wood splitters, snowblowers, and chippers. Engine and equipment manufacturers include, but are not limited to, John Deere, Komatsu, Honda, Ryobi, Electrolux (Husqvarna and Poulan, also supplies Craftsman), Fuji, Tecumseh, Stihl, American Yard Products, and Briggs and Stratton.

The EPA began regulating small engines in 1993 (Phase I) with standards that went into effect in 1997 and continued to reduce emission levels with new standards in 2002 (Phase II). The standards divide the equipment into handheld and non-handheld categories and categorize it based on different engine displacements. The regulations focus on hydrocarbons and nitrogen oxides emissions.

Emissions control technologies include, but are not limited to, use of a catalyst (i.e., John Deere's LE technology and Komatsu's “Stratified Scavenged” design), converting 2-stroke engines to 4-stroke, advanced injection systems (injection timing, injection pressure, rate shaping, common rail injection, electronic controls), or changing combustion chamber design (higher compression ratios, piston geometry, and injector location).

The recreational vehicle markets include off-highway motorcycles, snowmobiles, and all-terrain vehicles (ATVs). These are made by manufacturers and engine suppliers such as: Caterpillar, Cummins, Detroit Diesel, Ford Power Products, GM, Honda, John Deere, Kawasaki, Mitsubishi Motors, Nissan, Toyota, Yanmar, Arctic Cat, Bombardier, Brunswisk, International Powercraft, Polaris, Suzuki, and Yamaha.

The EPA began regulating recreational vehicles later than many other markets, though California had regulations in place beforehand. EPA has phase-ins from 2006-2009 for snowmobiles, and 2006-2007 for off-highway motorcycles and ATVs. The regulated pollutants include HC, CO, and NOx. Emission control technologies for recreational vehicles include, but are not limited to, converting 2-stroke engines to 4-stroke, advanced injection systems (injection timing, injection pressure, rate shaping, common rail injection, electronic controls), pulse air, or changing combustion chamber design (higher compression ratios, piston geometry, and injector location).

In mining, regulations are established by the Mine Safety and Health Administration. Mining is often considered one of the most taxing environments for equipment, due to the high levels of vibration, impact, and dust. Temperature and flammability are also larger concerns in mining. Diesel oxidation catalyst have been retrofitted on some mining equipment, while diesel particulate filters are becoming more common.

In the agriculture and construction markets, the EPA regulates both spark-ignition and compression-ignition engines. These can be used in tractors, forklifts, bulldozers, electric generators, pavers, rollers, trenchers, drill rigs, mixers, cranes, balers, compressors, etc. Manufacturers of engines and equipment include, but are not limited to: Agco, Komatsu, CNH Global, Caterpillar, Cummins, Daewoo, John Deere & Co, Dueutz, Detroit Diesel, and Kubota.

The EPA began regulating the diesel portion of these engines in 1994 (Tier 1) and has more recently increased the standards with Tier 2 (phased in from 2001-2006). The standards are slated to increase again with Tier 3 levels from 2006-2008. The Tier 3 levels will likely require the use of emissions control devices similar to those used on heavy-duty vehicles (such as tractor-trailers). The gasoline, liquid propane gas, or compressed natural gas (CNG) engines used in agriculture and construction applications have also had recent changes in regulations. Tier 1 levels began in 2004 and match those adopted earlier by CARB; Tier 2 levels are expected to start in 2007. A voluntary program for vehicles with lower emissions than the standards exists, named “Blue Skies Series.” Based on engine size and fuel type, the levels of particulates, carbon monoxide, nitrogen oxides, and non-methane hydrocarbons all must be significantly reduced for current phase-ins and for shortly forthcoming standards.

Emissions control technologies are similar to those used on heavy-duty vehicles and includes, but is not limited to, advanced injection systems (injection timing, injection pressure, rate shaping, common rail injection, electronic controls), exhaust gas recirculation, changes in combustion chamber design (higher compression ratios, piston geometry, and injector location), advanced turbocharging, ACERT, diesel particulate filters, NOx adsorbers, selective catalytic reduction, conventional catalytic converters, catalytic exhaust mufflers, and diesel oxidation catalysts. Exhaust gas recirculation (EGR) has been problematic due to its tendency to create sulfuric acid formation in the engine's intake. It also requires cooling, which necessitates a larger radiator, and thus a larger nose on the vehicle, creating aerodynamic and fuel economy constraints.

In marine applications, engines can generally be divided by use of gasoline or diesel fuel, personal or commercial use, or by engine size. Marine units range from personal watercraft, to yachts, to ferries, to tugs and ocean-going ships. Manufacturers and engine suppliers include, but are not limited to: Bombardier (Evinrude, Johnson, Ski Doo, Rotax, etc), Caterpillar, Cummins, Detroit Diesel, GM, Isuzu, Yanmar, Alaska Diesel, Daytona Marine, Marine Power, Atlantic Marine, Bender Shipbuilding, Bollinger Shipyards, VT Halter Marine, Eastern Shipbuilding, Gladding-Hearn, JeffBoat, Main Iron Works, Master Boat, Patti Shipyard, Quality shipyards, and Verret Shipyard, MAN B&W Diesel, Wartsila, Mitsubishi, Bath Iron Works, Electric Boat, Northrop Grumman (includes Avondale, Ingalls, and Newport News Shipyards).

The EPA regulates boats whether they are recreational, private, or commercial. The major category divisions are based on engine displacement, from recreational vehicles to tankers. Diesel marine non-recreational boats under thirty liter (30 L) displacement, including fishing boats, tugboats, towboats, dredgers, and cargo vessels, have new standards for NOx and PM going into effect between 2004 and 2007, depending on engine size. Diesel marine non-recreational boats over 30 L, including container ships, tankers, bulk carriers, and cruise ships, have NOx standards going into effect in 2004 (Tier 1) and additional HC, PM, and CO standards in 2007 (Tier 2). Diesel marine recreational boats, including yachts, cruisers, and other types of pleasure craft, have standards matching those of diesel marine non-recreational boats under 30 L displacement, but have later implementation dates, ranging from 2006-2009 based on engine size. Gasoline and diesel boats only have regulations currently applying HC emissions in outboard engines, personal watercraft, and jetboats. Sterndrive and inboard engines are inherently cleaner and are not yet regulated.

Emissions control technologies are similar to those used on heavy-duty vehicles and include, but are not limited to, using “green terminals” when the boat is at dock, conversion from 2-stroke to 4-stroke engines, water aftercooling, exhaust gas recirculation, diesel particulate filters, selective catalytic reduction, diesel oxidation catalyst, catalytic converters, advanced fuel injection (injection timing, injection pressure, rate shaping, common rail injection, electronic controls), advanced turbocharging, variable valve timing, and changing the combustion chamber design (higher compression ratios, piston geometry, and injector location). Using smaller engines for auxiliary power (e.g., auxiliary power unit, APU) also helps to control emissions. While salt water and its associated pollutants and cooling effect on boats present difficulties in aftertreatment, the APU may work well with an aftertreatment device.

The locomotive market relies principally on diesel fuel (coal and wood-fired have limited use) and includes trains used in freight and passenger rail, line-haul, local, and switch yard service. There are over 600 trains produced each year in the U.S. Manufacturers and engine suppliers include, but are not limited to, GM's Electromotive Division, GE Transportation Systems, Caterpillar, Detroit Diesel, Cummins, MotovePower, Peoria Locomotive Works, Republic Locomotives, Trinity, Greenbrier, and CSX.

Regulations on trains began in 2000 and largely imitated those of heavy-duty vehicles. The standards include levels for newly produced engines, as well as for engines that are remanufactured (which occurs approximately ever 4-8 years) and vary based on whether the engine is for switch or line-haul purposes. Tier 0 applies to engine model years (MY) from 1973-2001, Tier 1 to MY2002-2004, and Tier 2 to MY2005 and later. A non-compliance penalty can range up to $25,000 per engine per day. The pollutants regulated include particulate matter, NOx, HC, CO, and smoke opacity.

Emissions control technologies are similar to those used on heavy-duty vehicles and include, but are not limited to, advanced injection systems (injection timing, injection pressure, rate shaping, common rail injection, electronic controls), exhaust gas recirculation, changes to combustion chamber design (higher compression ratios, piston geometry, and injector location), selective catalytic reduction, diesel oxidation catalysts, and aftercoolers, split cooling, zeolite sieves, and NOx reduction catalysts. Using a smaller, auxiliary power unit is also becoming an emissions control strategy, one which has fewer restrictions around the use of an aftertreatment device

The aircraft market includes all types of aircraft, including planes made by Boeing, Airbus, Cessna, Gulfstream, and Lockheed Martin, among others. Both the EPA and European Union follow the International Civil Aviation Organization's (ICAO) emissions standards. The EPA adopted ICAO's current standards for CO and NOx in gas turbine engines in 1997, having adopted their HC levels in 1984. In the U.S., the FAA monitors and enforces these standards. Much of the emissions control is done through engine technologies and fuel changes.

Stationary sources include those sources of pollution that are non-mobile. The EPA has issued rules covering over 80 categories of major industrial sources, including power plants, chemical plants, oil refineries, aerospace manufacturers, and steel mills, as well as categories of smaller sources, such as dry cleaners, commercial sterilizers, secondary lead smelters, and chromium electroplating facilities. Power plants can use stationary diesel engines, stationary gas turbines, and nuclear power, among other sources. Each of these sources produces different pollutants; for instance, nuclear power plants produce iodine and hydrogen, gas turbines produce NOx, CO, SOx, CH4, and VOCs, and refineries produce gaseous vapors, CO, NOx, VOCs, CO2, CH4, and PM. Each industry requires different control technologies to reduce air emissions.

EPA regulations cover the six criteria pollutants and the additional 188 toxic air pollutants. Specific programs implemented include the Acid Rain Program, designed to reduce sulfur emissions and the Ozone Transport Commission's NOx Budget Program, designed to reduce NOx emissions. RECLAIM is a program established for trading NOx and SOx credits. In addition, cap and trade programs have been implemented in some industries and geographies, allowing companies to trade their emission credits.

The technology used to control emissions from stationary sources varies widely, but examples include filters, scrubbers, sorbents, selective catalytic reduction (SCR), precipitators, zero-slip catalysts, catalysts for turbines, or oxidation catalysts. Some of the suppliers of emissions control systems to stationary markets include: M+W Zander, Crystall, Jacobs E., Takasogo, IDC, ADP, Marshall, Bechtel, Megte, Angui, Adwest, Eisenmann, Catalytic Products, LTG, Durr, Siemens, Alston. Catalyst suppliers include: Nikki, BASF, Cormetech, W. R. Grace, Johnson Matthey, UOP, and Sud Chemie.

Due to the importance of improving air quality and complying with relevant laws and regulations, substantial time, money, and effort have been invested in technologies capable of reducing emissions. Three general areas of technology include, a) engine improvements, b) fuel improvements, and c) after-treatments. These approaches are typically not mutually exclusive or stand-alone solutions. Engine improvements include, but are not limited to, such technologies as: advanced injection systems, exhaust gas recirculation, electronic sensors and fuel controls, combustion chamber designs, advanced turbocharging, and variable valve timing. Fuel improvements include, but are not limited to, such formulations as: high cetane, low aromatics, low sulfur fuel, fuel borne catalysts, liquefied petroleum gas (LPG), oxygenation of fuels, compressed natural gas (CNG) and biodiesels. After-treatment technologies include, but are not limited to: catalytic converters (2, 3, and 4-way), particulate traps, selective catalytic reduction, NOx adsorbers, HC adsorbers, NOx reduction catalysts, and many others. Some systems incorporate various pieces of these and other technologies; ACERT by Caterpillar or catalyzed diesel particulate traps are examples of combination systems and devices. There are also some technologies that are currently limited in use, either by technological or commercial restrictions.

Advanced injection systems include changes in injection timing, injection pressure, rate shaping, air-assisted fuel injection, sequential multi-point injection, common rail injection, resizing or moving the injector holes, and some electronic controls. In the common-rail system, a microcomputerized fuel pump controls the flow and timing of fuel (e.g., the Mercedes-Benz E320 uses this system). Secondary air injection can promote HC and CO combustion in the manifold. Changing the injection system can reduce a variety of emissions and can also increase fuel economy; however, this requires significant work on the engine to ensure efficiency.

Exhaust gas recirculation (EGR) directs some of the exhaust gases back into the intake of the engine. By mixing the exhaust gases with the fresh intake air, the amount of oxygen entering the engine is reduced, resulting in lower nitrogen oxide emissions. EGR does not require regular maintenance and works well in combination with high swirl, high turbulence combustion chambers. EGR also has drawbacks, such as reduced fuel efficiency and engine life, greater demands on the vehicle's cooling system, limited to no effect on pollutants other than NOx, and it requires control algorithms and sensors. For these reasons, EGR is often used in parallel with another control technology. Companies involved in EGR technology include Doubletree Technologies, ETC, STT Emtec, Cummins, Detroit Diesel, Mack, and Volvo.

Optimizing the combustion chamber, or making incremental improvements to it, is another way manufacturers and developers are controlling emissions. Reducing the crevice volumes can limit trapping of unburned fuel (and thus HC formation), while reducing the amount of lubricating oil can also reduce HC formation and can limit catalyst poisoning. Other measures include: improving the surface finishes of cylinders and pistons, improving piston ring design and material, and improving exhaust valve stem seals. Also, a “fast burn” combustion chamber can be made by: increasing the rate of combustion, reducing the spark advance, adding a dilutent to the air-fuel mixture, and/or increasing turbulence in the chamber. While optimizing the combustion chamber can lead to reduced emissions, it is another technology that requires reworking of the engine, which can be an expensive process.

Variable valve timing involves calibrating the engine valves to open and close for maximum fuel and engine efficiency. Often, a sensor is used to detect the engine's speed and to adjust the valve openings and closings accordingly. This technology can increase engine torque and horsepower and can improve swirl and intake charge velocity, thus improving the efficiency of combustion. Variable valve technology does not reduce emissions as much as some other technologies and often leads to reductions in fuel efficiency.

Reformulating or using different fuels is another emissions control technique, as some fuels naturally pollute more than others, while some tend to poison the catalysts that would otherwise clean the exhaust air. For instance, the shift from leaded to unleaded fuel in the U.S. greatly decreased lead emissions. Lowering the sulfur content in fuel reduces SOx emissions and increases the efficiency of many catalytic converters, as sulfur can poison catalysts. Another type of fuel, natural gas, typically produces less particulate pollution than diesel fuel and also can reduce NOx and combustion noise. Conversely, natural gas also can increase vehicle weight (due to the need for high pressure tanks) and has refueling limitations.

Using an aftertreatment device—equipment that is used after the fuel is combusted—is very common in certain industries affected by emissions control regulations. One example of an aftertreatment device is a catalytic converter. Catalytic converters can vary widely and can have different functions, but the general description is a device that treats exhaust with the use of catalysts. The composition of the substrates and the catalysts that are on it have changed throughout the years, as has the placement and the number of converters.

A two-way catalytic converter performs oxidation of gas-phase pollution, such as the oxidation of HC and CO to CO₂and H₂O. Diesel oxidation catalysts (DOCs) are another type of two-way catalytic converter used with diesel engines. While these converters are effective at controlling HC and CO and require little maintenance, they can increase NOx emissions and are sensitive to sulfur.

A three-way catalytic converter performs both oxidation (conversion of CO and HC to CO₂and H₂O) and reduction (conversion of NOx to N₂gas) reactions. Since the 1970s, three-way catalytic converters have reduced vehicle emissions. Further performance improvements by these devices are limited by a number of factors, such as the temperature range and surface area of their substrates and by catalyst poisoning. To meet increasingly stringent regulations, some cars require multiple catalytic converters.

A four-way catalytic converter performs oxidation and reduction reactions, and traps particulates to burn them off (regeneration can occur in active or passive mode).

Suppliers of catalytic converters and their associated parts include, but are not limited to, Corning, NGK, Denso, Tbiden, Emitec, Johnson Matthey, Engelhard, Catalytic Solutions, Delphi, Umicore, 3M, Schwaibische Hütten-Werke GmbH (SHW); Hermann J. Schulte(HJS), Clean Diesel Technology, Cleaire, Clean Air Systems, ArvinMeritor, Tenneco, Eberspacher, Faurecia, Donaldson, and Fleetguard.

Particulate traps or filters are another type of aftertreatment device commonly used in diesel applications, as diesel fuel generates more particulate matter than gasoline or some alternative fuels. In a diesel particulate trap (DPT), particles in the exhaust stream pass through a filter that collects them. The removal of particulate matter that is collected on the trap is referred to as “regeneration” and can occur in multiple ways. One method uses external heaters to raise the temperature of the filter to a level necessary for the PM to “burn off.” Another method releases small amounts of diesel fuel in the exhaust stream. When the fuel particles come in contact with the filter, the fuel burns off at an elevated temperature. This higher temperature burns the PM off the filter as well. Yet another means is to use fuel borne catalysts to facilitate regeneration. In another approach, called a “catalyzed diesel particulate trap,” a catalyst is applied directly to the filter itself, which reduces the temperature necessary for the PM to burn off. Finally, an oxidation catalyst can be used in front of the filter to facilitate burn off of the PM. Johnson Matthey's Continuously Regenerating Trap (CRT) is such a system. Diesel particulate traps can reduce PM by as much as 85% in some applications. Traps utilizing a catalyst can also reduce other pollutants besides PM (e.g., HC, CO, and PM) with use of a catalyst (as mentioned earlier). Conversely, these traps can become clogged with PM, soot, and ash and catalyzed versions can be poisoned. They also add cost and weight to vehicles.

Diesel particulate traps can use a number of different types of filters, including: ceramic monolithic cell fiber (Corning, NGK), fiber-wound filter (3M), knitted fiber (BUCK), woven fiber (HUG, 3M), sintered metal fiber (SHW, HJS) or filter paper, among others. Suppliers of these devices and their related technologies include, but are not limited to, Donaldson, Engelhard, Johnson Matthey, HJS, Eminos, Deutz, Corning, ETG, Paas, and Engine Control Systems.

Selective catalytic reduction (SCR) is another example of an aftertreatment system. In this technology, a chemical capable of acting as a reducing agent, such as urea, is added before the exhaust reaches the catalyst chamber. Urea hydrolyzes to form ammonia. The ammonia then reacts with the NOx of the exhaust gas to yield N₂gas, thereby decreasing NOx emissions. The ammonia may be directly injected or be held in the form of solid urea, urea solution or in crystalline form. An oxidation catalyst is often used in parallel with SCR to reduce CO and HC. Unfortunately, while SCR is effective in reducing NOx and has low catalyst deterioration with good fuel economy, it requires an additional tank on the vehicle and an infrastructure for refilling the tank. It is also dependent on end user compliance; companies and drivers are required to refill the tank in order to maintain the emissions control. Suppliers of SCR or its components include, but are not limited to, Engelhard, Johnson Matthey, Miratech Corporation, McDermott, ICT, Sud Chemie, SK Catalysts, and PE Systems. While only used in the U.S. on a limited basis, SCR is expected to be widely used in Europe to reduce emissions, particularly in the heavy duty truck market.

NOx adsorbers are materials that store NOx under lean conditions and release and catalytically reduce it under fuel rich conditions (typically every few minutes). This technology can work in both gas and diesel applications, though gas provides a better fuel rich, high temperature environment. NOx adsorbers reduce the levels of HC, NOx, and CO, but have little to no effect on PM. They can function under a wide range of temperatures. Conversely, NOx adsorbing capacity decreases based on temperature, requires engine controls and sensors, and is functionally hindered or disabled by the sulfur content in fuel. In diesel applications, there are additional constraints, including the quantity of oxygen present in the exhaust, the HC utilization rate, the temperature range, and smoke or particulate formation.

A NOx reduction catalyst can also be used to control emissions by 1) actively injecting reductant into the system ahead of the catalyst and/or 2) using a washcoat with a zeolite that adsorbs HC, thus creating an oxidizing region conducive to reducing NOx. While this technology can reduce NOx and PM, it is more expensive than many other technologies and can lead to poor fuel economy or sulfate particulates.

HC adsorbers are designed to trap VOCs while the catalyst is cold and then release them once the catalyst is heated. This can be done by 1) coating the adsorber directly onto the catalytic converter substrate, which allows for minimal changes but less control, 2) locating the adsorber in a separate, but connected exhaust pipe before the catalytic converter and having the air switch channels once the converter is heated, and/or 3) placing the adsorber after the catalyst. The last two options require a cleaning option for the adsorber.

While this technology reduces cold start emissions, it is difficult to control and adds cost.

Since emissions have proven difficult to control, emissions control technologies are often combined in a system. Examples of combination systems include: a DeNOx and DPT (such as HJS' SCRT system), a catalytic converter placed in the muffler, SCR integrated with the muffler, or a catalyzed diesel particulate filter.

ACERT is another example of a system incorporating multiple emissions control technologies. ACERT, from Caterpillar, targets four areas—intake air handling, combustion, electronics, and exhaust aftertreament. Key components include single and series turbocharging for cooling intake air; variable valve actuation for improving fuel burns; electronic multiplexing for integrating computer control; and catalytic conversion for reducing tailpipe particulate emissions. Working in concert, these subsystems allow the company to increase fuel savings. A significant weakness of this technology is the high volume of catalyst needed.

There are many other emissions control technologies, some of which are not yet technically feasible.

Catalytic Converters

The concerns of pollution caused partly by the automobile led to the Clean Air Act of 1970 which required 90 percent reductions in auto exhaust. The mandatory reduction was considered controversial by some but generally recognized as an advance for clean air and better health.

The automobile industry initially offered resistance to the new proposed regulations. Part of the resistance may have stemmed from the industries' development of improved fuels. From the mid 1920's until the mid 1980's, motor gasoline fuel contained an additive, tetraethyllead (TEL). TEL improved fuel performance by preventing pre-ignition in the cylinders of the engine. Pre-ignition results when the fuel/air mixture ignites prematurely in the combustion chamber of an engine. This results in damage to the engine and efficiency and power reducing caused by knocking.

To attain the reduced emission standards set by the government, engineers invented the catalytic converter. The catalytic converter was added to vehicle exhaust systems starting about 1976. The catalytic converter was effective in reducing emissions to a certain degree. However, the common gasoline formulations containing TEL interfered with the function of the catalytic converter. Because the TEL in the fuel poisoned the metal catalysts of the catalytic converter, TEL was eventually removed from fuel.

While many people may be aware that many vehicles have a catalytic converter, it is generally an unappreciated piece of technology. The purpose of the catalytic converter is to convert, or change, exhaust gases that are pollutants to less harmful compounds, such as nitrogen (N₂, which makes up about 78% of the atmosphere), water (H₂O), and carbon dioxide (CO₂, a product of photosynthesis in plants).

The catalytic converter is used to facilitate the conversion of the unwanted pollutants to relatively harmless molecules such as N₂, H₂O, and CO₂. Basically, the catalytic converter provides a surface on which the pollutants are converted into the relatively harmless products. A catalyst allows the reaction to proceed faster (or at a lower temperature) by lowering the activation energy required. However, a catalyst is not used up in the reaction and can be used again (unless the catalyst is poisoned).

Typical pollutants in exhaust include nitrogen oxides (NOx), unburned hydrocarbons, carbon monoxide, and particulate matter. The nitrogen oxides can be reduced to form nitrogen. When an NO or NO₂molecule contacts the catalyst, the catalyst facilitates removal of nitrogen from the molecule, freeing oxygen in the form of O₂. Nitrogen atoms adhering to the catalyst then react to form N₂gas: 2 NO=>N₂+O₂and 2 NO₂=>N₂+2 O₂.

The carbon monoxide, unburned hydrocarbons, and particulate matter can be further oxidized to form nonpollutants. For example, carbon monoxide is processed as shown: 2 CO+O₂=>2 CO₂.

The overall result of the catalytic converter is to complete the combustion of fuel into nonpollutants.

Conventional catalytic converters have a number of limitations on their effectiveness of eliminating pollutants. For example, if they are located too close to an engine, they can crack from overheating or a quick change in temperature. As such, the filters of the conventional catalytic converters cannot be placed immediately next to or inside an engine exhaust manifold, which is an optimal location to take advantage of the in situ high temperatures before the temperature decreases due to radiant cooling from the high thermal conducting properties of exhaust pipe material. Engine vibration and the quick change in temperatures that exist near and within the exhaust manifold would cause conventional filter material to fatigue and dramatically shorten the life of the filters. In addition, some catalysts applied to conventional filters work less efficiently or even cease to function at high temperatures, i.e., above 500 degrees Celsius. Accordingly, the conventional catalytic converter filters are usually placed in the exhaust path in a location away from the engine.

Structures of Catalytic Converter and Particulate Filter

The components and materials of a catalytic converter are shown schematically in FIGS. 4a and 4b. The catalyst substrate is held within the converter shell (also called a canister) using packaging mat (most often made of ceramic fibers). The converter is connected to the vehicle's exhaust system through the end cones, which can be either welded to the shell or be formed as one part together with the shell, depending on converter packaging technology. The other components shown in the schematic—end seals and/or steel support rings—are optional; they are usually not present in modern passenger car converters, but may be required in more demanding applications, such as close-coupled converters, large converters for heavy-duty engines, or diesel particulate filters. Catalytic converters, especially those in gasoline applications, can be also equipped with steel heat shields (not shown in the schematic) to protect adjacent vehicle components from exposure to excessive temperatures.

Generally, a catalytic converter is composed of at least five main components: 1) a substrate; 2) a catalytic coating; 3) a wash-coat; 4) a matting; and 5) a canister. A general catalytic converter is shown in Figure X. In certain applications, as discussed in more detail below, the catalytic coating is optional.

Substrate

The substrate is a solid surface on which the pollutants can be converted to the nonpollutants. Physically, a substrate provides the interface for several molecular species, in any physical state such as solid, liquid, or gas, to react with each other. The substrate generally has a large surface area to provide a large area on which the pollutants can be converted to nonpollutants.

Over the past decades, many different materials and designs have been tested to act as the substrate for chemical reactions. For example, main physical structures include honeycomb monoliths and beads. (See FIG. 1). The honeycomb structure contains numerous channels, usually running parallel to each other along the length of the substrate. The substrate has channels that run the length of the substrate. The width of channels varies, often depending on the substrate material and applications for which it is used. These channels allow the exhaust gas to flow from the engine through the catalytic converter and out through exhaust pipe. While the exhaust gas flows through the channels of the substrate, the pollutant molecules are converted into nonpollutant molecules via chemical reactions and physical changes.

In the bead structure, the substrate is made of a collection of small beads (similar to putting a bunch of jelly beans in a tube). The exhaust can flow around the beads (through the channels and crevices). The pollutants are converted to nonpollutants as the exhaust gas hits the beads. The bead structure was one of the early attempts to maximize the surface area of substrate to which the exhaust molecules were exposed.

A number of different materials have been used as the substrate. These include ceramic, Fiber Reinforced Ceramic Matrix Composites (FRCMC), foam, powder ceramic, nanocomposite, metals, and fiber mat-type substrates. The most commonly used is a ceramic called cordierite, which is produced by Corning. Cordierite is a ceramic formed from refractory powders. FRCMC is an open celled foam wherein catalyst is disposed on the walls of the cells, the foam being disposed within a catalytic chamber such that exhaust gas must pass through a cell path of the foam to exit. Foams are solids containing numerous pores that are formed by bubbles from gas and burned-off voids. Powder ceramic substrates are different than cordierite and related ceramics in that the powder ceramic is formed from sintered ceramic powders. Nanocomposites are materials that use nano-powders and/or nano-fibers. Metals can also be used as a substrate. Generally, thin sheets of corrugated metal foil, such as steel, are rolled into a honeycomb-like structure. Fiber mat-type substrates are materials that are woven on a small scale. Certain fiber mat-type substrates utilize NEXTEL fibers, produced by 3M. Additionally, “two-dimensional” non-woven fibrous composites have also been tried where honeycomb structures were formed using rolled up pleating and/or corrugation. For example, see U.S. Pat. Nos. 4,894,070; 5,196,120; and 6,444,006 B1.

Catalytic Coating

The third component of current catalytic converters is a catalytic coating. As the name implies, the catalytic coating is the component which actually catalyzes the conversion of pollutants to non-pollutants.

A catalyst is usually defined as a substance which influences the rate of a chemical reaction but is not one of the original reactants or final products, i.e., it is not consumed or altered in the reaction. In several known catalytic reaction mechanisms, the catalyst forms intermediate compounds with reactants but is recovered in the course of the reaction. Many other catalytic processes are not explained fully or understood in their entirety. Neither are the principles governing the selection and preparation of catalysts for specific purposes. Many of the developments in this field are achieved through elaborate exploration programs involving trials of countless materials. Catalysts are widely used in chemical and petrochemical processing to facilitate reactions which otherwise are too slow, or which require high temperatures to yield good efficiencies. Catalysts are also used to convert harmful components of engine exhaust gases, such as hydrocarbons and carbon monoxide, into harmless substances, such as carbon dioxide and water vapor.

Catalysts are substances that have the ability to accelerate certain chemical reactions between exhaust gas components. In emission control catalysis, solid catalysts are used to catalyze gas phase reactions. The catalytic effect and the observed reaction rates are maximized by providing good contact between the gas phase and the solid catalyst. In catalytic reactors, this is usually realized by providing high catalytic surface area through finely dispersing the catalyst on high specific surface area carrier (support).

The catalytic coating is added to the substrate after the substrate is formed. The coating forms a layer on the surface of the substrate, the layer containing the catalyst. Different types of catalysts are needed depending, for example, on the chemical reaction, application needed, temperature conditions, economic factors, etc. A number of metal catalysts are known in the art. For example, the most commonly used are platinum, palladium and rhodium. Significant research has been done to develop new catalysts. See, for example,

The rate of chemical reactions, including catalytic reactions, generally increases with temperature. A strong dependency of conversion efficiency on temperature is a characteristic feature of all emission control catalysts. A typical relationship between the catalytic conversion rate of a pollutant and the temperature is shown as the solid line (A) in FIG. 4. The conversion, near-zero at low temperatures, increases slowly at first and then more rapidly, to reach a plateau at high gas temperatures. When discussing combustion reactions, the term light-off temperature is commonly used to characterize this behavior. The catalyst light-off is the minimum temperature necessary to initiate the catalytic reaction. Due to the gradual increase of the reaction rate, the above definition is not very precise. By a more precise definition, the light-off temperature is the temperature at which conversion reaches 50%. That temperature is frequently denoted T₅₀. When comparing activities of different catalysts, the most active catalyst will be characterized by the lowest light-off temperature for a given reaction.

In some catalyst systems, increasing the temperature may increase the conversion efficiency only up to a certain point, as illustrated by the dashed line (B) in FIG. 4. Further temperature increase, despite increasing reaction rates, causes a decrease in the catalyst conversion efficiency. The declining efficiency is usually explained by other competing reactions which deplete the concentrations of reactants or by thermodynamic reaction equilibrium constrains.

The temperature range corresponding to the high conversion efficiency is frequently called the catalyst temperature window. This type of conversion curve is typical for selective catalytic processes. Good examples include selective reduction of NO by hydrocarbons or ammonia.

Another important variable influencing the conversion efficiency is the size of the reactor. The gas flow rate through a catalytic reactor is commonly expressed, relative to the size of the reactor, as space velocity (SV). The space velocity is defined as the volume of gas, measured at standard conditions (STP), per unit time per unit volume of the reactor, as follows: (3)SV=V/V_rwhere V is the volumetric gas flow rate at STP, m³/h; V_ris the reactor volume, m³, and SV has the dimension of reciprocal time which is commonly expressed in 1/h or h⁻¹.

In various catalytic emission control applications, the space velocities range from 10,000 l/h to 300,000 l/h. Space velocities for monolithic reactors are calculated on the basis of their outside dimensions, e.g., diameter and length of a cylindrical ceramic catalyst substrate. Since this method does not take into account the geometric surface area of the substrate, cell density, wall thickness, or catalyst loading, it is not always appropriate for catalyst comparisons. Nevertheless, it is a commonly used and widely accepted industry standard.

Typical platinum loadings in filters used for off-road engines through the 1990's were between 35 and 50 g/ft³. These filters, installed on relatively high polluting engines, required minimum temperatures of nearly 400° C. for regeneration. Later, when catalyzed filters were applied to much cleaner urban bus and other highway vehicle engines, it was found that they were able to regenerate at much lower temperatures. However, higher platinum loadings were needed to support the low temperature regeneration. Filters used in clean engine, low temperature applications have typically platinum loadings of 50-75 g/ft³.

Wash Coat

In most cases, the catalytic coating includes a wash coat as a fourth component. The washcoat is applied to the surface of the substrate, thereby increasing surface area of the substrate. The washcoat also provides a surface to which the catalyst adheres. The metal catalyst may be impregnated on this porous, high surface area layer of inorganic carrier, (i.e., washcoat—the term “catalyst support” may be used to denote the ceramic/metallic substrate, as well as the carrier/washcoat material).

A number of substances can be used as a washcoat. Substances which are widely used for catalyst carriers include activated aluminum oxide and silicone oxide (silica).

The washcoat is a porous, high surface area layer bonded to the surface of the support. Its exact role, which is certainly very complex, is not clearly understood or explained. The main function of the washcoat is to provide very high surface area, which is needed for the dispersion of catalytic metals. Additionally, the washcoat can physically separate and prevent undesired reactions between components of a complex catalytic system.

Washcoat materials include inorganic base metal oxides such as Al₂O₃(aluminum oxide or alumina), SiO₂, TiO₂, CeO₂, ZrO₂, V₂O₅, La₂O₃and zeolites. Some of them are used as catalyst carriers. Others are added to the washcoat as promoters or stabilizers. Still others exhibit catalytic activity of their own. Good washcoat materials are characterized by high specific surface area and thermal stability. The specific surface area is determined by nitrogen adsorption measurement technique in conjunction with mathematical modeling known as the BET (Brunauer, Emmet, and Teller) method. Thermal stability is evaluated by exposing samples of given material to high temperatures in a controlled atmosphere, usually in the presence of oxygen and water vapor. The loss of BET surface area, which is remeasured at different time intervals during the test, indicates the degree of thermal deterioration of the tested material.

The washcoat can be applied to the catalyst support from a water based slurry. The wet washcoated parts are then dried and calcined at high temperatures. The quality of the catalyst washcoat can significantly influence the performance and durability of the finished catalyst. Since the noble metal is subsequently applied to the washcoated parts by impregnation, i.e., “soaking” the washcoat porosity with the catalyst solution, the washcoat loading will determine the noble metal catalyst loading in the finished product. Therefore, it is extremely important that the washcoating process produces a very repeatable and uniform washcoat layer. The details on the washcoating process and its parameters are guarded as trade secrets by all catalyst makers.

Canister

The substrate is packaged into a canister, e.g., a steel shell, to form a catalytic converter. The canister performs a number of functions. It holds the catalyzed substrate and protects the substrate from the external environment. Additionally, the canister forces exhaust gas to flow through and/or over the catalyzed substrate.

The catalyzed substrate can be also packaged inside mufflers, which are then referred to as “catalyst mufflers” or “catalytic mufflers.” In this case, one steel canister holds both the catalyst and the noise attenuation components, such as baffles and perforated tubing. Catalyst mufflers can offer more space saving design compared to the combination of a catalytic converter and a muffler.

The catalyzed substrate is usually placed inside the canister having a configuration made according to one of several methods, including: clamshell, tourniquet, shoebox, stuffing, and swaging, as shown in FIG. 28.

Matting

In addition to the canister, a matting material is often used to package the catalytic substrate in the canister. The packaging mats, usually made of ceramic fibers can be used to protect the substrate and to distribute evenly the pressure from the shell. The mats often include vermiculite, which expands at high temperatures, thus compensating for the thermal expansion of the shell and providing adequate holding force under all operating conditions.

For example, ceramic monoliths are wrapped in a special packaging material which holds them securely in the steel housing, uniformly distributing pressure and preventing cracking. Ceramic fiber mats are most commonly used for packaging of catalytic converters for both gasoline and diesel applications. These packaging mats can be classified as follows: intumescent (heat-expandable) mats; conventional (high vermiculite); reduced vermiculite; non-intumescent mats; or hybrid mats.

Heat Insulation

In many applications, the catalytic converter must be heat insulated to avoid damage to surrounding vehicle components (e.g., plastic parts, fluid hoses) or—in converters mounted closer the engine—to prevent an increase of engine compartment temperature. One of the methods of converter thermal management is to employ a steel heat shield positioned around the converter body. An alternative method is to provide an insulation layer inside the shell by either (1) increasing the thickness of the mounting mat, or (2) providing an additional layer of dedicated, low thermal conductivity insulation. While heat shields have been traditionally used in the underfloor location, it has been suggested that increased mat thickness offers the best solution for converters installed in the engine compartment (Said Zidat and Michael Parmentier, “Heat Insulation Methods for Manifold Mounted Converters,” Delphi Automotive Systems, Technical Centre Luxembourg, SAE Technical Paper Series 2000-01-0215). One of the advantages of using thicker mat rather than the heat shield is the lower average mat temperature, which minimizes the risk of destroying vermiculite mats in close-coupled gasoline engine applications.

Particulate Trap

Another device for removing pollutants from an exhaust gas is a particulate trap. A common particulate trap used on diesel engines is a diesel particulate trap (DPT). A main purpose of a particulate trap is to filter and trap particulate matter of various sizes from a stream of fluid, such as an exhaust gas flow. The effectiveness of a particulate filter is generally measured in its ability of filtering PM of different size, e.g., PM-2.5 and PM-10.

Diesel traps are relatively effective at removing carbon soot from the exhaust of diesel engines. The most widely used diesel trap is the wall-flow filter which filters the diesel exhaust by capturing the soot on the porous walls of the filter body. The wall-flow filter is designed to provide for nearly complete filtration of soot without significantly hindering the exhaust flow.

As the layer of soot collects on the surfaces of the inlet channels of the filter, the lower permeability of the soot layer causes a pressure drop across the filter and a gradual rise in the back pressure of the filter against the engine, causing the engine to work harder, thus affecting engine operating efficiency. Eventually, the pressure drop becomes unacceptable and regeneration of the filter becomes necessary. In conventional systems, the regeneration process involves heating the filter to initiate combustion of the carbon soot. In certain circumstances, the regeneration is accomplished under controlled conditions of engine management whereby a slow burn is initiated and lasts a number of minutes, during which the temperature in the filter rises from about 400-600° C. to a maximum of about 800-1000° C.

In certain applications, the highest temperatures during regeneration tend to occur near the exit end of the filter due to the cumulative effects of the wave of soot combustion that progresses from the entrance face to the exit face of the filter as the exhaust flow carries the combustion heat down the filter. Under certain circumstances, a so-called “uncontrolled regeneration” can occur when the onset of combustion coincides with, or is immediately followed by, high oxygen content and low flow rates in the exhaust gas (such as engine idling conditions). During an uncontrolled regeneration, the combustion of the soot may produce temperature spikes within the filter which can thermally shock and crack, or even melt, the filter. The most common temperature gradients observed are radial temperature gradients where the temperature of the center of the filter is hotter than the rest of the substrate and axial temperature gradients where the exit end of the filter is hotter than the rest of the substrate.

In addition to capturing the carbon soot, the filter also traps metal oxide “ash” particles that are carried by the exhaust gas. Usually, these ash deposits are derived from unburnt lubrication oil that accompanies the exhaust gas under certain conditions. These particles are not combustible and, therefore, are not removed during regeneration. However, if temperatures during uncontrolled regenerations are sufficiently high, the ash may eventually sinter to the filter or even react with the filter resulting in partial melting.

It would be considered an advancement in the art to obtain a filter which offers improved resistance to melting and thermal shock damage so that the filter not only survives the numerous controlled regenerations over its lifetime, but also the much less frequent but more severe uncontrolled regenerations.

Continuous Regeneration Trap

One conventional method for catalytic conversion is a diesel particulate trap (“DPT”). A DPT is a filter that collects particulate matter in the exhaust. The collected particulate matter must then be burned off before the filter becomes clogged. Burning off the particulate matter is referred to as “regeneration.” Several conventional methods exist for regeneration of DPTs. First, an application of precious metal catalysts or base-metal catalyst to the surface of the filter can reduce the temperature needed for oxidation of particulate matter. Second, the filter can be preceded with a chamber containing oxidation catalyst that creates NO₂, which helps to burn off particulate matter. Third, the system can utilize fuel-born catalysts. Finally, external source of heat may be employed, wherein soot burns at 550 degrees Celsius without catalysts or approximately 260 degrees Celsius with precious metal catalysts. Regeneration leaves behind ash residue as the carbon burns, requiring constant maintenance to clean the filter.

Yet another conventional method utilizes diesel oxidation catalysts (“DOCs”). DOCs are catalytic converters that oxidize CO and hydrocarbons. Hydrocarbon activity extends to the polynuclear aromatic hydrocarbons (“PAHs”) and the soluble organic fraction (“SOF”) of particulate matter. Catalyst formulations have been developed that selectively oxidize the SOF while minimizing oxidation of sulfur dioxide or nitric oxide. However, DOCs may produce sulfuric acid and increase the emission of NO₂.

The function of the catalyst in the catalyzed diesel particulate filter (CDPF) is to lower the soot combustion temperature to facilitate regeneration of the filter by oxidation of diesel particulate matter (DPM) under exhaust temperatures experienced during regular operation of the engine/vehicle, typically in the 300-400° C. range. In the absence of the catalyst, DPM can be oxidized at appreciable rates at temperatures in excess of 500° C., which are rarely seen in diesel engines during real-life operation. Reported substrates used in these catalyst applications include cordierite and silicon carbide wall-flow monoliths, wire mesh, ceramic foams, ceramic fiber media, and more. The most common type of a CDPF is the catalyzed ceramic wall-flow monolith.

Catalyzed ceramic traps were developed in early 1980's. Their first applications included diesel powered cars and, later, underground mining machinery. Catalyzed filters were commercially introduced for Mercedes cars sold in California in 1985. Mercedes models 300SD and 300D with turbocharged engines were equipped with 5.66″ diameter×6″ filters fitted between the engine and the turbocharger.

The use of diesel traps on cars was later abandoned, due to such issues as insufficient durability, increased pressure drop, and filter clogging. Today, even though not all of these problems have been solved, catalyzed ceramic traps remain one of the most important diesel filter technologies. CDPFs are increasingly used in a number of heavy-duty applications, such as urban buses and municipal diesel trucks. For a number of years, limited quantities of catalyzed filters have been also used in underground mining (North America and Australia) and in certain stationary engine applications.

Catalyzed ceramic filters are commercially available for a number of highway, off-road, and stationary engine applications as both OEM and aftermarket (retrofit) product. The list of suppliers includes Engelhard, OMG dmc2, as well as several smaller emission control manufacturers who specialize primarily in the off-road markets.

The main component of conventional filters is a ceramic (typically cordierite or SiC) wall-flow monolith. The porous walls of the monolith are coated with an active catalyst. As the diesel exhaust aerosol permeates through the walls, the soot particles are deposited within the wall pore network, as well as over the inlet channel surface. The catalyst facilitates DPM oxidation by the oxygen present in exhaust gas.

Pressure Drop

The flow of exhaust gas through a conventional catalytic converter creates a substantial amount of backpressure. The backpressure buildup in a catalytic converter is an important attribute to catalytic converter success. If the catalytic converter is partially or wholly clogged, it will create a restriction in the exhaust system. The. subsequent buildup of backpressure will cause a drastic drop in engine performance (e.g., horsepower and torque) and fuel economy, and may even cause the engine to stall after it starts if the blockage is severe. Conventional attempts to reduce pollutant emissions are very expensive, due to both the cost of materials and retrofitting or manufacturing an original engine with the appropriate filter.

High filtration efficiencies of wall-flow filters are obtained at the expense of relatively high pressure drop which increases with the filter soot load. Initially, the filter is clean. As the particulate start depositing within the pores in monolith walls (depth filtration), the pressure drop starts increasing with time in a non-linear manner. This phase is called the initial loading phase, during which pore attributes like permeability and filter porosity continuously change due to the increasing soot deposit inside the pore network. After the filtration capacity of the pores becomes saturated, soot starts depositing as a layer inside the inlet monolith channels (cake filtration phase). A linear increase in pressure drop with time (and with soot load) is observed during this period. One property that changes is the thickness of the soot layer. Some authors also distinguish an intermediate short transition phase, from the moment the particulates start depositing on the channel surface until the soot layer is fully established (Tan, J. C., et al., 1996, “A Study on the Regeneration Process in Diesel Particulate Traps Using a Copper Fuel Additive”, SAE 960136; Versaevel, P., et al., 2000, “Some Empirical Observations on Diesel Particulate Filter Modeling and Comparison Between Simulations and Experiments”, SAE 2000-01-0477).

Pressure drop modeling in clean filter substrates has been done. Relatively simple models that have been developed show excellent agreement with experimental results (Masoudi, M., et al., 2000, “Predicting Pressure Drop of Wall-Flow Diesel Particulate Filters—Theory and Experiment”, SAE 2000-01-0184; Masoudi, M., et al., 2001, “Validation of a Model and Development of a Simulator for Predicting the Pressure Drop of Diesel Particulate Filters,” SAE 2001-01-0911). Most of the filter pressure drop in real applications, however, is created by the soot deposit. In practical applications, the pressure drop of the clean wall-flow filter can be in the range of 1 to 2 kPa, while a loaded filter pressure drop of 10 kPa can be considered in certain circumstances low to moderate.

The total pressure drop of the particulate loaded filter, can be divided into the following four components: pressure drop due to sudden contraction and expansion at the inlet and outlet from the filter; pressure drop due to channel wall friction; pressure drop due to permeability of particulate layer; and pressure drop due to wall permeability.

Pressure drop due to sudden contraction and expansion at the inlet and outlet from the filter is similar to the same component in the clean filter, except that the effective channel size (hydraulic diameter) is now smaller due to the soot layer, resulting in more gas contraction.

Pressure drop due to channel wall friction also increases relative to the clean filter scenario, due to the decrease in the channel hydraulic diameter. With thick soot layers, ΔPchannel can become a very significant contributor to the total pressure drop.

Pressure drop due to permeability of particulate layer (ΔPparticulate) is can be a signficant contributor to the total pressure drop.

Pressure drop due to wall permeability (ΔPwall) is now also higher than in the clean filter, because the wall pores are partly filled with soot. The increase in ΔPwall that can be attributed to the initial soot loading phase in the pores is represented by ΔPI in FIG. 3.

The total pressure drop can be expressed as follows:
ΔP=ΔPin/out+ΔPchannel+ΔPparticulate+ΔPwall

Mathematical modeling of the pressure drop in soot loaded diesel filters becomes a complex and difficult task. Important properties of soot, such as the permeability and packing density, depend on the application, engine operating conditions, and other parameters. There is an ongoing effort to simulate pressure drop in wall-flow filters and increasingly more sophisticated models are being developed. Predicting the actual soot loading may require a theoretical model of the regeneration process itself.

Types of Catalytic Converters and Particulate Filters

Catalytic converters can be classified based on a number of factors including: a) the type of engine on which the converter is used, b) its location relative to the engine, c) the number and type of catalysts used in the converter, and d) the type and structure of the substrate used. In addition each of these catalytic converters are often used in conjunction with other emission-control devices, such as CRT, EGR, SCR, ACERT, and other devices and methods.

Engine

Catalytic converters are used on at least two types of engines: gasoline and diesel. Within these two general classes, there are numerous types of specific gasoline and diesel engines. For example, gasoline and diesel engines are manufactured having varying displacements and horsepower. Certain engines are equipped with a turbocharger and/or an intercooler. Most car and truck engines are water-cooled, while many motorcycle engines are air-cooled. Certain utilities require high available horsepower, while others maximize fuel economy. All of these variables, in addition to others, may affect the level of pollutants produced during combustion of the fuel. Moreover, depending on the use of the engine, e.g., on-road, off-road, or stationary, there are different regulatory requirements with respect to emissions standards.

Location

The catalytic converter can theoretically be placed anywhere along the exhaust stream of an engine. However, physical characteristics of conventional catalytic converters limit their location. Most commonly in vehicles, the catalytic converter is placed some distance from the engine block, closer to the muffler and underneath the body of the car. The catalytic converter is usually not placed close to the engine because the catalytic converter can fail for several reasons. Such reasons include extreme temperatures, thermal shock, mechanical vibration, mechanical stress, and space limitations near the engine. Also, physical setups of stationary engines may limit the location of a catalytic converter or particular filter.

For example, in its 2004 FOCU.S.™, Ford Motor Company managed to deploy a mani-cat as did Honda Motor Corporation in one of its offerings. These systems are in actuality adjacent to, rather than part of, the manifold. The higher temperatures and the extreme vibrational energy generated by cylinder explosions and moving parts would subject current catalytic converters, if placed in a manifold, to extremes in thermal and physical shock. Additionally, a design for a mani-cat was proposed by Northup Grumman Corporation in U.S. Pat. No. 5,692,373. It is believed that even the current cordierite substrate would find such an environment challenging to endure.

In other applications, for example such as motorcycles (e.g., Harley-Davidson), the presence of a catalytic converter in certain locations can cause serious injury to the user. Because of the high operating temperatures of a catalytic converter, it would be preferable to use a catalytic converter that is less prone to causing injury to a user, e.g., a smaller catalytic converter, a converter that does not get as hot, etc.

In certain instances, the exhaust system (for example, in a car) may contain more than one catalytic converter or particular filter along its exhaust flow. (See FIG. 4). For example, an exhaust system may have an additional catalytic converter between the engine and the main catalytic converter. This configuration is referred to as a pre-cat. The pre-cat may have denser configuration. Another set-up is a back-cat, which has second catalytic converter behind (or after) the main catalytic converter. The back-cat is also sometimes used for a retrofit catalytic converter.

Two Way vs. Three Way vs. Four Way

Catalytic converters can generally be classified as being a two-way, three-way, or four-way converter. There are at least the following types of converters commercially available: oxidation converters, three-way converters (no air), three-way-plus oxidation converters, and four-way converters.

Oxidation (two-way) converters represent the early generation of converters that were designed to oxidize hydrocarbons (HC) and carbon monoxide (CO). Although these units represent the most basic form of catalytic converter technology, they remain a viable pollution reduction option in some areas. Oxidation converters usually contain platinum or palladium. However, other non-noble metals can be used as well.

In the early 1980s, most vehicle manufacturers began using converters designed to reduce NOx, in addition to oxidizing HC and CO. These three-way converters, which were used in conjunction with computer controlled engine systems and oxygen sensors, were employed to more precisely control the air to fuel ratio. These converters are referred to as three-way converters because they deal with three compounds: HC, CO and NO_x.

Most modern cars are equipped with “three-way” catalytic converters typically having one or more substrates in tandem using Coming's clay extrusion technology. “Three-way” refers to the three regulated emissions the converter helps to reduce: carbon monoxide, volatile organic compounds (VOCs, e.g., unburned hydrocarbons), and NOx molecules. Such converters use two different types of catalysts, a reduction catalyst and an oxidization catalyst.

In a three-way catalytic converter, the reduction catalyst is usually found in the first stage of the catalytic converter and serves to reverse the oxidation of nitrogen that occurred in the combustion chamber. It commonly uses platinum and rhodium to help reduce NOx emissions. The oxidation catalyst, which can be composed of metals such as platinum and/or palladium, is commonly located in a second region of the catalytic converter.

Three-way converters that have a reduction and an oxidation catalyst together in one housing are sometimes called three-way-plus-oxidation converters. These converters use air injection between the two substrates. This air injection aids the oxidation chemical reaction.

Four-way converters process carbon monoxide, nitrogen oxide, unburnt hydrocarbons, and particulate matter. These include, for example, the QuadCAT Four-Way Catalytic Converter manufactured by Ceryx. It is a catalytic converter that that, according to its manufacturer, reduces four of the major sources of air pollution—NOx, hydrocarbons, carbon monoxide and particulate matter—to levels that will allow diesel engines to meet 2002/2004 emissions standards. Others include those described in U.S. Pat. Nos. 4,329,162; and 5,253,476.

The catalytic converter, like other catalysts, facilitates reactions by lowering the activation energy required to accomplish the desired reaction. For example, if particulates require a temperature of 550° C. before reacting with oxygen in the presence of catalysts, to burn off, this same reaction might require a temperature of only 260° C. This lower energy threshold permits one physically to locate a catalytic system downstream from the engine where space is more abundant, even though temperatures are cooler. Otherwise, the catalytic system will need to be placed upstream where temperatures are higher. However, this is impractical with current technology because there is more potential to damage the substrate when it is placed closer to the engine.

Diesel engines produce emissions that are high in NOx and particulate matter due to the high temperature and pressure, while relatively low CO and hydrocarbon production. The compression combustion is less complete than with a spark of a gasoline engine. However, because of the relatively lean mixture with high air content, diesel is able to provide better gas mileage than a gasoline engine. Three-way catalysts do not work well in diesel exhaust due to the excess air. NOx reduction catalysts typically require a well-maintained stoichiometric ratio of fuel-to-air which cannot be easily done in diesel combustion engines.

Catalytic converter technology may be applied to various applications, including internal combustion engines and stationary combustion engines. The internal combustion engine is the most common engine used for vehicles. A catalytic converter is installed as a device in the vehicle's exhaust system, so the entire exhaust gas stream passes through the substrate, contacting the catalyst before being discharged from the tailpipe. However, catalytic converters can be also part of fairly complex systems involving various active strategies, such as injection of reactants in front of the catalyst or sophisticated engine control algorithms. Examples include a number of diesel catalyst systems being developed for the reduction of NOx. The attributes of simplicity and passive character which have been listed among the advantages of catalysts may no longer apply to those systems.

Conventional attempts to reduce pollutant emissions can be very expensive, due partly to both the cost of materials and, in certain applications, to retrofitting or manufacturing an original engine with the appropriate filter.

Advances in Catalytic Converter and Particulate Filter Technology

An invention that lead to progress in catalytic converters was Coming's development of extruded cordierite honeycomb monoliths. (See U.S. Pat. No. 4,033,779). Since the 1970's, more than a billion pounds of pollutants have been removed from exhaust streams using this approach which employs catalysts (platinum, palladium, rhodium, etc.) from the noble and base metal families firmly lodged in a washcoat on the surface of a rugged substrate (generally cordierite) that can withstand the extreme environment of an engine exhaust system. Variations and improvements to this core technology have evolved in the years since, including variations in the placement of catalytic converters as well as in their composition and methods of manufacture. Still, however, there remain fundamental inadequacies that, to date, have not been overcome. Currently, the state of technology is reaching physical and economical limits with only minor improvements being made at great expense.

Limitations of Current Substrates

While the present state of catalytic converter and particulate matter filter technology is useful to some degree for reducing emission pollution, there are certainly drawbacks to the current technology. There are also characteristics that are not met by the present catalytic converters. Some inadequacies are inherent to the type of substrate used. Accordingly, an improved substrate for use in a catalytic converter or particulate filter would be a significant advance in the fundamental physical and chemical attributes of the materials used as catalyst substrates in the catalytic converter. Moreover, an improved substrate would dramatically enhance the quality and would enable manufacturers and users to meet more easily the emissions standards of 2007, and 2010, and later years.

The conventional monolithic catalytic converter substrate is generally formed through an extrusion process. This process, which is both complicated and relatively expensive, has been used for the past twenty-five years. However, there are limitations to the extrusion process. There is a limit as to how small channels can be created within the material and still maintain quality control. The extrusion process also limits the shapes of the catalytic converters to cylinders or parallelograms, or shapes that have sides parallel to the extrusion axis. This shape limitation has not been an issue with previous emission standards. However, the need to design a catalytic converter and particulate filter able to reach near-zero emissions performance may require non-linear and/or non-cylindrical filter design and vehicle integration.

Decreasing the wall thickness increases the surface area, e.g., in certain instances, decreasing wall thickness from 0.006 inches to 0.002 inches increases surface area by 54%. By increasing the surface area, more particulate matter may be deposited in less volume. FIG. 1