Automobile exhaust emission control

Belton, D. N. and Taylor, K. C. (1999) Automobile exhaust emission control by catalysts , Curr. Opin. Solid State. Mater. Sci., 4, 97. 

Augmented-plane-wave method, 34 246 Austemite, decarburization of, 21 332-334 Autocatalysis, 25 275, 34 15, 36 Automobile exhaust emission control, 34 275, 278... 

Since 1962 rare earths have been used to stabilize zeolite cracking catalysts for the petroleum industry (1, 2. Until recently this application to catalysis has been the only commercially significant one. Currently, however, a number of new applications of potential commercial significance are appearing. One of the most important of these is the use of cerium in catalysts for automobile exhaust emission control. We will emphasize this application in our review without neglecting other applications. 

Several of the early oxide studies have already been mentioned in the introduction. The copper-alumina oxidation catalyst, which finds applications for the synthesis of glyoxal from glycol and as the principal component of base-metal formulations for automobile exhaust emission control, has... 

AECC is an international association, based in Brussels, whose members are European companies in the business of making the technologies for automobile exhaust emissions control. The members are Allied Signal Environmental Catalysts, Coming, Degussa, Emitec, Engelhard Technologies, Johnson Matthey, NGK Europe and Rhone-Poulenc Chimie. 

Honeycomb monolith reactors are commonly used in automobile exhaust emission control and for NOx reduction in power-plant flue gases by catalytic reduction, but they also can be used for photocatalytic reactions in the gas phase (see Fig. 7.2c). This type of reactors contains certain number of channels of circular or square cross section. The photocatalyst is coated onto the inner walls of channels... 

Although the naturally occurring concentration of ozone at the earth s surface is low, the distribution has been altered by the emission of pollutants, primarily by automobiles but also from industrial sources which lead to the formation of ozone. The strategy for controlling ambient ozone concentrations arising from automobile exhaust emissions is based on the control of hydrocarbons, CO, and NO via catalytic converters. As a result, peak ozone levels in Los Angeles, for instance, have decreased from 0.58 ppm in 1970 to 0.33 ppm in 1990, despite a 66% increase in the number of vehicles. 

Emission Control Technologies. The California low emission vehicle (LEV) standards has spawned iavestigations iato new technologies and methods for further reducing automobile exhaust emissions. The target is to reduce emissions, especially HC emissions, which occur during the two minutes after a vehicle has been started (53). It is estimated that 70 to 80% of nonmethane HCs that escape conversion by the catalytic converter do so during this time before the catalyst is fully functional. 

Examples of multi-disciplinary innovation can also be found in the field of environmental catalysis such as a newly developed catalyst system for exhaust emission control in lean burn automobiles. Japanese workers [17] have successfully merged the disciplines of catalysis, adsorption and process control to develop a so-called NOx-Storage-Reduction (NSR) lean burn emission control system. This NSR catalyst employs barium oxide as an adsorbent which stores NOx as a nitrate under lean burn conditions. The adsorbent is regenerated in a very short fuel rich cycle during which the released NOx is reduced to nitrogen over a conventional three-way catalyst. A process control system ensures for the correct cycle times and minimizes the effect on motor performance. 

Congress attempted to correct that deficiency and other air pollution problems in a series of amendments to the 1963 act passed in 1965, 1966, 1967, and 1969. The 1965 amendments, for example, authorized the secretary of health, education and welfare to establish nationwide standards for automobile exhaust emissions. This legislation and later amendments also authorized the surgeon general to study the effects of air pollutants on human health, expanded local air quality programs, set compliance deadlines for meeting new air quality standards, established air quality control regions (AQCRs), and authorized research on low emission fuels and more fuel-efficient automobiles. 

Recent automobile exhaust emissions standards are summarized in Table III, and a review of the catalytic systems designed to meet these standards has recently appeared (26). Catalytic converters have been used as a part of emission control systems since 1975. One approach has been to use a dual bed catalytic converter where the reduction of NO to N2 occurs over the first bed, and excess O2 is provided to the second bed to oxidize the CO and hydrocarbons more completely. Typically, the exhaust contains compounds listed in Table IV plus some poisons containing Pb, P, S etc, (27). The catalytic system must reduce concentrations of CO, hydrocarbon and NOx to legally acceptable levels. 

One of the early problems with catalytic control of automobile exhaust emissions was during the few minutes immediately after starting the engine when the cold catalytic systems did not function. This was solved by developing a porous zeolite which traps the unburned hydrocarbons while the catalysts are still cold [15]. Once the catalysts have warmed up, the zeolite canister also warms, releasing the trapped hydrocarbons to the catalytic systems to perform their important control reactions. 

The relationship between automobile exhaust emission levels and stationary pollutant sources and air quality is not a direct one. Complex mathematical models have been developed for predicting trends in air quality. These models include as input information on vehicle populations, atmospheric chemistry, meteorological variables, and other variables which can impact on the air quality of an urban area. Predicting the level of control needed to meet air quality goals is complicated by the multiple inputs to the atmosphere in urban areas. 

The control of noxious emissions resulting from either the combustion of fossil fuels or from other industrial activities is one of the most immediate and compelling problems faced by nearly every country in the world. Enviromuental problems caused by two sources, automobile exhaust emissions and flue emissions from coal and oil fired power stations, have received much publicity over recent decades. 

Today, microprocessors are everywhere. Of course, they are in your computer and calculator, but microprocessors are also in many simple things we take for granted. Personal stereos, appliances with digital displays, automobiles with exhaust emission controls, even quartz watches and clocks (jumping second hand) all are controlled by microprocessors. One of the most common uses for microprocessors in the United States today is for controlling traffic lights. 

Air Pollution Control Device Meehanism or equipment that eleans emissions generated by a source (e.g., an incinerator, industrial smokestack or an automobile exhaust system) by removing pollutants that would otherwise be released to the atmosphere. 

In 1996, consumption in the western world was 14.2 tonnes of rhodium and 3.8 tonnes of iridium. Unquestionably the main uses of rhodium (over 90%) are now catalytic, e.g. for the control of exhaust emissions in the car (automobile) industry and, in the form of phosphine complexes, in hydrogenation and hydroformylation reactions where it is frequently more efficient than the more commonly used cobalt catalysts. Iridium is used in the coating of anodes in chloralkali plant and as a catalyst in the production of acetic acid. It also finds small-scale applications in specialist hard alloys. 

Iwamoto, M. and Mizimo, N. NOx emission control in oxygen-rich exhaust through selective catalytic reduction by hydrocarbon. Proceedings - IMechE Part D, J. Automobile Eng., 1993, Volume 207, Issue Dl, 23-33. 

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