Catalysts for Automotive Pollution Control

Automobiles contribute significantly to air pollution, especially in urban areas. Typical concentrations in the exhaust gases of a gasoline engine are given in Fig. 2.12. 

Catalysis has been remarkably successful in reducing emissions. Table 2.3 shows typical emissions for Otto (gasoline) engines with and without a three-way catalyst are shown. Data for diesel engines are also included. 

Emission of particulates, hydrocarbons, NOx, and CO for gasoline engines, gasoline engines with a catalyst and diesel engines 

For three-way catalysts in converters for Otto engines Pt/Rh supported on La-stabilized alumina are used. Promoters are present e.g., Ce02. The alumina is usually situated as a washcoat layer in a monolith (typically with a cell density of 400 cells/in2) consisting of cordierite. In practice, the catalysts appear to be very stable. In fact, the durability of the electronic control system (for the regulation of the X value in the converter) is more critical than the catalyst itself. 

Recently, in academic circles and in industry, a renewed interest can be observed in the development of non-noble metal catalysts, e.g., Cu-based catalysts. If lean-burning systems were to become available, oxidation would be the only reaction to be catalyzed and catalyst composition will certainly be changed accordingly. Catalytic converters are still in the development stage for diesel engines. 

---

Harold, M., Luss, D., Liu, Yi (2012) Dual Layered Catalysts for Lean Reduction of NOx by In Situ Generation of Ammonia, presentation at the Catalysts for Automotive Pollution Control 9 (CAPoC9), September 2012, Bmssels. 

Impens R. (1987) Automotive traffic, risk for the environment , in A. Crucq and A. Frennet (eds). Catalyst and automotive pollution control. Studies in surface science and catalysis, 30, Elsevier Sciences Publishers, Amsterdam. 

Cerium oxides are outstanding oxide materials for catalytic purposes, and they are used in many catalytic applications, for example, for the oxidation of CO, the removal of SOx from fluid catalytic cracking flue gases, the water gas shift reaction, or in the oxidative coupling reaction of methane [155, 156]. Ceria is also widely used as an active component in the three-way catalyst for automotive exhaust pollution control,... 

Exhaust gas catalysts has been widely used since the laimching of the 1970 Clean Air Act in the USA and especially after the introduction of stricter regulations in 1981. At present, one of the fastest growing areas of catalyst-based technology is automotive pollution control. All gasoline-fuelled vehicles sold in the USA, Japan and in the European Community must be equipped with exhaust aftertreatment in order to meet the emission standards. Oxidation catalysts for heavy-duty vehicles have only been used for a short period, but following the tightening emission standards there will be an increased demand for such systems. 

In the eighties, the european countries started to show some interest to that problem. It is only in June 1984 that the EC Commission proposed standarts of permissible pollutants in the exhaust gas from motor vehicles to be introduced in Europe these standarts were approved by the Ministers of the Environment one year later. Very quickly, a number of Academic research laboratories started working on the subject, and namely on the development of new catalysts. We thought that a need for exchange of results and of ideas had appeared and I have initiated the organization of international meetings on this topics at the University of Brussels under the title Catalysis and Automotive Pollution Control associated with the acronym CAPoC-... 

Loof, P., B. Kasemo, L. Bjomkvist, S. Andersson and A. Frestad, 1991b, TPD and XPS studies on CO and NO on highly dispersed Pt + Rh automotive exhaust catalysts Evidence for noble metal-ceria interaction, in Catalysis and Automotive Pollution Control II, ed. A. Crucg (Elsevier, Amsterdam) pp. 253-274. 

Taha, R., D. Duprez, N. Mouaddib-Moral and C. Gauthier, 1998, Oxygen storage capacity of three-way catalysts a global test for catalyst deactivation, in Catalysis and Automotive Pollution Control iy eds N. Kruse, A. Frennet and J.-M. Bastin (Elsevier, Amsterdam) pp. 549-558. Tani, E., M. Yoshimura and S. Somiya, 1983a, J. Am. Ceram. Soc. 66, 506. 

Ito, E., R.J. Hultermans, P.M. Lugt, M.H.W. Burgers, H. van Bekkum and C.M. van den Bleek, 1995b, Selective reduction of NO, with ammonia over cerium exchanged zeolite catalysts - Towards a solution for an ammonia slip problem, in Catalysis and Automotive Pollution Control III, eds A. Frennet and J.-M. Bastin, Vol. 96 of Studies in Surface Science and Catalysis (Elsevier, Amsterdam) pp. 661—673. 

Ball, D.J. and Stack, R.G., Catalysts for diesel powered vehicles. In Catalysis and Automotive Pollution Control II, (Ed Crucq, A.) Elsevier Science Publishers, Amsterdam, 337-51 (1991). 

In fact, depending on the driving, it is not unusual for a traditional TWC to meet temperatures up to 900 °C during operation. Furthermore, because of the continuously stricter limits for automotive pollutants demanded, the control of cold-start emissions through the concept of close-coupled catalysts (CCCs) has to... 

Automotive pollution control is a major application for Platinum group metals. In 1989, 42% of the western world demand for Platinum, 8% for Palladium and especially 81 % for Rhodium, were for the manufacture of automotive catalysts (Steel (1990)). Because of the high cost of these metals, the converter must be designed to obtain high pollutant conversions with a minimum amount of metals. 

Automotive Emission Control Catalysts. Air pollution (qv) problems caused by automotive exhaust emissions have been met in part by automotive emission control catalysts (autocatalysts) containing PGMs. In the United States, all new cars have been requited to have autocatalyst systems since 1975. In 1995, systems were available for control of emissions from both petrol and diesel vehicles (see Exhaust control, automotive). 

J. E. McEvoy, ed.. Catalysts for the Control of Automotive Pollutants, Advances in Chemistry Series, Vol. 143, American Chemical Society, Washington, D.C., 1975, p. 178. 

Serious research in catalytic reduction of automotive exhaust was begun in 1949 by Eugene Houdry, who developed mufflers for fork lift trucks used in confined spaces such as mines and warehouses (18). One of the supports used was the monolith—porcelain rods covered with films of alumina, on which platinum was deposited. California enacted laws in 1959 and 1960 on air quality and motor vehicle emission standards, which would be operative when at least two devices were developed that could meet the requirements. This gave the impetus for a greater effort in automotive catalysis research (19). Catalyst developments and fleet tests involved the partnership of catalyst manufacturers and muffler manufacturers. Three of these teams were certified by the California Motor Vehicle Pollution Control Board in 1964-65 American Cyanamid and Walker, W. R. Grace and Norris-Thermador, and Universal Oil Products and Arvin. At the same time, Detroit announced that engine modifications by lean carburation and secondary air injection enabled them to meet the California standard without the use of catalysts. This then delayed the use of catalysts in automobiles. 

Three-way catalysts (TWC), or equilibrium catalysts are designed for the simultaneous control of three automotive pollutants NO, CO, and hydrocarbons (HC). Since rhodium has the desired selectivity for the reduction of NO to with minimum NH-j formation and is also selective... 

The most widely known pollution control catalysts are those for auto emission control. Automotive catalysts can be of two types—monoliths and pellets. Monoliths now dominate the market. Pollution control catalysts are also used to control diesel emissions. 

J. E. McEvoy, Catalysts for the Control of Automotive Pollutants, American Chemical Society, Washington, 1975. 

---