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Catalysis automotive pollution control
389
universal solution to emission control. Choice of support, chemical components and careful control over chemical interactions is crucial to activity and durability. Over the 12 years of experience obtained from application to vehicles to date, the scientific basis of heterogeneous catalysis has advanced substantially and new and improved characterization techniques such as TPR, TPO and EXAFS are helping to meet the continuing challenges from existing markets (U.S.A., Japan) and the new requirements from large emerging markets (Europe, Australia, Korea, Brazil). Succeeding sections of the conference were devoted to papers relating to reaction mechanisms and surface states, catalyst support systems, metal-support interactions, base metal catalyst, practical studies and fuels and additives. Since the concept of automobile catalysis was first conceived in the late 196Os, considerable research work has been carried out both in academia and in industry, and it is noteworthy that a number of the papers presented at this conference resulted from university-industry collaboration. Amongst the most significant papers in the mechanistic section was that given by E. Koberstein and G. Wannemacher (Degussa) who reported kinetic measurements based on infra-red surface investigations under reaction conditions, and model calculations for the system CO/NO/O, on noble metal catalysts, attempting to understand the factors determining the width of the air/fuel ratio windows in TWCs. TWCs have been investigated since 1968 at the Ford Motor Company and H.S. Gandhi and M. Shelef reported their work on the development of catalyst systems based on a broad fundamental understanding of all the factors involved. These workers have been principally concerned with supported base and noble metal catalysts operating under oxidizing conditions at high temperatures. The use of ZrO, and a-alumina as supports for rhodium gives durability and stability so that the catalyst remains active at temperatures in excess of 600°C in an oxidizing environment. They also showed that palladium and rhodium are much more sensitive to poisoning by residual lead left in the fuel than is platinum. For an Optimum catalyst, each precious metal has a specific function to perform and needs to be carried on a specific support material to maximize activity and durability. Collaborative work between the Universitb Louis Pasteur, Strasbourg, France and Peugeot focussed on the reactivity of carbon monoxide and alkanes on platinum based bimetallic catalysts under oxygen and hydrogen atmospheres. Experiments involving the isomerization and hydrogenolysis of 2-methylpentane and methylcyclopentane showed that the addition of cobalt to platinum acts as a poison for isomerization reactions but that is the best promoter for carbon monoxide oxidation G.B. Fisher et al. (General Motors) used experiments run under ultra-high vacuum conditions to predict behaviour for carbon monoxide oxidation and nitric oxide reduction over rhodium at higher pressures. This work was done in collaboration with the University of Minnesota and the Surface Science Division of Sandia National Laboratories, and is helping to clarify the origin of the structure sensitivity of the carbon monoxide-nitric oxide reaction over rhodium. C.Z. Wan and J.C. Dettling (Englehard) studied rhodium-support interactions and showed that the interactions between rhodium and rare earths, especially cerium, were much stronger than that between rhodium and aluminium. In the section on supports, a paper by P. Not-tier and M. Soustelle (Rhone-Poulenc) considered the important r6le played by alumina in both pellets and wash-coated monoliths, where the potential problem of thermal ageing can be alleviated by the presence of silicon, lanthanum or zirconium. J.S. Howitt (Corning) emphasized the importance in catalyst system design of high geometrical surface area, good catalyst adhesion, low
applied Catalysis
-Volume
38 NO. 2 -
April 1988
universal solution to emission control. Choice of support, chemical components and careful control over chemical interactions is crucial to activity and durability. Over the 12 years of experience obtained from application to vehicles to date, the scientific basis of heterogeneous catalysis has advanced substantially and new and improved characterization techniques such as TPR, TPO and EXAFS are helping to meet the continuing challenges from existing markets (U.S.A., Japan) and the new requirements from large emerging markets (Europe, Australia, Korea, Brazil). Succeeding sections of the conference were devoted to papers relating to reaction mechanisms and surface states, catalyst support systems, metal-support interactions, base metal catalyst, practical studies and fuels and additives. Since the concept of automobile catalysis was first conceived in the late 196Os, considerable research work has been carried out both in academia and in industry, and it is noteworthy that a number of the papers presented at this conference resulted from university-industry collaboration. Amongst the most significant papers in the mechanistic section was that given by E. Koberstein and G. Wannemacher (Degussa) who reported kinetic measurements based on infra-red surface investigations under reaction conditions, and model calculations for the system CO/NO/O, on noble metal catalysts, attempting to understand the factors determining the width of the air/fuel ratio windows in TWCs. TWCs have been investigated since 1968 at the Ford Motor Company and H.S. Gandhi and M. Shelef reported their work on the development of catalyst systems based on a broad fundamental understanding of all the factors involved. These workers have been principally concerned with supported base and noble metal catalysts operating under oxidizing conditions at high temperatures. The use of ZrO, and a-alumina as supports for rhodium gives durability and stability so that the catalyst remains active at temperatures in excess of 600°C in an oxidizing environment. They also showed that palladium and rhodium are much more sensitive to poisoning by residual lead left in the fuel than is platinum. For an Optimum catalyst, each precious metal has a specific function to perform and needs to be carried on a specific support material to maximize activity and durability. Collaborative work between the Universitb Louis Pasteur, Strasbourg, France and Peugeot focussed on the reactivity of carbon monoxide and alkanes on platinum based bimetallic catalysts under oxygen and hydrogen atmospheres. Experiments involving the isomerization and hydrogenolysis of 2-methylpentane and methylcyclopentane showed that the addition of cobalt to platinum acts as a poison for isomerization reactions but that is the best promoter for carbon monoxide oxidation G.B. Fisher et al. (General Motors) used experiments run under ultra-high vacuum conditions to predict behaviour for carbon monoxide oxidation and nitric oxide reduction over rhodium at higher pressures. This work was done in collaboration with the University of Minnesota and the Surface Science Division of Sandia National Laboratories, and is helping to clarify the origin of the structure sensitivity of the carbon monoxide-nitric oxide reaction over rhodium. C.Z. Wan and J.C. Dettling (Englehard) studied rhodium-support interactions and showed that the interactions between rhodium and rare earths, especially cerium, were much stronger than that between rhodium and aluminium. In the section on supports, a paper by P. Not-tier and M. Soustelle (Rhone-Poulenc) considered the important r6le played by alumina in both pellets and wash-coated monoliths, where the potential problem of thermal ageing can be alleviated by the presence of silicon, lanthanum or zirconium. J.S. Howitt (Corning) emphasized the importance in catalyst system design of high geometrical surface area, good catalyst adhesion, low
applied Catalysis
-Volume
38 NO. 2 -
April 1988