Automotive exhaust catalysis

Application of ZrO2 as a catalyst and a catalyst support

The catalytic treatment of motor vehicle exhaust gas has been a feature of all passenger cars in the USA since the 1975 model year. It has since been adopted in all the developed countries as the principal means of con-trolling the emissions from vehicles powered by Otto-cycle internal com-bustion engines. These include passenger cars, light trucks, and heavy-duty trucks. Catalysts have been developed for motorcycles and even smaller power plants. The so-called three-way catalyst (TWC) has been in use since the 1979 model year. The name reflects the simultaneous treatment by this catalyst of the two reducing pollutants, carbon monoxide and uncombusted hydrocarbons, and the oxidizing pollutant, oxides of nitrogen.

Why Rhodium in Automotive Three-Way Catalysts?

The diesel oxidation catalyst (DOC) has been part of diesel exhaust systems since regulations were introduced to limit the amount of harmful emissions released to the environment from diesel engines. The DOC primary functions are oxidation of CO, unburned hydrocarbons, and NO, while active hydrocarbon oxidation can also be used to generate exotherms required for downstream components. This review will describe work that has attempted to understand the reactions, both desired and undesired, that occur over the catalyst. First, the history, configuration, and components of the DOC will be discussed, followed by in-depth coverage of the fundamental reactions that occur over a DOC, including reaction mechanisms, reaction inhibition, and other reactivity effects. Finally, DOC deactivation mechanisms and their effects on the DOC are described. While there is a lot of research literature regarding Pt- and Pd-based catalysts for many different reaction schemes, this review tries to highlight work most relevant to...

Diesel Oxidation Catalysts

Progress in developing a new class of support materials based on silicon carbide (SiC)is reviewed. Silicon carbide has superior mechanical and thermal properties which, coupled to chemical inertness,avoids several of the problems inherent in the use of commercial oxide and carbon based supports and catalysts. High surface area SiC can now be prepared easily in a commercially viable shape,with good mechanical properties,and at reasonable cost.I t can be shaped directly into monolith or honeycomb forms including some catalytically active material, rendering fabrication simple and cost effective. Furthermore, it can be modified for specific catalytic applications through the addition of metals. In many respects, it combines the best properties of oxide and carbon based supports without suffering many of their disadvantages.

H.K. Stepien

Papers

The effects of SO2 on the oxidation of hydrocarbons and carbon monoxide over Ptγ-Al2O3 catalysts

Metal-support interaction in automotive exhaust catalysts: Rh-washcoat interaction