Key Role of Competitive Adsorption in Environmental Catalysts

Under catalytic reactions involving multiple substrates, a strongly adsorbed substrate acts as a catalyst poison, thereby inhibiting the reaction.Automotive catalysts, such as three-way catalysts (TWCs) and diesel oxidation catalysts, work in the presence of various substrates (NO, CO, hydrocarbons, O 2 , etc.) in the exhaust gas, and competitive adsorption of these components becomes an important factor for controlling the activity.This review outlines the role of competitive adsorption in apparent catalytic activity, using environmental catalysts as an example.The maximum activity of a diesel oxidation catalyst is observed when the adsorption energies of hydrocarbon and oxygen are equivalent.The strong adsorption of CO on the metal inhibits the adsorption of oxygen, while the adsorption strength of CO can be controlled by the exposure of specific facets of metal particles and the formation of single atoms.To realize a noble metal-free TWC, separation of the roles of TWC is effective to avoid inhibition by oxygenated hydrocarbons on base metal oxide surface.