SURFACE-REACTIONS OF NO, CO, AND O2 NEAR THE STOICHIOMETRIC POINT .1. PT-ALUMINA

Infrared and integral reactor experiments showed that CO chemisorbed over reduced Pt sites appears to act as an inhibitor for the NOCO reaction at rich stoichiometries. A large fraction of the surface is covered by an isocyanate species which does not appear to participate in the reaction. Dissociatively chemisorbed O2 appears to act as an inhibitor for the NOCO reaction at lean stoichiometries. For a Pt-alumina catalyst, the well known operating window around stoichiometry (i.e., the range of stoichiometries where both NO and CO conversions are appreciable) is defined by the range of stoichiometries where the surface isocyanate and the CO chemisorbed on reduced Pt sites have been partially eliminated but the Pt surface has not yet been completely oxidized. Thus, the operating window has been defined in terms of the surface composition. © 1979.