REDUCTION OF NO BY CO OVER A SILICA-SUPPORTED PLATINUM CATALYST - INFRARED AND KINETIC STUDIES

The reduction of NO by CO was studied over a Pt/SiO2 catalyst at 300°C. Reaction rate data were obtained together with in situ infrared spectra of species adsorbed on the catalyst surface. The performance of the catalyst depended strongly on the ratio of CO/NO in the reactor. For net reducing conditions (CO/NO > 1) the catalyst deactivated with time. Measurements of kinetics taken during a period of slow deactivation showed that the rate of NO reduction was first order in NO and inverse second order in CO. Reactivation of the catalyst was obtained with both oxidizing and reducing pretreatments. Under net oxidizing conditions (CO/NO < 1) the catalyst was much more active than under reducing conditions and did not deactivate. In situ infrared spectra showed bands corresponding to CO chemisorbed on Pt and NCO and CN groups attached to the support as Si-NCO and Si-CN, respectively. Both the CO and NCO bands were more intense under reducing than oxidizing conditions. The kinetics and product selectivities observed under reducing conditions were found to be in good agreement with a mechanism based upon the dissociation of NO as the rate-limiting step. This mechanism further assumes that N2O is formed by reaction of adsorbed NO with an adsorbed nitrogen atom. It is proposed that the loss in catalyst activity is associated with a change in the electronic properties of the supported Pt crystallites, caused by the accumulation of large concentrations of NCO and CN groups on the support in areas adjacent to the crystallites. © 1979 Academic Press, Inc. All rights reserved.