Pd-xMo/Al2O3 catalysts for NO reduction by CO

The adsorption and reactivity of CO and NO in the CO + NO reaction on Pd/Al 2O3 and Pd-MoO3/Al2O3 catalysts was studied using DRIFTS, and the chemical state of the catalysts was examined by TRP and UV-DRS while the active site s were probed by TPD and chemisorption of CO and NO. The Pd8Mo catalyst pre sented a monolayer of Mo on an alumina surface resulting from a polymerizat ion process, identified by DRS measurements. With increasing Mo content MoO 3 crystals are formed. Mo was reduced to Mo+4 at lower temperatures in the presence of palladium particles, which favored the formation of bimetallic particles that produce a different kind of site for this reaction. TPD resu lts indicated that the presence of the Mo monolayer favors the formation of N-2 compared to the Pd/Al2O3 catalysts. DRIFTS results indicated NO adsorp tion on Pd+2, Pd-0, and Mo+delta sites as well as formation of isocyanate o n the Pd8Mo catalyst, while CO adsorption occurred on Mo during the reactio n at different temperatures. Activity studies showed that the Pd8Mo catalys t is much more active and more selective to N-2 than the monometallic catal yst. A model for the reaction is suggested which shows that Mo+delta is a p romoter in the catalytic cycle for NO reduction by CO. (C) 1999 Academic Pr ess.