PROMOTION BY SODIUM IN EMISSION CONTROL CATALYSIS - A KINETIC AND SPECTROSCOPIC STUDY OF THE PD-CATALYZED REDUCTION OF NO BY PROPENE

Sodium strongly promotes the reduction of NO by propene over Pd cataly sts supported on 8 mol% yttria stabilised zirconia (YSZ) in the temper ature range 520-720 K. Rate increases by an order of magnitude are ach ievable, while the selectivity towards to N-2 is improved from similar to 75% over the unpromoted Pd catalyst to >95% over the optimally Na- promoted catalyst. The results indicate that promotion is due to sodiu m-induced increases in the strength of NO chemisorption relative to pr opene. This is accompanied by weakening of the N-O bond, thus facilita ting NO dissociation, which process is proposed as the critical reacti on initiating step. The XPS and Auger data are consistent with this vi ew. These findings are in excellent accord with a recent study of the same reaction under conditions of electrochemical promotion (EP) (I. V . Yentekakis et al., J. PhJ s. Chem. B 101, 3759 (1997)). (C) 1998 Aca demic Press.