Mechanism of alkali promotion in heterogeneous catalysis under realistic conditions: application of electron spectroscopy and electrochemical promotion to the reduction of NO by CO and by propene over rhodium

XPS and Δφ measurements demonstrate that the potential of a Rh thin film in contact with a Na+ conducting solid electrolyte may be used to control ϑNa and hence the catalytic behaviour of the Rh surface. The system response is reversible and reproducible, catalyst work function and Na coverage varying linearly with catalyst potential over the experimentally accessible range. Coordinated reactor studies show that in the catalytic reduction of NO by CO or propene promotion is due to Na-induced NO dissociation, which process is the rate limiting step. As a result, very large increases in N2 selectivity may be achieved, along with useful increases in activity.