Energetics of CO-NO reactions on Pd, Cu and Pd-Cu alloys

Abstract

The bond order conservation -Morse potential (BOCMP) model has been used to investigate the CO oxidation and NO. reduction reactions on Pd( Ill), Cu( Ill) and the Pd-Cu( Ill) alloy surfaces. The activation barriers for the several reaction steps have been calculated and the rate-limiting step has been found. In the overall scheme of NO+CO. reaction, for the Pd (111) surface NO₅ + N₅ → N₂O₈, reaction is the rate-limiting step; while for the Cu (Ill) surface it is the CO₈ + O_8→Co₂ reaction which is rate-limiting. For the Pd-Cu alloy the surface segregation has been taken into account and the role of segregation on the activation barrier of the rate-limiting step has been studied. The effect is found to be smaIl. The activity of the Pd-Cu (111) alloy surface for the above two reactions has been calculated and the role of local environment on the reactions studied. It is found that for the NO₈, + N_8→N₂O₈, reaction the active sites are the three-fold hollow sites where  an adsorbed NO. has three Cu atoms as nearest neighbours. For the CO₈, + O_8→ CO₂ reaction, on the other hand, the most active sites are the three-fold hollow sites with three Cu nearest neighbours, and the sites with two Cu and one Pd .atom as nearest neighbours.