The effect of the Rh–Al, Pt–Al and Pt–Rh–Al surface alloys on NO conversion to N2 on alumina supported Rh, Pt and Pt–Rh catalysts

NO conversion to N2 in the presence of methane and oxygen over 0.03 at.%Rh/Al2O3, 0.51 at.%Pt/Al2O3 and 0.34 at.%Pt–0.03 at.%Rh/Al2O3 catalysts was investigated. δ-Alumina and precious metal–aluminum alloy phases were revealed by XRD and HRTEM in the catalysts. The results of the catalytic activity investigations, with temperature-programmed as well as steady-state methods, showed that NO decomposition occurs at a reasonable rate on the alloy surfaces at temperatures up to 623 K whereas some CH4 deNOx takes place on δ-alumina above this temperature. A mechanism for the NO decomposition is proposed herein. It is based on NO adsorption on the precious metal atoms followed by the transfer of electrons from alloy to antibonding π orbitals of NO(ads.) molecules. The CH4 deNOx was shown to occur according to an earlier proposed mechanism, via methane oxidation by NO2(ads.) to oxygenates and then NO reduction by oxygenates to N2.