The effect of the Rh-Al,Pt-Al and Pt-Rh-Al surface alloys on NO conversion to N_2 on alumina supported Rh,Pt and Pt-Rh catalysts

摘要

NO conversion to N_2 in the presence of methane and oxygen over 0.O_3 at.%Rh/Al_2O_3,0.51 at.%Pt/Al_2O_3 and 0.34 at.%Pt-0.O_3 at.%Rh/Al_2O_3 catalysts was investigated.delta-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 CH_4 deNO_x takes place on 8-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 pi orbitals of NO_(ads.)molecules.The CH_4 deNO_x was shown to occur according to an earlier proposed mechanism,via methane oxidation by NO_2_(sds.)to oxygenates and then NO reduction by oxygenates to N_2.