Promotional Mechanism of Sulfation on Selective Catalytic Reduction of NO by Methane in Excess Oxygen: A Comparative Study of Rh/Al2O3 and Rh/Al2O3/SO42-

The catalytic performance and reaction mechanism for selective catalytic reduction of NOx by methane in excess oxygen over Rh-loaded sulfated alumina were investigated. Sulfation was observed to influence the properties of catalysts in two aspects: (i) modify the dispersion and electronic state of surface rhodium species and (ii) deten-nine the surface NOy groups. Differences in Surface nitrates and their behaviors lead to different mechanisms for CH4-SCR of NO. On Rh/Al2O3, the adsorbed monodentate nitrates (1558 cm(-1)) could react with methane in the absence of oxygen, while remaining almost inert to the mixture of methane and an excess amount of oxygen. However, nitrates on Rh/Al2O3/SO42-, most probably bidentate nitrates (1600-1598 cm(-1)), were able to react with methane in the presence of oxygen. Moreover, a proportional relationship between NO conversion rates and intensities of nitrosyl (1936 cm(-1)) bands was found on Rh/Al2O3/SO42- and the rate-determining step of NO conversion was probably the reduction of nitrosyl.