Combined use of in situ and operando-FTIR, TPR and FESEM techniques to investigate the surface species along the simultaneous abatement of N2O and NO on Pt,Pd,Rh/TiO2-ZrO2 and Pt,Pd,Rh/TiO2-ZrO2-CeO2 catalysts

Abstract

Pt,Pd,Rh supported on TiO2-ZrO2 and TiO2-ZrO2-CeO2 show a promising catalytic behavior for the simultaneous selective catalytic reduction of NO and N2O with CH4 in the presence of O2 (SCRsim). The nature of the catalytic species and the formation of intermediate species on the catalyst surface were investigated by combining several techniques. The co-existence of fully and partly reduced noble metals are strictly dependent on the O2/CH4 ratio in the feed which is crucial for a good catalytic activity. When the O2/CH4 ratio is less than 1, NO and N2O were efficiently and simultaneously reduced with negligible formation of by-products. As the O2/CH4 ratio was higher than 1, CH4 combustion prevailed. The CeO2 made the catalyst slightly more efficient, likely improving the solid redox properties at the interface between noble metal particles and gaseous reactants. The operando FT-IR analysis identified some surface intermediate species involved in the reaction pathways. In the presence of NO, surface nitrite/nitrate species that are strongly adsorbed on the catalysts surface competed with the N2O adsorption sites. An assay of the SCRsim catalytic behaviour in the presence of water revealed that the catalyst with ceria has a good catalytic activity and stability along tests simulating nearly real conditions.