NO reduction by CO over CuO supported on CeO2-doped TiO2: the effect of the amount of a few CeO2

Abstract

This work is mainly focused on the investigation of the influence of the amount of a few CeO₂ on the physicochemical and catalytic properties of CeO₂-doped TiO₂ catalysts for NO reduction by a CO model reaction. The obtained samples were characterized by means of XRD, N₂-physisorption (BET), LRS, UV-vis DRS, XPS, (O₂, CO, and NO)-TPD, H₂-TPR, in situ FT-IR, and a NO + CO model reaction. These results indicate that a small quantity of CeO₂ doping into the TiO₂ support will cause an obvious change in the properties of the catalyst and the TC-60 : 1 (the TiO₂/CeO₂ molar ratio is 60 : 1) support exhibits the most extent of lattice expansion, which indicates that the band lengths of Ce–O–Ti are longer than other TC (the solid solution of TiO₂ and CeO₂) samples, probably contributing to larger structural distortion and disorder, more defects and oxygen vacancies. Copper oxide species supported on TC supports are much easier to be reduced than those supported on the pure TiO₂ and CeO₂ surface-modified TiO₂ supports. Furthermore, the Cu/TC-60 : 1 catalyst shows the highest activity and selectivity due to more oxygen vacancies, higher mobility of surface and lattice oxygen at lower temperature (which contributes to the regeneration of oxygen vacancies, and the best reducing ability), the most content of Cu⁺, and the strongest synergistic effect between Ti³⁺, Ce³⁺ and Cu⁺. On the other hand, the CeO₂ doping into TiO₂ promotes the formation of a Cu⁺/Cu⁰ redox cycle at high temperatures, which has a crucial effect on N₂O reduction. Finally, in order to further understand the nature of the catalytic performances of these samples, taking the Cu/TC-60 : 1 catalyst as an example, a possible reaction mechanism is tentatively proposed.