Promoting the catalytic activity and SO2 resistance of CeO2 by Ti-doping for low-temperature NH3-SCR: Increasing surface activity and constructing Ce3+ sites

Abstract

CeO2-based oxides are promising catalysts for low-temperature selective catalytic reduction of NOx with NH3 (NH3-SCR), but the poor SO2 poisoning resistance hampers its further application. Herein, we developed a Ti-doped CeO2 (Ti-CeO2) catalyst with high specific surface area by calcining TiSO4-doped Ce-MOF precursor for NO removal. On Ti-CeO2, abundant Ti3+ sites are generated by the thermally reducing carbon in the organic ligand during calcination, the electronic interaction between Ti3+ and Ce4+ leads to the generation of many more exposed Ce3+ sites, effectively preventing the sulphuration of surface Ce species to Ce2(SO4)3. Besides, the residual sulfate species provides plentiful Brønsted acid sites for NH3 adsorption. Therefore, both the catalytic performance and SO2 resistance of CeO2 are significantly enhanced after Ti-doping. Remarkably, above 80% NO conversion is obtained between 220 and 450 °C on Ti0.10-CeO2 (the molar ratio of Ti:Ce is 0.10 in the synthesis process), and the NO conversion maintains around 76.0% for 170 h in the presence of 100 ppm SO2 and 5 vol% H2O at 250 °C. The reaction on CeO2 and Ti-CeO2 follow the Langmuir-Hinshelwood (L-H) mechanism, but abundant Ce4+ in CeO2 having high oxidation ability leads to the generation of plentiful stable nitrate or nitrite to occupy the active sites. In contrast, the over oxidation of NO and SO2 adsorption are inhibited because of Ti-doping, resulting in superior catalytic performance in the SCR reaction.