Catalysis Surveys from Asia | 2021
Promotional Effects on NH3-SCR Performance of CeO2–SnO2 Catalysts Doped by TiO2: A Mechanism Study
Abstract
Abstract A novel Ti-doped Ce–\u2009Sn mixed oxide (Ce–Sn–Ti) catalysts were developed for the selective catalytic reduction (SCR) of NOx with NH 3 . The addition of titanium could improve SCR activity at a low-temperature window. By optimizing the element proportions, the NOx conversion of Ce 0.6 Sn 2.4 Ti 2 catalysts could reach more than 90% in a wide-operating temperature window (200\u2009–450\xa0°C). The appropriate doping Ti formed Sn–O-Ti, Sn–O-Ce and Ti–O-Ce structures, which could increase the content of Ce 3+ through electrons transfer from Sn or Ti to Ce (Ce 3+ \u2009+\u2009Ti 4+ \u2009↔\u2009Ce 4+ \u2009+\u2009Ti 3+ and 2Ce 4+ \u2009+\u2009Sn 2+ \u2009↔\u20092Ce 3+ \u2009+\u2009Sn 4+ ). The solid solution structure increased specific surface areas, active sites (Ce 3+ ), and Lewis acid sites over the Ce 0.6 Sn 2.4 Ti 2 catalysts. According to DRIFTS results, only bidentate nitrate could react with adsorbed NH 3 species. However, adsorbed NH 3 species could quickly react with the gaseous NO. The NH 3 -SCR reaction mechanism over Ce 0.6 Sn 2.4 Ti 2 catalysts mainly followed the Eley\u2009–Rideal mechanism. Graphic Abstract The electron transfer between tin, cerium, and titanium elements led to generate more active sites (Ce 3+ ) used for NH 3 and NO x activation/oxidation, which improved SCR activity. The NH3-SCR reaction mechanism over Ce 0.6 Sn 2.4 Ti 2 catalyst mainly followed the Eley−Rideal mechanism, in which adsorbed NH 3 species could quickly react with the gaseous NO to generate N 2 and H 2 O.