Promotional mechanism of activity of three-dimensionally ordered macroporous Cu-doped Ce-Fe mixed oxides for CO-SCR

A series of doped rather than supported 3DOM Ce0.7Fe0.2M0.1O2 and bulk Ce0.7Fe0.2Cu0.1O2 catalysts are prepared for CO-SCR reaction. The formation of 3DOM structure not only improves the reduction performance and surface active sites but also promotes the generation of more surface adsorbed oxygen species. So, 3DOM Ce0.7Fe0.2Cu0.1O2 catalyst shows high CO-SCR activity in a broad operating temperature window of 150-700 °C, with T50 at 150 °C and T100 at 350 °C. It also has the highest CO oxidation activity in a series of samples. Moreover, the appearance of Cu+-CO species and the fast transition between Ce4+ and Ce3+ (Cu2++Ce3+↔Cu++Ce4+) are the reason why 3DOM Ce0.7Fe0.2Cu0.1O2 has better catalytic activity than other catalysts at lower temperature. Simultaneously, the oxygen vacancies produced by the reduction of Fe3+→Fe2+ and those adjacent to Ce3+ are more momentous at higher temperatures, which are propitious to the dissociation of NO. The cause of the partial deactivation of the optimal catalyst under specific reaction conditions is also discovered, which further confirms the importance of Cu+ and the number of active sites. And the CO-SCR reaction on 3DOM Ce0.7Fe0.2Cu0.1O2 follows the mechanism of L-H and E-R at low temperature and high temperature, respectively.