Promotional mechanism of activity via three-dimensional ordered macroporous Cu-doped Ce–Fe mixed oxides for the CO-SCR reaction

Abstract

A series of doped rather than supported 3DOM Ce_0.7Fe_0.2M_0.1O₂ and bulk Ce_0.7Fe_0.2Cu_0.1O₂ catalysts were prepared for the CO-SCR reaction. The formation of the 3DOM structure not only improves the reduction performance and surface-active sites but also promotes the generation of more surface-adsorbed oxygen species. Thus, the 3DOM Ce_0.7Fe_0.2Cu_0.1O₂ catalyst shows high CO-SCR activity in the 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 reasons why 3DOM Ce_0.7Fe_0.2Cu_0.1O₂ 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 significant at higher temperatures, and are favorable for the dissociation of NO. The cause of partial deactivation of the optimal catalyst under specific reaction conditions is also discovered, which further confirms the importance of Cu⁺ and number of active sites. Further, the CO-SCR reaction on 3DOM Ce_0.7Fe_0.2Cu_0.1O₂ follows the mechanism of L–H and E–R at low and high temperatures, respectively.