Regulating the redox sites of MMoOx (M = Mn, Fe, Cr) catalysts for highly efficient selective catalytic oxidation of NH3

Redox sites and acidic sites are the main active sites of bimetallic oxide catalysts used for selective catalytic oxidation of NH₃ (NH₃-SCO). In this work, three MMoOx (M = Cr, Fe, and Mn) bimetallic oxides catalysts were prepared by simple grinding and calcination to investigate the effect of redox sites (M sites) on the NH₃-SCO performance. The NH₃-SCO test results showed that the activity of MMoOx is in the order of CrMoOx > MnMoOx > FeMoOx. The characterization results of H₂-TPR, O₂-TPD, NH₃-TPD, and in situ DRIFTS proposed that the NH₃-SCO reaction on MMoOx catalysts is proceed via i-SCR mechanism, and the formation of the intermediates of NH₃-SCR reaction is the decisive reaction step. Owing to the excellent ability in promoting the formation of nitrate/nitrite species, CrMoO_x and MnMoOx samples show much higher NH₃-SCO activity than FeMoOx sample. CrMoO_x can facilitate the formation of a large amount of –NH₂ species, which together with nitrate/nitrite species enhance the NH₃-SCO reaction via i-SCR reaction route. Therefore, CrMoO_x shows the highest NH₃-SCO activity among the MMoOx catalysts. Through this work, the redox sites of bimetallic oxide catalysts are demonstrated as a vital role in inducing the formation of reaction-active intermediates, which highlight the importance of choosing the redox sites in designing NH₃-SCO catalyst.