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

Abstract

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.