Unraveling the Mechanism of High N2 Selectivity in Ammonia Selective Catalytic Oxidation on Pt-V Tandem Catalyst.

V0.5/Pt/TiO2 tandem catalysts exhibit both an outstanding low-temperature NH3 conversion rate and high N2 selectivity in NH3-SCO reactions, but the mechanism of high N2 selectivity remains unclear. In this work, Vx/Pt/TiO2 tandem catalysts were synthesized through a two-step impregnation-deposition method. The modulating effect of the V loading mount on NH3-SCO performance was evaluated, and the relevant reaction mechanism was explored systematically. The results demonstrated that the synergistic effect of tandem NH3 oxidation and NH3-SCR reactions could be regulated by changing the V loading amount, thereby modulating N2 selectivity. Compared with other Vx/Pt/TiO2 catalysts and previously reported SCO catalysts, the V0.5/Pt/TiO2 catalyst with a V loading amount of 0.5 wt.% exhibited outstanding NH3-SCO performance, which achieved complete NH3 conversion and >90% of N2 selectivity within a range of 250-450 °C. XPS, NH3-TPD, and O2-TPD results suggested that the increase in the V loading amount from 0.1 wt.% to 0.5 wt.% was conducive to increasing the relative contents of Pt0 and V5+ species, as well as the amount of acid sites, oxygen species, and oxygen vacancies. Consequently, the synergistic effect of tandem NH3 oxidation and NH3-SCR reactions was significantly enhanced, enabling the catalyst to exhibit excellent N2 selectivity. A further increase in the V loading amount from 0.5 wt.% to 0.9 wt.% would bring about the opposite effect to the above, resulting in a decline in catalytic performance. In situ DRIFTS results showed that a V loading amount of 0.5 wt.% was beneficial for -NH2 species to participate in NH3-SCO reactions, thereby boosting N2 selectivity.