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

V/Pt/TiO tandem catalysts exhibit both an outstanding low-temperature NH conversion rate and high N selectivity in NH-SCO reactions, but the mechanism of high N selectivity remains unclear. In this work, V/Pt/TiO tandem catalysts were synthesized through a two-step impregnation-deposition method. The modulating effect of the V loading mount on NH-SCO performance was evaluated, and the relevant reaction mechanism was explored systematically. The results demonstrated that the synergistic effect of tandem NH oxidation and NH-SCR reactions could be regulated by changing the V loading amount, thereby modulating N selectivity. Compared with other V/Pt/TiO catalysts and previously reported SCO catalysts, the V/Pt/TiO catalyst with a V loading amount of 0.5 wt.% exhibited outstanding NH-SCO performance, which achieved complete NH conversion and >90% of N selectivity within a range of 250-450 °C. XPS, NH-TPD, and O-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 Pt and V species, as well as the amount of acid sites, oxygen species, and oxygen vacancies. Consequently, the synergistic effect of tandem NH oxidation and NH-SCR reactions was significantly enhanced, enabling the catalyst to exhibit excellent N 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 -NH species to participate in NH-SCO reactions, thereby boosting N selectivity.