Catalytic performance and mechanism of Pt VW catalyst for selective catalytic oxidation of high-concentration NH3

It is foreseeable that a high-concentration NH3 may exist in exhaust gas of NH3-fuel engines, which may result in some negative damages to ecological environment. Herein, a series of PtxVW catalysts with extremely low Pt doping amounts were synthesized with the aim to remove high-concentration NH3 efficiently via selective catalytic oxidation (SCO) method. The results showed that, Pt0.04VW catalyst (0.04 wt.% Pt) achieved a complete NH3 conversion at 250 ºC. Both catalytic activity and N2 selectivity of Pt0.04VW catalyst were much superior over Pt/Al2O3 catalyst (1 wt.% Pt) in a wide temperature range of 250-450 ºC. XPS, Raman and H2-TPR results indicated that Pt existed in the lattice of VOx and formed Pt-V bimetallic oxides. The interaction between Pt and V played a key role in the NH3-SCO reactions. DFT calculation demonstrated that dual electron transfer pathways between Pt and V atoms in PtxVW catalysts were beneficial for NH3 coordination on Lewis acid sites, then enhancing NH3-SCO reactions. In-situ DRIFTS and NH3-TPD product analysis suggested that NH3-SCO reactions on Pt0.04VW catalyst surface abide by internal selective catalytic reduction (i-SCR) and hydrazine mechanisms. Moreover, coordinated NH3 species on Lewis acid sites, bidentate nitrate species were the main intermediates in NH3-SCO reactions over Pt0.04VW catalyst.