The SCR performances and SO2 oxidation behaviors of various V2O5-MoO3/TiO2 catalysts with different surface area: The influences of vanadium polymerization states

In this study, a series of V 2 O 5 -MoO 3 /TiO 2 (VMo/Ti) catalysts were prepared using TiO 2 supports with varying specific surface area for selective catalytic reduction of NO x by ammonia (NH 3 -SCR). The activity tests revealed that the NO conversion of different samples showed a volcano-type variation with surface area rising, where the VMo/Ti-S3 catalyst with moderate surface area possessed the best SCR activity (>80% NO conversion at 250 °C). Meanwhile, the SO 2 oxidation ratio decreased at an elevated surface area. At 350 °C, the SO 2 oxidation ratio of VMo/Ti-S1 catalyst with lowest surface area was about 4.4%, which was around 4 times that of VMo/Ti-S4 sample with highest surface area. Characterization results indicated that, as the surface area increased, both the redox capacity and surface acidity were enhanced. And the vanadium oxides became less polymeric with a gradual increased ratio in dimeric vanadium species and finally more monomer VO x formation, corresponding to the highest SCR activity of VMo/Ti-S3 catalyst. Additionally, the characterization results indicated that the chemisorption of SO 2 was inhibited on high-surface-area catalysts, which was consistent with DFT results. And DFT simulations also confirmed an increased energy barrier for SO 2 oxidation to generate SO 3 process on less polymeric vanadium species. Both the results above indicated the critical role of vanadium polymerization state in SCR activity and SO 2 oxidation. This work offers new insights into the development of efficient SCR catalysts with low SO 2 oxidation rates for industrial applications.