In-situ inhibition mechanism of SO3 formation over MoS2 modified V2O5/TiO2 catalyst within selective catalytic reduction process

The utilization of commercial vanadium-titanium based catalysts (V 2 O 5 /TiO 2 ) within the selective catalytic reduction (SCR) process is a prominent contributor to the emergence of sulfur trioxide (SO 3 ) in coal-fired boiler environments. The direct modification of vanadium-titanium based catalysts has big potential to be an efficacious strategy for in-situ inhibiting SO 3 formation. This research evaluates the effectiveness of MoS 2 modified V 2 O 5 /TiO 2 catalyst on SO 2 oxidation under diverse conditions, using controlled condensation for SO 3 collection. The results showed that V 2 O 5 -MoS 2 /TiO 2 catalysts outperformed conventional V 2 O 5 /TiO 2 catalysts in inhibiting the oxidation from SO 2 to SO 3 between 200 and 400 °C, with optimal performance at 350 °C. No significant effect was observed on the catalytic oxidation of SO 2 when the O 2 concentration was lower than that of SO 2 , whereas the introduction of appropriate quantities of NO promoted the generation of SO 3 . The excessive inclusion of NH 3 nearly doubled the SO 3 generation rate, increasing it from 0.284 % to 0.434 %. The NO and NH 3 mixture markedly reduced SO 3 generation to 0.085 % at a 62 mL/min mixture concentration, just 30 % of the rate without the mixture. Following the reaction of SO 2 and O 2 , the reacted catalyst exhibited reduced pore volume, enhanced thermochemical stability, and lower susceptibility to SO 2 catalytic oxidation. The addition of low-valence sulfur improves catalyst reducibility, reduces V 5+ –OH reactions in various atmospheres, and decreases the formation of sulphate and gaseous SO 3 . The Mo-S-Mo group also effectively prevents the formation of HSO 4 − intermediates. Additionally, MoS 2 reacts with SO 3 via a reduction reaction, significantly lowering the SO 3 levels. Finally, in diverse atmospheric conditions, the catalysts maintained their V 5+ content and catalytic efficiency, thus improving SCR performance stability.