Bowen Li,Zhen Zhang,Tingfeng Shan,Qi Zhang,Yusi He,Xiangfu Wang,Hongmin Yang
The by-product SO 3 , generated by the conventional catalyst V 2 O 5 -WO 3 /TiO 2 employed in selective catalytic reduction (SCR) systems, has garnered attention in pollution control efforts. Studies on existing control have predominantly concentrated on the tail gas section, with insufficient understanding of in-situ suppression theories and methods at the source of SO 3 generation. We propose for the first time the introduction of low-valence reduced sulfur to synthesize a novel SCR catalyst, V 2 O 5 -WS 2 /TiO 2 , which elucidates the remarkable effect and in-situ mechanism of action in inhibiting SO 3 formation at its source. Compared to conventional catalysts, the new catalysts showed enhanced SO 3 inhibition, particularly at 350 °C, where SO 3 production was 64.1 % and 33.9 % lower than that with VTi and VW/Ti catalysts, respectively. This was due to their reduced surface area, smaller pore volume, and fewer alkaline sites, which hindered SO 2 adsorption and oxidation. The results revealed that S 2− on the catalyst surface reacts with V 5+ , reducing it to V 4+ and V 3+ . This reaction hinders the interaction between V 5+ -OH and adsorbed SO 2 , thereby reducing the formation of VOSO 4 intermediates. Furthermore, the W S bond in WS 2 impedes the formation of intermediate HSO 4 − , and the reduction of these intermediates ultimately leads to a decrease in SO 3 generation. Additionally, the incompletely depleted S 2− reacts with the final SO 3 produced, forming SO 2 and SO 4 2− , which further decreases the SO 3 generation rate and supports the maintenance of a reduced state on the catalyst surface. It is evident that low-valence reduced sulfur plays a crucial role in inhibiting SO 3 generation.
Tingfeng Shan,Zhen Zhang,Bowen Li,Qi Zhang,Xiangfu Wang,Yusi He,Hongmin Yang
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.
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