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Two-dimensional transition metal-sulfide-modified V2O5-WS2/TiO2 catalysts for SCR: Comprehensive mechanistic insights into the in situ inhibition of SO3 generation

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.