Simultaneous HCHO and SCR conversion in lean-burn gas engine exhaust using V2O5/WO3-TiO2 catalysts

Monolithic V₂O₅/WO₃-TiO₂ catalysts with vanadia loads between 0 and 3 wt% were investigated toward the simultaneous HCHO oxidation and SCR reaction in synthetic lean-burn CH₄ engine exhaust. The catalysts were characterized by N₂ physisorption, temperature programmed desorption of NH₃, X-ray diffraction, Raman spectroscopy, UV/Vis spectroscopy, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and inductively coupled plasma optical emission spectroscopy. The catalytic studies showed increasing NO_x and HCHO conversions with rising V₂O₅ content accompanied by side-production of HCN. At 250°C and above the HCN formation mainly occurred at the catalyst inlet followed by hydrolysis and oxidation of HCN along the monolith. Moreover, the correlation of the characteristics with the performance of the catalysts suggested that highly dispersed VO_x sites are predominately involved in the HCHO oxidation and HCN formation, whereas aggregated two-dimensional VO_x species are less active. Finally, in-situ diffuse reflectance infrared spectroscopic studies suggested that formamide acts as key intermediate of the HCN formation.