The modification of commercial SCR catalyst with low V loading for benzene degradation: Improvement of the COx selectivity and inhibition of transformation to PAHs

Abstract

V2O5-WO3/TiO2 (VWT) was modified by Fe and Mo to degrade benzene at selective catalytic reduction with NH3 (NH3-SCR) reaction temperature (350 °C). Mo modified catalyst (Mo-VWT) was found greatly increased COx selectivity from 74.80 % (VWT) to 94.00 %. Meanwhile, the transformation of benzene into polycyclic aromatic hydrocarbons (PAHs) was effectively inhibited, with the PAHs selectivity decreased from 3.04 % (VWT) to 0.34 %. According to X-ray photoelectron spectroscopy (XPS), Mo could play as the carrier to efficiently transform electron from V to W, increasing the amount of V5+ and oxygen vacancies (Ov). Temperature programmed reduction (TPR) experiments proved that Mo could also play as the carrier for surface lattice oxygen (W-Olat-s) migrating from W to V, replenishing adsorbed oxygen species (Oads) and keeping a higher amount of V5+-Oads for benzene degradation. Based on temperature programmed desorption of benzene (benzene-TPD) and in situ diffuse-reflectance infrared Fourier-transform spectroscopy (in situ DRIFTS) results, it was found that surface Mo-OH could provide new benzene activation sites to form strongly adsorbed phenol, which was easily oxidized by V5+-Oads. For VWT, benzene would be weakly activated to form the weakly adsorbed phenol, which would desorb as phenyl to transform into PAHs. When the degradation of benzene was carried out under NO + NH3, catalyst surface Oads and Olat-s tended to be occupied by NH3, which hindered the migration of W-Olat-s and weakened the oxidation of phenol. Therefore, more phenol would desorb and transform to PAHs.