Getting insight into the oxidation of SO2 to SO3 over P modified VW/Ti catalyst: Effect and inhibition mechanism

Commercial VW/Ti catalyst used in selective catalytic reduction (SCR) process is one of the major sources of SO3 in coal-fired boiler, and modification of VW/Ti catalyst by adding catalytic promoter has been demonstrated to be an effective way to inhibit SO3 generation. In this study, the effect of P addition on the activity of NOx conversion and SO2 oxidation over VW/Ti catalyst was investigated. The results showed that the P-modified VW/Ti catalyst not only enhanced the catalytic activity at low temperature, but also reduced the oxidation rate of SO2. The 1.5PVW/Ti catalyst exhibited the lowest SO2 oxidation rate at 360 degrees C and achieved about 30 % reduction in SO2 oxidation rate when compared to 0PVW/Ti catalyst, whereas the conversion of NOx was still above 95 %. The physicochemical properties of catalysts were comprehensively characterized with N-2 adsorption, XRD, H-2-TPR, NH3-TPD, XPS and DRIFTS. The results illustrated that the W-O-W structure was also the main reason for SO2 oxidation on P-modified VW/Ti catalyst, which oxidized SO2 to form intermediate products HSO4- and constantly replenished in the presence of O-2. The oxidation of SO2 was weakened by the generation of VOPO4 on P-modified VW/Ti catalyst surface, which inhibited the formation of VOSO4 by reducing the adsorption of SO2 on the catalyst. In addition, the release of P-OH and W=O were promoted with the addition of P, which led to a significant increase in the intensity of the Bronsted and Lewis acid sites, resulting in the increase in the conversion of NOx at low temperatures.

Automated summary

This study investigates the effect of phosphorus addition on the activity of NOx conversion and SO2 oxidation over VW/Ti catalyst. The results show that the P-modified VW/Ti catalyst not only enhances the catalytic activity at low temperature, but also reduces the oxidation rate of SO2. The 1.5PVW/Ti catalyst exhibits the lowest SO2 oxidation rate at 360 degrees C and achieves about 30% reduction in SO2 oxidation rate compared to the 0PVW/Ti catalyst, while the conversion of NOx is still above 95%.