Improving activity and SO2 resistance for NH3-SCR of NOx over V-Ce-Ox catalysts by phosphorylation treatment to regulate both oxidation property and acid sites

Abstract

SO2 poisoning remains an unresolved issue for NH3-SCR of NOx catalysts, particularly under low temperature conditions. In this study, a phosphorylation approach was used in preparation of V-Ce-Ox (VC) catalysts by regulating both oxidation property and acid sites to improve SO2 tolerance at low temperature in the NH3-SCR process. Among all the as-prepared catalysts, 2.4 wt%P-VC exhibited the widest temperature window (>90 % NO conversion, 240 ∼ 420 °C) and good resistance to SO2. A variety of characterization approaches were used to investigate the effects of the phosphorylation approach on the catalytic activity and microstructure of V-Ce-Ox catalyst. According to the characterization results, the improvement role of 2.4 wt%P-VC is connected to the balance between acidity and oxidation ability. This originates from the largest amount of Brønsted acid sites to adsorb NH3 and surface adsorbed oxygen species. The results also showed that different H3PO4 loading contents can promote or inhibit the NH3-SCR reaction, it is possible that this is because a lower H3PO4 content (≤2.4 wt%) can result in more Brønsted acid sites (P-O-NH4+), whereas the higher H3PO4 content (≥4.2 wt%) can cause a greater reduction in Lewis acid sites and the total surface acidity. Furthermore, the in-situ DRIFTS and SO2-TPD results reveal that the oxidation of SO2 is weakened by the formation of amorphous VOPO4 and CePO4 on xwt%P-VC catalysts, which reduces the formation of VOSO4 and Ce2(SO4)3 by reducing the oxidation of SO2 on the catalyst. This work eventually achieves the highest catalytic performance and the superior SO2 resistance of the V2O5-CeO2-based catalyst by presenting a viable technique for changing the acid and redox sites on the VC catalyst.