Ce promoted V2O5 catalyst in oxidation of SO2 reaction

Abstract

Harmful environmental effects of SO2 on the start-up of the sulfuric acid plant process motivated studying ceria as a promoter for V2O5 catalyst that is employed in SO2 oxidation. Effects of SO2(%), ceria percentage, temperature and O2/SO2 were investigated to optimize ceria loading on V2O5 catalyst. To determine the main and interaction effects, a full factorial design of experiments including 315 experiments was used. The results showed that the catalyst with 7wt% ceria (VaCe7) possessed the highest catalytic performance. To study the effect of more parameters on this catalyst, other 135 post-experiments with full factorial designs were performed after the optimization of Ce contents. The results revealed that mean SO2 conversion increased with increasing SO2 (%) and O2/SO2 ratio, and decreasing GHSV. Also, the maximum mean conversion was found at the reaction temperature of 450°C by the trade-off of kinetic and thermodynamic factors of the reversible exothermic reaction. VaCe7 was found to have more catalyst activities than that the without-ceria (VaCe0) case. The synthesized catalysts were characterized by XPS, BET, FTIR, SEM, XRD and ICP. The SEM mapping revealed that the cerium oxide had better distribution on VaCe7 than VaCe9&11. FTIR, XRD and XPS showed the presence of CeVO4 in the Ce-promoted catalyst and confirmed that ceria promotes V2O5 by the formation of CeVO4 network, reduces the activation energy of reduction–oxidation and increases the rate of SO2 oxidation reaction. The stability tests demonstrated good catalytic performance stability of the synthesized catalyst up to 50h in the reaction. Results at the initial times of the stability tests showed that the catalyst with ceria promoter (VaCe7) had higher activity than VaCe0 at the start-up time. Also, VaCe7 had higher activity at the start-up than its normal conditions, which could be related to the good oxygen storage capacity of ceria because the catalyst at the start-up is faced to the oxygen of air. This high startup activity caused to use it in starting up of sulfuric acid plants that decreases SO2 emission to the environment.