Chlorobenzene Oxidation over Phosphotungstic-Acid-Coated Cerium Oxide: Synergistic Effect of Phosphotungstic and Cerium Oxide and Inhibition Mechanism of Sulfur Dioxide

Abstract

Ce–based catalysts exhibit a poor stability and activity in chlorinated volatile organic compound (Cl–VOC) oxidation due to their rapid Cl poisoning. Herein, phosphotungstic acid (HPW) was coated on CeO2 to improve its activity and stability for chlorobenzene (CB) oxidation. The HPW coating not only promoted CB adsorption onto CeO2, but also provided Brønsted acid sites to CeO2 for Cl species removal as HCl, thus avoiding Cl poisoning. Hence, a synergistic effect of CeO2 and HPW on HPW/CeO2 was observed, resulting in superior CB oxidation activity and stability. Additionally, to improve the sulfur resistance of the catalyst, the inhibition mechanism of SO2 on CB oxidation by HPW/CeO2 was explored. HPW/CeO2 was prone to sulfation due to the formation of Ce2(SO4)3 from the reaction of SO2 and CeO2. Thus, the oxidation ability of HPW/CeO2; the amount of adsorption sites for CB adsorption; and the amounts of Ce4+ bonded with O2−, lattice oxygen species, and adsorbed oxygen species were decreased by SO2. Meanwhile, SO2 competed with CB for the adsorption sites on HPW/CeO2. Therefore, CB oxidation by HPW/CeO2 was remarkably restrained by SO2. The present work promotes further work on Cl–VOC removal by Ce-based catalysts for anti-SO2 poisoning modification in the future.