Mn-based catalysts are extensively used; herein, the poisoning mechanism of Pb2+ and SO2 on the gamma-MnO2 catalyst during the combustion of chlorobenzene (CB) was studied. The oxidizability/reducibility, surface acidity and water activation property of the Pb/SO42- modified gamma-MnO2 were analyzed by using XPS, H-2-TPR/O-2-TPD, NH3-TPD/Pyridine-IR and H2O-TPD. Catalytic performance and byproduct selectivity towards CB combustion were explored, indicating that Pb2+ and SO2 both impacted CB conversion and CO2 selectivity as indicated by the loss of oxidation properties and surface acidity. Analysis of the byproducts showed that Pb2+ and SO2 induced the formation of more toxic polychlorinated byproducts, thereby introducing new secondary environmental pollution risks. (C) 2019 Published by Elsevier Inc.