Phosphate- and ruthenium oxide-supported CeO2 (P/CeO2 and Ru/CeOO2), as typical CeO2-based catalysts, were comparatively studied to fully elucidate catalytic combustion of dichloromethane (DCM), especially for the effects of H2O and the formation of chlorinated by-products. The results indicated that the reversible inhibitive effect of H2O became increasingly intense in the following order: pristine CeO2 < Ru/CeO2 < R/CeO2, moreover, the inhibition was more notable at the lower reaction temperature but almost disappeared at temperatures above 300 degrees C. H2O-TPD and various DRIFTS techniques revealed that the adsorption strength of H2O depended on the surface properties of three CeO2-based catalysts and the reaction temperature, which eventually determined the degree of activity inhibition. Dechlorinated (monochloromethane, MCM) and ploychlorinated (CHCl3 and CCl4) by-products were more easily formed over non-metallic P/CeO2 and metallic Ru/CeO2, respectively, due to the different redox and metallic properties of these CeO2-based catalysts, which was also further confirmed by catalytic oxidation of other chlorinated volatile organic compounds (Cl-VOCs). Additionally, more complete oxidation (the formation of CO2 and Cl-2) occurred on Ru/CeO2.