Effects of Different Copper Species on the Combustion of Dichloromethane over Cu/HZSM-5 Zeolite Nanoporous Catalysts

This study compared the reaction behaviors of dichloromethane (DCM) catalytic combustion over Cu/HZSM-5 (H form of Zeolite Socony Mobil-5) nanoporous catalysts at different copper loadings. Among the samples investigated, Cu/HZSM-5 with 2.5 wt % Cu showed the best stability with a 90% DCM conversion at 320 °C during a 3 h reaction run. The analysis of the results showed different copper species (including cations and oxides particles) accounted for the diverse reaction behaviors observed. With a low copper loading (≤2.5 wt %), copper cations (such as isolated Cu+/Cu2+ and oxocations) were the dominant copper species, which were strongly resistant to chlorine poisoning. However, we found the continuous coking deactivation of Cu/HZSM-5 with 1 wt % Cu loading owing to its low redox capacity. With further increase in the Cu content, the proportion of bulk-like CuOx species quickly increased. During the reaction with DCM, CuOx particles were involved in a chlorination process at a bulk level with the formation of CuClx and Cux(OH)yCl crystalline phases, resulting in a rapid deactivation at the initial reaction stage. Cation-dominant copper nanomaterials are recommended for reaching a high stability in chlorinated volatile organic compound catalytic oxidation.