In situ fabrication of oxygen-vacancy-rich flower-like cerium-lanthanum oxide/HZSM-5 composites from waste polishing powder for dichloromethane degradation.

This study addresses the challenges in recycling rare earth polishing powder waste (REPPWs)-such as harsh leaching conditions, poor morphology control, and low value-added output-by proposing a synergistic "leaching-morphology control-zeolite loading" strategy. This approach enabled the successfully synthesize of flower-like CeOvLa/HZSM-5 composite catalyst using polishing powder as the primary raw material. This strategy involves three key elements: 1) co-leaching Ce3+/La3+ with a H2SO4-ascorbic acid system, 2) precisely constructing CeOvLa with abundant oxygen vacancies (Ovs) via controlled oxalic acid addition, and 3) obtaining the final catalyst by in-situ HZSM-5 growth on the CeOvLa. Density functional theory (DFT) calculations revealed that La doping reduced the formation energy of Ovs within the CeO2 lattice. Moreover, the incorporation of HZSM-5 further decreased this energy barrier while also provided abundant acidic sites. The synergistic interaction between these components enhanced the electronic environment and dispersion of active sites, thereby significantly promoting CCl bond cleavage and deep oxidation of dichloromethane (DCM). Experimental results demonstrated that the catalyst achieved 81.8% DCM conversion at 450 °C, with over 99% CO2 selectivity and minimal Cl2 byproduct formation. This work offers new insights into the value-added utilization of REPPWs and the efficient degradation of chlorinated volatile organic compounds (CVOCs).