Catalytic oxidation performance of CH₂Cl₂ over in-situ Cr-modified fly ash-based HZSM-5

In the catalytic combustion technology of chlorine-containing volatile organic compounds (CVOCs), the catalyst is prone to chlorine poisoning and exhibits insufficient deep oxidation capacity, which is the key bottleneck restricting its industrial application. In this study, a series of Cr-modified HZSM-5 catalysts were in-situ prepared by a one-step hydrothermal synthesis method using fly ash as the raw material. Advanced techniques such as XRD, UV-vis, XPS, N₂ adsorption-desorption, NH₃-TPD, O₂-TPD, and H₂-TPR were used to characterize the physical and chemical properties of the catalysts. Using dichloromethane（CH₂Cl₂） as the probe molecule, the effects of different Cr doping amounts and different Si/Al ratios on the catalytic purification and anti-chlorine poisoning were systematically studied. The results showed that in-situ Cr modification could effectively inhibit the formation of chlorine-containing by-products and significantly improve the oxidation performance of HZSM-5 zeolite for CVOCs. 1.2%Cr-HZSM-5 (Si/Al=50) had high surface acidity and redox properties, showing high ability for C-Cl bond cleavage and deep oxidation capacity toward CH intermediate components, with the highest CO₂ selectivity and lower Cl deposition. At 350℃, the conversion rate of dichloromethane reached 85%; the yields of CO₂ and HCl reached 75% and 60%, respectively; and no Cl₂ or other chlorine-containing by-products were detected. This study can provide a theoretical basis and experimental support for the development of a catalytic system for efficient degradation of CVOCs.