Synthesis, physicochemical characterizations and catalytic performance of Pd/carbon-zeolite and Pd/carbon-CeO_2 nanocatalysts used for total oxidation of xylene at low temperatures

摘要

In this work, xylene removal from waste gas streams was investigated via catalytic oxidation over Pd/ carbon-zeolite and Pd/carbon-CeO_2 nanocaiialysts. Activated carbon was obtained from pine cone chemically activated using ZnCl_2 and modified by H_3PO_4. Natural zeolite of clinoptilolite was modified by acid treatment with HCl, while nano-ceria was synthesized via redox method. Mixed supports of carbon-zeolite and carbon-ceria were prepared and palladium was dispersed over them via impregnation method. The prepared samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Brunauer-Emmett-Teller surface area (BET), Fourier transform infrared spectroscopy (FTIR) and thermogravi-metric (TG) techniques. Characterization of nanocatalysts revealed a good morphology with an average particle size in a nano range, and confirmed the formation of nano-ceria with an average crystallite size below 60 nm. BET analysis indicated a considerable surface area for catalysts (~1000 m~2·g~(-1)). FTIR patterns demonstrated that the surface groups of synthesized catalysts are in good agreement with the patterns of materials applied in catalyst synthesis. The performance of catalysts was assessed in a low-pressure catalytic oxidation pilot in the temperature range of 100℃-250℃. According to the reaction data, the synthesized catalysts have been shown to be so advantageous in the removal of volatile organic compounds (VOCs), representing high catalytic performance of 98% for the abatement of xylene at 250℃. Furthermore, a reaction network is proposed for catalytic oxidation of xylene over nanocatalysts.