Catalytic Removal Of Volatile Organic Compounds Over Cu-Ce-Zr Based Catalysts

The latest studies show that VOCs are also resulted in haze as well as NOx and SOx.Catalytic oxidation is one of the primary techniques for the removal of volatile organic compounds?VOCs?due to its various advantages,such as low onset temperature,enjoying high conversion and a relatively high flexibility.A series of CuCe_xZr_1-xO_y/ZSM-5 catalysts with different Ce/Zr molar contents?x = 0,0.25,0.5,0.75 and 1?and CuCe₃Zr₁/TiO₂ catalyst were prepared by impregnation.N2 adsorption/desorption,X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,temperature-programmed reduction by hydrogen?H2-TPR?,NH₃-TPD,UV-vis,FT-IR,were undertaken in order to correlate the morphological,structural and surface properties of all catalysts with their oxidation activities.Moreover,kinetic and mechanism of the ethyl acetate and toluene catalytic oxdation were further investigated over CuCe_xZr_1-xO_y/ZSM-5 catalysts.The main research results are listed as follows:?1?CuO,CeO₂,and ZrO₂ species were highly dispersed on the surfaces of ZSM-5 support,and copper is mostly in a Cu2+ and Cu+ co-existed.Surface adsorbed oxygen,hydroxyl group,and oxygen vacancies were detected after the introduction of Ce/Zr,which increased with the increasing of Ce/Zr molar ratio.The specific surface area was not the key factor governing the catalytic activity,however,the remarkable relationship between reducibility and catalyst activity were observed.The excellent reducibility of the catalyst would lead to an improvement in catalytic performance.The optimum performance was obtained with CuCe0.75Zr0.25/Z catalyst,which offered complete conversion of ethyl acetate into CO₂ at temperature as low as 270 ?,and the onset temperature was at 110 ?.Furthermore,the obtained catalyst possessed superior stability,and no deactivation phenomenon was observed during the catalytic oxidation in 60 h at 270 ?.?2?The characterization relusts of the different support of CuCe₃Zr₁/ZSM-5 and CuCe₃Zr₁/TiO₂ displayed that the average pore size,concentration of the oxygen vacancies and acidity were the key factor governing the catalytic activity.Compared with CuCe₃Zr₁/ZSM-5,pore size distribution curve of CuCe₃Zr₁/TiO₂ catalyst centered at the range of 6-60 nm attributing to mesoporous and macropore,which were beneficial to the adsorption,desorption and diffusion of VOCs.The higher peak intensity of UV-vis adsorption band for CuCe₃Zr₁/TiO₂ enhanced the concentration of the oxygen vacancies in composite oxides system and formed a defect band that further changed the energy of conduction band,moreover inhibited the by-product formation.According to the NH₃-TPD results,the desorption peak of strong acid sites moved to the high temperature for CuCe₃Zr₁/ZSM-5 catalyst,however,the peak of strong acid sites of CuCe₃Zr₁/TiO₂ shifted to lower temperature,and the latter can inhibit the carbon deposition effectively.The CuCe₃Zr₁/ZSM-5 and CuCe₃Zr₁/TiO₂ showed superior stability for catalytic removal of ethyl acetate and toluene in 60 h,and the conversions were always remained above 99%.In this study the catalytic activity of ethyl acetate and toluene on CuCe₃Zr₁/TiO₂ catalyst was obvious higher than that on CuCe₃Zr₁/ZSM-5 catalyst,with T90 being achieved at lower temperatures.?3?Power-law kinetic model can accurately describe the reaction rate of ethyl acetate for CuCe_xZr_1-xO_y/ZSM-5,ln?ri?was in line with with lnCi?r2?1?assigned to first-order kinetics equation.The catalytic oxidation of ethyl acetate and toluene over the CuCe₃Zr₁/ZSM-5 and CuCe₃Zr₁/TiO₂ catalysts involved a Mars-van Krevelen mechanism,where the VOCs were primarily oxidized by the lattice oxygen of metal oxides,the latter being re-oxidized by the gas-phase oxygen.