Catalytic Performance Of Ethyl Acetate Over Microfibrous Zeolite Membranes Catalyst Prepared By Chemical Vapor Deposition

With the rapid development of industries in various countries,air pollution has become a focal issue that needs to be solved in all countries.Volatile organic compounds?VOCs?in the air have a wide range of sources,various types,and complex compositions,which pose a serious threat to the atmospheric environment and human survival.At present,purification technologies for VOCs include:adsorption,absorption,condensation,membrane separation,biodegradation,photocatalytic degradation,low-temperature plasma,and catalytic combustion.Among them,catalytic combustion has attracted much attention due to its low combustion temperature,wide application range,high catalytic activity,and high purification efficiency.The preparation of the catalyst affects the catalytic performance of the catalyst.The impregnation method has the disadvantages of uneven distribution of the active components and serious agglomeration.Therefore,how to prepare a highly efficient,highly disperse,and stable catalystfor purifying VOCs have been recognized as a meaningful research topic.In this paper,copper-based molecular sieves were chosen as experimental objects.The preparation and characterization of granular zeolite CuO/ZSM-5 and microfiber zeolite membrane CuO/ZSM-5/PSSF catalysts were investigated.The catalytic combustion performance of ethyl acetate on a fixed bed reactor was discussed.Firstly,CuO/ZSM-5 catalysts were prepared by impregnation?IM?and chemical vapor deposition?CVD?methods,respectively.The performance of catalytic oxidation of ethyl acetate was conducted in the fixed-bed reactor based on CuO/ZSM-5 catalysts.A series of CuO/ZSM-5 catalysts with different copper loadings were prepared by impregnation?IM?and chemical vapor deposition?CVD?methods,respectively.Their physicochemical properties were investigated by N₂ adsorption/desorption,X-ray diffraction?XRD?,transmission electron microscopy?TEM?,X-ray photoelectronic spectra?XPS?,temperature-programmed reduction by hydrogen?H₂-TPR?and temperature-programmed desorption of NH₃?NH₃-TPD?.The catalytic performance of CuO/ZSM-5catalysts on ethyl acetate in a fixed-bed reactor was investigated.The effect of preparation method and loading on the activity of CuO/ZSM-5 was studied.The experimental results show that the main form of Cu in CuO/ZSM-5 catalysts prepared by the two methods is CuO,which is supported on the surface and channels of ZSM-5.The loadings affected the catalytic activity of CuO/ZSM-5catalysts.The 3 wt%CVD catalyst showed the best catalytic activity?T90=235°C?for ethyl acetate oxidation,the intermediate products were completely oxidized into CO₂ and H₂O at temperature as low as 288 ^oC.The preparation method also affects the catalytic activity of CuO/ZSM-5 catalysts.The CuO/ZSM-5 catalysts prepared by CVD exhibited higher catalytic activity thanthe IM catalysts incatalytic combustion of ethyl acetate at the same copper loadings,which may be attributed to the relatively small particle size,well dispersion and high specific surface area of the CVD catalyst.Secondly,the catalytic combustion performance of ethyl acetate on fixed-bed reactors of microfiber zeolite membrane CuO/ZSM-5/PSSF prepared by chemical vapor deposition was studied.The paper-like sintered stainless steel fiber?PSSF?was prepared by wet lay-up papermakingand sintering process.The porous ZSM-5/PSSF composites were preparedby secondary growth process on the surface of PSSF.Then,CuO/ZSM-5/PSSFcatalysts with various copper loadings were synthesized by chemical vapor deposition method.The physicochemical properties of CuO/ZSM-5/PSSF catalysts were characterized by SEM,EDS,XRD,N₂ adsorption/desorption isotherms,XPS and H₂-TPR.The catalytic performances of ethyl acetate were investigated over the zeolite membrane reactor based on the CuO/ZSM-5/PSSF catalysts.The effects of copper loading,calcination process,feed concentration as well as gas hourly space velocity on the activity of CuO/ZSM-5/PSSF catalysts were studied.The results show that thejunctures of stainless steel fibers were successfully sintered together to form a three-dimensional network structurethus improving the mechanical strength of the PSSF,and continuous ZSM-5 membrane with good crystalline forms grows densely on the surface of the PSSF support.The CuO/ZSM-5/PSSF catalysts were prepared successfully by chemical vapor deposition,and the copper oxides of the active components were uniformly distributed on the surface of the ZSM-5/PSSF support.The loading,calcination process,feed concentration and gas hourly space velocity affected the catalytic activity of CuO/ZSM-5 catalysts.The optimum process:copper loading was 3 wt%,the calcination temperature was 550°C,GHSV of 10000 h^-1 and 1000 ppm of ethyl acetate in the feed gas.The 3 wt%CuO/ZSM-5/PSSF catalyst also exhibits remarkable stability and the catalytic activity of catalystis also remained around 90%after being used at 262 ^oC for 48 h.Ethanol and acetaldehyde are found to be the intermediate products in the oxidation of ethyl acetate.The relative amounts of acetaldehyde and ethanol are determined by the selectivity of the catalyst towards acetaldehyde production from ethanol.The 3 wt%CuO/ZSM-5/PSSF membrane catalyst exhibits good performance and low byproducts selectivity towards the oxidation of ethyl acetate by preventing formation of ethanol and acetaldehyde compared to granular CuO/ZSM-5 catalyst.