Preparation Of V,Mo-doped Mesoporous SiO₂ Microsphere Catalysts And The Research Of Catalytic Performance For The Selective Oxidation Of Ethane And Propane

At present,the excessive consumption of petroleum resources leads to the crisis of chemical raw materials shortage.Selective oxidation of light alkanes can effectively alleviate the crisis and reduce the cost of chemical raw materials.It is one of the big challenges in catalytic field to make effective use of light alkanes that selective oxidation of ethane and propane to olefins and aldehyde oxygen compounds using O2 as oxidant.One of the most challenging issues is the difficulty in maintaining high conversion and target product selectivity.Molybdenum-based and vanadium-based catalysts exhibit good performance in the selective oxidation of light alkanes due to their modest redox capabilities.Many researches have shown that high dispersion active site catalysts have a special catalytic effect in the selective oxidation of light alkanes,and the highly dispersed reactive metal oxygens species are conducive to improving the selectivity of products such as olefins.In recent years,the development of mesoporous SiO2 microsphere catalysts has provided more abundant carrier materials for the selective oxidation of ethane and propane.Based on the literatures and our group's previous research work,the doped Mo-m-SiO2 and V-m-SiO2 catalysts were synthesized by emulsion method and the supported Mo/m-SiO2 and V/m-SiO2 catalysts were synthesized by the incipient-wetness impregnation method using molybdenum and vanadium as the active component,mesoporous SiO2 microsphere catalysts as supports.The effects of the doping content of the active component and the preparation method on the structure and properties of the catalyst were investigated.The main conclusions of this paper are as follows:The doped V-m-SiO2 and supported V/m-SiO2 catalysts were prepared by the emulsion method and impregnation method respectively,and the selective oxidation performances of ethane and propane were studied.The results show that the vanadium species are mainly present as highly dispersed and isolated VO4 tetrahedral structures on both doped and supported catalysts.The catalytic performance for selective oxidation of ethane over1.5V-m-SiO₂ and 1V/m-Si O₂ catalystsat 575 ^oC can reach the ethane conversion of 34.2%and30.0%,respectively.The selectivity of ethylene and acetaldehyde is 57.4%,3.9%and 55.3%,3.7%,respectively.And the corresponding ethylene yield is 18.1%and 16.6%.The catalytic performance for selective oxidation of propane reaction on 0.5Vm-Si O2 and 0.5V/m-SiO2catalysts at 575 ^oC can reach the propane conversion of 35.4%and 31.3%and the total selectivity of olefins,olefins and aldehydes of 65.3%,76%and 55.0%,65.5%respectively.And the corresponding total yield of olefins and aldehydes is 26.9%and 20.5%.The doped Mo-m-Si O2 and supported Mo/m-SiO2 catalysts were prepared by emulsion method and impregnation method and the selective oxidation performances of propane were studied.The results show that the molybdenum oxide of the doped Mo-m-SiO2 catalyst exists mainly in a highly dispersed form,while the dispersion degree of molybdenum oxygen species on the supported catalysts is greatly affected by the Mo loading amounts with low Mo loading amounts catalysts?x?5?showing better dispersion.The conversion of propane on3Mo-m-SiO₂ catalyst at 600 ^oC is 42.9%,and the total selectivity of olefins and aldehydes and total yield of 65.8%and 28.2%.The selectivity of olefins is found to be 56.3%over0.1Mo/m-SiO₂ catalysts at 625 ^oC with the total selectivity of olefins and aldehydes is 67.7%,the total yield of olefins and aldehydes is 35.0%.