Preparation Of Chromium-based Supported Mesoporous Silica Catalyst By Sol-gel Method And Its Application In The Oxidative Dehydrogenation Of Propane

Propylene is the basic raw material for plastics,synthetic rubbers and synthetic fibers.It is also an important chemical raw material with an increasing demand year by year.Besides traditional steam cracking,catalytic cracking and methane to propylene?MTO?methods,new propylene preparation methods have attracted more and more attentions.Propane is commonly used as a fuel,not only to drive vehicles but also to heat and cook.So the economic benefit of using it is really low.Therefore,the preparation of propylene by propane is particularly important.Currently,chromium-based catalysts have been used in industrial production of propane dehydrogenation.However,it is usually prepared by impregnation method.In contrast,catalysts prepared by the sol-gel process generally have better metal dispersion.In this paper,different chromium-based mesoporous silica catalysts were prepared by sol-gel method,the effects of changes in preparation conditions on their performance were investigated.Firstly,the chromium precursor Cr?NO₃?₃·9H₂O was added at different stages of preparation to prepare Cr/MSS-X catalysts by sol-gel method.The difference in catalytic performance of each catalyst was obtained by catalytic test.Advanced technical means was used to characterize each catalyst and the root causes of differences in catalytic performance was explored.The experimental result shows that the best catalytic performance was achieved when the active precursor is added after the initial nucleation of the synthesis,and the obtained catalyst has the best Cr dispersion.Then,water and the mixed solution of water and ethanol were used as solvent,TEOS and Cr?NO₃?₃·9H₂O were added in order or TEOS and Cr?NO₃?₃·9H₂O were premixed and added to the solution by sol-gel method.The difference in catalytic performance in different systems under premixed and unpremixed conditions was explored.The result shows that the catalytic performance of the unpremixed catalyst was better than that of the premixed catalyst in aqueous system.However,in the mixed solution of water and ethanol system,the catalytic performance of the premixed catalyst was better than that of the unpremixed catalyst.Finally,the mesoporous silica carrier with gradient pore structure whose core is a small hole and shell is a large hole was prepared by sol-gel and oil-water self-assembly method.After that,the traditional impregnation method was used to prepare the catalyst by impregnation of the active metal Cr on the carrier.The optimum loading capacity was obtained by characterization and activity test,and catalytic performance was compared with the conventional catalyst supported by a single mesoporous structure.The result shows that when Cr loading capacity of 5%,the catalytic performance was the best,and the stability was better than the catalyst supported by a single mesoporous structure.