Preparation And Characterization Of Mesoporous Alumina With High Specific Surface Area

Mesoporous alumina is an excellent catalysis and adsorption material which is widely used in the fields of macromolecular adsorption and separation,catalysis,functional materials and ceramics owing to its high surface area,suitable pore structure,high mechanical strength and good surface acidity.However,the performance of mesoporous alumina prepared by the present synthesis routes is poor,especially under high temperature,mesoporous alumina loss activity easily owing to the alumina phase transformates into thermodynamically stable corundum alumina phase.Therefore,it is of great theoretical and practical significance to research the process techniques for preparing mesoporous alumina with excellent properties and high thermal stability.Firstly,the process conditions of mesoporous alumina prepared by precipitation method with aluminum ammonium sulfate as Al source and ammonium hydrogen carbonate as precipitator were studied in this paper.The optimum process conditions for the preparation of mesoporous alumina are as follows: pH value is 9.5,reaction temperature is 60 °C and the wash agent is hot water.The surface area,pore volume and pore size of the sample calcinated at 500 °C are 571 m2/g,0.78 cm3/g and 6.15 nm,respectively.Secondly,the effects of PEG and EDTA on the thermal stability of mesoporous alumina were studied.It is found that both PEG and EDTA can improve the thermal stability of mesoporous alumina.PEG can effectively inhibit the phase transformation of ?-Al2O3 to ?-Al2O3.The optimal amount of PEG is 1 mol% and the surface area,pore volume and pore size of the modified sample by the calcination of 500 °C respectively are 589 m2/g,0.96 cm3/g and 6.69 nm and after calcinating at 1100 °C,the surface area and pore volume are 71 m2/g and 0.56 cm3/g.The optimal amount of EDTA is 6 mol% and the surface area,pore volume and pore size of the modified sample by the calcination of 500 °C respectively are 614 m2/g,0.97 cm3/g and 6.69 nm.Finally,the Si-doped and La-doped mesoporous alumina was prepared by precipitation-impregnation method,and the modified mesoporous alumina possesses excellent thermal stability.The optimal amount of Si is 12%.Compared with the unadded samples,the surface area increase rates of modified samples calcinated at 500 °C?700 °C?900 °C?1000 °C?1100 °C and 1200 °C are 4.9%,12.2%,36.7%,58.47%,69.79% and 71.11%,respectively.And the surface area,pore volume and pore size of the modified sample calcinated at 1100 °C respectively are 149 m2/g,0.52 cm3/g and 8.9 nm;calcinated at 1200 °C,the surface area and pore volume are 45 m2/g and 0.16 cm3/g.The optimal doping amount of La is 9% and the surface area of the modified sample calcinated at 1100 °C is 93 m2/g,which reflects the high thermal stability of modified mesoporous alumina.