Preparation Of Novel Spherical Alumina And Its Performance On Propane Dehydrogenation

In this work,two kinds of spherical alumina granules with different sizes were prepared by using the gel properties of alginic acid and pseudo-boehmite.They were pure alumina granules with diameter of 3-5nm and different metals hybrid alumina granules with diameter of 1-2nm,and Pt-based catalysts were prepared via impregnating Pt active component.The catalysts were characterited by N₂adsorption-desorption,XRD,SEM,NH₃-TPD,XPS and TEM.The effects of calcination temperature,hybrid metal species and content,ect.on the catalytic performance of propane dehydrogenation were investigated systematically.The results show that the pure alumina particles prepared by the combination of alginic acid sol-gel and extrusion have high specific surface area?100³00m²/g?,larger pore volume?0.8¹.1cm³/g?and average pore diameter?15³3nm?.With the increase of calcination temperature,the specific surface area and pore volume of the catalyst decrease,and the pore size increases until the pore structure disappeared.At the same time,the increase of the calcination temperature significantly reduces the surface acidity of the catalyst,but the high calcination temperature also reduces the acid activity center of the catalyst surface.However,the catalyst catalyzes the dehydrogenation of propane as a result of the interaction between the metal active center and the acid active center.Among the corresponding catalysts,PtSn/Al₂O₃-700 catalyst calcined at 700^oC showed the best propane dehydrogenation performance.The conversion of propane and propene yield was 36.2%and 31.2%respectively after reacting for 250min.The spherical Ca-Al₂O₃ and Zn-Al₂O₃ were prepared by alginic acid sol-gel method.Then the Pt-based catalyst with surface area 100²60m²/g,pore volume0.4⁰.6cm³/g and average pore diameter 8¹6nm was obtained by loading Pt and Sn.Different metal hybridization have different effects on the structural properties of the catalyst and its propane dehydrogenation.Ca-Al₂O₃ is beneficial to improve the thermal stability of the catalyst,so that it retained the higher specific surface area,and the catalyst prepared by Ca-Al₂O₃ with the CaO content of 2.5%had a higher initial conversion rate?48%?.Zn-Al₂O₃ support had larger pore size,and the catalysts prepared by Zn-Al₂O₃ with the ZnO content of 6.2%had a higher selectivity?above 90%?and stability.The Sn-Al₂O₃ support was prepared by introducing Sn in the forming process by the mechanism of alginate assistant sol-gel method,and the Pt/Sn-Al₂O₃ catalyst with surface area 110²30m²/g,pore volume 0.5⁰.8cm³/g and average pore diameter 9¹9nm was obtained by impregnating Pt.The hybridization of the Sn species could promote the dispersion of the Pt?average particle size was about 1nm?,reduce the surface acidity at a certain extent.Meanwhile,the amount of metal hybridization and calcination temperature of the supports have a great influence on the dehydrogenation performance of propane.The appropriate amount of metal hybridization and the appropriate calcination temperature made the metal function and acid function more match,which could to improve the performance of the catalyst.The Pt/Sn₁₅-Al₂O₃-800 catalyst with the Sn content of 4.1%showed the best propane dehydrogenation performance.After reaction for 250min,the conversion of propane was still higher than 37.5%and the selectivity was above 94%.