Study On The Preparation And Catalytic Performance Of Al₂O₃ Supported PtSn Catalysts For Propane Dehydrogenation

Propene is an important basic organic chemical raw material.With the increasing growth of economy,the need for propene will gradually increase in the future.Therefore,it is very important to enhance the yield of propene.With the increasing degree of the petroleum shortage,the production of propene is far from the needs of people.There are abundant natural gas,shale gas,coalbed gas and refinery gas resources in china,which contain a large amount of propane.It is of great economic value to directly convert the abundant and low-cost propane into propene.At present,propylene produced from propane has become one of the most important ways for increasing propene production.However,the catalyst of propane dehydrogenation process used in the world is easy to be deactivated by the accumulation of coke and sintering,so how to improve the catalyst with high activity and stability is an urgent problem to be solved.In this thesis,propane catalytic dehydrogenation reaction was studied based on supported Pt-based catalysts.The Pt-based catalysts were designed and prepared by using Al2O3 as support,Pt as active site and Sn,Mg as promoters.Based on the innovation of Al₂O₃ support,the Al₂O₃support with different morphologies and the MgAl composite oxide carrier were prepared.The catalysts were characterized by means of X-ray diffraction,N2-adsorption,scanning electron microscopy,transmission electron microscopy,H₂ temperature-programmed reduction,NH₃temperature-programmed desorption and UV-Raman.The relationships among the content of PtSn,the synthetic methods,structure and physic-chemical properties of the catalysts and their catalytic performance were investigated.The main conclusions are made as follows:?1?A series of PtSn/Al₂O₃ catalysts with different Pt and Sn loading amounts were prepared by an incipient-wetness impregnation method and their catalytic performances for propane dehydrogenation were tested.The results indicate that with the increasing of Pt and Sn loading amounts in PtSn/Al₂O₃ catalysts the size of PtSn nanoparticles increases and it is easy to form PtSn alloy.And the catalytic performance of propane dehydrogenation shows the tendency of firstly increaseing and then decreasing.The catalytic activity of PtSn/Al2O3 catalyst with 1 wt%of Pt and 2 wt%of Sn shows better catalytic performance.?2?The Al₂O₃ supports with different morphologies were prepared by hydrothermal method with controlling the molar ratio of urea to Al?NO₃?₃·9H₂O,and a series of PtSn/Al₂O₃ catalysts by loading Pt and Sn were prepared.The catalytic performances of the as-prepared catalysts were tested for propane dehydrogenation.The results indicate that,when the molar ratio of urea/Al is 9,the morphology of Al₂O₃ support is short stick and short sheets.And it shows large pore diameter and pore volume.The catalyst has low acid amount and acid strength,and the Pt dispersion on the support is high.Thus,it shows better catalytic performance.?3?The Mg-Al composite supports?MgAlO?with different Mg contents were prepared by hydrothermal method and they were used as supports.Then a series of PtSn/MgAlO catalysts were prepared and their catalytic performances were tested for propane dehydrogenation.The results indicate that Mg-Al composite support?MgAlO?shows low acidity,large BET surface area,high mechanical strength,high thermal stability properties,which can improve the dispersion of Pt significantly.Moreover,the higher the ratio of Mg/Al on support,the higher degree of MgAl2O4 crystallinity.The molar ratio of Mg/Al has a large effect on the catalytic performance of the catalysts.The suitable Mg/Al ratio can significantly improve the catalytic performance of the as-prepared catalysts.When the ratio of Mg/Al is 1/10,the catalyst can get high propene selectivity and good stability.