Oxide Supports Preparation And Study On Performance Of Supported Pt/Cr Catalysts For Propane Dehydrogenation To Propylene

As the demand for propylene increases,propane dehydrogenation to propylene becomes a major propylene production in addition to naphtha cracking and catalytic cracking.Therefore,it is of great significance to study high-efficiency catalysts for propane dehydrogenation to propylene.Al2O3 supports were prepared by the hydrothermal method,and AlZr composite supports were prepared by the hydrothermal method,the sol gel method and the template method.A series of Pt/Al2O3 and Cr/AlZr catalysts were prepared by impregnation.Physicochemical properties of supports,Pt/Al2O3 and Cr/AlZr catalysts were characterized by XRD,FTIR,TG-DSC,SEM-EDS,N2 physical adsorption-desorption,NH3-TPD,Pyridine-IR,H2 chemisorption and H2-TPR.The catalytic performance of catalysts for propane dehydrogenation to propylene was carried out in a fixed bed reactor.Effect of preparation conditions on the physicochemical properties of Al2O3 support was investigated.Effects of pH values of H2PtCl6 solution,the crystallization temperature of support,the type and amount of second additives on the catalytic performance of Pt/Al2O3 catalysts in propane dehydrogenation to propylene were also studied.The catalytic performance of propane dehydrogenation to propylene over Cr/AlZr catalysts with different the preparation method of the support,molar ratios of A1 to Zr and amount of Cr loading was studied.Conclusions are as follows:(1)Surfactants(glucose,sucrose,PVP,CTAB and PVA),the concentration of surfactant(glucose)and crystallization temperature affected the morphology,specific surface area,pore structure and surface acidity of A1203 supports.Al2O3 supports prepared by glucose as a surfactant at a concentration of 0.25 mol/L and a crystallization temperature of 180? has a regular and orderly arrangement,which is assembled into a dandelion flower-like microsphere with large specific surface area(165.8 m2/g).(2)The pH values of H2PtCl6 solution and the crystallization temperature of Al2O3 supports affected the catalytic performance of Pt/Al2O3 catalysts.The catalytic performance of Pt/Al2O3 catalysts prepared by A1203 with crystallization temperature of 180? and pH value of 8 showed the highest reactivity.After 270 min of reaction,the propane conversion,propylene selectivity and yield were 20%,81%and 16%,respectively.(3)After adding Sn additive(first additive)on Pt/Al2O3 catalysts,the dispersion of Pt was improved.When the mass ratio of Pt to Sn was 1:1,the dispersion of Pt increased from 7.1%to 13.2%.After 300 min of reaction,propane conversion,propylene selectivity and yield of PtSn/Al2O3 were 38%,81%and 31%,respectively.(4)A second additive(Mg,Ce,In,Zn)was added to the PtSn/Al2O3 catalysts(based on the mass of the Al2O3 support,the addition amount of additive was 0.5 wt.%),and the type and amount of the additive affected the performance of catalysts.Ce,as the second additive,the dispersion of Pt for catalyst(PtSnCe/Al2O3)increased.When 2.0 wt.%of C,e was added,the dispersion of Pt increased from 13.2%for PtSn/Al2O3 catalyst to 17.8%for PtSnCe2.0/Al2O3.After 300 min of reaction,the catalytic activity of PtSnCe2.0/Al2O3 catalyst was the highest among all catalysts tested,and the propane conversion,propylene selectivity and yield were 47%,79%and 38%,respectively.(5)The preparation method and the molar ratios of Al to Zr affected the morphology,crystal structure and surface acidity of the composite supports.Cr15/Al0.9Zr0.1 catalyst with Cr loading of 15 wt.%and Al0.9Zr0.1 composite supports prepared by hydrothermal method with a molar ratio of Al to Zr of 9:1 has no medium strong acid or strong acid sites.Moreover,the amounts of Cr6+species was the most in Cr15/Al0.9Zr0.1 catalyst compared to other catalysts.The initial conversion of propane over Cr15/Al0.9Zr0.1 catalyst was the highest(43%),and the selectivity and yield of propylene were 75%and 32%,respectively.