Alginate Ammonium Assisted Preparation Of Spherical Alumina Support And Its Performance On Isobutane Dehydrogenation

In this work,three types of spherical alumina were synthesized with ammonium alginate assistant sol-gel method,alumina support(1~2mm)by dropping synthesis,the pore-enlarged alumina support(1~2mm)by dropping synthesis combining with emulsion template method and alumina support(3~5mm)by intruding shaping method.The Pt-based catalysts were prepared via impregnating Pt,Sn,La active metal ions and promoters.The catalytic performance of these Pt-based catalysts over isobutane dehydrogenation was investigated,and the properties of the catalysts and/or alumina supports were characterized.The effects of synthetic condition of the alumina support and the catalysts on catalytic performance,textural properties,external acid properties,the states of the impregnated metal particles and the amounts of carbon deposit were evaluated.The synthetic condition of alumina support consisted of the types of gelation cations,the amount of the residual gelation cations and the pore-enlarged extent,while the synthetic condition of the catalyst was the amount of added-La.For the alumina support(3~5mm),the cations types,cation gelation time,acid treating time on the properties of the alumina was carried out.The main experimental results are as follows:(1)In the process of dropping synthesis,the amount of residual Ca was 0.89wt% with the gelation time of 10 s,and the catalytic performance and stability of the corresponding catalyst was the best,compared with those catalysts with longer gelation time.And a suitable addition of La could enhance the activity and stability of the catalysts,recede the external acidic property,increase the surface area,promote the dispersion of Pt particles and decrease the amount of carbon deposit over the catalyst.The appropriate loading of La was 1.1wt%.(2)Combining the dropping method and emulsion template method,pore-enlarged the catalysts with surface area 250~290m2/g,pore volume 0.5~1.0cm3/g,average pore diameter 8~13nm and the crush strength 20N/granule was prepared,with the impregnation of Pt,Sn and La.With increasing the amount of pore-enlarging agent,the surface area,pore volume and pore diameter increased significantly at the sacrifice of crush strength.The amount of weak acid sites increased and the amount of strong acid sites decreased with increasing the pore-enlarging agent.Higher surface area and larger pore size could promote the reducibility of PtOx and enhance the dispersion of Pt particles,but couldn't alter the chemical states of tin.With the augment in surface area and pore size,the catalytic performance of the pore-enlarged catalysts over isobutane dehydrogenation increased and the amount of carbon deposit declined.280~310m2/g.(3)The alumina support with surface area 280~310m2/g,pore volume 0.5~1.5cm3/g,pore diameter 7~18nm and crush strength >35N/granule,could be obtained with using intruding shape device.Compared with the alumina gelled in Al(NO3)3 solution,the alumina support gelled in Ca(NO3)2,Zn(NO3)2 and the sample without the gelation solution possessed higher surface area and textural structure,but with a lower crush strength.Among the corresponding Pt-based catalysts,the catalyst without gelation solution obtained a considerable conversion and isobutene yield,and their value was 58% and 49.5% after reacting for 220 min.