Preparation And Properties Of Pt Nanopolyhedron Catalyst Supported By ZnAl₂O₄ Spinel For Isobutane Dehydrogenation

The purpose of this study was to prepare a new platinum?Pt?catalyst to improve the selectivity and yield of isobutene,reduce the dosage of Pt and improve stability of the catalyst.As is well-known,the electron density of substance is actually sensitive to the surface structure,and different crystal facets could have diverse catalytic natures.Faceted platinum nanoparticles had been shown to exhibit higher catalytic activity compared to spherical particles.A new method for preparing a novel crystalline Pt catalyst was presented in the paper.The innovation lied in the active component of Pt nanocube loaded on the carrier of ZnAl₂O₄ spinel played a role of catalytic dehydrogenation.Firstly a regular shape,uniform size Pt nanopolyhedron could be prepared as active ingredient in W?CO?₆ by chemical reduction method.Studied the effect of anhydrous ethanol and hexane solvent in the process of centrifugal.Then ZnAl₂O₄ spinel was prepared by co-precipitation method,and explored the effect of centrifugation and filtration,concentration of sesbania powder,calcination temperature and calcination time to the carrier grain size.Finally,a regular shape and uniform dispersion of Pt crystal/ZnAl₂O₄ catalyst was prepared under optimal conditions of the carrier that was interacted wih Pt crystal.The samples were evaluated by a fixed bed dehydrogenation microreactor,then optimized conditions of isobutane dehydrogenation process and improved catalyst performance by introducing additive Sn as compared with conventional catalysts.The results showed that the particles of the products in ethanol were uniform and dispersed,while the collosol was formed in hexane,and the aggregation of Pt nanoparticles was serious.The filtration colloid had a higher grain size than the centrifuationl that was more suitable for the preparation of ZnAl₂O₄ spinel and the appropriate calcination temperature and time were 700?,2 h.Microreactor evaluation showed that the activity of catalyst loaded on ZnAl₂O₄ was higher than that of?-Al₂O₃,the initial conversion rate of Pt crystal/ZnAl₂O₄catalyst increased by 77.1%and the yield increased by 37.5%after 160 min as compared to Pt crystal/?-Al₂O₃.The Pt crystal/ZnAl₂O₄ activity was better and the selectivity was 97%when the reduction time was 1 h,the initial conversion rate increased by 17.6%and the yield of the isobutene increased by 5%after 160 min compared with the traditional Pt/ZnAl₂O₄ catalyst.The activity was best when the reaction airspeed was 3000 h^-1.The yield of isobutene was much higher when additive Sn was introduced by sub-step for Pt crystal-Sn/ZnAl₂O₄ catalyst.When atomic ratio of Pt crystal/Sn was 1:1.5,the yield of isobutene was the highest which could still reach more than 30 percent after 160 min reaction.The experiment verified the performance of Pt crystal as an active ingredient to prepare better dehydrogenation catalysts.Reason was that Pt nanocrystalline polyhedron can increase the contact area of isobutane feedstock and dehydrogenation active sites to a certain extent.Pt crystals dispersed uniformly in favor of reducing strong adsorption activity and increased selectivity and suppressed soot.