Effect Of Halides On The Performance Of Pt-In Bimetallic Catalysts For Isobutane Dehydrogenation

In recent years,as an important chemical raw material and one of organic chemical intermediates,the rapid development of isobutene downstream products has increased the demand significantly.And the direct dehydrogenation of isobutane to isobutene has become the most efficient and promising dehydrogenation technology at present due to the easy availability of raw materials and simple operation.Pt and Cr are two kinds of active metals commonly used in direct dehydrogenation of alkanes.The application of Cr is seriously affected by its carcinogenicity and harmfulness to the environment.Pt based catalysts are widely used because of their high activity and friendliness,but Pt metal is easy to be deactivated due to sintering and carbon depositions.In order to solve the deactivation problem of Pt,we not only selected In as promoter,but also added MgF₂ species and halogen promoters to adjust the properties of hydrotalcite-like derivatives,and also studied the effect of promoters on Pt-In metals.Among all dehydrogenation catalysts prepared,the catalysts with MgF₂ promoter and halogen promoters showed excellent catalytic performance.A series of catalysts,hydrotalcite-like derivatives modified with MgF₂ promoter as the supports,Pt as the active component and In as the metal promoter,were synthesized by a combination of hydrothermal,alkaline etching and impregnation methods and applied them to isobutane to directly dehydrogenate isobutene.The research results show that MgF₂ promoter has a great influence on the physical and chemical properties and dehydrogenation performance of the supported Pt catalyst.The formation of MgF₂ species as a catalyst modifier affects the pore structure of the catalyst and even the surface acidity.The isobutene selectivity of Pt In HTR-KF catalyst can be stabilized above 95%after 9 h of reaction,and the isobutne activity of Pt In HTR-NH₄F and Pt In HTR-Na F catalyst is stabilized above 60%.One of the reasons for the improvement of catalytic performance is that small particles of MgF₂and coordinate unsaturated MgF₂ can provide weak acid centers,which can inhibit carbon deposition.The addition of MgF₂ improves the performance of the catalyst,which is related to the formation of a suitable In³⁺/In⁰ ratio on the surface of the catalyst,the high dispersion of Pt and the good anti-sintering performance.The Mg-Al hydrotalcite precursors were prepared by the co-precipitation method,and the calcined samples were used as the support,and then impregnated with active metal Pt,metal promoter In and non-metal halogen promoter to synthesize dehydrogenation catalysts.This paper not only studied the influence of different halogen promoters on the dehydrogenation system of Pt-In system,but also studied the influence of different impregnation amount and different impregnation order on the dehydrogenation performance.The research results show that when F is selected as the non-metallic promoter,the impregnation amount is 3 wt%,and the impregnation sequence is F→Pt→In,the best reaction performance is shown.On the basis of maintaining the isobutene selectivity at 93.5%,the isobutane conversion is increased by 7%compared with Pt-In catalyst.