Preparation And Reaction Properties Of Propane Dehydrogenation Pt-based Catalysts

In recent years,propylene has been used as an important chemical raw material for the preparation of a series of chemical products such as polypropylene,cumene,carbonyl alcohol,acrylonitrile,propylene oxide and acrylic acid.The demand for propylene is increasing with the rapid development of society.The main source of propylene is by-products of naphtha cracking to ethylene and petroleum catalytic cracking processes,and production is constrained.In order to obtain high-yield propylene products,propane dehydrogenation to propylene technology?PDH?has been rapidly developed.This technology is currently widely researched and applied globally and brings significant economic value to the petrochemical industry.As the basis and core of PDH technology,the development of catalysts with excellent performance will directly affect the development speed of propane dehydrogenation technology and also determine the production of propylene.This paper focuses on the platinum-based dehydrogenation catalysts commonly used in propane dehydrogenation technology,and carries out catalyst improvement research from carrier selection,catalyst preparation methods and additive modification,and develops excellent platinum-based catalysts with high activity and high stability..Through the previous literature research,this paper determined the preparation of platinum-based catalysts using alumina as a carrier.The different preparation methods of the catalysts were investigated,and the catalysts were prepared by stepwise impregnation,co-impregnation and one-step synthesis.The catalyst prepared by the different methods is subjected to a propane dehydrogenation reaction,preferably an optimum catalyst.The catalysts prepared by different methods were tested by characterization means.According to the XRD characterization results of different catalyst samples,the catalyst was prepared in one step,and the crystallinity of the supported carrier?-Al₂O₃ was basically unchanged.The catalyst was prepared by co-impregnation and fractional impregnation,and the crystallinity of the supported carrier?-Al₂O₃ decreased with the active component.The N₂ adsorption-desorption test results show that the specific surface area and pore volume of the PtSn/Al-Y catalyst prepared by the one-step method are less different from the carrier physical properties,and the high specific surface area and large pore volume of the catalyst are maintained.From the dehydrogenation experiment,the catalyst prepared by one-step method has the highest conversion rate of propane to 50%,and the selectivity of propylene is about 71%.Based on the one-step preparation of catalysts,the effects of different auxiliaries?B,C,D,E?on the dehydrogenation performance of PtSn/Al-Y catalysts were investigated.It was found that the modification of the additive D can make the catalyst prepared by the one-step method exhibit better dehydrogenation performance in the reaction.The catalysts with different D contents were characterized by XRD,NH₃-TPD,H₂-TPR and TG-DTA.The results show that the addition of proper amount of D weakens the strong acidity of the catalyst,reduces the interaction between the active component of the catalyst and the support,and makes the active material PtOx easy to reduce.Excessive D addition causes the DAlO₃ crystal formed on the surface of the catalyst to agglomerate or cluster on the surface of the catalyst,block the pores of the catalyst,and aggravate the mass transfer resistance of the reactant product in the catalyst pores,which is not conducive to the dehydrogenation reaction.The experimental results show that the optimum loading of metal D is 2.2wt%,the catalyst dehydrogenation performance is optimal.After 12h reaction,the propane conversion rate is still above 35%,and the propylene selectivity is above 82%.The effects of different chelating agents?CA,OA and EDTA?on the dehydrogenation performance of D2.2-PtSn/Al-Y catalyst were investigated.The catalyst samples were analyzed by XRD,N₂ adsorption-desorption and TEM.The addition of different chelating agents allows the catalyst to retain a high specific surface area with a large pore size.The catalytically active Pt particles modified with CA are smaller and uniformly distributed on the catalyst.The aggregation of active Pt particles occurs in the catalysts modified by OA and EDTA,and the aggregation of active Pt particles is serious in the catalysts modified by OA.The results show that the catalyst modified by CA has high activity and stability in propane dehydrogenation.After 12 hours of reaction,the conversion of propane remained above 45%.