The Investugation On The Preparation And Modification Of Pt-based Catalysts For Propane Dehydrogenation

As one of the most important basic raw materials in the modern petrochemical industry,propene is widely used to prepare a series of intermediates such as polypropylene,isopropanol,propylene oxide and acrylic acid.The traditional supplies of propene are mainly from by-product of catalytic cracking of petroleum and cracking of naphtha.Recently,with the increase of propylene consumption in the market and the sustained exploit of downstream derivatives of propene,the yield of propene obtained from traditional technologies has become more and more under-supply.Propane catalytic dehydrogenation（PDH）,as a on-purpose production technology of propene,has the superiorities of low-budget and high propene yield,and is widely used to satisfy the increasing demand for propene.The basis and core of propane dehydrogenation technology is catalyst.Pt-based catalysts and Cr-based catalysts are widely used in this field,but they all have defects.In order to achieve high efficient dehydrogenation,the preparation of more superior catalysts has always been the key research direction of this technology.Based on the propane dehydrogenation reaction,the performance of Pt-based catalysts for the reaction was investigated in this thesis.In order to develop a propane dehydrogenation catalyst with batter performance,the catalyst is optimized from the aspects of adding appropriate additives,changing the support,and optimizing the process conditions and treatment methods.（1）M is added to further modify the catalyst to prepare Pt Sn K/x M-Al catalysts with different M contents on Pt Sn K/Al₂O₃ catalyst.The results revealed that an appropriate amount of M can enhance the PDH reaction performance.The addition of M can enhance the interaction between the carrier and Pt,prevent the polymerization of the Pt species during high temperature reduction and regeneration and improve its dispersion.Further more,M could help maintain the stability of the carrier.When the additive amount of M is 0.75 wt.%,the catalyst shows the best performance.After 10hours of reaction,the selectivity reached 86%.（2）The effects of Al₂O₃ and commercial activated carbon（AC）on the performance of propane dehydrogenation reaction were investigated,and it was found that the performance of Pt Sn/AC catalyst was better than that of Pt Sn/Al₂O₃ catalyst.Subsequently,different acids and bases were further used for different treatments on the activated carbon support so as to prepare different Pt Sn/AC-X catalysts.The results of PDH evaluation showed that the activated carbon-supported Pt Sn catalyst treated with nitric acid has the best dehydrogenation performance,with an initial conversion rate of 40.16%.After 10 hours of reaction,the conversion was still>35.32%and the selectivity was～82%.After further characterization and analysis,it was found that activated carbon has a larger specific surface area,which was conducive to the dispersion of active components.After treatment with HNO₃,more oxygen-containing functional groups,for example,-OH and-COOH groups,appeared on activated carbon,which led to the improvement of its reaction performance.（3）The influence of the concentration of HNO₃ on activated carbon was further investigated.The activated carbon support was treated at different HNO₃concentrations to prepare different Pt Sn/AC-x HNO₃ catalysts.The dehydrogenation evaluation experiments showed that the performance of the catalysts was improved after HNO₃ treatment.when the HNO₃ treatment concentration was 20%,the initial conversion of Pt Sn/AC-20HNO₃ was 43.53%.After 10 hours of reaction,the selectivity was>84%,and the conversion was still 36.35%.According to the characterization results,many pores were etched on the surface of the activated carbon after HNO₃ treatment,leading to an increase of the specific surface area,which could provide more sites for the adsorption of Pt.At the same time,some metal impurities on the activated carbon were removed.Besides,the existence of oxygen-containing functional groups,for example,-OH and-COOH groups,could enhance the interaction between metal and support,avoid the agglomeration of Pt under high temperature conditions,and improve the stability of the catalyst.