The Study Of Supported Platinum Catalysts And Catalytic Process For Propane Dehydrogenation

Propylene is an important raw material in petrochemical industry. Nowadays, most of the propylene is obtained as by-product of gasoline production by both thermal and catalytic cracking processes, thus, the gasoline market demands determine the availability of propylene. Due to the growing demand for propylene, the research of propane dehydrogenation to propylene becomes a key research field in petrochemical industry.In this work, the effects of metal oxide promoters and small amount of oxygen addition to catalytic system on the structure and the dehydrogenation performance of Pt-based catalyst are investigated. This work is of importance in developing novel and highly performance Pt-based catalysts and high efficient dehydrogenation technology.A series of metal oxide promoters (Sn, Ce, Zn, V, La, Cr, Fe, Zr and Mn) can improve the performance of Pt/γ-Al₂O₃ for propane dehydrogenation. The CeO₂ promotes the activity and stability of Pt/γ-Al₂O₃ catalyst and ZnO gives a great increase in selectivity of propylene. Combination the unique property of Zn and Ce on Pt/γ-Al₂O₃ catalyst, a novel Pt/Ce-Zn-γ-Al₂O₃ catalyst is developed. The performance of the novel Pt/Ce-Zn-γ-Al₂O₃ three components catalyst is superior to the common Pt-Sn catalyst.The effects of metal oxides addition on the structure and dehydrogenation performance of Pt-Sn catalyst are further investigated. The improvement effects of these metal oxide promoters on Pt-Sn catalyst are more distinctive than the common alkali metal promoters. Metal oxides promoters can greatly increase the disperstion and stability of Pt particles. The presence of CeO₂ in Pt-Sn/Ce-γ-Al₂O₃ catalyst can induce the strong interactions between Pt, promoter, and support, which results in a notable stability to Pt particles and the suface of alumina support. CeO₂ promoteralso helps to maintain the oxidative state of tin in reaction, which may further increase the stability of catalyst. It has been also found that the presence of zinc can change the electronic property of the Pt metallic phase. The distinct electronic effect will weaken the strength of the Pt-(C=C) bond and promote olefin desorption, then suppress the formation of coke on the metal and greatly promote the selectivity of propylene. These two novel three components catalysts, Pt-Sn/Ce-γ-Al₂O₃ and Pt-Sn/Zn-γ-Al₂O₃, are reported as the optimal catalyst for propane dehydrogenation to propylene in present literatures.The effects of oxygen addition to catalytic dehydrogenation system on the structure and the dehydrogenation performance of platinum catalysts are investigated. It is found that small amount of oxygen addition into the reaction system can greatly promote the conversion of propane. The addition of small amount of oxygen can decrease the pressure of hydrogen, eliminate coke and provide heat for catalytic dehydrogenation reaction. The propane dehydrogenation reaction mechanism in H₂/O₂ gas medium is also discussed. This reaction is of importance in the development of new dehydrogenation technology based on partial combustion of hydrogen to generate heat in situ to the endothermic dehydrogenation processes.