The Investigation On The Preparation And Performance Of Pt-Based Catalysts For Propane Dehydrogenation

Propylene,the most important chemical raw material and intermediate,is widely used to prepare some products such as polypropylene,propylene oxide,isopropanol,and other products.Moreover,the predominance role of propylene can still be maintained in the next few decades.Propane catalytic dehydrogenation to propylene has gradually become a relatively mature industrial production technology with the development of new green propane production technology,which is more economical and environmental-friendly than traditional processes such as steam cracking and fluid catalytic cracking to further improve the utilization of light alkanes and make up for the shortage of propylene.In order to design the Pt-based catalysts with better performance,a series of experiments based on the traditional PtSn/Al₂O₃ catalyst were investigated from the preparation methods,screening,modification,acid treatment,and performance optimization of the support in this paper.（1）The influence of ZrO₂-Al₂O₃ composite supports prepared via the sol-gel method,precipitation method,and wet mixing method in Pt-based catalysts were investigated.The results revealed that ZrO₂ can promote the reduction of PtSn species,which was so beneficial to the formation of PtSn alloys that the catalytic activity was much higher than that of traditional PtSn/Al₂O₃ catalysts.Moreover,the PtSn/5 wt.%ZrO₂-Al₂O₃ catalyst with more significant performance was prepared by the wet mixing method.The initial conversion of propane was 40.4%,and the selectivity of propylene reached 81.9%.（2）To a certain extent,it disclosed that ZrO₂ enhanced the surface acidity of the support and further led to serious coke formation on the catalysts after the screening of all composite catalysts.In order to solve this problem,a series of catalysts were prepared by adding different contents of alkali metal promoter M,which were based on the PtSn/5ZA catalyst with better performance.The result showed that not only the acidity of all catalysts was significantly reduced after modification with an appropriate amount of M,but did the stability and the selectivity of propylene as well.When the addition amount of M was 1.5 wt.%,the initial conversion of the better performance catalyst was 30.46%.After 10 hours of reaction,the conversion only decreased by3.08%,the initial selectivity of propylene reached 86.4%,and the deactivation constant was only 0.007 h^-1,respectively.（3）Compared with the PtSn/Al₂O₃ catalyst,the PtSn/ZrO₂ catalyst showed higher propylene selectivity but with poor stability in early experiments.In order to deal with the situation,the ZrO₂ supports were impregnated with certain concentrations of H₂SO₄,H₃BO₃,H₃PO₄,and HNO₃ to future prepare the PtSn-based catalysts.The results revealed that the specific surface area and pore volume of the catalysts decreased with different acids treatments,but the larger pore size was conducive to mass transfer and promoted the desorption of propylene.Moreover,the catalyst treated with HNO₃ showed optimal catalytic performance,which enhanced the interaction between the metal and the support and suppressed the agglomeration of active components to a certain extent.And the initial selectivity of propylene of the PtSn/HNO₃-ZrO₂ catalyst reached 88.4%,which was 8.8%higher than that of the PtSn/ZrO₂ catalyst.In addition,the deactivation constant was only 0.007 h^-1.