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

Propylene is widely used as the second largest petrochemical raw material in the chemical industry.With the continuous expansion of the scale of the propylene downstream industry,the demand for propylene is increasing,and the production of propylene from the traditional petrochemical industry is increasingly difficult to meet the demand for propylene.In the current situation of the sharp increase in propylene demand,efficient production technology of propylene is important.Propane dehydrogenation to propylene is an effective technique to improve the utilization rate of propane and effectively fill the gap in propylene production.The key to the development of propane dehydrogenation technology is the research of catalysts,which directly affects the production efficiency of the propane dehydrogenation process.In this thesis,Pt was used as the active component of the catalyst and MgAl₂O₄ was selected as the catalyst support.In order to prepare the Pt-based catalysts with superior performance,a series of experiments for preparing the PtSn/MgAl₂O₄ catalyst were conducted,including the preparation conditions of the support,the loading capacity of Sn,and the addition of the second promoter.（1）The research on the preparation conditions of MgAl₂O₄ support（MAS）indicated that,compared with the solid-phase method and the coprecipitation method,the sol-gel method can realize the mixing of the two reactants at the molecular level,to form a gel with good structure.And the crystallinity and crystal particle integrity of MAS increased with the increase in calcination temperature.The experimental results showed that the PtSn/MAS catalyst prepared by the sol-gel method with pseudo-boehmite as the aluminum source and 700℃as the calcination temperature exhibited the best reaction performance.The initial propane conversion over this catalyst was 34.7%and decreased to 27.7%after 10 h of reaction,in which the initial propylene selectivity was 78.6%,and the deactivation constant was 0.033 h^-1.（2）The effects of aging time and Sn loading on the dehydrogenation performance of PtSn/MAS catalysts prepared by the impregnation method were also investigated.It was found that the optimum aging time of the catalyst was 12 h.The prepared PtSn/MAS catalyst had a propane conversion of 33.3%and a propylene selectivity of80.9%.Then the loading amount of Sn was investigated,demonstrating that the addition of Sn significantly improved the particle size and dispersion of Pt species,increased the interaction between metal and support,and inhibited the carbon deposition during the catalyst reaction.The optimal loading amount of Sn was 0.3wt.%,and the prepared catalyst exhibited a propane conversion rate of 40.9%,a propylene selectivity of 82.5%,and a deactivation constant of 0.035 h^-1.（3）The second promoters were selected and introduced into the PtSn/MAS catalysts to further improve the propylene selectivity.The effect of the addition of X₁,X₂,X₃,X₄,and X₅ on the dehydrogenation performance of the prepared catalysts was sequentially investigated.It was found that the addition of X₃ could positively enhance the dehydrogenation performance of PtSn0.3X₃/MAS catalyst,which exhibited a propylene selectivity of 85.7%and a deactivation constant of 0.034 h^-1.Then,the investigation of the loading amount of component X₃ indicated that the optimum loading amount of component X₃ was 0.9 wt.%.And,the conversion of propane over the prepared was 35.7%,the selectivity of propylene was 92.6%,and the deactivation constant was 0.029 h^-1.