Hierarchical Structure Of Supported Pt-In Bi-metallic Catalysts For Propane Dehydrogenation

Propene is an important chemical raw material.With the development ofpetrochemical industry,China’s demand for propene is increasing gradually,and the existing output can not meet the demand.How to obtain propene more efficiently has become a key problem.The catalysts commonly used for propane dehydrogenation are mainly included Pt-based and Cr-based catalysts.A large number of studies are based on the characteristics of high activity and no pollution of Pt based catalyst,but there are disadvantages such as easily sintering of active phase and carbon deposition at high temperature.In this paper,a series of hydrotalcite with different morphologies were obtained,and excellent catalysts were obtained by supporting Pt-In bimetal on the hydrotalcite.The influence of hydrotalcite morphology on the dehydrogenation performance of propane was investigated,and the catalyst was further modified by Zn additive and ZnO carrier,and the influence of reduction conditions on the catalytic performance was studied.Firstly,hydrotalcite precursors with three different morphologies of ball flower-like,single plate and small flake stacked block mass were prepared,and then PtIn/Mg（Al）O-x catalyst with well-preserved morphologies was obtained by continuous calcination/impregnation of In³⁺ions,calcination/impregnation of Pt⁴⁺ions and calcination/reduction.The samples were characterized by various means.The results showed that the precursors of hydrotalcite with different morphologies after calcination and impregnated with metal ions,the structure was restored.Due to the topological properties of the hydrotalcite structure,the hierarchical structure can be maintained after subsequent calcination and reduction treatment.The morphology of catalyst have significant effects on the propane dehydrogenation reaction,at atmospheric pressure,600℃,with Pt,In loadings were 0.48 wt%and 1.38 wt%respectively,the gas molar composition of C3H8:H2:N2=8:7:35,WHSV=3 h^-1,flower-like catalyst showed the best performance at the condition with selective above 97%,conversion rate of nearly 50%,stable for more than 190 h.Secondly,the effect of Zn on the performance of propane dehydrogenation on the catalyst with different morphology was investigated.Studies have shown that addition of Zn can significantly improve the selectivity of propene,and the presence of Zn will further change the morphology,which have an impact on the impregantion-recovery process.The co-exist of Zn and In had different effects on the activity of three catalysts,mainly reflected in the initial activity.Finally,the performance of propane dehydrogenation and synthesis method of hydrotalcite precursors supported by ZnO with different morphology were studied.It was found that the flower-like samples could be obtained by loading magnesia-alumina hydrotalcite on ZnO carriers with different morphologies.Compared with the flower-like samples without ZnO carrier,the sheet structure grew more closely,and the new sheet structure after impregantion-recovery was larger and thinner.The carrier ZnO mainly exists as crystal nucleus and has little effect on the final morphology,but can significantly improve the initial activity and shorten the reaction induction period.