| In recent years, conversion of low alkanes to value-added olefins has drawn greater attention, because that the light alkenes are extensively utilized as the raw materials for polymer industry and other commodity chemicals.1-4 Currently, studies on propane dehydrogenation(PDH) mainly focus on preparing high-efficiency catalysts to attain a desirable yield of propylene. Among all the catalysts for propane dehydrogenation, Pt-based catalysts are considered as the most promising catalysts, especially with indium as promotor to further improve catalytic performances.The Mg(Al)O-x supports with different Mg/Al molar ratios and the supported bimetallic Pt-In catalysts are synthesized, characterized by several state-of-art methods and applied to propane dehydrogenation reaction. The results verify that the Mg/Al molar ratio markedly influences the structure, properties and catalytic performances of Pt In/Mg(Al)O-x catalysts for propane dehydrogenation reaction. It is found that the Pt In/Mg(Al)O-4 catalyst(Mg/Al molar ratio is 4:1) has nanoflake-like structure, the largest specific surface area, the smallest average metal particle size(2.5 nm), the highest Pt dispersion and harmonious acid-base properties of the catalyst. Meanwhile, the Pt In/Mg(Al)O-4 catalyst exhibits good reducibility of metal species due to the moderate interactions between metals and support. The highest propane conversion and propylene selectivity are got over Pt In/Mg(Al)O-4 catalyst, which nearly exhibits no deactivation during one 12 h once-through propane dehydrogenation reaction. Moreover, the Pt In/Mg(Al)O-4 catalyst possesses good reproducibility ability. After 8 reaction-regeneration cycles, the initial and final propane conversions still attain 66.4% and 43.5% accompanied with the propylene selectivity of above 95%.Numeral physical-chemical characterizations are employed to probe the reasons of activity variation and structure-activity relationships. The mechanism for the activity induction and deactivation is proposed by a schematic diagram. The XPS results prove that the valence state of In exhibits almost no change during the whole dehydrogenation reaction. The catalytic activity of Pt In/Mg(Al)O catalyst goes through ascent, stable and descent stages. The activity variation is attributed to the changes of metal particle size, the state of coke deposition, the specific surface area and the crystalline phase of the catalyst.The Pt In/Mg(Al)O-p X catalysts are prepared with co-precipitation method at different p H values(X=6-12), with an aim of investigating the effect of p H value on the catalytic performance of Pt In/Mg(Al)O-p X catalysts for propane dehydrogenation reaction. It is found that the co-precipitation p H value could strongly influence on the crystalline phase, the specific surface area, the surface morphology, the distribution of surface acidity, the reduction property of metal phase, surface chemical state, the distribution of metal particles and coke formation, giving rise to the different catalytic performances of Pt In/Mg(Al)O-p X catalysts with respect to the p H value. All the results reveal that the catalyst prepared at p H 8 shows the best catalytic performance, which possesses the primary crystal phase of periclase(Mg O) and specific area, the lowest fraction of strong acidic sites and In0 species, the strongest interaction between metal phase and support, the highest Pt dispersion(41.6%), the best distribution of Pt particles with the smallest Pt particle size(1.8nm) and the lowest coke amount. Furthermore, the highest once-though yield of 0.37 mol propylene can be obtained over the Pt In/Mg(Al)O-p8, when 0.60 mol propane is consumed in a whole dehydrogenation reaction period(28 h).The Zn(Al)O-x supports with different Zn/Al molar ratios and the supported bimetallic Pt-In catalysts are synthesized, characterized by several state-of-art methods and applied to propane dehydrogenation reaction. The results verify that the Zn/Al molar ratio markedly influences the structure, properties and catalytic performances of Pt In/Zn(Al)O-x catalysts for propane dehydrogenation reaction. Pt In/Zn(Al)O-2 catalyst(Zn/Al molar ratio is 2:1) has the suitable specific surface area and crystal phase, the optimal fractions of weak and medium acid sites, the moderate Pt reduction property and the strongest interaction between metal phases and support, leading to the best catalytic performance. The initial propane conversion(30.5 %) and propylene selectivity(above 93.0 %) can be obtained over this catalyst. However, Pt In/Zn(Al)O-1 catalyst exhibits the highest fraction of spinel Zn Al2O4 phase, the weakest metal-support interaction, the strongest acidity and the highest coke amount, resulting in the worst catalytic performance.
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