Experimental And Theoretical Studies On Supported Pt-based Catalysts For Catalytic Dehydrogenation Of Methylcyclohexane

The over-exploitation and massive consumption of fossil energy have caused serious environmental pollution,and hydrogen energy is a good alternative energy source.Yet,the large-scale utilization of hydrogen energy needs to overcome various storage and transportation problems caused by the low volume density of H₂.Liquid organic hydride hydrogen storage technology can solve these problems.In the liquid organic hydride hydrogen storage system,the dehydrogenation reaction is a strong endothermic reaction.Excessively high reaction temperature will destroy the structure of the catalyst and cause various side reactions.Therefore,researching and preparing dehydrogenation catalysts with high reactivity,selectivity and stability to clarify the reaction mechanism is the key to solving the reversible recycling of liquid organic hydride hydrogen storage systems.In this paper,under the condition of constant p H control,preparing the Cu-Mg-Al hydrotalcite carrier by the co-precipitation method and loading Pt by the method of ultrasonic assisted impregnation,the Pt-Cu/Mg-Al-O catalyst was finally prepared after the steps of calcining and hydrogen reduction.The reaction time in the preparation of Mg-Al hydrotalcite carrier was changed,then the active component Pt was loaded,and the Pt/Mg-Al-O-X catalysts with different reaction times were prepared by calcining and hydrogen reduction.With the help of various characterization methods,the physical and chemical properties of the above two catalysts were studied.Using density functional theory calculation methods,the electronic properties of Pt?111?and Pt/Cu?111?surfaces,the adsorption of various species,and the reaction mechanism of methylcyclohexane dehydrogenation to toluene were studied to further clarify the catalytic dehydrogenation of Cu.The dehydrogenation performance of Pt/Mg-Al-O-X and Pt-Cu/Mg-Al-O catalysts in the dehydrogenation of methylcyclohexane was tested.The effects of different preparation methods,Cu content,reaction temperature,reduction temperature,support reaction time,feed rate and other factors on the catalyst performance were investigated.The results show that the addition of a small amount of Cu can promote the dispersion of Pt,and the active component Pt can be reduced at a lower temperature.At the same time,the addition of Cu improves the reactivity and stability of the catalyst.For the Pt/Mg-Al-O-X catalyst,prolonging the reaction time during the preparation of the hydrotalcite carrier can increase the average pore size of the catalyst,promote the dispersion of Pt,reduce the particle size of Pt,and can effectively improve the reactivity and stability of the catalyst.Both catalysts show good resistance to carbon deposition.When the feed rate of Pt-Cu-0.1/Mg-Al-O catalyst is 0.10m L/min,the reaction temperature and reduction temperature are 350?,and the catalyst dosage is 0.5g,the average conversion rate of methylcyclohexane is 91.9%,the selectivity of toluene is99.9%and the hydrogen release rate is 887.3 mmol·g _Pt^-1·min^-1.When the feed rate of Pt/Mg-Al-O-2 catalyst is 0.20m L/min,the reaction temperature and the reduction temperature are 350?,and the catalyst dosage is 0.5g,the average conversion rate of methylcyclohexane is 98.0%,the selectivity of toluene is 99.9%and the hydrogen release rate is 1892.3 mmol·g _Pt^-1·min^-1.The results of DFT calculation show that the addition of Cu enhances the adsorption of various species on the catalyst surface,makes the d-bond of the Pt atom more localized,and enhances the dehydrogenation activity of Pt.