Preparation And Dehydrogenation Properties Of Supported Pt-Ni Bimetallic Dehydrogenation Catalysts

Over-exploitation of non-renewable fossil energy has caused an increasingly serious energy crisis and many ecological problems,and the use of hydrogen energy as an alternative energy has broad development prospects.Hydrogen energy has many advantages including abundant reserves,cleanness,high combustion calorific value and various storage forms.However,hydrogen storage technologies such as hydrogen storage via hydride and traditional physical hydrogen storage methods have significant limitations,in contrast,liquid organic hydride has larger industrial application value for hydrogen storage.The core of this hydrogen storage technology is the dehydrogenation process,the ideal dehydrogenation catalyst should show better activity,target product selectivity and hydrogen release rate at lower temperatures.Under the condition of stable pH value,Ni-Mg-Al hydrotalcite carrier was prepared by co-precipitation method,and after the active component Pt was loaded by ultrasonic-assisted over-volume impregnation method,Pt-Ni/Mg-Al bimetallic dehydrogenation catalyst precursor was prepared.The precursor turned into Pt-Ni/Mg-Al bimetallic dehydrogenation catalyst after further drying,high-temperature calcination and H₂thermal reduction.XRD,BET,H₂-TPR,NH₃-TPD,CO₂-TPD,TEM,XPS,TG and other characterization techniques were used to study the physical and chemical properties of the support,catalyst precursor and catalyst.The dehydrogenation performance of the prepared Pt-Ni catalysts was evaluated using methylcyclohexane as hydrogen storage medium on a fixed-bed microreactor device.The effects of Ni content,reduction temperature,reaction temperature,catalyst filling method and feed rate on the reaction results were investigated,the results were as follows.1.All Pt-Ni catalysts with different Ni content outperformed pure Pt catalyst,when the Ni content is 0.5 wt%,Pt-Ni catalyst has the best performance.2.The reduction temperature can affect the composition of active components and the structure of the catalyst.3.When the reaction temperature increased from 250°C to 350°C,the dehydrogenation conversion rate increased from6.5%to 98.1%.4.When the catalyst is loaded,the physical mixing of quartz sand particles can enhance the dehydrogenation activity of the catalyst,which is more significant at higher temperatures.5.Increasing the feed flow rate will shorten the residence time of the reactants,which will lead to an obvious decrease in the catalyst's reactivity.For Pt-Ni-0.5-350 catalyst,under the conditions of 1 atm,catalyst dosage=0.5 g,methylcyclohexane feed flow rate=0.1 m L/min,reactor mass space velocity=9.48 h^-1,and reaction temperature=350?,its average MCH conversion was98.1%,the selectivity towards toluene was close to 100%,and the hydrogen release rate reached 947.1 mmol/g _Pt·min.Through first-principles calculations,the adsorption properties of related species in the mechanism of the stepwise dehydrogenation of methylcyclohexane on Pt-Ni?111?surface were investigated,the optimal dehydrogenation path in theory was proposed,and the superiority of Pt-Ni bimetallic surface for dehydrogenation was revealed.Mulliken population analysis results showed that on Pt-Ni?111?surface,Pt atoms seized part of the electrons of Ni atoms,so an electron transfer from Ni to Pt occured.Compared with Pt?111?plane,this may result in weaker chemical bonds between related species in the dehydrogenation process and surface metal atoms on Pt-Ni?111?plane.Moreover,after adding Ni to the Pt surface,the weakening of the adsorption strength of related species may have a greater effect on the dehydrogenation reaction,which ultimately brought about better dehydrogenation performance for Pt-Ni catalyst.