Preparation And Properties Of Supported Pt Catalyst Based On Dehydrogenated Of Methylcyclohexane

Global warming is a major challenge of the times,mainly caused by the large-scale use of fossil fuels.It is essential to find a pollution-free alternative energy source.Hydrogen,as an ideal alternative energy source,can produce hydrogen through the residual energy of renewable energy,and then store and transport it as chemical energy in the form of a hydrogenated liquid organic hydrogen carrier（LOHC）,in which the methylcyclohexane-toluene（MCH-TOL）cycle,including reversible hydrogenation and dehydrogenation,is considered the best LOHC method.However,recovering hydrogen from MCH media requires reactive heat.So the preparation of a catalyst with high dehydrogenation activity and high stability at low temperature is an urgent problem.Two types of carriers,calcium-modified Ca-Mg-Al hydrotalcite and silica-modified Mg-Al-Si O₂,were prepared by the constant p H value co-precipitation method.Then the Pt is loaded by the ultrasonic-assisted isometric impregnation method,and the Pt/Ca-Mg-Al and Pt/Mg-Al-Si catalysts are obtained after drying,high-temperature calcination and H₂ thermal reduction.After that,the two types of catalysts were subjected to XRD,BET,H₂-TPR,FT-IR,CO-Chemisorption,NH₃-TPD,CO₂-TPD,TEM,TG and Raman spectroscopy and other characterization tests.In a fixed bed reactor,using methylcyclohexane as the hydrogen storage medium,the dehydrogenation performance of the two prepared catalysts were evaluated,and the effect of Ca content,Si O₂ addition amount,reduction temperature,reaction temperature,preparation method and feed rate on the dehydrogenation performance of the catalyst was investigated.The result shows:（1）For the Pt/Ca-Mg-Al series catalysts,the introduction of Ca enhances the interaction between Pt and the support,greatly promotes the dispersion of Pt,thereby reducing the particle size of Pt.For Pt/Mg-Al-Si series catalysts,the addition of Si O₂increases the specific surface area of the catalyst by about 100 m²/g,and reduces the reduction temperature of Pt.As the reaction temperature increases,the dehydrogenation activity of the catalyst increases,and both of these two catalysts have a strong ability to resist carbon deposition.（2）When the catalyst dosage is 0.5 g,the feed flow rate is 0.1 m L/min,the mass space velocity of the reactor is 9.48 h^-1,and the reaction temperature is 310℃,the toluene selectivity of the two catalysts exceeds 99.9%.Among them,the average conversion rate of methylcyclohexane catalyzed by the Pt/Ca（5）-Mg-Al-350 catalyst is 98.0%,and the hydrogen release rate is 56.7 mol/g _Pt/h.The average conversion rate of methylcyclohexane catalyzed by the Pt/Mg-Al-3Si-350 catalyst is 97.2%,and the hydrogen release rate is 56.3 mol/g _Pt/h.（3）By comparison,it is found that the dehydrogenation activity of the two catalysts at 330℃is equivalent,while the dehydrogenation activity of Pt/Mg-Al-3Si-350 at the reaction temperature of 290℃is greater than that of Pt/Ca（5）-Mg-Al-350 catalyst.In addition,the Pt/Mg-Al-3Si-350 catalyst still has a MCH conversion rate of 91.6%and a hydrogen release rate of 79.5 mol/g _Pt/h at a reaction temperature of 310℃and a MCH feed flow rate of 0.15 m L/min.