Preparation Of Rhodium Catalyst Supported By Porous Materials And Study On Its Hydrolysis And Dehydrogenation Performance Of Ammonia Boran

The rapid development of industry has led to the massive consumption of fossil fuels.The energy crisis and environmental problems caused by this are the key scientific problems to be solved urgently.As a renewable energy source,hydrogen is expected to be an ideal alternative to fossil fuel due to its wide sources,cleanliness,and high calorific value.However,due to the inherent gas properties of hydrogen,it is not conducive to storage and transportation.Among chemical hydrogen storage materials,ammonia borane has the advantages of high hydrogen storage capacity and non-toxic,which is expected to be used to solve the problem of hydrogen storage and transportation.However,ammonia borane is very stable at ambient temperature,so it is difficult to achieve rapid hydrolysis for hydrogen production.To improve the hydrolysis rate of ammonia borane and simplify the preparation method of the catalyst,mesoporous alumina supported rhodium-based catalyst was prepared by mechanochemical one-pot method.Rh/Al₂O₃ catalysts with mesoporous structure and high specific surface area were prepared by changing alumina precursor and adjusting the type and dosage of template agent.The catalytic activity of Rh/Al₂O₃-CTAB-400,Rh/Al₂O₃-CTAB（0.4）-500 catalysts for the hydrolysis dehydrogenation reaction of ammonia borane was tested by drainage method.In addition,the structure of these catalysts were characterized by SEM,TEM,XPS,XRD,BET and ICP.And the mechanism of catalytic hydrolysis reaction of ammonia borane by the catalyst was investigated.（1）An effective strategy synthesis of Rh/meso-Al₂O₃ catalysts was demonstrated by mechanochemistry for hydrolytic dehydrogenation of ammonia borane（AB）.These catalysts are characterized systematically by N₂ adsorption-desorption isotherms,X-ray diffraction,X-ray photoelectron spectrometry,scanning electron microscope,and transmission electron microscope.The results show that the turnover frequency（TOF）and activation energy（E_a）are 246.8 mol _H2·mol _Rh^-1·min^-1 and 47.9 kJ·mol^-1 for hydrolytic dehydrogenation of at 298 K catalyzed by Rh/Al₂O₃-CTAB-400,obviously higher than those previously reported catalysts.Furthermore,catalyst Rh/Al₂O₃-CTAB-400 can be recycled by simple centrifugal separation and the catalytic activity is still well maintained after five cycles.In addition,a plausible mechanism for hydrolytic dehydrogenation of AB has also been proposed.This mechanochemical synthesis method exhibits great application prospects for the preparation of heterogeneous catalysts.（2）Aluminium oxide（Al₂O₃）is a promising catalyst support due to its excellent stability,high specific surface area,low price,and wide applicability.At present,most of the synthesis methods of Al₂O₃ are wet chemical process,and the solid-state synthesis of catalysts is underdeveloped under solvent-free conditions.In this study,we proposed a novel strategy for solvent-free synthesis of Rh/Al₂O₃ catalysts via mechanochemistry.The pore properties of the catalysts can be tuned by simply adjusting the amount of template CTAB and calcination temperatures.As a proof of concept,as-prepared catalysts are used to catalyze hydrolytic dehydrogenation of ammonia borane.The best catalyst Rh/Al₂O₃-CTAB（0.4）-500 achieves a total turnover frequency of 186.0 mol _H2·mol _Rh^-1·min^-1 at 298 K and the activation energy is 44.8kJ·mol^-1.It also exhibits good cycling properties for catalyzing the hydrolysis of ammonia borane completely even after five runs.The catalysts were also characterized by various methods,including SEM,TEM,XPS,XRD,etc.,to study the relationship between their structure and catalytic performance.The results show that the high activity of the catalyst is closely related to its large BET specific surface area and appropriate average pore size.