Catalytic Performance Of Supported Ruthenium-Based Catalysts For Hydrolysis Of Ammonia Borane To Hydrogen

Hydrogen energy is a clean and recyclable secondary energy source.The advantages of high efficiency,safety,and environmental protection make hydrogen energy one of the most hot research fields.Ammonia borane（NH₃BH₃,AB）as a hydrogen storage material is very stable at room temperature and has a hydrogen content of up to 19.6 wt%.Hydrolysis of ammonia borane at room temperature is a safe,low-consumption and high-efficiency method for hydrogen production,but the development of high-activity metal catalysts is one of the keys to its high-efficiency hydrogen generation.The agglomeration and shedding of metal particles during the process of preparation and catalytic reaction are the main reasons for the loss of catalytic activity.In this thesis,we select suitable catalyst supports to prepare a series of highly dispersed ruthenium-based metal catalysts by chemical reduction.The catalytic performance for the hydrolysis of ammonia borane is investigated.Moreover,the hydrolysis mechanism of ammonia borane is explored by theoretical calculation.The main research contents are as follows:（1）The Ru/γ-Al₂O₃-C catalyst was synthesized by in-situ reduction method.Theγ-Al OOH precursor was synthesized by hydrothermal method and the p H value of the reaction solution was adjusted by changing the urea concentration.The effect of urea concentration on the morphology and catalytic performance of Ru/γ-Al₂O₃-C was studied.Further reducing the Ru content,Ru/γ-Al₂O₃-C₂can still maintain superior catalytic activity.At 298 K,its TOF value is 175 mol _H2·mol _Ru^-1·min^-1and the activation energy is33.0 k J·mol^-1.（2）The Ru/MgAl-LDHs catalyst was synthesized by in-situ reduction method.The surface of MgAl-LDHs synthesized by simple hydrothermal method is rich in a large number of hydroxyl groups and has a strong ability to anchor metal particles.Different Mg/Al ratios in MgAl-LDHs have a significant impact on the performance of the catalyst.Ru/Mg₁Al₁-LDHs showed excellent catalytic activity in the process of catalyzing the hydrolysis of ammonia borane,with a TOF value of 137.1 mol _H2·mol _Ru^-1·min^-1and an activation energy of 30.8 k J·mol^-1.After ten cycles of testing,the catalytic activity can still be maintained at 58.8%of the first time.Through the theoretical calculations,the reaction process of water molecules and ammonia borane was simulated:Ru/MgAl-LDHs catalyst has a suitable electronic structure,which is conducive to the adsorption of ammonia borane and water molecules,thereby promoting the hydrolysis of ammonia borane.The facile activation of water molecules could accelerate the rate of water molecules splitting to form OH bonds.（3）A series of Ru/Co Ni-LDH and Ru/Co Ni-LDO catalysts were synthesized by liquid-phase reduction and gas-phase reduction method,respectively.The effect of different carriers,different Ru content,different reduction methods and auxiliary materials-citric acid（CA）on the catalytic hydrolysis of ammonia borane to produce hydrogen was systematically investigated.Among them,2 wt%Ru-CA/Co Ni-LDO-G exibits excellent catalytic performance.At 298 K,the TOF value is 501.4mol _H2·mol _Ru^-1·min^-1and the activation energy is 25.9 k J·mol^-1.The reaction path of ammonia borane and water molecule adsorption activation on the catalyst surface is simulated through theoretical calculations.Both Ru/LDO-L and Ru/LDO-G can accelerate the cracking of water molecules,but Ru/LDO-G strongly adsorbs ammonia borane.