Synthesis And Catalytic Performance Of Magnetic Nanoparticles For Hydrogen Generation From Ammonia Borane

With the large consumption of fossil fuels and environment pollution,hydrogen as an efficient clean energy gradually become the focus of world attention,hydrogen storage materials are also inevitable become the object of widely research.Ammonia borane(NH3BH3,AB)is considered as one of the most promising solid hydrogen storage materials because of high quality hydrogen storage density,good water solubility and no toxicity.Under the suitable metal catalyst,ammonia borane can release hydrogen completely through hydrolysis at room temperature or even zero degree.In recent years,the magnetic catalysts have attracted attention of researchers because of its advantages of easy recycling.This study aims to synthesis magnetic catalyst for hydrolysis of AB with high activity and low cost,the bimetallic and trimetallic nanoparticles were synthesized by using in situ reduction method,respectively.The relationship between catalyst structure and catalytic performance,magnetism property was explored by the means of multiple characterization techniques on nanoparticles and catalyst.At room temperature,some Fe-based bimetallic nanoparticles were obtained by using NaBH4 and AB as reductants simultaneously,the synthesized CoFe nanoparticles showed the best activity for hydrolysis of AB and indicated the synergistic effect,which exhibited better catalytic activity than monometallic Co and Fe nanoparticles.The as-synthesized CoFe nanoparticles was characterized by TEM,XRD,EDS,showing that the particles are spherical and amorphous.Furthermore,the CoFe nanoparticles were supported on ketjon carbon to catalysis the hydrolysis of AB.catalysis the hydrogen generation from hydrolysis of AB by loading on the active carbon.The results prove that the composition of the CoFe nanoparticles is closely related to the activity performance.Among the tested compositions of CoFe/C,the Co0.7Fe0.3/C has the highest catalytic activity with a total turnover frequency value of 42.5 min-1.Kinetic study indicated that the hydrolysis of AB catalyzed by Co0.7Fe0.3/C is first order with respect to the catalyst concentration and the activation energy is determined to be 35.5 kJ/mol.Besides,the synthesized Co0.7Fe0.3 nanoparticles and Co0.7Fe0.3/C catalyst has good magnetic performance with magnetic saturation intensities of 36.8 emu/g and 14.5 emu/g,respectively.According to the different redox potentials between metals,magnetic nanoparticles Pd@CoNi/C catalyst was successfully synthesized via in situ reduction by using PdCl2,Co(NO3)2,Ni(NO3)2 as the metal precursors and AB as mild reducing agent.In the same condition,PdCoNi/C was synthesized by using NaBH4 as strong reducing agent,and catalytic result showed the Pd@CoNi/C was better than PdCoNi/C towards hydrolysis of AB.The synthesized Pd@CoNi/C catalyst was applied to the hydrolysis of AB after loading on active carbon,and the catalytic activity of the Pd@CoNi/C catalyst is better than that of corresponding monometallic and bimetallic catalyst.The catalytic activity of Pd@CoNi are related to the composition of various metals,and Pd0.1@(Co0.5Ni0.5)0.9/C is the most active among the tested catalysts with the TOF value of 34.2 min-1.The kinetics has been investigated,which indicate that the hydrolysis of AB catalyzed by Pd0.1@(Co0.5Ni0.5)0.9/C is first order with respect to the catalyst concentration and the activation energy is determined to be 35.5 kJ/mol.In addition,Pd0.1@(Co0.5Ni0.5)0.9/C catalyst can still maintain 70%of initial catalytic activity after 5 runs.Pd0.1@(Co0.5Ni0.5)0.9 and Pd0.1@(Co0.5Ni0.5)0.9/C display a magnetic saturation intensity of 12.1 emu/g and 4.2 emu/g,respectively.In order to further improve magnetic property of catalyst,Fe3O4@C-1 and Fe3O4@C-2 were synthesized by using classic hydrothermal method as magnetic carrier instead of Ketjon C and were applied for hydrolysis of AB.The results indicated that the method can improve the magnetic performance of the catalyst with the magnetic saturation intensity of 30.2 emu/g and 41.3 emu/g.Besides,the as-synthesized two catalysts can also maintain desirable catalytic activity in hydrolysis of AB with the TOF of 27.2 min-1 and 20.45 min-1,respectively.