Preparation Of New Bimetallic Nanomaterials And Catalytic Properties For Hydrogen Production

Environmental problems are becoming increasingly serious and fossil energy is decreasing.It is the general trend to develop clean,pollution-free and sustainable energy.Hydrogen energy is known as the most promising ideal energy carrier because of its non-pollution to the environment,high energy density and multiple forms of utilization,but its safe storage and transportation is a difficult problem.Therefore,it is of far-reaching significance to develop safe and stable chemical hydrogen storage materials and find suitable catalysts to release hydrogen under mild conditions.Ammonia borane,dimethylamine borane,hydrazine hydrate and formic acid in chemical hydrogen storage materials have attracted wide attention due to their high hydrogen content,stable properties and easy transportation.In the research of catalysts,the cost of noble metal catalysts is high.Bimetal catalysts can not only reduce the reaction cost but also improve the hydrogen production rate.Based on this situation,this paper uses bimetallic catalysts to apply to different hydrogen storage materials,and the specific research contents are as follows:Magnetic Co-Pd/C bimetallic nanocomposites were prepared on Pd/C and Co（NO₃）₂ as raw materials by in-situ reduction method and were used to synergistically promote the hydrolysis of ammonia borane to produce hydrogen.The results showed that the particle size of the catalyst was mainly concentrated at 3-4 nm,forming a relatively dispersed and smaller particle size distribution.TEM and EDX analysis showed that the magnetic Co-Pd/C nanocomposite had a core/shell structure.When the ratio of Co Pd is 1:20,its catalytic effect is the best.The TOF value is 263.39 mol _H2·mol_cat^-1·min^-1,which is 10 times of Pd/C(only 26.97mol _H2·mol_cat^-1·min^-1).The E_a of AB hydrolysis is significantly reduced from 57.92 k J/mol（Pd/C）to 35.70 k J/mol（Co-Pd/C）.Different bimetallic catalysts（FePt/C,CoPt/C,NiPt/C and CuPt/C）were prepared using Pt/C and different metal salts as raw materials,and used to catalyze the hydrogen production of dimethylamine borane.The results show that Pt and Ni have good dispersion on C carrier,and the agglomeration of nanoparticles is not obvious after cycling,and they still have good catalytic activity.Among the four catalysts,the TOF value of Ni Pt/C is the highest,4151.7mol _H2·mol_cat^-1·h^-1,which is 7.2 times that of Pt/C(only 578.4 mol _H2·mol_cat^-1·h^-1).The E_a of DMAB hydrolysis has rapidly decreased from 56.34 k J/mol（Pt/C）to 39.97 k J/mol（Ni Pt/C）.In addition,the catalyst still showed excellent catalytic activity in the hydrogen production experiment of hydrazine hydrate,with a TOF of 1012.2 mol _H2·mol_cat^-1·h^-1,while Pt/C did not have such catalytic activity.Using dopamine hydrochloride,ammonia water and formaldehyde as materials,CNS was prepared,and then Pt Ni/CNS bimetallic catalyst was obtained through Na BH₄ reduction,which was used to catalyze hydrazine hydrate to produce hydrogen.The results show that the CNS and Pt Ni/CNS are spherical,and Pt Ni/CNS contains abundant O and N functional groups,which is conducive to the stability of Pt Ni bimetallic nanoparticles.When the ratio of Pt Ni is1:1,the catalytic performance for dehydrogenation of hydrazine hydrate to release H₂ is the highest,the H₂ selectivity is 100%,the TOF is 3928 mol _H2·mol_cat^-1·h^-1,and the E_a is 37.97k J/mol.In addition,the most important thing is that by adjusting the p H value,the highly selective"on-off"control of hydrogen released on demand during the hydrogen production process of hydrazine hydrate has been successfully realized,so as to effectively and safely produce,carry and deposit hydrogen.The Ag₁₆-Pd₁/C bimetallic catalyst was prepared by simple alloying using Pd/C and Ag NO₃ as raw materials,and was used to promote the hydrogen production of formic acid.The results show that the selectivity of hydrogen evolution of formic acid is 100%and there is no side reaction.The two H atoms in the H₂ gas produced in the hydrogen production of formic acid are from formic acid.In this reaction,the TOF of Ag₁₆-Pd₁/C bimetallic catalyst is the highest,2444.10 mol _H2·mol _Pd^-1·h^-1,while the TOF of commercial Pd/C is only 619.39mol _H2·mol _Pd^-1·h^-1,and E_a has been effectively reduced from 40.45 k J/mol（commercial Pd/C）to 32.27 k J/mol(Ag₁₆-Pd₁/C).By adding 0.4 M OH^-and H⁺to adjust the acid-base environment of formic acid reaction system,the H₂ release of formic acid reaction process was realized.