Synthesis Of IrNi And CuNi Nanomaterials Supported By Rare Earth And Catalytic Performance For Hydrogen Production

Hydrogen is one of the promising efficient energy carrier and an environmentally attractive fuel for future energy application.However,on-demand controllable storage and release of hydrogen are the well-known technological barriers.Nitrogen-based hydrides chemical hydrogen storage materials hydrazine hydrate?N₂H₄·H₂O?and hydrazine borane?N₂H₄BH₃?have been widely concerned by researcher due to their high energy density and they can exist safely and stably at room temperature.Hydrazine hydrate has a high hydrogen storage capacity?8.0 wt%?and the by-product of potential liquid chemical hydrogen storage material hydrazine hydrate is only N₂.Hydrazine borane?15.4 wt%?can be completely converted to H₂ via hydrolysis of BH₃ group and selective dehydrogenation of the N₂H₄ moiety to N₂ and H₂.With appropriate catalysts,full hydrogen production can be achieved.However,to enable hydrazine hydrate and hydrazine borane for practical hydrogen storage,there may be side reactions that produce ammonia?NH₃?,and the complete decomposition of N₂H₄moiety is more difficult.Therefore,the development of catalysts with high selectivity,high activity and high stability is the key to hydrogen production as for N₂H₄·H₂O and N₂H₄BH₃.In this thesis,several metal nanomaterials have been designed and synthesized.The main contents are as follows:A series of NiIr alloy nanoparticles immobilized on lanthanum oxycarbonate?NiIr/La₂O₂CO₃?have been successfully synthesized through a sodium-hydroxide-assisted reduction approach at room temperature.Transmission electron microscopy?TEM?characterizations showed that ultrafine NiIr nanoparticles with an average size of around 2.4 nm were effectively and highly dispersed on La₂O₂CO₃.The NiIr/La₂O₂CO₃ nanocomposites prepared with the assisted of NaOH showed much higher catalytic activity and H₂ selectivity toward the N₂H₄BH₃dehydrogenation reaction as compared to that of prepared without addition of NaOH?NiIr/La₂O₂CO₃-N?.Among all of the tested samples,the optimized Ni_0.75Ir_0.25/La₂O₂CO₃ exhibited the highest catalytic performance with 100%hydrogen selectivity for hydrogen generation from aqueous solution of N₂H₄BH₃.The total turnover frequency?TOF?of Ni_0.75Ir_0.25/La₂O₂CO₃ for this dehydrogenation reation was measured to be 1250 h^-1 at 50 ^oC,which is among the highest values ever reported.This excellent catalytic performance could be attributed to the high dispersion of metal nanoparticles and the strong interaction between metal and support as well as the promotion effect of NaOH.A series of non-precious metal CuNi nanoparticles were successfully dispersed on the composite material?CuNi/La₂O₂CO₃/rGO?by a simple impregnation reduction method.TEM characterization shows that the size of the catalyst CuNi nanoparticles is about 3.2 nm,which is much smaller than the CuNi nanoparticles on the single-carrier nanocatalyst CuNi/La₂O₂CO₃?6.4 nm?and CuNi/rGO?14.3 nm?.The optimal nanocatalyst Cu_0.5Ni_0.5/La₂O₂CO₃/rGO showed the highest catalytic performance and 100%hydrogen selectivity for decomposition of hydrazine hydrate with a TOF value of 114.3 h^-1 under 70 ^oC alkali?2.0 M?conditions.Moreover,other rare earth compounds?Re=La,Ce,Y,and Gd?combined with rGO supported CuNi nanoparticles were aslo showed excellent catalytic activities for hydrogen production from hydrazine hydrate.