摘要
采用一种简单的浸渍-还原工艺制备出镍-铱/氧化铝(Ni-Ir/Al2O3)负载型催化剂用于水合肼(N2H4·H2O)催化分解制氢.该催化剂是将活性组分Ni-Ir负载于颗粒状Al2O3载体上制备而成,采用TEM、XRD、XPS、BET和H2-TPD等对其结构进行表征,并结合N2H4·H2O催化分解制氢实验开展了催化剂配方优化、催化反应动力学及循环耐久性研究.结果表明,粒径2～4 nm的Ni-Ir合金活性金属均匀负载于Al2O3载体表面,Ni60Ir40/Al2O3催化剂在293～353 K温度范围内均表现出优异的肼催化分解活性(>200 h-1),在该宽温域范围内的制氢选择性高达99%以上,且该催化剂具有优异的耐久性,在303 K条件下循环5 cyc后仍保持99%以上的氢选择性,而反应速率仅由249.2 h-1略减至225.0 h-1,活性衰减约9.7%.此外,对N2H4·H2O分解制氢反应动力学及各相关参数的影响进行了研究,包括温度、N2H4·H2O浓度、NaOH助剂浓度和催化剂用量,得到其反应动力学方程为r =-k[N2H4·H2O]0.346/0.054[NaOH]0.307[Catalyst]1.004,并初步探究了催化剂在制氢反应过程的活性衰减原因.
Abstract
Hydrogen is clean energy that can replace traditional fossil fuels in the future because of its high energy density,easy recharging,and availability of current liquid fuel infrastructure.However,the polymer-electrolyte membrane fuel cell requires controlled storage and efficient hydrogen release.Re-cently,liquid-phase chemical hydrogen storage materials with high gravimetric hydrogen density have emerged as promising candidates to overcome such challenges.Among these materials of interest,hy-drous hydrazine(N2H4·H2O)is the best candidate;however,it has not been fully explored as an alterna-tive for chemical hydrogen storage applications.A catalyst is essential to hydrogen production at a suffi-cient reaction rate for N2H4·H2O-based hydrogen generation systems.In this study,a series of supported Ni100-xIrx/Al2O3 catalysts were prepared using simple impregnation,roasting,and reduction method.The ef-fect of reaction conditions on the activity and selectivity was evaluated in decomposing N2H4·H2O to hydro-gen.The phase/structure of the catalysts was characterized using XRD,TEM,XPS,BET,and H2-TPD to gain insight into the catalytic performance of the Ni100-xIrx/Al2O3 catalysts.It indicated that the Ni60Ir40/Al2O3 catalyst,comprising Ni-Ir alloy nanoparticles with an average size of 2-4 nm and crystalline γ-Al2O3,ex-hibited excellent catalytic activity(>200 h-1)and selectivity(>99%)toward hydrogen generation from N2H4·H2O at different temperatures,from 293 K to 353 K.The Ni60Ir40/Al2O3 catalyst is durable and stable;however,the catalytic activity decreased from 249.2 to 225.0 h-1(～9.7%)after five runs with 99%H2 selectiv-ity at 323 K toward the dehydrogenation of N2H4·H2O.In addition,parameters,such as temperature,N2H4·H2O and NaOH concentration,and catalyst mass on N2H4·H2O decomposition were investigated over the Ni60Ir40/Al2O3 catalyst.The kinetic rate equation for catalytic decomposition of N2H4·H2O could be repre-sented using the following expression:r =-k[N2H4·H2O]0.346/0.054[NaOH]0.307[Catalyst]1.004,where k = 4.62×109exp(-5088.49/T).The results could provide a theoretical foundation for applying N2H4·H2O as a prom-ising hydrogen storage material.
基金项目
陕西省特种能源化学与材料重点实验室开放基金(SPCF-SKL-2020-0006)
万方数据