Ni-Ir/Al_(2)O_(3)负载型催化剂的制备及其用于水合肼分解制氢性能

Preparation of Ni-Ir/Al_(2)O_(3)Catalyst and Its Application for Hydrogen Generation from Hydrous Hydrazine

采用一种简单的浸渍-还原工艺制备出镍-铱/氧化铝(Ni-Ir/Al_(2)O_(3))负载型催化剂用于水合肼(N_(2)H_(4)·H_(2)O)催化分解制氢。该催化剂是将活性组分Ni-Ir负载于颗粒状Al_(2)O_(3)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N_(2)H_(4)·H_(2)O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Al_(2)O_(3)载体表面,Ni_(60)Ir_(40)/Al_(2)O_(3)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N_(2)H_(4)·H_(2)O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、N_(2)H_(4)·H_(2)O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[N_(2)H_(4)·H_(2)O]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。

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.Recently,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,hydrous hydrazine(N_(2)H_(4)·H_(2)O)is the best candidate;however,it has not been fully explored as an alternative for chemical hydrogen storage applications.A catalyst is essential to hydrogen production at a sufficient reaction rate for N_(2)H_(4)·H_(2)O-based hydrogen generation systems.In this study,a series of supported Ni100-xIrx/Al_(2)O_(3)catalysts were prepared using simple impregnation,roasting,and reduction method.The effect of reaction conditions on the activity and selectivity was evaluated in decomposing N_(2)H_(4)·H_(2)O to hydrogen.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/Al_(2)O_(3)catalysts.It indicated that the Ni_(60)Ir_(40)/Al_(2)O_(3)catalyst,comprising Ni-Ir alloy nanoparticles with an average size of 2-4 nm and crystallineγ-Al_(2)O_(3),exhibited excellent catalytic activity(>200 h^(-1))and selectivity(>99%)toward hydrogen generation from N_(2)H_(4)·H_(2)O at different temperatures,from 293 K to 353 K.The Ni60Ir40/Al_(2)O_(3)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 selectivity at 323 K toward the dehydrogenation of N_(2)H_(4)·H_(2)O.In addition,parameters,such as temperature,N_(2)H_(4)·H_(2)O and NaOH concentration,and catalyst mass on N_(2)H_(4)·H_(2)O decomposition were investigated over the Ni60Ir40/Al_(2)O_(3)catalyst.The kinetic rate equation for catalytic decomposition of N_(2)H_(4)·H_(2)O could be represented using the following expression:r=−k[N_(2)H_(4)·H_(2)O]0.346/0.054[NaOH]0.307[Catalyst]1.004,where k=4.62×10^(9)exp(-5088.49/T).The results could provide a theoretical foundation for applying N_(2)H_(4)·H_(2)O as a promising hydrogen storage material.