Preparation of Ni-Ir/Al2O3 Catalyst and Its Application for Hydrogen Generation from Hydrous Hydrazine
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.
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