Synthesis of Fe/Co/Ni based catalysts and NH3 cracking performance for H2 production
Hydrogen energy is considered to be the most promising alternative energy source to fossil fuels due to its advantages of efficient,clean and sustainable.As a kind of hydrogen storage material,ammonia has many advantages such as high hydrogen storage density and easy liquefaction,so hydrogen production by ammonia decomposition is an ideal method for hydrogen preparation.The development of highly selective,active and inexpensive catalysts for ammonia decomposition at low and medium temperatures is of great significance for the development and utilization of hydrogen energy.Ru-based catalysts are the most active single-metal catalysts for ammonia decomposi-tion,but their costs are high,and transition metals such as Fe,Co and Ni are suitable substitutes for Ru.Meanwhile,the choice of cata-lyst carrier is a key factor in the preparation of efficient catalysts.A series of ammonia decomposition catalysts with γ-Al2O3,SiO2,MgO and TiO2 as the carriers and Fe,Co and Ni as the active components were prepared by the impregnation method,and the catalyst activity evaluation test was carried out in the ammonia catalytic cracking reaction platform at 400 ℃ to 700 ℃ and the air-velocity ratios of 18 000 h-1.On the basis of this,the synthesized catalysts were characterized by XRD,BET,SEM and TEM to investigate the effects of different activ-ity combinations,carrier types,reaction temperatures and other factors on the ammonia catalytic cracking.The results show that the Ni/Al2O3 catalyst has the highest activity,and the ammonia decomposition rate reaches 91.67％at 18 000 h-1 and 600 ℃,and the complete decomposition of ammonia could be basically achieved at 650℃.The activities of Ni-based catalysts are overall higher than those of Fe-and Co-based catalysts,except for SiO2 carrier.Characterisation reveales that a composite oxide structure formed by NiO and γ-Al2O3 existed in the Ni/γ-Al2O3 catalysts,while the larger specific surface area and pore volume of the γ-Al2O3 carriers are conducive to the improvement of the ammonia decomposition conversion rate.
ammoniahydrogenammonia decompositiontransition metal catalystscarrier
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