Preparation of Porous Ni Catalysts from Ni-Ti Amorphous Alloy and Their Application in Hydrogen Production from Hydrogen Carrier Molecule

Synopsis : Skeletal Ni catalysts were prepared by the combined process of thermal treatment, mechanical milling, and dealloying using Ni40Ti60 amorphous alloy as a starting material. The influence of processing sequence on the catalytic activity of the prepared catalyst was investigated. The skeletal Ni catalyst prepared via i) thermal treatment at around the crystallization temperature (ca. 743 K), ii) mechanical milling, iii) dealloying by immersion in 1.0 mol/L HF aqueous solution showed the highest catalytic activity in the dehydrogenation reaction from ammonia borane compared with other skeletal Ni analogues prepared via different processing sequences. Thermal treatment around the crystallization temperature caused atomic rearrangement, which lead to a formation of electron-deficient Ni species on the surface of skeletal Ni alloy after dealloying treatment. SEM morphological observation and surface-area measurement indicated that thermal treatment decreased mechanical strength of the Ni-Ti alloy and that mechanical milling allowed the formation of finer Ni-Ti particles, which facilitated the formation of high-surface-area skeletal Ni after dealloying treatment. We found that processing sequence on Ni-Ti amorphous alloy made drastic impacts on surface area and electronic state of the resulting skeletal Ni, which consequently affected the catalytic performance in the dehydrogenation reaction.