In global carbon dioxide recycling for prevention of global warming and supply of renewable energy, fluctuating power generated by solar cells in remote deserts will be converted to H₂ by seawater electrolysis and then to methane by the reaction of H₂ and CO₂ at desert coasts, so as to use currently existing infrastructures for natural gas for transportation and combustion. One of the authors (KH) and his coworkers found effective catalysts derived from amorphous Ni-Zr-rare earth element alloys for hydrogenation of CO₂ with extremely high reaction rate and almost 100% selectivity. The high activity was attributed to the formation of nickel supported by tetragonal zirconia in contrast to the low activity of nickel supported by monoclinic zirconia. Although the stable polymorph is monoclinic, tetragonal zirconia is stabilized by doping of rare earth elements in zirconia lattice. Because amorphous alloy precursors are not suitable for mass production, we developed conventional method for preparation of the catalysts consisting of nickel supported by tetragonal zirconia and evidenced the effectiveness of such catalysts. The present work aimed to determine suitable composition and preparation method for catalysts composed of nickel supported by samarium-stabilized tetragonal zirconia. Zirconia sol with samarium nitrate and nickel nitrate were calcined at 500°C. The oxide mixtures were treated in hydrogen stream at 300°C for 5 h to form the catalysts. X-ray diffraction revealed that the catalysts consisted of metallic nickel supported by tetragonal zirconia. The methanation performance of the catalysts was examined passing a gas mixture of CO₂ and H₂ (1:4 volume ratio) at an atmospheric pressure through the catalyst. After reaction the gas was analyzed using a gas chromatograph equipped with a thermal conductivity detector. The catalyst with the best performance was determined by changing the ratio of nickel to oxide and that of zirconium to samarium in the oxide.

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1. Spontaneous passivity of bulk amorphous Ni-Cr-Ta-Mo-Nb-P alloys in concentrated hydrochloric acids
2. Energy-saving seawater electrolysis for hydrogen production
3. Materials and Technology for Global Carbon Dioxide Recycling -For supply of renewable energy and prevention of global warming