THE REACTION CHARACTERISTICS OF CARBON DIOXIDE METHNATION ON Ni/(Zr-Sm OXIDE) CATALYSTS

摘要

For the use of renewable energy in the form of usable fuel via electrolytic hydrogen generation we have been studying the conversion of carbon dioxide to methane by the reaction with hydrogen. For the formation of methane, we found very effective catalysts (1). When the gas mixture of CO2 + 4H2 was passed at ambient pressure on an amorphous Ni-40Zr alloy at 200-300°C, the conversion of carbon dioxide occurred very rapidly and exclusively to methane with almost 100 % selectivity. In the reaction environment, the amorphous Ni-Zr alloys were transformed to conventional catalysts consisting of Ni supported on Zr02. The key was the structure of ZrO2 type oxide. A high portion of tetragonal ZrO2 was formed, in spite of the fact that the stable form of ZrO2 in this temperature region is monoclinic. The nickel supported on tetragonal ZrO2 was just the catalyst with high activity for methanation of carbon dioxide. At the construction of the ZrO2 lattice by oxidation of zirconium in Ni-Zr alloys, Ni~(2+) ions were also included in the lattice. The inclusion of lower-valent Ni~(2+) ions than Zr~(4+) ions in the lattice is accompanied by the formation of oxygen vacancies which stabilizes the tetragonal ZrO2 structure. For the enhancement of the catalytic activity the stabilization of the tetragonal ZrO2 structure by inclusion of other elements than nickel is effective. Since rare earth element ions stabilize the tetragonal ZrO2 structure the further higher activity was found by using amorphous Ni-Zr-rare earth element alloys as catalyst precursors (2).