Methanation of carbon dioxide on catalysts derived from amorphous Ni-Zr-rare earth element alloys

The nano-grained Ni/ZrO₂ catalysts containing rare earth element oxides were prepared by oxidation-reduction pretreatment of amorphous Ni-(40-x) at% Zr-x at% rare earth element (Y, Ce and Sm; x=1-10) alloy precursors. The conversion of carbon dioxide on the catalysts containing 1 at% rare earth elements was almost the same as that on the rare earth element-free catalyst, but the addition of 5 at% or more rare earth elements increased remarkably the conversion at 473 K. In contrast to the formation of monoclinic and tetragonal ZrO₂ during pretreatment of amorphous Ni-Zr alloys containing 1 at% rare earth elements, tetragonal ZrO₂, which is generally stable only at high temperatures, was predominantly formed during the pretreatment of the catalysts containing 5 at% or more rare earth elements. The surface area of the catalysts increased with the content of rare earth element. Thus, the increase in the surface area and stabilization of tetragonal ZrO₂ seem to be responsible for the improvement of catalytic activity of the Ni-Zr alloy-derived catalysts by the addition of rare earth elements.