Ni/: Rare Earth Effect on the Catalytic Performance in the Dry Reforming and Partial Oxidation of Methane

In order to clarify the role of R[sub.2]O[sub.3] in the metal-oxide catalysts derived from complex oxide precursors, a series of R[sub.1.5]Ca[sub.0.5]NiO[sub.4] (R = Nd, Sm, Eu) complex oxides was obtained. A significant systematic increase in the orthorhombic distortion of the R[sub.1.5]Ca[sub.0.5]NiO[sub.4] structure (K[sub.2]NiF[sub.4] type, Cmce) from Nd to Eu correlates with a corresponding decrease in their ionic radii. A reduction of R[sub.1.5]Ca[sub.0.5]NiO[sub.4] in the Ar/H[sub.2] gas mixture at 800 °C causes a formation of dense agglomerates of CaO and R[sub.2]O[sub.3] coated with spherical 25-30 nm particles of Ni metal. The size of metal particles and oxide agglomerates is similar in all Ni/(R[sub.2]O[sub.3],CaO) composites in the study. Their morphology is rather similar to the products of redox exsolution obtained by the partial reduction of complex oxides. All obtained composites demonstrated a significant catalytic activity in the dry reforming (DRM) and partial oxidation (POM) of methane at 700-800 °C. A systematic decrease in the DRM catalytic activity of composites from Nd to Eu could be attributed to the basicity reduction of R[sub.2]O[sub.3] components of the composite catalysts. The maximum CH[sub.4] conversion in POM reaction was observed for Ni/(Sm[sub.2]O[sub.3],CaO), while the maximum selectivity was demonstrated by Nd[sub.2]O[sub.3]-based composite. The possible reasons for the observed difference are discussed.