Ni/(R 2 O 3 ,CaO) Nanocomposites Produced by the Exsolution of R 1.5 Ca 0.5 NiO 4 Nickelates (R = Nd, Sm, Eu): Rare Earth Effect on the Catalytic Performance in the Dry Reforming and Partial Oxidation of Methane.

In order to clarify the role of R 2 O 3 in the metal-oxide catalysts derived from complex oxide precursors, a series of R 1.5 Ca 0.5 NiO 4 (R = Nd, Sm, Eu) complex oxides was obtained. A significant systematic increase in the orthorhombic distortion of the R 1.5 Ca 0.5 NiO 4 structure (K 2 NiF 4 type, Cmce) from Nd to Eu correlates with a corresponding decrease in their ionic radii. A reduction of R 1.5 Ca 0.5 NiO 4 in the Ar/H 2 gas mixture at 800 °C causes a formation of dense agglomerates of CaO and R 2 O 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 2 O 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 2 O 3 components of the composite catalysts. The maximum CH 4 conversion in POM reaction was observed for Ni/(Sm 2 O 3 ,CaO), while the maximum selectivity was demonstrated by Nd 2 O 3 -based composite. The possible reasons for the observed difference are discussed.