Metal-oxide nanocomposites by low temperature exsolution from perovskite-like La nickelates: Synthesis, morphology, and catalytic properties in CO2 hydrogenation.

• Thermal reduction of LaNiO 3 and perovskite-like La 3 Ni 2 O 6+ x occurs in two stages;. • Their crystal structure and morphology are almost retained during the first stage;. • This process is accompanied by the appearance of Ni nanoparticles at the surface;. • Apart from high temperature redox exsolution, this process occurs at t ≤ 400 °C;. • As-obtained Ni/oxide nanocomposites demonstrate a significant catalytic activity. Thermal decomposition of the citrate-gel precursors with La/Ni = 1/1 and La/Ni = 3/2 results in the formation at T ≥ 700 °C the single phase perovskite LaNiO 3 and the disordered perovskite-like phase La 3 Ni 2 O 6+ x. A reduction of both compounds during thermal processing in a 5 % H 2 /Ar gas mixture proceeds in two definite steps. The first stage of LaNiO 3 reduction at 250 - 350 °C results in the formation of an O-deficient La 2 Ni 2 O 5 compound. A similar process during the reduction of La 3 Ni 2 O 6+ x occurs at 300–400 °C with the lack of significant changes in the XRD pattern. An unusual feature of these processes deals with the formation of Ni0 nanoparticles on the surface of both reduction intermediates at 350–400 °C while similar processes are usually observed during redox exsolution of metals from several complex oxides at T > 700 °C only. As-obtained Ni/La x NiO y nanocomposites demonstrated significant catalytic activity and excellent selectivity and stability in the Sabatier reaction. [Display omitted] [ABSTRACT FROM AUTHOR]