The effect of structural features of Ce–Zr–La–O complex oxides and electronic state of supported Pt on their catalytic activity in methane selective oxidation and steam reforming has been studied. Ce–Zr–La–O (1, 10 and 30 mol. % of La) fluorite-like oxides were prepared by inorganic sol-gel method. As it was shown earlier the indicated composites demonstrate a high and stable activity in CH₄ selective oxidation and steam reforming into syngas as well as high electrocatalytic performance as anode catalysts in solid oxide fuel cells. The structure of the samples was characterized by XRD, XPS, TEM, EDXA, EPR and FTIR-spectroscopy. The Ce–Zr–La–O samples annealed in the range of 600-1100 °C have cubic structure with particle size less than 10 nm. Detailed analysis revealed co-existence of the following nano-phases with similar crystalline structures: Ce_1-x(La,Zr)_xO_2-d (solid solution), La₂Zr₂O₇, La_0.1Zr_0.9O_2-d, Zr_0.4Ce_0.4O₂, Ce_0.1Zr_0.9O₂. Their amount depends on La content and the annealing temperature. The phases can be arranged as fragments within a single nano-crystal and have shared crystallographic planes (CeO₂: a = 5.4113 Å, Fm3m; La₂Zr₂O₇: a/2 = 5.3965 Å, Fd3m; Zr_0.4Ce_0.6O₂: a = 5.3049 Å, Fm3m; ZrO₂: a = 5.09 Å, Fm3m). Both catalytic features and thermal stability of the nano-heterophased Ce–Zr–La–O material were found to depend on the character of interaction between the separate phases and between the phases and Pt(Ru).

A model of mixed active center consisting of various Pt (Pt⁰, Pt²⁺) states and [Pt^d+–Zr^(n-d)+] charge transfer complex has been proposed based on XPS study. Oxidized platinum states are important for the effective oxygen and CH₄ activation in the selective methane oxidation process and stabilizing small Pt clusters. The [Pt^d+–Zr^(n-d)+] complex is mainly localized at the surface of La_xZr_1-xO_2-d fragments.

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