Ex Situ and in Situ Studies of the Structural Features of Ruthenium-Containing Ru/Ce0.75Zr0.25O2 Catalysts of CO2 Methanation

Heterogeneous catalysts xRu/Ce_0.75Zr_0.25O₂ (x = 1, 5 wt.%) are prepared by the sorption-hydrolytic precipitation. It is shown that these catalysts are active in the methanation of carbon dioxide. The composition and structural features of these compounds are studied by a complex of methods such as powder XRD, high-resolution electron microscopy, chemisorption, and X-ray photoelectron spectroscopy (XPS). It is established that catalysts obtained by the sorption-hydrolytic method contain the active component in a highly dispersed state. The catalyst with 1 wt.% Ru contains ruthenium compounds in the form of atomic clusters, while that with 5 wt.% Ru contains, along with ultrafine forms, also crystallized ruthenium-containing particles. It is shown that the initial catalysts contain oxide ruthenium compounds that are reduced to the metallic state under the methanation reaction conditions. In situ studies by powder XRD, XPS studies, temperature-programmed reduction in the hydrogen atmosphere (H2-TPR) show that metal ruthenium particles, which were obtained by the activation treatment of the catalysts as a result of heating in a hydrogen-enriched flow, promote the process of the partial reduction of the support material particles due to the spillover effect.