Investigation of the Structure and Interface Features of Ni/Ce1–xZrxO2 Catalysts for CO and CO2 Methanation

The structural features and reduction-induced structural evolution of Ni/Ce1–xZrxO2 catalysts for the methanation of carbon oxides were investigated. The catalysts prepared by the impregnation technique were investigated by ex situ and in situ X-ray diffraction (XRD) analysis, atomic pair distribution function (PDF) analysis, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), and temperature-programmed reduction by H2. The main part of nickel was established to exist on the support surface as bulk NiO and Ni0 nanoparticles in as-prepared and reduced under reaction conditions catalysts, respectively. The metal–support interaction with incorporation of Ni2+ ions into the Ce1–xZrxO2 crystal lattice was also revealed. In situ XRD and XPS studies allowed one to monitor the structural evolution of the Ni/Ce1–xZrxO2 catalysts during their heating under H2 atmosphere in the temperature range of 25–450 °C. The formation of Ni0 nanoparticles was shown to favor reduction of Ce1–xZrxO2 oxide via hydrogen spillover. In situ XRD results revealed reversible expansion and contraction of the Ce1–xZrxO2 crystal lattice in reductive and oxidative atmospheres, which are associated with Ce4+ ↔ Ce3+ transitions and redistributions of oxygen vacancies. The elucidated metal–support interaction and synergism of redox properties of the Ni/Ce1–xZrxO2 catalysts are relevant for high activity in the CO2 and CO methanation reactions.