Investigation of the Structure and Interface Features of Ni/Ce_{1- x}Zr_xO₂Catalysts for CO and CO₂Methanation

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.