Ni/Y2O3-ZrO2 catalysts for dry reforming of methane: Increased Y content boosted the performance via enhancing metal-support interaction and surface oxygen species

Abstract

Dry reforming of methane is an alternative route to realize the efficient recycling of carbon resources. This work aims to unravel the effects of the Y/Zr molar ratio in the Y2O3-ZrO2 supports on metal-support interaction (MSI) and surface oxygen species, where the former is related to Ni dispersion and the anti-sintering ability and the latter is corresponded to CO2 activation and anti-carbon deposition ability. Interestingly, the characterization results reveal that increasing Y content in the catalyst effectively enhances MSI, improves Ni dispersion, and enriches the surface oxygen species. Also, the higher Y content in the catalyst makes carbon deposition more active and easier to be removed, and the nature of carbon deposition, rather than the amount, is the crucial factor for catalyst deactivation. As a result, the catalyst with high Y content shows the superior performance. Specially, Ni/Y2O3 exhibits the highest CH4 and CO2 conversion (∼80 % and 85 %, respectively) among the representative catalysts at 700 °C, and its activity (CH4 conversion: ∼88 %, CO2 conversion: ∼93 %) can maintain at least 3600 min at 750 °C. Moreover, the origin of the excellent performance over the catalyst with high Y content is elucidated and the reaction mechanisms are discussed using in situ experiment techniques. The metallic Ni species are active sites to dissociate CH4 and the oxygen species react with the carbonaceous species derived from CH4 cracking to produce CO or CO2. After consuming the adsorbed oxygen species, the re-exposed oxygen vacancies and hydroxyl groups adsorb CO2 to form the active intermediates again, including the bicarbonate and carbonate species. Furthermore, the bicarbonate species are verified to be more active than the other carbonates, and they can react with the carbonaceous species to produce CO or transform into the carbonates.