Monitoring by in situ NAP-XPS of active sites for CO2 methanation on a Ni/CeO2 catalyst. (June 2022)

• Record Type: Journal Article
• Authors: López-Rodríguez, Sergio; Davó-Quiñonero, Arantxa; Bailón-García, Esther; Lozano-Castelló, Dolores; Villar-Garcia, Ignacio J.; Dieste, Virginia Perez; Calvo, Jon Ander Onrubia; Velasco, Juan Ramón González; Bueno-López, Agustín
• Is Part Of: Journal of CO₂ utilization. Volume 60(2022)
• Publication Date: 2022-06
• Subjects: CO2 methanation -- Ceria -- Nickel -- NAP–XPS -- Redox active sites; Carbon dioxide -- Periodicals; Carbon dioxide -- Environmental aspects -- Periodicals; Carbon dioxide mitigation -- Periodicals; Carbon dioxide; Carbon dioxide -- Environmental aspects; Carbon dioxide mitigation; Periodicals; 628.53205
• DOI: 10.1016/j.jcou.2022.101980
• Languages: English
• ISSNs: 2212-9820

Abstract

Abstract: Ni/CeO2 catalysts are very active and selective for total hydrogenation of CO2 to methane, but the nature of the active sites is still unclear. The surface of a Ni/CeO2 catalyst has been monitored under CO2 methanation conditions by Near Ambient Pressure-XPS (NAP-XPS) using synchrotron radiation, and has been concluded that t he species involved in the redox processes taking place during the CO2 methanation mechanism are the Ni 2+ -CeO2 /Ni 0 and Ce 4+ /Ce 3+ pairs. In addition, a small fraction of nickel is present on the catalyst surface forming NiO and Ni 2+ -carbonates/hydroxyls (around 20% of the total surface nickel), but these species do not participate in the redox processes of the methanation mechanism. Under CO2 methanation conditions the H2 reduction rate of the Ni 2+ -CeO2 /Ni 0 and Ce 4+ /Ce 3+ couples is much faster than their CO2 reoxidation rate (2 times faster, at least, at 300ºC), but a certain proportion of nickel always remains oxidized under reaction conditions. The high activity of Ni/CeO2 catalysts for CO2 methanation is tentatively attributed to the simultaneous presence of Ni 2+ -CeO2 and Ni 0 active sites where CO2 and H2 are expected to be efficiently dissociated, respectively. Graphical Abstract: ga1 Highlights: The redox processes during CO2 methanation involve the Ni 2+ -CeO2 /Ni 0 and Ce 4+ /Ce 3+ pairs. H2 reduction rate of the Ni 2+ -CeO2 /Ni 0 and Ce 4+ /Ce 3+ couples is faster than their CO2 reoxidation rate. Ni/CeO2 catalysts keep simultaneously Ni 2+ -CeO2 and Ni 0 active sites under reaction conditions. NiO and Ni 2+ -carbonates/hydroxyls do not participate in redox processes