Suchergebnisse

This study addresses the yet unresolved CO2 methanation mechanism on a Ru/CeO2 catalyst by means of near-ambient-pressure X-ray photoelectron spectroscopy (NAP–XPS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) complemented with periodic density functional theory (DFT) calculations. NAP–XPS results show that the switch from H2 to CO2 + H2 mixture oxidizes both the Ru and CeO2 phases at low temperatures, which is explained by the CO2 adsorption modes assessed by means of DFT on each representative surface. CO2 adsorption on Ru is dissociative and moderately endergonic, leading to polybonded Ru-carbonyl groups whose hydrogenation is the rate-determining step in the overall process. Unlike on Ru metal, CO2 can be strongly adsorbed as carbonates on ceria surface oxygen sites or on the reduced ceria at oxygen vacancies as carboxylates (CO2–δ), resulting in the reoxidation of ceria. Carboxylates can then evolve as CO, which is released either via direct splitting at relatively low temperatures or through stable formate species at higher temperatures. DRIFTS confirm the great stability of formates, whose depletion relates with CO2 conversion in the reaction cell, while carbonates remain on the surface up to higher temperatures. CO generation on ceria serves as an additional reservoir of Ru-carbonyls, cooperating to the overall CO2 methanation process. Altogether, this study highlights the noninnocent role of the ceria support in the performance of Ru/CeO2 toward CO2 methanation. ; The authors thank the financial support of the Spanish Ministry of Economy and Competitiveness (Project CTQ2015-67597-C2-2-R and grant FJCI-2015-23769), the Spanish Ministry of Science and Innovation (PID2019-105960RB-C22), Generalitat Valenciana (Project PROMETEO/2018/076), and the EU (FEDER funding). A.D.-Q. and M.G.-M. acknowledge the financial support from the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement no. 713567 and Science Foundation Ireland Research Centre award 12/RC/2278_P2. F.C.H. acknowledges the Argentinian National Research Council (CONICET) for the financial support. C.E. acknowledges funding from the MICINN/FEDER RTI2018-093996-B-32 project. The computational results of this research have been achieved using the DECI resource Salomon based in the Czech Republic at the IT4Innovations National Supercomputing Center with support from the PRACE aisbl. The DJEI/DES/SFI/HEA Irish Centre for High-End Computing (ICHEC) is also acknowledged for the provision of computational facilities.