Morphology Effect of La2O2CO3 on CO2 Methanation over Ni-Based Catalysts

CO2 methanation is regarded as an efficient method for upgrading CO2 to fuels and reducing environmental impacts of greenhouse gas emission. In this study, we developed Ni/ La2O2CO3 low temperature CO2 methanation catalysts by tuning the metal-support interaction via changing the morphology of catalyst supports. La2O2CO3 supports with various morphologies including nanotriangles (La2O2CO3-T), nanorods (La2O2CO3-R), and nanoparticles (La2O2CO3-P), were synthesized as the supports of Ni catalysts for CO2 methanation reaction. The CO2 methanation performance of the synthesized Ni/La2O2CO3 catalysts was found to be markedly superior to that of conventional Ni/SiO2 catalysts with the following orders: Ni/La2O2CO3-T > Ni/La2O2CO3-R > Ni/La2O2CO3-P > Ni/SiO2. In the comparative characterization of Ni/La2O2CO3 catalysts with various morphologies, TEM and H-2-TPR results reveal that the Ni/La2O2CO3-T catalysts exhibit better dispersion of Ni nanoparticles and higher reducibility. Moreover, X-ray photoelectron spectroscopy (XPS), O-2 and H-2 temperature programmed desorption (O-2-TPD, H-2-TPD) results indicate that the Ni/La2O2CO3-T catalysts possess a lower oxygen vacancy formation energy leading to a higher concentration of interfacial oxygen vacancies, which enhances the adsorption hydrogen at these interfacial oxygen vacancy sites. CO2-TPD results further reveal that Ni/La2O2CO3-T catalysts own higher concentration of medium basic sites, which promote the adsorption and activation of CO2. Consequently, Ni/La2O2CO3-T catalysts demonstrate superior low-temperature CO2 methanation activity by hydrogenation of CO2 adsorbed as surface carbonates on the La2O2CO3 surfaces with hydrogen spilled over from the Ni surfaces via the interfacial oxygen vacancies to the catalyst support.