Solution Combustion Synthesised Cu-CeO2 Catalysts For CO2 Hydrogenation to Methanol- the Effect of the Fuel

The tunability of structural properties such as oxygen vacancies, Cu surface composition, reducibility of CuO, and basicity by solution combustion synthesised (SCS) Cu-CeO2 catalysts was investigated. Five different fuels, viz. urea (U), tartaric acid (TA), citric acid (CA), ethylene glycol (EG) and oxalyl dihydrazide (ODH), were employed in the synthesis of the catalysts. Raman spectroscopy, O-2-TPD and XPS revealed that the urea synthesised catalyst had the highest concentration of oxygen vacancies, the amount of which was controlled by the fuel used. The oxygen vacancies were the catalytic sites for CO2 adsorption and promoted electron donation to Cu at the Cu-CeO2 junction, thus improving H-2 adsorption and spillover, which was beneficial for methanol synthesis. The better catalytic performance of the urea synthesised Cu-CeO2 catalyst with a methanol STY of 163 g(CH3OH) kg(cat)(-1) h(-1) compared to the other solution combustion synthesis fuels, was attributable to higher oxygen vacancies, more facile Cu reduction, larger Cu surface area and higher Cu surface composition. Based on the absence of the Cu+ species capable of directing the methanol synthesis reaction through the CO intermediate based on XPS data, we surmised that the formate route was the preferred pathway for the studied Cu-CeO2 catalysts.