Surface effect of nano-sized cerium-zirconium oxides for the catalytic conversion of methanol and CO2 into dimethyl carbonate

Abstract

The direct synthesis of Dimethyl carbonate (DMC) from methanol and CO2 is a green process which allows CO2 valorization. Among efficient catalysts, ceria, zirconia and cerium-zirconium mixed oxides are often reported as the most active catalysts. In a recent report, we discovered that cerium-zirconium mixed oxides prepared by Flame Spray Pyrolysis (FSP) show greater catalytic activities than those prepared by precipitation, although both exhibit very similar surface area and bulk features. The objective of this study was to find out the origins of the superior catalytic activities obtained by flame spray pyrolysis synthesis method by a deeper analysis of bulk and surface properties. We have opted to focus on mixed ceria-zirconia of equimolar composition (Ce0.5Zr0.5O2) as it exhibits maximum catalytic activity for both synthesis methods. Combining bulk and surface characterization as well as surface adsorption measurements using probe molecules, we propose that flame spray pyrolysis enables a surface enrichment in cerium oxide still in interaction with zirconium oxide that leads to a high concentration of adsorbed methanol at the surface, which might explain the greater activity of the catalysts prepared using this method. Beyond the application of DMC synthesis, we can anticipate that Flame Spray Pyrolysis synthesis should generate relative high surface area mixed oxides with different catalytic performances with respect to mixed oxides prepared at lower temperature owing their metastable nature.