Selective hydrogenation of cinnamaldehyde in supercritical CO2 over Me–CeO2 (Me = Cu, Pt, Au): Insight of the role of Me–Ce interaction

Abstract

The performance of platinum, gold and copper catalysts with low (0.1wt%) and high (2–3.8wt%) metal loadings, supported on ceria with high surface area (240m2/g), are contrasted in the hydrogenation of cinnamaldehyde. Two reaction solvents were tested: single-phase near critical CO2+isopropanol mixture and supercritical CO2, both performed at 323K and 20MPa. Exceptionally high activities were measured under supercritical CO2 for low loaded platinum and gold catalysts, while selectivities to cinnamyl alcohol were in the range of 80–90%. The same trends, but in a lower degree, were observed for the corresponding copper sample. The catalytic pattern in near critical condition was between the ones corresponding to supercritical CO2 and classical gas–liquid, as previously reported for platinum based catalysts. The enhancement of the selectivity can be explained by a combined effect of the supercritical CO2–substrate interaction and by the adsorption of cinnamaldehyde on sites of the metal–ceria interface. Based on the TPR and XPS characterizations, it was concluded that the rise of the activity would be due to a major concentration of these active sites in the low loaded samples.