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

The performance of platinum, gold and copper catalysts with low (0.1 wt%) and high (2-3.8 wt%) metal loadings, supported on ceria with high surface area (240 m(2)/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 323 K and 20 MPa. 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. (C) 2015 Elsevier B.V. All rights reserved.