Unraveling the Role of Low Coordination Sites in a Cu Metal Nanoparticle : a Step toward the Selective Synthesis of Second Generation Biofuels

The acidity of a prereduced Cu/SiO2 catalyst was extensively investigated by means of FT-IR of adsorbed pyridine and by titration with 2-phenylethylamine in cyclohexane. Comparison with the parent CuO/SiO2 material, which was already shown to exhibit Lewis acid sites due to the high dispersion of the CuO phase, provided evidence that reduction of this phase to the metallic state increases the acidity of the material. This allowed us to set up a bifunctional catalyst showing acidic and hydrogenation activity, both ascribable to the presence of the metal particle, without the need of an acidic support. This catalyst was tested in the one-pot transformation of γ−valerolactone into pentyl valerate and showed comparable activity (91% vs 92% conversion) and improved selectivity (92% vs 72%) with respect to the previously reported copper catalyst supported on acidic material. The role of Cu in activating the substrate was also evidenced through FTIR of adsorbed γ-valerolactone.