A green solvent diverts the hydrogenation of γ–valerolactone to 1,4 - pentandiol over Cu/SiO2

A new process for the selective hydrogenation of γ-valerolactone (GVL) to 1,4-pentanediol (1,4-PDO), interesting biobased monomer, has been set up. It relies on the use of a non-noble, nontoxic metal such as Cu on a very simple oxide support, namely silica in a green solvent such as Cyclopentyl Methyl Ether (CPME). The role of the solvent was not only to ensure more sustainable experimental conditions but also to influence the activity and selectivity of the catalyst by tuning the surface acidity. Thus, the activity of Cu catalysts supported on different types of silica was found to depend on some parameters, such as: the support wettability, determined through contact angle and TGA measurements, Cu-dispersion, determined by X-ray photoelectron spectroscopy (XPS) and, in particular, on the nature and effective number of the acid sites on the surface. The last ones were measured through volumetric liquid-solid acid-base titrations with 2-phenylethylamine probe carried out in different reaction solvents and pyridine titrations by Fourier-transform infrared spectroscopy (FT-IR), respectively. Once the best silica support in terms of wettability, in turn affecting Cu dispersion, was identified, CPME was found to be able to boost the catalyst activity and selectivity by modifying the number and strenght of surface acidic sites. The use of this solvent and the fine tuning of the hydrophilic/hydrophobic properties of the silica allowed to reach 78% yield in 1,4-PDO at 160 °C and P(H2) of 50 bar.