Hydrogenation of Furfural to Cyclopentanone in Tert–Butanol-Water Medium: A Study of the Reaction Intermediates Reactivity Using Cu/ZnO/Al2O3 as Catalyst

Abstract

The catalytic transformation of furfural to cyclopentanone has been investigated using two different liquid phases as solvent: water and 30 wt.% tert–butanol in water. When using neat water at 160 °C, 40 bar of H2, and after 2 h of reaction time, furfural polymerizes, and the yield of cyclopentanone is just 42% with a low carbon balance, indicating that furfural is transformed to non-detected by-products, likely heavy resins. When using 30 wt.% tert–butanol in water, the yield of cyclopentanone is ca. 20%, and the major product is furfuryl alcohol with a 47% yield. We have studied the catalytic transformation of the most relevant reaction intermediates in the overall conversion of furfural to cyclopentanone. In the presence of tert–butanol, two steps are inhibited in the overall pathway: (i) the Piancatelli rearrangement of furfuryl alcohol and (ii) the transformation of cyclopentenone. This inhibition is attributed to the neutralization of protons from water dissociation by surface sites on the catalyst, preventing their participation in the overall reaction. To counteract these inhibitions when tert–butanol is present, higher H2 pressure (60 bar) and temperatures (200 °C) are required. We have been able to obtain productivities per gram of catalyst and mols of Cu basis of 411 gprod·h−1·gcat−1 and 14 gprod·s−1·molCu−1, respectively, which is substantially above that found for other copper-based catalysts.