Furfural valorisation to γ-valerolactone in a liquid-phase continuous-flow reactor exploiting CTH mechanism

Furfural is an important biomass-derived platform molecule obtained from hemicellulose hydrolysis and dehydration, currently used mainly to produce furfuryl alcohol for furan resins. Nevertheless, it can be upgraded into a wide range of high-value products, including fuels, solvents, and γ-valerolactone (GVL). Conventional GVL synthesis relies on high-pressure hydrogen and noble-metal catalysts, leading to safety concerns and high costs. Catalytic transfer hydrogenation (CTH) offers a safer and cheaper alternative by using alcohols, such as isopropanol, as hydrogen donors under mild conditions. This approach requires bifunctional catalysts with a balanced combination of Lewis and Brønsted acid sites to efficiently drive the multi-step reaction cascade. Most studies on furfural conversion to GVL via CTH have been performed in batch reactors, while continuous-flow investigations are scarce and often focus only on reaction intermediates. This work aims to develop and evaluate bifunctional catalysts for the full conversion of furfural to GVL in a liquid-phase continuous-flow reactor using isopropanol as an internal hydrogen source. Various catalysts were synthesized using different methods and metal combinations to tune acidity and were thoroughly characterized using physicochemical techniques. Their catalytic performance was tested under continuous-flow conditions, representing one of the first comprehensive studies of this process. Mixed oxide catalysts, including titania–zirconia-based systems modified with cerium, iron, or copper, were investigated. Although some catalysts showed full furfural conversion and high selectivity toward intermediates, bare titania–zirconia remained the most effective for GVL production. Sepiolite-supported catalysts were highly selective toward furfuryl isopropyl ether, while zeolite-supported systems, particularly Zr-, Nb-, and Sn-based HY zeolites, achieved relatively high GVL selectivity and stability, with effective regeneration protocols. Comparison with literature data showed that the best catalysts exhibited high Brønsted-to-Lewis acid site ratios, metal dispersion, and synergistic bimetallic effects. Although continuous-flow systems showed lower selectivity than batch processes, they remain promising for process intensification with further optimization.