Novel noble metal-free and recyclable Co-CoOx-FeNiCo/γ-Al2O3 catalyst for selective hydrogenation of 5-hydroxymethylfurfural to 2,5-dimethylfuran or 2,5-Bis(hydroxymethyl)furan

The efficient production of the liquid fuel 2,5-dimethylfuran (DMF) from biomass-derived 5-hydroxymethylfurfural (HMF) is very complicated because of the presence of the aldehyde group, hydroxyl group, and CC bond. In this study, a novel Co-CoOx –FeNiCo/γ-Al2O3 catalyst was developed for selective hydrogenation of HMF to DMF. The catalyst was characterized by using XRD, TEM, SAED, BET, XPS, NH3-TPD, and H2-TPR techniques. The catalyst reduced at 500 °C exhibited excellent catalytic performance and the highest DMF yield (>99.9%) was obtained at 190 °C and 4 h. During the reaction, metal sites selectively hydrogenated the CO bond while acid sites (CoOx acid sites) selectively hydrogenolyzed CO bond. Appropriate surface acidity of the catalyst and the balance between metal and metal oxide species are the main factors for achieving a high yield of DMF. At reaction temperatures below 150 °C, DMF was not produced and HMF has completely converted into 2,5-Bis(hydroxymethyl)furan (BHMF), an important furan diol for polymers production. 100% BHMF yield was also obtained for the HMF hydrogenation over 300 °C reduced catalysts due to the high concentration of strong acid sites. The catalyst recyclability exhibited excellent stability and the original activity was maintained after six reuses. A reaction mechanism was also proposed.