Liquid phase catalytic transfer hydrogenation of furfural over a Ru/C catalyst

Methyl furan production through catalytic transfer hydrogenation of furfural in the liquid phase has been investigated over a Ru/C catalyst in the temperature range of 120–200 °C using 2-propanol as a solvent. It has been found that furfural hydrogenation produces furfuryl alcohol, which undergoes hydrogenolysis to methyl furan. Small amounts of furan and traces of tetrahydrofurfuryl alcohol are also produced via furfural decarbonylation and furfuryl alcohol ring hydrogenation, respectively. Furfuryl alcohol can dimerize or produce ether with 2-propanol. The yield of methyl furan is enhanced with increasing reaction temperature and/or reaction time. Optimum results are attained after 10 h of reaction at 180 °C, where furfural conversion and methyl furan yield reach 95% and 61%, respectively, which is the highest reported yield in the liquid phase at temperatures lower than 200 °C. The reaction network has been investigated by analysing the evolution of reaction intermediates and products and by starting from furfuryl alcohol, methyl furan, and furan hydrogenation. Intermediates, as well as methyl furan, are produced faster when starting with furfuryl alcohol as the reactant, rather than furfural, indicating that initial hydrogenation of furfural to furfuryl alcohol is slow. Catalyst recycling experiments over spent Ru/C catalyst show that, although furfural conversion does not decrease significantly, furfuryl alcohol yield increases at the expense of methyl furan. The initial catalytic activity and selectivity are regained completely after catalyst regeneration. We show evidence that the active phase of the catalyst involves Ru and RuOx.