Recent advances in the hydrogenolysis of furfural and its derivatives to 1,5-pentanediol

Biomass is an abundant and renewable organic carbon resource on earth. The conversion biomass to chemicals and fuels is of great significances in terms of reducing the consumption and dependences of fossil resource. Furfural is one of the most important biomass platform molecules and can be converted to various of useful chemicals, such as furfural alcohol, tetrahydrofurfuryl alcohol, 2-methylfuran, 1,5-pentanediol, 1,2-pentanediol, and so on. Recent studies have shown that 1,5-pentanediol based polymer materials was found have better safety in the field of children’s products. Due to the high cost and complex process of synthesizing 1,5-pentanediol from traditional petrochemical routes, it is more promising to synthesize it from biomass. Catalytic conversion of biomass substrates (furfural and its derivatives) to 1,5-pentanediol has attracted much attention in the past decade. Some noble metal and none-noble catalysts had been screened (such as Ir, Rh, Pt, Ni based catalysts), and several reaction mechanisms were proposed. However, there remain open questions on the reaction pathways and catalytic mechanisms. In addition, the use of non-precious metal catalysts to catalyze the hydrogenolysis of furfural and its derivatives to achieve high yields of 1,5-pentanediol remains a significant challenge. In this paper, we reviewed the recent research progress of the selective hydrogenation of tetrahydrofurfuryl alcohol, furfural and furfuryl alcohol to 1,5-pentanediol. This review consists of two parts, which concerned on the hydrogenolysis of tetrahydrofurfuryl alcohol, and the hydrogenolysis of furfural and furfuryl alcohol, respectively. To the hydrogenolysis of tetrahydrofurfuryl alcohol to 1,5-pentanediol, metal-oxide (A-BO x ) type catalysts showed excellent catalytic performances. In the first part of this review, we compared the catalytic performances of the A-BO x type catalysts in the references. We also describe the synergistic effects of metals and oxides in representative catalysts, the critical role of oxide acidity, and the effect of solvents on selectivity, and introduce several widely accepted catalytic mechanisms. The atomic ratio between A and B is critical for hydrogenolysis activity. This atomic ratio determines the dispersion of BO x on metal A, which results in different reaction rates. The acidity of BO x component was also important for the adsorption of the substrates and the ring-opening reaction. As the most used solvent, water played key roles in the hydrogenolysis of tetrahydrofurfuryl alcohol to 1,5-pentanediol. The existence of water was helpful for the transfer of hydride, for stabilizing the carbonium and decreasing the energy barrier of ring opening, and for the form of Bronsted acid and hydrogen bonds, etc. We also review the attempts of hydrogenolysis of furfural and furfural alcohol to 1,5-pentanediol. The 1,5-pentanediol could be obtained by the tandem reaction of hydrogenation of furfural to tetrahydrofurfuryl alcohol and the hydrogelolysis of tetrahydrofurfuryl alcohol to 1,5-pentanediol; or by directly ring-opening of furfural/furfural alcohol and followed by hydrogenation. However, the yield of 1,5-PDO is not satisfactory enough due to the complex secondary reactions. Currently, the most study in this field concerned on the noble metal catalysts with surface oxides modifications. It is expected that non-noble metal catalysts can obtain desired catalytic performances once the synergistic of adsorption of tetrahydrofurfuryl alcohol, the activation of C−O bond, the formation of hydrides is well understood and controlled.