Electrocatalytic Hydrogenation and Deoxygenation of Glucose on Solid Metal Electrodes

This Full Paper addresses the electrocatalytic hydrogenation of glucose to sorbitol or 2-deoxysorbitol on solid metal electrodes in neutral media. Combining voltammetry and online product analysis with high-performance liquid chromatography (HPLC), provides both qualitative and quantitative information regarding the reaction products as a function of potential. Three groups of catalysts clearly show affinities toward: (1)hydrogen formation [on early transition metals (Ti, V, Cr, Mn, Zr, Nb, Mo, Hf, Ta, We, and Re) and platinum group metals (Ru, Rh, Ir, and Pt)], (2)sorbitol formation [on late transition metals (Fe, Co, Ni, Cu, Pd, Au, and Ag) and Al (sp metal)], and (3)sorbitol and 2-deoxysorbitol formation [on post-transition metals (In, Sn, Sb, Pb, and Bi), as well as Zn and Cd (d metals)]. Ni shows the lowest overpotential for the onset of sorbitol formation (0.25V) whereas Pb generates sorbitol with the highest yield (<0.7mMcm2). Different from a smooth Pt electrode, a large-surface-area Pt/C electrode hydrogenates glucose to sorbitol from 0.21V with relatively low current. This emphasizes the importance of the active sites and the surface area of the catalyst. The mechanism to form 2-deoxysorbitol from glucose and/or fructose is discussed according to the observed reaction products. The yield and selectivity of hydrogenated products are highly sensitive to the chemical nature and state of the catalyst surface.