Platinum-Catalyzed Aqueous-Phase Hydrogenation of D-Glucose to D-Sorbitol

Aqueous-phase hydrogenation of n-glucose to D-sorbitol was systematically investigated over silica-supported Pt nanoparticles to elucidate structure reactivity relations and mechanistic insight. D-Glucose hydrogenation over large Pt particles competes with its isomerization to D-fructose over low-coordination (electron-deficient) Pt sites; D-sorbitol production by the former process was structure insensitive for nanoparticles spanning 3-17 nm, whereas isomerization was favored by smaller particles, with both pathways independent of the choice of fumed silica or mesoporous SBA-15 support. While n-fructose was readily hydrogenated to D-mannitol under the same reaction conditions, the latter underwent minimal isomerization to D-sorbitol, which is, therefore, a direct product of D-glucose ring opening and subsequent hydrogenation of the aldose conformer. D-Sorbitol production was favored by low D-glucose concentrations (<10 wt %), high H-2 pressures (>40 bar), and low reaction temperatures (<140 degrees C), which suppressed undesired polymerization side reactions.