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

Aqueous-phase hydrogenation of d-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 d-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 H2 pressures (>40 bar), and low reaction temperatures (<140 °C), which suppressed undesired polymerization side reactions.