Boosting selectivity in glucose hydrogenation to sorbitol by optimizing Fe distribution in alloys and supports

Abstract

The hydrogenation of glucose to sorbitol using Raney-Ni is a well-established process in industry, but it faces challenges such as high mannitol content, nickel leaching, and catalyst pyrophoricity. Here, Ni₆Fe₁/Al₂O₃ nanoflower with high sorbitol selectivity and stability was synthesized from Ni_xFe_y/Al-LDH precursors, where the distribution of iron in the alloy phase and support can be well-regulated. XANES and FT-EXAFS spectra verified the presence of Fe in the catalyst as NiFe alloy and FeO_x. Multiple evidences unveiled that the NiFe alloy phase significantly improving the yield of sorbitol and the iron oxide species can regulate the acidity of the support, thus effectively reducing the byproduct mannitol. Delightfully, the optimal Ni₆Fe₁/Al₂O₃ catalyst achieved a sorbitol yield of 99% and a mannitol yield of 0.45%, showing a significant advantage over Ni/Al₂O₃ (77% and 1.3%) and Raney-Ni (57% and 1.3%) catalysts. Theoretical calculations indicate that the NiFe alloy surface is more conducive to glucose adsorption and sorbitol desorption, and the intrinsic high activity of NiFe alloy phase is due to the downshift of d-band center, which facilitates H* dissociation from the anti-bonding orbital. This study provides significant insights for designing catalysts with high activity and selectivity in converting lignocellulosic biomass.