Ring opening hydrogenolysis of 5-hydroxymethyl furfural over supported bimetallic catalysts

Abstract

The selective conversion of biomass-derived 5-hydroxymethylfurfural (HMF) to 1,6-hexanediol (1,6-HDO) is a promising pathway for sustainable production of chemicals from renewable feedstock. Here, we report the catalytic performance of various supported platinum catalysts, including monometallic Pt nanoparticles on different supports (CeO₂, MgO, hydrotalcite, and hydroxyapatite) and bimetallic (PtPd, PtCo, PtRu, and PtRe) nanoparticles supported on hydroxyapatite for this reaction under batch reaction conditions. Among the monometallic catalysts, Pt supported on hydroxyapatite (Pt/HAP) demonstrated the highest selectivity (30%) for 1,6-HDO at 85% HMF conversion. This superior performance is attributed to the amphoteric properties of the hydroxyapatite support. Notably, the incorporation of Ru as a second metal in the Pt nanoparticles significantly improved catalytic efficiency. The bimetallic PtRu/HAP catalyst achieved an impressive selectivity of 62% for 1,6-HDO at 85% conversion. Characterization by X-ray Photoelectron Spectroscopy (XPS) and Electron Microscopy revealed that the addition of Ru to Pt nanoparticles resulted in smaller bimetallic nanoparticle sizes compared to monometallic Pt nanoparticles, contributing to the enhanced 1,6-HDO selectivity observed for the bimetallic system. The effects of reaction temperature and pressure on 1,6-hexanediol selectivity were also studied. Additionally, the acidity and basicity of the hydroxyapatite supported catalyst were analysed using the surface Ca/P ratio as well the CO₂ and NH₃ TPD data. The results show that the PtRu/HAP catalyst has optimal acidic site density and least basic sites compared to the monometallic catalysts. This unique combination of acidic and basic surface properties, together with the synergistic effects of the finely dispersed smaller bimetallic PtRu nanoparticles, makes this material one of the most active catalysts for the selective hydrogenolysis of HMF to 1,6-HDO.