Nickel - Titania Supported Catalysts for Direct Selective Hydrodeoxygenation of 5-Hydroxymethylfurfural to 5-Methylfurfural

The 5-Hydroxymethylfurfural (HMF) platform molecule can be derived from biomass feedstocks and catalytically hydrogenated into various added-value molecules. Its conversion to 5-methylfurfural (5-MF), a versatile synthetic intermediate and perfuming agent, is particularly challenging, the selective hydrodeoxygenation of the C–OH group in HMF being by far less favourable kinetically and thermodynamically than the hydrogenation of the C=O group that gives 2,5-bis-hydroxymethylfuran (BHMF). Herein, for the first time we showed that Ni/TiO2 catalysts can be tuned to promote the selective removal of a hydroxy group in the presence of an aldehyde moiety, and give high 5-MF yield. Among various synthesis approaches, the direct ion exchange incorporation of Ni into a TiO2 network prepared by an alginate synthesis route allowed the key-factors orientating the reaction selectivity towards 5-MF to be identified. The highest 5-MF selectivity (86%) at nearly full conversion was favoured by high acidity and ultra-high dispersion of Ni atoms at the surface, while the prime role of titania was discussed. By contrast, increasing the reduction temperature up to 700°C strongly lowered the acidity and formed larger Ni particles, which favour the C=O activation, and is thereby promoting the selectivity switch towards BHMF at 86% also at nearly full conversion.