Hydrodeoxygenation of C4–C6 sugar alcohols to diols or mono-alcohols with the retention of the carbon chain over a silica-supported tungsten oxide-modified platinum catalyst

Abstract

The hydrodeoxygenation of erythritol, xylitol, and sorbitol was investigated over a Pt–WO_x/SiO₂ (4 wt% Pt, W/Pt = 0.25, molar ratio) catalyst. 1,4-Butanediol can be selectively produced with 51% yield (carbon based) by erythritol hydrodeoxygenation at 413 K, based on the selectivity over this catalyst toward the regioselective removal of the C–O bond in the –O–C–CH₂OH structure. Because the catalyst is also active in the hydrodeoxygenation of other polyols to some extent but much less active in that of mono-alcohols, at higher temperature (453 K), mono-alcohols can be produced from sugar alcohols. A good total yield (59%) of pentanols can be obtained from xylitol, which is mainly converted to C2 + C3 products in the literature hydrogenolysis systems. It can be applied to the hydrodeoxygenation of other sugar alcohols to mono-alcohols with high yields as well, such as erythritol to butanols (74%) and sorbitol to hexanols (59%) with very small amounts of C–C bond cleavage products. The active site is suggested to be the Pt–WO_x interfacial site, which is supported by the reaction and characterization results (TEM and XAFS). WO_x/SiO₂ selectively catalyzed the dehydration of xylitol to 1,4-anhydroxylitol, whereas Pt–WO_x/SiO₂ promoted the transformation of xylitol to pentanols with 1,3,5-pentanetriol as the main intermediate. Pre-calcination of the reused catalyst at 573 K is important to prevent coke formation and to improve the reusability.