(50g) Selective Hydrodeoxygenation of 1,4-Anhydroerythritol to Tetrahydrofuran over MoOx-Pd/TiO2 catalysts

The development of catalytic materials that can selectively cleave hydroxyl groups from oxygen-rich feedstocks is a challenge in the production of chemicals from lignocellulosic biomass. Recently, heterogeneous catalysts comprised of supported palladium and rhenium oxide species have been reported for the selective removal of vicinal hydroxyls in biomass-derived sugar alcohols, such as erythritol and 1,4-anhydroerythritol (1,4-AHERY).^1-3 In this presentation, we describe our findings on the development of heterogeneous catalysts comprised of molybdenum oxide and palladium supported on titanium oxide (MoO_x-Pd/TiO₂) for the hydrodeoxygenation (HDO) of 1,4-AHERY to tetrahydrofuran (THF) in high yields. The activity and stability of the catalysts are comparable to other materials reported for this chemistry. However, in contrast to other catalysts, it eliminates the use of expensive rhenium metal. The relationship between catalyst structure and performance of MoO_x-Pd/TiO₂ was studied by a combination of reaction kinetic and characterization studies. Reaction kinetic studies suggest there are possibly two distinct catalytic sites for hydrogen and 1,4-AHERY activation. Characterization studies, including X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) suggest that isolated monomeric Mo⁶⁺ species supported on TiO₂ are reduced to catalytically active Mo⁴⁺ species by spillover hydrogen dissociated over Pd metal surfaces. Based on these results, we propose that the reaction pathway over MoO_x-Pd/TiO₂ involves the deoxydehydration of 1,4-AHERY to 2,5-dihydrofuran followed by hydrogenation of the C=C bond to produce THF. Furthermore, we demonstrate that MoO_x-Pd/TiO₂ shows remarkable catalytic stability upon multiple reaction cycles.

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3. Xi, Y., Yang, W., Ammal, S.C., Lauterbach, L., Pagan-Torres, Y.J. and Heyden A., Catal. Sci. Technol., 8, 5750–5762 (2018).