The effect of oxide acidity on HMF etherification

Abstract

The liquid-phase (69 bar) reaction of 5-hydroxymethylfurfural (HMF) with 2-propanol for production of furanyl ethers was studied at 413 and 453 K over a series of oxide catalysts, including γ-Al₂O₃, ZrO₂, TiO₂, Al₂O₃/SBA-15, ZrO₂/SBA-15, TiO₂/SBA-15, H-BEA, and Sn-BEA. The acidity of each of the catalysts was first characterized for Brønsted sites using TPD-TGA of 2-propanamine and for Lewis sites using TPD-TGA of 1-propanol. Catalysts with strong Brønsted acidity (H-BEA and Al₂O₃/SBA-15) formed 5-[(1-methylethoxy)methyl]furfural with high selectivities, while materials with Lewis acidity (γ-Al₂O₃, ZrO₂, TiO₂, and Sn-BEA) or weak Brønsted acidity (ZrO₂/SBA-15 and TiO₂/SBA-15) were active for transfer hydrogenation from the alcohol to HMF to produce 2,5-bis(hydroxymethyl)furan, with subsequent reactions to the mono- or di-ethers. Each of the catalysts was stable under the flow-reactor conditions but the selectivities varied with the particular oxide being investigated.