Stable vapor-phase conversion of tetrahydrofurfuryl alcohol into 3,4-2H-dihydropyran

Vapor-phase synthesis of 3,4-2H-dihydropyran (DHP) from tetrahydrofurfuryl alcohol (THFA) was investigated over acidic catalysts modified with transition metals. Catalytic activity of alumina was seriously deactivated in the reaction of THFA in nitrogen at 300 °C although the initial activity was high. Tetragonal ZrO2 showed the catalytic activity to produce DHP at 350 °C. Alumina modified with Cu exhibits stable catalytic activity with high selectivity to DHP under hydrogen flow conditions, and the optimum activity was obtained at CuO contents of 5–10 wt.%: the selectivity to DHP was as high as 85%. Prior to the reaction, CuO was reduced to metallic Cu, which probably works as a product remover together with hydrogen to prevent coke formation. The reaction pathway from THFA to DHP was discussed: it is speculated that THFA is initially rearranged into 2-hydroxytetrahydropyran, which rapidly dehydrated to DHP.

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► Conversion of tetrahydrofurfuryl alcohol to 3,4-2H-dihydropyran was studied.
► Alumina effectively catalyzed the reaction, but along with decay in the activity.
► Supported CuO together with H2 flow stabilizes the catalytic activity of alumina.
► The amount of coke deposited is reduced over the Al2O3-supported CuO in H2 flow.