Gas-phase dehydration of tetrahydrofurfuryl alcohol to dihydropyran over γ-Al2O3

Gas-phase dehydration of tetrahydrofurfuryl alcohol (THFA) to 3,4-2H-dihydropyran (DHP) was studied over solid acid catalysts. A γ-Al2O3 catalyst resulted in 90% DHP yield from THFA. The γ-Al2O3 deactivated due to solid coke formation but was nearly fully re-generable upon a high temperature calcination step (only 2.5% activity loss after 3rd regeneration). The high catalytic activity and selectivity of γ-Al2O3 was correlated to its high Lewis to Brϕnsted acid site ratio, as confirmed by ammonia temperature-programmed desorption (NH3-TPD) and isopropylamine temperature-programmed desorption (IPA-TPD). Based on isotopic-labelling studies, a reaction mechanism was proposed in which THFA initially dehydrates into a carbenium intermediate prior to Wagner-Meerwien rearrangement into DHP. A kinetic model of THFA dehydration over γ-Al2O3 was developed according to kinetic experimental data. The best-fit model suggested the rate-determining step was the surface reaction of adsorbed THFA dissociating into adsorbed DHP and water.