(425a) Origin of Selective Tetrahydrofurfuryl Alcohol Ring Opening over Wox-Modified Pt(111), a DFT Study

Heterocyclic biomass-derived oxygenates such as tetrahydrofurfuryl alcohol (THFA) can be upgraded into value-added diol molecules with selective ring-opening pathways via C-O bond scission. The ring-opening reaction of THFA is catalyst dependent, and bifunctional catalysts such as the inverse oxide WO_x/Pt have demonstrated selective C-O bond scission in the saturated furan ring to produce 1,5-pentanediol (1,5-PeD). Despite these catalytic properties, a fundamental atomistic understanding of the active sites and reaction intermediates is needed to further improve the catalytic performance. In this work, we utilize Density-Functional Theory (DFT) to understand the ring opening and further reduction of THFA on model WOx/Pt(111) and Pt(111) catalysts.

DFT simulations show that WOx/Pt(111) catalysts can promote ring opening of THFA via an oxocarbenium ion-like transition state which is stabilized by hydrogen bonding with the hydroxyl groups of WOx. Further, hydroxyl formation on WOx is facile via a bi-functional catalytic pathway. The hydrogenation of the ring opened 5-hydroxyvaleraldehyde to pentane-diol is shown to be feasible via Brønsted acid sites present on WOx, without any utilization of Pt sites. The reaction mechanism is also analyzed on pure Pt(111) and it is found that, under relevant reaction conditions, the Pt surface will be covered in H* (0.75-1ML). The presence of H* is then shown to increase the barrier for THFA ring opening due to adsorbate-adsorbate repulsion, which is followed by a facile C—C bond breakage of the ring opened intermediate.

Our results are in-line with experiments performed for THFA ring opening on inverse WOX/Pt catalyst under UHV conditions and shed light on the importance of Brønsted acid sites on WOx in stabilizing the transition states for THFA ring opening as well as subsequent reduction to form pentanediol. This study will now assist in discovering new catalysts that can selectively promote biomass feedstock reduction to value-based products.