DFT Studies of the Selective C-O Hydrogenolysis and Ring-Opening of Biomass-Derived Tetrahydrofurfuryl Alcohol over Rh(111) surfaces

摘要

Tetrahydrofurfuryl alcohol (THFA) has been identified as a platform chemical of interest because of its production from biomass. It can be converted into valuable alcohols and ethers by selective hydrogenation/hydrogenolysis reaction over Rh-based metal catalysts. To better understand the chemistry of THFA, the reaction energies and the corresponding energy barriers of selective C-O bond hydrogenolysis and ring-opening of THFA on Rh(111) for the formation of 2-methyltetrahydrofuran (2-MeTHF), 1,5-pentanediol (1,5-PeD), and 1,2-pentanediol (1,2-PeD) were studied using density functional theory (DFT) calculations. The results indicate that starting from THFA to produce 2-MeTHF, the direct C-O bond cleavage of the CH2OH group is not favored. Alternatively and more preferentially, the reaction occurs through the initial activation of C-H bond on the side chain, followed by dehydroxylation and hydrogenation. On the other hand, in the metal catalyzed ring-opening process of THFA to 1,5-PeD and 1,2-PeD, the first dehydrogenation of secondary CH-O or primary CH2-O moiety in the ring decreases the barriers of the subsequent C-O bond dissociation. Moreover, the energy span theory shows that the ring-opening at the sterically less-hindered primary C-O bond exhibits a lower effective barrier than that for ring-opening at the more sterically hindered secondary C-O bond, as well as hydrogenolysis at the side CH2OH chain, suggesting that the formation of 1,2-PeD is much kinetically favored than the formation of 1,5-PeD and 2-MeTHF. Our theoretical results give a good explanation for the experimental fact that 1,2-PeD was the dominant product observed on unprompted Rh/SiO2.