A research team in China has developed a one-pot method to produce octane from bio-derived furans under low temperatures. In an open-access paper in the RSC journal Green Chemistry, they report a 96.6% yield of octane obtained by catalytic conversion with Pd/C and phosphotungstic acid (HPW) under 1 MPa H₂ at 130 ˚C for 4h.

Their work showcases a promising reaction pathway for an efficient catalytic hydrodeoxygenation (HDO) system to obtain alkanes from bio-derived furans under mild conditions.

Lignocellulosic biomass is an inexhaustible natural carbon source to make high-energy-density liquid alkane fuels after removal of oxygen atoms. However, direct catalytic conversion of carbohydrates are restrained to provide alkanes no more than six carbon number. An alternative resolution was developed to produce furfural from carbohydrates and convert it to biomass high carbon furans (HCFs) through C-C coupling reactions. The HCFs, known as liquid fuel intermediates, have been widely used to produce long-chain alkanes through catalytic hydrodeoxygenation (HDO).

However, the structural complexity of HCFs require to integrate various elementary reactions to cleave different C- O bonds, as well as avoid the competitive etherification and self-condensation reactions. Thus, realizing HDO under mild conditions has the potential to inhibit undesired side-reaction, which plays a critical role in selectively producing long-chain alkanes.

—Li et al.

Three main reaction pathways have already been proposed for this type of reaction, the researchers said—a saturated-tetrahydrofuran (sTHF) route; a polyketone route; and a diol route. Each offers advantages and disadvantages.

The diol route inspired us to develop a novel reaction pathway to hydrogenolyse furans without deoxygenations by adjusting metal-acid sites, in order to accomplish one-pot HDO reaction at a lower temperature.

The reasonable possibility of octanediol-route was thermodynamically illustrated by experimental validations and DFT simulations. The catalytic mechanism was also investigated by characterizations from the prospective of the modification effect of HPW. In addition, the direct evidence of a water-promoted hydrogen transfer process was manifested through isotope labeling techniques.

—Li et al.

Resources

• S. Li, Q. Ma, W. Zhong, X. Zhao, X. Wei, X. Zhang, Q. Liu, C. Wang, L. Ma and Q. Zhang (2021) “One-pot hydrodeoxygenation of bioderived furans into octane under low temperatures via octanediol-route” Green Chem. doi: 10.1039/D1GC00916H.