U Delaware team develops efficient catalyst for production of renewable jet-fuel-range alkanes from biomass under mild conditions
A team at the University of Delaware has synthesized renewable jet-fuel-range alkanes by hydrodeoxygenation of lignocellulose-derived high-carbon furylmethanes over ReOx-modified Ir/SiO2 catalysts under mild reaction conditions (170 ˚C, 5 MPa). Their paper is featured on the cover of the journal ChemSusChem.
In their work, they found that Ir−ReOx/SiO2 with a Re/Ir molar ratio of 2:1 exhibits the best performance, achieving a combined alkanes yield of 82–99% from C12–C15 furylmethanes. The catalyst can be regenerated in three consecutive cycles with only about 12% loss in the combined alkanes yield.
Production of jet fuel, a mixture of C8-C16 hydrocarbons, especially from abundant, inexpensive and carbon-neutral lignocellulose, is of significant interest to the International Air Transport Association. Jet-fuel ranged branched alkanes can be synthesized from cellulose or hemicellulose derived furans (e.g., furfural and 2-methylfuran) in two steps. High carbon furylmethanes with branched chain backbone are first synthesized by C-C coupling of furans with carbonyl functional groups, which are then hydrodeoxygenated (HDO) to alkanes. C-C coupling reactions over acid or base catalysts have been reported, e.g., hydroxyalkylation/alkylation (HAA), aldol condensation, alkylation, benzoic condensation, giving high yields.
In contrast, the HDO step is challenging due to the need of high reaction temperatures and H2 pressure, with concomitant, high energy consumption and undesirable C-C cracking leading to low yield of desired alkanes.—Liu et al.
SiO2 supported partially reduced rhenium oxide modified iridium catalysts (Ir-ReOx/SiO2) are known to be effective catalysts for a number of applications, including HDO and hydrogenation. The Delaware team hypothesized that the catalyst could also catalyze HDO of furylmethanes to the corresponding branched chain alkanes with high carbon efficiency.
The researchers determined that the main pathway involves hydrogenation of the furan rings to saturated rings, followed by ring opening to hydroxyl containing chains. A minor parallel pathway involves ring opening of the unsaturated furans to mono-keto and mono-hydroxy units.
These parallel pathways lead to the formation of several oxygenated intermediates. Sequential hydrogenolysis of these oxygenates over Ir-ReOx/SiO2 forms alkanes via a cascade pathway.
This work was supported as part of the Catalysis Center for Energy Innovation, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences.Ú
Liu, S., Dutta, S., Zheng, W., Gould, N. S., Cheng, Z., Xu, B., Saha, B. and Vlachos, D. G. (2017), “Catalytic Hydrodeoxygenation of High Carbon Furylmethanes to Renewable Jet-fuel Ranged Alkanes over a Rhenium-Modified Iridium Catalyst.” ChemSusChem doi: 10.1002/cssc.201700863