(167f) Effective Hydrodeoxygenation of Biomass-Derived Oxygenates By MoO3 Catalyst With Low H2 Pressures

Prasomsri, T. A., Massachusetts Institute of Technology
Nimmanwudipong, T., Massachusetts Institute of Technology

Hydrodeoxygenation (HDO) is the most promising route to improve the quality of biomass-derived bio-oil. The key challenges faced by HDO processes is achieving a highdegree of oxygen removal, while simultaneously preserving the carbon backbone of the product, and minimizing hydrogen consumption. Several classes of catalysts have been explored for HDO including metal catalysts and non-precious metal catalysts. However, they are not selective toward carbon-oxygen bonds, and require high H2 pressures that result in the complete hydrogenation of all unsaturated bonds.  The industrial HDO catalysts based on Co-Mo-Ni formulations give a superior performance in HDO, but undergo rapid deactivation due to coke formation and water poisoning. Metal oxides such as molybdenum oxide and tungsten oxide have been used for the oxidation of olefins to aldehydes and ketones due to their unique redox capability. Here, we found that biomass-derived oxygenate compounds are efficiently transformed into hydrocarbons by the use of MoO3 catalysts at low H2 pressures, presumably via reverse Mars-van Krevelen reactions. The model compounds used in this study were acetone, 2-hexanone, cyclohexanone, anisole, 2-methylfuran, and 2,5-dimethyfuran and all investigations were performed in packed-bed flow reactor. The effect of H2 pressure and water conten on catalyst performance is also reported.

We show that regardless of the type of oxygenate used, the HDO selectivity toward hydrocarbon production exceeded 97%. For instance, conversion, acetone was mainly converted to a mixture of propylene, hexenes. In contrast to acetone, no dimerized products were detected from the conversion of 2-hexanone. Instead, hexadienes, the dehydrogenated products of hexenes, were observed. The data show that the subsequent dehydrogenation of the deoxygenated product was more pronounced for cyclohexanone, compared to 2-hexanone. Interestingly, anisole was selectively converted to aromatic products. Specifically, at the reaction conditions investigated, the final products yielded benzene, toluene, xylenes, and alkylbenzenes, suggesting that this catalyst promotes deoxygenation and transalkylation reactions of the phenolic derivative. Finally, pentenes and hexenes were readily obtained from 2-methylfuran and 2,5-dimethylfuran, respectively. We hypothesize that a reverse Mars-van Krevelen cycle is responsible for the HDO behavior in which oxygenate compounds interact with oxygen vacancies to form an Mo–O bond, followed by cleavage of the C–O bond, and desorption of the resulting hydrocarbon products.