Developing Catalytic Processes for Deoxygenation of Biomass-Derived Feedstocks: Vicinal Diols to Olefins

Friederike Jentoft, Chemical Engineering, University of Massachusetts, Amherst, USA
Bryan Sharkey, Chemical Engineering, University Of Massachusetts, Amherst, Usa



Feedstocks obtained through hydrolysis of lignocellulosic biomass are characterized by an abundance of hydroxyl groups, which must be removed or replaced by more useful functionalities to obtain fuels or chemicals. An attractive catalytic upgrading step for vicinal diols is deoxydehydration (DODH), that is, the simultaneous removal of one oxygen atom (using a sacrificial reductant) and a molecule of water. The olefinic product is a versatile intermediate. Most reports focus on homogeneous catalysis with rhenium, molybdenum, or vanadium complexes. Only rhenium has been employed in solid catalysts, and leaching is a problem. The goal of this work are viable solid catalysts for DODH.
SiO2, Al2O3, TiO2, Fe2O3 and ZrO2 were tested as supports for oxo-rhenium species ReOx, which were deposited by the incipient wetness method. At a temperature of 150 °C, all catalysts converted a model compound, 1,2-decanediol, with high selectivity to the corresponding terminal olefin, 1-decene. The consumption of the reductant, triphenylphosphine, was nearly stoichiometric, demonstrating the efficiency of the catalysts. Leaching and catalyst recyclability were linked. Significant amounts of ReOx species leached from SiO2 and TiO2, resulting in a lower activity of the recovered solid. The best supports with respect to catalyst stability were Fe2O3 and ZrO2. Spectroscopic investigations of the reaction mixture indicated that rhenium may only be temporarily soluble through complex formation with the reactant, opening the principal possibility of re-deposition.
The same oxides were used as supports for oxo-molybdenum species, MoOx. A temperature of 180 °C and reaction times of 24 h were required to achieve catalytic turnover. Selectivities to the target olefin were less than 20%, but improvement is anticipated through optimization of these first known solid molybdenum DODH catalysts.