Furfural hydrogenation, hydrodeoxygenation and etherification over MoO2 and MoO3: A combined experimental and theoretical study

Abstract

Valorization of lignocellulosic biomass, particularly catalytic hydrotreatment of hemicellulose-based furfural (FUR), has been studied for the production of value-added chemicals. A three-phase batch reactor has been used for hydrotreatment in isopropanol over various commercially available unsupported MoOx catalysts, at various temperatures (170–230 °C), pressures (0–80 bar H2), catalyst loadings (0–2 wt%), and reactant concentrations (5–20 wt%). No significant difference in catalytic activity or selectivity has been observed among the three different MoO3 and one MoO2 catalysts, while NiMo/Al2O3, Mo2C and WO3 were much less active. Data-points collected have been used to propose a detailed reaction pathway network for a micro-kinetic model, which also took into consideration the thermodynamics, and adsorption, desorption, and surface reaction kinetics. The alcoholysis of FUR yielded valuable isopropyl levulinate (IPL) as the major product under all tested reaction conditions, while other value-added compounds (furfuryl alcohol, isopropyl furfuryl ether, furfuryl acetone, angelica lactone) were observed in smaller quantities. It was found that neither the presence nor the absence of the gaseous H2 pressure contributes to the global reaction rate, or selectivity, since the solvent acts as a sufficient hydrogen donor. Additionally, density functional theory (DFT) calculations provided further insight into the active planes present by the implementation of the Wulff construction. Furthermore, the reaction mechanism was explained based on reaction energies, which were in silico determined and compared for several surfaces. The results were consistent with the characterization and activity-testing results. The furfural ring-opening reaction, yielding valuable IPL in the absence of gaseous H2, over a cheap bulk MoOx is reported for the first time.