Integration of C–C coupling reactions of biomass-derived oxygenates to fuel-grade compounds

Ceria-zirconia mixed oxides with different compositions including pure ceria and pure zirconia were prepared and characterized using temperature-programmed desorption (TPD) of CO2 and NH3, X-ray diffraction (XRD), and BET surface area measurements. Bi-functional catalysts for C–C coupling of ketones by aldol condensation/hydrogenation were prepared by depositing palladium on these ceria-zirconia mixed oxides, and these catalysts were studied for the conversion of 2-hexanone, a representative ketone that can be derived from sugars in biomass. The Pd/ZrO2 catalyst showed the best resistance to inhibition by CO2, an important factor in catalyst performance because of the presence of CO2 in biomass-derived feed streams. Furthermore, this catalyst displayed high activity for aldol condensation, as well as good resistance to inhibition by water. These properties make Pd/ZrO2 a desirable catalyst for integration in a single reactor of aldol condensation/hydrogenation reactions with ketonization processes, the latter of which convert carboxylic acids to ketones plus CO2 and H2O. The feasibility of this integration was studied with the mixture of a carboxylic acid (butanoic acid) and a ketone (2-hexanone) in a double bed system, and the integrated process showed high activity as well as selectivity to C–C coupling products.