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Integrating reaction steps is of key interest in the development of processes for transforming lignocellulosic materials into drop-in fuels. We propose a procedure for performing the aldol condensation (reaction between furfural and acetone is taken as model reaction) and the total hydrodeoxygenation of the resulting condensation adducts in one step, yielding n-alkanes. Different combinations of catalysts (bifunctional catalysts or mechanical mixtures), reaction conditions, and solvents (aqueous and organic) have been tested for performing these reactions in an isothermal batch reactor. The results suggest that the use of bifunctional catalysts and aqueous phase lead to an effective integration of both reactions. Therefore, selectivities to n-alkanes higher than 50 % were obtained using this catalyst at typical hydrogenation conditions (T = 493 K, P = 4.5 MPa, 24 h reaction time). The use of organic solvent, carbonaceous supports, or mechanical mixtures of monofunctional catalysts leads to poorer results owing to side effects; mainly, hydrogenation of reactants and adsorption processes.

A new procedure for improving the performance of the most common catalysts used in aqueous-phase aldol condensation (Mg-Zr mixed oxides) reactions is presented. This reaction is of interest for upgrading carbohydrate feedstocks. The procedure involves supporting Mg-Zr oxides on non-microporous carbonaceous materials, such as carbon nanofibers (CNFs) or high-surface-area graphites (HSAGs), using either incipient wetness or coprecipitation procedures. The use of HSAGs together with the coprecipitation method provides the best performance. Results obtained for the cross-condensation of acetone and furfural at 323 K reveal that the catalyst performance is greatly improved compared to the bulk oxides (96.5 % conversion vs. 81.4 % with the bulk oxide; 87.8 % selectivity for C13 and C8 adducts vs. 76.2 % with the bulk oxide). This difference is even more prominent in terms of rates per catalytically active basic site (four and seven times greater for C8 and C13 adducts, respectively). The improved performance is explained in terms of a more appropriate basic site distribution and by greater interaction of the reactants with the carbon surface. In addition, deactivation behavior of the catalyst is improved by tuning the morphology of the carbonaceous support. An important enhancement of the catalytic stability can be obtained selecting a HSAG with an appropriate pore diameter. With HSAG100 the activity decreased by less than 20 % between successive reaction cycles and the selectivity for the condensation products remained almost unaltered. The decrease is greater than 80 % for the bulk oxides tested at these conditions, with important increases in the selectivity for by-product formation.

The use of cyclopentanone, instead of acetone, in the synthesis of diesel precursors by furfural aldol condensation is proposed. This reaction is catalyzed by a magnesium–zirconium mixed oxide. To optimize the C15 selectivity, different temperatures (293, 303, 313, and 323 K) and initial furfural/cyclopentanone ratios (1:1, 3:1, 5:1, and 10:1) were tested. Under the optimum conditions, yields for the desired C15 adduct are higher than 60 % in less than 4 h under mild conditions (303 K).

The hydrodeoxygenation (HDO) of aldol condensation adducts is of key interest in the preparation of biofuels from biomass by catalytic routes. In this work, furfuryldeneacetoneis taken as model of biomass-derived condensation adduct with furanic rings, unsaturations and carbonyl functionalities. Four noble metal catalysts (alumina-supported Ru, Rh, Pd and Pt) were tested. Obtained results show thatRh and Ru catalysts are only active for the hydrogenation of aliphatic double bonds; whereas Pd, and specially Pt catalysts, are active for the total HDO of the adduct, yielding n-octane, with selectivities higher than 30 % at 493 K after 24 h on stream (total conversion and carbon balance closure higher than 90 %). Based on these results, a mechanism (considering serial, parallel and equilibrium steps) and the corresponding kinetic model have been proposed for explaining the different selectivity trends observed for these metals.