DOI: 10.1002/cssc.201402236 One-pot Aldol Condensation and Hydrodeoxygenation of Biomass-derived Carbonyl Compounds for Biodiesel Synthesis Laura Faba, Eva Díaz, and Salvador OrdóÇez* [a] 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-al- kanes. Different combinations of catalysts (bifunctional cata- lysts 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, selec- tivities 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, carbo- naceous supports, or mechanical mixtures of monofunctional catalysts leads to poorer results owing to side effects; mainly, hydrogenation of reactants and adsorption processes. The preparation of drop-in fuels from lignocellulosic biomass (second-generation biofuels) is nowadays of key interest. Many of these technologies, such as pyrolysis or gasification followed by Fischer–Tropsch synthesis, are trade-offs in terms of energy because of the high reaction temperatures they require. [1] In addition, they lead to complex hydrocarbon mixtures that ne- cessitate distillation units with high energy demands. Conse- quently, the carbon footprints of these products are similar to fossil fuels. [2] On the other hand, liquid-phase processes have attracted much attention because of the lower reaction temperatures and the higher selectivities that can be obtained. [3] Moreover, the separation is easier because of the immiscibility of the re- sulting organic and the aqueous phases. At this point, Dumesic and co-workers have proposed a scheme for obtaining diesel- quality biofuels from cellulosic and hemicellulosic materials using a cascade of four catalytic steps: (i) hydrogenolysis of the biopolymer; (ii) dehydration of the resulting sugars, yielding carbonylic species (furfural and hydroxymethylfurfural); (iii) condensation of these species (in the most usual approach, by adding compounds with two carbons with a-hydrogen atoms, such as acetone); and (iv) hydrodeoxygenation of the resulting condensation adducts. [4] The first three steps are done in the aqueous phase, whereas the last one is more usually per- formed in the organic phase. Concerning the catalysts: the first two steps involve acid cat- alysis and can be easily integrated using a variety of mineral acids such as HCl, H 2 SO 4 , or H 3 PO 4 , [5] or solid catalysts (zeolites) at temperatures lower than 580 K. [6] On the other hand, basic catalysts are needed for aldol condensation whereas metal par- ticles catalyze hydrodeoxygenation reactions. [7, 8] Considering the compatibility of both functionalities, the main scope of this Communication is the integration of these last steps is in order to obtain liquid n-alkanes from furfural (a dehydrated derivative of pentoses). This integration leads to a two-step process for obtaining biofuels from cellulosic mate- rials, taking advantage of the hemicellulosic fraction. In the case of actual biomass, a water pretreatment allows to sepa- rate the hemicellulose, recovering almost the complete amount of xylo-oligomers at low cost and without any damage to the cellulose and lignin. [9] These fractions can be in- tegrated into other biomass conversion technologies obtaining energy, fuels, and chemicals simultaneously (in the context of biorefineries). [10] Considering the decrease in costs of such cop- roduction, the main techno-economic disadvantage of this configuration should be the use of hydrogen. However, the hy- drogen required (5.5 mol of H 2 per mol of furfural, considering total selectivity to n-tridecane) can be obtained in situ by gasification of residual fractions of the biomass, with a consid- erable reduction in costs. [11] When considering the integration mentioned above more deeply, different problems arise, mainly related to develop- ment of the catalyst. The aldol condensation is carried out in the aqueous phase (where encountering the carbonyl precur- sors is more likely) and requires a very specific distribution of basic sites. [7, 12] This distribution is present in bulk mixed oxides (such as Mg–Zr mixed oxides), [7] being even more favorable when these oxides are dispersed onto inert supports, such as high-surface-area graphites (HSAG). [12] On the other hand, the introduction of active metals in these materials can lead to un- controlled changes in the basicity patterns and the morpholo- gy (decrease in pore volume), affecting the selectivity to the desired compounds. [13] Operating with mixtures of basic cata- lysts and conventional hydrogenation catalysts, such as noble- metal catalysts supported on alumina or activated carbon, might overcome this problem. [a] Dr. L. Faba, Dr. E. Díaz, Prof. S. OrdóÇez Department of Chemical and Environmental Engineering University of Oviedo C/Juliµn Clavería, s/n—33006—Oviedo—Asturias (Spain) Fax: (+ 34) 985103434 E-mail : sordonez@uniovi.es Supporting Information for this article is available on the WWW under http://dx.doi.org/10.1002/cssc.201402236.  2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim ChemSusChem 2014, 7, 2816 – 2820 2816 CHEMSUSCHEM COMMUNICATIONS