The hydrodeoxygenation of furfural has been investigated over three different metal catalysts, Cu, Pd and Ni supported on SiO 2 , on a continuous-flow reactor under atmospheric pressure of hydrogen in the 210-290°C temperature range. The distribution of products is a strong function of the metal catalyst used. High selectivity to furfuryl alcohol is obtained over Cu/SiO 2 , with the formation of only small amounts of 2-methyl furan at the highest reaction temperature studied. In contrast to Cu catalyst, the conversion of furfural over Pd/SiO 2 mainly produces furan by decarbonylation. Furan can further react with hydrogen to form tetrahydrofuran (THF). Finally, on Ni/SiO 2 catalysts ring opening products (butanal, butanol and butane) can be obtained in significant amounts. The different product distributions are explained in terms of the strength of interaction of the furan ring with the metal surface and the type of surface intermediates that each metal is able to stabilize.

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The conversion of furfural has been investigated in vapor and liquidphases over a series of supported monometallic Pd and bimetallic Pd-Fe catalysts. Over the monometallicPd/SiO 2 catalyst, the decarbonylation reaction dominates, yieldingfuran as the main product. By contrast, over the bimetallic Pd-Fe/SiO 2 catalyst a high yield of 2-methylfuran is obtained with much lower yield to furan. Interestingly, changing the catalyst support affects the product distribution. For instance, using-Al 2 O 3 instead of SiO 2 as support of the bimetallic catalyst changed the dominant product from 2-methylfuran to furan. That is, Pd-Fe/-Al 2 O 3 behaves more like monometallic Pd/SiO 2 than bimetallic Pd-Fe/SiO 2. A detailed characterization of the catalysts via XPS, XRD, and TEM indicatedthat a Pd-Fe alloy is formed on the SiO 2 support but not on the-Al 2 O 3 support.Theoreticaldensity functional theory calculations suggest that on the Pd-Fe alloy binding of the furan ring to the surface is weakened compared to on pure Pd. This weakening disfavorsthe ring hydrogenation and decarbonylation paths, while the oxophilic nature of Fe atoms enhances the interaction of the C=O and theOH groups with the metal surface, whichfavors the C=O hydrogenation and CO bond cleavage paths. The presence of the solvent has a less pronounced effect, but clearly has a stronger inhibition on CC bond cleavage (decarbonylation to furan) than on CO bond cleavage (hydrogenolysis to methyl furan). *FOL = furfuryl alcohol, THF= tetrahydrofuran, MF= 2-methylfuran, THFOL= tetrahydrofurfuryl alcohol, MTHF= 2-methyltetrahydrofuran, CPON =cyclopentanone.