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Acid sites, in particular Brønsted sites, are often reported to enhance the catalytic performance of metal catalysts, like platinum, in hydrogenation. The significant boost in catalytic performance suggests that a bifunctional mechanism takes place under such conditions. Therefore, aiming to unravel the mechanism behind the synergy effect in the hydrogenation reaction observed on bifunctional zeolite/metal catalysts, the hydrogenation of pyridine adsorbed on *BEA (HBEA) and γ-Al2O3(Al2O3– A) promoted by platinum at low pressure, i.e., P≤ 150 mbar was investigated. The hydrogenation reaction was followed by FTIR spectroscopy aiming to identify the different phenomena linked to pyridine coordinated on Lewis (PyL) and protonated on Brønsted sites (PyH+), the formation of the reaction products, and modifications on the catalyst. Three series of catalysts with different levels of intimacy between the active sites, an important parameter for bifunctional reactions, were used: PtHBEA < PtA + HBEA < PtAHBEA PtAl2O3 ∞. The experimental results indicate a link between the enhanced hydrogenation activity and the intimacy between zeolites acid sites and the metal sites. The lack of desorption of pyridine and piperidine from HBEA during the reaction clearly indicates that the diffusing hydrogen species, i.e., HSP, are responsible for the conversion of pyridine adsorbed on HBEA acid sites. Indeed, a larger diffusion length between Pt and zeolite led to a slower conversion of the adsorbed pyridine, indicating that a bifunctional mechanism is at play. Hence, when the zeolite and metal are in close proximity a hydrogenation mechanism, complementary to the standard metal hydride and involving HSPand an adsorbed unsaturated molecule, occurs leading to an enhanced catalytic performance.

Wastes from lignocellulosic materials, especially hemicellulose, are extremely promising resources to produce fuels from renewable raw materials. Furfural, resulting from the depolymerization of hemicellulose, is often considered as an extremely interesting platform molecule. Particularly, new biofuels containing molecules with 8 and 13 carbon atoms can be produced from aldol condensation of furfural and acetone followed by a deoxygenation reaction. In this work, several magnesium hydroxide fluorides MgF2−x(OH)xwere prepared by a sol–gel method with various F/Mg ratios (0 to 2) at 100 °C. All solid samples were fully characterized by several techniques (nitrogen adsorption–desorption, TEM, IR, XRD and ICP). MgF2−x(OH)xwere mainly composed of an intimate mixture of MgF2and Mg(OH)2−x(OCH3)xand exhibited both acid–base properties and high surface areas. From CO2adsorption experiments, a basicity scale corresponding to basic sites with moderate strength was established: MgF1.5(OH)0.5> MgF(OH) ∼ MgF1.75(OH)0.25> MgF0.5(OH)1.5> Mg(OH)2 MgF2. It was proposed that the presence of fluorine allowed stabilization of the basic sites with moderate strength at ambient atmosphere. The aldol condensation of furfural and acetone was carried out under mild reaction conditions (50 °C, Patm) over MgF2−x(OH)x. These catalysts were involved in this reaction without using a classical activation step for basic solid catalysts, which constitutes a major advantage of energy conservation and thus, economic efficiency. The solid with a F/Mg ratio equal to 1.5 (MgF1.5(OH)0.5) exhibited the highest activity, the furanic dimer (1,5-di(furan-2-yl)penta-1,4-dien-3-one) being the main product. A good correlation between the catalytic activity and the basicity scale was highlighted. Based on these results, the nature of active sites was proposed: a combination of a Lewis acid site (coordinatively unsaturated metal site) in the vicinity of a basic site (hydroxyl groups of Mg(OH)2−x(OCH3)x). The effect of the furfural/acetone ratio on the catalytic properties of MgF1.5(OH)0.5was also investigated.