NobleFreeCat

The hydrogenation of sugars into polyols is often carried out on noble metals such as ruthenium Ru or on Raney nickel, with little work reported on supported non-noble metals. However, the cost of noble metals is high, their abundance is low, and both their cost and availability are prone to large fluctuations. Substitutes to noble metals should be found in the first period of transition metals, which encompasses especially abundant and cheap metals, but that may deactivate upon reaction or, like nickel, induce hydrogenolysis side-reactions. In this context, the potential of iron-based bimetallic combinations deserves to be fully explored. However, the hydrogenation/hydrogenolysis balance of the catalyst is not simply governed by the ratio between the two metals, but also by their degree of interplay, i.e., alloyed vs. segregated metals, a crucial point to take into account for a metal sensitive to oxidation like Fe. The possibility to synthesize precisely controlled Fe-based bimetallic nanoparticles appears to be limited when the catalyst is prepared by standard methods, with particles of different size, structure or composition coexisting in the catalyst. As a consequence, no firm conclusion can currently link the catalyst formulation and the catalytic properties of Fe-based systems owing to a lack of control of the nature of the nanoparticles at the nanometer level, leading to difficulties to interpret, reproduce, extrapolate and rationalize catalytic results. The NobleFreeCat project brings together four academic teams with complementary expertise in synthesis of metal nanoparticles and catalysis (Unité de Catalyse et Chimie du Solide, Laboratoire de Chimie de Coordination, Institut de Chimie des Milieux et Matériaux de Poitiers, Laboratoire de Chimie Physique), to develop scalable synthesis routes towards bimetallic Fe-based supported nanoparticles well-controlled in terms of size, chemical composition and chemical order, for their use as tunable and low-cost substitutes to noble metals in the catalytic hydrogenation of sugars. Three systems whose activity in selective hydrogenation has been recently described in the literature will be explored: Fe-Ni, Fe-Cu and intermetallic Fe-Al compounds. Supported catalysts on silica and zirconia will be prepared by deposition-precipitation, impregnation in the presence of organic additives, and radiolytic methods. Alloyed or core-shell systems prepared by organometallic route or mechanochemistry will be used as standards for the determination of the alloys stability, for structural characterization of supported systems, and as references for catalytic testing. The hydrogenation of a monosaccharide, xylose, to xylitol and that of a disaccharide, maltose, to maltitol, seldom tackled in the academic literature but of great interest for the industry, will be tested both in aqueous phases under hydrothermal conditions and in water-free deep-eutectic solvents. A unique combination of characterization techniques (in situ X-ray diffraction and X-ray absorption spectroscopy, STEM-EDX and -EELS subnanometric mapping, XPS/LEIS, Mössbauer spectroscopy) will be implemented to overcome the difficulty to distinguish poorly Z-contrasting elements and to probe both the bulk and surface composition of individual nanoparticles, along their whole cycle of use: reduction, reaction, exposure to air, catalyst regeneration. The establishment of correlations between synthesis route, chemical composition and catalytic activity will allow the consortium to lay the groundwork for subsequent technological maturation, furthered by the participation of representatives of sugar-derivatives producer Tereos in the steering committee of the project.