Solid-Liquid Interface at Molecular-scale for Catalysis – SLIMCAT

The rational understanding and prediction of chemical phenomena occurring at the solid-liquid interface (SLI, and more specifically oxide-water interface) of alumina supported catalysts represent a double industrial challenge raised by the catalysts' preparation and the optimization of catalytic processes working in liquid water. This is the case for biomass conversion and Fischer-Tropsch (FT) synthesis. Moreover, gamma-alumina is used as the industrial support in numerous catalytic processes particularly in the petrochemical and refining industry (including those previously cited). Regarding the active phase itself, cobalt is playing a central role in FT and hydrotreating (HDT) catalysts. In both cases, the improvement of the preparation (impregnation and drying) in presence of oxygenated organic molecules (additives) is crucial for maximizing the number of accessible metallic active sites and thus minimizing the number of cobalt atoms lost either in a refractory (oxide) phase or in the support.
The SLIMCAT project aims thus at determining key molecular-scale descriptors tuning the SLI properties: pKa of hydroxyl sites of aluminas, spectroscopic/energetic/structural descriptors, interfacial energies, energy scale of interactions between cobalt precursors, oxygenated organic molecules and the alumina surface, molecular mechanisms at SLI… Note that the oxygenated molecules chosen here (polyols, ethers, carboxylic acids) are representative of additives present at the catalyst preparation stages and are also representative of chemical functions of biomass oxygenated derivatives present during the reaction.
To reach this goal, we propose a multidisciplinary and bottom up approach combining cutting-edge experiments (Streaming Potential, SHG, EXAFS, AFM, UV-vis, ATR-IR, calorimetry) and state of the art ab initio molecular dynamics (AIMD) techniques, based on the recognized expertise of 4 academic laboratories (IRCP, ICGM, LRS, LAMBE) and a state-owned industrial and commercial establishment (“EPIC” in French), IFP Energies nouvelles. The project contains 3 work packages (WP) combining challenging experimental and theoretical achievements. WP1 is devoted to a surface-science approach (using monocrystalline alpha-alumina) in aqueous solution (containing additives and/or Co precursors). WP2 focuses on the experimental and theoretical studies of SLI of gamma-alumina supported cobalt catalysts including the effects of relevant preparation parameters. WP3 investigates the implications for the dried catalysts for samples prepared in WP1 and WP2. A fourth WP4 is dedicated to the dissemination of results and the organization of an international scientific workshop on the topic of molecular aspects of solid-liquid interfaces.
In order to improve the design of future catalysts, we expect to furnish rational and innovative guides based on the revisited quantification of aluminas in water, the cobalt precursors speciation at alumina surfaces, the role and/or choice of oxygenated molecules orienting the cobalt speciation and stability of alumina in water, the optimized preparation parameters (impregnation/drying sequences in presence of additives). Regarding the preparation aspects of Cobalt containing catalysts (FT and HDT), SLIMCAT meets the ANR society challenge on the “renewal of the industrial sector”. Even if less predominant, SLIMCAT meets also the secondary societal challenge "Clean, safe and efficient energy” because it addresses the question of the stability and acid-basic properties of alumina in the presence of water and oxygenated molecules as encountered in biomass processes.