Inorganic Fluorides-Hydroxides-Oxides nanomaterials as a new family of tunable and selective Basic Catalysts. – FluHOMat

The FluHOMat project aims to create a paradigm shift in heterogeneous basic catalysis. Indeed, in the past decades, acid catalysis was largely developed for the oil processing, keeping base catalysis on the back side. Regarding the transformation of biomass, that contains a large amount of oxygenated functions, base catalysis has to be developed for industrial perspectives, to offer reliable alternatives to acid catalysis and perform new efficient and selective reactions. To address this question, it must be considered that the reactions catalyzed by bases involve usually a deprotonation as a first step in which a basic site is necessary to abstract the proton, but an acidic center must also help to stabilize the deprotonated species. So, the deprotonation ability (Brønsted basic character) of a solid, is strongly linked both to the Lewis acidic and basic properties of the acid-base pairs sites. In this aim, we plan to prepare new nanomaterials with tunable acido-basic properties, allowing to control the activity and the selectivity of base catalyzed reactions and to limit CO2 adsorption which is a major drawback of heterogeneous base catalysts. Different oxide hydroxide fluorides with various alkaline-earth (Mg, Ba, Ca), high specific surface area, controlled O(OH)/F ratio and crystallographic structure will be explored by different synthesis methods such as sol-gel or microwave assisted solvothermal routes. The controlled content of fluorine in the structure should allow to finely tune the acid-base properties but also to avoid CO2 adsorption, thus the use of expensive and energy consuming thermal treatment to active them. Moreover, the incorporation of transition metals (Fe, Mn) and/or p elements (Al, Ga) will be studied to change the environment (by changing the crystallographic and electronic structure and/or the bond length) of Lewis/Bronsted acid/basic sites in the oxide hydroxide fluorides allowing a better control of their catalytic properties. Tuning the iono-covalent character of chemical bonding by the simultaneous presence of fluorine, hydroxyl and oxygen anions in the vicinity of metallic centers to induce variable acidic/basic properties is fundamental in catalysis. Creating new mixed anions compounds will give rise to new concepts in reactivity and catalysis. The advanced and in-depth characterization of these solids will be performed with a complete set of characterization methods combining classical techniques (XRD, FTIR, TEM, XPS, etc.) as well as specific ones (photoluminescence spectroscopies, PDF, NMR, protic and non protic probe molecules adsorption followed by FTIR, etc.). The assignment of the spectroscopic data will benefit from DFT calculations by comparison of experimental spectra and predictions for relevant model surfaces. The understanding of the catalytic properties will be particularly evaluated through the use of model reactions both in the gas phase (2-methyl-3-butyn-2-ol (MBOH) and isopropanol conversion) and in the liquid phase (aldol condensation of furfural and acetone). The determination of the structure/composition and catalytic properties relationships will be at the center of this project and will help to improve the catalyst designs. The final aim will be to propose a new family of basic catalysts with a very large range of properties in term of nature and strength of the acid-base pair allowing to use them in numerous reactions involving base catalysts.
The results that will be obtained on inorganic fluorides-hydroxides-oxides nanomaterials will provide valuable data for the international catalysis and inorganic material communities, and would constitute a real breakthrough in the base catalysis and related applications (bio based products and energies). In the long-term, it will help to shift large sectors of the petroleum-based economy to the bio based economy. For the above mentioned reasons, the economic and environmental impact of the project is very significant.