Non-hydrolytic sol-gel synthesis of stable catalysts for aqueous-phase hydrogenation of biomass derivatives – NHYSCAB

The use of renewable resources is essential for a sustainable society. Developing clean catalytic processes to produce value-added chemicals from renewable materials such as wood or plants has become a major goal for chemists. The bio-feedstocks issued from lignocellulose after either enzymatic fermentation or acidic deconstruction consist mainly of water-soluble molecules containing many oxygenated groups ((di)acids, alcohols, ethers), which must be subsequently transformed to find applications as monomers, solvents, etc. For this purpose, the design of new water-stable catalysts able to withstand rather harsh reaction conditions in term of pH, temperature and pressure is required.
The NHYSCAB project aims at the synthesis of hydrothermally stable promoted metallic catalysts, based on a supported noble metal (e.g. Pd, Ru) modified with an oxophilic promoter (Re or Mo). They will be used for catalytic hydrogenation/hydrogenolysis of biosourced molecules in aqueous phase, at temperatures in the range 100 to 200°C and hydrogen pressure in the range 50 to 150 bar, at acidic to neutral pH. This project is based on the collaboration between two complementary public partners, IRCELYON (coordinator) and ICGM Montpellier, which are internationally recognized for their expertise in the fields of biomass catalytic upgrading and of non-hydrolytic sol-gel (NHSG) synthesis of mixed oxides, respectively.
The first part of the project consists in the design of advanced mesoporous catalyst supports using the NHSG process which offers powerful synthetic routes to hydrothermally stable mesoporous oxides (TiO2, ZrO2) and mixed oxides incorporating the promoter species (Re-Ti, Mo-Ti), which after an appropriate thermal treatment are dispersed at the surface of the oxide. The hydrothermal stability of these supports will be assessed under the reaction conditions. Noble metal will be deposited on the stable supports with well-defined compositions and structures in order to prepare efficient promoted metallic catalysts.
The second part concerns the evaluation of the synthesized catalysts in the reference reaction of aqueous-phase hydrogenation of biosourced acids (succinic acid and levulinic acid) to the corresponding diols (1,4-butane- and 1,4-pentane- diols). The catalysts will also be evaluated in the challenging hydrogenolysis of tetrahydrofurfuryl alcohol from the furfural platform into the corresponding 1,2- or 1,5- pentanediols. The expected products can find many applications, including as monomers.
The design of well-defined, thoroughly characterized solids is essential to optimize the selective synthesis of targeted chemicals. Therefore, extensive characterization of the solids (supports and catalysts) will be performed at different stages (oxides, mixed oxides, supported metallic catalysts, before and after reaction) and their stability will be investigated under the reaction conditions. These will allow us to determine the texture/structure/composition of the solids, to validate their stability and to correlate the characteristics of the catalysts and their performance. To reach the highest activity or selectivity, the study will focus not only on the catalyst design but also on the optimization of reaction conditions. After screening of catalyst compositions using a batch reactor, the catalytic reaction will be conducted in a continuous trickle-bed reactor to further study the stability of the selected catalytic systems.