Catalysis in water by super hydrophobe hollow shells as solid micelles – CATCALL

To achieve these ambitious objectives, three scientific locks will be leveraged:

• Synthesis, material chemistry. The synthesis of ship-in-a-bottle type catalysts is a major challenge. The microporous walls of the supports - of the zeolitic or MOF type - could allow the diffusion of the reagents/products but also be superhydrophobic to prevent the diffusion of water. In addition, the catalysts must have a size greater than the diameter of the micropores in order to ensure their permanent retention at the heart of the particles. These two points are in themselves a real challenge, but the skills developed in recent years in our consortium have already made it possible to synthesize this type of system.

First main results on the design of super hydrophobe capsule have been published!

The design of efficient separation and catalytic processes in nanoporous adsorbents requires to finely tune gas adsorption in their porosity. Here, using a large set of Si-rich zeolites (Silicalite-1, Beta, Chabazite, ITQ-13), we report on an experimental study of vapor adsorption in zeolites showing the pivotal role of the hydroxyl concentration. By studying the adsorption of water and methanol in zeolites assisted with in situ IR and 29 Si NMR measurements, we find that adsorption switches from non-wetting to wetting as the hydroxyl surface density reaches the same critical value ~2.5 OH/nm2. While this hydroxyl concentration-induced crossover is well-known for water, we extend here the concept of a critical concentration by showing that a consistent picture arises when different polar substrates are considered. In particular, by establishing a generic behavior between the two protic substrates (H2O, MeOH), we pave the way for the rational design of hydrophobic adsorbents

Dimerization and oligomerization of light olefins is an important route to produce linear and branched higher olefins. Molecular complexes based on transition metals (Zn, Cr, Ni, Ti, etc.) are effective catalysts for producing linear alpha olefins (C4, C8 and C10) which are the main products of interest. However, in industrial processes, the catalyst is lost in the products and therefore cannot be reused or recycled. In some cases, the presence of a cocatalyst (often an alkyl aluminum salt) is necessary to initiate the catalytic cycle. Nevertheless, the stability of the cocatalyst in the presence of water is an obstacle to its use in a non-anhydrous or aqueous medium because they hydrolyse easily and lose their activity. In this context, we wish to design hydrophobic porous support materials protecting the molecular catalyst and its cocatalyst.

1/ The Pivotal Role of Critical Hydroxyl Concentration in Si-Rich Zeolites for Switching Vapor Adsorption
HAL Id : hal-03420234, version 1
DOI : 10.1021/acs.jpcc.1c07124

CATCALL deals with the discovery of selective and stable catalysts in water media without the use of noble metals.
The objecives are to design and to understand the mechanisms of SOLID superhydrophobe catalysts in multiphasic processes.

The role of the superhydrophobic catalyst support is to 1) prevent water to access to catalytic sites and 2) enable an overconcentration of substrates on catalytic sites in a kind of 'Liquid with Permanent Porosity"