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INGENIERIE+MP

Pickering emulsions are surfactant-free dispersions of two immiscible fluids that are kinetically stabilized by colloidal particles. For ecological reasons, these systems have undergone a resurgence of interest to mitigate the use of synthetic surfactants and solvents. Moreover, the use of colloidal particles as stabilizers provides emulsions with original properties compared to surfactant-stabilized emulsions, microemulsions, and micellar systems. Despite these specific advantages, the application of Pickering emulsions to catalysis has been rarely explored. This Minireview describes very recent examples of hybrid and composite amphiphilic materials for the design of interfacial catalysts in Pickering emulsions with special emphasis on their assets and challenges for industrially relevant biphasic reactions in fine chemistry, biofuel upgrading, and depollution.

Stabilization of oil/oil Pickering emulsions using robust and recyclable catalytic amphiphilic silica nanoparticles bearing alkyl and propylsulfonic acid groups allows fast and efficient solvent-free acetalization of immiscible long-chain fatty aldehydes with ethylene glycol.

No abstract

The lack of selectivity for the direct amination of alcohols with ammonia, a modern and clean route for the synthesis of primary amines, is an unsolved challenge. Here, we combine first-principles calculations, scaling relations, kinetic simulations and catalysis experiments to unveil the key factors governing the activity and selectivity of metal catalysts for this reaction. We show that the loss of selectivity towards primary amines is linked to a surface-mediated C-N bond coupling between two N-containing intermediates: CH 3 NH and CH 2 NH. The barrier for this step is low enough to compete with the main surface hydrogenation reactions and can be used as a descriptor for selectivity. The combination of activity and selectivity maps using the C and O adsorption energies as descriptors is used for the computational screening of 348 dilute bimetallic catalysts. Among the best theoretical candidates, Co 98.5 Ag 1.5 and Co 98.5 Ru 1.5 (5 wt% Co) are identified as the most promising catalysts from experiments.

International audienceHere we report the homogeneously-catalyzed etherification of glycerol with short chain alkyl alcohols. Among the large variety of Brønsted and Lewis acids tested, we show here that metal triflates are not only the most active but are also capable of catalyzing this reaction with an unprecedented selectivity. In particular, in the presence of Bi(OTf )3, the targeted monoalkylglyceryl ethers were obtained with up to 70% yield. Although tested Brønsted acids were also capable of catalyzing the etherification of glycerol with alkyl alcohols, they were found however less active and less selective than Bi(OTf )3. By means of counter experiments, we highlighted that the high activity and selectivity of Bi(OTf )3 may rely on a synergistic effect between Bi(OTf )3 and triflic acid, a Brønsted acid that can be released by in situ glycerolysis of Bi(OTf )3. The scope of this methodology was also extended to other polyols and, in all cases, the monoalkylpolyol ethers were conveniently obtained with fair to good yields

Can I borrow hydrogen? Direct amination of biomass‐derived platform alcohols can be efficiently performed through the borrowing hydrogen mechanism, offering high activity and selectivity at low‐to‐moderate temperatures. Unlike nucleophilic substitution, the catalyst behaves as a tandem system involving the temporary removal of H2 from the reaction medium.