Multiphase Microreactors Based on Liquid–Liquid and Gas–Liquid Dispersions Stabilized by Colloidal Catalytic Particles

Abstract

Pickering emulsions, foams, bubbles, and marbles are dispersions of two immiscible liquids or of a liquid and a gas stabilized by surface‐active colloidal particles. These systems can be used for engineering liquid–liquid–solid and gas–liquid–solid microreactors for multiphase reactions. They constitute original platforms for reengineering multiphase reactors towards a higher degree of sustainability. This Review provides a systematic overview on the recent progress of liquid–liquid and gas–liquid dispersions stabilized by solid particles as microreactors for engineering eco‐efficient reactions, with emphasis on biobased reagents. Physicochemical driving parameters, challenges, and strategies to (de)stabilize dispersions for product recovery/catalyst recycling are discussed. Advanced concepts such as cascade and continuous flow reactions, compartmentalization of incompatible reagents, and multiscale computational methods for accelerating particle discovery are also addressed.

{2-Phases 2-reactions 1-catalyst} concept for the sustainable performance of coupled reactions

“…In summary, the biphasic model system designed here (i) offers a very simple way to separate reduction and oxidation reactions, (ii) requires only one catalyst and one reactor to perform two redox reactions and (iii) does not demand a complicated preparation of the catalyst compared to previously reported multiphasic reaction systems. [75][76][77][79][80][81] Consequently, the {2-phases 2-reactions 1-catalyst} concept is a sustainable and economical methodology for performing coupled reactions.…”

“…[75][76][77] Furthermore, the use of POMs as catalysts in biphasic media is only rarely investigated so far, 78 except for photocatalytic active POM-surfactants 79 and Pickering-emulsion stabilizing POM particles. 80,81 Nevertheless, in these systems only one reaction (either oxidation or reduction) are performed and/or the preparation of the catalyst requires multi-step synthesis, i.e. synthesis of nano particles or covalently bound POM-surfactants.…”

Tunable Multi‐Phase System for Highly Chemo‐Selective Oxidation of Hydroxymethyl‐Furfural

“…Accordingly, 2,5-hexanedione (47.8 mol %) or γ-hydroxyvaleric acid (84 mol %) were achieved as major products using Ru or Pd-based catalysts, respectively. [18,19] Other works, instead, explored the direct conversion of sugars (mostly fructose), to HMF derivatives. In an integrated continuous microfluidic system, a tandem transformation of fructose to furan chemicals was designed by which after an initial step of sugar dehydration, the resulting HMF solution (in DMSO solvent) was delivered to a tube-in-tube reactor whose inner walls were magnetically decorated with metal core-shell catalysts (Fe 3 O 4 @SiO 2 @Mn salen-metal complex, RuÀ Cu@Fe 3 O 4 /NrGO).…”

“…Authors claimed that emulsification enhanced the liquid/solid/liquid interfacial area, thereby favoring phase selectivity, i. e., the exclusive conversion of molecules in only one of the liquid phases. Accordingly, 2,5‐hexanedione (47.8 mol %) or γ‐hydroxyvaleric acid (84 mol %) were achieved as major products using Ru or Pd‐based catalysts, respectively [18,19] . Other works, instead, explored the direct conversion of sugars (mostly fructose), to HMF derivatives.…”

Microfluidic Device for Monitoring Catalytic Events on Armored Bubbles

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Despite the advances in the field of microfluidics, its implementation for preparing monodisperse particle-stabilized emulsions and foams has only been realized recently. [3] While the vast majority of studies have focused on the use of microfluidics in aqueous systems, very few examples of particle-stabilized gas bubbles and foams in organic solvents have been documented. [3,4] Besides, while droplet trapping using microfluidics has been achieved for simple emulsions and gas-core multiple emulsions, [5] transposition of proposed solutions to G-L systems has not been demonstrated so far owing to the low surface tension of organic liquids.

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