Aquivion Perfluorosulfonic Superacid as an Efficient Pickering Interfacial Catalyst for the Hydrolysis of Triglycerides

Pickering Emulsions Biocatalysis: Recent Developments and Emerging Trends

Biocatalysis within biphasic systems is gaining significant attention in the field of synthetic chemistry, primarily for its ability to solve the problem of incompatible solubilities between biocatalysts and organic compounds. By forming an emulsion from these two-phase systems, a larger surface area is created, which greatly improves the mass transfer of substrates to the biocatalysts. Among the various types of emulsions, Pickering emulsions stand out due to their excellent stability, compatibility with biological substances, and the ease with which they can be formed and separated. This makes them ideal for reusing both the emulsifiers and the biocatalysts. This review explores the latest developments in biocatalysis using Pickering emulsions. It covers the structural features, methods of creation, innovations in flow biocatalysis, and the role of interfaces in these processes. Additionally, the challenges and future directions are discussed in combining chemical and biological catalysts within Pickering emulsion frameworks to advance synthetic methodologies.

Particle shape anisotropy in pickering interfacial catalysis for Knoevenagel condensation

Dispersions of two immiscible liquids stabilized by solid particles are termed as Pickering emulsions. Stability of such emulsions is affected by various parameters such as amount of solid particle, method of emulsification, size, and shape of particles, etc. In this study, MgO samples prepared by different methods and characterized by XRD, FESEM, HRTEM, DLS, and CO2-TPD techniques were utilized for stabilizing o/w Pickering emulsions. The effect of particle shape on Pickering Interfacial Catalysis (PIC) for Knoevenagel condensation was investigated. It was found that in the case of rod and plate shaped particles, emulsion stability and catalytic activity were higher as compared to those obtained with other MgO samples prepared. The applicability of the MgO-PIC system is also successfully demonstrated for gram scale synthesis (85 % yield in 30 min). The MgO-PIC system was found to be reusable for at least five cycles without substantial loss in activity.

Enhanced Biphasic Reactions in Amphiphilic Silica Mesopores

In this study, we investigated the effect of the pore volume and mesopore size of surface-active catalytic organosilicas on the genesis of particle-stabilized (Pickering) emulsions for the dodecanal/ethylene glycol system and their reactivity for the acid-catalyzed biphasic acetalization reaction. To this aim, we functionalized a series of fumed silica superparticles (size 100-300 nm) displaying an average mesopore size in the range of 11-14 nm and variable mesopore volume, with a similar surface density of octyl and propylsulfonic acid groups. The modified silica superparticles were characterized in detail using different techniques, including acid-base titration, thermogravimetric analysis, TEM, and dynamic light scattering. The pore volume of the particles impacts their self-assembly and coverage at the dodecanal/ethylene glycol (DA/EG) interface. This affects the stability and the average droplet size of emulsions and conditions of the available interfacial surface area for reaction. The maximum DA-EG productivity is observed for A200 super-SiNPs with a pore volume of 0.39 cm3·g-1 with an interfacial coverage by particles lower than 1 (i.e., submonolayer). Using dissipative particle dynamics and all-atom grand canonical Monte Carlo simulations, we unveil a stabilizing role of the pore volume of porous silica superparticles for generating emulsions and local micromixing of immiscible dodecanal and ethylene glycol, allowing fast and efficient solvent-free acetalization in the presence of Pickering emulsions. The micromixing level is interrelated to the adsorption energy of self-assembled particles at the DA/EG interface.

Preparation and Emulsifying Properties of Carbon-Based Pickering Emulsifier

Water is increasingly being used as a solvent in place of organic solvent in order to meet the demand for green chemical synthesis. Nevertheless, many of the reaction substrates are organic matter, which have low water solubility, resulting in a low reaction interface and limiting the development of organic-water biphasic systems. A surfactant is typically added to the two-phase system to form an emulsion to increase the contact area between the organic phase and the water. Compared to ordinary emulsion stabilized with the surfactant, Pickering emulsion offers better adhesion resistance, biocompatibility, and environmental friendliness. It possesses unrivaled benefits as an emulsifier and catalyst in a two-phase interfacial catalysis system (PIC). In this study, the amine group (NNDB) was employed to alter the surface of graphene oxide (GO). A stable Pickering emulsion was created by adsorbing GO-NNDB on the toluene–water interface. It was determined that the emulsion system had good stability by analyzing digital photographs and microscope images of droplets at various temperatures, and fluorescence microscopy images of emulsion droplets created by both newly added and recovered emulsifiers. This work provided the groundwork for future applications of Pickering emulsion in interfacial catalysis.

Pickering Emulsion Catalysis: Interfacial Chemistry, Catalyst Design, Challenges, and Perspectives

Pickering emulsions are particle-stabilized surfactant-free dispersions composed of two immiscible liquid phases, and emerge as attractive catalysis platform to surpass traditional technique barrier in some cases. In this review, we have comprehensively summarized the development and the catalysis applications of Pickering emulsions since the pioneering work in 2010. The explicit mechanism for Pickering emulsions will be initially discussed and clarified. Then, summarization is given to the design strategy of amphiphilic emulsion catalysts in two categories of intrinsic and extrinsic amphiphilicity. The progress of the unconventional catalytic reactions in Pickering emulsion is further described, especially for the polarity/solubility difference-driven phase segregation, "smart" emulsion reaction system, continuous flow catalysis, and Pickering interfacial biocatalysis. Challenges and future trends for the development of Pickering emulsion catalysis are finally outlined.

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

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.

CO2 -Enabled Biomass Fractionation/Depolymerization: A Highly Versatile Pre-Step for Downstream Processing

Lignocellulosic biomass is inevitably subject to fractionation and depolymerization processes for enhanced selectivity toward specific products, in most cases prior to catalytic upgrading of the three main fractions-cellulose, hemicellulose, and lignin. Among the developed pretreatment techniques, CO₂ -assisted biomass processing exhibits some unique advantages such as the lowest critical temperature (31.0 °C) with moderate critical pressure, low cost, nontoxicity, nonflammability, ready availability, and the addition of acidity, alongside easy recovery by pressure release. This Review showcases progress in the study of sub- or supercritical CO₂ -mediated thermal processing of lignocellulosic biomass-the key pre-step for downstream conversion processes. The auxo-action of CO₂ in biomass pretreatment and fractionation, along with the involved variables, direct degradation of untreated biomass in CO₂ by gasification, pyrolysis, and liquefaction with relevant conversion mechanisms, and CO₂ -enabled depolymerization of lignocellulosic fractions with representative reaction pathways are summarized. Moreover, future prospects for the practical application of CO₂ -assisted up- and downstream biomass-to-bioproduct conversion are also briefly discussed.

Pickering Interfacial Catalysis-Knoevenagel Condensation in Magnesium Oxide-Stabilized Pickering Emulsion

In the present study, a novel catalytic route for the Knoevenagel condensation reaction has been developed by Pickering interfacial catalysis using magnesium oxide (MgO) as both an emulsion stabilizer and a base catalyst. MgO was prepared by the precipitation method using sodium hydroxide or ammonium hydroxide as the precipitating agent and calcined at different temperatures. The calcined samples were characterized by XRD, SEM, TEM, AFM, BET, and DLS techniques. The catalytic application of the emulsions stabilized by MgO was investigated for the Knoevenagel condensation reaction of benzaldehyde and its derivatives with malononitrile. All of the reactions were carried out at an ambient temperature (30 °C) under static conditions without stirring. Both the emulsion-stabilizing ability and the catalytic activity of MgO were found to be affected by the method of preparation, calcination temperature, and the nature of the oil phase. It was observed that the method of preparation varied the texture and morphology of MgO and thus the stability and droplet size of the emulsion formed. This was further reflected in the catalytic activity. The highest yield (87%) of the condensation product was obtained with MgO prepared by precipitation using a strong base (NaOH) and further calcined at 400 °C. The developed catalytic system offers several green chemistry advantages such as reusable solid-base catalyst and use of a single material as both emulsion stabilizer and catalyst. Room-temperature reaction under static conditions is an additional advantage of the developed catalytic system.

Impact of shaping Aquivion PFSA on its catalytic performances

The shaping of Aquivion PFSA into micropellets is a good compromise between its catalytic performances, its ease of recovery at the end of the reaction and its deactivation rate.

Aquivion-Carbon Composites with Tunable Amphiphilicity for Pickering Interfacial Catalysis

A key demand in biomass conversion is how to achieve high reactivity with immiscible reagents with the use of neither cosolvents nor additives. Pickering interfacial catalysis encompassing the design of amphiphilic catalysts behaving concomitantly as emulsifiers offers an elegant solution. In this study, we prepared a systematic series of amphiphilic Aquivion-carbon composites by the hydrothermal carbonization of guar gum with Aquivion perfluorosulfonic superacid. By tuning the Aquivion-carbon composition, materials with tunable hydrophilic-lipophilic properties could be prepared, showing high versatility for conducting biphasic reactions without stirring. In particular, an optimal formulation based on 5:1 Aquivion-carbon could be developed, showing high activity in the transesterification reaction of glyceryl trioleate with methanol at 100 °C with good reusability due to the genesis of stable Pickering emulsions.

Methylation of Polyols with Trimethylphosphate in the Presence of a Lewis or Brønsted Acid Catalyst

The alkylation of alcohols and polyols has been investigated with alkylphosphates in the presence of a Lewis or Brønsted acid catalyst. The permethylation of polyols was developed under solvent-free conditions at 100 °C with either iron triflate or Aquivion PW98, affording the isolated products in yields between 52 and 95 %. The methodology was also adjusted to carry out peralkylation with longer alkyl chains.