Catalysis science and technology increased efforts recently to progress beyond conventional "thermal" catalysis and face the challenges of net-zero emissions and electrification of production. ...Nevertheless, a better gaps and opportunities analysis is necessary. This review analyses four emerging areas of unconventional or less-conventional catalysis which share the common aspect of using directly renewable energy sources: (i) plasma catalysis, (ii) catalysis for flow chemistry and process intensification, (iii) application of electromagnetic (EM) fields to modulate catalytic activity and (iv) nanoscale generation at the catalyst interface of a strong local EM by plasmonic effect. Plasma catalysis has demonstrated synergistic effects, where the outcome is higher than the sum of both processes alone. Still, the underlying mechanisms are complex, and synergy is not always obtained. There is a crucial need for a better understanding to (i) design catalysts tailored to the plasma environment, (ii) design plasma reactors with optimal transport of plasma species to the catalyst surface, and (iii) tune the plasma conditions so they work in optimal synergy with the catalyst. Microfluidic reactors (flow chemistry) is another emerging sector leading to the intensification of catalytic syntheses, particularly in organic chemistry. New unconventional catalysts must be designed to exploit in full the novel possibilities. With a focus on (a) continuous-flow photocatalysis, (b) electrochemical flow catalysis, (c) microwave flow catalysis and (d) ultrasound flow activation, a series of examples are discussed, with also indications on scale-up and process industrialisation. The third area discussed regards the effect on catalytic performances of applying oriented EM fields spanning several orders of magnitude. Under well-defined conditions, gas breakdown and, in some cases, plasma formation generates activated gas phase species. The EM field-driven chemical conversion processes depend further on structured electric/magnetic catalysts, which shape the EM field in strength and direction. Different effects influencing chemical conversion have been reported, including reduced activation energy, surface charging, hot spot generation, and selective local heating. The last topic discussed is complementary to the third, focusing on the possibility of tuning the photo- and electro-catalytic properties by creating a strong localised electrical field with a plasmonic effect. The novel possibilities of hot carriers generated by the plasmonic effect are also discussed. This review thus aims to stimulate the reader to make new, creative catalysis to address the challenges of reaching a carbon-neutral world.
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•Gaps and opportunities in plasma catalysis for optimal synergy are identified.•Flow chemistry is an emerging sector to intensify catalytic syntheses.•External electric field reduces activation energy and generates surface charging.•Plasmonic effect generates a localised electrical field influencing catalysis.•Novel possibilities to exploit hot carriers generated in plasmonic catalysis.
Wastewater polluted by organics can be treated by using electro-generated active chlorine, even if this promising route presents some important drawbacks such as the production of chlorinated ...by-products. Here, for the first time, this process was studied in a microfluidic electrochemical reactor with a very small inter-electrode distance (145 μm) using a water solution of NaCl and phenol and a BDD anode. The potential production of chloroacetic acids, chlorophenols, carboxylic acids, chlorate and perchlorate was carefully evaluated. It was shown, for the first time, up to our knowledge, that the use of the microfluidic device allows to perform the treatment under a continuous mode and to achieve higher current efficiencies and a lower generation of some important by-products such as chlorate and perchlorate. As an example, the use of the microfluidic apparatus equipped with an Ag cathode allowed to achieve a high removal of total organic carbon (about 76%) coupled with a current efficiency of 17% and the production of a small amount of chlorate (about 30 ppm) and no perchlorate. The effect of many parameters (namely, flow rate, current density and nature of cathode) was also investigated.
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•Electrochemical wastewater treatment by active chlorine was done in microfluidic cells.•Higher current efficiencies and lower generation of ClO3− and ClO4− were achieved.•The performance of the process improved using an Ag cathode.
•Kinetic rate constants for both steps of diphenhydramine synthesis are calculated.•Kinetics are developed by in-situ Raman and in-line low-field NMR spectroscopies.•Quantitative models are developed ...on a low-field NMR spectrometer.•The Arrhenius and Eyring parameters are calculated for the etherification step.•A discussion of the mechanistic implications of the solvent properties.
Diphenhydramine is a first-generation antihistamine that is available over-the-counter to treat maladies such as allergic reactions and insomnia. Despite its ubiquity in society and high demand, the kinetics for either step of diphenhydramine synthesis have not been explored in detail. In this work, for the first step, a methodology has been devised to obtain kinetics from the heterogeneous halogenation of benzhydrol with hydrochloric acid in a batch reactor equipped with in-situ Raman probe and further verified with ex-situ low-field NMR spectroscopy. For the second step, the kinetics of etherification have been explored using a microfluidic flow reactor and at-line NMR spectroscopy in a variety of solvents. Arrhenius and Eyring parameters are determined for Step 2. We find that the reaction performance is well correlated with the acceptor number of the solvent indicating that the Lewis acidity of the solvent plays a significant role in the overall performance.
Paired electrosynthesis has received considerable attention as a consequence of simultaneously synthesizing target products at both cathode and anode, whereas the related synthetic efficiency in ...batch reactors is still undesirable under certain circumstances. Encouragingly, laminar microfluidic reactor offers prospective options that possess controllable flow characteristics such as enhanced mass transport, precise laminar flow control and the ability to expand production scale progressively. In this comprehensive review, the underlying fundamentals of the paired electrosynthesis are initially summarized, followed by categorizing the paired electrosynthesis including parallel paired electrosynthesis, divergent paired electrosynthesis, convergent paired electrosynthesis, sequential paired electrosynthesis and linear paired electrosynthesis. Thereafter, a holistic overview of microfluidic reactor equipment, integral fundamentals and research methodology as well as channel extension and scale-up strategies is proposed. The established fundamentals and evaluated metrics further inspired the applications of microfluidic reactors in paired electrosynthesis. This work stimulated the overwhelming investigation of mechanism discovery, material screening strategies, and device assemblies.
In this review, we demonstrate a simplified nomenclature system of paired electrosynthesis and elaborate the microfluidic reactor equipment, integral fundamentals and research methodology as well as various applications to provide new insights into correlation paired electrosynthesis and industrial implementation. Display omitted
•The underlying react fundamentals and categorization strategy of the paired electrosynthesis were discussed.•Microfluidic reactor equipment, integral fundamentals and research methodology in electrochemistry were investigated.•The existing implementation and the immense potential for future development were summarized.
•A microfluidic electrochemical reactor is developed for hydrogen evolution.•The developed MER optimizes the bubble behavior on the electrode surface.•The mass transport is enhanced and active site ...release is promoted.•Efficient and stable performance of hydrogen evolution is achieved.
Hydrogen production from water electrolysis provides an effective bridge between the existing energy system and the layout of green renewable energy. Electrochemical hydrogen gas evolution on the electrode surface will occupy the limited active sites thus significantly increasing the reaction overpotential. It is crucial to study and optimize the bubble behavior on the electrode surface to improve reaction efficiency and lower the energy loss. Herein, a microfluidic electrochemical reactor (MER) has been constructed to optimize the surface gas-liquid two-phase flow behavior during the gas evolution process. The obtained results demonstrate the feasibility of microfluidic design in manipulating the bubble behavior at the electrode interface accompanied with the self-generated gas-liquid two-phase flow, which can directly reduce the overpotentials by facilitating the mass transfer and refreshing catalytic active sites. Compared with conventional H-cell, state-of-the-art efficient and stable performance of hydrogen evolution has been achieved, where the increase in current density was more than 5 times. This work reveals a new strategy for guiding the design of the electrochemical reactor for water splitting.
A cationic conjugated polyelectrolyte PPET3-N2 was used as a photosensitizer for photocatalytic oxidation of organic sulfides, including thioanisole, ethyl phenyl sulfide, 4-methylphenyl methyl ...sulfide, etc., to form sulfoxides with good yields and high selectivity. Oxidation reactions were performed in both batch and microfluidic reactors, where the microfluidic reactor can significantly promote the conversion of photocatalytic oxidation reaction to over 98% in about 8 min. Further studies of the photocatalytic oxidation of the antitumor drug ricobendazole in the microfluidic reactor demonstrate the potential application of the polymer material in organic reactions given its high selectivity, good efficiency, and operation convenience.
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•Anodic •OH role in cathodic electro-precipitation is investigated for the first time.•Anodic •OH reacts with CO32– and decrease cathodic CaCO3 electroprecipitation yield.•A new model ...is proposed to predict evolution of cathodic CaCO3 electroprecipitation.
Electrochemical systems are attracting increasing interest in environmental protection as relatively sustainable processes, particularly in wastewater treatment and reuse. However, cathode scaling in electrochemical processes for wastewater treatment is a major issue that is often overlooked. It is proposed for the first time to investigate the anodic contribution towards CaCO3 electroprecipitation phenomena under the advanced electrooxidation conditions applied to remove organic biorecalcitrant pollutants. The contribution of the reaction of the hydroxyl radical (•OH) with carbonates, which reduces cathodic scaling at a micrometric interelectrode distance (500 µm) and at a high current density (16 mA cm−2), is described in detail. In addition, the anti-scaling effect of local anodic acidification should be considered. A new kinetic model of electroprecipitation fits the experimental curves well (root mean square error (RMSE) < 0.19 for Ca2+) and confirms this anodic role, combined with the gas hindrance and scale detachment induced by gas bubble electrogeneration at sufficiently high current intensities.
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•Fluorescent molecularly imprinted polymers (FMIPs) targeting ovalbumin were prepared.•The FMIPs have pH-dependent property for the recognition of ovalbumin.•The FMIPs can be used for ...ovalbumin assay in real samples with high recovery rate.
Here, fluorescent artificial antibodies for sensing ovalbumin in food were synthesized by molecular imprinting technique in a microfluidic reactor. A phenylboronic acid-functionalized silane was employed as the functional monomer to enable the polymer has pH-responsive property. Fluorescent molecularly imprinted polymers (FMIPs) could be produced continuously in a short time. Both fluorescein isothiocyanate (FITC) and rhodamine B isothiocyanate (RB)-based FMIPs can specifically recognize the target ovalbumin, particularly FITC-based FMIP, giving an imprinting factor of 2.5 and cross-reactivity factors of 2.7 (ovotransferrin), 2.8 (β-lactoglobulin) and 3.4 (bovine serum albumin), and was applied for the detection of ovalbumin in milk powder with recovery rates of 93–110%; moreover, the FMIP can be reused at least four times. Such FMIPs have promising future in replacing the fluorophore-labelled antibodies to fabricate fluorescent sensing devices or establish immunoassay methods, which have extra merits of low-cost, high stability and recyclability, easy to carry and store at ambient environments.
Modern bioreactors primarily focus on fixing enzymes on materials to form fixed bed reactors, but the reaction efficiency is unstable. More importantly, the enzymes easily fall off or even ...inactivate, and the fluid risks leaking due to excessive pressure during flow. In this study, a directional channel continuous microfluidic reactor with laccase covalently immobilized in the internal channel is made from natural wood. After dimethylacetamide/lithium chloride (DMAc/LiCl) treatment of delignified wood, the micropores (ray cells, pits and nanopores) in directional channel walls are fully exposed. When the fluid passes through, the turbulence near the pits increases, resulting in good mass and heat transfer, which enhances the catalytic efficiency of laccase. The reactor has good stability and maintains more than 80% substrate conversion in the pH range of 3–7 and the temperature range of 15–55 ℃. In the degradation of 4-nitrophenol (4-NP), a 94.42% degradation rate is achieved in only 30 min, and 86.93% efficiency is maintained after 25 cycles of catalysis, indicating its excellent reusability. The directional reactor with porous inner walls is simple to prepare and easy to scale up, which provides excellent convenience for continuous industrial production and shows great commercial application potential.
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•The wood-based reactor with pores fully exposed in the inner wall was constructed.•The reactor had low pressure and high mass transfer efficiency under fluid reaction.•The immobilized laccase in the reactor was more stable than free laccase.•The conversion was still stable even after 25 repetitions.
Integrating microchannel flow boiling heat transfer with nanofluids is an effective method for cooling electronic devices. However, traditional methods have significant limitations in achieving ...facile synthesis of nanofluids with desirable properties. In this study, we propose a straightforward synthesis strategy using microfluidic reactors, which enables continuous and high-throughout synthesis of Al2O3 nanofluids with high purity and long-term stability. These nanofluids were found to enhance boiling heat transfer performance by delaying bubbles coalescence, increasing surface nucleation sites, improving the nucleation rate, and enhancing wettability by observation of the bubble behavior. Specifically, the critical heat flux (CHF) and corresponding heat transfer coefficient (HTC) are increased by a maximum of 32 % and 26 %, respectively, with negligible change in pressure drop. Moreover, the heat transfer performance deteriorates with increasing concentration of alumina nanofluids. These findings not only provide guidance of microchannel flow boiling with nanofluids, but also present valuable insights for the application of nanofluids in two-phase cooling systems for electronic devices.
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