pH-Switchable Pickering miniemulsion enabled by carbon quantum dots for quasi-homogenized biphasic catalytic system.

A quasi-homogenized miniemulsion system enabled by carbon quantum dot solid nanoparticles for biphasic catalysis is proposed, which breaks existing limits for an immiscibly biphasic system and overcomes issues for large-sized solid particle-stabilized emulsion droplets. The presented Pickering miniemulsion features pH-responsive behavior, finally triggering facile product separation and catalyst recycling in one reaction vessel.

A Liquid-Liquid-Solid System to Manipulate the Cascade Reaction for Highly Selective Electrosynthesis of Aldehyde.

Electrocatalytic synthesis of aldehydes from alcohols exhibits unique superiorities as a promising technology, in which cascade reactions are involved. However, the cascade reactions are severely limited by the low selectivity resulting from the peroxidation of aldehydes in a traditional liquid-solid system. Herein, we report a novel liquid-liquid-solid system to regulate the selectivity of benzyl alcohol electrooxidation. The selectivity of benzaldehyde increases 200-fold from 0.4 % to 80.4 % compared with the liquid-solid system at a high current density of 136 mA cm-2 , which is the highest one up to date. In the tri-phase system, the benzaldehyde peroxidation is suppressed efficiently, with the conversion of benzaldehyde being decreased from 87.6 % to 3.8 %. The as-produced benzaldehyde can be in situ extracted to toluene phase and separated from the electrolyte to get purified benzaldehyde. This strategy provides an efficient way to efficiently enhance the selectivity of electrocatalytic cascade reactions.

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.

Microscopic-Level Insights into the Mechanism of Enhanced NH3 Synthesis in Plasma-Enabled Cascade N2 Oxidation-Electroreduction System.

Integrated/cascade plasma-enabled N2 oxidation and electrocatalytic NOx- (where x = 2, 3) reduction reaction (pNOR-eNOx-RR) holds great promise for the renewable synthesis of ammonia (NH3). However, the corresponding activated effects and process of plasma toward N2 and O2 molecules and the mechanism of eNOx-RR to NH3 are unclear and need to be further uncovered, which largely limits the large-scale deployment of this process integration technology. Herein, we systematically investigate the plasma-enabled activation and recombination processes of N2 and O2 molecules, and more meaningfully, the mechanism of eNOx-RR at a microscopic level is also decoupled using copper (Cu) nanoparticles as a representative electrocatalyst. The concentration of produced NOx in the pNOR system is confirmed as a function of the length for spark discharge as well as the volumetric ratio for N2 and O2 feeding gas. The successive protonation process of NOx- and the key N-containing intermediates (e.g., -NH2) of eNOx-RR are detected with in situ infrared spectroscopy. Besides, in situ Raman spectroscopy further reveals the dynamic reconstruction process of Cu nanoparticles during the eNOx-RR process. The Cu nanoparticle-driven pNOR-eNOx-RR system can finally achieve a high NH3 yield rate of ∼40 nmol s-1 cm-2 and Faradaic efficiency of nearly 90%, overperforming the benchmarks reported in the literature. It is anticipated that this work will stimulate the practical development of the pNOR-eNOx-RR system for the green electrosynthesis of NH3 directly from air and water under ambient conditions.

Passivating the pH-Responsive Sites to Configure a Widely pH-Stable Emulsifier for High-Efficiency Benzyl Alcohol Oxidation.

Widely pH-stable emulsions configured by solid emulsifiers with high chemical stabilities and anti-corrosion properties under strong acid or alkaline conditions are highly sought after for practical and wide application of Pickering interfacial catalysis. Herein, a unique strategy was reported for synthesis of a widely pH-stable and novel emulsifier by passivating the pH-responsive sites on graphene oxide nanoribbon (GONR) surface using ionic liquid (IL). The suitable wettability of GONR-IL was derived from the positive binding energy between IL and water, which ensured the stability of the emulsion in a wide pH range. Benefiting from the passivated surface chemistry of GONR, the emulsion microreactor stabilized by GONR-IL exhibited a remarkable stability over a wide range of pH values. A GONR-IL-supported Pd catalyst stabilized at the toluene-water interface achieved an excellent emulsion catalytic activity for benzyl alcohol oxidation (conversion of 92 %), which was exceedingly higher than that of Pd/GONR (<1 %), Pd/CNTs-IL (51 %), or Pd/GO-IL (8 %).

Recognition of Water-Induced Effects toward Enhanced Interaction between Catalyst and Reactant in Alcohol Oxidation.

Pickering emulsion stabilized by solid nanoparticles provides a diverse solvent microenvironment and enables to promote the phase transfer of reaction substrates/products in catalytic reactions, but the intrinsic role of solvent is still not clear. Herein, using benzyl alcohol (BA) as a model reactant, we demonstrate the nature of the water-promoted activity for alcohol oxidation over the Pd/MgAl-LDO catalyst. Depending on the water in the solvent, we observe different reactivities regarding the proportion of the water in the system. Kinetic isotope effects confirm the participation and positive effects of water for oxidation of BA. The water promotion effects are recognized and identified by the water vapor pulse adsorption coupled with temperature program desorption. Moreover, the adsorption behavior of BA or benzaldehyde at the interface of water and Pd/MgAl-LDO is also investigated by quasi-in-situ Raman spectroscopy. In addition, the mechanism of water-promoted alcohol oxidation is rationally proposed based on the Langmuir-Hinshelwood mechanism. The general applicability of the water promotion effects is further demonstrated over different supports and substrates, which well achieves excellent catalytic activity and selectivity in Pickering emulsion compared to that in the pure toluene system.

Low-Temperature Fast Production of Carbon and Acetic Acid Dual-Promoted Pd/C Catalysts.

The Pd/C catalysts are widely used in synthesis of fine chemicals in industry, but their production suffers from a complicated two-step process involving impregnation and reduction, and requires large amounts of solvents and reductant, which would lead to a series of issues such as time consumption, resource waste and environmental pollution. Herein, ultra-small Pd nanoparticles uniformly anchored on carbon nanotubes (Pd/CNTs) were synthesized by using a one-pot and low-temperature reduction strategy. The present process/technology is very sensitive to and controlled by the supports and solvents, and the carbon support and acetic acid synergistically play crucial and decisive roles in the fast production of Pd/C catalysts. Also, the used solvents can be recycled and reutilized, which meets the requirements of sustainable chemistry and green economy. When the as-obtained Pd/CNTs catalyst was used to catalyze the oxidation of benzyl alcohol to benzaldehyde, it achieved a conversion efficiency as high as 99.3 % and a high selectivity up to >99.9 %. The simple, scalable and environmentally friendly strategy can be extended to anchor Pd nanoparticles on various carbon substrates, which sheds a new light on the synthesis of Pd/C catalysts.

Copper-catalysed intramolecular O-arylation: a simple and efficient method for benzoxazole synthesis.

A wide range of 2-substituted benzoxazoles can be efficiently synthesized from N-(2-iodo-/bromo-phenyl)benzamides, and even the less reactive N-(2-chlorophenyl)benzamides, via Cu-catalysed intramolecular coupling cyclization reactions using methyl 2-methoxybenzoate as the ligand under mild reaction conditions. In addition, the benzoxazoles can be easily prepared from the primary amides coupling with o-dihalobenzenes in a single step.