Selective Conversion of Propane by Electrothermal Catalysis in Proton Exchange Membrane Fuel Cell

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Selective Conversion of Propane by Electrothermal Catalysis in Proton Exchange Membrane Fuel Cell

Combining electrosynthesis with thermocatalysis: A strategy for efficient conversion of propane to high value-added C3 oxygenated products is developed by coupling the electrosynthesis of H2O2 on oxygen-doped carbon electrocatalyst for 2e− oxygen reduction reaction with thermocatalysis of propane oxidation over MIL-53 (Al, Fe) active sites in the proton exchange membrane fuel cell.


Abstract

Electrochemical conversion of alkanes to high value-added oxygenated products under a mild condition is of significance. Herein, we effectively couple the electrocatalysis of H2O2 with the thermo-catalysis of propane oxidation in the cathode of proton exchange membrane fuel cell. Specifically, H2O2 is in-situ generated on the nitric acid-treated carbon black (C-acid) via 2e− process of oxygen reduction reaction, and then transports to the Fe active sites of MIL-53 (Al, Fe) metal–organic frameworks for propane oxidation. Based on this strategy, the space-time yield of C3 oxygenated products of propane oxidation reaches 2.65 μmol h−1 cm−2, which represents a new benchmark for electrochemical alkane oxidation in the fuel-cell-type electrolyzer. This study highlights the importance of multifunctional composite catalysts in the field of electrosynthesis.

Merging Organocatalysis and Photocatalysis: A New Momentum in Covalent Radical Catalysis

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Merging Organocatalysis and Photocatalysis: A New Momentum in Covalent Radical Catalysis

This Concept article describes the contribution of photocatalysis in the field of covalent radical catalysis to control the generation and reactivity of radical catalysts. The synthetic perspectives offered by such catalytic combinations are discussed from a mechanistic point of view.


Abstract

The use of free radicals as organocatalysts constitutes a powerful strategy to activate and functionalize unsaturated carbon chains. Indeed, the unique affinity of open-shell species for alkenes and alkynes can be rerouted to achieve the catalytic covalent activation of the substrate and control a subsequent radical cascade. However, the field of covalent radical catalysis has remained challenging for decades due to important issues in terms of catalyst handling, reaction design and viability. Recently, these pitfalls have been addressed one by one by the use of photocatalysis to control the generation and the reactivity of radical catalysts. This Concept article aims to highlight recent achievements in the field of photocatalyzed covalent radical catalysis and the perspectives offered by such catalytic combinations. The reaction mechanisms and the interconnection between the catalytic cycles are reviewed with the hope of demonstrating the synthetic potential of this approach and foster a rapid growth of this nascent topic.

Experimental and Theoretical Structure Elucidation of the [2 : 1] Complex Ion of Carbo[n]helicene with n=6, 7 and 8 and Ag+

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Experimental and Theoretical Structure Elucidation of the [2 : 1] Complex Ion of Carbo[n]helicene with n=6, 7 and 8 and Ag+

Gas-phase complexes of [n]helicenes with n=6, 7 and 8 and silver(I) cation are generated. Besides the well-established [1 : 1] helicene/Ag+-complex in which the helicene provides a tweezer-like surrounding for the Ag+, there is also a [2 : 1] complex formed. The second helicene attaches via π-π stacking to the first helicene of the [1 : 1] tweezer complex. Using [n]helicene mixtures, tweezer complexes of Ag+ are preferably formed with the larger helicenes.


Abstract

Gas-phase complexes of [n]helicenes with n=6, 7 and 8 and the silver(I) cation are generated utilizing electrospray ionization mass spectrometry (ESI-MS). Besides the well-established [1 : 1] helicene/Ag+-complex in which the helicene provides a tweezer-like surrounding for the Ag+, there is also a [2 : 1] complex formed. Density functional theory (DFT) calculations in conjunction with energy-resolved collision-induced dissociation (ER-CID) experiments reveal that the second helicene attaches via π-π stacking to the first helicene, which is part of the pre-formed [1 : 1] tweezer complex with Ag+. For polycyclic aromatic hydrocarbons (PAHs) of planar structure, the [2 : 1] complex with silver(I) is typically structured as an Ag+-bound dimer in which the Ag+ would bind to both PAHs as the central metal ion (PAH–Ag+–PAH). For helicenes, the Ag+-bound dimer is of similar thermochemical stability as the π-π stacked dimer, however, it is kinetically inaccessible. Coronene (Cor) is investigated in comparison to the helicenes as an essentially planar PAH. In analogy to the π-π stacked dimer of the helicenes, the Cor−Ag+−Cor−Cor complex is also observed. Competition experiments using [n]helicene mixtures reveal that the tweezer complexes of Ag+ are preferably formed with the larger helicenes, with n=6 being entirely ignored as the host for Ag+ in the presence of n=7 or 8.

Fabrication of Hyperbranched Photomechanical Crystals Composed of a Photochromic Diarylethene

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Fabrication of Hyperbranched Photomechanical Crystals Composed of a Photochromic Diarylethene

The sublimation process where the thin films of 1,2-bis(2,5-dimethyl-3-thienyl)perfluorocyclopentene are formed on a concave surface of the spherical glass substrate, accompanying the movement of boundaries between the thin film domains under the higher relative humidity condition, leads to the fabrication of the hollow crystals having the highly branched shapes.


Abstract

We report the fabrication of hyperbranched hollow crystals of 1,2-bis(2,5-dimethyl-3-thienyl)perfluorocyclopentene on a concave surface of the spherical glass substrate by sublimation and their practical photomechanical behaviors. The number of units of the branched structure of the hollow crystals composed of this compound is proportional to the substrate curvature of the substrate. Compared with the sublimation process of the same compound on the flat glass substrate, two kinds of the thin film domains are generated separately in the center and around the edge of the spherical glass substrate. Especially under the high relative humidity condition, the boundaries between these thin film domains move gradually around the edge through the center during as long as 6 h of sublimation time so that the hyperbranched hollow crystals are densely produced on the entire surface of the substrate. These hyperbranched hollow crystals can be prepared with the highly ordered molecular packing due to the very slow formation process of the crystalline walls of the hollow structures. Furthermore, the photo-induced bending behaviors in the few- and highly-branched hollow crystals have the practical roles in moving and bending the minute objects according to their characteristics of these branched shapes.

Flexible Composites for Piezocatalysis

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Despite piezoelectric materials have a long history of application, piezoelectric catalysis has continued to be a hot topic in recent years. Flexible piezoelectric materials have just emerged in recent years due to their versatility and designability. In this paper, we review the recent advances in flexible piezoelectric materials for catalysis, discuss the fundamentals of the catalytic properties of composite materials, and detail the typical structures of these materials. We pay special attention to the types of filler in flexible piezoelectric composites, their role and the interaction between the particles and the flexible substrate. Notable examples of flexible piezoelectric materials for organic pollutants degradation, enhanced piezo-photocatalysis and antibacterial are also presented. Finally, we present key issues and future prospects for the development of flexible piezoelectric catalysts.

Purification and Fractionation of Lignin via ALPHA: Liquid–Liquid Equilibrium for the Lignin–Acetic Acid–Water System

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In order to effectively practice the Aqueous Lignin Purification with Hot Agents (ALPHA) process for lignin purification and fractionation, the temperatures and feed compositions where regions of liquid–liquid equilibrium (LLE) exist must be identified. To this end, pseudo-ternary phase diagrams for the lignin–acetic acid–water system were mapped out at 45-95 °C and various solvent: feed lignin mass ratios (S:F). For a given temperature, the accompanying SL (solid–liquid), SLL (solid–liquid–liquid), and one-phase regions were also located. For the first time, ALPHA using acetic acid (AcOH)–water solutions was applied to a lignin recovered via the commercial LignoBoost process. In addition to determining tie-line compositions for the two regions of LLE that were discovered, the distribution of lignin and key impurities (the latter can negatively impact lignin performance for materials applications) between the two liquid phases was also measured. As a representative example, lignin isolated in the lignin-rich phase was reduced 7x in metals and 4x in polysaccharides by using ALPHA with a feed solvent composition of 50-55% AcOH and an S:F of 6:1, with said lignin being obtained at a yield of 50-70% of the feed lignin and having a molecular weight triple that of the feed.

Tailoring Cu Electrodes for Enhanced CO2 Electroreduction through Plasma Electrolysis in Non‐Conventional Phosphorus‐Oxoanion‐Based Electrolytes

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Tailoring Cu Electrodes for Enhanced CO2 Electroreduction through Plasma Electrolysis in Non-Conventional Phosphorus-Oxoanion-Based Electrolytes

Plasma electrolysis of Cu electrodes in P-based electrolytes generates distinct surface structures, including octahedral nanocrystals, besides nanoporous and microporous features. Cu electrodes polarized in Na2HPO3 and Na3PO4 exhibit high selectivity for C2 products, establishing in-liquid plasma as an attractive option for developing efficient Cu electrocatalysts for sustainable CO2 conversion.


Abstract

This study presents a green, ultra-fast, and facile technique for the fabrication of micro/nano-structured and porous Cu electrodes through in-liquid plasma electrolysis using phosphorous-oxoanion-based electrolytes. Besides the preferential surface faceting, the Cu electrodes exhibit unique surface structures, including octahedral nanocrystals besides nanoporous and microporous structures, depending on the employed electrolyte. The incorporation of P-atoms into the Cu surfaces is observed. The modified Cu electrodes display increased roughness, leading to higher current densities for CO2 electroreduction reaction. The selectivity of the modified Cu electrodes towards C2 products is highest for the Cu electrodes treated in Na2HPO3 and Na3PO4 electrolytes, whereas those treated in Na2H2PO2 produce the most H2. The Cu electrode treated in Na3PO4 produces ethylene (23 %) at −1.1 V vs. RHE, and a comparable amount of acetaldehyde (15 %) that is typically observed for Cu(110) single crystals. The enhanced selectivity is attributed to several factors, including the surface morphology, the incorporation of phosphorus into the Cu structure, and the formation of Cu(110) facets. Our results not only advance our understanding of the influence of the electrolyte's nature on the plasma electrolysis of Cu electrodes, but also underscores the potential of in-liquid plasma treatment for developing efficient Cu electrocatalysts for sustainable CO2 conversion.