Monthly Archives: March 2024

2D Boron Nanosheets for Photo‐ and Electrocatalytic Applications

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2D Boron Nanosheets for Photo- and Electrocatalytic Applications

Two-dimensional boron nanosheets (borophene) exhibit promising catalytic properties for energy and environmental applications. This review summarizes the theoretical and experimental applicability of borophene and its heterostructures towards efficient hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), CO2 reduction reaction (CO2RR), N2 reduction reaction (N2RR), photocatalytic degradation, etc.


Abstract

Borophene, a new member of the two-dimensional (2D) materials family, has attracted researchers since its first experimental synthesis. Borophene (2D boron nanosheet) differs significantly from other 2D materials due to its low energy requirement to form defects, anisotropy, electron-deficient structure, multicentered bonding, etc. The uniqueness in properties of borophene compared to other 2D materials makes it suitable for applications in catalysis, sensing, energy storage, etc. The present review summarizes the development of borophene synthesis and emphasizes its applications in catalysis. Different synthesis approaches and their advantages and limitations are discussed briefly as substantial reviews are available on borophene synthesis. The applications of pristine borophene and their modified heterostructure in the field of catalysis were thoroughly reviewed, focusing on the electrocatalysis applications. Finally, the review discussed the future scope of borophene in designing new materials as well as opportunities to be utilized for other application fields. Since there is a lack of a good number of experimental reports on the applications of borophene and its derivatives, a huge opportunity is waiting for the researchers to explore the unknown world of borophene. In this regard, this review will help the researchers in an excellent manner.

Solution Combustion Synthesis of Ce‐based Composite Oxygen Carriers for Chemical Looping Reforming of Methane

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Solution Combustion Synthesis of Ce-based Composite Oxygen Carriers for Chemical Looping Reforming of Methane

Solution combustion is an efficient, simple and fast method to prepare oxygen carriers for the chemical looping reforming of methane, which can yield oxygen carriers with high reactivity and excellent cyclic stability.


Abstract

Efficient activation and the conversion of methane to value-added products have long attracted interest. Chemical looping reforming has become a competitive technology to transform methane into syngas that can act as raw material for various chemicals. In this paper, the methane chemical looping reforming reactivity of the Ce−Co composite oxygen carriers fabricated with different preparation methods, including solution combustion, ball-milling, hydrothermal, and co-precipitation method, are investigated on a fixed-bed. Various bulk/surface characterizations (TEM, XRD, BET, XPS, Raman, etc.) were applied to reveal the effect of preparation methods on the properties of these oxygen carriers. The results indicate that the oxygen carrier prepared by the solution combustion method exhibits excellent methane conversion, high syngas yield, and desirable H2/CO ratio, as well as stable regenerability because of its relatively small crystal size, large specific surface area, high oxygen vacancy concentration and Ce3+/Ce4+ ratio. This work may be helpful in the preparation of highly active and stable oxygen carriers for chemical looping reforming reaction of methane.

Photocatalytic Water Splitting for H2 Production via Two‐electron Pathway

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Photocatalytic Water Splitting for H2 Production via Two-electron Pathway

Photocatalytic water splitting via two-electron pathway offers a more fascinating and kinetically favorable way to produce H2 compared with traditional four-electron pathway. The review highlights the mechanism and advancements of photocatalytic H2 production via a two-electron pathway. Additionally, it addresses the challenges and opportunities for the commercial application of photocatalytic water splitting via the two-electron pathway.


Abstract

In response to energy and environmental crises, solar-driven pure water splitting is a promising way to produce and store renewable energy sources without environmental pollution. Photocatalytic water splitting via two-electron pathway (2H2O→H2+H2O2) is a more kinetically favorable way to produce H2 compared with traditional four-electron pathway. Although numerous efforts have been devoted to investigate the application of two-electron pathway water splitting, drawbacks still inhibit the efficiency of H2 generation. This review discusses the mechanism and challenges of photocatalytic water splitting via a two-electron pathway. Then, recent developments in novel photocatalyst preparation and modification strategies for effective H2 generation via two-electron pathway were discussed, such as morphology and structure modulation, elemental doping, co-catalyst loading, and heterostructure construction. In addition, the development of stepwise two-electron pathway which further decomposed H2O2 and release O2 was also introduced. Appropriate co-catalyst with high H2O2 decomposition activity that is essential for stepwise process was discussed. Finally, challenges and opportunities for commercial application of photocatalytic water splitting via two-electron pathway were briefly outlined.

Studying the structure‐reactivity relationship of CuO/CeO2 for catalytic soot particulate combustion: on the monolayer dispersion threshold effect

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Studying the structure-reactivity relationship of CuO/CeO2 for catalytic soot particulate combustion: on the monolayer dispersion threshold effect

The surface-active oxygen amount increases with the increasing of CuO loading until it reaches the monolayer dispersion capacity, at which the most active catalyst is obtained. The surface active O2 − sites play an important role for soot combustion.


Abstract

To elucidate structure-reactivity relationship and prepare improved catalysts for soot combustion, a series of CuO/CeO2 with different loadings have been fabricated by the impregnation method. With XRD and XPS extrapolation methods, it is disclosed that CuO disperses finely on the CeO2 support to form a monolayer with a capacity around 1.06 mmol 100 m−2, which equals to 2.9 wt. % CuO loading. Below this capacity, CuO is in a sub-monolayer state. However, above this capacity, CuO micro-crystallites are formed, and co-exist with the monolayer CuO. By increasing CuO loading, soot combustion activity of the catalysts increases as well until it reaches the monolayer dispersion capacity. Further increasing the CuO loading to 5 % decreases the activity slightly, and then remains constant. Therefore, an apparent monolayer dispersion threshold effect is observed for soot combustion on CuO/CeO2 catalysts. It is found that the amount of surface-active O2 − sites plays critical role for the catalytic activity. To obtain the most active CuO/CeO2 catalyst, a monolayer amount of CuO should be loaded on the supports.

Chemodivergent Dehydrogenative Coupling of Alcohols by 3d Metal Catalysts

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Chemodivergent Dehydrogenative Coupling of Alcohols by 3d Metal Catalysts

Text for Table of Contents: An overview of the chemodivergent dehydrogenative coupling of alcohols by the Earth-abundant transition metal catalysts is discussed.


Abstract

Chemodivergent synthesis by transition metal catalysts is a straightforward and sustainable approach to achieving valuable organic compounds. Especially, the chemodivergent dehydrogenative couplings of alcohols with organic motifs to develop various saturated and unsaturated compounds are highly environmentally benign due to the reduced waste generation. In this concept review, we presented the 3d transition metal (Mn, Fe, Co, and Ni)-catalyzed chemodivergent synthesis of imines and amines, saturated and unsaturated carbonyl/alcohol compounds, saturated and unsaturated nitriles, N-heterocycles, and N-/C-alkylated indoles. The discussed reaction commanded two or three different products with high chemoselectivity by changing specific reaction parameters, but keeping the catalyst unchanged. Generally, the acceptorless dehydrogenative coupling (ADC) provides unsaturated moieties, whereas the borrowing-hydrogen (BH) process results in saturated compounds.

Reaction of (N4Py)Fe with H2O2 and the relevance of its Fe(IV)=O species during and after H2O2 disproportionation

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Reaction of (N4Py)Fe with H2O2 and the relevance of its Fe(IV)=O species during and after H2O2 disproportionation

Catalytic decomposition of H2O2 by an iron catalyst is shown to via a Fe(III)OOH intermediate. Surprisingly the expected homolysis of the O−O bound to yield Fe(IV)=O species does not occur significantly and oxidation products are due to radical chain reactions.


Abstract

The catalytic disproportionation of by non-heme Fe(II) complexes of H2O2 the ligand N4Py (1,1-bis(pyridin-2-yl)-N,N-bis(pyridin-2-ylmethyl)methanamine) and the formation and reactivity of Fe(III)-OOH and Fe(IV)=O species is studied by UV/Vis absorption, NIR luminescence, (resonance) Raman and headspace Raman spectroscopy, 1O2 trapping and DFT methods. Earlier DFT studies indicated that disproportionation of H2O2 catalysed by Fe(II)-N4Py complexes produce only 3O2, however, only the low-spin state pathway was considered. In the present study, DFT calculations predict two pathways for the reaction between Fe(III)-OOH and H2O2, both of which yield 3O2/H2O2 and involve either the S=1/2 or the S=3/2 spin state, with the latter being spin forbidden. The driving force for both pathways are similar, however, a minimal energy crossing point (MECP) provides a route for the formally spin forbidden reaction. The energy gap between the reaction intermediate and the MECP is lower than the barrier across the non-adiabatic channel. The formation of 3O2 only is confirmed experimentally in the present study through 1O2 trapping and NIR luminescence spectroscopy. However, attempts to use the 1O2 probe ( -terpinene) resulted in initiation of auto-oxidation rather than formation of the expected endoperoxide, which indicated formation of OH radicals from Fe(III)-OOH, e. g., through O−O bond homolysis together with saturation of methanol with 3O2. Microkinetic modelling of spectroscopic data using rate constants determined earlier, reveal that there is another pathway for Fe(III)-OOH decomposition in addition to competition between the reaction of Fe(III)-OOH with H2O2 and homolysis to form Fe(IV)=O and hydroxyl radical. Notably, after all H2O2 is consumed the decay of the Fe(III)-OOH species is predominantly through a second order self reaction (with Fe(III)-OOH). The conclusion reached is that the rate of O−O bond homolysis in the Fe(III)-OOH species to form Fe(IV)=O and an hydroxyl radical is too low to be responsible for the observed oxidation of organic substrates.

CO2 Photoreduction Product Selectivity with TiO2−Cu Nanocatalysts under Different Reaction Media

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CO2 Photoreduction Product Selectivity with TiO2−Cu Nanocatalysts under Different Reaction Media

Targeting the CO2 photoreduction products with the TiO2−Cu catalyst can be done by changing the electrolytes in the reaction medium. Alkaline pH causes greater ethanol production, while acidified media favor the evolution of H2 in the presence of sodium oxalate. Furthermore, acetic acid caused a large production of methanol, resulting from the cleavage of the acid‘s carbon bond.


Abstract

This study explores photocatalytic conversion of CO2 using TiO2−Cu heterojunctions with different Cu contents and investigates influence of different reaction media on the process efficiency. The use of KOH favored liquid products, especially ethanol. An analysis of H2 production as the main competitive reaction was done. Sodium oxalate led to an increase in H2 evolution by approximately 600 μmol g-1 compared to pure water, in the presence of CO2 in the reaction medium, but the blank test (without CO2) indicates a lower H2 yield (~136 μmol g−1), which suggests that the competitive reaction with CO2 also plays a role in H2 production. This role was related to the decrease of the initial pH from approximately 8.5 to 5.2, stabilizing at 5.5 at the end of the 6 h reaction. In an environment saturated with N2, the pH increases to 9 and stabilizes at 7.8 at the end of the process. In the presence of acetic acid, both CO and H2 production were suppressed, with a significant increase in the selectivity for methane via cleavage of the acid‘s carbon bond. The findings underscore the importance of optimizing reaction conditions to achieve higher yields of desired products in the photocatalytic conversion of CO2.

Deamination‐ or N‐nitrosation‐based methods for m6A Profiling

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Abstract

The addition of various chemical modifications to RNA introduces an additional layer of complexity to the regulation of gene expression. Among all RNA modifications, N 6-methyladenosine (m6A) has earned its status as the most abundant and well-studied post-transcriptional modification in mammalian mRNA. Nevertheless, understanding the role of m6A in shaping the fate of RNA molecules and its influence on gene expression heavily depends on the development and application of detection technologies. Among all m6A detection methods, chemical-based sequencing methods show unique advantages. Our group recently developed an absolute quantification method named GLORI, which employs nitrite and glyoxal to convert adenosine to inosine efficiently. With its potential to emerge as the gold standard for m6A detection, GLORI showcases the promise of nitrite-based approaches. This review provides a comprehensive overview of m6A detection techniques based on deamination or nitrosation, evaluating their strengths and limitations. Furthermore, we offer insights into the future directions of innovative approaches in m6A profiling.

Methylation of Phenyl Rings in Ester‐Stabilized Phosphorus Ylides Vastly Enhances Their Protonophoric Activity

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Methylation of Phenyl Rings in Ester-Stabilized Phosphorus Ylides Vastly Enhances Their Protonophoric Activity

An ester-stabilized triphenylphosphonium ylide precursor can carry protons across artificial and natural membranes. Methylation of aryl groups together with alkyl length shortening of this protonophore preserving its lipophilicity resulted in a 20-fold increase in the flip-flop rate constant of its cationic form. Accordingly, increased proton transport across lipid membranes and enhanced uncoupling of mitochondria were observed.


Abstract

We have recently discovered that ester-stabilized phosphorus ylides, resulting from deprotonation of a phosphonium salt such as [Ph3PCH2COOR], can transfer protons across artificial and biological membranes. To create more effective cationic protonophores, we synthesized similar phosphonium salts with one ((heptyloxycarbonylmethyl)(p-tolyl)bromide) or two ((butyloxycarbonylmethyl)(3,5-xylyl)osphonium bromide) methyl substituents in the phenyl groups. The methylation enormously augmented both protonophoric activity of the ylides on planar bilayer lipid membrane (BLM) and uncoupling of mammalian mitochondria, which correlated with strongly accelerated flip-flop of their cationic precursors across the BLM.