Journal of Chemical Sciences最新文献

Hydrophobic surface modification is an emerging concept for electrochemical gas-phase reactions like nitrogen reduction reaction to ammonia as the restricted surface wettability helps to surpass the competitive hydrogen evolution reaction. However, the extensive studies on this strategy lack a discussion on the influence of substrates on the stability of the hydrophobic coating. The present work summarizes a case study on the substrate-dependent electrochemical behaviour of the alkanethiol-coated flattened Cu foil and porous dendritic Cu foam surfaces. NRR studies reveal that the porous dendritic architecture with electrified tips and the hydrophobic coating-induced gas diffusion layer proved to be beneficial for NRR activity in Cu foam-SH. However, for a prolonged experimental hour, the flattened surface of the Cu foil could better hold the hydrophobic coating. The results corresponded with water contact angle as well as double layer capacitance measurements and a detailed X-ray photoelectron spectroscopy study. It is supposed that the prolonged exposure to applied potential alters the polarization of the Cu dendritic tips and weakens the Cu–S bond, loosening the alkanethiol layer over Cu foam.

Graphical abstract

Hydrophobic Cu substrates facilitate electrochemical nitrogen reduction reactions owing to the better N₂ diffusion and trapping underneath the hydrophobic coating. While the NRR activity gets accelerated at the electrified dendritic tips of Cu foam, the steady hydrophobic layer over the flattened Cu foil surface ascertains long-term use of the material.

For relatively newer developments such as Li–S battery, polysulphide shuttle effect, volume expansion, and low conductivity of sulphur have been the main hurdles in the path towards its commercialisation. To get rid of the polysulphide shuttle effect, we looked at the binder material of the cathode component. An attempt at keeping up with the capacity while making components sustainable led us to explore a protein-based biopolymer, zein. The carbonyl-rich binder helped to glue the components together while the long chain of amino acids aided in preserving the performance. The UV-visible spectroscopy technique verified the adsorption of polysulphides by zein and activated carbon. The carbon host used for this study possessed a high Bruner Emmet Teller (BET) surface area of around 1900 m² g^–1, which helped to load higher amounts of sulphur, as revealed by thermogravimetric analysis. Owing to a porous host, the volume expansion effect could also be buffered to maintain the performance as observed through stability studies. The cycling study of zein binder containing cathode showed an enhanced performance of around 100 mAh g^–1 throughout the 250 cycles compared to the PVDF binder containing cathode.

Catalysts based on KL-zeolite exchanged with alkali metal ions (Rb⁺ and Cs⁺) were studied for conversion of ethanol to oligomerization through the Guerbet reaction pathway. The catalysts were characterized by techniques such as ICP-AES, FESEM-EDX, N₂-adsorption-desorption, and CO₂-TPD to assess their physio-chemical properties. Effects of operating parameters, namely reaction temperature, pressure, and feed flow rate on catalytic activity for the conversion of ethanol to n-butanol were examined. Furthermore, influence of alkali metal loading on KL-zeolite was explored. Substantial ethanol conversion (42.6%) and n-butanol yield (13.9%) were achieved at 450°C and 30 kg/cm² after a 6 h reaction employing Cs-KL zeolite catalyst. Observations indicated that the butanol selectivity is highest among the reported literature. Additionally, this catalyst has exhibited low deactivation rate attributable to coke formation. Spent catalysts were studied for XRD and DTG/TGA analysis. Present investigation establishes that KL-zeolite, particularly when modified with alkali metal ions, proves to be an efficient catalyst for the Guerbet conversion of ethanol, highlighting its potential for ethanol upgrading.

Efficient and durable non-precious cathode catalysts are needed at this hour for the development of fuel cells and metal-air batteries. The instability of one of the well-studied non-precious catalysts, Fe–N–C, in acidic electrolytes and its inferior bifunctional electrocatalytic activity in alkaline electrolytes, shifts the attention towards other electrocatalysts based on Ni and Co. Herein, we demonstrate the synthesis of nitrogen and transition metal (M=Co, Ni) co-doped mesoporous carbon (Co/Ni–N–mC) catalysts for bifunctional oxygen electrocatalysis. The synthetic approach involves the thermal annealing-induced transformation of the graphitic carbon nitride (g–C₃N₄) to nitrogen-doped graphitic mesoporous carbon (N–mC). The Co–N–mC catalyst has superior bifunctional oxygen electrocatalytic activity. It promotes the 4-electron pathway for the reduction of oxygen to water and is highly durable in alkaline electrolyte. The bifunctional activity is evaluated in terms of the potential gap (ΔE). The small ΔE for Co–N–mC makes it suitable for metal-air batteries. The rechargeable zinc-air battery is fabricated with Co–N–mC and it delivers a specific capacity of 718 mAh g⁻¹_Zn and a power density of 122.2 mW/cm² with long-time charge-discharge cycling stability for 100 h. The synergistic effect between metal nanoparticles and nitrogen-doped carbon matrix, as well as the post-synthetic surface engineering-induced morphological changes, account for the enhanced activity.

Graphical abstract

The transformation of supramolecular aggregate-derived metal-doped graphitic carbon nitride to electrocatalytically highly active nitrogen-doped mesoporous carbon and its electrocatalytic performance for aqueous rechargeable zinc-air battery is demonstrated.

In this work, we present the CO oxidation by molecular and atomic oxygen on the Cu₃ site of the Cu₁₉ cluster employing the density functional theory (DFT)-PW91PW91/[LANL2DZ, 6-31G(d)] level. The computed results demonstrate that the O atom, O₂, and CO molecule adsorptions on the copper cluster are all chemical. For the CO oxidation by O₂ molecules that leads to the formation of C–O bonds and the dissociation of O–O bonds, the Langmuir–Hinshelwood (LH) mechanism is preferred. On the other hand, the Eley–Rideal (ER) mechanism is slightly favored by the oxidation of CO by atomic oxygen. According to the intrinsic reaction coordinate (IRC) calculation, the activation energy for CO oxidation is 4.02 kcal/mol for molecular oxygen and 3.17 kcal/mol for atomic oxygen. Therefore, molecular and atomic oxygen are very reactive for CO oxidation on the Cu₁₉ cluster. To check the applicability of the global hardness response (GHR) profile satisfying the maximum hardness principle along the IRC in the metal cluster reactions, the GHR profile for the oxidation reaction of CO with molecular oxygen and atomic oxygen was computed. The results indicate that this meets the principle of maximum hardness, effectively showcasing the use of DFT methods to analyze the global hardness profile using frontier molecular orbital energy in the context of metal cluster reaction pathways.

Graphical abstract

The CO oxidation by molecular and atomic oxygen on the Cu₃ site of the Cu₁₉ cluster employing the density functional theory has been studied. The results show that the CO oxidation by atomic oxygen slightly favors the Eley–Rideal (ER) mechanism, while the CO oxidation by molecular oxygen prefers the Langmuir–Hinshelwood (LH) mechanism. Both molecular and atomic oxygen are very reactive for CO oxidation. Furthermore, the global hardness profile along the intrinsic reaction coordinate follows the maximum hardness principle.

This paper discusses synthesizing green, recyclable, heterogeneous nickel–chromium oxide (NiCr₂O₄) catalyst and its application in solvent-free, room-temperature Knoevenagel condensation reaction. Nickel–chromium oxides (Ni–Cr oxides) were prepared using the coprecipitation method in various proportions, such as 2:1, 1:1, and 1:2 ratios. The synthesized catalysts were characterized using X-ray diffraction, SEM-EDX, and BET-surface area analysis. The synthesized catalysts were employed as heterogeneous catalysts in the Knoevenagel condensation model reaction of 4-chlorobenzaldehyde and malononitrile under room temperature, solvent-free grinding reaction conditions, and the results were compared. This paper will discuss the most suitable catalyst and its possible mechanism.

A study on the interaction of non-metal oxide with water is very critical in order to understand the formation of acidic species and polyanions. It is very easy to understand the interaction of non-metal oxides with water by employing density functional theory (DFT). First-principles DFT is used to simulate the water cluster with three-dimensional continuums by defining a supercell with dimensions (13.49 times 12.696 times 3.174) ų. The geometry-optimized non-metal oxides are placed on the water clusters and allow for interactions. The geometry and stability of the chemical species formed are discussed and the results are correlated with the experiments. The phonon calculations are also carried out to confirm the chemical species formed and match well with the literature.

Graphical abstract

First-principles DFT is used to simulate the water cluster with three-dimensional continuums by defining a supercell with dimensions (13.49 times 12.696 times 3.174 ) ų. Interactions of water cluster with non-metal oxides furnished H₂CO₃, ({text{HSO}}_{3}^{-}), ({text{SO}}_{4}^{2-}), and ({text{NO}}_{3}^{-}) for CO₂, SO₂, SO₃, and ({{text{N}}_{2}text{O}}_{5}) respectively

The Sonogashira coupling reaction and hydration of nitriles were demonstrated using a facile catalytic system comprising a readily available cobalt salt and an environmentally friendly room-temperature ionic liquid, choline hydroxide (ChOH). The present system offers an alternative pathway for constructing C_sp–C_sp2 bonds through the alkynylation of aryl iodides in an aqueous environment, without the need for palladium- or copper-metal catalysts, phosphine ligands, or any external bases, albeit with some limited scope. Building upon the advantages and drawbacks of the present system employed in the Sonogashira coupling, we further extend its application to showcase the conversion of nitriles into amides, revealing the respective roles of ChOH and cobalt salt in the hydration of nitriles.

Graphic Abstract

The Sonogashira coupling and nitrile hydration were accomplished with cobalt salt and choline hydroxide (ChOH). Aryl iodides underwent alkynylation without external additives, albeit with limitations. Roles of ChOH and cobalt salt in nitrile hydration were also demonstrated.

Dinitrogen and dihydrogen ligated metal complexes [(L)_nM−H₂/N₂] have been known to chemists for nearly four decades. These species are captivating for their unusual bonding interactions between transition metal atoms and closed-shell diatomic molecules like H₂/N₂. Some of these complexes are part of the textbook, with emphasis given to their surprising stability, often without the formation of an electron-sharing M−H₂/N₂ bond. The nature of chemical bonding in these complexes is speculated due to M−H₂/N₂ bond distances and mode of binding (side-on or end-on). In the past, spectroscopic and other tools have studied the nature of the chemical bonds. We report on the energy decomposition analysis coupled with natural orbital for chemical valence (EDA-NOCV) calculations to shed light on the deeper insight of the quantitative pairwise bonding interactions in previously isolated/reported (L)Co−N₂ and (L)Co−H₂ complexes [L = three P- and one E-donor ligand; E = Si, B; Co is either Co(I) or Co(0)]. A comparative EDA-NOCV analysis shows that N₂ is a better π-acceptor while, in contrast, H₂ is a superior σ-donor although both ligands (H₂, N₂) are σ-donor and σ/π-acceptor. The extent of backdonation from Co to H₂/N₂ also depends on E atoms of the chelating ligands (L). The overall intrinsic interaction energy of the Co−N₂ bond is significantly higher by 5–10 kcal/mol than that of the Co−H₂ bond. EDA-NOCV analyses have also studied two Fe−H₂ complexes.

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