Category Archives: ChemCatChem

Photoredox‐catalyzed Decyanative Radical Cross‐coupling Reactions of Aromatic Nitriles

Posted on 8 March 2024 by nFei Chao, nHai‐Bin Yang, nYanxiong Fangn

This review summarizes the recent advancements in photoredox-catalyzed decyanative functionalization of (hetero)aromatic nitriles which involves the cross-coupling between a persistent cyano-substituted aryl radical and a transient radical as the key step.

Abstract

(Hetero)arenes are one kind of important structural motifs existed extensively in clinical pharmaceutics, pesticides, and so on. Developing novel method for introducing (hetero)aryl group through the employment of cheap and abundant feedstocks has attracted considerable attentions from synthetic community. In this review, we summarize the recent advancements in photoredox-catalyzed decyanative cross-coupling reactions based on the persistent aromatic nitrile-derived radical. We separate the review into redox-neutral and reductive cross-coupling reactions according to whether an external reducing agent is required. The diverse strategies of overcoming the redox potential limitation of photocatalyst are emphasized in the discussion of specific reaction.

Regulation of Pt Loading on Co/Al2O3 Catalysts for Selective Hydrogenation and Hydrogenolysis of 5‐Hydroxymethylfurfural to 2,5‐Bis(hydroxymethyl)furan and 2,5‐Dimethylfuran

Posted on 8 March 2024 by

Highly selective production of 2,5-bis(hydroxymethyl)furan (>99 % yield) and 2,5-dimethylfuran (>86 % yield) towards hydrogenation and hydrogenolysis of 5-hydroxymethylfurfural were has been successfully discovered by regulating the nanosized Pt loading on Co/Al₂O₃ catalysts

Abstract

Selective hydrogenation and hydrogenolysis of 5-hydroxymethylfurfural (HMF) to 2,5-bis(hydroxymethyl)furan (BHMF) and 2,5-dimethylfuran (DMF) were explored by regulating the nanosized Pt on Co/Al₂O₃ catalysts. Characterization results revealed that the catalyst acidity was influenced by adjusting the Co/Pt composition, while the addition of more Pt loading on Co/Al₂O₃ catalysts resulted in a facilitation of H₂ reduction process. Lower size of catalyst particles was obtained for the Co−Pt system in comparison to the monometallic Co/Al₂O₃ catalyst. Additionally, the structural characterizations by XRD, XANES, and XPS established the co-existences between metallic Pt⁰/Co⁰ and oxophilic PtO₂/CoO_x, acting as the active components for the reactions. Operated under a full HMF conversion, the Co₁Pt_0.050Al catalyst with high Pt loading gave >99.9 % BHMF selectivity at 40 °C; whereas, an 86.7 % of DMF selectivity was noticeable over low Pt loading of the Co₁Pt_0.013Al catalyst at 160 °C. This investigation evidenced that the selective production of BHMF or DMF towards hydro-conversion of HMF was relied on the amount of Pt contents on Co/Al₂O₃ catalyst, in which the metal sizes and acidity had meaningful effects on the hydrogenation and hydrogenolysis processes.

Recent Advances in Hydrogen Production from Hybrid Water Electrolysis through Alternative Oxidation Reactions

Posted on 8 March 2024 by nLi Fan, nDi Wang, nKui Ma, nChang‐An Zhou, nHairong Yuen

In this review, we provide comprehensive overview of potential anodic oxidation systems that can replace OER, focusing on hybrid electrolysis of water. The advantages, challenges and outlooks of using alcohols and aldehydes, biomass derived compounds, amines, and other small molecules as anodes alternative reactants for electrolytic hydrogen production have been discussed in detail.

Abstract

Water splitting driven by green electricity from renewable energy input to produce H₂ has been widely considered as a promising strategy to realize the goals for future clean energy. However, in conventional overall water electrolysis, the sluggish kinetics and high onset potential of anode OER limit the cathode HER rate, which lowers the overall energy conversion efficiency. Over the past decade, an innovative concept involving hybrid water electrolysis by replacing OER with thermodynamically more favorable oxidation reactions coupling with the cathodic hydrogen evolution reaction has been devised to alleviate the limitations associated with the anodic OER. In this review, we summarize the recent progress concerning electrochemical hydrogen production by coupling the oxidation of molecules incorporating hydroxyl, aldehyde, and amino functional groups, with special emphasis on alternative reactions involving CO and sulfide. Finally, the remaining challenges and future perspectives are also discussed. We hope this review will accelerate the development of novel strategies for practicable H₂ production from hybrid water electrolysis.

Electrochemical Promotion of Bimetallic Palladium‐Cobalt Nano‐Catalysts for Complete Methane Oxidation

Posted on 8 March 2024 by

A comparison of electrochemical polarization of bimetallic Pd−Co nanoparticles for three methane oxidation reaction conditions resulted in the rate increase upon anodic polarization resulted in non-Faradaic electrochemical modification of catalytic activity (Λ≫1) in reducing and oxidizing conditions and Faradaic or electrochemical enhancement (Λ<1) in stoichiometric reaction conditions.

Abstract

The catalytic activity and electrochemical promotion of catalysis (EPOC) of the bimetallic Pd−Co nanoparticles (10 nm) deposited on yttria-stabilized zirconia were investigated for complete methane oxidation. The reaction was conducted under open-circuit and under polarization in a temperature range of 320–400 °C in reducing, stoichiometric, and oxidizing conditions. The catalytic activity of the catalyst nanoparticles increased to 40 % upon positive polarization in all gaseous compositions. A comparison of three reaction conditions revealed that the highest reaction rate increase (enhancement ratio, ρ=1.4) occurs under reducing conditions. The reaction rate increased upon anodic polarization, resulting in non-Faradaic electrochemical modification of catalytic activity (Λ≫1) in reducing and oxidizing conditions and Faradaic or electrochemical enhancement (Λ<1) in stoichiometric reaction condition. This work demonstrates that the formation of different Pd and Co oxide phases can be accurately controlled by electrochemical stimuli and, in reducing conditions, result in pseudo-capacitor behaviour.

Metallic Nanoclusters for Electrochemical Water Splitting

Posted on 8 March 2024 by nXiaodong Shao, nMinseo Kim, nMengfang Liang, nHyoyoung Leen

In this review, the recent progress of various design and synthesis strategies of transition metal nanoclusters (NCs) on different supporting materials are summarized and discussed. Combined with the reported experimental and theoretical results, the design principles of the structure, morphology, and electronic structure of NCs for boosting the electrochemistry water splitting performance are also introduced.

Abstract

Electrocatalytic water splitting is regarded as one of the most promising strategies for producing clean and sustainable energy sources (H₂ and O₂) in cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER), respectively. Currently, transition metal nanoparticles (NPs) such as commercial Pt/C, IrO_2, and RuO₂ are still popular catalysts for industrial-level HER and OER processes. However, both the high cost and low atomic utilization of NPs can not satisfy the requirements of atomic economy and green chemistry. Compared with NPs, metallic nanoclusters (NCs), which have higher atom utilization and optimized electronic structure than NPs, show unique activities for water splitting. In this review, the recently reported advanced design strategies for preparing various NCs are discussed in detail. The methods to control the particle size, coordinated environment, and morphology of NCs are also summarized. The electrochemical activity and stability of NCs can be influenced by the synergistic effect between NCs and supporting materials, which is also mentioned. Then, the recently reported state-of-art-catalysts for both HER and OER along with the detailed catalytic mechanism are described to show the advanced design principles. Finally, the future perspectives and some remaining challenges are also presented.

Interfacial Coupling of NiPx/MoS2/CC Hybrid Catalysts for Effective Electrocatalytic Oxidation of Urea and Energy‐Saving Hydrogen Evolution

Posted on 8 March 2024 by nSongjie Hu, nQiuhan Cao, nHu Yao, nYuxin Jia, nXiaohui Guon

Interfacial engineering was employed to construct a large intimately coupled heterogenous interface between NiP_x and MoS₂, interfacial coupling can ensure seamless heterogeneous interfaces were formed during the deposition process, which enables fast electron transfer at the interface and provides rich active sites, thus improving both UOR and HER performance.

Abstract

Urea oxidation reactions (UOR) coupled with hydrogen generation simultaneously is a promising strategy for developing sustainable energy conversion technologies, but the complexity of urea oxidation dynamics and the high coupling hydrogen evolution potential through a single catalyst limit its industrial application. Herein, a kind of novel bifunctional NiP_x/MoS₂/CC hybrid catalyst can be fabricated via a hydrothermal method followed by a facile in-situ electrodeposition process. The prepared NiP_x/MoS₂/CC catalyst exhibits an overpotential of only 88 mV at 10 mA cm⁻² for HER while the potential for UOR was only 1.36 V at 10 mA cm⁻². Further, the urea electrolytic cell assembled of the NiP_x/MoS₂/CC catalyst displays low potential (1.45 V@10 mA cm⁻²) and better long-term durability. The improved electrocatalytic performances are mainly attributed to the intimately coupled interface between NiP_x and MoS₂, enormously improving the conductivity and increasing the heterogenous interface active area. Additionally, the closely incorporated heterogeneous interfaces trigger charge redistribution, which induces the fast electron transfer from the NiP_x to MoS₂. In a word, the present results can provide a feasible research strategy for design advanced multi-functional catalysts via interfacial engineering for clean energy conversion applications.

First‐Row Transition Metal‐Catalyzed Single Hydroelementation of N‐Heteroarenes

Posted on 8 March 2024 by nSehoon Parkn

In this review, we outline the first-row transition metal-catalyzed hydroelementation of pyridines and quinolines with dihydrogen (from H₃N⋅BH₃), hydrosilanes, or hydroboranes to selectively provide the 1,2- or 1,4-dihydro products. We also describe the regioselectivity and working mode of the catalytic systems on the basis of experimental and/or computational mechanistic observations and insights.

Abstract

Catalytic partial reduction of N-heteroarenes with H₂ or H[E] (E=Si, B-based) has been a useful and general method for synthesis of a broad range of dihydropyridines (DHP) and dihydroquinolines (DHQ). In recent seven years, one of the most notable advances in this context is being able to utilize earth-abundant and inexpensive first-row transition metal-based catalytic systems. These catalytic procedures are generally considered more environmentally benign and sustainable when compared to conventional catalytic systems relying on precious metals. This Review describes 20 molecular catalytic systems based on first-row transition metals for selective single hydroelementation of pyridines and quinolines with H₂ surrogate, hydrosilanes, and hydroboranes providing 1,2- or 1,4-dihydropyridines and -dihydroquinolines. The observed reaction profiles such as scope and activity are briefly presented, while the proposed working modes over a series of elemental steps – H−[E] bond cleavage, hydride (H⁻) or hydrogen atom (H⋅) transfer, and product release, are discussed in detail on the basis of experimental and/or computational mechanistic observations and insights.

Recent Understanding of Water‐Assisted CO2 Hydrogenation to Alcohols

Posted on 8 March 2024 by

Continuously removing water is desired to alleviate thermodynamic barriers during CO₂ hydrogenation. However, at low concentrations, water can enhance alcohol productivity. Here, we discuss the main findings that led to an atomic-level understanding of water promotional effects in CO₂ hydrogenation to alcohols.

Abstract

Alcohol production from CO₂ hydrogenation is a cutting-edge process in sustainable chemistry that holds vast promise for addressing climate change by recycling and repurposing emissions. Many strategies have been proposed to improve the process efficiency. In-situ generated, and trace amounts of water added to the feed stream have recently proved to be determinant to promote key reaction steps, increasing alcohol selectivity and yield. Here, we discuss the main findings that led to an atomic-level understanding of water promotional effects in CO₂ hydrogenation to alcohols. H₂O and the products resultant from its dissociation (OH and O) can act in different ways, stabilizing intermediates and active sites or participating in the hydrogen transfer mechanisms during the reaction. Gaining insights into the mechanisms underlying water promotion offers a cost-effective strategy for enhancing alcohol production efficiency.

Pushing the Efficiency of the Selective and Base‐free Air‐Oxidation of HMF by Varying the Properties of Carbon‐based Supports

Posted on 8 March 2024 by

Support for base-free: Pt supported on various activated carbon and carbon black materials was prepared and tested for the base-free, selective air-oxidation of 5-(Hydroxymethyl)furfural to 2,5-Furandicarboxylic acid. Depending on the chemical properties (graphitization degree, O-containing functional groups) of the supports as determined by comprehensive characterization, highly active and selective catalysts were found due to the active role of the support.

Abstract

The selective oxidation of 5-(Hydroxymethyl)furfural (HMF) to 2,5-Furandicarboxylic acid (FDCA) is highly attractive for the production of renewable monomers as substitute for fossil-based monomers. To achieve a sustainable synthesis, we report on advances for a base-free approach, reducing waste from the process, using air as oxidant and heterogeneous catalysts. Various Carbon-based supports, which can be bio-sourced and cost-efficient, for Pt particles were investigated as they allow for an easy reuse and at the end-of-life Pt can be recycled to enable a closed cycle. Commercially available supports with varying properties, which might replace the base, were studied with Pt particles of similar size and loading. Significant differences in the catalytic activity were observed, which were correlated with the O-functionalities and graphitization degree of the supports derived from Raman spectroscopy, temperature-programmed desorption, and X-ray photoelectron spectroscopy. An activated carbon (Norit ROX) rich in quinone/pyrone-type groups and a carbon black-based catalyst with graphene-layers pushed the efficiency with enhanced FDCA-yields enabling the complete substitution of the homogeneous base. This allows to circumvent the base in this process which together with high selectivity, air as oxidant, a reusable catalyst, and the use of bio-based feedstock contributes to the sustainability of the production of renewable monomers.

Unlocking the Mysteries of Technical Catalyst Deactivation: A View from Space

Posted on 8 March 2024 by nShweta Sharma, nFlorian Maurer, nPatrick Lott, nThomas L. Sheppardn

The paper highlights spatially–resolved characterization techniques for investigating deactivation of technical catalysts. Employing advanced analytical tools, such studies can provide deep insights into the heterogeneous nature of catalyst deactivation. The importance of spatial mapping and scale–bridging analyses is clear to connect observations and understanding of catalyst deactivation from model to technical scale.

Abstract

Modern analytical techniques enable researchers to study heterogeneous catalytic systems at extended length scales and with local probing methods which were previously impractical. Such spatially–resolved analyses are ideal for exploring the complex dynamics governing catalytic activity, and more specifically, deactivation. Here we highlight significant experimental concepts and milestones in the spatially–resolved analysis of technical catalysts, where it is now possible to study catalyst behavior even up to industrially relevant scale. At such extended length scales and in contrast to many model systems, spatial heterogeneities in solid catalyst bodies may play a crucial role in controlling catalytic properties and may be closely linked to catalyst deactivation. Spatially–resolved studies can therefore provide a unique source of information about such local phenomena. Researchers can gain a deeper insight into the operational life of a catalyst by understanding deactivation patterns, which are one of many factors influencing the dynamics of catalytic reactions. In turn, this information promotes the design of more robust and sustainable catalytic systems. We therefore outline the current state of spatially–resolved characterization, together with its role in deconvoluting the complexity of technical catalysts and their deactivation.