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.

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.

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.

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.

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.

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.

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.

Ru−O bonding interactions are enhanced via Ir regulation, stabilizing the solvation of RuO_x at high potentials, thus greatly improving the activity and stability towards OER.

Abstract

Highly active and stable oxygen evolution reaction (OER) catalysts are crucial for the large-scale application of proton exchange membrane water electrolyzers. However, the dynamic reconfiguration of the catalyst surface structure and active centers is still undefined, which greatly hinders the development and application of efficient OER catalysts. Herein, we report an Ir_0.3Ru_0.7O_x/C catalyst with a facile low-temperature synthesis route, which can reach 10 mA cm⁻² at an overpotential of 217 mV with a Tafel slope as low as 39.4 mV dec⁻¹, and yields a mass activity 61 times that of commercial IrO₂/C at an overpotential of 300 mV. The lattice oxygen structure of RuO_x is stabilized by the introduction of Ir species, thus greatly promoting the OER activity and durability. Further in situ Raman reveals that RuO_x emerges as the active species at high potentials, and Ru−O bonding interactions are enhanced with Ir regulation, stabilizing the solvation of Ru at high potentials and accelerating the nucleophilic attack of water molecules, leading to the improved OER performance. This work deepens the fundamental understanding of OER and offers an effective way to advance the utilization of Ru-based OER catalysts.

The Cover Feature shows the efforts of scientists to modify transition-metal containing MFI topologies to achieve the highest activity and N₂ selectivity for NH₃-SCR-DeNO _x and NH₃ oxidation. MFI-based catalysts are still used commercially for these processes and are of great interest for future study, in particular to better understand structure-activity relationships. In their Review, M. Jabłońska, M. E. Potter and A. M. Beale critically review and discuss the salient physico-chemical properties that influence the performance of these catalysts together with the strategies for the development of ZSM-5 based catalysts with enhanced catalytic lifetime, supported by the investigations of reaction mechanisms.More information can be found in the Review by M. Jabłońska, A. M. Beale et al.