Ni-Co Alloy Nanoparticles Catalyze Selective Electrochemical Coupling of Nitroarenes into Azoxybenzene Compounds in Aqueous Electrolyte

Electrochemical hydrogenative coupling of nitrobenzene into azobenzene over a mesoporous palladium-sulfur cathode

Azobenzene (AZO) and its derivatives are of great importance in the dyestuff and pharmaceutical industries; however, their sustainable synthesis is much slower than expected due to the lack of high-performance catalysts. In this work, we report a robust yet highly efficient catalyst of PdS mesoporous nanospheres (MNSs) with confined mesostructures and binary elemental composition that achieved sustainable electrosynthesis of value-added AZO by selective hydrogenative coupling of nitrobenzene (NB) feedstocks in H2O under ambient conditions. Using a renewable electricity source and H2O, binary PdS MNSs exhibited a remarkable NB conversion of 95.4%, impressive AZO selectivity of 93.4%, and good cycling stability in selective NB hydrogenation reaction (NBHR) electrocatalysis. Detailed mechanism studies revealed that the confined mesoporous microenvironment of PdS MNSs facilitated the hydrogenative coupling of key intermediates (nitrosobenzene and phenylhydroxylamine) into AZO and/or azoxybenzene (AOB), while their electron-deficient S sites stabilized the Pd-spillovered active H* and inhibited the over-hydrogenation of AZO/AOB into AN. By coupling with the anodic methanol oxidation reaction (MOR), the (-)NBHR‖MOR(+) two-electrode system exhibits much better NB-to-AZO performance in a sustainable and energy-efficient manner. This work thus paves the way for designing functional mesoporous metal alloy electrocatalysts applied in the sustainable electrosynthesis of industrial value-added chemicals.

Boron Doping Induced Strong Anchor Effect Between Bimetal NiCo Alloy and Carbon Support for Efficient Electrocatalytic Nitrate Reduction to Ammonia

The electrochemical reduction of nitrate to ammonia presents a promising alternative to the conventional Haber-Bosch process. In this study, a bimetallic NiCo alloy embedded in metal-organic framework derived carbon layer with B doping electrocatalyst NiCo@BC was first successfully developed, which exhibits excellent electrochemical nitrate reduction to ammonia (ENO3RR) performance. In-depth in situ experiments and a machine-learning potential (MLP)-based simulation reveal that B doping within the carbon layer has a crucial anchor effect that induces strong binding between bimetal NiCo alloy and carbon support. Moreover, B doping leads to a decrease in the coordination numbers around the metals, which results in a reduction of the excessively strong intermediates adsorption in the ENO3RR process, thereby significantly enhancing catalytic activity. The fabrication strategy of this electrocatalyst provides a new avenue on ENO3RR research.

Unlocking the catalytic potential of heterogeneous nonprecious metals for selective hydrogenation reactions

Selective hydrogenation has been employed extensively to produce value-added chemicals and fuels, greatly alleviating the problems of fossil resources and green synthesis. However, the design and synthesis of highly efficient catalysts, especially those that are inexpensive and abundant in the earth's crust, is still required for basic research and subsequent industrial applications. In recent years, many studies have revealed that the rational design and synthesis of heterogeneous catalysts can efficaciously improve the catalytic performance of hydrogenation reactions. However, the relationship between nonprecious metal catalysts and hydrogenation performance from the perspective of different catalytic systems still remains to be understood. In this review, we provide a comprehensive and systematic overview of the recent advances in the synthesis of nonprecious metal catalysts for heterogeneous selective hydrogenation reactions including thermocatalytic hydrogenation/transfer hydrogenation, photocatalytic hydrogenation and electrocatalytic reduction. In addition, we also aim to provide a clear picture of the recent design strategies and proposals for the nonprecious metal catalysed hydrogenation reactions. Finally, we discuss the current challenges and future research opportunities for the precise design and synthesis of nonprecious metal catalysts for selective hydrogenation reactions.

Moderate Active Hydrogen Generation over a Ni2P/CoP Heterostructure for One-Step Electrosynthesizing of Azobenzene with High Selectivity

Through hydrogenation and N-N coupling, azobenzene can be produced via highly selective electrocatalytic nitrobenzene reduction, offering a mild, cost-effective, and sustainable industrial route. Inspired by the density functional theory calculations, the introduction of H* active Ni2P into CoP, which reduces the water dissociation energy barrier, optimizes H* adsorption, and moderates key intermediates' adsorption, is expected to assist its hydrogenation ability for one-step electrosynthesizing azobenzene. A self-supported NiCo@Ni2P/CoP nanorod array electrode was synthesized, featuring NiCo alloy nanoparticles within a Ni2P/CoP shell. By virtue of the thermodynamically optimal Ni2P/CoP heterostructure, along with overall fast electron transport in a core-shell integrated electrode, NiCo@Ni2P/CoP with abundant interfacial structure attains a great nitrobenzene conversion of 94.3%, especially prominent azobenzene selectivity of 97.2%, and Faradaic efficiency of 94.1% at -0.9 V (vs Hg/HgO). High-purity azobenzene crystals can also self-separate under refrigeration postelectrolysis. This work provides an energy-efficient and scalable pathway for the economical preparation of azobenzene in the electrocatalytic nitrobenzene hydrogenation.

Electric Field-Induced Synergetic Enhancement of Local Hydroxyl Concentration and Photogenerated Carrier Density for Removal of COads in Electrocatalytic Formic Acid Oxidation

Direct formic acid fuel cell (DFAFC) is an efficient power generation device, due to its high energy density, low fuel crossover and low emission. However, the anodic reaction of DFAFC, formic acid oxidation (FAOR), inevitably proceeds through an indirect pathway, adsorbing carbon monoxide intermediate (COads), resulting in a rapid decline of activity for FAOR. Therefore, effectively removing COads is the key to the development of DFAFC. In this work, Pd/CeO2 catalyst is synthesized by in situ growth of Pd nanoparticles on the hollow CeO2. Due to the difference of work function between Pd and CeO2, a built-in electric field from Pd side to CeO2 side is formed, which induces a synergistic enhancement of the photogenerated carrier density and the local high hydroxyl concentration at the Pd/CeO2 interface, thus promoting the oxidative removal of COads and significantly improving the stability of FAOR. Therefore, in photo-assisted electrocatalytic FAOR, Pd/CeO2 not only possessed high mass activity (4161.72 mA mg-1 Pd), and its mass activity decreases by only 20.1% after 40000 s chronoamperometry test, which is superior to most Pd-based catalysts. This work provides a new strategy for efficient removal of COads in FAOR through constructing built-in electric fields, which promotes the DFAFC application.

5-Hydroxymethylfurfural and its Downstream Chemicals: A Review of Catalytic Routes

Biomass assumes an increasingly vital role in the realm of renewable energy and sustainable development due to its abundant availability, renewability, and minimal environmental impact. Within this context, 5-hydroxymethylfurfural (HMF), derived from sugar dehydration, stands out as a critical bio-derived product. It serves as a pivotal multifunctional platform compound, integral in synthesizing various vital chemicals, including furan-based polymers, fine chemicals, and biofuels. The high reactivity of HMF, attributed to its highly active aldehyde, hydroxyl, and furan ring, underscores the challenge of selectively regulating its conversion to obtain the desired products. This review highlights the research progress on efficient catalytic systems for HMF synthesis, oxidation, reduction, and etherification. Additionally, it outlines the techno-economic analysis (TEA) and prospective research directions for the production of furan-based chemicals. Despite significant progress in catalysis research, and certain process routes demonstrating substantial economics, with key indicators surpassing petroleum-based products, a gap persists between fundamental research and large-scale industrialization. This is due to the lack of comprehensive engineering research on bio-based chemicals, making the commercialization process a distant goal. These findings provide valuable insights for further development of this field.

Recent Progress Toward Electrocatalytic Conversion of Nitrobenzene

Despite that extensive efforts have been dedicated to the search for advanced catalysts to boost the electrocatalytic nitrobenzene reduction reaction (eNBRR), its progress is severely hampered by the limited understanding of the relationship between catalyst structure and its catalytic performance. Herein, this review aims to bridge such a gap by first analyzing the eNBRR pathway to present the main influential factors, such as electrolyte feature, applied potential, and catalyst structure. Then, the recent advancements in catalyst design for eNBRR are comprehensively summarized, particularly about the impacts of chemical composition, morphology, and crystal facets on regulating the local microenvironment, electron and mass transport for boosting catalytic performance. Finally, the future research of eNBRR is also proposed from the perspectives of performance enhancement, expansion of product scope, in-depth understanding of the reaction mechanism, and acceleration of the industrialization process through the integration of upstream and downstream technologies.

Guanine-derived carbon nanosheet encapsulated Ni nanoparticles for efficient CO2 electroreduction

Developing novel electrocatalysts for achieving high selectivity and faradaic efficiency in the carbon dioxide reduction reaction (CO2RR) poses a major challenge. In this study, a catalyst featuring a nitrogen-doped carbon shell-coated Ni nanoparticle structure is designed for efficient carbon dioxide (CO2) electroreduction to carbon monoxide (CO). The optimal Ni@NC-1000 catalyst exhibits remarkable CO faradaic efficiency (FECO) values exceeding 90% across a broad potential range of -0.55 to -0.9 V (vs. RHE), and attains the maximum FECO of 95.6% at -0.75 V (vs. RHE) in 0.5 M NaHCO3. This catalyst exhibits sustained carbon dioxide electroreduction activity with negligible decay after continuous electrolysis for 20 h. More encouragingly, a substantial current density of 200.3 mA cm-2 is achieved in a flow cell at -0.9 V (vs. RHE), reaching an industrial-level current density. In situ Fourier transform infrared spectroscopy and theoretical calculations demonstrate that its excellent catalytic performance is attributed to highly active pyrrolic nitrogen sites, promoting CO2 activation and significantly reducing the energy barrier for generating *COOH. To a considerable extent, this work presents an effective strategy for developing high-efficiency catalysts for electrochemical CO2 reduction across a wide potential window.

Tandem Electrocatalytic Alkyne Semihydrogenation over Bicomponent Catalysts through Hydrogen Spillover

Electrocatalytic alkyne semihydrogenation under mild conditions is a more attractive approach for alkene production than industrial routes but suffers from either low production efficiency or high energy consumption. Here, we describe a tandem catalytic concept that overcomes these challenges. Component (i), which can trap hydrogen effectively, is partnered with component (ii), which can readily release hydrogen for hydrogenation, to enable efficient generation of active hydrogen on component (i) at low overpotentials and timely (i)-to-(ii) hydrogen spillover and facile desorptive hydrogenation on component (ii). We examine this concept over bicomponent palladium-copper catalysts for the production of representative 2-methyl-3-butene-2-ol (MBE) from 2-methyl-3-butyne-2-ol (MBY) and achieve a record high MBE production rate of 1.44 mmol h-1 cm-2 and a Faraday efficiency of ~88.8 % at a low energy consumption of 1.26 kWh kgMBE -1. With these catalysts, we further achieve 60 h continuous production of MBE with record high profit space.

Recent Advances in the Synthesis of Aromatic Azo Compounds

Aromatic azo compounds have -N=N- double bonds as well as a larger π electron conjugation system, which endows aromatic azo compounds with wide applications in the fields of functional materials. The properties of aromatic azo compounds are closely related to the substituents on their aromatic rings. However, traditional synthesis methods, such as the coupling of diazo salts, have a significant limitation with respect to the structural design of aromatic azo compounds. Therefore, many scientists have devoted their efforts to developing new synthetic methods. Moreover, recent advances in the synthesis of aromatic azo compounds have led to improvements in the design and preparation of light-response materials at the molecular level. This review summarizes the important synthetic progress of aromatic azo compounds in recent years, with an emphasis on the pioneering contribution of functional nanomaterials to the field.