Encapsulation of Nonprecious Metal into Ordered Mesoporous N-Doped Carbon for Efficient Quinoline Transfer Hydrogenation with Formic Acid

Electricity-driven organic hydrogenation using water as the hydrogen source

Hydrogenation is a pivotal process in organic synthesis and various catalytic strategies have been developed in achieving effective hydrogenation of diverse substrates. Despite the competence of these methods, the predominant reliance on molecular hydrogen (H2) gas under high temperature and elevated pressure presents operational challenges. Other alternative hydrogen sources such as inorganic hydrides and organic acids are often prohibitively expensive, limiting their practical utility on a large scale. In contrast, employing water as a hydrogen source for organic hydrogenation presents an attractive and sustainable alternative, promising to overcome the drawbacks associated with traditional hydrogen sources. Integrated with electricity as the sole driving force under ambient conditions, hydrogenation using water as the sole hydrogen source aligns well with the environmental sustainability goals but also offers a safer and potentially more cost-effective solution. This article starts with the discussion on the inherent advantages and limitations of conventional hydrogen sources compared to water in hydrogenation reactions, followed by the introduction of representative electrocatalytic systems that successfully utilize water as the hydrogen source in realizing a large number of organic hydrogenation transformations, with a focus on heterogeneous electrocatalysts. In summary, transitioning to water as a hydrogen source in organic hydrogenation represents a promising direction for sustainable chemistry. In particular, by exploring and optimizing electrocatalytic hydrogenation systems, the chemical industry can reduce its reliance on hazardous and expensive hydrogen sources, paving the way for safer, greener, and less energy-intensive hydrogenation processes.

Adaptive Catalysts for the Selective Hydrogenation of Bicyclic Heteroaromatics using Ruthenium Nanoparticles on a CO2 -Responsive Support

Ruthenium nanoparticles (NPs) immobilized on an amine-functionalized polymer-grafted silica support act as adaptive catalysts for the hydrogenation of bicyclic heteroaromatics. Whereas full hydrogenation of benzofuran and quinoline derivatives is achieved under pure H2 , introducing CO2 into the H2 gas phase leads to an effective shutdown of the arene hydrogenation while preserving the activity for the hydrogenation of the heteroaromatic part. The selectivity switch originates from the generation of ammonium formate species on the surface of the materials by catalytic hydrogenation of CO2 . The CO2 hydrogenation is fully reversible, resulting in a robust and rapid switch between the two states of the catalyst adapting its performance in response to the feed gas composition. A variety of benzofuran and quinoline derivatives were hydrogenated to fully or partially saturated products in high selectivity and yields simply by altering the composition of the feed gas from H2 to H2 /CO2 . The adaptive catalytic system thus provides controlled access to valuable products using a single catalyst rather than two specific and distinct catalysts with static reactivity.

Metal-organic framework-derived CoNx nanoparticles on N-doped carbon for selective N-alkylation of aniline

N-alkylation of anilines by alcohols can be used as an efficient strategy to synthesise a wide range of secondary amines. In this respect, a hydrogen borrowing methodology has been explored using precious metal-based catalysts. However, the utilisation of cheap and readily available transition metal based catalysts is required for large-scale applications. In this work, we have reported metal-organic framework-derived CoNx@NC catalysts for the selective N-alkylation of anilines with different types of alcohols. The Co-N coordination in CoNx@NC was found to be extremely important to improve the conversion efficiency and yield of the product. As a result, CoNx@NC produced 99% yield of the desired amines, which is far better than that of Co@C (yield = 65%). In addition, CoNx@NC showed remarkable recyclability for six cycles with a minimum drop in the yield of the desired product.

New insights into engineering the core size and carbon shell thickness of Co@C core-shell catalysts for efficient and stable Fenton-like catalysis

Herein, we engineered the cobalt core size and carbon shell thickness of Co@C by molten salt electrolysis (MSE) to investigate the enhanced essence of decreasing core size as well as the shell thickness dependence-mediated transition of catalytic mechanisms. We found that the reaction activation energy (RAE) of Co@C/peroxymonosulfate (PMS) systems was intimately dependent on the core sizes for sulfamethoxazole (SMX) degradation. The smaller core size of 26 nm provided a lower RAE of 13.39 kJ mol^-1. In addition, increasing carbon shell thicknesses of Co@C altered the catalytic mechanisms from a radical pathway of SO₄^•- and •OH to to a non-radical pathway of ¹O₂ and electron-transfer process (ETP), which were verified by experimental results and density functional theory (DFT) calculations. Interestingly, increasing carbon shell thicknesses promoted the charge transfer between Co metal slab and carbon shell, increased the adsorption energy of PMS molecule on the Co@C slab, and decreased the length of OO, which favoured the occurrence of non-free radical processes.

In Situ Reconstruction of Metal Oxide Cathodes for Ammonium Generation from High-Strength Nitrate Wastewater: Elucidating the Role of the Substrate in the Performance of Co3O4-x

In situ electrochemical reconstruction is important for transition metal oxides explored as electrocatalysts for electrochemical nitrate reduction reactions (ENRRs). Herein, we report substantial performance enhancement of ammonium generation on Co, Fe, Ni, Cu, Ti, and W oxide-based cathodes upon reconstruction. Among them, the performance of a freestanding ER-Co₃O_4-x/CF (Co₃O₄ grown on Co foil subjected to electrochemical reduction) cathode was superior to its unreconstructed counterpart and other cathodes; e.g., an ammonium yield of 0.46 mmol h^-1 cm^-2, an ammonium selectivity of 100%, and a Faradaic efficiency of 99.9% were attained at -1.3 V in a 1400 mg L^-1 NO₃^--N solution. The reconstruction behaviors were found to vary with the underlying substrate. The inert carbon cloth only acted as a supporting matrix for immobilizing Co₃O₄, without appreciable electronic interactions between them. A combination of physicochemical characterizations and theoretical modeling provided compelling evidence that the CF-promoted self-reconstruction of Co₃O₄ induced the evolution of metallic Co and the creation of oxygen vacancies, which promoted and optimized interfacial nitrate adsorption and water dissociation, thus boosting the ENRR performance. The ER-Co₃O_4-x/CF cathode performed well over wide ranges of pH and applied current and at high nitrate loadings, ensuring its high efficacy in treating high-strength real wastewater.

Electrocatalytic hydrogenation of quinolines with water over a fluorine-modified cobalt catalyst

Room temperature and selective hydrogenation of quinolines to 1,2,3,4-tetrahydroquinolines using a safe and clean hydrogen donor catalyzed by cost-effective materials is significant yet challenging because of the difficult activation of quinolines and H₂. Here, a fluorine-modified cobalt catalyst is synthesized via electroreduction of a Co(OH)F precursor that exhibits high activity for electrocatalytic hydrogenation of quinolines by using H₂O as the hydrogen source to produce 1,2,3,4-tetrahydroquinolines with up to 99% selectivity and 94% isolated yield under ambient conditions. Fluorine surface-sites are shown to enhance the adsorption of quinolines and promote water activation to produce active atomic hydrogen (H*) by forming F⁻-K⁺(H₂O)₇ networks. A 1,4/2,3-addition pathway involving H* is proposed through combining experimental and theoretical results. Wide substrate scopes, scalable synthesis of bioactive precursors, facile preparation of deuterated analogues, and the paired synthesis of 1,2,3,4-tetrahydroquinoline and industrially important adiponitrile at a low voltage highlight the promising applications of this methodology.

Selective hydrogenation of quinolines with easy-to-handle hydrogen donors and cost-effective catalysts is desirable. Here electrocatalytic quinoline hydrogenation to 1,2,3,4-tetrahydroquinolines is reported with water over a fluorine-modified cobalt.

A Novel Tannic Acid-Based Carbon-Supported Cobalt Catalyst for Transfer Hydrogenation of Biomass Derived Ethyl Levulinate

The catalytic conversion of ethyl levulinate (EL) to γ-valerolactone (GVL) is an important intermediate reaction in the conversion and utilization of biomass resources. The development of novel and efficient catalysts is significantly important for this reaction. In this work, using the biomass-derived tannic acid as carbon precursor and the transition metal cobalt as active component, a novel tannic acid carbon supported cobalt catalyst (Co/TAC) was prepared by pyrolysis and subsequent hydrazine hydrate reduction method. The hydrogenation of EL and other carbonyl compounds by hydrogen transfer reaction was used to evaluate the performance of the catalysts. The effects of different preparation and reaction conditions on the performance of the catalysts were investigated, and the structures of the prepared catalysts were characterized in detail. The results showed that the carbonization temperature of the support had a significant effect on the activity of the catalyst for the reaction. Under the optimized conditions, the Co/TAC-900 catalyst obtained the highest GVL yield of 91.3% under relatively mild reaction conditions. Furthermore, the prepared catalyst also showed high efficiency for the hydrogenation of various ketone compounds with different structures. This work provides a new reference for the construction of the catalysts during the conversion of biomass and a potential pathway for the high-value utilization of tannin resource.

General Synthetic Strategy to Ordered Mesoporous Carbon Catalysts with Single-Atom Metal Sites for Electrochemical CO2 Reduction

The electrochemical carbon dioxide reduction reaction (CO₂ RR) is a transformative technology to reduce the carbon footprint of modern society. Single-site catalysts have been demonstrated as promising catalysts for CO₂ RR, but general synthetic methods for catalysts with high surface area and tunable single-site metal composition still need to be developed to unambiguously investigate the structure-activity relationship crossing various metal sites. Here, a generalized coordination-condensation strategy is reported to prepare single-atom metal sites on ordered mesoporous carbon (OMC) with high surface areas (average 800 m²  g^-1 ). This method is applicable to a broad range of metal sites (Fe, Co, Ni, Cu, Pt, Pd, Ru, and Rh) with loadings up to 4 wt.%. In particular, the CO₂ RR to carbon monoxide (CO) Faradaic efficiency (FE) with Ni single-site OMC catalyst reaches 95%. This high FE is maintained even under large current density (>140 mA cm^-2 ) and in a long-term study (14 h), which suits the urgently needed large-scale applications. Theoretical calculations suggest that the enhanced activity on single-atom Ni sites results from balanced binding energies between key intermediates, COOH and CO, for CO₂ RR, as mediated by the coordination sphere.

Functionalized Activated Carbon for Competing Adsorption of Volatile Organic Compounds and Water

The interfacial interaction of activated carbon with volatile organic compounds (VOCs) is seriously affected by water vapor. Therefore, it is vital to enhance the hydrophobic performance of activated carbon for expanding its application in industrial and environmental fields. Herein, a series of hydrophobic activated carbon was fabricated by tailored mixed siloxane and applied in dynamic competitive adsorption at 0, 50, and 90% humidity. Simultaneously, the diffusion molecular models and multicomponent adsorption experiments were used to study the adsorption and diffusion mechanisms. The hydrophobicity of activated carbon was significantly improved by loading of mixed siloxane, in which the equilibrium water absorption decreased from 21.9 to 7.2% and the contact angles increased by 70.10°. Meanwhile, dynamic competitive adsorption at different humidities indicated that the siloxane-functionalized activated carbons (SACs) showed much better competitive adsorption performances for VOCs than original activated carbon, which was further confirmed by the theoretical calculations of adsorption energy. In addition, a remarkable adsorption selectivity and reusability could be demonstrated to VOCs with different polarities on SACs. This study not only provides a new strategy for the hydrophobic modification of activated carbon materials but also offers theoretical guidance for the treatment of gas streams with significant water contents.

Highly Dispersed CoNi Alloy Embedded in N-doped Graphitic Carbon for Catalytic Transfer Hydrogenation of Biomass-derived Furfural

The development of efficient, stable, and cost-effective heterogeneous catalysts for catalytic transfer hydrogenation (CTH) of biomass-derived furfural (FAL) is highly desired. Herein, series of N-doped graphitic carbon embedded CoNi bimetallic alloy nanoparticles were fabricated and used for the CTH of FAL to value-added furfuryl alcohol (FOL) with renewable isopropanol as hydrogen donor. Intrinsic catalytic activity examination indicated the catalytic performance of Ni_x Co_y @NGC (x:y=1 : 3, 1 : 1, 3 : 1) nanocatalysts were sensitive to their chemical compositions. The optimal Ni₁ Co₁ @NGC nanocatalyst with Ni/Co mole ratio of 1 : 1 afforded a largest FOL yield of 89.3% with nearly full conversion of FAL. The synergistic effect enabled by bimetallic alloys and the abundant N-based Lewis base sites and surface Co-N active species were revealed based on systematic structural characterization, responsible for the excellent catalytic efficiency of bimetallic Ni₁ Co₁ @NGC nanocatalyst for CTH of FAL.

Recent Advances on Heteroatom-Doped Porous Carbon/Metal Materials: Fascinating Heterogeneous Catalysts for Organic Transformations

Design and preparation of low-cost, effective, and novel catalysts are important topics in the field of heterogeneous catalysis from academic and industrial perspectives. Recently, heteroatom-doped porous carbon/metal materials have received significant attention as promising catalysts in divergent organic reactions. Incorporation of heteroatom into the carbon framework can tailor the properties of carbon, providing suitable interaction between support and metal, resulting in superior catalytic performance compared with those of traditional pure carbon/metal catalytic systems. In this review, we try to underscore the recent advances in the design, preparation, and application of heteroatom-doped porous carbon/metal catalysts towards various organic transformations.

Biogenic Synthesis of Gold Nanoparticles on a Green Support as a Reusable Catalyst for the Hydrogenation of Nitroarene and Quinoline

Direct attachment of gold nanoparticles to a green support without the use of an external reducing agent and using it for removing toxic pollutants from wastewater, i. e., reduction of nitroarene to amine, are described. A novel approach involving the reduction of gold by the jute plant (Corchorus genus) stem-based (JPS) support itself to form nanoparticles (AuNPs) to be used as a catalytic system ('dip-catalyst') and its catalytic activity for the hydrogenation of series of nitroarenes in aqueous media are presented. AuNPs/JPS catalyst was characterized using SEM, UV-Vis, FTIR, TEM, XPS, and ICP-OES. Confined area elemental mapping exhibits uniform and homogeneous distribution of AuNPs on the support surface. TEM shows multi-faceted AuNPs in the range of 20-30 nm. The reactivity of AuNPs/JPS for the transfer hydrogenation of nitroarene as well as hydrogenation of quinoline under molecular H₂ pressure was evaluated. Sodium borohydride, when used as the hydrogen source, demonstrates a high catalytic efficiency in the transfer hydrogenation reduction of 4-nitrophenol (4-NP). Quinoline is quantitatively and chemoselectively hydrogenated to 1,2,3,4-tetrahydroquinoline (py-THQ) using molecular hydrogen. Reusability studies show that AuNPs are stable on the support surface and their selectivity is not affected.

Tuning the Catalytic Performance of Cobalt Nanoparticles by Tungsten Doping for Efficient and Selective Hydrogenation of Quinolines under Mild Conditions

Non-noble bimetallic CoW nanoparticles (NPs) partially embedded in a carbon matrix (CoW@C) have been prepared by a facile hydrothermal carbon-coating methodology followed by pyrolysis under an inert atmosphere. The bimetallic NPs, constituted by a multishell core-shell structure with a metallic Co core, a W-enriched shell involving Co7W6 alloyed structures, and small WO3 patches partially covering the surface of these NPs, have been established as excellent catalysts for the selective hydrogenation of quinolines to their corresponding 1,2,3,4-tetrahydroquinolines under mild conditions of pressure and temperature. It has been found that this bimetallic catalyst displays superior catalytic performance toward the formation of the target products than the monometallic Co@C, which can be attributed to the presence of the CoW alloyed structures.

Recent developments of nanocatalyzed liquid-phase hydrogen generation

Hydrogen is the most effective and sustainable carrier of clean energy, and liquid-phase hydrogen storage materials with high hydrogen content, reversibility and good dehydrogenation kinetics are promising in view of "hydrogen economy". Efficient, low-cost, safe and selective hydrogen generation from chemical storage materials remains challenging, however. In this Review article, an overview of the recent achievements is provided, addressing the topic of nanocatalysis of hydrogen production from liquid-phase hydrogen storage materials including metal-boron hydrides, borane-nitrogen compounds, and liquid organic hydrides. The state-of-the-art catalysts range from high-performance nanocatalysts based on noble and non-noble metal nanoparticles (NPs) to emerging single-atom catalysts. Key aspects that are discussed include insights into the dehydrogenation mechanisms, regenerations from the spent liquid chemical hydrides, and tandem reactions using the in situ generated hydrogen. Finally, challenges, perspectives, and research directions for this area are envisaged.

Tandem synthesis of tetrahydroquinolines and identification of the reaction network by operando NMR

Bifunctional MOF supported Pd nanoparticles for the one-pot tandem synthesis of substituted tetrahydroquinolines were developed, and operando high-pressure MAS-NMR were performed to understand the complex reaction network.

Codoped Phosphotungstate as an Efficient Heterogeneous Catalyst for the Synthesis of n-Butyl Oleate

A quaternary ammonium and titanium codoped phosphotungstate (QA_0.5Ti_0.5H_0.5PW) catalyst was prepared by the ion exchange method and used as a solid acid catalyst for the synthesis of n-butyl oleate. The catalyst was characterized by Fourier transform infrared, elemental analyzer, energy-dispersive X-ray spectrometry, Brunauer-Emmett-Teller, scanning electron microscopy, and Hammett indicator methods. QA_0.5Ti_0.5H_0.5PW showed a higher catalytic activity than other phosphotungstate solid acid catalysts reported by literature, and the esterification rate reached 99% under optimized conditions. Moreover, QA_0.5Ti_0.5H_0.5PW exhibited well reusability. An esterification rate of 90.1% was still obtained in the eighth run.

Cobalt-Polypyrrole/Melamine-Derived Co-N@NC Catalysts for Efficient Base-Free Formic Acid Dehydrogenation and Formylation of Quinolines through Transfer Hydrogenation

It is highly desired but remains a great challenge to develop non-noble metal heterogeneous catalysts to supersede noble metal catalysts for formic acid (FA) dehydrogenation and the corresponding transfer hydrogenation reactions. Herein, we developed a simple and feasible melamine-assisted pyrolysis strategy for the preparation of atomic cobalt-nitrogen (Co-N)-anchored mesoporous carbon with high metal loading (>6.8 wt %) and high specific surface area (750 m² g^-1). Systematic investigation reveals that both the organic carbon source polypyrrole and the nitrogen source melamine are crucial for the successful generation of such Co-N-based materials. The obtained samples (Co-N)_n@NC were demonstrated to be highly efficient and robust catalysts for FA dehydrogenation and formylation of quinolines through transfer hydrogenation, exhibiting a very high hydrogen production rate of 16 451 mL·g_Co^-1·h^-1 for FA dehydrogenation and affording excellent yields (up to 99%), selectivity (up to 98%), and stability for transfer hydrogenation. This work may provide a promising route for the fabrication of more low-cost metal-nitrogen catalysts for green fine chemical synthesis.

Synergistic catalysis on Fe-N x sites and Fe nanoparticles for efficient synthesis of quinolines and quinazolinones via oxidative coupling of amines and aldehydes

In this paper, we developed a reusable heterogeneous non-precious iron nanocomposite comprising metallic Fe-Fe3C nanoparticles and Fe-N x sites on N-doped porous carbon, which allows for highly efficient synthesis of quinolines and quinazolinones via oxidative coupling of amines and aldehydes using H2O2 as the oxidant in aqueous solution under mild conditions. A set of quinazolines and quinazolinones were synthesized in high yields with a broad substrate scope and good tolerance of functional groups. Characterization and control experiments disclose that a synergistic effect between the metallic Fe nanoparticles and built-in Fe-N x sites is primarily responsible for the outstanding catalytic performance. Furthermore, the iron nanocomposite could be readily recovered for successive use without appreciable loss in catalytic activity and selectivity. This work provides an expedient and sustainable method to access pharmaceutically relevant N-heterocycles.