Co-based Catalysts Research Articles

Modulating the Oxygen Evolution Reaction of Single-Crystal Cobalt Carbonate Hydroxide via Surface Fe Doping and Facet Dependence.

The oxygen evolution reaction (OER) is a critical half-reaction in water splitting and metal-air cells. The sensitivity of the OER to the composition and structure of the electrocatalyst presents a significant challenge in elucidating the structure-property relationship. In this study, highly stable single-crystal cobalt carbonate hydroxide [Co2(OH)2CO3, CoCH] was used as a model to investigate the correlations among structure, composition, and reactivity. Single-crystal CoCH nanowires (denoted as CoCH NWs) and Fe-doped CoCH nanowires (denoted as Fe-CoCH NWs) with an exposed (210) facet and Fe-doped CoCH nanosheets (denoted as Fe-CoCH NSs) with an exposed (2-13) facet were synthesized using electrochemical and one-step hydrothermal strategies, respectively. Their OER activity decreased in the following order: Fe-CoCH NWs > Fe-CoCH NSs > CoCH NWs. Theoretical investigation suggested that the doped Fe sites serve as active sites, and the crystal-facet dependence can finely adjust the 3d configuration of Fe sites, resulting in the optimal adsorption strengths and energy barriers for potential-determining steps on the (210) facet of CoCH. This renders the as-prepared Fe-CoCH NWs as some of the most promising Co-based OER catalysts.

Tunning valence state of cobalt centers in Cu/Co-CoO1-x for significantly boosting water-gas shift reaction

Dual active sites with synergistic valence state regulation under oxidizing and reducing conditions are essential for catalytic reactions with step-wise mechanisms to modulate the complex adsorption sites of reactant molecules on the surfaces of heterogeneous catalysts with maximized catalytic performances, but it has been rarely explored. In this work, uniformly dispersed CuCo alloy and CoO nanosheet composite catalysts with dual active sites are constructed, which shows huge boost in activity for catalyzing water-gas shift reaction (WGSR), with a record high reaction rate reaching 204.2 μmolCO gcat.−1 s−1 at 300 °C for Cu1Co9Ox amongst the reported Cu-based and Co-based catalysts. A synergistic mechanism is proposed that Coδ+ species can be easily reduced by CO adsorbed on Cu and Co0 can be oxidized by H2O. Systematic in situ characterization results reveal that the addition of Cu can regulate the redox properties of Co species and thus modulate the adsorption properties of catalysts. Particularly, doping of Cu0 sites weakens the affinity of the surface to CO or CO2 to a moderate level. Moreover, it also promotes the oxidation of *CO to *COOH and the desorption of the product CO2, reducing the carbon poisoning of the catalyst and thus increasing the reactivity. The results would provide guidance for the construction of novel heterogeneous catalyst with dual active sites and clarify its underlying reactivity enhancement mechanism induced by the tunning of valence state of metal centers for heterogeneous catalytic reactions.

Ammonia Decomposition Catalyzed by Co Nanoparticles Encapsulated in Rare Earth Oxide.

We fabricated Co-based catalysts by the low-temperature thermal decomposition of R-Co intermetallics (R = Y, La, or Ce) to reduce the temperature of ammonia cracking for hydrogen production. The catalysts synthesized are nanocomposites of Co/ROx with a metal-rich composition. In the Co13/LaO1.5 catalyst derived from LaCo13, Co nanoparticles of 10-30 nm size are enclosed by the LaO1.5 matrix. The nanocomposite exhibited superior catalytic activity (91% at 500 °C), which was attributed to dual advantages; the low workfunction of the supporter, O-deficient LaO1.5-x nanoparticles, promotes electron donation to the Co catalyst in the interface, which leads to enhanced N-H bond dissociation. Moreover, such a composite structure is effective in suppressing the grain growth of Co nanoparticles because the LaO1.5 layer works as a diffusion barrier against Co. The thermal decomposition of intermetallics is a new route for the facile synthesis of catalysts having an electronically active support.

Solid-State Reaction Synthesis of CoSb2O6-Based Electrodes Towards Oxygen Evolution Reaction in Acidic Electrolytes: Effects of Calcination Time and Temperature

Mitigating global warming necessitates transitioning from fossil fuels to alternative energy carriers like hydrogen. Efficient hydrogen production via electrocatalysis requires high-performance, stable anode materials for the oxygen evolution reaction (OER) to support the hydrogen evolution reaction (HER) at the cathode. Developing noble metal-free electrocatalysts is therefore crucial, particularly for acidic electrolytes, to avoid reliance on scarce and expensive metals such as Ir and Ru. This study investigates a low-cost, solvent-free solid-state synthesis of CoSb2O6, focusing on the influence of calcination time and temperature. Six samples were prepared and characterized using powder X-ray diffraction (PXRD), energy-dispersive X-ray spectroscopy (EDX), Brunauer–Emmett–Teller (BET) analysis, field-emission scanning electron microscopy (FESEM), and electrochemical techniques. A non-pure CoSb2O6 phase was observed across all samples. Electrochemical testing revealed good short-term stability; however, all samples exhibited Tafel slopes exceeding 200 mV dec−1 and overpotentials greater than 1 V. The sample calcined at 600 °C for 6 h showed the best performance, with the lowest Tafel slope and overpotential, attributed to its high CoSb2O6 content and maximized {110} facet exposure. This work highlights the role of calcination protocols in developing Co-based OER catalysts and offers insights for enhancing their electrocatalytic properties.

Electrically driven gaseous ammonia decomposition on Co-based SiC composite catalysts for low-temperature H2 production

Electrically driven gaseous ammonia decomposition on Co-based SiC composite catalysts for low-temperature H2 production

Enhanced electrocatalytic nitrate-to-ammonia performance from Mott-Schottky design to induce electron redistribution.

Constructing highly efficient electrocatalysts via interface manipulation and structural design to facilitate rapid electron transfer in electrocatalytic nitrate-to-ammonia conversion is crucial to attaining superior NH3 yield rates. Here, a Mott-Schottky type electrocatalyst of Co/In2O3 with a continuous fiber structure has been designed to boost the electrocatalytic nitrate-to-ammonia performance. The optimized Co/In2O3-1 catalyst exhibits an impressive NH3 yield rate of 70.1 mg cm-2 h-1 at -0.8 V vs. the reversible hydrogen electrode (RHE), along with an NH3 faradaic efficiency (FE) of 93.34% at 0 V vs. RHE, greatly outperforming the single-component Co and In2O3 samples. The yield rate of Co/In2O3-1 is also superior to that of most currently reported Co-based catalysts and heterostructured ones. Evidence from experiments and theoretical results confirms the formation of a Mott-Schottky heterojunction, which achieves a Co site enriched with electrons, coupled with an In2O3 facet enriched with holes, inducing an electron redistribution to promote the utilization of electroactive sites. Consequently, the reaction energy barrier for nitrate-to-ammonia conversion is significantly reduced, further enhancing its yield efficiency.

Effective catalytic elimination of dichloromethane under humid environment over Co-based oxides

This study tackles issues in Cl-VOCs catalytic ozonation by synthesizing Co-based catalysts for water-promoted ozonation, turning water poisoning into an advantage for waste gas purification.

Hydrogen Production from Formic Acid Using KIT-6 Supported Non-NobleMetal-Based Catalysts.

The aim of this study is to investigate the activity of KIT-6 supported nickel (Ni) and cobalt (Co) catalysts, and the effect of Co incorporation to the Ni@KIT-6 catalyst in the formic acid (FA) dehydrogenation. Ni and Co are inexpensive and readily available non-noble transition metals that are considered ideal for dehydrogenation reactions due to their high activity against C-C and C-H bond breaking. In this study, KIT-6 supported catalysts were tested for hydrogen production from FA in a conventionally heated packed-bed continuous-flow system. N2 adsorption-desorption isotherms of the samples were found to be consistent with Type-IV according to the International Union of Pure and Applied Chemistry (IUPAC) classification. The introduction of metal loading resulted in the preservation of the mesoporous structure of the support material. X-ray diffraction (XRD) patterns of the catalysts exhibited the characteristic amorphous silica structure. Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFT) analysis, Lewis acidity of Co-based catalysts was found to be higher than the Ni-based catalysts. The complete formic acid conversion was observed at 200-350 °C. The highest H2 selectivity was obtained with the 3Ni@KIT-6 catalyst. The Co-based catalysts exhibited relatively lower catalytic activity, which was linked to increased coke formation within these catalysts.

Engineering the electron localization of metal sites on nanosheets assembled periodic macropores for CO2 photoreduction

Photocatalytic conversion of CO2 into syngas is highly appealing, yet still suffers from the undesirable product yield due to the sluggish carrier transfer and the uncontrollable affinity between catalytic sites and intermediates. Here we report the fabrication of Co sites with tunable electron localization capability on two dimensional (2D) nanosheets assembled three dimensional (3D) ordered macroporous framework (3DOM-NS). The as-prepared Co-based 3DOM-NS catalysts exhibit attractive photocatalytic performances toward CO2 reduction, among which the cobalt sulfide one (3DOM Co-SNS) shows the highest syngas generation rate up to 347.3 μmol h−1 under the irradiation of visible light and delivers a remarkable catalytic activity (1150.7 μmol h−1) in a flow reaction system under natural sunlight. Mechanism studies reveal that the high electron localization of metal sites in 3DOM Co-SNS strengthens the interaction between Co and HCOO* via the orbital interactions of dyz/dxz-p and s-s, thus facilitating the cleaving process of C-O bond. Additionally, the ordered macroporous framework with nanosheet subunits elevates the transfer efficiency of photoexcited electrons, which contributes to its high activity.

Acid washing-assisted synthesis of porous Co3O4 nanosheet catalyst featuring efficient benzene oxidation performance

Co-based catalysts exhibit considerable catalytic activity in oxidative reactions, yet challenges remain in synthesizing Co3O4 materials featuring both large surface area and high activity. Here, ultrathin La0.029CoOx nanosheets were post-treated with various concentrations of dilute nitric acid to obtain the two-dimensionally geometric Co3O4-H nanosheets catalysts. Among them, the resultant Co3O4-0.1H catalyst disclosed significantly enhanced catalytic activity, enabling to achieve 100 % conversion of benzene at 230 °C under an ultrahigh weight hourly space velocity (WHSV) of 60,000 mL·g−1·h−1. Additionally, the catalyst also displayed excellent catalytic durability and well catalytic stability over 5 cyclic tests and 45 h of long-period operation. A thorough characterization results revealed that the superior catalytic performance of Co3O4-0.1H was attributed to its distinct nanosheet morphology, high specific surface area and abundant surface defect sites. This work highlights the effectiveness and simplicity of acid washing treatment strategy in improving the catalytic oxidation activity of transition metal oxide catalysts.

Selective Electrochemical Nitrate Reduction to Ammonia on Co-Based Catalysts

About 150 million metric tons of ammonia (NH3) were produced in 2023 mainly for agricultural purposes as a fertilizer [1]. This compound is industrially produced by the conventional Haber-Bosch process under high temperatures (350 – 550 °C) and high pressure (150 – 350 atm), thus, its production accounts for 1.8 tons of CO2 emissions per ton and 2% of the energy consumed in the world [2]. These factors have led to an interest in developing green alternative methods that allow the production of large amounts of NH3. Therefore, it has been demonstrated that the electrocatalytic synthesis of NH3 is a viable route that can be developed via the reduction of nitrate (NO3 -) to simultaneously mitigate its pollution in water sources, which has become a major human health concern when it is consumed [3]. Since the electrochemical reduction of NO3 - involves a complex eight – electron process, it is vital to design a highly selective, active, and stable catalyst. In this work, the performance of Co-based catalysts in alkaline conditions was evaluated and our studies demonstrated that a three-dimensional (3D) Co substrate can achieve a faradaic efficiency (F.E.) of up to 86% at +0.023 V vs RHE (Reversible Hydrogen Electrode) with a partial current density of 23 mA cm-2. However, in the presence of an excess of NH3, Co corrosion is promoted while creating a Co-NH3 complex. In order to avoid this, the thermo-oxidation of Co foam at 400, 600, and 800 °C was performed, proving that a larger oxide layer improves the stability as well as increases the active surface area of the electrode. Furthermore, the samples could reach greater current densities when subjected to a pre-reduction treatment. The sample oxidized at 600 °C presented superior performance, achieving a F.E. of 66% at +0.023V vs RHE, a partial current density of 170 mA cm-2, and approximately 8 h of stability. This work has provided an opportunity to explore the influence of the oxide layer on NH3 synthesis, as well as the necessity of advancing novel strategies to enhance the selectivity and stability of the proposed catalyst.[1] Production of ammonia worldwide from 2010 to 2023. Statista (2024). Retrieved from: https://www.statista.com/statistics/1266378/global-ammonia-production/#:~:text=Ammonia%20production%20has%20remained%20fairly,approximately%2064.6%20million%20metric%20tons.[2] Wang, J., Cai, C., Wang, Y., Yang, X., Wu, D., Zhu, Y., Li, M., Gu, M., & Shao, M. (2021). Electrocatalytic Reduction of Nitrate to Ammonia on Low-Cost Ultrathin CoOx Nanosheets. ACS Catalysis, 11(24), 15135–15140. https://doi.org/10.1021/acscatal.1c03918[3] Xu, H., Ma, Y., Chen, J., Zhang, W., & Yang, J. (2022). Electrocatalytic reduction of nitrate: a step towards a sustainable nitrogen cycle. Chemical Society Reviews, Issue 7. https://pubs.rsc.org/en/content/articlelanding/2022/cs/d1cs00857a

Tracing the Structure-Activity Correlation in Cobalt-Doped Heteroatom-Enriched Nanoporous Material for CO2 Electroreduction

The electrochemical CO2 reduction reaction (CO2RR) to value added chemicals (CO, HCOOH, CH4, CH3OH, C2H5OH etc.) utilizing renewable energy sources has attracted considerable attention to close carbon cycle. [1,2] It has several advantages over other approaches such as 1) CO2 could be reduced under mild temperature and pressure conditions, 2) process could be controlled by adjusting the various reaction parameters such as potential etc., and 3) process is compact and feasible for scale up application. [1-3] However, this process has some limitations such as high overpotential, low selectivity & faradaic efficiency for products. Therefore, the designing of highly active electrocatalysts is required to improve catalytic efficiency. Among various reported catalysts, cobalt doped nitrogen enriched materials with atomically dispersed Co–N sites have displayed superior activities and selectivity in electrochemical process for the reduction of CO2. [1-4] However, the effect of synthesis conditions and composition of active species on product selectivity is not rigorously studied yet.In this research, a series of Co-doped multifunctional nitrogen-enriched nanoporous polymer (n-Co@MNENP) with amine and hydroxyl functionalities has been synthesized by condensation of 2-hydroxy-1,3,5-benzenetricarbaldehyde and melamine with calculated amount of cobalt chloride hexahydrate for incorporating n% (n = 10, 50 and 100) of Co content followed by pyrolysis at temperature 550 (designated as n-Co@MNENP-550) and 700 °C (designated as n-Co@MNENP-700). The structure of the synthesized in-situ and pyrolyzed specimens was confirmed by spectroscopic investigations such as FT-IR, and XPS. The Co content was estimated from ICP analysis. The thermal stability of the specimen was investigated using TGA/DTG. The FE-SEM and EDAX revealed almost spherical agglomerated nanoparticles with homogeneous distribution of Co species. PDF and total scattering (TS) analysis confirmed the presence of Co-N species in 10% and 100% samples while 50% sample has metallic Co(fcc/hcp) and CoO/N active species. Further, synthesized specimens have been explored for CO2RR. Among all the electrocatalysts, n-Co@MNENP-700 have shown the higher activity in CO2RR in which 10-Co@MNENP-700 and 100-Co@MNENP-700 could only produce CO, while 50-Co@MNENP-700 results in CO and C2H5OH production. These results reveal that atomically dispersed cobalt–nitrogen sites are responsible for CO generation while CoO, metallic Co species in combination with Co-N sites are responsible for CO and C2H5OH generation which confirmed that the compositions of Co-based catalysts greatly influence CO2RR activity and selectivity.

Achieving Excess Hydrogen Output via Concurrent Electrochemical and Chemical Redox Reactions on P-Doped Co-Based Catalysts with Electron Manipulation and Kinetic Regulation.

Electrolytic hydrogen production is of great significance in energy conversion and sustainable development. Traditional electrolytic water splitting confronts high anode voltage with oxygen generation and the amount of hydrogen produced at cathode depends entirely on the quantity of electric charge input. Herein, excess hydrogen output can be achieved by constructing a spontaneous hydrazine oxidation reaction (HzOR) coupled hydrogen evolution reaction (HER) system. For the hydrazine oxidation-assisted electrolyzer in this work, both the external input electrons and the electrons produced by spontaneous chemical redox reaction can reduce water, producing more hydrogen than traditional electrolytic water splitting system. The ultrafast kinetics of bifunctional P-doped Co-based catalysts plays a key role in the spontaneous feature of HzOR/HER redox reaction and low working voltage of hydrazine oxidation-assisted electrolyzer (12 mV@100mA cm-2). Theoretical calculation results and ex situ/in situ spectra demonstrate that doped P could optimize electronic structure, regulate adsorption energy of intermediates, and thus endows catalysts with ultrafast kinetics. This work provides a new pathway for the development of spontaneous oxidation-assisted hydrogen production, to achieve excess hydrogen output via concurrent electrochemical and chemical redox reactions.

Novel Roles of Catalysts in Producing High-Purity High-Pressure Hydrogen from Sodium Borohydride.

Hydrogen has received enormous attention as a clean fuel with its high specific energy (HHV=142 MJ kg-1). To apply hydrogen as a practically available energy vector, the direct production of high-pressure hydrogen with high purity is pivotal as it allows for circumventing the mechanical compression process. Recently, the concept of utilizing sodium borohydride (SBH) dehydrogenation as a chemical compressor that can generate high-pressure hydrogen gas was demonstrated by adopting formic acid as an acid catalyst. However, the presence of impurities (e.g., CO, CO2) in the final gas product requires an alternative method to enhance the use of SBH as a chemical compressor. Here, we highlighted the feasibility of producing high-purity, high-pressure hydrogen gas from the SBH dehydrogenation with and without Co-based catalysts. The scrutiny behind the thermodynamics and kinetics of the SBH dehydrogenation was conducted under the elevated pressure condition. As a result, the dual roles of the catalysts as proton collectors and heat sources were revealed, both of which are essential for improving hydrogen production efficiency. We hope that our research stimulates subsequent research that pave the way to exploit hydrogen as an energy vector and achieve a more sustainable future society.

Recent advances in the application of in situ X-ray diffraction techniques to characterize phase transitions in Fischer–Tropsch synthesis catalysts

Fischer–Tropsch synthesis (FTS), an important route for the conversion of syngas into high-value-added chemicals, often relies on Fe- and Co-based catalysts. Catalyst performance has been improved by promoters, supports, and optimization of the activation process; however, in-depth studies on the evolution of the phase during catalyst activation, reaction, and deactivation are still lacking. In situ X-ray diffraction (XRD) effectively reveals the phase evolution of catalytic materials in real time. In this review, the use of in situ XRD to elucidate the influence of activation mode, promoters, and supports on the phase evolution and performance of Fe- and Co-based catalysts is examined. The challenges and opportunities in studying the phase evolution of FTS catalysts using in situ XRD techniques are summarized and discussed, and theoretical guidance for the design of FTS catalysts is provided in order to promote their development.

Study on the mechanism of methane activation on Co-based catalysts with variable valence

Methane is an important hydrocarbon gas that plays a key role in energy production and utilization. In this study, the mechanism of methane activation on Co (100), CoO (100), and Co3O4 (110) surfaces is thoroughly analyzed using density functional theory, revealing the performance differences in methane activation due to different valence states of cobalt. On the Co (100) surface, methane dehydrogenation mainly proceeds through direct dehydrogenation and O-assisted dehydrogenation, with the O-assisted dehydrogenation having a higher energy barrier. The energy barrier on the CoO (100) surface is significantly higher than that on the Co (100) surface, thus it is not favorable for methane activation. In contrast, the energy barrier for methane dissociation and dehydrogenation on Co3O4 (110) is the lowest, with Co3+ exhibiting the best catalytic performance. Additionally, the activation effect of Co2+ sites on methane is similar to that on the CoO (100) surface, and is less effective than Co0 and Co3+, indicating that the Co2+ and Co3+ on the Co3O4 (110) surface do not show a significant synergistic effect in catalytic reactions. These research findings help to reveal the mechanistic role of different cobalt valence states in methane activation at the atomic level, providing important guidance for the design of efficient methane catalytic conversion catalysts.

Oxygen-coordinated cobalt single atom steered by doped-O and CoO for efficient hydrogen evolution at industrial current densities

The exploration and design of highly active, low-cost, transition metal-based electrocatalysts are crucial for large-scale green hydrogen production. Here, the heterostructure of oxygen-coordinated cobalt single atoms with O-doped carbon and CoO nanowires (Co-O-C-O/CoO/CF) is constructed for efficient and stable HER at industrial current densities. Benefiting from the synergistic effect of O doping and CoO nanowires, Co-O-C-O/CoO/CF exhibits extremely low overpotentials of 24.8, 229, and 239 mV to achieve current densities of 10, 500, and 1000 mA cm−2 in 1.0 M KOH solution, respectively, and operates stably for 1000 h at 1000 mA cm−2. Additionally, when coupled with NiFe-LDH in a self-assembled electrolyzer, it delivers a high current density of 1000 mA cm−2 at 1.97 V, along with outstanding stability, outperforming Pt/C||NiFe-LDH and most reported electrolyzers. Density functional theory (DFT) calculations reveal that the optimized d-band center and binding strength of H* and OH* intermediates for Co-O-C-O/CoO/CF lower the energy barrier of the rate-determining step. This work provides a new pathway for engineering Co-based catalysts for green hydrogen production at industrial current densities.

Efficient Adsorption and Degradation of Tetracycline Hydrochloride Using Metal-Organic Framework-Derived Cobalt-Based Catalysts and Mechanism Insight.

High-performance Co-based catalysts were derived by pyrolysis using synthesized MOFs as self-sacrificial templates. Various catalytic systems were constructed by peroxymonosulfate (PMS) to degrade tetracycline hydrochloride (TC). Adsorption-degradation efficiencies, cycle performance, dynamics, and the adsorption catalytic mechanism of various catalytic systems for TC were studied. The effects of different synthetic solvents, pyrolysis temperatures, and single/bimetallic element compositions on degradation efficiency were innovatively compared. The optimal catalyst and PMS dosage for the experiment were determined to be 10 mg and 0.1 mL, respectively. The results indicated that all catalytic systems could efficiently degrade TC and have a high acid-base resistance. The catalyst activity was significantly influenced by the pyrolysis temperature. The optimum pyrolysis temperatures for Zn@Co-N-C-T, CH3OH@Co-N-C-T, and H2O@Co-N-C-T were 1000, 900 and 900 °C, respectively. More abundant pore structures and active sites were generated in Zn@Co-N-C-1000, exhibiting an excellent TC degradation efficiency and adsorption capacity, achieving 94.73% and 167.564 mg/g, respectively. Meanwhile, the total organic carbon (TOC) of TC (50 mL, 50 mg/L) achieved a removal rate (TOC/TOC0) of 50.28%. Zn@Co-N-C-1000/PMS maintained over 83.27% TC degradation after five cycles. The adsorption mechanism of the catalyst for TC was investigated through the analysis of adsorption kinetics and isotherm models. The quenching test and EPR results indicated that TC was primarily degraded through the nonradical pathway. The efficient degradation of TC is attributed to the rapid electron transfer processes occurring at the two-phase interface and the redox cycling of Co0/Co2+/Co3+. Finally, LC-MS was used to analyze the intermediate products of TC degradation in the Zn@Co-N-C-1000/PMS system, and two degradation pathways were proposed.

A highly efficient Co-based catalyst for peroxymonosulfate activation for rapid degradation of RhB over a wide pH range

Cobalt-based materials have been demonstrated to be effective heterogeneous catalysts for peroxymonosulfate activation in degrading many refractory organic pollutants. In this study, a new cobalt-based catalyst was prepared using cobalt chloride hexahydrate (CoCl2·6H2O) as the Co2+ source, 2,3-pyrazine dicarboxylic acid and 3,6-DI-4-pyridyl-1,2,4,5-tetrazine (4-PYTZ) as ligands. This catalyst was employed as a peroxymonosulfate activator for the degradation of Rhodamine B(RhB). The results indicated that the prepared Co-based catalyst can effectively degrade RhB dye in aqueous solution by activating peroxymonosulfate (PMS). Specifically, when the initial concentration of RhB was 20 mg/L, its degradation rate exceeded 98 % within merely 9 min. The factors influencing the activation of PMS by the Co-based catalyst were examined, including PMS concentration, reaction temperature, solution pH, and the concentration of organic pollutants. Stability and reusability tests demonstrated that the prepared catalyst exhibited good stability, with the degradation rate of RhB remaining above 97 % after four repetitive experiments. Free radical quenching experiments and electron paramagnetic resonance (EPR) analyses revealed that sulfate radicals (SO4−) and hydroxyl radicals (OH) are the primary reactive radicals accountable for the degradation process. Additionally, it displayed excellent adaptability over a wide pH range, particularly within the pH levels ranging from 5 to 9. This study demonstrates that the prepared Co-based catalyst can serve as a stable and effective option for degrading organic dyes in wastewater treatment applications.

Combination of nanoparticles with single-metal sites synergistically boosts co-catalyzed formic acid dehydrogenation

The development of hydrogen technologies is at the heart of a green economy. As prerequisite for implementation of hydrogen storage, active and stable catalysts for (de)hydrogenation reactions are needed. So far, the use of precious metals associated with expensive costs dominates in this area. Herein, we present a new class of lower-cost Co-based catalysts (Co-SAs/NPs@NC) in which highly distributed single-metal sites are synergistically combined with small defined nanoparticles allowing efficient formic acid dehydrogenation. The optimal material with atomically dispersed CoN2C2 units and encapsulated 7-8 nm nanoparticles achieves an excellent gas yield of 1403.8 mL·g−1·h−1 using propylene carbonate as solvent, with no activity loss after 5 cycles, which is 15 times higher than that of the commercial Pd/C. In situ analytic experiments show that Co-SAs/NPs@NC enhances the adsorption and activation of the key intermediate monodentate HCOO*, thereby facilitating the following C-H bond breaking, compared to related single metal atom and nanoparticle catalysts. Theoretical calculations show that the integration of cobalt nanoparticles elevates the d-band center of the Co single atoms as the active center, which consequently enhances the coupling of the carbonyl O of the HCOO* intermediate to the Co centers, thereby lowering the energy barrier.