Cobalt-based Catalysts Research Articles

Confined highly dispersed trace cobalt species in shell porous carbon for activating peroxymonosulfate: Role of superoxide radical and singlet oxygen

The high cobalt leaching of cobalt-based catalysts during the activation of PMS is one of the bottlenecks in SR-AOPs. Herein, a series of trace cobalt confined in carbon shell catalysts (HDCo@C-X) with well-defined structures were designed using NH2-SiO2 nanospheres as a template via the surface-grafting−anchoring method, which was the innovation of the catalysts. AO7 removal rates were in an order of HDCo@C-700 (100%) ≈ HDCo@C-800 (100%) > HDCo@C-600 (80.4%) > Co/C-700 (43.8%). The apparent rate constant of AO7 in HDCo@C-700/PMS (0.0691 min−1) was 8.03 times higher than that of Co/C-700/PMS (0.0086 min−1). The synergistic index (SI) value was introduced to characterize the synergistic relationship between the active sites and confined structures of the catalyst. The SI value of HDCo@C-700/PMS system was 5.2, indicative of a strong synergistic effect between active sites and confined structures. The activation mechanism of HDCo@C-700 for PMS coexisted with free-radical (SO4•−, •OH, and O2•-) and non-radical (1O2 and electron transfer) pathways, and both O2•-and 1O2 played a major role in AO7 degradation. The catalytic activity of HDCo@C-700 gradually decreased to 39.6% and 27.0% for the 2nd and 3rd reuse, respectively, mainly ascribed to the surface oxidation of the carbon shell and the ultra-trace leaching of Co ions. Finally, the intermediates of AO7 in the HDCo@C-700/PMS system were detected by LC-MS, and a possible degradation path was proposed. The in silico toxicity predictions suggested the non-overlooked transformation-derived risks from the degradation products of AO7. This study provides a new insight into the design of PMS activators.

Outlook of Cobalt-Based Catalysts for Heterogeneous Hydroformylation of Olefins: From Nanostructures to Single Atoms

Outlook of Cobalt-Based Catalysts for Heterogeneous Hydroformylation of Olefins: From Nanostructures to Single Atoms

Levofloxacin degradation by porous Cox/CN activated peroxymonosulfate: Investigation of efficiency, mechanism, and degradation pathways

Co is a transition metal with a promising catalytic effect. Catalytic activation of peroxymonosulfate (PMS) and peroxydisulfate (PDS) using cobalt-based catalysts has received increasing attention as a promising technology that can remove difficult-to-degrade pollutants from water. Herein, a porous Co-doped g-C3N4 catalyst Cox/CN with non-uniform pores was synthesized to investigate the degradation of levofloxacin (LEV) by its activated peroxymonosulfate (PMS). The results showed that Co was uniformly distributed in g-C3N4 in the form of CoN bonds, which provided more active sites for the activation of PMS. The catalytic performance of Cox/CN was investigated by factors such as Co doping, catalyst dosing, PMS dosing, initial pH of the solution, and reaction temperature, and it was found that Cox/CN could maintain good catalytic activity in the pH range of 5–9. The cyclic catalytic degradation experiments showed that Cox/CN has good stability and reusability. The degradation mechanisms and pathways of LEV were also revealed such that SO4− was the main reactive oxidizing species (ROS), and LEV was degraded to organic compounds of smaller molecular mass through six pathways. This study offered a new strategy for synthesizing structurally diverse non-homogeneous Co-based catalysts and for the degradation of antibiotics.

Manganese as a structural promoter in silica-supported cobalt Fischer-Tropsch catalysts under simulated high conversion conditions

Understanding the deactivation mechanism of cobalt-based Fischer-Tropsch catalysts is of significant practical importance. Herein, we explored the role of manganese as a structural promoter on silica-supported cobalt nanoparticles under simulated high CO conversion conditions, i.e., high relative humidity. The structural changes in cobalt dispersion and oxidation state were followed by in situ Mössbauer emission spectroscopy. Adding manganese oxide to silica-supported cobalt enhanced the dispersion of metallic cobalt in the reduced catalysts. This higher cobalt dispersion, however, led to a stronger tendency of cobalt silicate formation under humid conditions. Without manganese, the cobalt particles sintered, and the larger ones were prone to transformation into cobalt carbide under high conversion conditions. As such, silica is not preferred as a support for practical FTS.

In-situ construction of mesoporous CuCo2O4 decorated CNTs networks as a long-lasting peroxymonosulfate activator for rapid removal of aqueous micropollutants

The sluggish redox cycle occurring during the oxidation processes and the biological toxicity caused by the leaching of dissociated cobalt ions dramatically hinder the practical application of cobalt-based catalysts. Herein, we synthesized the hydroxylated multi-walled CNTs coated with mesoporous CuCo2O4 (M-CuCo2O4@CNTs) to enhance peroxymonosulfate (PMS) activation. The introduction of CNTs enabled M-CuCo2O4@CNTs with a much better thermal stability. M-CuCo2O4@CNTs with dual electron-rich active sites (≡Co and ≡Cu) exhibited a long-lasting reactivity for the rapid degradation of micropollutants under mild conditions. In the process of PMS activation, the Cu+/Cu2+ redox couple as an electron donor participated in the conversion of Co3+ to Co2+ through rapid charge transfer. More importantly, this functional material with a highly interconnected conductive network and a strong surface adsorption effect significantly limited the leaching of cobalt ions. Meanwhile, the acute toxicity (LC50 and EC50) and the chronic toxicity (ChV) of the intermediates of RAN were significantly reduced compared with RAN after the treatment of the M-CuCo2O4@CNTs/PMS reaction system. DFT calculations were coupled with experiments to prove that PMS molecules were more favorable to be activated at ≡Co sites compared with ≡Cu sites. Finally, this study offered a new perspective for the activation mechanism of PMS-induced heterogeneous oxidation and an attractive alternative for micropollutants elimination in water treatment.

Ni-Doped La0.6Sr0.4CoO3 Perovskite as an Efficient Electrocatalyst for Oxygen Reduction and Evolution Reactions in Alkaline Media

The Co-based perovskite La0.6Sr0.4CoO3 has received significant attention as a potential electrocatalyst for its oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) due to its abundance, facile synthesis, and high oxygen kinetics. However, research on the catalytic performance of Ni-doped La0.6Sr0.4Co1−xNixO3 as a bifunctional cathode catalyst for Zn-air batteries (ZABs) is still scarce. In this work, lanthanum strontium cobalt-based perovskite catalysts with various Ni contents (La0.6Sr0.4Co1−xNixO3, x = 0, 0.2, 0.5, and 0.8) were synthesized using a simple combustion method. The effects of Ni doping on the morphology, structure, surface oxygen-related species, and valence states of the transition metals of the perovskite were characterized. The electrochemical behaviors of the perovskite catalysts in both ORR and OER were also assessed. The characterization results revealed that proper Ni doping can decrease particle size, increase surface oxygen vacancies, and create mixed valence states of the transition metal and, thus, lead to improvement of the electrocatalytic activity of perovskite catalysts. Among the different perovskite compositions, La0.6Sr0.4Co0.8Ni0.2O3 exhibited the best ORR/OER activity, with a higher limiting current density, smaller Tafel slope, higher half-wave potential, lower overpotential, and lower potential difference than the other compositions. When La0.6Sr0.4Co0.8Ni0.2O3 was applied as the cathodic catalyst in a primary ZAB, it delivered a peak power density of 81 mW cm−2. Additionally, in rechargeable ZABs, the La0.6Sr0.4Co0.8Ni0.2O3 catalyst exhibited a lower voltage gap (0.94 V) and higher stability during charge–discharge cycling than the commonly used catalyst Pt/C. These results indicate that Ni-doped La0.6Sr0.4Co0.8Ni0.2O3 is a promising bifunctional electrocatalyst for ZAB.

The oscillating Fischer-Tropsch reaction.

The mechanistic steps that underlie the formation of higher hydrocarbons in catalytic carbon monoxide (CO) hydrogenation at atmospheric pressure over cobalt-based catalysts (Fischer-Tropsch synthesis) have remained poorly understood. We reveal nonisothermal rate-and-selectivity oscillations that are self-sustained over extended periods of time (>24 hours) for a cobalt/cerium oxide catalyst with an atomic ratio of cobalt to cerium of 2:1 (Co2Ce1) at 220°C and equal partial pressures of the reactants. A microkinetic mechanism was used to generate rate-and-selectivity oscillations through forced temperature oscillations. Experimental and theoretical oscillations were in good agreement over an extended range of reactant pressure ratios. Additionally, phase portraits for hydrocarbon production were constructed that support the thermokinetic origin of our rate-and-selectivity oscillations.

Kinetics of Hydrogen Evolution during Ammonia Borane Hydrolysis with Cobalt-Based Catalysts

Kinetics of Hydrogen Evolution during Ammonia Borane Hydrolysis with Cobalt-Based Catalysts

Discrepancy of alkaline/neutral hydrogen evolution activity from NiCoSe2/NC and Co–NiSe/NC derived from in-situ thermal and solution processing selenizations of ZIF-67

Constructing cobalt-based selenide catalyst with accessible active site and superior charge transfer capability by simultaneous tailoring chemical component and structure through the feasible strategy is the key to display improved hydrogen evolution reaction (HER) activity. Herein, the bimetal NiCoSe2/nitrogen-doped carbon (NC) with novel flake structure (NiCoSe2/NC/NF) and particle-like cobalt-doped NiSe/NC (Co–NiSe/NC/NF) were synthesized by the in-situ thermal and solution processing selenizations of ZIF-67/NF, respectively. The intrinsic catalytic activity of NiCoSe2, the further accelerated charge-transfer capability originated from the fresh NC and two-dimensional layer structure, and mutually reinforcing kinetics from the closely integrated NiCoSe2 nanoparticles and NC plate endow NiCoSe2/NC/NF with 141 and 284 mV to reach 10 mA cm−2 under alkaline and neutral electrolytes, respectively, accompanying with Tafel slope of 109 and 206 mV dec−1, which were obviously higher than that of the HER properties of Co–NiSe/NC/NF (η10 = 179 mV and Tafel slope of 127 mV dec−1 at alkaline condition, η10 = 301 mV and Tafel slope of 235 mV dec−1 at neutral condition). Meanwhile, the NiCoSe2/NC/NF and Co–NiSe/NC/NF were exhibited well electrochemical stability under alkaline/neutral conditions. This study offers practicable strategy for intuitive comparing the influence of selenization procedures on the whole alkaline/neutral HER activity of cobalt-based catalysts.

Interfacial synergy within bimetallic oxide promotes selective hydrogenolysis of furfuryl alcohol to 1,5-pentanediol

Cobalt-based catalysts have displayed intrinsic activity for selective hydrogenolysis of furfural alcohol (FFA) to 1,5-pentanediol (1,5-PDO), but how to efficiently enhance 1,5-PDO selectivity remain a challenge. We prepared a series of CoPtLa-Hx catalysts by different reduction temperatures, and found the interfacial synergy within the bimetallic oxide CoOx-PtOx of the CoPtLa-H5 catalyst not only boosted the dispersion of Co species and Pt species, also increased electronic interactions within the bimetallic oxide which promoted the formation of the content of Co2+ that are critical to C-O bond rupture of FFA. The interfacial synergy significantly enhanced the 1,5-PDO yield (40.3 %) and favored high catalyst stability. We found that the formations of 1,5-PDO, 1,2-PDO and tetrahydrofurfuryl alcohol (THFA) are competing reactions, which is helpful to the design of highly selective catalysts towards the conversion FFA to 1,5-PDO.

Monolithic CoMgAl mixed metal oxide nanosheets on Al2O3 granules for the efficient advanced oxidation process

Cobalt-based catalysts are good candidates for the degradation of organic pollutants in wastewater treatment due to their high activity, while powdered catalysts for practical applications face challenges like difficulty in regeneration. To solve the problem, this work designs a monolithic catalyst by in-situ growth of CoMgAl mixed metal oxide (CoMgAl-MMO) nanosheets on the Al2O3 granules. The obtained catalyst possesses a developed mesoporous structure with highly-dispersed Co on the surface. The catalytic activity of CoMgAl-MMO/AG in the dye degradation is dependent on the Co/Mg molar ratio. All monolithic catalysts show high degradation performance, of which the CoMgAl-MMO/AG catalyst with Co/Mg ratio of 0.8/1.2 exhibited the highest degradation rate, achieving 95 % acid orange (AO7) removal in 10 min testing.

Different peroxymonosulfate activation and utilization pathways of typical cobalt oxides, cobalt-carbon and carbonaceous composites derived from metal-organic frameworks for pollutant oxidation in wastewater

Cobalt-based persulfate activation system has attracted increasing interests in recent years. However, few studies have focused on the corresponding relationship between different types of catalysts and peroxymonosulfate (PMS) utilization pathway in PMS activation process. To unravel this, three typical cobalt-based catalysts derived from ZIF materials (metal oxides ZMs, metal–carbon composite ZMCs, and etching metal–carbon composite ZCs) were applied in PMS activation system, and acetaminophen (APAP) was used as target contaminant. Quenching experiments and electron paramagnetic resonance (EPR) investigation testified that SO4·− were considered as the dominant reactive oxygen species (ROS) in the ZMs/PMS system, whereas non-radical pathway was dominant in the ZMCs/PMS and ZCs/PMS system. More Co-N species in ZMCs promoted the adsorption of PMS molecules and the formation of metastable PMS-catalyst complex. Electrochemical analysis proved that the improved intrinsic redox potential of metastable PMS-catalyst complex was due to the strong combination of PMS with positively charged Co-N species, resulting in the mass consumption of PMS. In addition, the CoⅣ=O species were mainly generated from single atomic Co or encapsulated Co sites in ZMCs and ZCs. Major degradation intermediates of APAP were detected by liquid chromatograph mass spectrometer (LC-MS) and differences in degradation pathway in three reaction systems were proposed. This study provides new insight into the PMS utilization mechanism during PMS activation process and offered environmentally friendly catalytic process for the degradation of pharmaceutical contaminants in wastewater.

A novel Co–CoAl2O4/exfoliated montmorillonite composite with improved nanoparticle dispersion for methyl orange removal via coupling peroxydisulfate

The degradation of refractory pollutants via the activation of peroxydisulfate (PDS) by Co-based nanostructures as catalysts has been gaining significant attention. However, most cobalt-based catalysts suffer from severe aggregation and metal ion leakage, resulting in a loss of activity and potential environmental threats. In this study, exfoliated montmorillonite (EMMT) loaded Co–CoAl2O4 composites were elaborately constructed through a facile coprecipitation-reduction method. The effects of the calcination temperature, the EMMT addition content, the pH of the precursor, and the reduction temperature on the microstructure of the Co–CoAl2O4/EMMT composites were investigated, and the optimum synthesis conditions were determined. In the optimal sample, well-crystallized CoAl2O4 nanoparticles were uniformly deposited onto the EMMT nanosheets with a considerably large specific surface area, while ultrafine metallic Co nanoparticles were homogeneously immobilized on the CoAl2O4 surface. This sample exhibited a superior activity (90% within 70 min) and reusability during methyl orange (MO) degradation. In the catalytic reaction, the superior adsorption property of EMMT facilitated the rapid transfer of MO molecules to the catalytically active sites. Moreover, CoAl2O4 acted as a transition layer which provided a cobalt source for the subsequent reduction process and regulated the growth of metallic Co nanoparticles, which increased the number of active sites for catalysis. Simultaneously, the metallic Co can not only activate PDS by being an electron donor, but also initiate the formation of Co-based redox pairs. This study offers new insights into the synthesis of efficient and cost-effective supported Co-based catalysts.

Enantioconvergent 6π Electrocyclization Enabled by Photoredox Racemization.

This study presents a novel photoredox-enabled enantioconvergent catalytic strategy used to construct chiral 2H-1,3-benzoxazines via an unprecedented oxa-6π electrocyclization utilizing racemic α-substituted glycinates as substrates. The approach leverages a cobalt-based chiral Lewis acid catalyst, which promotes the transformation under thermal or photoredox conditions. While the thermal reaction selectively converts only the (S)-configured glycinates into enantioenriched 2H-1,3-benzoxazines (up to 96:4 e.r.), the addition of 0.5 mol % of a commercially available iridium photocatalyst under visible light irradiation transforms the reaction into an enantioconvergent process. Detailed mechanistic and time course studies of optically pure α-deuterated substrates revealed the presence of an enantiospecific kinetic isotope effect, which helped to clarify the role of both the photo- and chiral Lewis acid catalyst in the reaction sequence. In this dual catalytic system, the photocatalyst promotes a dynamic interconversion between the substrate enantiomers─a process not accessible via ground-state chemistry─while the chiral Lewis acid selectively transforms only the (S)-configured substrates. Further mechanistic evidence for the proposed mechanism is provided by linear free energy relationship analysis, which suggests that the stereodetermining step involves a 6π electrocyclization under both thermal and photoredox conditions.

Kinetics of Hydrogen Evolution during Amminborane Hydrolysis with Cobalt-Based Catalysts

Kinetics of Hydrogen Evolution during Amminborane Hydrolysis with Cobalt-Based Catalysts

Sustainable production of hydrogen and carbon nanotubes/nanofibers from plastic waste through microwave degradation

Plastic waste pyrolysis to clean energy (H2) and valuable carbon nanotubes or nanofibers (CNTs/CNFs) is the most promising waste management and energy regeneration process. In this study, microwave-mediated single-step pyrolysis is used to produce COx-free hydrogen and CNTs/CNFs from real-world plastic films. Nickel, iron, and cobalt-based catalysts were prepared by the incipient wet-impregnation method and tested for real-world polyethylene plastic film degradation. In addition, the quality of CNTs produced and hydrogen yield were also compared for these catalysts. Various characterization tools were used to characterize the calcined catalysts, spent catalysts, and CNTs. Further, the effect of temperature ramp rate on hydrogen yield and CNTs properties was also analyzed. The results show that the iron-based catalyst produces a high yield of hydrogen and low-diameter and uniform-quality CNTs compared to other catalysts.

In Situ Transmission Electron Microscopy to Study the Location and Distribution Effect of Pt on the Reduction of Co3 O4 -SiO2.

The addition of Pt generally promotes the reduction of Co3 O4 in supported catalysts, which further improves their activity and selectivity. However, due to the limited spatial resolution, how Pt and its location and distribution affect the reduction of Co3 O4 remains unclear. Using ex situ and in situ ambient pressure scanning transmission electron microscopy, combined with temperature-programmed reduction, the reduction of silica-supported Co3 O4 without Pt and with different location and distribution of Pt is studied. Shrinkage of Co3 O4 nanoparticles is directly observed during their reduction, and Pt greatly lowers the reduction temperature. For the first time, the initial reduction of Co3 O4 with and without Pt is studied at the nanoscale. The initial reduction of Co3 O4 changes from surface to interface between Co3 O4 and SiO2 . Small Pt nanoparticles located at the interface between Co3 O4 and SiO2 promote the reduction of Co3 O4 by the detachment of Co3 O4 /CoO from SiO2 . After reduction, the Pt and part of the Co form an alloy with Pt well dispersed. This study for the first time unravels the effects of Pt location and distribution on the reduction of Co3 O4 nanoparticles, and helps to design cobalt-based catalysts with efficient use of Pt as a reduction promoter.

Enhanced photo-Fenton-like performance of biotemplated manganese-doped cobalt silicate catalysts

Cobalt-based catalysts are one of the preferred materials for effective activation of hydrogen peroxide, and metal element doping and active site dispersion are effective methods to enhance their catalytic activity. In this work, manganese-doped cobalt silicate@diatomite composites with enhanced photo-Fenton-like oxidation performance were prepared and used for degradation of methyl orange (MO) dyes. Experiments showed that manganese doping increased the specific surface area of the samples and decreased the band gap energy of the materials. Moreover, the samples doped with manganese elements had better photo-Fenton-like properties. The degradation of methyl orange by Co0.25MnSi@DE/H2O2-UV reached more than 95%. In addition, density-functional theory (DFT) calculations showed that the Mn-doped samples were more prone to activate H2O2 than non-manganese-doped samples, and the synergistic effect from using a bimetallic catalyst increased the photo-Fenton oxidation activity in the system. ESR spectroscopy and bursting tests indicated that the possible degradation mechanism consisted of hydroxyl radicals and superoxide radicals generated by the synergistic effect of cobalt ions and manganese under UV radiation. This study thus presents a feasible idea for the preparation of cobalt-based photo-Fenton catalysts that also provides a basis for understanding the catalytic mechanism analysis of other types of bimetallic catalysts.

Size and Electronic Effects on the Performance of (Corrolato)cobalt-Modified Electrodes for Oxygen Reduction Reaction Catalysis.

Considering the worldwide efforts for designing catalysts that are not based on platinum group metals while still reserving the many advantages thereof, this study focused on the many variables that dictate the performance of cathodes used for fuel cells, regarding the efficient and selective reduction of oxygen to water. This was done by investigating two kinds of porous carbon electrodes, modified by molecular cobalt(III) complexes chelated by corroles that differ very much in size and electron-withdrawing capability. Examination of the electronic effect uncovered shifts in the CoII/CoIII redox potentials and also large differences in the affinity of the cobalt center to external ligands. Spontaneous absorption of the catalysts was found to depend on the size of the corrole's substituents (C6F5 ≫ CF3 ≫ H) and the metal's axial ligands (PPh3 versus pyridine), as well as on the porosity of the carbon electrodes (BP2000 > Vulcan). The better-performing cobalt-based catalysts were almost as active and selective as 20% platinum on Vulcan in terms of the onset potential and the only 2-10% undesirable formation of hydrogen peroxide. Durability was also addressed by using the best-performing modified cathode in a proper anion-exchange membrane fuel cell setup, revealing very little voltage change during 12 h of operation.

Current Mechanism of Peroxymonosulfate Activation by Cobalt-Based Heterogeneous Catalysts in Degrading Organic Compounds

Current Mechanism of Peroxymonosulfate Activation by Cobalt-Based Heterogeneous Catalysts in Degrading Organic Compounds