Dispersed Cobalt Research Articles

Molecular self-assembled synthesis of highly dispersed Co single-atom coordinated 2-methylimidazole modified carbon nitride for peroxymonosulfate activation

Although single-atom catalysts are pioneers in peroxymonosulfate (PMS) activation, selection of substrates and enhanced binding remains ambiguous. Here, a novel highly dispersed cobalt single-atom loaded 2-methylimidazole (MeIm) ligand-modified carbon nitride catalyst (Co-MCAMeIm) was prepared by a molecular self-assembly strategy. The densely distributed SA-Co with Co-N sites were corroborated by HAADF-STEM and XAFS analysis. The strong chelation of pre-dispersed ligands and triazine ring of g-C3N4 confers higher stability to the catalyst, reducing Co leaching. Meanwhile, the g-C3N4 substrate offers additional adsorption sites to shorten the reaction distance. The embedded Co-N functions as an electron donor capable of bridging N-rich carbon networks, hence accelerating the electron transport. Experimental findings demonstrated that sulfamethoxazole (SMX) could be effectively cleared through Co-MCAMeIm/PMS process (99.1%, 0.13 min−1). Several key influencing factors like Co to MeIm molar ratio, PMS concentration, Co-MCAMeIm dosage, pH value, anions, and humic acid were examined. The catalytic pathway is dominated by the activation of PMS with SA-Co-N as active sites to form 1O2. Meanwhile, a multi-ROS process with occurrence of SO4•-, O2•- and •OH was confirmed. Additionally, the SMX degradation routes and toxicity variations were derived and analyzed. Herein, the research may provide new insights for stable single-atom catalyst towards water treatment.

Synergistically enhanced sodium ion storage from encapsulating highly dispersed cobalt nanodots into N, P, S tri-doped hexapod carbon framework

Development of multitudinous heteroatoms co-doped carbon nanomaterials with pleasurable electrochemical behavior for sodium ion batteries is still an enormous challenge. Herein, high dispersion cobalt nanodots encapsulating into N, P, S tri-doped hexapod carbon (H-Co@NPSC) have been victoriously synthesized via H-ZIF67@polymer template strategy with using poly (hexachlorocyclophos-phazene and 4,4′-sulfonyldiphenol) as both carbon source and N, P, S multiple heteroatom doping sources. The uniform distribution of cobalt nanodots and the Co-N bonds are conducive to form a high conductive network, which synergistically increase a lot adsorption sites and lessens the diffusion energy barrier, thereby improving the fast Na+ ions diffusion kinetics. Consequently, H-Co@NPSC delivers the reversible capacity of 311.1 mAh g−1 at 1 A g−1 after 450 cycles with 70% capacity storage rate, while obtains the capacity of 237.1 mAh g- 1 after 200 cycles at the elevated current densities of 5 A g−1 as an excellent anode material for SIBs. These interesting results pave a generous avenue for the exploitation of promising carbon anode materials for Na+ storage.

CoZn-ZIF and melamine co-derived double carbon layer matrix supported highly dispersed and exposed Co nanoparticles for efficient degradation of sulfamethoxazole

Metal-organic framework (MOF)-derived carbon materials have drawn tremendous attention as activators of peroxymonosulfate (PMS) for the degradation of antibiotics. However, it is still challenging to construct MOF-derived materials with well-dispersed and highly-exposed metal active sites. Herein, the bimetallic Cobalt-Zinc-zeolite imidazolate framework and melamine co-derived double layer nitrogen-doped porous carbon matrix supported highly dispersed cobalt nanoparticles (Co NPs) (denoted as Co-NC-C) with the exposure of more Co NPs sites was developed by one-step pyrolysis method. The transmission electron microscopy results demonstrate that double layer carbon matrix as a dispersant can effectively inhibit the agglomeration of Co NPs, and Co-NC-C possessed more exposure of Co active sites compared with Co-NC without melamine. Co-NC-C efficiently activated PMS to remove over 96.67% of sulfamethoxazole (SMX) at a widespread range of pH within 120 min due to its the highly-exposed Co active sites and high graphitization degree. Additionally, the degradation mechanism dominated by the singlet oxygen was demonstrated. Finally, four products and two probable degradation pathways of SMX were confirmed. Half of the products were less toxic than SMX based on the ecological structure activity relationships analysis results. The study provides valuable insights for the development of MOF-derived catalysts with well-dispersed and highly-exposed metal active sites.

Metal-organic framework-derived Co-C catalyst for the selective hydrogenation of cinnamaldehyde to cinnamic alcohol

The liquid phase selective hydrogenation of cinnamaldehyde has been investigated over the catalysts Co-C-T (T = 400–700 °C), which were derived from the carbonization of the MOF precursor Co-BTC at different temperatures in inert atmosphere. Co-C-500 exhibited a higher conversion (85.3%) than those carbonized at other temperatures, with 51.5% selectivity to cinnamyl alcohol, under a mild condition (90 °C, 4 h, 2 MPa H2, solvent: 9 ml ethanol and 1 ml water). The high catalytic activity of Co-C-500 can be ascribed to the large specific surface area of the catalyst, the uniformly dispersed metallic cobalt nanoparticles, and the more defect sites on the carbon support. Moreover, Co-C-500 showed excellent reusability in 5 successive cycles, mainly related to the uniformly dispersed cobalt nanoparticles embedded in carbon support.

CO2 electroreduction to multicarbon products from carbonate capture liquid

CO2 electroreduction to multicarbon products from carbonate capture liquid

Graphene nanoplatelets promoted CoO-based catalyst for low temperature CO2 methanation reaction

Methanation of CO2 is an important reaction for reducing CO2 emissions in a power-to-gas system. Compared to cobalt supported on gamma-Al2O3, cobalt supported on graphene nanoplatelets (GNPs) showed significantly better performance for CO2 methanation. Cobalt supported on GNPs was capable of 15% conversion of CO2 to CH4 at temperatures below 250°C, compared to 5% for cobalt supported on Al2O3. In situ thermogravimetric analysis (TGA) demonstrated that the Co/GNP catalyst was stable to 400°C. The maximum catalyst mass-specific CH4 yield was obtained at a Co loading of 5wt% on GNPs; however, high Co loading on GNPs deactivated the reactivity of the Co/GNP catalyst. Transmission electron microscopy (TEM) demonstrated that 5wt% Co/GNPs had the smallest and most dispersed cobalt nanoparticles. Excessive loading of cobalt tended to form isolated large Co nanoparticles. X-ray photoelectron spectroscopy (XPS) and Raman spectrometry revealed that more CoO phases were maintained on the surface of 5wt% Co/GNPs, indicating that the interaction between the Co and the GNPs had more of an impact on cobalt’s redox capacity than did particle size, which ultimately affected cobalt’s active phase during the CO2 reduction process. Furthermore, Raman spectrometry demonstrated that Co loading led to an increase in graphene defects. Higher Co loading on GNPs resulted in fewer interfaces between Co and GNPs due to the agglomeration of Co nanoparticles.

Preparation of highly dispersed silicon spheres supported cobalt-based catalysts and their catalytic performance for Fischer-Tropsch synthesis

A series of silicon spheres supported cobalt catalysts were prepared by incipient wetness impregnation followed by decomposition under treatment of glow discharge plasma with different intensities. The catalysts were characterized by X-ray powder diffraction, N2 physical adsorption-desorption, H2 temperature-programmed reduction, transmission electron microscope and Fourier-Transform Infrared spectroscopy. The Fischer-Tropsch synthesis performance were tested on a fixed bed reactor. The influence of plasma treatment on cobalt dispersion, reducibility and cobalt-support interaction were analyzed and discussed. The results showed that the plasma-treated catalysts had better catalytic performance than the calcined sample. The Co/SP-P650W catalyst showed the highest reaction activity due to the proper cobalt dispersion and higher cobalt reducibility.

CO2 methanation vs reverse WGS activity on Co/γ-Al2O3 catalysts at atmospheric pressure: effect of cobalt loading and silica addition on selectivity and stability

Catalysts containing 5 wt% and 13.6 wt% cobalt on pure alumina and 5 wt% silica-containing alumina were prepared by conventional impregnation procedure and calcined at 1023 K for 5 h. The samples were characterized both as prepared, pre-reduced and after reaction by means of X-ray Diffraction, FTIR and DR-UV-Vis-NIR spectroscopies and by X-ray Pholotoelectron Spectroscopy. After pre-treatment in H2/N2 atmosphere, they were tested in CO2 hydrogenation at atmospheric pressure in the temperature range 523–773 K. The material with 5 wt% Co on pure γ-Al2O3 was found predominantly active as a reverse Water Gas Shift (rWGS) catalyst producing mainly CO and approaching rWGS forecasted thermodynamic equilibrium at the highest temperatures. The addition of silica decreases selectivity to CO, with an enhanced methanation activity. Instead, the materials with 13.6 wt% Co on pure γ-Al2O3 was found to act mainly as a methanation catalyst, although with the coproduction of limited amounts of CO. The rWGS catalytic activity is apparently stable while slight deactivation for methanation was found, attributed to deposits of stick-like carbon residues. Investigated 13.6 wt% Co/γ-Al2O3 is less selective for methanation than comparable Ni/γ-Al2O3 catalysts while but more stable than unsupported cobalt and Co/SiO2 catalysts. Silica addition to 13.6 wt% Co does not modify significantly the catalytic activity while it slightly decreases stability. The effect of silica is a combination of two partially contrasting phenomena, i.e. the increase of the total surface area of the support and the decrease of the available surface area fraction for cobalt dispersion.

Nanoconfined Molecular Catalysts in Integrated Gas Diffusion Electrodes for High‐Current‐Density CO2 Electroreduction

AbstractMolecular catalysts are promising catalysts to electrochemically convert CO2 into CO with high selectivity. However, achieving industrial‐level current density remains challenging due to the limitation of charge‐ and mass‐transport in gas diffusion electrode. Herein, a novel gas diffusion electrode architecture by confining highly dispersed cobalt(II) phthalocyanine (CoPc) molecules into ‐graphene oxide (GO) nanosheets (denoted as CoPc@GO) is designed. Benefiting from the accelerated CO2 diffusion and charge transport in the nanoconfined structure, the designed electrode achieves a high CO partial current density of 481.65 ± 12.50 mA cm−2 and a cathode energy efficiency over 64% for CO. The experimentally measured CO2 transport dynamics and molecular dynamics simulation confirm the accelerated CO2 diffusion, while theoretical calculations reveal the decreased energy barrier of the CO2 activation in the confined space. This study paves a new way for electrode architecture design that would accelerate the implementation of CO2 electrolysis technology.

Role of benzene tricarboxylic acid in regulating cobalt-titania interface-interaction to access highly dispersed cobalt nanoparticles catalyst

Finding a robust cobalt catalyst with highly exposed metallic, active sites has been challenging but highly desirable. Extending our in-situ hybridization route, herein we prepared a highly dispersed and accessible CoOx#TiO2 catalyst via interface engineering induced by the benzene tricarboxylic acid (BTC). At the optimized content of BTC (molar ratio of BTC/Co=1), the introduced BTC exerted two vital roles in providing active cobalt center, one is retarding the creation of hard-reducible cobalt titanate (CoTiO3) to facilitate the reduction of CoOx species, the other is stabilizing the anatase phase and retaining a relatively high surface area to well-disperse the cobalt nanoparticles. As a result, the selected CoOx#TiO2, affording a large number of accessible metallic cobalt sites, showed an excellent furfuryl alcohol productivity of 31 gFOL·gCo-1·h-1 at 140 oC and 2.0 MPa, which is among the top values reported by other scientists. SynopsisThe BTC ligands can stabilize the anatase and retard the creation of hard-reducible cobalt titanate (CoTiO3), affording high number of accessible metallic cobalt species. An excellent FOL productivity of 31 gFUR·gCo-1·h-1 at 140 oC and 2.0 MPa was achieved.

Oxidation of α C H bonds in alkyl aromatics with O2 catalyzed by highly dispersed cobalt(II) coordinated in confined reaction channel of porphyrin-based POFs with simultaneously enhanced conversion and selectivity

To obtain oxidative functionalization of αCH bonds in alkyl aromatics with O2, 3D POFs were constructed as heterogeneous catalysts based on metalloporphyrin. In 3D POFs, porosity was designed as confined reaction channel to control excessive expansion of free radical quantity, and heterogeneous catalysis was employed to reduce oxidative transformation of partial oxidation products induced by homogeneous catalytic sites. Applied to partial oxidation of αCH bonds, enhanced conversion and selectivity were achieved simultaneously, especially in employment of POFs with residual -Br and -B[OC(CH3)2]2 being capped. In oxidation of 1-ethyl-4-nitrobenzene, conversion was increased from 38.9% to 63.1%, meanwhile selectivity towards 4-nitroacetophenone was increased from 65.5% to 91.3%. Simultaneously enhanced conversion and selectivity was attributed to controlled expansion of free radical quantity, reduced oxidative transformation of partial oxidation products, and lower temperature. An instructive reference was provided for efficient functionalization of CH bonds with O2, and for other chemical transformations involved free radicals.

Regulation of Impedance Matching and Dielectric Loss Properties of N-Doped Carbon Hollow Nanospheres Modified With Atomically Dispersed Cobalt Sites for Microwave Energy Attenuation.

The rational design of lightweight, broad-band, and high-performance microwave absorbers is urgently required for addressing electromagnetic pollution issue. Metal single atoms (M-SAs) absorbers receive considerable interest in the field of microwave absorption due to the unique electronic structures of M-SAs. However, the simultaneous engineering of the morphology and electronic structure of M-SAs based absorbers remains challenging. Herein, a template-assisted method is utilized to fabricate isolated Co-SAs on N-doped hollow carbon spheres (NHCS@Co-SAs) for high-performance microwave absorption. The combination of atomically dispersed Co sites and hollow supports endows NHCS@Co-SAs with excellent microwave absorption properties. Typically, at an ultralow filler content of 8wt%, the minimum reflection loss and effective absorption bandwidth of the NHCS@Co-SAs are up to -44.96dB and 5.25GHz, respectively, while the absorbing thickness is only 2mm. Theoretical calculations and experimental results indicate that the impedance matching characteristic and dielectric loss of the NHCSs can be tuned via the introduction of M-SAs, which are responsible for the excellent microwave absorption properties of NHCS@Co-SAs. This work provides an atomic-level insight into the relationship between the electronic states of absorbers and their microwave absorption properties for developing advanced microwave absorbers.

CoMn catalysts derived from partial decomposed layered CoMn-MOF materials for higher alcohol synthesis from syngas

Direct and selective conversion of syngas to higher alcohols (C2+OH, HA) is highly attractive but remains challenges in improving the high catalytic performance. Herein, a series of catalysts were prepared by thermal decomposing layered-structured CoMn-MOF materials and used in the HA synthesis.Characterization results showed that the MOF framework could partially maintain after calcination at 350 °C under N2 flow, in which the Co2+ species can provide extra non-dissociative adsorption CO sties, leading to an improved alcohol selectivity. And the addition of manganese could promote the cobalt dispersion and Co2C formation. The synergistic catalysis of these active species allowed the optimal CoMn-350 catalyst to display a superior selectivity to HA, specifically the alcohol selectivity reached 57.5% and the distribution of C2+OH in total alcohols was up to 82.4 % when the CO conversion was 51.5%. The catalyst with remaining MOF framework also showed an excellent stability during 250 h reaction. This work highlights a feasible strategy for the design of highly efficient catalysts for HA synthesis via the partial decomposing MOF materials.

Synthesis and photocatalytic activity of the Co-containing materials based on amorphous SiO2

Functional materials based on highly dispersed amorphous silica and cobalt compounds have been obtained by solvothermal and mechanochemical methods. The formation of silicate Co3(Si2O5)2(OH)2 under hydrothermal conditions has been established. This composition, in comparison with mechano-mixes, provides better photoactivity in the hydroquinone decomposition reaction under ultraviolet irradiation, herewith maintaining the surface characteristics of amorphous SiO2.

A Heterogeneous Single Atom Cobalt Catalyst for Highly Efficient Acceptorless Dehydrogenative Coupling Reactions.

A fundamental understanding of metal active sites in single-atom catalysts (SACs) is important and challenging in the development of high-performance catalyst systems. Here, a highly efficient and straightforward molten-salt-assisted approach is reported to create atomically dispersed cobalt atoms supported over vanadium pentoxide layered material, with each cobalt atom coordinated with four neighboring oxygen atoms. The liquid environment and the strong polarizing force of the molten salt at high temperatures potentially favor the weakening of VO bonding and the formation of CoO bonding on the vanadium oxide surface. This cobalt SAC achieves extraordinary catalytic efficiency in acceptorless dehydrogenative coupling of alcohols with amines to give imines, with more than 99% selectivity under almost 100% conversion within 3h, along with a high turnover frequency (TOF)of 5882h-1 , exceeding those of previously reported benchmarking catalysts. Moreover, it delivers excellent recyclability, reaction scalability, and substrate tolerance. Density functionaltheory(DFT) calculations further confirm that the optimized coordination environment and strong electronic metal-support interaction contribute significantly to the activation of reactants. The findings provide a feasible route to construct SACs at the atomic level for use in organic transformations.

Atomically Dispersed Co-N/C Catalyst for Divergent Synthesis of Nitrogen-Containing Compounds from Alkenes.

Alkene functionalization with a single-atom catalyst (SAC) which merges homogeneous and heterogeneous catalysis is a fascinating route to obtain high-value-added molecules. However, C-N bond formation of alkene with SAC is still unexplored. Herein, a bimetal-organic framework-derived Co-N/C catalyst with an atomically dispersed cobalt center is reported to show good activity of chemoselective aziridination/oxyamination reactions from alkene and hydroxylamine, and late-stage functionalization of complex alkenes and diversified synthetic transformations of the aziridine product further expand the utility of this method. Moreover, this system proceeds without external oxidants and exhibits mild, atom-economic, and recyclable characters. Detailed spectroscopic characterizations and mechanistic studies revealed the structure of the catalytic center and possible intermediates involved in the mechanism cycle.

Speciation of Oxygen Functional Groups on the Carbon Support Controls the Electrocatalytic Activity of Cobalt Oxide Nanoparticles in the Oxygen Evolution Reaction.

The effective use of the active phase is the main goal of the optimization of supported catalysts. However, carbon supports do not interact strongly with metal oxides, thus, oxidative treatment is often used to enhance the number of anchoring sites for deposited particles. In this study, we set out to investigate whether the oxidation pretreatment of mesoporous carbon allows the depositing of a higher loading and a more dispersed cobalt active phase. We used graphitic ordered mesoporous carbon obtained by a hard-template method as active phase support. To obtain different surface concentrations and speciation of oxygen functional groups, we used a low-temperature oxygen plasma. The main methods used to characterize the studied materials were X-ray photoelectron spectroscopy, transmission electron microscopy, and electrocatalytic tests in the oxygen evolution reaction. We have found that the oxidative pretreatment of mesoporous carbon influences the speciation of the deposited cobalt oxide phase. Moreover, the activity of the electrocatalysts in oxygen evolution is positively correlated with the relative content of the COO-type groups and negatively correlated with the C═O-type groups on the carbon support. Furthermore, the high relative content of COO-type groups on the carbon support is correlated with the presence of well-dispersed Co3O4 nanoparticles. The results obtained indicate that to achieve a better dispersed and thus more catalytically active material, it is more important to control the speciation of the oxygen functional groups rather than to maximize their total concentration.

Highly dispersed Co anchored on Ce-doped hydroxyapatite as a dual-functional catalyst for selective hydrogenolysis of 5-hydroxymethylfurfural.

Hydrodeoxygenation (HDO) is an indispensable approach to produce renewable biofuels and value-added chemicals using natural biomass and its derivatives. 2,5-Dimethylfuran (DMF) is considered to be a very promising liquid biofuel, and it can be fabricated by HDO of the biomass derivative 5-hydroxymethylfurfural (HMF). Herein, a highly efficient bifunctional catalyst, Co/HAP(Ce), was fabricated by anchoring highly dispersed Co on Ce-doped hydroxyapatite (HAP(Ce)). Co/HAP(Ce) displayed excellent HDO catalytic activity to convert HMF to DMF, and 99% HMF conversion and 96% DMF selectivity can be obtained under 150 °C, 2 MPa H2 conditions for 5 h. Density functional theory calculations revealed that H2 can be more easily activated by Co/HAP(Ce). Systematic studies confirmed that the high activity of Co/HAP(Ce) can be ascribed to the desired acid-alkali properties, highly dispersed cobalt species and strong metal-support interactions. This research provides a cost effective approach for designing efficient catalysts for HDO of biomass and its derivatives.

Hierarchically ordered porous carbon with atomically dispersed cobalt for oxidative esterification of furfural

Co-SA/3DOM-NC catalysts with a three-dimensional ordered macropore structure and highly dispersed CoN4sites are successfully fabricated, and show high catalytic activity and selectivity in the oxidative esterification of furfural.

Correction: Hierarchically ordered porous carbon with atomically dispersed cobalt for oxidative esterification of furfural

Correction for ‘Hierarchically ordered porous carbon with atomically dispersed cobalt for oxidative esterification of furfural’ by Wen Yao et al., Ind. Chem. Mater., 2023, 1, 106–116, https://doi.org/10.1039/D2IM00045H.