Metallic Cobalt Nanoparticles Research Articles

Synergistic restriction of polysulfides enabled by cobalt@carbon spheres embedded CNTs: A facile approach for constructing sulfur cathodes with high sulfur content

Despite the bright fortune of lithium-sulfur (Li-S) batteries as one of the next-generation energy storage systems owing to the ultrahigh theoretical energy density and earth-abundance of sulfur, crucial challenges including polysulfide shuttling and low sulfur content of sulfur cathodes need to be overcome before the commercial survival of sulfur cathodes. Herein, cobalt/carbon spheres embedded CNTs (Co-C-CNTs) are rationally designed as multifunctional hosts to synergistically address the drawbacks of sulfur cathodes. The host is synthesized by a facile pyrolysis using Co(OH)2 template and followed with the controllable etching process. The hierarchical porous structure owning high pore volume and surface area can buffer the volume change, physically confine polysulfides, and provide conductive networks. Besides, partially remained metallic cobalt nanoparticles are favorable for chemical adsorption and conversion of polysulfides, as validated by density functional theory simulations. With the combination of above merits, the S@Co-C-CNTs cathodes with a high sulfur content of 80 wt% present a superior initial capacity (1568 mAh g−1 at 0.1C) with ultrahigh 93.6% active material utilization, and excellent rate performance (649 mAh g−1 at 2C), providing feasible strategies for the optimization of cathodes in metal-sulfur batteries.

Si nanoparticles enclosed in hierarchically structured dual-component porous carbon as superior anode for lithium-ion batteries: Structure formation and properties investigation

The volume effect of Si hinders its application as anode for lithium-ion batteries. To address these challenges, composites consisting of Si nanoparticles enclosed in a hierarchically structured carbon matrix are constructed. Firstly, Si nanoparticles are embedded in the metal-organic framework of ZIF-67 with a surface modification directed epitaxial growth. Subsequently, the Si embedded ZIF-67 are further integrated into microspheres of polysaccharide using spray drying, achieving encapsulation of the Si nanoparticles in a hierarchically structured carbon sphere after calcination. Metallic cobalt nanoparticles are derived from the decomposition of ZIF-67, which act as a catalyst and facilitate in turn the decomposition of the organic ligands along with the extensive growth of carbon nanotubes (CNTs). The CNTs formed in-situ act as reinforcing and conductive networks, providing the compact and robust interfaces between the Si and the carbon matrix. The dual-component carbon substrates induce a thinner and inorganic carbonate-rich solid electrolyte interface (SEI) during cycling. The novel structure endows the composite a specific capacity of 1018 mAh g−1 after 1200 cycles at a current density of 1000 mA g−1 for half-cell and exhibits a high capacity retention rate of 76.9 % after 200 cycles for full cell paired with lithium iron phosphate as cathode.

Co nanoparticle-loaded porous carbon for high-performance supercapacitors

Porous carbon materials doped with transition metals have emerged as promising electrode materials in the field of energy storage due to their higher theoretical capacitance and cost-effectiveness. In this study, metallic cobalt nanoparticles (Co NPs) were successfully loaded into porous carbon via one-step carbonization method for electrochemical research applications as electrode materials (Co/CM). A comparative investigation was conducted by varying the content of polystyrene microspheres (PS) to optimize the porous morphology. Scanning electron microscopy (SEM) analysis revealed that the Co/CM-3 composite displayed a plate-like porous structure, while transmission electron microscopy (TEM) confirmed the uniform loading of Co NPs within the porous carbon skeleton. The composite with the optimal PS content (Co/CM-3) exhibited a specific capacitance of up to 810 F g−1 (at 1 A g−1) in the three-electrode system. Furthermore, asymmetric supercapacitors assembled with the prepared electrode as the positive electrode and activated carbon as the negative electrode demonstrated an impressive energy density of up to 40 Wh kg−1 (at a power density of 746 W kg−1). Remarkably, the capacitance retention rate remained at 88.24 % even after 5000 consecutive charge and discharge cycles, highlighting the promising potential of this electrode material for practical applications in energy storage.

Synergistic role of Co and CoP on highly dispersed cobalt nanoparticles embeded in porous carbon for efficient PH3 decomposition

Efficient resourceful treatment of phosphine tail gas is a huge challenge. In this study, a series of cobalt nanoparticles embeded in porous carbon (Co@C) catalysts were obtained via pyrolysis of Co-based MOF as precursor for catalytic decomposition of phosphine (PH3) by regulating the ratio of reactants of MOFs. The composition, morphology and structure of the catalysts were characterized by inductively coupled plasma, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and BET measurement. The effect of Co@C catalysts with different reactant ratio on the catalytic decomposition of PH3 was tested, and the catalysts before and after the reaction were compared. It was found that the catalyst with MOF as the precursor after pyrolysis can still retain the porosity and large specific surface area of MOF. The metal cobalt nanoparticles and its oxides can be uniformly distributed in time under high loading, which is conducive to the reaction with phosphine to form metal phosphide (CoP), and the rapid and efficient decomposition of PH3 was completed under the synergistic effect of the two kinds of active sites of Co and CoP. The best catalytic decomposition efficiency is Co@C-5 catalyst, which can achieve 100 % decomposition efficiency at 350 °C and has good stability.

Hydrazine metal complexes as a single source in the mechanochemical preparation of metallic magnetic nanoparticles and investigation of their magnetic hyperthermia properties

Ferromagnetic metallic cobalt and nickel nanoparticles were synthesized by intramolecular metal-hydrazine ligand oxidation reduction reaction in basic media and the solid state. Nickel nanoparticles Ni1 and Ni2 are obtained from two complexes, Ni(N2H4)2(C2O4) and Ni(N2H4)2(HCO2)2, respectively. X-ray powder diffraction (XRD) and energy-dispersive X-ray (EDX) data show pure fcc crystal structures of nanoparticles. Scanning electron microscopy (SEM) images revealed both Ni1 and Ni2 nanoparticles have agglomerated sphere morphologies. The crystallite size estimated by using the Scherer method for Ni1 and Ni2 were 18.7 and 6.2 nm. Vibrating sample magnetometer (VSM) data show the coercivity of metallic nickel samples Ni1 and Ni2 are 50 and 153 Oe, respectively. Both nanoparticles cause an increase in the temperature of water under applied alternative magnetic field and showed specific loss power (SLP) of 70 W/g and 104.8 W/g, respectively. The same method is used in preparation of cobalt nanoparticles from two complexes, Co(N2H4)2(C2O4) and Co(N2H4)2(HCO2)2. XRD analysis data show both nanoparticles have hcp crystal structure. SEM images show nanosheet structure with sheet thickness of 10 to 30 nm. Coercivity of Co1 and Co2 nanoparticles obtained by VSM and Hc are 182 and 171 Oe, respectively. In spite of high coercivity in both Co1 and Co2 nanoparticles, the magnetic hyperthermia heating effects are not observed in practice and specific loss power (SLP) is zero.

CO2 hydrogenation to synthetic natural gas with light hydrocarbons on Mn-promoted mesoporous Co3O4-Al2O3 metal oxides

Direct CO2 conversion into synthetic natural gas (SNG, CH4) with simultaneous small production of light paraffinic C2-C4 hydrocarbons to enhance a heating value of SNG was investigated with ordered mesoporous CoMnAl mixed metal oxides (denoted as m-CoMnAl). CO2 hydrogenation activity to form hydrocarbons with small CO byproduct formed by a reverse water gas shift reaction (RWGS) was strongly affected by the MnO2 promoter content in the ordered Co3O4-Al2O3 mesoporous structures. The m-CoMnAl structures with proper amount of Mn promoter were found to be effective to enhance CO2 conversion to methane with small amount of light hydrocarbons formation, which were mainly attributed to the presence of abundant oxygen vacant sites with a stable preservation of the partially oxidized cobalt nanoparticles in the ordered mesoporous Co3O4-Al2O3 structures even under a reductive hydrogenation condition. Selective methanation of CO2 was found to be more favorable on the highly reduced metallic cobalt nanoparticles formed with smaller amount of Mn promoter (m-CoMnAl(0.05)), however, excessive Mn content such as Mn/Co ratio > 1 (m-CoMnAl(1.0)) revealed less structural stability of ordered mesoporous structures with lower CO2 conversion with relatively higher CO selectivity of 1.4 % with lower olefin selectivity through severe phase segregations of the Co-Mn-Al mixed metal oxides with selective formations of MnCO3 phases.

Cobalt Encapsulated in Nitrogen-Doped Graphite-like Shells as Efficient Catalyst for Selective Oxidation of Arylalkanes.

Selective oxidation of ethylbenzene to acetophenne is an important process in both organic synthesis and fine chemicals diligence. The cobalt-based catalysts combined with nitrogen-doped carbon have received great attention in ethylbenzene (EB) oxidation. Here, a series of cobalt catalysts with metallic cobalt nanoparticles (NPs) encapsulated in nitrogen-doped graphite-like carbon shells (Co@NC) have been constructed through the one-pot pyrolysis method in the presence of different nitrogen-containing compounds (urea, dicyandiamide and melamine), and their catalytic performance in solvent-free oxidation of EB with tert-butyl hydrogen peroxide (TBHP) as an oxidant was investigated. Under optimized conditions, the UCo@NC (urea as nitrogen source) could afford 95.2% conversion of EB and 96.0% selectivity to acetophenone, and the substrate scalability was remarkable. Kinetics show that UCo@NC contributes to EB oxidation with an apparent activation energy of 32.3 kJ/mol. The synergistic effect between metallic cobalt NPs and nitrogen-doped graphite-like carbon layers was obviously observed and, especially, the graphitic N species plays a key role during the oxidation reaction. The structure-performance relationship illustrated that EB oxidation was a free radical reaction through 1-phenylethanol as an intermediate, and the possible reaction mechanistic has been proposed.

Propane Dehydrogenation over Cobalt Aluminates: Evaluation of Potential Catalytic Active Sites

Non-oxidative propane dehydrogenation (PDH) is becoming an increasingly important approach to propylene production, while cobalt-containing catalysts have recently demonstrated great potential for use in this reaction, providing efficiencies comparable to those of industrially employed Pt- and Cr-based catalytic systems. It is therefore essential to clarify the nature of their active sites, especially since contradictory opinions on this issue are expressed in the literature. In this study, efforts were made to determine the state of Co in cobalt aluminates (CoAl2O4-Al2O3) responsible for PDH under typical operating conditions (600 °C, 1 atm). It is shown that the catalyst with a low cobalt content (Co/Al = 0.1) ensured the highest selectivity to propylene, ca. 95%, while maintaining significant propylene conversion. The structural motifs such as cobalt oxide and metallic cobalt nanoparticles, in addition to tetrahedral Co2+ species in the CoAl2O4 spinel system, were evaluated as potential active-site ensembles based on the obtained catalytic performance data in combination with the XRD, H2-TPR, TEM and XPS characteristics of as-synthesized, spent and spent–regenerated catalysts. It is revealed that the most likely catalytic sites linked to PDH are the Co-oxide forms tightly covering alumina or embedded in the spinel structure. However, additional in situ tuning is certainly needed, probably through the formation of surface oxygen vacancies rather than through a deeper reduction in Co0 as previously thought.

Engineering conductive and catalytic triple-phase interfaces for high efficiency polysulfides conversion in Li-S batteries

The well-known shuttle effect of lithium polysulfides (LiPSs) in the ether-based liquid electrolyte and polymer solid electrolytes are the main roadblocks of Li-S batteries to perform high discharge capacity with a long cycling lifespan. Herein, a triple phase interface among carbon/catalysts (vanadium single atoms (VSAs) and metallic cobalt nanoparticles (CoNPs))/electrolyte is proposed for the high-performance Li-S batteries. At the triple-phase interfaces, the LiPSs are chemically immobilized and electrocatalytically transformed into insoluble Li2S at the rate-determining process of liquid–solid conversion. The nucleation and growth of Li2S precipitates were dominated by the interface chemistry and the dispersion of catalysts (3D reconstruction image). In the Li-S batteries with liquid ether-based electrolytes, a discharge capacity of 1343 mAh g−1 was achieved at 0.1 C and the decay of capacity was decelerated with 0.05% per cycle for 500 cycles at 1 C, as well as superb rate capability (808 mAh·g−1 at 5 C). The triple phase interfaces also exhibited high performance in solid state Li-S batteries with solid polymer electrolytes, which the discharge capacity reaches 1289 mAh·g−1 at 0.05 C and 849 mAh·g−1 at 0.5 C.

Hydrogen-Rich Gas Production by Steam Reforming and Oxidative Steam Reforming of Methanol over La0.6Sr0.4CoO3-δ: Effects of Preparation, Operation Conditions, and Redox Cycles.

La0.6Sr0.4CoO3-δ (LSC) perovskite, as a potential catalyst precursor for hydrogen (H2)-rich production by steam reforming of methanol (SRM) and oxidative steam reforming of methanol (OSRM), was investigated. For this purpose, LSC was synthesized by the citrate sol-gel method and characterized by complementary analytical techniques. The catalytic activity was studied for the as-prepared and prereduced LSC and compared with the undoped LaCoO3-δ (LCO) at several feed gas compositions. Furthermore, the degradation and regeneration of LSC under repeated redox cycles were studied. The results evidenced that the increase in the water/methanol ratio under SRM, and the O2 addition under OSRM, increased the CO2 formation and decreased both the H2 selectivity and catalyst deactivation caused by carbon deposition. Methanol conversion of the prereduced LSC was significantly enhanced at a lower temperature than that of as-prepared LSC and undoped LCO. This was attributed to the performance of metallic cobalt nanoparticles highly dispersed under reducing atmospheres. The reoxidation program in repetitive redox cycles played a crucial role in the regeneration of catalysts, which could be regenerated to the initial perovskite structure under a specific thermal treatment, minimizing the degradation of the catalytic activity and surface.

Novel Samarium Cobaltate/Silicon Carbide Composite Catalyst for Dry Reforming of Methane into Synthesis Gas

The paper describes a specifically developed novel samarium cobaltate/silicon carbide composite that transforms into a high-performance carbon-resistant catalyst for dry reforming of methane into syngas (DRM). This 30%SmCoO3/70%SiC composite without hydrogen prereduction was tested in DRM at atmospheric pressure and GHSV 15 L g–1 h–1 (of an equimolar CH4–CO2 mixture). During the test, the yields of hydrogen and carbon monoxide reached 92 and 91 mol %, respectively, at 900°C, and 20 and 28 mol % at 700°C. Using XRD, TGA, and SEM examination, zero carbonization of the catalyst surface was demonstrated. It was found that, in the course of DRM, the initial composite transformed into a material that contained silicon carbide, samarium silicate, and samarium oxide, as well as metallic cobalt nanoparticles (20 nm).

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.

The antimicrobial efficacy of copper, cobalt, zinc and silver nanoparticles: alone and in combination

With the advent of nanotechnology, there has been an extensive interest in the antimicrobial potential of metals. The rapid and widespread development of antimicrobial-resistant and multidrug-resistant bacteria has prompted recent research into developing novel or alternative antimicrobial agents. In this study, the antimicrobial efficacy of metallic copper, cobalt, silver and zinc nanoparticles was assessed against Escherichia coli (NCTC 10538), S. aureus (ATCC 6538) along with three clinical isolates of Staphylococcus epidermidis (A37, A57 and A91) and three clinical isolates of E. coli (Strains 1, 2 and 3) recovered from bone marrow transplant patients and patients with cystitis respectively. Antimicrobial sensitivity assays, including agar diffusion and broth macro-dilution to determine minimum inhibitory and bactericidal concentrations (MIC/MBC) and time-kill/synergy assays, were used to assess the antimicrobial efficacy of the agents. The panel of test microorganisms, including antibiotic-resistant strains, demonstrated a broad range of sensitivity to the metals investigated. MICs of the type culture strains were in the range of 0.625–5.0 mg ml−1. While copper and cobalt exhibited no difference in sensitivity between Gram-positive and Gram-negative microorganisms, silver and zinc showed strain specificity. A significant decrease (p < 0.001) in the bacterial density of E. coli and S. aureus was demonstrated by silver, copper and zinc in as little as two hours. Furthermore, combining metal nanoparticles reduced the time required to achieve a complete kill.

Novel Samarium Cobaltate/Silicon Carbide Composite Catalyst for Dry Reforming of Methane into Synthesis Gas

The paper describes a specifically developed novel samarium cobaltate/silicon carbide composite that transforms into a high-performance carbon-resistant catalyst for dry reforming of methane into syngas (DRM). This 30%SmCoO3/70%SiC composite without hydrogen prereduction was tested in DRM at atmospheric pressure and GHSV 15 L g–1 h–1 (of an equimolar CH4–CO2 mixture). During the test, the yields of hydrogen and carbon monoxide reached 92 and 91 mol %, respectively, at 900°C, and 20 and 28 mol % at 700°C. Using XRD, TGA, and SEM examination, zero carbonization of the catalyst surface was demonstrated. It was found that, in the course of DRM, the initial composite transformed into a material that contained silicon carbide, samarium silicate, and samarium oxide, as well as metallic cobalt nanoparticles (<20 nm).

Colorimetric detection of uric acid based on enhanced catalytic activity of cobalt-copper bimetallic-modified molybdenum disulfide

A method for the quantification of uric acid (UA) by colorimetry using a four-in-one nanocomposite MoS2/PDA/CoCu as a novel nanozyme was proposed. The nanocomposite was prepared based on the deposition of metal cobalt and copper nanoparticles onto the surface of MoS2 nanosheets using polydopamine (PDA) as a stabilizer. The Michaelis-Menten model was used to monitor the catalytic efficiency of peroxidase-like reactions, and the results showed that the Michaelis constant Km (0.0076 mM and 0.0032 mM) values calculated by the Lineweaver-Burk equation were much lower than those of horseradish peroxidase and other reported nanozymes, demonstrating that MoS2/PDA/CoCu has excellent peroxidase-like activity. Theoretically, uric acid can produce allantoin and H2O2 in the presence of uricase and oxygen, respectively. The nanocomposite efficiently catalyzes H2O2 to produce hydroxyl radicals (•OH) that then oxidize colorless 3, 3′, 5, 5′-tetramethylbenzidine (TMB) to the blue oxidation product (ox-TMB) which corresponds to the characteristic absorption peak at 652 nm. Using optimal conditions, we constructed a sensitive visible visual colorimetric method combined with a designed smartphone for UA detection (0.5–200 μM, R2 = 0.995) with a limit of detection (S/N = 3) of 0.13 μM. When UA was detected in serum and urine samples, good recovery rates were obtained, indicating the great potential of this method for the detection of uric acid in clinical and daily life applications.

Schiff base coordination compounds including thiosemicarbazide derivative and 4-benzoyl-1,3-diphenyl-5-pyrazolone: Synthesis, structural spectral characterization and biological activity

A new thiosemicarbazone ligand containing an allyl group and a 5-pyrazolone derivative has been prepared. The reaction of this ligand (H2L) with chloride and nitrate salts of Co(II), Cu(II), Pd(II), and Ni(II), Cu(II) ions resulted in the formation of different chelates having variable chemical formulas. Structural characterization of H2L ligand and its chelates has been established employing microanalytical, molar conductivity, magnetic moment measurements as well as spectral techniques including IR, UV–vis, NMR, mass, XRD, and ESR spectra. The spectral and microanalytical data achieved the monobasic tridentate binding mode with the metal(II) ion through SNO and NNO donor sites in complexes (2,5) and (3,4), respectively. In addition, the thiosemicarbazone ligand acts as a neutral bidentate species (NS) and neutral or mononegative bidentate species (NO) in complexes (6) and (1), respectively. Based on electronic spectra analyses (UV–vis) and magnetic moment measurements, all chelates, with the exception of those of Co(II) and Pd(II) ions, which have square planar geometrical structures, revealed a square pyramidal structure. Furthermore, the ESR spectra of Cu(II) chelates (3–5) have been investigated, yielding 2B1g as an axial ground state. The chemical formulae for the metal chelates were determined using thermogravimetric investigations (TG and DTG), demonstrating both their thermal stability and the presence of various crystalline solvents. Metal oxide (MO) or metal with traces of carbon was the residue of the thermal degradation processes. Based on XRD analysis, the structures of allopalladium (O-dopped Pd), monoclinic CuO, and tetragonal metallic cobalt nanoparticles obtained thermally from chelates (1,3,4,6) were elucidated. Copper(II) chelates (3) and (4) display the highest anticancer activity against hepatocellular carcinoma cells (Hep G-2) testes, according to the biological studies for the ligand and some of its chelates.

Ultrafine metallic cobalt nanoparticle encapsulated in N‐doped carbon as high‐efficiency catalysts for reduction of 4‐nitrophenol

Novel and efficient ultrafine metallic cobalt nanoparticles encapsulated in N‐doped carbon catalysts are prepared via a facile method from pyrolysis of ZIF‐67‐x%CTAB, which is modified by CTAB (cetyltrimethyl ammonium bromide). The content of surfactant CTAB can control the crystal size of ZIF‐67, which further determines the Co particle size of Co@CN‐x%CTAB. The as‐prepared ZIF‐67‐x%CTAB and Co@CN‐x%CTAB were characterized by X‐ray powder diffraction (XRD), scanning electron microscopy (SEM), high‐resolution transmission electron microscopy (HRTEM), Brunauer−Emmett−Teller (BET), and X‐ray photoelectron spectroscopy (XPS). Co@CN‐0%CTAB could not maintain the primary morphologies of ZIF‐67‐0%CTAB with the collapse of skeleton. However, the Co@CN‐3%CTAB and Co@CN‐5%CTAB catalysts inherit the original morphologies with skeleton constriction. It indicated that Co@CN catalysts could maintain the skeleton structure of ZIF‐67 by adding CTAB during the preparation process. The particle size of Co@CN decreased with the increasing of CTAB content. Moreover, the addition of CTAB facilitated the formation of Co‐Nx species on catalyst surface. The kinetic rate constant of Co@CN‐5%CTAB catalyst was 0.99 min−1, which is 2.5 times as high as that of Co@CN‐0%CTAB catalyst for 4‐nitrophenol reduction. The excellent catalytic performance of Co@CN‐5%CTAB may be due to the presence of Co (0) species generated in situ during the calcination process, the smaller Co nanoparticles and more Co‐Nx site on the surface of the catalyst.

Construction of step-scheme g-C3N4/Co/ZnO heterojunction photocatalyst for aerobic photocatalytic degradation of synthetic wastewater

In this paper, ternary g-C3N4/Co/ZnO heterojunction photocatalyst has been reported for dye degradation. The simple ultrasonic and sol-gel method is used to synthesize g-C3N4/Co/ZnO nanocomposite and the physicochemical characteristics are used to determine the phase structure, particle size, morphology, surface area, size distribution, elemental analysis, electronic structure, energy potential positions, and separation and transfer efficiency of photogenerated electron-holes. The data indicate that an intimate stable and efficient heterojunction is established. The aerobic photocatalytic efficiency of the step scheme (S-scheme) g-C3N4/Co/ZnO photocatalyst was evaluated using methylene blue (MB), crystal violet (CV), and Rhodamine B (RhB) cationic dyes as model pollutants under visible light irradiation. Degradation removal of 96.3%, 74.5%, and 75.14% was observed for MB, CV, and RhB dyes, respectively. In order to compare the degradation efficiency under different light irradiations, RhB was irradiated under visible and sunlight and the degradation efficiency increased to 91.6% under sunlight. The surface plasmon resonance (SPR) effect of metallic Cobalt (Co) nanoparticles in this S-scheme hybrid photocatalyst facilitates vectorial interfacial electron transport and enhances the response of the photocatalyst to sunlight. As a result, the optimized S-scheme g-C3N4/Co/ZnO photocatalyst was employed to treat the complex wastewater and degraded up to 91.26% within 120 min under sunlight. The superior photocatalysis behavior and its recyclability make it a promising photocatalyst for several environmental applications.

Propane Dehydrogenation on Co-N-C/SiO2 Catalyst: The Role of Single-Atom Active Sites

Recently, significant attention has been drawn to carbon materials containing cobalt coordinated to nitrogen, as the promising inexpensive catalysts of a wide range of applications. Given that non-oxidative propane dehydrogenation to propylene (PDH) is also becoming increasingly important, we present the results on PDH over Co-N-C/SiO2 composites. The latter were prepared by pyrolysis of silicone gel enriched with Co(II) salt and triethanolamine. According to XRD, HRTEM and XPS characterizations, the resulting materials consist of metallic cobalt nanoparticles of about 5 to 10 nm size and subnano-sized cobalt species (cobalt single atom sites coordinated to nitrogen/carbon), which are uniformly distributed in mesoporous silica of high specific surface area (up to 500 m2 g−1). The composites demonstrated significant catalytic activity in PDH, which was examined under typical reaction conditions (600 °C, 1 atm) using a fixed bed flow reactor. The subnano-sized Co centers proved to be the real active catalytic sites responsible for the target reaction, while carbon deposition induced by Co nanoparticles provided the catalyst deactivation. It is shown that the catalyst can be reactivated by the treatment with oxygen, which, in addition, notably increases selectivity to propylene (up to 98%) and enhances the catalyst stability in the next operation cycle. This remarkable change in catalytic behavior is shown to be due to the dramatic structural modification of the catalyst upon high-temperature oxidation.

Fischer-Tropsch synthesis over lignin-derived cobalt-containing porous carbon fiber catalysts

Cobalt-containing lignin-based fibers were synthesized in one step by electrospinning of Alcell lignin solutions as carbon precursor, a low-cost and renewable co-product of the paper making industry. The lignin fibers were thermostabilized in air to avoid the fusion during the carbonization process between 500 and 800 °C to obtain cobalt-containing porous carbon submicron fibers. These carbon fibers catalysts were studied for the Low-Temperature Fischer-Tropsch synthesis. The lignin-derived fibers containing Co catalyst located on the overall carbon fiber surface (internal and external) heat-treated at 500 °C (Co@CF-500) showed the best catalytic performance after 70 h on stream, with 75% and 60% selectivity to C5+ at 220 °C and H2/CO ratios of 1 and 2, respectively, attributed to the high Co dispersion, optimal Co-particle size and better Co accessibility. Higher heat-treatment temperatures leaded to Co-containing carbon fibers with larger metallic cobalt nanoparticles encapsulated in graphitic-type carbon, which rendered them inaccessible for FTS.