Cobalt Loading Research Articles

Novel Cobalt Catalysts Supported on Metal–Organic Frameworks MIL‐53(Al) for the Fischer–Tropsch Synthesis

Metal–organic framework of MIL‐53(Al) (Al(OH)‐[O2C‐C6H4‐CO2]) with exceptional thermal stability (as high as ≈550 °C in dynamic conditions) are synthesized via a solvothermal method, which serve as a porous host matrix of Co‐based catalysts for Fischer–Tropsch synthesis (FTS). MIL‐53(Al) shows large micropores and lattice dynamic flexibility, which make this material a promising support for active cobalt species. The as‐synthesized Co/MIL‐53(Al) catalysts with different cobalt loadings are characterized by powder X‐ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), X‐ray photoelectron spectroscopy (XPS), thermogravimetry (TG), Fourier‐transform infrared (FT‐IR) spectroscopy, and temperature programmed reduction. The results show that the immobilization of Co nanoparticles on the MIL‐53(Al) support could be beneficial to obtain novel effective catalysts for FTS. Moreover, compared with the Co/γ‐Al2O3 catalyst of the same cobalt loading, the catalytic performance of Co/MIL‐53(Al) catalyst shows higher FTS activity. Interestingly, the gasoline selectivity over the Co/MIL‐53(Al) catalyst is much higher than that of the Co/γ‐Al2O3 catalyst, close to the optimal value for maximum gasoline and diesel production.

Loading and promoter effects on the performance of nitrogen functionalized graphene nanosheets supported cobalt Fischer-Tropsch synthesis catalysts

The effects of nitrogen functional groups on graphene surface and also the effects of cobalt loading and ruthenium promoter on the performance of nitrogen functionalized graphene nanosheets (N-GNS) supported cobalt catalysts in Fischer–Tropsch synthesis (FTS) are investigated. A 15 wt% Co/PGNS catalyst, a series of Co/N-GNS (15–30 wt% loading) and ruthenium promoted catalysts (25 wt% Co,0.5 wt% Ru/N-GNS and 25 wt% Co,0.5 wt% Ru/PGNS) were prepared by impregnation method. The purified GNS and functionalized GNS and all catalysts were characterized by Raman spectroscopy, FTIR, SEM, EDS, ICP, BET, TEM, XRD and TPR. The catalysts assessed in FTS in a fixed bed micro-reactor at 220 °C, 1.8 Mpa and H2/CO ratio of 2. Functionalization of GNS shifted the TPR reduction peaks to lower temperature, increased the dispersion of cobalt particles and increased the percentage CO conversion from 70.6% to 74.5%. Increasing the cobalt loading resulted in increasing the average cobalt cluster size, improvements in the reducibility of Co3O4. The maximum FTS activity for N-GNS supported catalyst is achieved at 30 wt % cobalt loading. The C5+ selectivity for the 30 wt % cobalt catalyst was higher than that of the 15 wt % Cobalt catalyst. Addition of 0.5 wt%Ru increased the FTS rate (gCH/(gcat·h)) from 0.377 to 0.412 and the liquid products selectivity from 86.5% to 91.2%.

Valorization of Char From Biomass Gasification as Catalyst Support in Dry Reforming of Methane

This study responds to the need of finding innovative routes for valorizing char derived from biomass gasification. Char is currently treated as a waste representing an energetic and economic loss for plant owners. However, it displays many similarities to activated carbon (AC) and could replace it in several applications. In this regard, the current work investigates the use of gasification derived char as catalyst support in dry reforming of methane (DRM) reactions. Char collected from a commercial biomass gasifier currently in operation was characterized and employed for the synthesis of cobalt catalysts. The catalysts were characterized and tested in an atmospheric pressure fixed bed reactor operating at 850°C with CH4:CO2 = 1 and a weight hourly space velocity of 6,500 mL g−1 h−1. The effectiveness of the synthesized catalysts was defined based on CO2 and CH4 conversions, the corresponding H2 and CO yields and their stability. Accordingly, catalysts were synthesized with cobalt loading of 10, 15 and 20 wt.% on untreated and HNO3 treated char, and the catalyst with optimum comparative performance was promoted with 2 wt.%MgO. Catalysts prepared using untreated char showed low average conversions of 23 and 17% for CO2 and CH4, yields of 1 and 14% for H2 and CO, and deactivated after few minutes of operation. Higher metal loadings corresponded to lower conversion and yields. Although HNO3 treatment slightly increased conversions and yields and enhanced the stability of the catalyst, the catalyst deactivated again after few minutes. On the contrary, MgO addition boosted the catalyst performances leading to conversions (95 and 94% for CO2 and CH4) and yields (44 and 53% for H2 and CO) similar to what obtained using conventional supports such as Al2O3. Moreover, MgO catalysts proved to be very stable during the whole duration of the test.

Construction of three-dimensional nitrogen-doped graphene aerogel (NGA) supported cobalt catalysts for Fischer-Tropsch synthesis

Abstract Co/NGA catalysts were one-step hydrothermal synthesized during the construction of three-dimensional nitrogen-doped graphene aerogel (NGA). The structure and properties of the catalysts were characterized by TGA, Raman, FTIR, XRD,TEM, SEM, XPS and H2-TPR, and their catalytic performance was tested by Fischer-Tropsch synthesis (FTS) reaction. Characterization and reaction results showed that higher cobalt dispersion was found on the catalyst with higher cobalt loading, and majority of cobalt species in the freeze-dried samples was fcc phase Co°. Excessive cross linking originated by high Co2+ concentration during the construction of 3D NGA led to the restraint of mass transfer of reactants to cobalt active sites, and therefore, lower FTS activity was observed on the catalysts with higher cobalt loadings. The fcc phase Co° in fresh Co/NGA catalysts was transformed in to hcp phase Co° during FTS reaction, and as a result, catalytic activity was increased with increasing time on stream.

Aerosol synthesis of porous SiO2-cobalt-catalyst with tailored pores and tunable metal particle size for Fischer-Tropsch synthesis (FTS)

Cobalt nanoparticles supported on a well-defined porous structure are a promising catalyst for the Fischer-Tropsch synthesis (FTS). The catalytic efficiency of the porous catalyst depends on the properties of the support and on the properties of the active component. Methods such as wet-chemistry and flame synthesis are often limited by their variability in terms of support structure and size of the integrated active metal components. In this work, well-organised porous structures were produced using spray-drying of colloidal silica suspensions containing dissolved cobalt nitrate. This technique allows to synthesize catalyst particles with tunable specific surface area, pore size, cobalt particle size, and cobalt loading. The dried silica particles show interconnected pores, which makes it especially suitable for use as a catalyst support. Moreover, it is shown that the pore sizes and active metal particle sizes can be varied independently. In addition, the mass of cobalt oxide per silica support surface was identified as a controlling parameter for the metal oxide nanoparticle size for a given calcination temperature.

Effects of annealing conditions on the oxygen evolution activity of a BaTaO2N photocatalyst loaded with cobalt species

Precise engineering of the cocatalyst-photocatalyst interface and optimization of the cocatalyst dispersion are essential for improving the activity of particulate semiconductor photocatalysts. Herein, we report the effects of varying the conditions used to load cobalt oxide (CoOx) as a cocatalyst on the O2 evolution activity of a particulate BaTaO2N photocatalyst, based on trials in an aqueous silver nitrate solution under visible light irradiation. Annealing under an N2 flow after loading the Co species increased the O2 evolution rate threefold compared to that obtained following conventional annealing under an NH3 flow. Subsequent annealing under an H2 atmosphere exposed the BaTaO2N surface as a result of the aggregation of CoOx particles, and further enhanced the photocatalytic O2 evolution by a factor of two, yielding an apparent quantum efficiency of 0.55% at 420 nm. These results indicate the importance of intimate contact between cocatalyst particles and the photocatalyst, as well as the necessity of exposing the photocatalyst surface to make it available for reduction reactions during photocatalytic water oxidation.

Effects of Cobalt Loading, Particle Size, and Calcination Condition on Co/CNT Catalyst Performance in Fischer–Tropsch Reactions

The strong electrostatic adsorption (SEA) method was applied to the synthesis of a cobalt (Co) catalyst on a multi-walled carbon nanotube (CNT) support. In order to uptake more of the cobalt cluster with higher dispersion, the CNT was functionalized via acid and thermal treatment. The Co/CNT catalyst samples were characterized by a range of methods including the Brunauer–Emmet–Teller (BET) surface area analyzer, transmission electron microscopy (TEM), X-ray powder diffraction (XRD) analysis, atomic absorption spectroscopy (AAS), and H2-temperature programmed reduction (H2-TPR) analysis. The data from the TEM images revealed that the catalyst was highly dispersed over the external and internal walls of the CNT and that it demonstrated a narrow particle size of 6–8 nm. In addition, the data from the H2-TPR studies showed a lower reduction temperature (420 °C) for the pre-treated catalyst samples. Furthermore, a Fischer–Tropsch synthesis (FTS) reaction was chosen to evaluate the Co/CNT catalyst performance by using a fixed-bed microreactor at different parameters. Finally finding the optimum value of the cobalt loading percentage, particle size, and calcination conditions of Co/CNT catalyst resulted in a CO conversion and C5+ selectivity of 58.7% and 83.2%, respectively.

Ultralow Loading Cobalt-Based Nanocatalyst for Benign and Efficient Aerobic Oxidation of Allylic Alcohols and Biobased Olefins

The synthesis of α,β-unsaturated ketones from aerobic oxidation of allylic alcohols and biobased olefins serves as an important topic in green and sustainable chemistry. In this work, we report the utilization of a sacrificial template ZIF-8 for preparation of mesoporous Co0.05/N–C material with an ultralow cobalt loading of 0.05 wt %, in which the excellent catalytic performance in aerobic oxidation of α-pinene and cinnamyl alcohol was achieved with an 85% yield of verbenone and a yield of cinnamaldehyde, respectively. The results of control experiments and several characterization investigations further illustrate that the sacrificial template ZIF-8 plays a key role to disperse well metallic cobalt in the Co0.05/N–C-800 catalyst and an appropriate cobalt content of 0.05 wt % is beneficial for benign and efficient aerobic oxidation of various allylic alcohols and biobased olefins. In addition, the Co0.05/N–C-800 catalyst also exhibited good stability and reusability for recovering and reusing at least six times without obvious decrease in catalytic activity. The presented efficient nanocatalyst thus triggers facile synthesis of a series of α,β-unsaturated aldehydes/ketones in high yields.

Highly efficient catalytic soot combustion performance of hierarchically meso-macroporous Co3O4/CeO2 nanosheet monolithic catalysts

Herein, we facilely synthesized the Co3O4/CeO2 nanosheets on monolithic Ni foam (Co/Ce-NS) via the tandem hydrothermal and impregnation methods. The constructed hierarchically meso-macroporous nano-structures increase the soot-catalysts contact chances, and promote mass transfer of gaseous reactants and products in catalytic soot combustion. The deposition of Co3O4 nanoparticles onto CeO2 nanosheets enhances the redox properties of the catalysts, because the Co-Ce interaction generates active surface adsorbed oxygen species for soot combustion. Our results reveal that the adsorbed oxygen species on the Co-Ce interfaces are more active than these on surface CeO2 or Co3O4. The 0.6Co/Ce-NS catalyst with the optimal cobalt loading has more superficial Co2+-□-Ce3+ couples than other catalysts, consequently generating more active surface adsorbed oxygen species for catalytic soot oxidation. The 0.6Co/Ce-NS catalyst exhibits comparable catalytic activity with the 1%Pt/Al2O3 catalyst under the loose contact condition. Moreover, the 0.6Co/Ce-NS catalyst has the excellent thermal stability and water resistance. Therefore, the hierarchically meso-macroporous Co3O4/CeO2 nanosheet monolithic catalysts have potential industrial application in catalytic soot elimination and other related heterogeneous catalytic systems.

Selective CO2 Reduction Catalyzed by Single Cobalt Sites on Carbon Nitride under Visible-Light Irradiation

Framework nitrogen atoms of carbon nitride (C3N4) can coordinate with and activate metal sites for catalysis. In this study, C3N4 was employed to harvest visible light and activate Co2+ sites, without the use of additional ligands, in photochemical CO2 reduction. Photocatalysts containing single Co2+ sites on C3N4 were prepared by a simple deposition method and demonstrated excellent activity and product selectivity toward CO formation. A turnover number of more than 200 was obtained for CO production using the synthesized photocatalyst under visible-light irradiation. Inactive cobalt oxides formed at relatively high cobalt loadings but did not alter product selectivity. Further studies with X-ray absorption spectroscopy confirmed the presence of single Co2+ sites on C3N4 and their important role in achieving selective CO2 reduction.

An Optimization Study of Cobalt Supported on Activated Carbon for the Catalytic Ozonation of Oxalic Acid: Effect of Operating Parameters and Synergetic Combination

ABSTRACTIn this study, new heterogeneous cobalt (Co) catalysts supported on activated carbon (Co/AC) were developed using a wetness impregnation process. The effect of preparation conditions on catalyst characteristics was examined. This work focused on two key parameters: the impregnation rate and the calcination atmosphere (temperature and time). Different catalysts were prepared by varying the Co loading on AC. Various catalysts were characterized by means of nitrogen sorptiometry at 77K, Boehm and pHpzc analysis. It was found that the catalyst properties and the functional surface groups were affected by the operating conditions. The best surface area was 997.5 m2/g obtained when the activated carbon was impregnated with 5% Co loading and calcined at 350°C for 2 h. The effects of parameters, such as cobalt loading, pH, catalyst dose, and ozone dose, were explored on oxalic acid removal (OA). Results show that the use of Co/AC for heterogeneous catalytic ozonation enhanced the degradation efficiency of oxalic acid (OA) significantly compared with simple ozonation and O3/AC. The main results indicate that the optimum catalytic activity was observed when 5% (wt/wt) of Co was supported on AC reaching a catalytic ozonation efficiency of 95%. The results of total organic carbon removal of 91% were achieved at optimum conditions.

Ultra small cobalt nanoparticles supported on MCM41: One-pot synthesis and catalytic hydrogen production from alkaline borohydride

Ultra small nano-sized cobalt catalysts supported on MCM41 have been prepared via simple one-pot synthesis procedure, the microstructure of as-prepared catalysts was characterized by XRD, N2 adsorption-desorption, SEM, TEM and ICP-AES. The results indicated that the Co/MCM41 catalysts possessed well-ordered mesoporous morphology, and the cobalt loading had negligible influence on MCM41 support. Catalytic hydrogen production experiments demonstrated that the catalyst with the cobalt loading of 0.5 wt% (Co/MCM41–0.5w) exhibited the highest catalytic activity over all investigated catalysts, its turn-over frequency is higher than that of Ru/C catalyst and comparable to that of Co-P/Ni foam catalyst.

Cobalt Nanocrystals Encapsulated in Heteroatom-Rich Porous Carbons Derived from Conjugated Microporous Polymers for Efficient Electrocatalytic Hydrogen Evolution.

Cobalt nanocrystals encapsulated in N,O-dual-doped porous carbons as efficient and stable electrocatalysts for hydrogen evolution reaction (HER) are reported. A heteroatom-rich-conjugated microporous polymer is first chemically deposited on a carbon fiber cloth, and after addition of a cobalt salt, pyrolyzed to produce a heteroatom-doped C/Co nanocrystal composite. With this process, the use of additional binders for preparation of electrodes can be avoided. With a trace cobalt loading (0.46 wt%), the electrodes achieve a low Tafel slope of 46 mV dec-1 and overpotential of only 69 mV at a current density of 10 mA cm-2 in 0.5 m H2 SO4 . Experimental and computational studies reveal that the superior HER behavior is due to a decreased free energy of hydrogen adsorption, induced by i) electrons transferred from the cobalt nanocrystals to graphite layers and ii) N,O-dual doping reduced the Fermi level of neighboring C atoms.

High Performance of NO Oxidation Over Co/Zr0.2Ce0.8O2 Catalysts Prepared by One-pot Method

Cobalt supported on Zr0.2Ce0.8O2 with different cobalt loading for catalytic oxidation of NO to NO2 were prepared by the one-pot method using citric acid as complexing agent. The samples were characterized by XRD, H2-TPR, O2-TPD and NO-TPD and the catalytic performance was investigated. The results showed that the Co/Zr0.2Ce0.8O2 catalyst containing 10 wt.% of Co3O4 exhibited excellent activity at a wide temperature window ranged from about 240 °C to 380 °C with NO conversion above 50%. The high catalytic performance of Co/Zr0.2Ce0.8O2 samples should be attributed to the active component related with cobalt species.

Tailoring the crystallite size of Co3O4/SiO2 catalyst using organic-metal matrix method

Abstract In this work, a series of SiO2 supported Co catalysts have been prepared by adding urea or ruthenium to the cobalt precursor solution compared with the catalysts prepared without using urea. The characterization results show that cobalt is present as Co3O4 over the silica supports. The addition of urea to the catalyst precursor helps to generate smaller crystallite even at very high cobalt loading, while impregnation without using urea results in larger crystallite size as Co loading increases. Likewise, the addition of Ru to the catalyst precursor leads to a more uniform crystallite of Co3O4, and can help to lower the Co3O4 crystallite size to some extent, which has the similar effect on the catalyst prepared with urea. We have also shown that the support pore size and volume do have significant effect on the crystallite size of the cobalt oxide. The catalytic performances of the Co/SiO2 catalysts prepared with and without adding urea have been evaluated for Fischer Tropsch synthesis and the catalyst prepared using urea demonstrates significantly improved catalyst activity as well as selectivity to C5+.

Synergetic Effect of Cobalt-Incorporated Acid-Activated GAC for Adsorptive Desulfurization of DBT under Mild Conditions

The present study explores the usage of acetic-acid-treated cobalt-modified activated carbon as an adsorbent material for the adsorptive desulfurization of DBT-containing model oil. Modification of granular activated carbon (GAC) with acetic acid treatment and incorporation of cobalt species in GAC framework significantly improved its adsorption capacity by improving oxygen-containing functional groups and acidic sites. The surface area of GAC improved from 257 to 393.8 m2/g when it was treated with cobalt species and acid. The average size of the Co3O4 crystallites in the Co-loaded activated carbon was found to be 13.8 nm. The effect of various operating parameters such as cobalt loading, adsorbent dose, temperature, and time was studied. Furthermore, the reusability of spent adsorbent and the effect of the presence of other aromatics compounds were also investigated. Under optimized operating conditions, ∼92% of DBT removal was achieved. The equilibrium data of DBT adsorption were analyzed by Langmuir, ...

Mechanochemical synthesis of supported cobalt oxide nanoparticles on mesoporous materials as versatile bifunctional catalysts

Supported Co3O4 nanoparticles on SBA-15 aluminosilicates (Al-SBA-15) with different cobalt loadings (0.5, 1, 5, 10 wt %) were synthesized by ball-milling. The synthesized materials were characterized by different techniques including, N2 adsorption measurements, XRD, TEM, EDX, ICP-MS, DRIFTs of pyridine among others. The catalysts were studied in the microwave assisted benzyl alcohol oxidation as well as in the akylation of toluene with benzyl chloride. Co3O4 catalysts exhibited moderate conversions in the selective oxidation of benzyl alcohol, with a high selectivity towards benzaldehyde. Lewis acidity increases upon the incorporation of cobalt nanoparticles onto the surface of the support which was found to significantly influence the materials in the alkylation of toluene with benzyl chloride. The high active sites accessibility of ball-milling prepared materials leads to high conversions to alkylated derivatives in short periods of time (>99 mol %, 30 min). A direct correlation acidity/activity could not be obtained in the systems, for which nanoparticle sizes and distribution could influence the observed activities.

MOF-Derived Nanocobalt for Oxidative Functionalization of Cyclic Amines to Quinazolinones with 2-Aminoarylmethanols

By employing a MOF-templated method, we have developed a highly dipersed and ultralow loading cobalt nanocatalyst, which has been applied in the oxidative functionalization of easily available cyclic amines with 2-aminoarylmethanols to ring-fused quinazolinones, the core structures of numerous valuable products. The developed catalytic transformation proceeds with the merits of broad substrate scope, good functional group tolerance and chemoselectivity, high step- and atom-efficiency, and use of the naturally abundant Co/O2 system, which offers a practical way for the preparation of quinazolinones with structural diversity. The work presented has built an important basis for direct conversion of cyclic amine motifs into functional frameworks.

Plasma-Assisted Preparation of Highly Dispersed Cobalt Catalysts for Enhanced Fischer–Tropsch Synthesis Performance

Glow discharge plasma (GDP) was used for the preparation of Co/TiO2 Fischer–Tropsch synthesis (FTS) catalysts promoted by Pt. This technique was compared with conventional thermal calcination for decomposing cobalt precursor. In this study, Pt was added as a reduction promoter in order to improve the reducibility of Co/TiO2 catalysts because the strong interaction between Co and TiO2 is detrimental to the FTS performances. It was found that plasma treatment can effectively decompose the cobalt precursor at a low temperature in a short time (1–4 h). As compared to thermal calcination, the cobalt species prepared by GDP is highly dispersed on TiO2 support. CoPt/TiO2 catalyst with homogeneously and highly dispersed cobalt particles (∼1 nm) was achieved by prolonging plasma treatment from 1 to 4 h. This is difficult to accomplish via conventional calcination method on preparing this loading cobalt catalyst (12 wt %) without the use of extra chemicals and a complicated process. Furthermore, we found that a sho...

Electrospun magnetic cobalt–carbon nanofiber composites with axis-sheath structure for efficient peroxymonosulfate activation

Cobalt–carbon nanofiber composites (Co-CNFs) were synthesized by electrospinning and subsequent carbonization and their performance for peroxymonosulfate (PMS) activation was evaluated. Co-CNFs have a large aspect ratio (150 nm in diameter and several millimeters in length) to avoid aggregation and large specific surface area (1304 m2/g) to provide more reaction sites for enhancing catalytic activities. Zero valence cobalt was proved to be the main cobalt species of axis or core of the fiber, which might account for its excellent magnetic response, and Co3O4 was the main cobalt species of sheath or coat according to XRD and XPS results. The Co-CNFs exhibited higher catalytic performances than Co3O4 or CNFs for PMS activation and dyes were completely removed in a short time in the Co-CNFs/PMS system. The Co-CNFs derived from cobalt acetate demonstrated the highest catalytic performance and their Co leaking was similar to that of catalysts derived from other cobalt salts. The degradation efficiency increased with the carbonization temperature, cobalt loading, degradation temperature, PMS and catalyst dosage. The dye degradation processes followed pseudo-first-order kinetics. The activation energy of Co-CNFs/PMS/orange G system was derived as 29.8 kJ/mol by the Arrhenius equation. The Co-CNFs exhibited high catalytic performances and excellent stability for five repetitive usage. The possible orange G degradation pathway was proposed based on intermediate detection.