Catalytic Performance Of Co Research Articles

Effect of the support on physicochemical properties and catalytic performance of cobalt based nano-catalysts in Fischer-Tropsch reaction

In this paper, comparative investigations of the effects of CNTs and γ-Al2O3 on the physicochemical properties and catalytic performances of Co based nano-catalyst during FTS have been presented. Catalysts were prepared via a wet impregnation method and characterized by various analytical techniques such as transmission electron microscopy (TEM), temperature programmed reduction (H2-TPR), carbon dioxide temperature programmed desorption (CO2-TPD) and X-ray photoelectron spectroscopy (XPS). Fischer-Tropsch reaction (FTS) was carried out in a fixed-bed microreactor (220°C and 1atm and with H2/CO=2v/v, SV of 12L/gh). Various characterization techniques revealed that Co nanocatalysts supported on CNTs and Al2O3 were different in physicochemical properties. There was a stronger interaction between Co and Al2O3 support compared to that of CNTs support. CNTs support increased the reducibility, dispersion, active metal surface area and decreased Co particle size. A significant increase in% CO conversion and FTS reaction rate was also observed over CNTs support compared to that of Co/Al2O3. Co/CNTs resulted in higher C5+ hydrocarbons selectivity compared to that of Co/Al2O3 catalyst.

Facile synthesis and catalytic performance of Co3O4 nanosheets in situ formed on reduced graphene oxide modified Ni foam.

A three-dimensional (3D) catalyst electrode of Co3O4 nanosheets in situ formed on reduced graphene oxide modified Ni foam (Co3O4/rGO@Ni foam) for H2O2 electroreduction is prepared by a two-step hydrothermal method. In the first step, graphene oxide sheets are reduced and formed on the skeleton of Ni foam and Co3O4 nanosheets are synthesized intermixed with the rGO sheets through the second step. The Co3O4 nanosheets are made up of plentiful nanoparticles and there are many nanoholes among these nanoparticles which are beneficial for the sufficient contact between H2O2 and the catalyst. The morphology and phase composition of the Co3O4/rGO@Ni foam electrode are studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrocatalytic activity of the as-prepared electrode is investigated by cyclic voltammetry (CV) and chronoamperometry (CA). From the results, it can be seen that in 2 mol L-1 NaOH and 0.5 mol L-1 H2O2, the reduction current density of H2O2 on the Co3O4/rGO@Ni foam electrode is 450 mA cm-2 at -0.8 V which is much higher than that on Co3O4 directly supported on Ni foam. This obvious increase of the current density can be attributed to the increase of the surface area of the electrode after the addition of rGO. Also, the interpenetration of rGO and Co3O4 nanosheets improves the electron and ion transport ability of the electrode which leads to a good electrocatalytic activity and stability of the Co3O4/rGO@Ni foam electrode.

Robust Co-catalytic Performance of Nanodiamonds Loaded on WO3 for the Decomposition of Volatile Organic Compounds under Visible Light

Proper co-catalysts (usually noble metals), combined with semiconductor materials, are commonly needed to maximize the efficiency of photocatalysis. Search for cost-effective and practical alternatives for noble-metal co-catalysts is under intense investigation. In this work, nanodiamond (ND), which is a carbon nanomaterial with a unique sp3(core)/sp2(shell) structure, was combined with WO3 (as an alternative co-catalyst for Pt) and applied for the degradation of volatile organic compounds under visible light. NDs-loaded WO3 showed a highly enhanced photocatalytic activity for the degradation of acetaldehyde (∼17 times higher than bare WO3), which is more efficient than other well-known co-catalysts (Ag, Pd, Au, and CuO) loaded onto WO3 and comparable to Pt-loaded WO3. Various surface modifications of ND and photoelectochemical measurements revealed that the graphitic carbon shell (sp2) on the diamond core (sp3) plays a crucial role in charge separation and the subsequent interfacial charge transfer. As a...

Engineering the Edges of MoS2 (WS2) Crystals for Direct Exfoliation into Monolayers in Polar Micromolecular Solvents.

Synthesizing transition metal dichalcogenide (TMDC) monolayers through the liquid exfoliation of bulk crystals in low boiling point polar micromolecular solvents, such as water, is paramount for their practical application. However, the resulting hydrodynamic forces only appear on the crystal edges due to the mismatch in surface tension between the polar micromolecular solvents and the bulk crystals and are insufficient to overcome the strong van der Waals attraction between adjacent microscale layers. Herein, we present the novel strategy of engineering the lateral size of TMDC (MoS2 and WS2) crystals in the nanoscale to increase the fraction of edges, leading to their direct and ready exfoliation in polar micromolecular solvents, even in pure water, to produce monolayer MoS2 and WS2 nanosheets in high yield. To examine one of their important applications, their catalytic hydrogen evolution activities were evaluated when used as cocatalysts with a photoharvester semiconductor (cadmium sulfide, CdS) in a reaction driven by solar energy. These exfoliated MoS2 (WS2) monolayers exhibited superior cocatalytic performance in the photocatalytic hydrogen evolution reaction (HER). Notably, the cocatalytic performance of monolayer WS2 nanosheets is even higher than that of platinum (Pt), which is a state-of-the-art catalyst for catalytic hydrogen evolution. This work elucidates the importance of decreasing the lateral size of layered crystals to significantly enhance their exfoliability, providing a new strategy for the large-scale preparation of nanoscale TMDC monolayers by liquid exfoliation.

Mechanistic Study of Low-Temperature CO2 Hydrogenation over Modified Rh/Al2O3 Catalysts

The hydrogenation of CO2 on Rh/Al2O3 catalysts modified with Ni and K was studied by in situ and operando DRIFTS spectroscopy comprising transient and isotopic exchange experiments to study the influence of this modification on the catalytic performance in CO and methane formation at 250–350 °C and to gain mechanistic insight. Catalytic testing and spectroscopic studies revealed that the modification with particularly K promotes the formation of CO being the highest over Rh, K, Ni/Al2O3, whereas methane formation is preferred over the unmodified catalyst. It was found that CO2 does not dissociatively adsorb but is adsorbed at the support, forming mainly hydrogen carbonate, and in the presence of K, also carbonate species. The dissociative adsorption of H2 proceeds on Rh. The activated H2 reacts mainly with the hydrogen carbonate species forming CO adsorbed on Rh and formate (F1) species stably adsorbed on the support. On the K-containing catalysts, an additional formate species (F2) was identified as more...

Size-engineerable NiS2 hollow spheres photo co-catalysts from supermolecular precursor for H2 production from water splitting

NiS2 hollow spheres with controllable size have been synthesized by a facile hydrothermal method through the exchanging reaction between rod-like supramolecular precursor and l-cysteine. Through modifying the diameter of rod-like precursor as template, accompanied by concomitant Rayleigh instability and chemical nonequilibrium interdiffusion, the size of NiS2 hollow sphere can be tuned ranging from nanosize to microsize. The hollow morphology of as-obtained product was attributed to the Kirkendall effect involving different transport rates for Ni and S ions. Owing to the relatively large specific area, the as-obtained nanoscale NiS2 hollow sphere manifest remarkable photo co-catalytic performance for H2 production, which generate 5.8mmol of H2 gas under the irradiation of visible light after 6h and 0.97mmol/h of average H2 production rate, indicating superior H2 production performance of NiS2 hollow spheres.

A DFT study of planar vs. corrugated graphene-like carbon nitride (g-C3N4) and its role in the catalytic performance of CO2 conversion.

Graphene-like carbon nitride (g-C3N4), a metal-free 2D material that is of interest as a CO2 reduction catalyst, is stabilised by corrugation in order to minimise the electronic repulsions experienced by the N lone pairs located in their structural holes. This conformational change not only stabilises the Fermi level in comparison with the totally planar structure, but also increases the potential depth of the π-holes, representing the active sites where the catalytic CO2 conversion takes place. Finally, as a result of corrugation, our DFT-D3 calculations indicate that the reaction Gibbs free energy for the first H(+)/e(-) addition decreases by 0.49 eV with respect to the totally planar case, suggesting that corrugation not only involves the material's stabilisation but also enhances the catalytic performance for the selective production of CO/CH3OH.

Catalytic performance of Co–Fe mixed oxide for NH3-SCR reaction and the promotional role of cobalt

Co-modified iron oxide (Co-FeOx) catalysts were prepared by a citric acid method for the low temperature NH3-SCR of NO in the presence of O2.

Facile synthesis of Mn-doped Fe2O3 nanostructures: enhanced CO catalytic performance induced by manganese doping

A promoting influence of manganese species on the controllable synthesis and catalytic property on CO conversion of the manganese-iron oxide is observed.

Highly efficient Pd-doped ferrite spinel catalysts for the selective catalytic reduction of NO with H2 at low temperature

Palladium-doped ferrite spinels with various divalent metals (Co, Cu or Zn) were prepared using the sol–gel auto-ignition method for use in the selective catalytic reduction of NO with hydrogen (H2-SCR). The activity of the Co–FePd catalyst was greatly enhanced by adding a small amount of palladium and resulted in approximately 96% NO conversion in the 170–250°C range. In TPD and TPR analyses, Co–FePd exhibited a larger peak area and a lower reductive temperature than the other studied materials, indicating that this catalyst possesses stronger reduction ability and larger acidity; these properties were very important for the catalytic performance of Co–FePd, which showed the best SCR activity of the tested materials. The catalytic activities ranked in the following order: Co–FePd>Zn–FePd>Cu–FePd. Adding H2O to the reacting gas mixture slightly decreased NO conversion by the Co–FePd oxide. When the H2O content was increased from 3% to 5%, no further decline of NO conversion occurred. The presence of 100ppm SO2 in the gas phase decreased the SCR activity of Co–FePd by approximately 19%, but no further deactivation was observed when the concentration was increased to 150ppm. When SO2 was removed from the feed stream, NO conversion recovered rapidly; however, the conversion was not restored to the original level, indicating that SO2 has both a reversible and an irreversible effect on the H2-SCR reaction.

Enhanced catalytic performance of Co–Sn composite oxide in styrene epoxidation with air

A simple calcination process was used to obtain Co–Sn composite oxides, the structure of which was confirmed by the XRD analysis. For comparison, the pure cobalt oxide was also prepared under the same calcination condition. According to TEM measurements, the composite oxide prepared in the presence of Sn had lower particle size than pure cobalt oxide. Accordingly, the presence of Sn increased the specific surface area as evidenced by the BET analysis data. The as-prepared Co–Sn composite oxides were applied as heterogeneous catalysts in the epoxidation of styrene with air and exhibited catalytic activity with 77.9 mol % of styrene converted and 87.1% selectivity for epoxide. These results exceed those obtained for pure cobalt oxide. However, the addition of ions of other metals such as Fe, Ni, Cu, Zn and Mn to the catalyst had a detrimental effect on the styrene epoxidation. The mechanistic considerations are also presented and suggestion is given that the DMF solvent plays a key role in the catalytic epoxidation. Results of the study indicate that Co–Sn composite oxides are efficient heterogeneous catalysts for the epoxidation of styrene with air in DMF.

Size-controllable Ni5TiO7 nanowires as promising catalysts for CO oxidation.

Ni5TiO7 nanowires with controllable sizes are synthesized using PEO method combined with impregnation and annealing at 1050oC in air, with adjustment of different concentrations of impregnating solution to control the dimension of nanowires. The resulting nanowires are characterized in details using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray analysis. In addition, the CO catalytic oxidation performance of the Ni5TiO7 nanowires is investigated using a fixed-bed quartz tubular reactor and an on-line gas chromatography system, indicating that the activity of this catalytic system for CO oxidation is a strong dependency upon the nanocrystal size.When the size of the Ni5TiO7 nanowires is induced from 4 μm to 50 nm, the corresponding maximum conversion temperature is lowered by ~100 oC.

Cobalt catalysts embedded in N-doped carbon derived from cobalt porphyrin via a one-pot method for ethylbenzene oxidation

A template-free method was employed to synthesize cobalt catalysts embedded in N-doped carbon (Co–N–C) through heating cobalt(II) meso-tetraphenyl porphyrin (CoTPP) precursor at different temperature (600°C, 700°C, 800°C). These catalysts were characterized by techniques such as BET, TG-DTA, TEM, STEM, XRD, Raman and XPS. The selective oxidation of ethylbenzene under solvent-free condition with molecular oxygen was carried out to explore the catalytic performance of Co–N–C. 13.4% conversion of ethylbenzene with 73.3% selectivity to acetophenone was achieved over Co–N–C and the catalytic performance of the catalyst was similar to the fresh even after six runs (i.e., 12.5% of ethylbenzene conversion and 72.2% of selectivity to acetophenone). The results show that the stable catalytic performance of the catalysts may be attributed to the stable N-doped graphitic carbon, the stability of carbon-encapsulated Co nanoparticles and the synergistic effect between N–C structure and cobalt oxide.

Thermal decomposition mechanism of Co–ANPyO/CNTs nanocomposites and their application to the thermal decomposition of ammonium perchlorate

This research reported the preparation, characterization, thermal decomposition mechanism and catalytic performance of Co–ANPyO/CNTs nanocomposites.

A multi-component polyoxometalate and its catalytic performance for CO2 cycloaddition reactions

A multi-component polyoxometalate based on earth-abundant elements (NH4)10[Co8(H2O)10V10Mo23O104(OH)6]·34.5H2O () has been successfully obtained and characterized. Furthermore, compound acted as a Lewis acid catalyst and promoted the conversion of carbon dioxide to a cyclic carbonate under mild reaction conditions.

Enhanced Catalytic Performance of Co–Sn Composite Oxide in Styrene Epoxidation with Air

Enhanced Catalytic Performance of Co–Sn Composite Oxide in Styrene Epoxidation with Air

Flexible Pd/CeO2–TiO2 nanofibrous membrane with high efficiency ultrafine particulate filtration and improved CO catalytic oxidation performance

Flexible CeO2–TiO2 fibrous membrane was prepared by an electrospinning combined sol–gel method.

Rapid hydrothermal synthesis of CeO2 nanoparticles with (2 2 0)-dominated surface and its CO catalytic performance

Uniform CeO2 nanoparticles with diameter in the range of 13–17nm were synthesized through a one-step rapid hydrothermal strategy. The characterization indicated that (220) surface is the majority of the exposed CeO2 surfaces. The reaction conditions including reactant amounts, reaction time were studied and optimized. The addition of hexamethylenetetramine is the key to the formation of (220)-dominated surface structure. The product shows better catalytic performance on CO conversion corresponding to the result of temperature-programmed reduction under a H2 environment.

Influence of heat treatment on catalytic performance of Co–N–C/SiO2 for selective oxidation of ethylbenzene

The effect of heat treatment on the Co–N–C/SiO2 catalysts prepared through supported metalloporphyrin has been investigated for selective oxidation of ethylbenzene. And techniques such as BET, XRD, FT-IR, UV–vis, TEM, TG–DTA and XPS are used to explore the relationship between heat temperature and the catalytic performance of the catalysts. The results show that Co–N–C/SiO2 catalyst heated at 500°C exhibits much higher activity for ethylbenzene oxidation compared with its counterparts such as Co–N–C/SiO2 catalysts heated at 300°C, 400°C, 600°C and 700°C, respectively. This may be attributed to the formation of much more Co–N4–C active sites on the surface of Co–N–C/SiO2 catalyst heated at 500°C.

Metal nanoparticle-embedded super porous poly(3-sulfopropyl methacrylate) cryogel for H2 production from chemical hydride hydrolysis

Poly(3-sulfopropyl methacrylate) (p(SPM)) cryogel was prepared under cryogenic conditions (T = −18 °C) and used as template for in situ metal nanoparticle preparation of Co, Ni and Cu. These metal nanoparticle-containing super macroporous cryogel composites were tested for H2 production from hydrolysis of sodium borohydride (NaBH4) and ammonia borane (AB). It was found that amongst p(SPM)-M (M: Co, Ni, and Cu) composite catalyst systems, the catalytic performances of Co- and Ni-containing p(SPM) cryogel composite catalyst systems were the same, however in hydrolysis of NH3BH3, the order of performance of the catalysts was Co > Ni > Cu. Interestingly, p(SPM)-Co cryogel composite demonstrated better catalytic performances in salt environments e.g., faster H2 production rate in sea and tap water compared to DI water, and almost no effect of ionic strength of the solution medium was observed, but the salt types were found to affect the H2 generation rate. Other parameters that affect H2 production rate such as metal type, temperature, water source, salt concentration, amount of metal nanocatalyst and reusability were investigated. It was found that the hydrogen generation rate (HGR) was increased to 2836 ± 90 from 1000 ± 53 (ml H2)(g of Co min)−1 by multiple loading and reduction cycles of Co catalyst. Also, it was found that TOF values are highly temperature dependent, and increased to 15.1 ± 0.8 from 2.4 ± 0.1 (mol H2)(mol catalyst min)−1 by increasing the temperature from 30 to 70 °C. The activation energy, activation enthalpy and activation entropy were determined as 40.8 kJ (mol)−1, 37.23 kJ (mol K)−1, and −170.87 J (mol K)−1, respectively, for the hydrolysis reaction of NaBH4 with p(SPM)-Co catalyst system, and 25.03 kJ (mol)−1, 22.41 kJ (mol K)−1, and −182.8 J (mol K)−1, respectively, for AB hydrolysis catalyzed by p(SPM)-Co composite system.