Catalytic Activity Of Co Research Articles

Computationally Guided Discovery of a Catalytic Cobalt-Decorated Metal–Organic Framework for Ethylene Dimerization

The catalytic performance of a cobalt(II) single-site catalyst supported on the zirconia-like nodes of the metal organic–framework (MOF) NU-1000 is herein characterized by quantum chemical methods and compared to an iso-structural analogue incorporating nickel(II) as the active transition metal. The mechanisms of atomic layer deposition in MOFs and of catalysis are examined using density functional theory. We compare the catalytic activity of Co and Ni installed on the zirconia-like nodes for ethylene dimerization, considering three plausible pathways. Multiconfigurational wave function theory methods are employed to further characterize the electronic structures of key transition states and intermediates. Finally, we report confirmation of Co catalytic activity for ethylene dimerization from experiments that were prompted by the computational prediction.

Hydrothermal synthesis of β-Co(OH)2 nanoplatelets: A novel catalyst for CO oxidation

A facile, cost-effective, template-free chemical method was developed for the synthesis of β-Co(OH)2 nanoplatelets under the different preparation conditions. The morphology and microstructure of as-synthesized samples were examined by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectrum (XPS), respectively. The observations revealed the formation of a single phase of the hexagonal brucite-like β-Co(OH)2, which had an irregular hexagonal disk with angles of adjacent edges of 120°, edge lengths ranging from 200 to 300nm, and thicknesses of 20–40nm. When investigated as catalyst for CO oxidation, the β-Co(OH)2 nanoplatelets exhibited good catalytic activity for CO. Among β-Co(OH)2 nanoplatelets, the sample prepared at 100°C for 8h performed the best, giving the T100% (the temperature required for achieving a CO of 100%) of 120°C for the oxidation of CO. There are good correlations of Co3+/Co2+, the absorbed Ox− ions and surface OH group with catalytic activity of the samples for CO oxidation.

Fluoro functional groups substituted cobalt(II), iron(II) phthalocyanines and their catalytic properties on benzyl alcohol oxidation

In this study, phthalocyanine complexes (Co and Fe) bearing (2-{2-[3-(trifluoromethyl)phenoxy]ethoxy}ethoxy) groups at peripheral position were synthesized using the phthalonitrile derivative and characterized by IR, 1H-NMR, UV–Vis and mass spectrometry. Catalytic activity of Co(II) and Fe(II) phthalocyanines were investigated in the oxidation of benzyl alcohol with different oxygen sources. Determination of the optimal conditions for oxidation of benzyl alcohol, the catalytic reactions were carried out change the reaction temperature, oxidant/cat ratio, types of oxidants and subst./catalyst ratio.

Noble-Metal-Free Photocatalytic H2 Generation: Active and Inactive 'Black' TiO2 Nanotubes and Synergistic Effects.

Over the past five years a number of different synthesis approaches has been reported to obtain so-called 'black' titania. One of the outstanding features of the material is that certain synthesis processes lead to the formation of an intrinsic co-catalytic center and thus enable noble-metal free photocatalytic H2 -generation. In the present work, using TiO2 nanotube layers, we compare three common 'blackening' approaches, namely i) the original high-pressure hydrogenation (HPT-H2 ), ii) a classic high temperature reduction in Ar, and iii) an electrochemical (cathodic) reduction. We demonstrate that except for high pressure hydrogenation also cathodic reduction leads to an activation of TiO2 - that is, it exhibits noble-metal-free photocatalytic H2 generation. Moreover, we show that a combination of cathodic reduction/high pressure hydrogenation leads to a synergistic effect, that is, a significant enhancement of the combined co-catalytic activity.

On the design of Pt-Sn efficient catalyst for carbon monoxide and ethanol oxidation in acid and alkaline media

Pt-Sn catalysts supported on carbon, with different Pt-Sn atomic ratios (3:1, 1:1, 1:3), were prepared through the formic acid method (FAM) and supported on different carbon supports (nanofibers and carbon blacks) to study their behavior toward CO stripping and ethanol oxidation reaction (EOR). PtSn/C catalysts and supports were physicochemically characterized by XRD, EDX, XPS, TEM and TPD. Good particle dispersion onto the carbon support, similar particle sizes (around 4–5nm) and the presence of tin oxides were observed in all cases. Sn insertion favored the development of the Pt3Sn1 phase and the presence of higher oxidation states of both metals in the catalyst. Ethanol and adsorbed CO oxidation were studied at these materials both in acid and alkaline media, by linear sweep voltammetry and chronoamperometry. Higher EOR current densities were obtained with the increase in the amount of Sn in the samples, been those materials supported on CNF the ones with the best CO tolerance and catalytic activity toward this reaction. As expected, a great improvement of the EOR activity was found in alkaline media compared to sulfuric acid media, providing good expectative for these materials as catalysts for alkaline direct ethanol fuel cells.

Formation of Ru Shell on Co/Al2O3 by Galvanic Deposition Method and Its High Catalytic Performance for Three-Way Conversion

Abstract A supported Ru catalyst was prepared by a galvanic deposition (GD) of Ru on Co particles supported on Al2O3 (Ru/Co-GD). The structure and chemical state of Ru/Co-GD was characterized by using a pulsed CO chemisorption technique, STEM-EDS, XAFS, XPS, CO adsorption FT-IR spectroscopy, and temperature-programed reduction (TPR) method. It is indicated that Ru/Co-GD forms Ru shell on Co nanoparticles. Such a unique structure was not formed on Ru/Co/Al2O3 prepared by a conventional sequential impregnation method (Ru/Co-seq). The Ru shell of Ru/Co-GD showed higher reducibility than Ru species of Ru/Co-seq as well as higher than Ru/Al2O3. Owing to the Ru shell having high reducibility, Ru/Co-GD showed enhanced catalytic activity for NO–C3H6 reaction. In addition, Co oxide on Ru/Co-GD exhibited high catalytic activity for CO and C3H6 oxidation. As a result, Ru/Co-GD showed superior performance for NO–C3H6–CO–O2 reaction compared to the conventional catalysts. The Ru shell structure also contributed to the suppression of Ru vaporization.

One Step Template-Free Synthesis of Mesoporous MnOx/CeO2 Nanocomposite Oxides with Enhanced Low Temperature Catalytic Activity for CO and Hydrocarbon Oxidation

A green environment-friendly preparation method with template-free facile redox precipitation strategy was proposed to synthesize a series of mesoporous MnOx/CeO2 nano-composite oxides and were applied to catalytic oxidation diesel engine exhaust of CO and CH. The catalysts were characterized by XRD, N2 adsorption–desorption, TEM/SEM, XPS, H2-TPR and O2-TPO. Among these catalysts, the optimized sample MnOx/CeO2-64 achieved high catalytic activity (CO: T100 = 150 °C; C3H6: T100 = 190 °C; C3H8: T100 = 230 °C) and good durability. The superior catalytic activity of the catalyst could be ascribed to the generation of a large number of active oxygen species due to a synergetic catalytic effect between Ce/Mn with multiple oxidation states. The results of H2-TPR and O2-TPO indicated that stronger redox capacity contributed to the excellent catalytic oxidation performance. In addition, a possible reaction pathway was proposed for clarification this catalytic process. We propose a facile template-free strategy to prepare mesoporous nano-composites by one step redox precipitation method using H2O2 as reductant-oxidant, which shows the advantages of mild condition, simple process and environmental protection.

Synthesis of polyfluoro substituted Co(II), Fe(II) phthalocyanines and their usage as catalysts for aerobic oxidation of benzyl alcohol

Peripherally tetra substituted Co(II) and Fe(II) phthalocyanine complexes bearing (2-{2-[2,3,5,6-tetrafluorophenoxy]ethoxy}ethoxy) groups were synthesized using the phthalonitrile derivative 1 and verified by IR, 1H NMR, UV–Vis and mass spectrometry. Catalytic activity of Co(II) and Fe(II) phthalocyanines were investigated in the oxidation of benzyl alcohol with different oxygen sources. Different parameters that effect the oxidation process were examined for finding optimal conditions of catalysis. Co(II) phthalocyanine shows excellent catalytic performance on benzyl alcohol oxidation with high yield and selectivity. It shows that this kind of catalysis system is very active, selective and suitable for the oxidation of benzyl alcohol.

A comparative study of the catalytic activity of Co- and CoFe2O4-NPs in C–N and C–O bond formation: synthesis of benzimidazoles and benzoxazoles from o-haloanilides

Herein, new methods and a comparison of the results for dehalogenative intramolecular C–X bond formation using two inexpensive and efficient catalysts are reported.

High catalytic activity of Co3O4 nanoparticles encapsulated in a graphene supported carbon matrix for oxygen reduction reaction

A simple method has been adopted for the synthesis of Co3O4 nanoparticles encapsulated in graphene supported carbon matrix, which could exhibit higher catalytic performance for oxygen reduction reaction than the commercial Pt/C.

The ultrasound-assisted synthesis of effective monodisperse nickel nanoparticles: magnetic characterization and its catalytic activity in CO2 methanation

High performance nickel–zirconia nanocatalysts based on monodisperse nickel nanoparticles have been developed via a simple and continuous two-step ultrasonic method.

Dual functionality of amphiphilic 1-alkyl-3-methylimidazolium hydrogen sulfate ionic liquids: surfactants with catalytic function

A series of amphiphilic 1-alkyl-3-methylimidazolium hydrogen sulfate ILs were synthesized. Their co-catalytic activities have been determined and discussed in terms of their structure and surface properties.

Boronic acid/Brønsted acid co-catalyst systems for the synthesis of 2H-chromenes from phenols and α,β-unsaturated carbonyls.

Protocols for the synthesis of substituted 2H-chromenes from α,β-unsaturated carbonyls and phenols are described. Optimal combinations of arylboronic acids and Brønsted acids have been identified, such that both can be employed in catalytic quantities to accelerate these condensations. The method has been used to synthesize a variety of substituted 2H-chromenes, as well as photochromic naphthopyrans. The use of pentafluorophenylboronic acid and diphenylphosphinic acid enabled an expansion of the electrophile scope to include α,β-unsaturated ketones. Hall's 'phase-switching' of boronic acids has been exploited to achieve the separation of the two co-catalysts from unpurified reaction mixtures by a simple liquid-liquid extraction.

Synthesis, structures and properties of a meso-substituted pyrazolyl porphyrin and its Co(II) porphyrin complex

In this work, one new porphyrin, 5, 10, 15, 20-tetrakis(4-N-pyrazolyl)phenyl porphyrin (H2Pp) was synthesized and characterized. The single crystal structures of H2Pp and its cobalt(II) porphyrin (Co(II)Pp) were obtained with a space group of P1− and I2/c, respectively. The porphyrin macrocycle is close to a perfect plane in H2Pp, while Co(II)Pp exhibits a saddle-type distortion due to the formation of shorter Co–N coordination bonds. In H2Pp, the molecules are interconnected through π⋯π and C–H⋯π interactions to form 3D architecture, while in Co(II)Pp the porphyrin molecules are interlinked only by C–H⋯π interactions to yield 3D structure. We examined the UV–vis spectra and fluorescent spectra of H2Pp and Co(II)Pp in CH2Cl2 and solid state at room temperature. In addition, the catalytic activities of Co(II)Pp to the ethylbenzene oxidation was examined, the results indicate that Co(II)Pp exhibits a high selectivity to acetophenone (>99%) with the conversion of 83%.

The role of pillaring in MCM-22 on the dispersion of noble metals and catalytic activity

The aim of this work was to evaluate the effect of pillaring of MCM-22 zeolite on Pt and Au dispersion and catalytic activity in CO and methanol oxidation as well as to analyze the similarities and differences in the surface and catalytic properties of Au and Pt loaded on pillared MCM-22-pil. The role of pillaring in the functionalization by APTMS (3-aminopropyl-trimethoxysilane) before metal loading was also considered. The difference in the effect of platinum and gold dispersion on the rate of CO oxidation confirmed reports in the literature. The stability of Pt-containing zeolites in CO oxidation for the second run of the reaction is pointed out. An increase in activity of gold catalysts in the second cycle of the reaction was found and is discussed. The difference found in the methanol conversion and selectivity in alcohol oxidation between gold-containing MCM-22 and MCM-22-pil is discussed.

POPd/TBAB co-catalyzed Suzuki cross-coupling reaction of heteroaryl chlorides/bromides with 4-fluorophenylboronic acid in water

An organic solvent free and efficient heterogeneous synthesis for bridging heteroaryl halides and 4-fluorophenylboronic acid was studied in aqueous media according to the Suzuki cross-coupling protocol. High yields of heteroaryl-aryl fluorides were successfully obtained with: chloro-/bromo-substituted pyridine, thiophene, indole, and inzole in neat water using palladium phosphinous acid complexes (POPd)/tetrabutylammonium bromide (TBAB) as co-catalysts. A possible mechanism for the heterogeneous coupling reaction is proposed and discussed according to the function of the TBAB interphases. The notable properties of the reported method are highly co-catalytic activity, hetero-atom tolerance, simple separating procedure and little environmental disposal impact.

Catalytic Activity and Thermal Stability of Arc Plasma Deposited Pt Nano-Particles on CeO2-Al2O3.

In this study, catalytic activity and thermal stability of the arc plasma deposited (APD) Pt nano-particles on A12O3 and CeO2-Al2O3 were compared with that of the conventionally prepared Pt/Al2O3. All the catalysts were characterized by BET-surface area, transmission electron microscopy, X-ray photoelectron spectroscopy, CO-pulse chemisorption, H2-temperarture programmed reduction and X-ray absorption near edge spectroscopy. Through the quantum chemical calculations of different metal oxide support, CeO2 was identified as a suitable anchoring material with high energy level between the Pt species (Pt(0) and PtO(x)) on ceria. Subsequently, the results of XPS and XANES revealed the presence of abundant Pt(0) metal species in APD catalysts. The addition of ceria to Al2O3 support enhanced the dispersion of Pt nano-particles. The H2-TPR of Pt/CeO2-Al2O3 (APD) catalyst showed high-temperature reduction peaks corresponding to the interaction of Pt with ceria on alumina by Pt-O-Ce. Consequently, the Pt nano-particles deposited on CeO2-Al2O3 by APD attained strong thermal resistance at high temperatures. In addition, superior catalytic activities for CO and C3H6 oxidation and NO(x) reduction were obtained for the Pt/CeO2- Al2O3 (APD) catalyst.

Significant hydrogen-bonding effect on the reactivity of high-valent manganese(V)–oxo porphyrins in C–H bond activation: A DFT study

The stereo electronic effects as well as hydrogen bonding effects of imidazole, pyridine and 2,6-dimethylpyridine as N-donor axial ligands on the C–H oxidation activity of high-valent manganese(V)–oxo meso-tetraphenylporphyrin (TPP) and meso-tetrakis(pentaflourophenyl)porphyrin (TPFPP), are investigated by DFT calculations. The electronic and steric properties of axial donors and porphyrin ligands affected on the activation energy of cyclohexane hydroxylation as well as the Mn–O bond strength of the oxo species in transition state. Imidazole with the strong [Formula: see text]-donating ability and the least steric hindrance showed greater co-catalytic activity than those of pyridine and in particularly hindered 2,6-Me2 pyridine in the presence of simple [(TPP)MnO][Formula: see text]. Nevertheless, the C–H bond activation by hindered and electron-deficient perfluorinated catalyst [(TPFPP)MnO][Formula: see text] is in the order of pyridine >2, 6-Me2 pyridine >imidazole. AIM analysis showed hydrogen bonding (HB) between the C–H [Formula: see text] bonds of pyridine (C[Formula: see text]-H of ring) and 2,6-Me2Py (C[Formula: see text]-H of methyl groups) with ortho-C–F bond of phenyl rings of TPFPP in Mn[Formula: see text]O species (C–H…..F–C hydrogen bond) which might be responsible for this unusual behavior. These results are supported by natural bond orbital (NBO) analysis.

A Thermally Stable Cr–Cu Nanostructure Embedded in the CeO2 Surface as a Substitute for Platinum-Group Metal Catalysts

High catalytic activities for CO–O2 and CO–NO reactions that were superior to or comparable with those of platinum-group metal catalysts were achieved by synchronous dual-mode arc plasma deposition of a very small amount of Cr and Cu (0.07 wt % each) onto CeO2, followed by subsequent thermal aging at 900 °C for 25 h. The turnover frequency for CO oxidation over Cr–Cu/CeO2 was 3-fold higher than that over Cu/CeO2 and exceeded values for the Rh, Pd, and Pt catalysts loaded on CeO2, despite a significant decrease in the surface area from 169 to 5 m2 g–1 caused by thermal aging. Experimental structure characterization and density functional theory calculations based on CeO2 (111) surface slab models revealed that Cu+ substitution for surface Ce atoms leads to the formation of asymmetric 3-fold oxygen coordination sites capable of efficient CO chemisorption and catalytic activity. In addition, Cr3+ was incorporated into the surface structure of CeO2; it plays an important role in enhancing the surface concentration of Cu+. A CO oxidation rate with nearly zero partial orders with respect to O2 and isotopic C16O–18O2 reactions yielding C16O2 as the primary product demonstrated that the reaction proceeds via the Mars–van Krevelen mechanism.

Factors influencing catalytic activity of Co–Zn double-metal cyanide complexes for alternating polymerization of epoxides and CO2

Co–Zn double-metal cyanides (DMCs) show good catalytic activity towards copolymerization of epoxides and CO2. A deep insight into the structural aspects of the catalysts that control their catalytic performance is addressed in this work. Method of preparation of DMC catalysts was found to have influence on their structure, which in turn dictated their catalytic activity. Complexing agent (t-BuOH) and density of strong acid sites of DMC catalysts were found critical factors responsible for their activity. Selectivity of DMC towards polycarbonates depends on the amount of alkali ion content in their composition. Induction period of the catalysts was governed by the strength of acid sites and by the presence of dispersed ZnCl2 in the composition. This study provides an understanding of the prime features of DMC catalysts that can be tuned for high productivity of polycarbonates.