Monometallic Cobalt Research Articles

Supported Metal Oxide Catalysts: Their Activity to Vapor Phase Oxidation of Ethylbenzene

Mesoporous MCM-41 and Al-MCM-41 (Si/Al = 99 and 158) molecular sieves were synthesized hydrothermally and characterized by low-angle X-ray powder diffraction (XRD), nitrogen adsorption isotherms, FT-IR, and TG-DTA techniques. Monometallic manganese and cobalt oxides and also their bimetallic forms impregnated Si-MCM-41 and Al-MCM-41 catalysts were prepared by wet method and characterized by XRD, AAS, DRS UV−vis, and ESR techniques. The presence of Mn2+ and Co3+ in the mono- and bimetal impregnated catalysts was evident through DRS studies. The analysis with DRS-UV−vis spectroscopy showed independent existence of manganese and cobalt oxides in the bimetallic catalysts. AAS analysis showed higher loading of manganese than cobalt, and the same difference was also observed for bimetal impregnated catalysts. The catalytic activity of the impregnated catalysts was studied for the vapor phase oxidation of ethylbenzene with air (CO2-free) at 250, 300, 350, 375, and 400 °C. The major products were found to be acet...

Co and Mn impregnated MCM-41: their applications to vapour phase oxidation of isopropylbenzene

The mesoporous molecular sieves Si-MCM-41 and Al-MCM-41 (Si/Al = 99) were synthesized and their structures were elucidated by XRD, N 2-adsorption isotherm and TG-DTA technique. Monometallic cobalt and manganese oxides and also their bimetallic forms impregnated Si-MCM-41 and Al-MCM-41 catalysts were prepared by wet method and characterised by XRD, AAS, DRS-UV–vis and ESR techniques. The presence of Co 3+ and Mn 2+ in the mono and bimetal impregnated catalysts was evident through DRS studies. The analysis with DRS-UV–vis-spectroscopy showed independent existence of cobalt and manganese oxides in the bimetallic catalysts. AAS analysis showed higher loading of manganese than cobalt and the same difference was also observed for bimetal impregnated catalysts. The vapour phase oxidation of isopropylbenzene with CO 2-free air was studied over cobalt and manganese oxide impregnated Si-MCM-41 and Al-MCM-41 catalysts. Isopropylbenzene conversion increased with increase in temperature from 200 to 300 °C, but at 325 °C it decreased. Formation of coke has been noted at all the temperatures. Cumene hydroperoxide, 1,2-epoxy isopropylbenzene, acetophenone and styrene were the products observed in this reaction. Among the products, cumene hydroperoxide was found to have more selectivity than other products over all the catalysts. Both cobalt and manganese oxide impregnated catalysts were found to have nearly the same activity. The study of time-on-stream indicated decrease in conversion with stream due to coke formation.

Transition Metal Derivatives of a ((Dimethylamino)ethyl)cyclopentadienyl Ligand. Synthesis and Structures of Amino-Containing Cyclopentadienyl Derivatives of Cobalt(I) and -(III) Including Water-Soluble Compounds.

The synthesis of monometallic cobalt(III) and -(I) complexes of ((dimethylamino)ethyl)cyclopentadienyl are reported. The presence of the basic amino group facilitates these synthesis using the corresponding cyclopentadiene complexes as starting material. A cobaltocenium green complex [{eta(5)-C(5)H(4)(CH(2))(2)N(H)Me(2)}(2)Co(III)](3+)(Cl(-))(3) (3) was obtained from C(5)H(5)(CH(2))(2)NMe(2) (1) or from its salt M[C(5)H(4)(CH(2))(2)NMe(2)] (M = Na, Li) (2) upon reaction with Co(II)Cl(2) in THF. The structure of the complex [{(eta(5)-C(5)H(4)(CH(2))(2)NMe(2))(eta(5)-C(5)H(4)(CH(2))(2)N(H)Me(2))}Co(I)(II)](PF(6))(2) (4), prepared from 3 by treatment with NH(4)PF(6) in aqueous solutions, was solved in the triclinic space group P&onemacr; with one molecule in the unit cell, the dimensions of which were a = 6.314(2) Å, b = 7.137(2) Å, c = 13.452(2) Å, alpha = 103.66(2) degrees, beta = 90.25(2) degrees, gamma = 92.89(2) degrees, and V = 588.2(3) Å(3). Adjacent molecules in the unit cell of 4 are hydrogen bonded via a H(+) through their -NMe(2) side chains. The reaction of Co(2)(CO)(8) with C(5)H(5)(CH(2))(2)NMe(2) (1) leads to the formation of [{eta(5)-C(5)H(4)(CH(2))(2)NMe(2)}Co(I)(CO)(2)] (5). Treatment of 5 with HBF(4) in ether solutions yielded [{eta(5)-C(5)H(4)(CH(2))(2)N(H)Me(2)}Co(I)(CO)(2)](+)BF(4)(-) (6). Oxidation of 5 with I(2) or Cl(2) gas yielded [{eta(5)-C(5)H(4)(CH(2))(2)NMe(2)}Co(III)I(2)] (7a) and [{eta(5)-C(5)H(4)(CH(2))(2)NMe(2)}Co(III)Cl(2)] (7b). Addition of HBF(4) to complex 7a resulted in the breaking of the Co(III)-NMe(2) bond, producing the dimeric complex [{(eta(5)-C(5)H(4)(CH(2))(2)N(H)Me(2))Co(III)I(2)}(2)](2+)(BF(4)(-))(2) (9). The bridged diiodo dimer 10, [{(eta(5)-C(5)H(4)(CH(2))(2)NMe(2))CoI}(2)](2+)(BF(4)(-))(2), on the other hand, could be obtained from complex 7a upon addition of AgBF(4) in CH(2)Cl(2).

Promoting effect of doped cobalt on catalysis of SiO2-supported rhodium for propylene hydroformylation

According to infrared spectroscopy and temperature programmed reduction (TPR), doped Coo to Rho/SiO2 can play an electron-donating role and prevent the oxidation of Rho by surface OH−. The interaction between monometallic cobalt and rhodium particles which are probably in close contact results in a strong enhancement of catalytic propylene hydroformylation.

Characterization and catalytic activity of Al2O3-supported Pt-Co catalysts

A series of Pt-Co supported on γ-alumina have been prepared from acetylacetonate precursors with 2 wt% as total metal loading and different atomic contents. The catalysts were characterized by hydrogen chemisorption, TPR, TEM, XPS and they were tested in two different reactions: methylcyclohexane dehydrogenation and n-butane hydrogenolysis. The results have shown that platinum is in reduced state and cobalt is mainly in an oxidized state. Additionally, TEM results evidence an increase in the particle size as cobalt content is increased, in agreement with chemisorption results. Monometallic platinum and cobalt supported catalysts showed large differences in the dehydrogenation of methylcyclohexane, while the bimetallic catalysts have activities in the same order of magnitude with respect to the pure platinum catalyst. In n-butane hydrogenolysis all the catalysts show a large decrease in activity compared to other, previously studied Pt-based bimetallic catalysts.

Fischer–Tropsch Synthesis with Supported Cobalt Catalyst. Promoting Effects of Lanthanum Oxide for Cobalt/Silica Catalyst

Abstract The promotional effects of metal oxides for a silica-supported cobalt catalyst were investigated by using X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Temperature Programmed Reaction (TPR), and Fourier Transform-Infrared Spectroscopy (FT-IR) techniques. The La-modified cobalt catalyst with 3% La loading which was prepared by simultaneous impregnation showed higher catalytic activity while keeping slightly higher selectivity of C2+ hydrocarbons. TPR, FT-IR, and TEM studies revealed that CO is adsorbed on the La-modified cobalt catalyst in a more active state compared to the monometallic cobalt catalyst, which was caused by the agglomeration of cobalt.

Improved alkene selectivity in carbon monoxide hydrogenation over silica supported cobalt-molybdenum catalyst

Abstract The Fischer-Tropsch synthesis performance of a Co-Mo bimetallic catalyst containing 6Co:lMo:4K:100SiO 2 has been studied and compared with a similar monometallic cobalt catalyst. The bimetallic system showed nearly 100% improvement in alkene-alkane ratio at the experimental conditions of 101 kPa and 280°C (553 K) and CO-H 2 ratio of 1:19 to 19:1. Ethylene-to-methane ratio (EMR) over the Co-Mo catalyst was about 70-100% better than the cobalt catalyst over the wide composition range studied. The kinetics over the Co-Mo catalyst also followed conventional Anderson-Schulz-Flory (ASF) polymerisation kinetics suggesting that there is no fundamental change in the reaction mechanism. The increase in chain growth probability and alkene content was attributed to substantial methane suppression caused by the introduction of molybdenum to the catalyst. Activation energy values for the light hydrocarbons over the bimetallic catalyst were in the range 85–120kJ/mol and about 10-15% lower than the corresponding estimates over the monometallic system.

EXAFS Study of the Local Order in Metastable Cobalt and Iron Films

The knowledge of the crystallography of metastable cobalt and iron films prepared by deposition on suitable substrates is the key for the understanding of their unusual magnetic properties; their local structure is determined precisely by SEXAFS. This technique allows a measure of the asymmetry of the first shell radial distribution function in monometallic cobalt and iron films prepared by vapor condensation on a low temperature amorphous substrate. In both cases the measured profile allows to conclude the existence of true amorphous monometallic samples and compares well with the calculated one assuming a random packing of hard spheres. Following the evolution of the local order with increasing temperature we show that the cobalt amorphous films crystallize abruptly at a temperature dependent on their thickness, while the iron amorphous films crystallize slowly. Moreover EXAFS has been used to investigate the local structure of f.c.c. iron films which have puzzling magnetic properties. These metastable films grown on Cu(100) have a structure strongly dependent on their temperature of growth: Both the short range order and the amplitude of the thermal vibrations measured at room temperature are higher in films prepared at higher temperatures. These different crystallographic structures can be the origin of the conflicting results produced in the study of their magnetic properties.