Silica-supported Cobalt Catalysts Research Articles

Selective Propene Synthesis from Ethene without Metathesis on Silica Supported Cobalt Catalyst

Selective Propene Synthesis from Ethene without Metathesis on Silica Supported Cobalt Catalyst

TiO2 promoted Co/SiO2 catalysts for Fischer–Tropsch synthesis

The addition of small amount of TiO2 to silica-supported cobalt catalysts significantly increasing the dispersion of cobalt and Co metallic surface area resulting in the remarkable enhancement of the Fisher–Tropsch synthesis (FTS) activity in the slurry-phase reaction. The addition of TiO2 adjusted the interaction between cobalt and silica support quite well to realize the favorite dispersion and reduction degree of supported cobalt, leading to high catalytic activity in FTS. The properties of various catalysts were characterized by in-situ DRIFT, XRD, TPR, N2 physisorption and H2 chemisorption.

Effect of Thermal Treatment on Structure and Catalytic Activity of Supported Fischer-Tropsch Nano-Cobalt Catalysts for Clean Fuels

A series of 15%Co/Al2O3 catalysts were prepared by incipient wetness impregnation under various calcination conditions (90500C), and were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy experiments (XPS), temperature programmed reduction, and catalytic measurements of hydrogenation of carbon monoxide to long-chained hydrocarbons leading to clean fuels (Fischer-Tropsch synthesis). The results of XPS show the presence of incompletely decomposed cobalt nitrate for catalysts calcined at 90200C, and the presence of Co3O4 for catalysts calcined at 200500C. For the four alumina-supported nano-cobalt catalysts with different thermal treatment (200500C), XRD and XPS results illustrated that there were mainly nano Co3O4 crystalite phases of 910 nm and the size of cobalt nano-particles did almost not change with the different temperature of thermal treatment. This was different from that of silica-supported cobalt catalysts. The supported cobalt catalyst (CoAp340 sample) calcinated at 340C presented a better activity for Fischer Tropsch synthesis to clean fuels, at mild conditions like atmospheric pressure (100 kPa), 1800 mL/g/h and 190C; rather than high pressure (2 MPa or more).

Chemistry of Silica-Supported Cobalt Catalysts Prepared by Cation Adsorption. 1. Initial Localized Adsorption of Cobalt Precursors

The speciation of cobalt ethanediamine (en) complexes [Co(en)x(H2O)6-2x]2+ (x = 1, 2, and 3) in aqueous solution changes when a silica support is introduced into the solution ((en/Co = 1), (en/Co = 2), and (en/Co = 3) preparations). The pH-buffering effect of the silica support causes speciation shifts, especially for the precursor complex [Co(en)2(H2O)2]2+ in solution, which transform into [Co(en)1(H2O)4]2+, as the main species. Once adsorbed on silica and after drying (25 and 100 °C), UV−visible and XAS characterization show that, for the (en/Co = 1) and (en/Co = 2) preparations, the Co(en)1 complexes form dimers bonded to silica through one silanol group per Co ([(SiO)(en)(H2O)2CoII]2(μ-O)). For the (en/Co = 3) preparation, the adsorbed Co(II) complexes are monomeric and contain two ethanediamine ligands. Upon drying at 100 °C, residual water molecules in the coordination sphere of adsorbed Co(II) complexes may be lost reversibly, causing the establishment of an octahedral/tetrahedral coordination equilibrium. Upon calcination at 450 °C, the ethanediamine ligands are eliminated. The monomeric complex in (en/Co = 3) probably becomes grafted onto silica through two bonds ((SiO)2CoII(OH2)4), while the dimer initially formed in (en/Co = 1) and (en/Co = 2) mostly gives rise to species reminiscent of Co silicate germs.

Improved electrochemical storage of lithium into multi-walled carbon nanotubes by light irradiation

Multi-walled carbon nanotubes (MWNTs) were synthesized by catalytic decomposition of acetylene at 750 °C over silica supported cobalt catalysts. The effects of xenon light irradiation on electrochemical storage of lithium into MWNTs were investigated by various electrochemical testing techniques. The as-prepared MWNTs demonstrate a high reversible capacity of 237 mAh g −1 with good cycling stability at a current density of 30 mA g −1. Upon illumination, the reversible capacity for the MWNTs reaches about 270 mAh g −1 at the initial cycle, and remains above 250 mAh g −1 after 25 cycles. The results from CV and EIS analysis reveal that the light irradiation on the MWNTs may allow easy insertion/extraction of lithium into/from the nanotubes, and therefore leading to higher reversible capacity than that without light irradiation.

Kinetic characterization of the reduction of silica supported cobalt catalysts

The reduction process of silica supported cobalt catalyst was studied by thermal analysis technique. The reduction of the catalyst proceeds in two steps: $$ Co_3 O_4 + H_2 \to 3CoO + H_2 O, 3CoO + 3H_2 \to 3Co + 3H_2 O $$ which was validated by the TPR and in-situ XRD experiments. The kinetic parameters of the reduction process were obtained with a comparative method. For the first step, the activation energy, Ea, and the pre-exponential factor, A, were found to be 104.35 kJ mol−1 and 1.18·106∼2.45·109 s−1 respectively. The kinetic model was random nucleation and growth and the most probable mechanism function was found to be f(α)=3/2(1−α)[−ln(1−α)]1/3 or in the integral form: g(α)=[−ln(1−α)]2/3. For the second step, the activation energy, Ea, and the pre-exponential factor, A, were found to be 118.20 kJ mol−1 and 1.75·107∼2.45 · 109s−1 respectively. The kinetic model was a second order reaction and the probable mechanism function was f(α)=(1−α)2 or in the integral form: g(α)=[1−α]−1−1.

Selective ethene homologation reaction on silica supported cobalt catalyst

When ethene alone was contacted with silica supported cobalt catalyst (Co/SiO2), ethene homologation took place with considerable activity. Moreover, the propene metathesis reaction was suppressed ca. 1/6 fold as much as in the case using MoOX/SiO2 catalyst. The possibility of selective homologation with a lower activity for metathesis was suggested for the cobalt-based catalyst system.

Effects of impregnation solvent on Co/SiO2 catalyst for Fischer-Tropsch synthesis: A highly active and stable catalyst with bimodal sized cobalt particles

Silica-supported cobalt (20 wt%) catalysts were prepared by incipient-wetness impregnation of silica with different cobalt nitrate solutions. The catalyst prepared from dehydration ethanol solution exhibited stable and the highest activity, as well as significantly low methane selectivity. Cobalt crystalline size of the catalyst prepared from dehydrated ethanol was smaller than that of the catalyst prepared from aqueous solution, and existed two different size where the large particles showed low bulk density with cluster-like structure. But only larger clusters existed in the catalyst prepared from aqueous solution. The increased amount of active sites and more reactive adsorbed CO on the surface determined the highest activity of the catalyst prepared from dehydrated ethanol solution in liquid-phase Fischer-Tropsch synthesis (FTS) reaction.

The key role of support surface tuning during the preparation of catalysts from reverse micellar-synthesized metal nanoparticles

Abstract Silica-supported cobalt catalysts have been prepared by depositing cobalt nanoparticles synthesized in reverse micellar systems. Two different reverse microemulsions comprising both a neutral (Triton X114) or an ionic (AOT) surfactant were used for the synthesis of nanoparticles. The materials have been characterized by 29Si MAS NMR, XRD, FTIR, H2-TPR, and TEM. Protection of the hydroxyl groups on the silica surface by silylation prior to loading of the cobalt nanoparticles has been found crucial for attaining the desired metal dispersions in the final catalyst owing to a higher chemical compatibility between the hydrophobic support surface and the microemulsion during the deposition step.

Promotional Effects of Al2O3 Addition to Co/SiO2 Catalysts for Fischer−Tropsch Synthesis

The addition of a small amount of Al2O3 to silica-supported cobalt catalysts significantly increased the dispersion of cobalt and Co−metallic surface area, resulting in the remarkable enhancement of the Fischer−Tropsch synthesis (FTS) activity in the slurry-phase reaction. The addition of Al2O3 adjusted the interaction between cobalt and the silica support quite well, realizing the favored dispersion and reduction degree of supported cobalt and leading to high catalytic activity in FTS. The properties of various catalysts were characterized by in situ DRIFT, XRD, TPR, N2 physisorption, and H2 chemisorption.

TiO<sub>2</sub> Promoted Co/SiO<sub>2</sub> Catalysts for Fischer-Tropsch Synthesis

The addition of small amount of TiO2 to silica supported cobalt catalysts significantly increased the dispersion of cobalt and Co metallic surface area, resulting in the remarkable enhancement of the Fisher-Tropsch synthesis (FTS) activity in the slurry-phase reaction. The addition of TiO2 adjusted the interaction between cobalt and silica support quite well, to realize the favorite dispersion and reduction degree of supported cobalt at the same time, leading to high catalytic activity in FTS.

TiO2 Promoted Co/SiO2 Catalysts for Fischer-Tropsch Synthesis

The addition of small amount of TiO 2 to silica supported cobalt catalysts significantly increased the dispersion of cobalt and Co metallic surface area, resulting in the remarkable enhancement of the Fisher-Tropsch synthesis (FTS) activity in the slurry-phase reaction. The addition of TiO 2 adjusted the interaction between cobalt and silica support quite well, to realize the favorite dispersion and reduction degree of supported cobalt at the same time, leading to high catalytic activity in FTS.

Metal-support interaction in mesoporous silica supported cobalt Fischer-Tropsch catalysts

The pore structure of silica supports (SiO2 or MCM-41) has little influence on the metal-support interaction in silica supported cobalt catalysts. Cobalt dispersion, reduction behavior, and catalytic properties for the Fischer-Tropsch synthesis were primarily affected by the metal particle size.

Fischer–Tropsch synthesis: Water effects on Co supported on narrow and wide-pore silica

The effect of water on the performance of narrow and wide-pore silica-supported cobalt catalysts was investigated during Fischer–Tropsch synthesis in a continuously stirred tank reactor (CSTR). In these studies the added water replaced an equivalent amount of inert gas so that all other reaction conditions remained the same before, during and after water addition. A low cobalt loading of 12.4 wt.% on wide-pore silica exhibited a beneficial effect on CO conversion with the addition of water up to 25 vol.% of the total feed. In contrast, the addition of up to 20 vol.% water to a 20 wt.% Co on narrow- or wide-pore silica did not significantly alter the CO conversion. It appears that the CO conversion mainly increases when cobalt clusters are small enough to fit inside the silica pores.

Hydroformylation of 1-hexene for oxygenate fuels on supported cobalt catalysts

The supported Co/SiO 2 and Co/active carbon (A.C.) catalysts were studied as heterogeneous catalysts in the liquid-phase hydroformylation of 1-hexene. The pore size of silica support significantly influenced the activity and selectivity of Co/SiO 2 catalysts in hydroformylation of 1-hexene. The silica supported cobalt catalyst exhibited the best hydroformylation reaction performance at 403 K, and catalytic activity for this kind of catalyst increased with the increasing initial reaction pressure. The addition of small amount of noble metal significantly improved the activity and selectivity for Co/SiO 2. The solvent effects for Co/SiO 2 and Co/A.C. catalysts in the hydroformylation reaction of 1-hexene were investigated and alcoholic solvents promoted the oxygenate formation significantly.

Enhancement in the reducibility of cobalt oxides on a mesoporous silica supported cobalt catalyst

The silylation of SBA-15 enhances the reducibility of cobalt oxides on a SBA-15 supported cobalt catalyst, and consequently increases the catalytic activity for Fischer-Tropsch synthesis of hydrocarbons from syngas and selectivity for longer chain products.

Influence of the Pore Structure of MCM-41 and SBA-15 Silica Fibers on Atomic Layer Chemical Vapor Deposition of Cobalt Carbonyl

Mesoporous high surface area MCM-41 and SBA-15 type silica materials with fibrous morphology were synthesized and used as support materials for the ALCVD (atomic layer chemical vapor deposition) preparation of Co/MCM-41 and Co/SBA-15 catalysts. Co/MCM-41 and Co/SBA-15 catalysts were prepared by deposition of Co2(CO)8 from the gas phase onto the surfaces of preheated support materials in a fluidized bed reactor. For both silica materials, two different kinds of preparation methods, direct deposition and a pulse deposition method, were used. Pure silica supports as well as supported cobalt catalysts were characterized by various spectroscopic (IR) and analytical (X-ray diffraction, Brunauer-Emmett-Teller, elemental analysis) methods. MCM-41 and SBA-15 fibers showed considerable ability to adsorb Co2(CO)8 from the gas phase. For MCM-41 and SBA-15 silicas, cobalt loadings of 13.7 and 12.1 wt % were obtained using the direct deposition method. The cobalt loadings increased to 23.0 and 20.7 wt % for MCM-41 and SBA-15 silicas, respectively, when the pulse deposition method was used. The reduction behavior of silica-supported cobalt catalysts was found to depend on the catalyst preparation method and on the mesoporous structure of the support material. Almost identical reduction properties of SBA-15-supported catalysts prepared by different deposition methods are explained by the structural properties of the mesoporous support and, in particular, by the chemical structure of the inner surfaces and walls of the mesopores. Pulse O2/H2 chemisorption experiments showed catalytically promising redox properties and surface stability of the prepared MCM-41- and SBA-15-supported cobalt catalysts.

β-Selective epoxidation of Δ5-steroids by O2 using surface functionalised silica supported cobalt catalysts

Abstract A general catalytic and relatively environment friendly method for β-epoxidation of Δ5-steroids has been developed, which uses silica supported cobalt as catalysts and molecular oxygen as the oxidant. The reactions are regio- and stereoselective. A whole range of Δ5-steroids, with different functional groups such as hydroxyl, carbonyl or acetyl, as well as different side chains, were conveniently converted to the corresponding biologically interesting 5β,6β-epoxides with high degree of stereoselectivity and high yields.

Physico-Chemical and Catalytic Study of the Co/SiO2Catalysts

This paper is focused on the physico-chemical and catalytic properties of Co/SiO 2 catalysts. Silica-supported cobalt catalysts were prepared by sol-gel and impregnation methods and characterized by BET measurements, temperature programmed reduction (TPR H2 ), X-ray diffraction (XRD), and thermogravimetry-mass spectroscopy (TG-DTA-MS). The sol-gel method of preparation leads to metal/support catalyst precursor with a homogenous distribution of metal ions into bulk silica network or on its surface. After drying the catalysts were calcined at 500, 700, and 900°C. The reducibility of the supported metal oxide phases in hydrogen was determined by TPR measurements. The influence of high temperature-atmosphere treatment on the phase composition of Co/SiO 2 catalysts was investigated by XRD and TG-DTA-MS methods. At least five crystallographic cobalt phases may exist on silica: metallic Co, CoO, Co 3 O 4 , and two different forms of Co 2 SiO 4 cobalt silicate. Those catalysts in which cobalt was chemically bonded with silica show worse reducibility as a result of strongly bonded Co-O-Si species formed during high-temperature oxidation. The TPR measurements show that a gradual increase in the oxidation temperature (500-900°C) leads to a decrease in low-temperature hydrogen reduction effects (<600°C). The decrease of cobalt oxide reduction degree is caused by cobalt silicate formation during the oxidation at high temperature (T ≤ 1000°C). The catalysts were tested by the reforming of methane by carbon dioxide and methanation of CO 2 reactions.

Fischer–Tropsch synthesis over silica supported cobalt catalysts: mesoporous structure versus cobalt surface density

The effect of support mesoporous structure and cobalt content on cobalt dispersion and reducibility was studied using two series of Fischer–Tropsch (FT) silica supported cobalt catalysts. The first series of the catalysts was supported by an SBA-15 periodic mesoporous silica with narrow pore size distribution, the second series was supported by a commercial mesoporous silica with broader pore size distribution. It was shown that in a wide range of cobalt surface densities (0–50 Co/nm 2), cobalt dispersion in silica supported catalysts was largely influenced by support texture. Cobalt dispersion was higher in Co catalysts supported by the SBA-15 silica with a pore diameter of 9.1 nm than in the commercial mesoporous silica with an average pore diameter of 33 nm. A more than 10-fold increase in cobalt surface density did not result in any noticeable sintering of Co 3O 4 particles in SBA-15 periodic mesoporous silicas; the cobalt dispersion seems to be maintained by catalyst mesoporous structure. The effect of support pore diameter on cobalt dispersion was less significant for the catalysts supported by commercial silicas with broader pore size distribution. At the range of cobalt surface densities from 5 to 15 Co/nm 2, higher Fischer–Tropsch reaction rates were observed over cobalt catalysts supported by the SBA-15 periodic mesoporous silica. This effect was attributed to higher cobalt dispersion in these catalysts. An increase in cobalt surface densities did lead to any significant changes in hydrocarbon selectivities and in chain growth probabilities for both series of supported catalysts.