Silica-supported Cobalt Catalysts Research Articles

Impact of Inverse Manganese Promotion on Silica-Supported Cobalt Catalysts for Long-Chain Hydrocarbons via Fischer–Tropsch Synthesis

One of the challenges in Fischer–Tropsch synthesis (FTS) is the high reduction temperatures, which cause sintering and the formation of silicates. These lead to pore blockages and the coverage of active metals, particularly in conventional catalyst promotion. To address the challenge, this article investigates the effects of the preparation method, specifically the inverse promotion of SiO2-supported Co catalysts with manganese (Mn), and their reduction in H2 for FTS. The catalysts were prepared using stepwise incipient wetness impregnation of a cobalt nitrate precursor into a promoted silica support. The properties of the catalysts were characterized using XRD, XPS, TPR, and BET techniques. The structure–performance relationship of the inversely promoted catalysts in FTS was studied using a fixed-bed reactor to obtain the best performing catalysts for heavy hydrocarbons (C5+). XRD and XPS results indicated that Co3O4 is the dominant cobalt phase in oxidized catalysts. It was found that with increase in Mn loading, the reduction temperature increased in the following sequence 10%Co/SiO2 < 10%Co/0.25%Mn-SiO2 < 10%Co/0.5%Mn-SiO2 < 10%Co/3.0%Mn-SiO2. The catalyst with the lowest Mn loading, 10%Co/0.25%Mn-SiO2, exhibited higher C5+ selectivity, which can be attributed to less MSI and higher reducibility. This catalyst showed the lowest CH4 selectivity possibly due to lower H2 uptake and higher CO chemisorption.

Effect of a Second Promoter on the Performance of a Potassium Doped Silica-Supported Cobalt Catalyst During CO2 Hydrogenation to Hydrocarbons

In this study, the promoting effects of ruthenium, palladium, and copper on the performance of a 15%Co-1%K/SiO2 catalyst were evaluated during CO2 hydrogenation in a fixed-bed reactor. Reactions were carried out at atmospheric pressure and 270 °C with H2/CO2 ratio of 3. All catalysts were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) and temperature-programmed reduction (TPR). Ruthenium, palladium and copper facilitated the reduction of cobalt oxides and increased cobalt dispersion. In terms of catalyst’s performance, ruthenium addition led to increased CO2 conversion and methane selectivity with a detrimental effect on C5+ hydrocarbons. Palladium also presented a similar pattern at lower loading but a drop in CO2 conversion and increased reverse water–gas shift activity were observed at 3 wt % Pd loading. Promoting with copper resulted in decreased activity, methane selectivity and C5+ hydrocarbons productivity with a much higher CO selectivity.Graphical

Investigation into the Reaction Pathways and Catalyst Deactivation for Polyethylene Hydrogenolysis over Silica-Supported Cobalt Catalysts

Investigation into the Reaction Pathways and Catalyst Deactivation for Polyethylene Hydrogenolysis over Silica-Supported Cobalt Catalysts

Ammonia Decomposition Over Cobalt-Based Silica-Supported Fischer-Tropsch Synthesis Catalysts

Decomposition of ammonia over silica-supported cobalt catalysts for Fischer–Tropsch synthesis has been studied at a pressure of 0.1 MPa, a gas hourly space velocity range of 1000–6000 h–1 and a temperature range of 400–650°C in a tubular fixed bed reactor in a flow-through mode. It was found that silica-supported cobalt catalysts for hydrocarbons synthesis via the Fischer–Tropsch protocol also exhibit high activity in ammonia decomposition. Both activity and hydrogen productivity decrease in the series: Co–Ru/SiO2 Co–Al2O3/SiO2 Ru/SiO2 Co–Al2O3/SiO2(35%)/ZSM-5(30%)/Al2O3(35%). The relatively low values of effective activation energies estimated for all catalysts indicate that the reaction can proceed with a high conversion at moderate temperatures.

Alumina-supported cobalt catalysts in the hydrogenation of CO2 at atmospheric pressure

20 wt.% cobalt catalysts supported on pure and 5 wt.% silica-containing alumina have been prepared and characterized by X-Ray Diffraction, IR and DR-UV-vis-NIR spectroscopies and Field-Emission Scanning Electron Microscopy (FE-SEM). The presence of a cobalt-containing surface spinel phase Co3-xAlxO4 and, for the silica-containing sample, of a segregated Co3O4 phase is evident. These catalysts have been tested in CO2 hydrogenation at atmospheric pressure in steady state conditions in the temperature range 523–773 K. Both catalysts are active in CO2 hydrogenation to methane (methanation) and to CO (reverse Water Gas Shift, rWGS). CO2 hydrogenation activity is higher on freshly pre-reduced silica-free Co/Al2O3, while selectivity to methane is slightly higher on the silica-containing sample. Spent catalysts contain clustered or amorphous cobalt metal centers as active sites for methanation. The silica-containing catalyst shows slow deactivation in CO2 hydrogenation upon 13 h experiments, with quite stable or even slightly increasing rWGS activity and decreasing CH4 selectivity. This confirms previous data suggesting that, over cobalt catalysts, sites for methanation are metal centers prone to deactivation by carbon deposition. However, in contrast with what happens with unsupported and silica-supported cobalt catalysts, where deactivation is very fast, over these alumina-based catalysts carbon deposition and deactivation occur much more slowly. Sites for rWGS are unreduced cobalt centers which do not undergo such a deactivation phenomenon.

Activity and selectivity enhancement of silica supported cobalt catalyst for alcohols production from syngas via Fischer-Tropsch synthesis

Synthesis of mixed alcohols together with clean fuels from syngas via Fischer-Tropsch synthesis is an attractive route for the utilization of coal, natural gas and biomass. In this work, a monometallic cobalt catalyst (Co/SiO2-EOAM) was synthesized by impregnation using ethanolamine modified silica pellet as support and employed for the conversion of syngas. The combustion of carbon and nitrogen species during the calcination of catalyst facilitated the interaction between cobalt and support, which promoted the cobalt dispersion while inhibited the reduction of cobalt oxide. The Co/SiO2-EOAM catalyst exhibited much higher activity and selectivity to alcohols compared to un-modified silica supported cobalt catalyst (Co/SiO2). The higher activity was resulted from the improved cobalt dispersion. The co-existence of abundant metallic cobalt and Co2+ species were responsible for the increasing of alcohols selectivity.

Effect of Silica Encapsulation on Cobalt-Based Catalysts for Fischer–Tropsch Synthesis under Different Reaction Conditions

Cobalt nanoparticles prepared by a solvothermal treatment were encapsulated in silica with different shell thicknesses by the Stöber method. The application of these materials as catalysts in Fischer–Tropsch synthesis was investigated under different reaction conditions, and their behaviors were compared to a silica-supported cobalt catalyst. The protective effect displayed by the silica shell avoided sintering of the active phase and influenced the reaction selectivity and activity in comparison with the supported catalyst. The silica shell thickness also played an important role in catalytic performance. A decrease in shell thickness caused an enhancement in selectivity toward C19–C24 hydrocarbons, indicating the occurrence of a confinement effect by silica pores over hydrocarbon growth. Furthermore, a high production of methane might be related to the occurrence of CO diffusion limitations due to the thicker silica shell. The activity and selectivity remained similar at different reaction temperatures. However, the use of a lower temperature caused an increase in stability.

Electro-assisted sulfite activation by a silica supported cobalt catalyst for the degradation of organic pollutants in near-neutral pH condition

The desulfurization by-product (e.g. sulfite) treatment and water pollution are two widespread concerns, while the sulfite activation by transition metals can be adopted to solve both of them simultaneously. In this study, a silica-supported cobalt catalyst (CoSi) was used to activate sulfite for the degradation of organic pollutants in an electrochemical system (the EC/CoSi/sulfite system), which demonstrated remarkable water treatment efficiencies due to sulfate radical oxidation. The synergy mechanisms of the EC/CoSi/sulfite system were revealed. (i) The as-prepared CoSi played the dual roles as an electro-adsorbent and a catalyst for sulfite activation. (ii) The electrolytic oxygenation supported the conversion of cobalt species and the chain reactions of oxysulfur radicals. (iii) The anodic oxidation of sulfite also generated oxysulfur radicals. The influencing factors and operating parameters were investigated and optimized systematically. Moreover, the efficient degradation of highly concentrated X-3B and non-selective oxidation of various organic compounds confirmed the promising application of the EC/CoSi/sulfite system in practical water treatment. Overall, the EC/CoSi/sulfite system created new value of the industrial waste (e.g. sulfite) for further application in the environmental remediation.

Cobalt Plasmonic Superstructures Enable Almost 100% Broadband Photon Efficient CO2 Photocatalysis.

The efficiency of heterogeneous photocatalysis for converting solar to chemical energy is low on a per photon basis mainly because of the difficulty of capturing and utilizing light across the entire solar spectral wavelength range. This challenge is addressed herein with a plasmonic superstructure, fashioned as an array of nanoscale needles comprising cobalt nanocrystals assembled within a sheath of porous silica grown on a fluorine tin oxide substrate. This plasmonic superstructure can strongly absorb sunlight through different mechanisms including enhanced plasmonic excitation by the hybridization of Co nanoparticles in close proximity, as well as inter- and intra-band transitions. With nearly 100% sunlight harvesting ability, it drives the photothermal hydrogenation of carbon dioxide with a 20-fold rate increase from the silica-supported cobalt catalyst. The present work bridges the gap between strong light-absorbing plasmonic superstructures with photothermal CO2 catalysis toward the complete utilization of the solar energy.

Superior Fischer-Tropsch performance of uniform cobalt nanoparticles deposited into mesoporous SiC

Electrochemically-derived well-crystalline mesoporous silicon carbide (pSiC) was used as a host for cobalt nanoparticles to demonstrate superior catalytic performance during the CO hydrogenation according to Fischer-Tropsch. Colloidal Co nanoparticles (9 ± 0.4 nm) were prepared independently using colloidal recipes before incorporating them into pSiC and, for comparison purposes, into commercially available silica (Davisil) as well as foam-like MCF-17 supports. The Co/pSiC catalyst demonstrated the highest (per unit mass) catalytic activity of 117 μmolCO gCo−1 s−1 at 220 °C which was larger by about one order of magnitude as compared to both silica supported cobalt catalysts. Furthermore, a significantly higher C5+ hydrocarbons selectivity was observed for Co/pSiC. The stable performance of the catalyst is attributed to the high dispersion of the active phase and the use of pSiC acting as a thermally conductive and chemically inert mesoporous support.

Development and characterization of silica supported cobalt oxides for ethanol oxidation using different preparation methods

Cobalt oxide in spinel structure (Co3O4) is an efficient catalyst for ethanol oxidation due to its potential as an oxygen source. To enhance the catalytic performance, Co3O4 is dispersed on silica (SiO2). The degree of dispersion and form of oxides on the support depend on the preparation method. The objective of this work is to compare physicochemical properties and catalytic performance in ethanol oxidation of silica-supported cobalt catalysts from different preparation methods. The catalysts were prepared by incipient wetness impregnation (IP), precipitation with reverse micelle (RM), and precipitation with NH4OH (PN) methods. The forms and dispersion of cobalt species were investigated by X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS) and X-ray photoelectron spectroscopy (XPS). The cobalt species from RM and IP methods were mainly Co3O4, but that from PN method was the mixed phases of Co3O4, CoO and Co2SiO4. The RM method provided the best dispersion of Co3O4, surface Co3+ and lattice O2− on SiO2. Consequently, the catalyst from RM method provided the highest ethanol conversion and CO2 yield from all temperature ranges.

Support effects in metal catalysis: a study of the behavior of unsupported and silica-supported cobalt catalysts in the hydrogenation of CO2 at atmospheric pressure

Abstract Two 20 wt.% Co/SiO2 catalysts were prepared using silica gel as a support and cobalt acetate and nitrate as precursors, respectively. As a comparison unsupported amorphous cobalt nanoparticles (10–80 nm) were synthesized by decomposing cobalt carbonyl. They were characterized before and after reaction using XRD, IR spectroscopy in the range of framework vibrations, DR-UV–vis-NIR spectroscopies and FE-SEM microscopy. They are active in CO2 methanation at atmospheric pressure. However, unsupported cobalt and the silica-supported catalyst prepared using cobalt acetate deactivate fast at 623–673 K, also due to formation of encapsulating carbon. On the other hand, they retain more stable activity in the reverse water gas shift (rWGS) reaction, producing CO. Methanation and rWGS appear to occur on independent sites. The silica-supported catalyst produced from cobalt nitrate show more stable methanation activity, attributed to the presence of smaller cobalt particles (10–20 nm) that resist deactivation. For both unsupported CoNPs and Co/SiO2, the significant parameters for catalysts deactivation have been determined for CO2 methanation. The differences observed among catalysts produced starting from cobalt acetate and cobalt nitrate, can be associated to the different pH of the impregnating solution.

Effect of Operating Temperature, Pressure and Potassium Loading on the Performance of Silica-Supported Cobalt Catalyst in CO2 Hydrogenation to Hydrocarbon Fuel

Potassium (1–5 wt.%)-promoted and unpromoted Co/SiO2 catalysts were prepared by impregnation method and characterized by nitrogen physisorption, temperature-programmed reduction (TPR), CO2 temperature-programmed desorption (TPD), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. They were evaluated for CO2 hydrogenation in a fixed bed reactor from 180 to 300 °C within a pressure range of 1–20 bar. The yield for hydrocarbon products other than methane (C2+) was found to increase with an increase in the operating temperature and went through a maximum of approximately 270 °C. It did not show any significant dependency on the operating pressure and decreased at potassium loadings beyond 1 wt.%. Potassium was found to enhance the catalyst ability to adsorb CO2, but limited the reduction of cobalt species during the activation process. The improved CO2 adsorption resulted in a decrease in surface H/C ratio, the latter of which enhanced the formation of C2+ hydrocarbons. The highest C2+ yield was obtained on the catalyst promoted with 1 wt.% of potassium and operated at an optimal temperature of 270 °C and a pressure of 1 bar.

Selective hydroconversion of levulinic acid to γ-valerolactone or 2-methyltetrahydrofuran over silica-supported cobalt catalysts

Levulinic acid can be hydrodeoxygenated either to γ-valerolactone or to 2-methyltetrahydrofuran over the Co/SiO2 catalyst. Selectivity was controlled by the hydrogenation activity of the catalyst.

Silver addition to a cobalt Fischer–Tropsch catalyst

Silver is known to promote F–T catalysts as a reduction promoter, although it has also been observed to affect catalytic performance of, for instance, cobalt nanoparticles. In this work, a series of silica-supported cobalt catalysts with a constant platinum content (0.04 wt%) and varying silver content were characterized and tested. Characterization shows that mainly coordinatively unsaturated cobalt atoms are substituted at low silver content (probed by N2 IR). Adding more silver results in replacement of both coordinatively unsaturated sites and planar sites (probed by H2-chemisorption and TEM-EDS). The presence of silver on the cobalt surface affects both structure-sensitive CO dissociation and structure-insensitive hydrogenation reactions. The Boudouard reaction shows that the CO dissociation rate decreases with increasing silver content. Hampered CO dissociation is also apparent from temperature-programmed CO IR spectroscopy. However, even at high silver content the surface still contains step-edge sites that can dissociate CO and a small amount of carbon is deposited (quantified by TPH). During the CO hydrogenation at 260 °C, CO conversion is reduced by less than 30% when 8.8 wt% silver is added. This does not correlate well with the loss in cobalt surface area measured by chemisorption (decreases by 93%) or CO dissociation rate probed by CO disproportionation (decreases by 90%). This mismatch is mainly because that the CO consumption rate under methanation condition is largely controlled by carbon and oxygen hydrogenation, rather than CO dissociation. On the other hand, transient experiments show that silver accelerates oxygen-removal steps. It turns out that CO conversion is only moderately affected by silver. The coverage of hydrogenation sites – mostly terrace sites – by silver causes slower CH4 formation. Longer residence of CHx intermediates (determined by SSITKA) accordingly leads to an increase in chain-growth probability and therefore higher C2+ selectivity. SSITKA also confirms that the decrease in steady-state CO/CHx coverage qualitatively correlates to the loss in cobalt surface area. Another consequence of slower hydrogenation is that the olefins-to-paraffins ratios are higher when silver is added to the catalyst. Importantly, covering the cobalt surface with silver affects the F–T product distribution in a similar manner as graphitic carbon deposited on terrace sites as we reported earlier.

Fischer–Tropsch Synthesis with Cu-Co Nanocatalysts Prepared Using Novel Inorganic Precursor Complex

The structural properties and activities of Cu-Co catalysts used in Fischer-Tropsch synthesis are explored according to their method of preparation. Impregnation, co-precipitation, and a novel method of thermal decomposition were applied to an inorganic precursor complex to generate the Cu-promoted alumina- and silica-supported cobalt catalysts. The precursors and the catalysts obtained by their calcination underwent powder x-ray diffraction, thermal gravimetric analysis, specific surface area measurement using the Brunauer-Emmett-Teller method, scanning electron microscopy, and Fourier Transform InfraRed (FT-IR) spectroscopy. The catalytic performance of all calcined catalysts used in Fischer-Tropsch synthesis was investigated at 280 to 360 °C. The Cu-Co/SiO2 catalyst was prepared by thermal decomposition of [Cu(H2O)6][Co(dipic)2].2H2O/SiO2, which served as an optimal precursor for synthesis gas conversion into light olefins. The results highlight the advantages of this novel procedure over impregnation and co-precipitation approaches for effective and durable preparation of cobalt catalysts for Fischer-Tropsch synthesis.

Mesoporous silica supported cobalt catalysts for gas phase hydrogenation of nitrobenzene: role of pore structure on stable catalytic performance

Mesoporous silica supported Co catalysts (Co/COK-12 and Co/SBA-16) are active for hydrogenation of nitrobenzene to aniline. The support pore architecture is decisive in maintaining stable catalytic performance.

Mechanism of Cobalt-Catalyzed CO Hydrogenation: 2. Fischer-Tropsch Synthesis.

Fischer–Tropsch (FT) synthesis is one of the most complex catalyzed chemical reactions in which the chain-growth mechanism that leads to formation of long-chain hydrocarbons is not well understood yet. The present work provides deeper insight into the relation between the kinetics of the FT reaction on a silica-supported cobalt catalyst and the composition of the surface adsorbed layer. Cofeeding experiments of 12C3H6 with 13CO/H2 evidence that CHx surface intermediates are involved in chain growth and that chain growth is highly reversible. We present a model-based approach of steady-state isotopic transient kinetic analysis measurements at FT conditions involving hydrocarbon products containing up to five carbon atoms. Our data show that the rates of chain growth and chain decoupling are much higher than the rates of monomer formation and chain termination. An important corollary of the microkinetic model is that the fraction of free sites, which is mainly determined by CO pressure, has opposing effects on CO consumption rate and chain-growth probability. Lower CO pressure and more free sites leads to increased CO consumption rate but decreased chain-growth probability because of an increasing ratio of chain decoupling over chain growth. The preferred FT condition involves high CO pressure in which chain-growth probability is increased at the expense of the CO consumption rate.

Efficient utilization of bimetallic catalyst in low $$\hbox {H}_{2}/\hbox {CO}$$ H 2 / CO environment syngas for liquid fuel production

Application of Fischer-Tropsch synthesis (FTS) in the utilization of low $$\hbox {H}_{2}/\hbox {CO}$$ ratio (0.5–1.5) gas obtained from coal and biomass gasification can be done by selecting a catalyst system active for both FTS and WGS reaction. The enhancement of $$\hbox {H}_{2}$$ content depends on the extent of water gas shift (WGS) reaction and can be quantified by measuring usage ratio define as a mole of $$\hbox {H}_{2}$$ to CO converted. With an attempt to utilize low $$\hbox {H}_{2}/\hbox {CO}$$ ratio syngas bimetallic $$(\hbox {Fe}/\hbox {Co}/\hbox {SiO}_{2})$$ were prepared and compared with monometallic ( $$\hbox {Fe}/\hbox {SiO}_{2}$$ and $$\hbox {Co}/\hbox {SiO}_{2}$$ ) catalysts. The catalysts were tested in fixed bed reactor at industrial relevant FTS conditions (T: $$220{-}260\,^{\circ }\hbox {C}$$ , P: 2.0 MPa, GHSV-1.2 SL/gcat-h, $$\hbox {H}_{2}/\hbox {CO}$$ : 1–1.5). The incorporation of Fe-Co bimetallic catalyst facilitates both FT and WGS reaction because of the presence of iron and cobalt phases. Compared to monometallic catalyst there is a significant increase in CO conversion over the bimetallic catalyst. Also, the yield of $$\hbox {C}_{5+}$$ was significantly higher over bimetallic catalyst compared to iron catalyst, where olefin was the major product. Selected catalyst $$(\hbox {Fe}/\hbox {Co}/\hbox {SiO}_{2})$$ was tested for their activity toward WGS reaction. Effects of temperature, pressure, and feed composition on WGS reaction over bimetallic catalyst were studied. Lower value usage ratio (1.62 and 1.58) reveals the occurrence WGS reaction Fe-Co bimetallic catalyst at 240 $$^{\circ }\hbox {C}$$ and 260 $$^{\circ }\hbox {C}$$ . At 240 $$^{\circ }\hbox {C}$$ , 72% CO conversion, and 60% $$\hbox {C}_{5+}$$ selectivity show that the catalyst efficiently utilizes the increased $$\hbox {H}_{2}/\hbox {CO}$$ ratio in the production of liquid hydrocarbon. Synopsis: A novel Fe-Co catalyst combination has been optimised for the conversion of biomass derived syngas, having low $$\hbox {H}_{2}/\hbox {CO}$$ ratio (1– 1.5mol/mol). The addition of iron onto silica supported cobalt catalyst facilitates the WGS reaction activity for higher $$\hbox {H}_{2}/\hbox {CO}$$ ratio internally and thus improves FTS activity. $$\hbox {10Fe}/\hbox {20Co}/\hbox {SiO}_{2}$$ catalyst resulted optimum WGS and FTS activity with 72% CO conversion, and 60% $$\hbox {C}_{5+}$$ selectivity.

Effect of hierarchical meso–macroporous structures on the catalytic performance of silica supported cobalt catalysts for Fischer–Tropsch synthesis

A series of meso–macroporous silica supports with the same macroporous diameter but different mesoporous diameters were prepared by introducing phase separation into a sol–gel process and used to prepare cobalt catalysts for Fischer–Tropsch synthesis.