Alumina-supported Cobalt Catalysts Research Articles

β-Cyclodextrin for design of alumina supported cobalt catalysts efficient in Fischer–Tropsch synthesis

Addition of β-cyclodextrin during catalyst preparation strongly affects the structure and catalytic performance of alumina supported cobalt catalysts for Fischer-Tropsch synthesis. Impregnation of the support with solutions containing β-cyclodextrin leads to higher metal dispersion and spectacularly enhances both reaction rate and heavy hydrocarbons productivity in Fischer-Tropsch synthesis.

The impact of ruthenium, lanthanum and activation conditions on the methanation activity of alumina-supported cobalt catalysts

The influence of catalyst activation conditions and the presence of promoters (La, Ru) on the performance of γ-alumina-supported Co catalysts for the methanation reaction has been investigated. Physicochemical properties, Co crystallite size and the extent of Co 3O 4 reduction to metallic Co for both the monometallic and promoted catalysts were evaluated. Combined La and Ru addition produced the greatest activity improvement for converting carbon monoxide (CO) and hydrogen (H 2) to methane. Reduction conditions used to activate the catalyst were also found to have a direct influence on methanation activity. Maintaining the catalyst at 400 °C for 10 h during reduction enhanced catalyst activity, as well as increasing the H 2 concentration in the reducing gas stream. Characterisation of the reduced catalysts demonstrated that the extent of Co-oxide reduction to Co metal was the key to the improved methanation activity.

Structure and catalytic performance of Pt-promoted alumina-supported cobalt catalysts under realistic conditions of Fischer–Tropsch synthesis

The structure of alumina-supported cobalt catalysts promoted with platinum and their catalytic performance in Fischer–Tropsch synthesis were investigated under realistic reaction conditions ( P = 20 bar, T = 493 K) using in situ time-resolved X-ray diffraction with simultaneous analysis of reaction products. The catalysts were prepared via incipient wetness impregnation and characterized by a wide range of ex situ techniques. Direct in situ measurements were indicative of considerable versatility of alumina-supported cobalt catalysts during Fischer–Tropsch synthesis. Cobalt sintering occurred at the first hours of the reaction and resulted in a significant drop of the catalytic activity. In addition to sintering, partially oxidized catalysts containing smaller cobalt particles (mean particle size <5 nm) were slowly reducing during Fischer–Tropsch reaction. Treatment of cobalt catalysts in pure carbon monoxide led to selective transformation of cobalt metallic phases to Co 2C cobalt carbide. Cobalt carbidization followed by hydrogenation selectively led to cobalt hcp metallic phase, which seems to be more active in Fischer–Tropsch synthesis than cobalt fcc phase. Cobalt oxidation by water was not significant in the catalysts with metal particles larger than 5 nm even at high water concentrations.

Fischer–Tropsch Synthesis: TPR-XAFS Analysis of Co/Silica and Co/Alumina Catalysts Comparing a Novel NO Calcination Method with Conventional Air Calcination

A novel conversion of cobalt nitrate to cobalt oxide using nitric oxide (Sietsma et al., patent applications WO 2008029177 and WO 2007071899) was utilized to prepare silica- and alumina-supported cobalt catalysts, in order to evaluate the materials for their sensitivity to Fischer–Tropsch synthesis process parameters by kinetics. In the current contribution, TPR-XAFS was used to probe the differences in reducibility and crystallite size resulting from the two procedures over two catalysts having widely different degrees of support interaction with the cobalt oxides. The nitric oxide calcination method resulted in smaller cobalt oxide crystallites compared to the air calcination method, and their increased surface contact with the support resulted in a slower, more broadened, reduction profile. A much more significant impact on crystallite size and reducibility was observed for the more weakly interacting Co/silica catalyst. That is, the already existing strong interaction between alumina and cobalt oxides dictated a small crystallite size upon reduction of the air calcined catalyst, and a measurable but more modest decrease in crystallite size was afforded by the nitric oxide calcination procedure for the alumina supported catalyst.

H2-rich synthesis gas production over Co/Al2O3 catalyst via glycerol steam reforming

Alumina-supported cobalt catalyst has been employed in a fixed bed reactor for the direct production of synthesis gas from glycerol steam reforming. Physicochemical properties of the Co/Al2O3 catalyst were determined from N2 physisorption, H2 chemisorption, CO2 and NH3-temperature-programmed desorption measurements as well as X-ray diffraction analysis. Both weak and strong acid sites are present on the catalyst surface. The acidic:basic site ratio is about 6. Glycerol steam reforming gave relatively large H2:CO ratio (6 to 12) and near-stoichiometric values of H2:CO2 ratio (2 to 2.30) were obtained depending on feed composition (30 to 60 wt.% glycerol mixture). The glycerol consumption rate appeared to be a weak function of glycerol (0.1) and has 0.4 order with respect to the steam partial pressure. Increased glycerol partial pressure led to high carbon deposition (total organic carbon values of 20 to 24%). However, removal of the deposited carbon was essentially complete following a temperature-programmed oxidation (air)–temperature-programmed reduction (H2) scheme.

In situXRD investigation of the evolution of alumina-supported cobaltcatalysts under realistic conditions of Fischer-Tropsch synthesis

The structure-activity relations in the alumina-supported cobalt catalysts are studied at the realistic conditions of Fischer-Tropsch synthesis using in situ time-resolved XRD and catalytic measurements. Cobalt sintering during the first 3-5 h of the reaction and cobalt carbidisation at a longer time on stream (>8 h) coincide with catalyst deactivation.

H2-poor bio-syngas in Fischer-Tropsch synthesis over un-promoted and rhenium promoted alumina-supported cobalt catalysts: Effect of water addition

The effect of water addition on Fischer-Tropsch synthesis (FTS) over 12%Co/Al2O3 and 12%Co-0.5%Re/Al2O3 catalysts was investigated in a fixed bed reactor with model mixtures of biomass-derived syngas (bio-syngas). The bio-syngas model mixtures consist of H2 and CO of different molar H2/CO-ratios (1.0, 1.5 and 2.1). The FT-reaction requires a H2/CO molar ratio of approximately 2.1 above the catalyst surface. For the ratios lower than 2.1, an in situ water-gas shift (WGS) activity is desired in order to increase the H2/CO-ratio. However, the studied catalysts had quite low WGS activities. The addition of water slightly increased the WGS activity for all types of bio-syngases and for both catalysts. The highest WGS activity was found for the un-promoted Co-catalyst at the inlet H2/CO-ratio = 1.0. Water addition also results in an increase in selectivity to C5+ and a decrease in selectivity to CH4 . Interestingly, for both of catalysts the selectivity to C5+ and CH4 were rather similar for inlet H2/CO-ratios of 2.1 and 1.5, while the highest selectivity to C5+ and the lowest selectivity to CH4 were also found for the inlet ratio = 1.0. All catalysts were deactivated by water addition but the catalyst activity is partly recovered in H2/CO-ratio inlets = 1.0 and 1.5. The Co/Al2O3 was affected by water more severely in H2/CO ratios = 2.1. The Re-promoted Co catalyst was considerably more active and selective to longer hydrocarbons than the un- promoted one. The conclusion of this study is that in order to utilize the advantages of a bio-syngas with a low H2 content (higher selectivity to C5+, lower selectivity to CH4, no WGS-unit needed prior to FT-reactor), the catalyst must possess a much higher WGS activity than the ones studied.

The interaction of cobalt species with alumina on Co/Al 2O 3 catalysts prepared by atomic layer deposition

Alumina supported cobalt catalysts were prepared by atomic layer deposition (ALD) of cobalt acetylacetonate precursors (Co(acac) 2 and Co(acac) 3). The main modes of interaction between the acetylacetonate precursors and the support were found to be the exchange reaction between the alumina OH-groups and the acac-ligands of the precursor and dissociative adsorption on coordinatively unsaturated Al 3+ sites. The amount of precursor that could adsorb on the support was determined by steric hindrance. Samples were prepared using 1–5 reaction cycles, i.e. subsequent precursor addition (Co(acac) 2) and calcination, resulting in catalysts containing ca. 3–10 wt.% Co. Samples were also prepared where the last calcination step was omitted, i.e. uncalcined catalysts. Calcination at 450 °C decreased the reducibility of the Co(acac) 2/Al 2O 3 catalysts due to formation of a cobalt oxide phase strongly interacting with the support and aluminate type surface species. The reducibility increased with metal loading on both calcined and uncalcined catalysts; however the reducibility of the calcined catalysts remained lower than of the uncalcined ones. The dispersion was found to be lower on the calcined catalysts. The cobalt particle sizes on the calcined samples was ca. 8 nm and on the uncalcined 4–5 nm, for cobalt loadings of ca. 6–10 wt.%. Catalytic activity was tested by gas phase hydrogenation of toluene in temperature programmed mode (30–150 °C).

Preparation of a Novel Super Active Fischer-Tropsch Cobalt Catalyst Supported on Carbon Nanotubes

The potential of carbon nanotubes (CNT) supported cobalt catalysts for Fischer- Tropsch (FT) reaction is shown. Using the wet impregnation method cobalt on carbon nanotubes catalysts were prepared with cobalt loading varying from 15 to 45 wt. %. The catalysts are characterized by different methods including: BET physisorption, X-ray diffraction, hydrogen chemisorption, and temperature-programmed reduction. The activity and product selectivity of the catalysts were assessed and compared with alumina supported cobalt catalysts using a continuous- stirred tank reactor (CSTR). Using carbon nanotubes as cobalt catalyst support was found to decrease the reduction temperature of Co3O4 to CoO from 440 to 347 o C and that of CoO to Co o from 640 to 574 o C. The strong metal-support interactions are reduced to a large extent and the reducibility of the catalysts improved by 67.7 %. CNT aided in well dispersion of metal clusters and average cobalt clusters size of the reduced cobalts is decreased from 5.3 to 4.9 nm. Results are presented showing that the hydrocarbon yield obtained by CNT supported cobalt catalyst is 74.6 % more than that obtained from cobalt on alumina supports. The maximum concentration of active surface Co o sites and FTS activity for CNT supported catalysts are achieved 40 wt. % cobalt loading. CNT caused a slight decrease in the FTS product distribution to lower molecular weight hydrocarbons.

Synthesis of cobalt on cobalt-aluminate via solvothermal method and its catalytic properties for carbon monoxide hydrogenation

Abstract The study focused on synthesis of cobalt on cobalt-aluminate catalyst in one-pot via the solvothermal process. The obtained catalysts apparently exhibited higher activities than that prepared from the conventional solvothermal-derived alumina-supported cobalt catalyst without any changes in product selectivity during methanation. Enhanced activities can be attributed to the smaller amount of non-reducible cobalt-aluminate formed (at temperature

Influence of Residual Chloride Ions in Alumina-Supported Cobalt Catalysts on Catalytic Activity in Ketone and Aldehyde Hydrogenation

Abstract The influence of residual chloride ions on the catalytic activity of Co/Al2O3 was investigated for liquid-phase hydrogenation of ketones and aldehydes using Cl−-free and Cl−-containing catalysts. The Cl−-free catalyst showed high activity for hydrogenation of both, whereas the Cl−-containing catalysts showed very low activity for ketone hydrogenation.

The Inhibition Effect of Potassium Addition on Methane Formation in Steam Reforming of Acetic Acid over Alumina-supported Cobalt Catalysts

Abstract The inhibition effect of potassium addition on methane formation in steam reforming of acetic acid over alumina-supported cobalt catalyst has been studied. Co–K/Al2O3 catalyst showed much higher activity for hydrogen generation and much lower selectivity for methane than Co/Al2O3. Potassium addition resulted in the inhibition of methanation process. The similar effect was also observed in methanol and ethanol reforming reactions.

Partial oxidation of methane to synthesis gas over Co/Ca/Al 2O 3 catalysts

A series of calcium-modified alumina-supported cobalt catalysts were prepared with a two-step impregnation method, and the effect of calcium on the catalytic performances of the catalysts for the partial oxidation of methane to syngas (CO and H 2) was investigated at 750 °C. Also, the catalysts were characterized by XRD, TEM, TPR and ( in situ) Raman. At 6 wt.% of cobalt loading, the unmodified alumina-supported cobalt catalyst showed a very low activity and a rapid deactivation, while the calcium-modified catalyst presented a good performance for this process with the CH 4 conversion of ∼88%, CO selectivity of ∼94% and undetectable carbon deposition during a long-time running. Characterization results showed that the calcium modification can effectively increase the dispersion and reducibility of Co 3O 4, decrease the Co metal particle size, and suppress the reoxidation of cobalt as well as the phase transformation to form CoAl 2O 4 spinel phases under the reaction conditions. These could be related to the excellent catalytic performances of Co/Ca/Al 2O 3 catalysts.

Cobalt supported on carbon nanotubes — A promising novel Fischer–Tropsch synthesis catalyst

An extensive study of Fischer–Tropsch synthesis (FTS) on carbon nanotubes (CNT) supported and γ–alumina-supported cobalt catalysts with different amounts of cobalt are reported. Up to 40 wt.% of cobalt is added to the supports by the impregnation method. The effect of the support on the reducibility of the cobalt oxide species, dispersion of the cobalt, average cobalt clusters size, water–gas shift (WGS) activity and activity and selectivity of FTS is investigated. Using carbon nanotubes as cobalt catalyst support was found to cause the reduction temperature of cobalt oxide species to shift to lower temperatures. The strong metal-support interactions are reduced to a large extent and the reducibility of the catalysts improved significantly. CNT aided in well dispersion of metal clusters and average cobalt clusters size decreased. Results are presented showing that the hydrocarbon yield obtained by inventive CNT supported cobalt catalyst is surprisingly much larger than that obtained from cobalt on alumina supports. The maximum concentration of active surface Co° sites and FTS activity for alumina and CNT supported catalysts are achieved at 34 wt.% and 40 wt.% cobalt loading respectively. CNT caused a slight decrease in the FTS product distribution to lower molecular weight hydrocarbons.

Fischer–Tropsch synthesis on sulphur poisoned Co/Al2O3 catalyst

Abstract The effect of sulphur poisoning (in the range 0–2000 ppm) on the characteristics and catalytic performances in the Fischer–Tropsch synthesis (FTS) of a bench-scale alumina supported cobalt catalyst is investigated in this study. It is found that sulphur did not lead to appreciable variations in the catalyst morphological characteristics; however, the catalyst reducibility/hydrogenating capability is significantly modified upon increasing the sulphur loading. The comparison between the catalytic performances of the sulphured samples pointed out that the presence of sulphur remarkably affected the productivity and the selectivity of the reaction. In particular for low S amounts ( These effects have been tentatively associated with different effects of sulphur on the catalyst active sites, i.e. on the sites (or site ensembles) responsible for CO hydrogenation and for the chain growth processes. Finally, the experimental data of CO conversion decay with S-loading were nicely described according to a simple deactivation model which implies a strong effect of sulphur on the catalyst active sites.

Effect of cobalt carboxylate precursor chain length on Fischer-Tröpsch cobalt/alumina catalysts

Abstract The effect of the cobalt carboxylate chain length (C2, C5 and C9) on the preparation of alumina supported cobalt catalysts has been studied by TPR, XRD and hydrogen chemisorption techniques. The activity and selectivity of the prepared catalysts have been evaluated for Fischer-Tropsch (FT) activity in a stirred basket reactor. It is shown that for catalysts with Co content of 10 wt.% the activity increases as the carboxylate chain length increases while the selectivity towards methane and light hydrocarbons decreases with the carboxylate chain length. This change relates to the effect of the chain length on the catalyst particle size. The catalyst prepared using cobalt acetate was found to present the highest metal–support interaction and the poorest performance for the Fischer-Tropsch reaction. When the metal content was increased to 15 and 20 wt.% Co, respectively, the metal–support interaction for the catalyst particles prepared from cobalt acetate significantly decreased making it a better catalyst for the FT reaction compared to the catalyst particles prepared from C5 and C9 cobalt carboxylates.

COBALT LOADING EFFECTS ON THE STRUCTURE AND ACTIVITY FOR FISCHER-TROPSCH AND WATER-GAS SHIFT REACTIONS OF CO/AL2O3 CATALYSTS

An extensive study of Fischer-Tropsch synthesis (FTS) on alumina-supported cobalt catalysts with different amounts of cobalt is reported. Up to 40 wt % of cobalt, is added to the catalysts by impregnation method. The effect of the cobalt loading on the reducibility of the cobalt oxide species, dispersion of the cobalt, average clusters size, water-gas shift (WGS) activity and activity and selectivity of FTS is investigated. Increasing the cobalt loading resulted in increasing the average cobalt cluster size, improvements in the reducibility of Co3O4, decreasing the cobalt surface interaction with the support and decreasing the dispersion of cobalt. The maximum concentration of active surface Co o sites and FTS activity are achieved for the 34 wt% cobalt loading. While the maximum WGS activity is achieved for the 40 wt % cobalt loading. The methane selectivity in the catalyst with 40 wt % of cobalt loading was about 43.7 % less compared to that of the less reducible 8 wt % cobalt catalyst. The C5 + selectivity for the 40 wt % cobalt catalyst was 60.8% higher than that of the 8 wt % Cobalt catalyst.

The promoting effect of halogen ions on selective hydrogenation of (E)-2-butenal to (E)-2-buten-1-ol over alumina-supported cobalt catalyst

The promoting effects of halogen ions (Cl −, Br −, I −) on catalytic activity and selectivity in the hydrogenation of (E)-2-butenal to form (E)-2-buten-1-ol were investigated using alumina-supported cobalt catalyst in a liquid phase. The addition of Cl − or Br − to the reaction media greatly promoted the formation of (E)-2-buten-1-ol and simultaneously suppressed the formation of butanal, whereas the addition of I − prevented C C bond hydrogenation. The promoting effects increased with increasing electronegativity of the halogen atoms. The rate ratio of C O bond hydrogenation to C C bond hydrogenation was increased eightfold when Cl − was used under optimum conditions.

Effects of Different Loadings of Ru and Re on Physico-Chemical Properties and Performance of 15% Co/Al2O3 FTS Catalysts

An extensive study of Fischer-Tropsch synthesis (FTS) on alumina-supported cobalt catalysts promoted with different amounts of ruthenium and rhenium is reported. Up to 2 wt% of promoters, are added to the catalyst by coimpregnation. The catalysts are characterized by different methods including: BET physisorption, X-ray diffraction, hydrogen chemisorption, and temperature-programmed reduction. The effect of the promoters on the reducibility of the cobalt oxide species, dispersion of the cobalt, and activity and selectivity of FTS is investigated. The Re enhances the reducibility of the CoO to Co0 and small cobalt oxide particles with higher interaction with the support. However, Ruthenium was found to enhance the reducibility of Co3O4 to CoO and that of CoO to Co0 and small cobalt oxide particles with higher interaction with the support. 1wt% Ru and 1.4wt% Re increased the activity of the catalyst by a factor of 2.8 and 2.5 respectively. Both promoters enhance the selectivity of Fischer-Tropsch synthesis towards the higher molecular weight hydrocarbons. However, the effect of Re is less pronounced.

Effect of magnesia on alumina-supported cobalt Fischer–Tropsch synthesis catalysts

A series of magnesia-modified alumina-supported cobalt catalysts were prepared with a two-step impregnation method using the incipient wetness technique. N 2 physisorption, X-ray diffraction (XRD), laser Raman spectroscopy (LRS), X-ray photoelectron spectroscopy (XPS), H 2 temperature-programmed reduction (H 2-TPR), H 2 temperature-programmed desorption (H 2-TPD) and oxygen titration were used for the characterization of the catalysts. A cobalt surface phase, which has strong interaction with the support, was detected by XPS, and its content decreased with introduction of the magnesia into the catalysts, indicating that Mg modification can inhibit the interaction between the cobalt oxide and the support. However, large amounts of magnesia caused a decrease in the catalysts reducibility due to the formation of MgO–CoO solid solution. Small amounts of magnesia were found to improve the activity of cobalt catalysts for Fischer–Tropsch synthesis but larger amounts of magnesia decreased the activity, and the methane and CO 2 selectivity increased for all the magnesia-modified catalysts; furthermore, the olefin to paraffin ratio increased with an increase in magnesia content. These observed effects of magnesia on the catalytic performance of cobalt catalysts could deduce from poor reducibility of higher magnesia content catalysts and/or magnesia content-dependent catalyst surface reconstruction suppression.