Cobalt–aluminum co-precipitated catalysts and their performance in the Fischer–Tropsch synthesis

doi:10.1016/S1381-1169(00)00529-X

Journal of Molecular Catalysis A: Chemical

Volume 168, Issues 1–2, 1 March 2001, Pages 193-207

https://doi.org/10.1016/S1381-1169(00)00529-X Get rights and content

Abstract

Cobalt–aluminum catalysts were prepared using either Co²⁺ precipitation onto freshly prepared Mg–Al or Zn–Al hydrotalcite (promoted samples) or co-precipitation of Co²⁺ and Al³⁺ (non-promoted samples). The evolution of initial hydrotalcite structure was monitored during its calcination and reductive treatment. It has been shown that, at moderate temperatures, hydrotalcites results decomposition yields a Co oxide phase supported by a highly defective inverted spinel-like structure. Cations Co²⁺ enter the support structure, and occupy both tetrahedral and octahedral positions. Octahedron coordinated Co species are reduced at 580–620°C. After the reduction at 470–480°C catalyst phase composition shows Co⁰ supported on inverted spinel-like structure, which contains Co²⁺ in the octahedral coordination. Further reduction at 600°C transforms the support to ‘ideal’ spinel, which contains no octahedron coordinated Co²⁺. Chemical properties of the Co–Al catalysts, including their performance in the Fischer–Tropsch synthesis (FTS), were found to depend on the catalyst reduction temperature, and thus on the support structure. Metal-support interaction is supposed to explain the observed properties of metallic cobalt.

Introduction

Cobalt–alumina catalysts are well known to be active in hydrogenation reactions, CO hydrogenation to hydrocarbons (the Fischer–Tropsch synthesis, FTS) in particular. There are many papers reporting on the properties of these catalysts in the FTS [1], [2], [3], [4], [5], [6]. Some of them discuss catalyst deactivation under reaction conditions (see for example [4]). Deactivation of Co–Al catalysts is attributed to the oxidation of Co⁰ species by water molecules, which are the primary FTS product. It may be assumed that Co⁰ is oxidized to Co²⁺ cations, which are located in the surface octahedrons of alumina support. Other studies report on the effect of catalyst preparation conditions on the extent of Co species reduction in Co–Al catalysts [5], [6], [7], [8]. However, further investigations are necessary to clarify the nature of interaction between the Co²⁺ cations and the support.

Here we report on the model cobalt–aluminum catalysts, prepared by either precipitaion of Co²⁺ onto freshly prepared Mg–Al or Zn–Al hydrotalcite (promoted samples) or co-precipitation of Co²⁺ and Al³⁺ (unpromoted samples). Investigation focuses on the nature of the interaction between Co²⁺ species and hydroxycompounds of Al and promoting metal, on the effect of support composition and its structure on the reducibility of Co species, as well as on the catalytic properties of Co–Al catalysts. Below are investigation results related to the structural evolution of Co–Al precipitated catalysts during their activation, and to their catalytic performance in FTS.

Section snippets

Preparation of the catalysts

Eight samples were prepared. Table 1 presents their composition and their preparation procedure. Precipitation was performed from a stoichiometric 10 wt.% aqueous solution of corresponding nitrates (‘pure for chemical analysis’ grade, Uralian plant of chemicals, Russia) at 60–70°C. A mixture of 7.5 wt.% water solutions of NaOH and Na₂CO₃ or 7.5 wt.% water solution of NH₄HCO₃ were used as precipitants. Precipitated catalysts were washed thoroughly by distilled water, and dried overnight under an IR

Uncalcined catalysts

The IR spectra of uncalcined samples were registered to determine their phase composition (see Fig. 1). According to [13], [14], [15] these spectra evidence, that all dry samples seem to contain the phase of a hydrotalcite-type structure. Absorption bands at 350–600 cm⁻¹ are attributed to the lattice vibrations of cations, those at ca. 620–635 cm⁻¹ to Me²⁺–Al–OH bend vibrations, at ca. 660–680 cm⁻¹ to Me²⁺–Al–OH stretch vibrations. Vibrations of hydrotalcite lattice CO₃²⁻ groups are registered at

Discussion

According to the data described above properties of Co–Al precipitated catalysts change dramatically, if their reduction temperature is elevated to 600°C. The catalytic properties of precipitated samples reduced at temperature below 500°C differ a lot from the properties of samples reduced at 600°C. In addition, catalytic properties of promoted samples reduced at 600°C slightly differ from those of unpromoted samples also reduced at 600°C. The structures of their active components seem to be

Conclusions

1.
The transformation of hydrotalcite-type structure into Me²⁺ aluminate during calcination proceeds gradually through an inverted spinel structure with a composition of (Me²⁺_1−xAl³⁺_x)(Me²⁺_xAl³⁺_2−x)O_4−2y−z(OH)_2y(CO₃²⁻)_z. Spinel phase structure inversion is supposed to be thermodynamically favorable only due to the presence of some anionic admixtures.
2.
Reduction of Co²⁺ species, located in the octahedron sites of inverted spinel phase (support), occurs at 580–620°C, and is accompanied by anionic

Acknowledgements

This research work was implemented by the finance by PEC, Japan.

References (37)

R Oukaci et al.
Appl. Catal. A: Gen.
(1999)
A Lapidus et al.
Appl. Catal.
(1991)
J van de Loosdrecht et al.
Appl. Catal. A: Gen.
(1997)
Y.L Zhang et al.
J. Catal.
(1999)
P Arnoldy et al.
J. Catal.
(1985)
D.A.M Monti et al.
J. Catal.
(1983)
B Ernst et al.
Appl. Catal. A: Gen.
(1999)
A Navrotsky et al.
J. Inorg. Nucl. Chem.
(1967)
M.A Vannice
J. Catal.
(1975)
S Vada et al.
Top. Catal.
(1995)

A.M Hilmen et al.

Catal. Lett.

(1996)

J. van de Loosdrecht, Preparation and properties of supported Fischer–Tropsch catalysts, Ph.D. thesis, Universiteit...

T.A Krieger et al.

Mater. Sci. Forum

(1999)

P.A. Ramachandran, R.V. Chaudhari, Three-Phase Catalytic Reactors, Gordon and Breach, New York,...

J.T Kloprogge et al.

Appl. Catal. A: Gen.

(1999)

M.J Hernandez-Moreno et al.

Phys. Chem. Miner.

(1985)

S Kannan et al.

J. Mater. Sci. Lett.

(1992)

K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, Wiley, New York,...

Cited by (61)

The role of aluminium in metal–organic frameworks derived carbon doped with cobalt in electrocatalytic oxygen evolution reaction
2023, Materials and Design
Water electrolysis is one of the most crucial processes in the development of new energy sources, where ultra-clean fuel is produced - hydrogen. Oxygen evolution reaction (OER) is the sluggish process of overall water splitting. Therefore, this study presents the design, characterization and electrochemical study of cobalt-based electrocatalysts embedded into porous carbons derived from an Al-metal–organic framework (MOF). The key aspects to be revealed were carbonization temperature and aluminium impact on the composite electrochemical performance. It was found that aluminium presence boosts the OER performance of the anode via lowering electrolyte resistance, reaching an overpotential of 380 mV at the current density of 10 mA/cm⁻², which is improved by 80 mV compared to the composite without aluminium. Similar effect was present in EIS measurement, where the electrocatalyst functionalized with cobalt in the presence of aluminium showed the lowest resistances, 0.89 Ω and 2.82 Ω for R1 and R2. This is due to the formation of additional electrocatalytically active species in the form of Al-Co alloy what was clearly proved by the XPS study. It shows that cobalt favoured aluminium to act simultaneously as active sites accelerating the efficiency of the OER process. Additionally, carbon played the role of a booster of the OER activity of cobalt with sustained high durability during cycling. Therefore, a facile procedure to tune the structure of carbon-based structures derived from Al-based metal–organic frameworks is proposed and the resulting cobalt/aluminium modification serves as a robust electrocatalyst for OER.
Microwave-assisted synthesis of ZnAl-LDH/g-C<inf>3</inf>N<inf>4</inf> composite for degradation of antibiotic ciprofloxacin under visible-light illumination
2021, Chemosphere
Ciprofloxacin (CIP) is a fluoroquinolone family antibiotic pollutant. CIP existence in water environment has been rising very fast in day-to-day life and subsequently, it gives enormous health issues for humans because of its potent biological activity. To encounter this, current researchers are focusing on the development of highly efficient visible light semiconductor nanocomposites with potential photocatalytic activity. In the present work, we have successfully synthesized highly efficient zinc-aluminum layered double hydroxides with graphitic carbon nitride (ZALDH/CN) composites via a simple microwave irradiation method first time for the degradation of CIP under visible light. The fabricated materials are subsequently characterized by various spectroscopic techniques. UV–Vis DRS, TRFL, XRD, FT-IR, BET, FE-SEM, TEM, and XPS for optical, crystal structure, morphological, and elemental analysis. The main reactive intermediates which are formed during the photocatalytic degradation process were analyzed by LC-MS analysis. It is worth to note that, the optimized ZALDH/CN-10 composite showed the highest photo-degradation rate constant of 1.22 × 10⁻² min⁻¹ with 84.10% degradation is higher than bare CN and ZALDH photocatalysts. Based on the electron-hole pair trapping experiment results, possible CIP photo-degradation mechanism was also explained in the present study. With all results, this work demonstrates the ZALDH/CN composite materials showed a high synergistic effect with more specific surface area. Highest specific surface area leads to enhanced visible light adsorption capacity. Subsequently improved number of catalytically active sites. Furthermore, as compared with pure materials, composites of ZALDH/CN are having low electron-hole pair recombination. Consequently, the composites ZALDH/CN showed superior photocatalytic activity for antibiotic pollutant CIP degradation under visible-light illumination.
Mn doping of Co-Al spinel as Fischer-Tropsch catalyst support
2021, Applied Catalysis A: General
Mn-doped spinel oxides CoAl₂O₄ marked as CMA-m (m = Co/Mn atom ratio) herein were synthesized and evaluated for the first time as supports of Co-based Fischer-Tropsch synthesis (FTS) catalysts. HAADF-STEM images showed that Mn doping caused more crystal defects on the surface of CMA-m grains, which may provide more attachment sites for cobalt loading, leading to much smaller Co⁰ particle size of 15Co/CMA-m than that of 15Co/CoAl₂O₄. Data of H₂/CO chemisorption showed that the interaction of highly dispersed Co⁰ with lattice Mn-doped CMA-m grain has a promotive effect on CO adsorption capability. FTS evaluation results demonstrate that 15Co/CMA-20 showed the highest CO conversion, C₅₊ selectivity and C₅₊ STY, benefiting from its high Co⁰ dispersion and CO chemisorption capability as a result of suitable Mn doping into the lattice of CoAl₂O₄, which was confirmed very different from the influence of impregnated Mn oxide over CoAl₂O₄.
Hydrogen production by methane decomposition over Co-Al mixed oxides derived from hydrotalcites: Effect of the catalyst activation with H<inf>2</inf> or CH<inf>4</inf>
2017, International Journal of Hydrogen Energy
This study examines the influence of catalyst activation for methane decomposition over Co-Al mixed oxides derived from hydrotalcites. Samples were prepared by coprecipitation and characterized by surface area measurements and temperature-programmed reduction. Spent catalysts and carbon produced in the reaction were characterized by X-ray diffractometry, temperature-programmed oxidation and scanning electron microscopy. Activity runs using previously reduced samples with H₂ or activated under CH₄ flow were carried out in a fixed-bed reactor between 500 and 750 °C using in-line gas chromatography analysis. The specific surface area decreases as the Co/Al ratio increases, which is related to the increased Co₃O₄ phase rather than Co-Al mixed oxides. The TPR results indicate the reduction of four types of Co species: Co³⁺ and Co²⁺ species from Co₃O₄, and Co from inverse spinel (Co₂AlO₄) and normal spinel (CoAl₂O₄). Reduction with hydrogen at 750 °C was very severe. Samples reduced with H₂ showed large Co° crystallites, which increased with the Co/Al ratio. Co-Al catalyst activation under methane flow leads to lower crystallite size and higher thermal stability for hydrogen production by methane decomposition.
Vapor phase hydrogenation of furfural over nickel mixed metal oxide catalysts derived from layered double hydroxides
2016, Applied Catalysis A: General
The hydrogenation of furfural is investigated over various reduced nickel mixed metal oxides derived from layered double hydroxides (LDHs) containing Ni-Mg-Al and Ni-Co-Al. Upon reduction, relatively large Ni(0) domains develop in the Ni-Mg-Al catalysts, whereas in the Ni-Co-Al catalysts smaller metal particles of Ni(0) and Co(0), potentially as alloys, are formed, as evidenced by XAS, XPS, STEM and EELS. All the reduced Ni catalysts display similar selectivities towards major hydrogenation products (furfuryl alcohol and tetrahydrofurfuryl alcohol), though the side products varied with the catalyst composition. The 1.1Ni-0.8Co-Al catalyst showed the greatest activity per titrated site when compared to the other catalysts, with promising activity compared to related catalysts in the literature. The use of base metal catalysts for hydrogenation of furanic compounds may be a promising alternative to the well-studied precious metal catalysts for making biomass-derived chemicals if catalyst selectivity can be improved in future work by alloying or tuning metal-oxide support interactions
Magnetic Co/Al<inf>2</inf>O<inf>3</inf> catalyst derived from hydrotalcite for hydrogenation of levulinic acid to γ-valerolactone
2015, Cuihua Xuebao/Chinese Journal of Catalysis
The efficient hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) over a hydrotalcite-derived non-precious metal Co/Al₂O₃ catalyst was achieved. Its core-shell structure and a strong interaction between Co and Al species stabilized the Co particles against leaching and sintering. This magnetic non-precious metal catalyst showed a comparable catalytic performance to a commercial Ru/C for the liquid hydrogenation of LA. It was easily separated from the reaction medium with an external magnet. The catalyst exhibited excellent recyclability, complete LA conversion and >99% GVL selectivity, and would be useful in a large scale biorefinery.

View all citing articles on Scopus

View full text

Cobalt–aluminum co-precipitated catalysts and their performance in the Fischer–Tropsch synthesis

Abstract

Introduction

Section snippets

Preparation of the catalysts

Uncalcined catalysts

Discussion

Conclusions

Acknowledgements

Appl. Catal. A: Gen.

Appl. Catal.

Appl. Catal. A: Gen.

J. Catal.

J. Catal.

J. Catal.

Appl. Catal. A: Gen.

J. Inorg. Nucl. Chem.

J. Catal.

Top. Catal.

Catal. Lett.

Mater. Sci. Forum

Appl. Catal. A: Gen.

Phys. Chem. Miner.

J. Mater. Sci. Lett.