Fischer–Tropsch synthesis: An XAS/XRPD combined in situ study from catalyst activation to deactivation

Tsakoumis, Nikolaos E.; Voronov, Alexey; Rønning, Magnus; Beek, Wouter van; Borg, Øyvind; Rytter, Erling; Holmén, Anders

doi:10.1016/j.jcat.2012.04.018

Cited by 76 publications

(124 citation statements)

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“…We have previously done this test 13 and observed a slight decrease in the CoO peak intensities, indicating further reduction of the cobalt catalysts. We have also monitored the cobalt catalysts using XANES (Xray absorption near edge structure), which is sensitive to oxidation state, during the reaction for 6 h at 210°C and 18 bar 13 and for 32 h at 220°C and 18 bar 3 . No reoxidation could be detected in these XANES experiments, and it is unlikely that it would happen in the present study performed under similar experimental conditions.…”

Section: ■ Discussionmentioning

confidence: 99%

“…Δρ depends also on the X-ray wavelength through energy-dependent dispersion corrections. 32 F(Q) is the form factor amplitude which contains information about the particle shape; for spheres it can be calculated analytically to be F sphere (Q) = 3[sin(QR) − QR cos(QR)]/(QR) 3 , where R is the particle radius. 33 The structure factor S(Q) describes the interference of scattering from different particles and thus contains information about the spatial correlations between the particles.…”

Section: ■ Saxs Analysis For Heterogeneous Catalysismentioning

confidence: 99%

“…The experimental conditions are summarized in Table 1, where also parameters from related studies discussed in this article are listed. 3,13 The X-ray scattering experiments were performed at beamline B1 of the DORIS III synchrotron storage ring of Hasylab at DESY. The main experiment was done using an Xray energy of 16.0 keV and a sample-to-detector distance of 3575 mm.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

“…3 Understanding the mechanisms behind this behavior is of high commercial and academic interest. Tsakoumis et al 3 combined in situ X-ray absorption spectroscopy (XAS) and X-ray powder diffraction to investigate the cobalt catalyst nanoparticles during the FTS synthesis.…”

Section: ■ Introductionmentioning

confidence: 99%

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Morphology Changes of Co Catalyst Nanoparticles at the Onset of Fischer–Tropsch Synthesis

et al. 2014

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Cobalt nanoparticles play an important role as catalysts for the Fischer− Tropsch synthesis, which is an attractive route for production of synthetic fuels. It is of particular interest to understand the varying conversion rate during the first hours after introducing synthesis gas (H 2 and CO) to the system. To this end, several in situ characterization studies have previously been done on both idealized model systems and commercially relevant catalyst nanoparticles, using bulk techniques, such as X-ray powder diffraction and X-ray absorption spectroscopy. Since catalysis takes place at the surface of the cobalt particles, it is important to develop methods to gain surface-specific structural information under realistic processing conditions. We addressed this challenge using small-angle X-ray scattering (SAXS), a technique exploiting the penetrating nature of Xrays to provide information about particle morphology during in situ experiments. Simultaneous wide-angle X-ray scattering was used for monitoring the reduction from oxide to catalytically active metal cobalt, and anomalous SAXS was used for distinguishing the cobalt particles from the other phases present. After introducing the synthesis gas, we found that the slope of the scattered intensity in the Porod region increased significantly, while the scattering invariant remained essentially constant, indicating a change in the shape or surface structure of the particles. Shape-and surface change models are discussed in light of the experimental results, leading to an improved understanding of catalytic nanoparticles. ■ INTRODUCTIONThe Fischer−Tropsch synthesis (FTS) is a set of chemical reactions that forms hydrocarbon chains from a mixture of CO and H 2 . The product can be upgraded to petroleum substitutes, for example synthetic diesel.1 Typical commercial FTS catalysts consist of cobalt nanoparticles of diameter ∼20 nm dispersed on a porous support material, 2 such as γ-alumina. Optimal particle size, temperature, and pressure are required for obtaining high activity and high selectivity to long-chain hydrocarbons. The reaction output is dependent on the temperature and the pressure in the reactor cell; the standard industrial process operates at T ≈ 220°C and pressure of 25− 45 bar, conditions favorable for producing waxes.1 At ambient pressure the CO conversion is still high, but the products are predominantly short molecules, thus tending to remain in the gas phase.The FTS shows an initial stage lasting a few hours where the conversion rate increases to a high level, followed by a much slower decrease of the reaction rate that continues on a time scale of days and months.3 Understanding the mechanisms behind this behavior is of high commercial and academic interest. Tsakoumis et al.3 combined in situ X-ray absorption spectroscopy (XAS) and X-ray powder diffraction to investigate the cobalt catalyst nanoparticles during the FTS synthesis. The deactivation was detected by mass spectrometry, but no apparent changes in the X-ray signal could be...

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Section: ■ Discussionmentioning

confidence: 99%

Section: ■ Saxs Analysis For Heterogeneous Catalysismentioning

confidence: 99%

Section: ■ Experimental Sectionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

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Morphology Changes of Co Catalyst Nanoparticles at the Onset of Fischer–Tropsch Synthesis

et al. 2014

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“…The reduction of promoted and un-promoted γ-alumina supported Co3O4 NPs has been studied in detail either by conventional temperature programed reduction (TPR) [7][8][9] or by advanced in situ techniques including X-ray powder diffraction (XRPD) 10 , X-ray absorption spectroscopy (XAS) [11][12][13][14] and transmission electron microscopy (TEM) 15 . From the majority of the reports, it is evident that the reduction is a two-step process that reaches the polycrystalline metallic Co through a CoO intermediate.…”

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Capturing metal-support interactions in situ during the reduction of a Re promoted Co/γ-Al₂O₃ catalyst

et al. 2016

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The reduction of a Re promoted Co/γ-Al2O3 catalyst was monitored in situ by synchrotron X-ray powder diffraction (XRPD) under H2 environment. Whole powder pattern analysis showed a non-linear expansion of the unit cell of γ-Al2O3 during the reduction process suggesting the diffusion of cobalt cations into the structure of the γ-Al2O3 support material. The cell expansion coincided with the formation of CoO phase. Evidence for the negative effect of the partial pressure of indigenous H2O on the reduction process was obtained by alternating XRPD probing of the inlet and outlet ends of the reactor.Catalyst activation is a critical step of the start-up procedure for most industrial catalytic processes. 1 Commonly a solid precursor is been subjected to specific conditions that allow transformation to the catalytically active component, ex situ or in situ. In many catalytic applications, the metallic surface of nanoparticles is the active component and therefore reduction of supported metal oxide precursors precedes. The reduction process is affected by various parameters such as the nature of the precursor, the size of the nanoparticles, the reactivity of the support, the reducing atmosphere. The execution of the activation step has an impact on catalyst structure and performance, avoiding risks of sintering or a lower final degree of reduction. 2 In the last decades, in situ investigations have boosted catalysis research and allowed the deconvolution of such complex phenomena. 3 Cobalt nanoparticles (NPs) supported on high surface area porous materials such as γ-Al2O3 are used in various processes. One of the most important industrial applications is the FischerTropsch synthesis (FTS). 4 FTS is the heart of Gas-to-Liquid (GTL) technologies and a tool for the utilization of synthesis gas derived from different feedstocks i.e. natural gas, coal and biomass. In cobalt based FTS carbon monoxide and hydrogen are converted into a mixture of linear long-chain hydrocarbons while significant amounts of steam are co-produced. The active metallic Co is commonly formed by reduction in H2 of the Co3O4 spinel precursor produced after drying and calcination of the impregnating source. The activation procedure is important for the optimization of catalysts selectivity 5 and stability 6 .The reduction of promoted and un-promoted γ-alumina supported Co3O4 NPs has been studied in detail either by conventional temperature programed reduction (TPR) 7-9 or by advanced in situ techniques including X-ray powder diffraction (XRPD) 10 , X-ray absorption spectroscopy (XAS) 11-14 and transmission electron microscopy (TEM) 15 . From the majority of the reports, it is evident that the reduction is a two-step process that reaches the polycrystalline metallic Co through a CoO intermediate. The use of dopants can either promote or impede this reduction process. Co3O4 + H2 → 3CoO + H2O(1)CoO + H2 → Co 0 + H2O (2) Although most of the reports agree on the steps of the reduction procedure the formation of mixed compounds of Co with the γ-Al2O3 support ...

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In SituX-ray Diffraction and XAS Methods

Senkovska

Bon

2016

The Chemistry of Metal-Organic Frameworks: Synthesis, Characterization, and Applications

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Fischer–Tropsch synthesis: An XAS/XRPD combined in situ study from catalyst activation to deactivation

Cited by 76 publications

References 59 publications

Morphology Changes of Co Catalyst Nanoparticles at the Onset of Fischer–Tropsch Synthesis

Morphology Changes of Co Catalyst Nanoparticles at the Onset of Fischer–Tropsch Synthesis

Capturing metal-support interactions in situ during the reduction of a Re promoted Co/γ-Al₂O₃ catalyst

In SituX-ray Diffraction and XAS Methods

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Fischer–Tropsch synthesis: An XAS/XRPD combined in situ study from catalyst activation to deactivation

Cited by 76 publications

References 59 publications

Morphology Changes of Co Catalyst Nanoparticles at the Onset of Fischer–Tropsch Synthesis

Morphology Changes of Co Catalyst Nanoparticles at the Onset of Fischer–Tropsch Synthesis

Capturing metal-support interactions in situ during the reduction of a Re promoted Co/γ-Al2O3 catalyst

In SituX-ray Diffraction and XAS Methods

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Capturing metal-support interactions in situ during the reduction of a Re promoted Co/γ-Al₂O₃ catalyst