Combined Use of Synchrotron‐Radiation‐Based Imaging Techniques for the Characterization of Structured Catalysts

Basile, Francesco; Benito, Patricia; Bugani, Simone; Nolf, Wout De; Fornasari, Giuseppe; Janssens, Koen; Morselli, Luciano; Scavetta, Erika; Tonelli, Domenica; Vaccari, Angelo

doi:10.1002/adfm.201001004

Cited by 42 publications

(40 citation statements)

References 67 publications

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“…This has however been attempted using synchrotron radiation. 172,173 The same sort of experiment using a pencil beam has also been carried out coupled with a 2D detector to record the diffraction pattern. This was used to nondestructively reconstruct the map of the diffraction pattern in the acquired slice.…”

Section: Chemical Tomographymentioning

confidence: 99%

Quantitative X-ray tomography

Maire¹,

Withers²

2013

International Materials Reviews

1,089

601

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X-ray computer tomography (CT) is fast becoming an accepted tool within the materials science community for the acquisition of 3D images. Here the authors review the current state of the art as CT transforms from a qualitative diagnostic tool to a quantitative one. Our review considers first the image acquisition process, including the use of iterative reconstruction strategies suited to specific segmentation tasks and emerging methods that provide more insight (e.g. fast and high resolution imaging, crystallite (grain) imaging) than conventional attenuation based tomography. Methods and shortcomings of CT are examined for the quantification of 3D volumetric data to extract key topological parameters such as phase fractions, phase contiguity, and damage levels as well as density variations. As a non-destructive technique, CT is an ideal means of following structural development over time via time lapse sequences of 3D images (sometimes called 3D movies or 4D imaging). This includes information needed to optimise manufacturing processes, for example sintering or solidification, or to highlight the proclivity of specific degradation processes under service conditions, such as intergranular corrosion or fatigue crack growth. Besides the repeated application of static 3D image quantification to track such changes, digital volume correlation (DVC) and particle tracking (PT) methods are enabling the mapping of deformation in 3D over time. Finally the use of CT images is considered as the starting point for numerical modelling based on realistic microstructures, for example to predict flow through porous materials, the crystalline deformation of polycrystalline aggregates or the mechanical properties of composite materials.

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Section: Chemical Tomographymentioning

confidence: 99%

Quantitative X-ray tomography

Maire¹,

Withers²

2013

International Materials Reviews

1,089

601

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“…Herein, we describe dynamic X-ray diffraction computed tomography (XRD-CT) and demonstrate its capability to image a catalyst body impregnated with a Ni-(en)-Cl precursor (en = ethylenediamine) undergoing a thermal treatment as a route to the formation of the active phase. XRD-CT [20][21][22][23][24][25][26] requires that the sample is exposed to X-ray radiation with a series of transmission "projection" measurements being made at several angles. An image slice is then reconstructed from these measurements using a suitable algorithm.…”

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confidence: 99%

Dynamic X‐Ray Diffraction Computed Tomography Reveals Real‐Time Insight into Catalyst Active Phase Evolution

et al. 2011

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Dedicated to the Fritz Haber Institute, Berlin, on the occasion of its 100th anniversary Metals and metal oxides anchored to porous support materials are widely used as heterogeneous catalysts in a number of important industrial chemical processes. These catalysts owe their activity to the formation of unique metal/metal oxide support interactions, typically resulting in highly dispersed actives stabilized in a particular electronic or coordination state. [1][2][3] They are employed in fixed-bed reactors as extruded or pelletized millimeter-sized "catalyst bodies" minimizing pressure drops along the length of the reactor. Since the efficiency of the whole catalytic system depends on the behavior and efficiency of the catalyst body per se, its design has very great importance. Crucial to this design is an understanding of the factors which influence the distribution and nature of the active phase during preparation. The type of desired distribution is very much dependant on catalytic process and required products; for example, an egg-shell distribution (as opposed to uniform, egg-white, or egg-yolk), where the active phase is located at the edges of the catalyst body, can be favored if the product forms readily. [4,5] Herein, we study catalyst bodies of nickel supported on gAl 2 O 3 . These catalysts are widely employed for hydrogenation. [1][2][3]6] They are often prepared using highly soluble nickel nitrate or chloride precursor salts, which allow for the preparation of catalysts with high metal loadings in a single impregnation step. Two problems are commonly encountered with the preparation of these catalysts: the formation of unwanted metal aluminate (spinel) phases and poor metal dispersion within the catalyst body. The dispersion of the metal ions within the alumina can be controlled by the addition of complexing agents to the impregnation solution, thereby changing the molecular structure of the precursor (through ligand exchange) as well as the interactions of the precursor with the support. Additionally, the presence of chelating ligands in the precursor increases both the metal oxide reducibility and dispersion. [7][8][9][10] In recent times, absorption, spectroscopic, and scattering techniques have been developed to obtain spatial information on the distribution of chemical species in catalyst bodies, which allows the phenomena taking place during their preparation to be monitored. [7] These techniques include Raman, IR, and UV/Vis microspectroscopy; magnetic resonance imaging (MRI); tomographic energy dispersive diffraction imaging (TEDDI); and micro-computed tomography (mCT). [11][12][13][14][15][16][17] Importantly, both MRI and TEDDI are able to probe in a non-invasive manner in two dimensions, thus providing time-resolved information on both the impregnation and calcination/activation processes. Whilst the former is limited to the study of paramagnetic species and is therefore almost exclusively limited to probing the impregnation stage, TEDDI provides detailed information regarding elemental and ...

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“…The preliminary characterization by XRD and FT-IR (fourier-transform infrared spectroscopy) of electrodeposits over FeCrAlloy plates confirmed the formation of the HT phase intercalated with nitrate anions. After calcination at 900 • C, the more powerful µ-XRD/XRF (micro X-ray diffraction/X-ray fluorescence) synchrotron tomography allowed to characterize the as-prepared coatings [66]. The characterization of the spatial distribution of the elements and crystalline phases revealed that they were made of NiAl 2 O 4 and NiO phases, characteristic of HT-derived catalysts ( Figure 5b), and in agreement with H 2 -TPR (hydrogen temperature programmed reduction) results.…”

Section: Ni/al Catalystsmentioning

confidence: 99%

“…Properties and catalytic activity of Ni/Al HT-derived catalysts coated on FeCrAlloy foam at −1.2 V vs. SCE for 1000 s and calcined at 900 • C for 12 h. (a) SEM images, (b) µ-XRF/XRD tomography images: elemental (lower row) and phase (upper row) maps obtained by XRF/XRPD tomography [240 µm (3 µm steps) × 180 • (2 • steps)]. Identification by comparison with the ICDD PDF-2 database yields: Al 2 O 3 (75-1862), NiAl 2 O 4 (73-0239) and NiO (89-7390), (c) Catalytic activity for SR of CH 4 at P = 20 bar, S/C = 1.7, T oven = 900 • C, contact time τ = 4 s.Figure 5awas adapted from[62],Figure 5bfrom[66] andFigure 5cfrom[48].…”

mentioning

confidence: 99%

Hydrotalcite-Type Materials Electrodeposited on Open-Cell Metallic Foams as Structured Catalysts

Ho¹,

Scavetta²,

Tonelli³

et al. 2018

Inorganics

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Structured catalysts based on hydrotalcite-derived coatings on open-cell metallic foams combine tailored basic/acidic sites, relatively high specific surface area and/or metal dispersion of the coating as well as low pressure drop and enhanced heat and mass transfer of the 3D metallic support. The properties of the resulting structured catalysts depend on the coating procedure. We have proposed the electro-base generation method for in situ and fast precipitation of Ni/Al and Rh/Mg/Al hydrotalcite-type materials on FeCrAlloy foams, which after calcination at high temperature give rise to structured catalysts for syngas (CO + H 2 ) production through Steam Reforming and Catalytic Partial Oxidation of CH 4 . The fundamental understanding of the electrochemical-chemical reactions relevant for the electrodeposition and the influence of electrosynthesis parameters on the properties of the as-deposited coatings as well the resulting structured catalysts and, hence, on their catalytic performance, were summarized.Inorganics 2018, 6, 74 2 of 18 electrode, which is the substrate that must be coated. For the deposition of metallic particles, the applied potential and the bath solution must be chosen so that the direct electrochemical reduction of the metal precursors occurs. On the contrary, in the deposition of hydroxides or oxides the electro-base generation method is applied. The basic medium at the electrode-electrolyte interface provokes the chemical precipitation of the cations in the solution directly on the electrode surface. The reduction of some electroactive species, e.g., dissolved oxygen, water, and nitrate consumes H + or generates OH − , thus being responsible of the pH increase. The electrodeposition of hydroxides was originally developed for the modification of small and simple-shaped electrodes with Ni(OH) 2 [33,34] and it was later extended to the deposition of more complex hydrotalcite-type (HT) compounds, also called layered double hydroxides, with general formulaand Co/Al or Co/Cr HTs [36] were initially synthesized onto a Pt-foil cathode then Ni/Co, Ni/Fe, and Co/Fe formulations were applied as sensors [37], redox supercapacitors [38,39] and, more recently, as electrocatalysts, mainly for oxygen evolution reaction [40][41][42]. In these two latter fields, there is a growing interest in replacing conventional 2D by 3D supports such as fibers [43,44] and open-cell foams [45][46][47].In this context, we reported for the first time in 2008 the electro-base generation method to coat FeCrAlloy foams with HT compounds for the preparation of H 2 production structured catalysts [48]. Later, electrodeposition has been used to coat FeCrAlloy foams by Rh [49], Pt [50] and Pt-CeO 2 [51], as gas-phase structured catalysts. The integration of HT compounds on metallic open-cell foams results in structured catalysts that take advantage of both the above commented properties of open-cell foams and the intrinsic properties of HT materials, e.g., high specific surface area and/or metal dispersion, basicity, thermal stab...

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Combined Use of Synchrotron‐Radiation‐Based Imaging Techniques for the Characterization of Structured Catalysts

Cited by 42 publications

References 67 publications

Quantitative X-ray tomography

Quantitative X-ray tomography

Dynamic X‐Ray Diffraction Computed Tomography Reveals Real‐Time Insight into Catalyst Active Phase Evolution

Hydrotalcite-Type Materials Electrodeposited on Open-Cell Metallic Foams as Structured Catalysts

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