Combined EXAFS and XRD for the in situ structural elucidation of solid catalysts under operating conditions

Thomas, John Meurig; Greaves, G.N.

doi:10.1007/bf00769306

Cited by 32 publications

(20 citation statements)

References 13 publications

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“…To date X-ray diffraction (XRD) has been the main structural tool by which zeolite collapse and recrystallization have been followed. , Adsorption capacity can also give a measure of the fraction of intermediate phase that is formed , In conjunction with specially designed furnaces, it has been possible to correlate the substantial changes in long-range order obtainable from XRD with alterations in short-range order deduced from XAFS. One of the initial demonstrations of this technique was the collapse of magnesium-exchanged sodium zeolite-B (zeolite Mg/Na-B).…”

Section: Introductionmentioning

confidence: 99%

Collapse and Recrystallization Processes in Zinc-Exchanged Zeolite-A: A Combined X-ray Diffraction, XAFS, and NMR Study

et al. 1997

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The collapse and recrystallization of zinc-exchanged sodium zeolite-A has been observed in situ using combined X-ray spectroscopy and diffraction. The temperature at which this occurs is reduced by the presence of zinc, but the precipitation of NaAlSiO4 (nepheline) is blocked by the nucleation of ZnAl2O4 (gahnite), which persists to at least 1100 °C. Within the hydrated zeolite phase zinc occupies disordered octahedral sites that become less disordered with calcination. When zeolite-A collapses, zinc adopts a tetrahedral but strongly disordered geometry, suggesting nonhomogeneity in the amorphous phase from which ZnAl2O4 precipitates. Combined X-ray methods have been complemented by solid-state 27Al and 29Si NMR, which have enabled estimates to be made of the extent of disorder in the starting zinc-exchanged zeolite-A structure as well as the degree of crystallinity in the gahnite aluminosilicate glass ceramic that develops after collapse.

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Section: Introductionmentioning

confidence: 99%

Collapse and Recrystallization Processes in Zinc-Exchanged Zeolite-A: A Combined X-ray Diffraction, XAFS, and NMR Study

et al. 1997

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“…Currently, there are several manufacturers of hightemperature chambers for commercially available diffractometers [13][14][15][16][17][18][19]. In addition, it can be very effective to use, in studying fast processes by diffraction methods, the more powerful synchrotron radiation (SR), which allows one to obtain a good quality diffraction pattern in much less time [19][20][21][22]. Apart from a powerful source of radiation, the use of a positionsensitive detector, which records the diffraction pattern simultaneously for a whole range of angles of reflection 2θ, allows the monitoring of solid-phase transformations in movie mode.…”

Section: Modern Experimental Techniques: Instrumentation Requirementsmentioning

confidence: 99%

In situ high-temperature X-ray diffraction measurements: Application to the study of heterogeneous catalysts

Plyasova

Kardash

2012

J Struct Chem

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When characterizing the phase composition and structure of catalysts, researchers are faced with the problem of reversible effects of temperature and gas medium during their preparation, activation, or operation. Therefore, particular attention is paid to the methods of their research in appropriate conditions, i.e., in situ high-temperature X-ray diffraction. The theoretical framework and experimental features of high-temperature X-ray diffraction techniques are examined. Examples are given of their effective application to the study of the structural features of oxide catalysts under close-to-real conditions. Keywords: in situ high-temperature X-ray diffraction, thermal X-ray diffraction, oxide catalysts, phase composition, structure in the model conditions of preparation, activation, and operation.

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“…[4], or combinations of two X-ray based techniques like X-Ray Diffraction (XRD) and Quick EXAFS (QUEXAFS) [5], or XRD with Small Angle X-ray Scattering (SAXS) [6]. Obviously the study of cordierite ceramic formation was not the single problem for which such combinations were required, but many other areas, in particular heterogeneous catalysis, solid-state reactions and many others [7][8][9][10][11][12][13].…”

Section: Introductionmentioning

confidence: 99%

Influence of dopant metal ions on the formation of cordierite using combined SAXS/WAXS and EXAFS/WAXS techniques

Sankar

Dent

Dobson

et al. 2016

Journal of Non-Crystalline Solids

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Time-resolved combined scattering and spectroscopic techniques were used to understand in detail the formation of cordierite ceramic from two sources, (a) zeolite B and (b) cordierite glass systems. Time-resolved in situ combined EXAFS/XRD (at the Zn K-edge) investigation of the zinc oxide mixed zeolite B reveal that a series of transformations occur before the formation of cordierite ceramic. In particular the study revealed that addition of small amounts of zinc oxide promote the transformation of cordierite, through the formation of ZnAl2O4, at lower temperatures compared to the system without zinc oxide. Using in situ time-resolved SAXS/WAXS technique chromium doped in the cordierite glass system was investigated which revealed that, in addition to the formation of phase pure cordierite phase some amount of MgCr2O4 spinel phase are also produced.

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Combined EXAFS and XRD for the in situ structural elucidation of solid catalysts under operating conditions

Cited by 32 publications

References 13 publications

Collapse and Recrystallization Processes in Zinc-Exchanged Zeolite-A: A Combined X-ray Diffraction, XAFS, and NMR Study

Collapse and Recrystallization Processes in Zinc-Exchanged Zeolite-A: A Combined X-ray Diffraction, XAFS, and NMR Study

In situ high-temperature X-ray diffraction measurements: Application to the study of heterogeneous catalysts

Influence of dopant metal ions on the formation of cordierite using combined SAXS/WAXS and EXAFS/WAXS techniques

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