A study of cation environment and movement during dehydration and reduction of nickel-exchanged zeolite Y by x-ray absorption and diffraction

Dooryhée, E.; Catlow, C. Richard A.; Couves, J. W.; Maddox, Peter J.; Thomas, J. M.; Greaves, G. Neville; Steel, Andrew T.; Townsend, Rodney P.

doi:10.1021/j100164a062

Cited by 101 publications

(84 citation statements)

References 7 publications

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“…The structural stability and activity of zeolites have been established over a wide range of conditions, especially in situ under realistic working conditions for adsorption and catalysis. For example, as an early example of the study of the activation of a zeolitic catalyst, Ni 2+ cation migration within Ni-Y has been followed in situ by diffraction and X-ray absorption spectroscopy [67]. In addition, the high temperature limits to structural stability have been probed by both diffraction and inelastic scattering methods, through which a model for the amorphization of zeolite structure has been established [68,69].…”

Section: Discussionmentioning

confidence: 99%

Structural Chemistry of Zeolites

Wright

Pearce

2010

Zeolites and Catalysis

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IntroductionZeolites are tetrahedrally connected framework solids, based on silica, with intricate structures that possess channels and cages large enough to contain extra-framework cations and to permit the uptake and desorption of molecules varying from hydrogen to complex organics up to 1 nm in size. Their crystalline structure directly controls their properties and consequently their performance in applications such as ion exchange, separation, and catalysis, and is therefore of great interest to academics and technologists alike. A ''ball and stick'' representation of the most widely used zeolite A, with tetrahedral Al and Si atoms linked by O atoms and with chargebalancing Na + cations, is given in Figure 7.1.Originally discovered as aluminosilicate minerals, synthetic zeolites with a range of compositions are now widely prepared and subsequently modified for a wide range of applications. Many excellent articles, reviews, and books describe the structures of these solids, often in well-illustrated texts [1-3] and online resources [4]. Here we start by summarizing their structural chemistry, beginning with the key features of the best known and most widely used zeolites A and Y. Besides covering the periodic structures of these solids, other features such as secondary mesoporosity are also important to their performance and are discussed. This is followed by a summary of the structural chemistry of some of the important zeolite types prepared using inorganic and simple organic cations prior to the 1990s.Over the last 20 years there has been a major international effort to prepare new zeolitic materials, in the search for improved adsorbents and catalysts. Much of this has focused on the exploration of the use of complex organic alkylammonium ions, synthesized specifically as potential ''templates,'' giving high-silica-content zeolites or pure silica polytypes. The diversity of structures has also been increased by the inclusion of elements other than Al for Si in the framework, which may be either aliovalent (2+ or 3+) or isovalent (4+), and the search for new materials is encouraged by the tantalizing arrays of hypothetical structures that have been shown to be energetically feasible [5,6]. The remarkable products of this ongoing odyssey continue to show new structural features that are both intriguing and of practical importance or potential: increased crystallographic complexity leading to structures with novel

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Section: Discussionmentioning

confidence: 99%

Structural Chemistry of Zeolites

Wright

Pearce

2010

Zeolites and Catalysis

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“…Taking into account sites occupancies [3], a corrected Ni-O value of 2.16 Å was estimated [5]. This value is significantly higher than the Ni-O distances (from 1.87 to 2.05 Å ) determined for dehydrated samples by EXAFS (Extended X-ray Absorption Fine Structure) [5][6][7], the number of nearest oxygen neighbours being furthermore lower (between 3 and 4). These discrepancies prompted us to analyse precisely the evolution upon rehydration of the coordination shell around Ni 2+ in a NiNaX sample and this was made possible owing to the recent development of dispersive-EXAFS for the in situ study of catalytic materials, allowing the recording of complete absorption spectra in very short times [8,9].…”

Section: Introductionmentioning

confidence: 93%

“…Rietveld refinement indicates that, after dehydration above 573 K, Ni 2+ is preferentially located in sites SI (centre of the hexagonal prism) and the average Ni-O distance varies between 2.21 and 2.37 Å , with a coordination number of 6 [1][2][3]. It has been pointed out that this distance could be overestimated, since XRD gives long range average information, whereas, at the local level, all six O(3) oxygens around each Ni 2+ cation shift 0.5 Å toward the centre of the double six-member ring [4,5]. Taking into account sites occupancies [3], a corrected Ni-O value of 2.16 Å was estimated [5].…”

Section: Introductionmentioning

confidence: 99%

“…It has been pointed out that this distance could be overestimated, since XRD gives long range average information, whereas, at the local level, all six O(3) oxygens around each Ni 2+ cation shift 0.5 Å toward the centre of the double six-member ring [4,5]. Taking into account sites occupancies [3], a corrected Ni-O value of 2.16 Å was estimated [5]. This value is significantly higher than the Ni-O distances (from 1.87 to 2.05 Å ) determined for dehydrated samples by EXAFS (Extended X-ray Absorption Fine Structure) [5][6][7], the number of nearest oxygen neighbours being furthermore lower (between 3 and 4).…”

Section: Introductionmentioning

confidence: 99%

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Real time monitoring of the evolution of Ni2+ environment in faujasite upon rehydration by in situ dispersive-EXAFS

et al. 2005

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“…Also, in situ studies of reaction kinetics have been carried out by following the structural changes during the adsorption, removal of the template, catalysis and other processes taking place on microporous surfaces (Ciraolo et al, 2001;Milanesio et al, 2003;Dalconi et al, 2003;Muncaster et al, 1999). Combined use of XRD and XAFS has been applied to in situ studies of microporous materials, monitoring processes involving metal atoms, to chart changes in the metal ion environment, migrations, changes in oxidation state and catalytic processes Dooryhee et al, 1991;Dent et al, 1995;Thomas & Sankar, 2001).…”

Section: Introductionmentioning

confidence: 99%

The use of softer X-rays in the structure elucidation of microporous materials

Helliwell

Jones

Kaučič

et al. 2005

J Synchrotron Radiat

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Microporous materials, such as zeolites and aluminophosphates, have many applications as molecular sieves and shape-selective catalysts. This is due to their three-dimensional frameworks, which contain regular pores and channels, to their high acidity, arising from Brønsted and Lewis acid active sites, and to the incorporation of transition metal atoms into framework sites. This review firstly provides an introduction into the nature and properties of these materials, and their important applications; the difficulties in their full characterization and possible methods of elucidating their structures are then outlined; finally, methods of characterization, utilizing 'softer X-rays' are introduced. The first method is the determination of low concentrations of transition metals, incorporated into the frameworks using single crystal anomalous dispersion crystallography; synchrotron radiation is used to tune to the absorption edge of the metal atom in question, in order to change its signal relative to that of the rest of the structure, thereby allowing the pinpointing of its positions and the determination of its concentration at each site in the framework. Secondly, the use of longer wavelengths in powder diffraction studies is described, which, by stretching out the powder pattern, thereby reduces the overlapping of the diffraction peaks, thus allowing the structure to be solved by conventional direct methods. Finally, the use of X-ray absorption spectroscopy to determine the metal incorporation and the nature of coordination at the metal atom sites, in Mn silicalite-1 and FAPO-36, are described.

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A study of cation environment and movement during dehydration and reduction of nickel-exchanged zeolite Y by x-ray absorption and diffraction

Cited by 101 publications

References 7 publications

Structural Chemistry of Zeolites

Structural Chemistry of Zeolites

Real time monitoring of the evolution of Ni2+ environment in faujasite upon rehydration by in situ dispersive-EXAFS

The use of softer X-rays in the structure elucidation of microporous materials

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