Standard Test Method for Determination of Relative Crystallinity of Zeolite Beta by X-Ray Diffraction

Importancia y uso:

4.1 Zeolite Beta is a siliceous zeolite that can be crystallized with SiO₂/Al₂O₃ ratio greater than 20. Zeolite Beta, upon modification to the H-cation form in a post-crystallization step, has been used in catalytic NOx reduction, isomerization of waxes, alkylation of aromatics, hydrocarbon adsorption from exhaust gas emission, etc.

4.2 This X-ray procedure is designed to allow a reporting of the relative degree of crystallinity upon manufacture of zeolite Beta. The relative crystallinity of zeolite Beta number has proven useful in technology, research, and specifications.

4.3 The Integrated Peak Area Method (Procedure A) is preferred over the Peak Height Method (Procedure B) since it calculates XRD intensity as a sum from several peaks rather than utilizing just one peak. Drastic changes in intensity of individual peaks in the XRD pattern of zeolite Beta can result from changes in distribution of electron density within the unit cell of the zeolite Beta. The electron density distribution is dependent upon the following factors:

4.3.1 Extent of filling of pores with guest molecules and the nature of these guest molecules.

4.3.2 Type of cations and extent of their presence (these cations may also affect the absorption of X rays by the zeolite Beta sample).

4.3.3 In this XRD method, the guest molecule H₂O completes the filling of the pores. Other guest molecule types may also be present, including one of numerous amines, diamines, and quaternary ammonium cations that can function as a template for crystallization of the zeolite Beta structure.

4.3.4 Because of the factors mentioned in 4.3.1 – 4.3.3 that could vary the intensities of the XRD peaks in zeolite Beta, this XRD method will provide the best determination of relative crystallinity when the reference zeolite Beta and sample zeolite Beta have a similar history of preparation and composition.

4.4 If crystalline phases other than zeolite Beta are present in the sample, their diffraction peaks may overlap with some of the zeolite Beta peaks selected for the Integrated Peak Area Method (Procedure A). If there is reason to suspect the presence of such components, then the Peak Height Method (Procedure B) should be chosen for analysis, provided that there is no interference with the 22.5° 2θ peak that is used for the calculation.

Subcomité:

D32.05

Volúmen:

05.06

Número ICS:

71.040.30 (Chemical reagents)

Palabras clave:

crystallinity; X-ray diffraction; zeolite Beta;