【国外标准】 Standard Test Method for Determination of Relative Crystallinity of Zeolite Beta by X-Ray Diffraction

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.1.1 This test method covers a procedure for determination of the relative crystallinity of zeolite Beta containing samples using selected peaks from the X-ray diffraction (XRD) pattern of the zeolite.1.2 The test method provides a number that is the ratio of intensity of a portion of the XRD pattern of the sample zeolite Beta to intensity of the corresponding portion of the pattern of a reference zeolite Beta. The intensity ratio, expressed as a percentage, is then labeled percent XRD relative crystallinity of zeolite Beta. This type of comparison is commonly used in zeolite technology and is often referred to as percent crystallinity.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.