Significance and Use
Zeolites Y and X, particularly for catalyst and adsorbent applications, are a major article of manufacture and commerce. Catalysts and adsorbents comprising these zeolites in various forms plus binder and other components have likewise become important. Y-based catalysts are used for fluid catalytic cracking (FCC) and hydrocracking of petroleum, while X-based adsorbents are used for desiccation, sulfur compound removal, and air separation.
This X-ray procedure is designed to monitor these Y and X zeolites and catalysts and adsorbents, providing a number more or less closely related to percent zeolite in the sample. This number has proven useful in technology, research, and specifications.
Drastic changes in intensity of individual peaks in the XRD patterns of Y and X can result from changes of distribution of electron density within the unit cell of the zeolite. The electron density distribution is dependent upon the extent of filling of pores in the zeolite with guest molecules, and on the nature of the guest molecules. In this XRD method, the guest molecule H2O completely fills the pores. Intensity changes may also result if some or all of the cations in Y and X are exchanged by other cations.
4.3.1 Because of the factors mentioned in 4.3 that could vary the intensities of the XRD peaks, this XRD method will provide the best determination of relative crystallinity when the reference and sample have a similar history of preparation and composition.
Corrections are possible that can make this XRD method accurate for measuring percent zeolite in many specific situations. These corrections are well known to those skilled in X-ray diffraction. It is not practical to specify those corrections here.
1.1 This test method covers determining relative zeolite diffraction intensities.
1.2 The term "zeolite" here is restricted to those zeolites having the faujasite crystal structure, including X and Y zeolites, the various cation exchange forms, and the dealuminized, decationated, and ultrastable forms. These zeolites have cubic symmetry with unit cell parameter within the limits 24.2 and 25.0 A (2.42 and 2.50 nm). The samples contemplated include zeolite preparations in the various forms and catalysts containing these zeolites.
1.3 The term "intensity of an X-ray powder diffraction (XRD) peak" is the "integral intensity," either the area of counts under the peak or the product of the peak height and the peak width.
1.4 The method provides a number that is the ratio of intensity of portions of the XRD pattern of the sample to intensity of the corresponding portion of the pattern of a reference zeolite, NaY. (Laboratories may use other zeolite, for example, REY as a secondary standard.) The intensity ratio, expressed as a percentage, is then labeled "% XRD intensity/NaY."
1.5 Under certain conditions such a ratio is the percent zeolite in the sample. These conditions include:
1.5.1 The zeolite in the sample is the same as the reference zeolite.
1.5.2 The absorption for the X-rays used is the same for the zeolite and the nonzeolite portions of the sample.
1.6 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 and health practices and determine the applicability of regulatory limitations prior to use.