Factors Affecting X-ray Diffraction Characteristics of Catalyst Materials

Abstract

X-ray diffraction (XRD) is a major tool employed to identify and characterize catalytic materials. A brief review of the diffraction phenomenon and the effect of crystallite size is presented.Appli cations of XRD to catalyst characterization are illustrated, including correlation of XRD powder patterns to molecular structural features, deter mination of Pt crystallite size and others. Factors that affect the appearance of XRD powder patterns, such as framework structure perturbations, extra framework material, crystal morphology, impurities, sample preparation, instrument configurations, and x-ray sources, are discussed.X-ray diffraction (XRD), in particular x-ray powder diffraction, has been used extensively to identify and characterize materials used as catalysts in the petroleum refining and petrochemical industries. This is not surprising, since many of the materials are crystalline; i.e., the atoms can be arranged in threedimensional periodic arrays. Every atom in a crystalline solid contributes to the observed XRD pattern, thus making the pattern characteristic of the material-a virtual fingerprint. The diffraction data obtained for catalytic materials can tell us many things about these materials, ranging from the structural nature of the crystalline components to the average Pt crystallite size on a supported-metal catalyst. It can be used to monitor and correlate molecular structural features to catalytic process and reaction variables, or to specify composition for patent definition. In short, XRD is an invaluable technique in catalyst research and development. This discussion will illustrate some of the applications of XRD to catalyst characterization and point out some of the factors that affect the appearance of x-ray powder diffraction patterns of these materials.

Application of the overlap integral in X-ray diffraction powder pattern recognition

“…Success or failure of an identification often depends upon errors in the experimentally determined interplanar d spacings. In addition, sample, as well as instrumental, effects can introduce subtle or even profound effects on a pattern, often making identification difficult (Rohrbaugh and Wu, 1989). Examples of sample effects that can alter a pattern are: changes in symmetry, such as the transformation of a structure from one crystal system to another, or a change of space group within one crystal system; structural disorder, involving perturbations in the periodic arrangement of atoms; isomorphous substitution, in which one atomic element, such as aluminum, is substituted for another, such as silicon; extra-framework material, such as cations [e.g., Na + , Ba 2+ , N(CH 3 ) 4 + ] or neutral inorganic and organic molecules (e.g., water, ammonia, or sorbed organics) in channels and cavities of porous materials such as feldspars and zeolites; the influence of crystal morphology on sample packing, resulting in preferred orientation; the presence of impurities; and the effects of absorption, crystallite size, and strain.…”

Synthesis of advanced carbon nanomaterials from renewable and waste carbon sources

“…5.2b displays the distinct difference of diffraction peak of (200) among different MgO. MgO-H with lowest peak area of diffraction peaks indicated its highest preferential growth along (200) lattice plane followed by MgO, MgO-F and MgO-A [156]. The morphology of commercial alkali-earth metal oxides characterized by FESEM is shown in According to the data of N2 adsorption, XRD analysis and FESEM characterization, there were significant variations in the morphology, porous properties and crystal geometry of selected catalysts.…”