Heating-oscillating X-ray diffractometer study of selected catalysts

Abstract

In many materials used as catalysts, isomorphous substitutions within the lattice, lattice defects, and differences in exchangeable cation composition are significant with regard to the properties of the catalysts. Many of these minor changes in the atomic structure cannot readily be detected by regular X-ray diffraction methods. Heating-oscillating X-ray diffractometry often can give insight into these problems. The heating-oscillating method combines features of differential thermal-analysis with X-ray diffraction wherein a specimen is heated at a controlled rate while oscillating over a diffraction maximum. By this means, the temperature and rate at which structural changes take place can be readily observed. This method has the advantage over conventional X-ray methods in that the changes are observed at the temperature at which they actually take place. That is, the samples are not heated and then cooled to room temperature and the subsequent X-ray diffraction patterns obtained. Often, heating-oscillating is carried out over several of the diffraction maxima, thus resulting in a series of diagrams which when composited represent the diffraction pattern at any temperature within the range studied. Heating-oscillating diffractometer studies have been carried out on a variety of catalysts. It has been found that structural differences can be detected that were not observed from regular X-ray diffraction patterns obtained at room temperature.