Search

This tutorial discusses the fundamental principles of X-ray diffraction and its applications in zeolite science. The early sections review the physics of diffraction, crystal symmetry, and reciprocal space. We discuss how the intensity of diffracted radiation is affected both by geometric effects involving detection (the Lorentz-polarization factor) and by the arrangement of atoms within the crystal (the structure factor). The differences between powder diffraction and singlecrystal diffraction are then described, and differences between X-ray and neutron diffraction are also discussed. Later sections describe the effects of symmetry, lattice substitution, crystallite size, residual strain, preferred orientation, and X-ray absorption. Special emphasis is placed on the proper application of the Scherrer analysis in reporting crystalize size. The principles of structure solution from direct methods and Patterson methods are then introduced, and a description of Rietveld analysis is given. Finally the effects of stacking disorder on a powder diffraction pattern are presented.

Adsorption, binding, behavior and decomposition of Ni(CO)4 and Fe(CO)5 on zeolites and alumina have been investigated using 13C-NMR spectroscopy. Their decompositions result in highly dispersed metallic particles. The nickel tetracarbonyl, which can be easily distorted, interacts more strongly with the various surfaces and this interaction increases with increasing acidity. During the thermal decomposition of Fe(CO)5, a small (4 ppm) low field shift of these precursors was observed, while a large (−9 ppm) high field shift is characteristic of the photochemical decomposition. These results can be explained unambiguously by more charge transfer to the surface in the photochemical decomposition. The re adsorption of CO stopped at Fe(CO) at room temperature which demonstrates clearly the monodispersed nature of the iron atoms.