Structural characterization of heterogeneous catalysts: Systematic application of computational chemistry and spectroscopy

The structural characterization of solid materials can often prove to be a difficult task. This is especially true when the preferred direct methods, such as single crystal X-ray diffraction, are unavailable to the compounds of interest. In many cases answers regarding the structure of hard to characterize materials are not definitive, and often represent the convergence of many methods of study, rather than unilateral examination by a single method. It is this second, multi-pronged approach that has been utilized in the studies presented in this work.; Structural characterization is often valuable when studying a catalyst before, during, and after a reaction. Great insights into reaction mechanism and the nature of a catalyst can be obtained from resolving structural changes that occur upon reactive interaction of a catalyst with its reactants. In some cases information on structural change can confirm the actual presence of a chemical reaction. This is true for the deprotonation of zeolites by adsorbed bases. The protonation of the adsorbed base is visualized in changes in the NMR spectra that occur upon structural rearrangement as a result of the deprotonation of the zeolite. These reactions are often opaque, resulting in controversy as to whether the proton has transferred. However, knowing the structural characteristics of the zeolite-adsorbate complex works to alleviate this controversy.; The issue of structure determination also carries great weight in fields other than catalysis. In the area of Organic Light Emitting Diodes structural problems abound, as the materials utilized in the active devices have often undergone multiple transformations prior to, and during their use. As the devices degrade, difficult structural questions arise that have significant implications for the longevity of the devices. Even without the difficulties that develop as a result of complicated treatments and use, there have been questions regarding the structure of the materials before they are treated or used in devices. We demonstrate how these questions can be answered in a manner similar to those used in answering questions regarding the proton transfer reaction in zeolites.; Examining the proton transfer reaction in zeolites was best achieved by the use of adsorbates predicted to have strong to moderate interactions with the zeolite. The converse to this prior approach is the use of xenon, which as a noble gas has minimal chemical interaction with the catalyst. Instead of displaying various degrees of bonding type interactions, the xenon interacts with the catalyst by way of van der Waals interactions. As a result of its large and diffuse electron cloud, even small perturbations to xenon have a pronounced effect on its NMR chemical shift. Thus, small interactions between the xenon and the catalyst cause discernible changes in the xenon chemical shift, which can be extrapolated to provide information regarding the morphology of a catalyst.