Isomorphous substitution of zeolites and particle size determination of cobalt clusters in zeolites

Date of Completion

January 1992


Chemistry, Inorganic|Chemistry, Organic|Engineering, Chemical




An increasing demand for new energy sources and efforts to cleanup the environment have created a renewed interest in zeolite science and technology. In the fields of catalytic science and research, zeolites have been widely used as catalysts or supports for metals due to their shape-selective character, high surface area, acidic nature, and well-defined structure. The purpose of this research is the preparation, characterization, and application of newly developed, modified or improved zeolites.^ The first part of this thesis presents synthesis, characterization, and testing of isomorphously substituted ZSM-5 and ZSM-11 zeolites. These materials are useful in the transformation of low olefins to environmentally and commercially useful products such as branched olefins, aromatics or gasoline range distillates. The incorporation of catalytically active species such as boron, iron, and gallium into zeolites significantly changes the acidic character and zeolite structure, thereby changing catalytic properties. New synthetic methodologies were introduced and unique characterization methods such as calcination, rehydration and deuteration, and ion-exchange were developed to study isomorphously substituted zeolite structures. Optical and magnetic spectroscopy techniques have been used to study the distribution of isomorphous cations in zeolites. These studies suggest that three different species tetrahedrally coordinated framework species, defect species, and extraframework oxide species exist in these materials. Finally, these isomorphously substituted zeolites were tested as catalysts for upgrading of olefins via oligomerization to gasoline range distillates. In this context, the volatile fraction of gasoline hydrocarbons such as volatile linear olefins may be removed and transformed into less volatile commercially useful products in order to improve air quality.^ The second part of this thesis presents data on preparation, characterization, and applications of small metal particles in zeolites. The goal of this research is the preparation of highly dispersed materials such as metal clusters in the zeolite. Highly dispersed superparamagnetic cobalt clusters have been prepared in the pores of zeolite Na-X by use of microwave plasma decomposition of Co$\sb2$(CO)$\sb8$. Magnetic spectroscopy techniques have been used and ferromagnetic data have been simulated to determine cobalt particle sizes in these zeolites. ^