Characterization of surface structure in heterogeneous catalysts by high-resolution transmission electron microscopy

Model catalysts consisting of an active phase dispersed on nonporous oxide particles of submicron size with simple. geometric shapes are described. These model catalysts provide information about surface structure from the dispersed phase in heterogeneous catalysts. Morever, surface structure can be correlated with measurements of catalytic activity from the same catalyst and thereby provide better understanding of the working catalyst surface and the interaction of the active phase with the support. The use of model supports permits direct visualization of oxide dissolution and restructuring that occurs in Al₂O₃, TiO₂ and MgO supports when acidic precursors are used. Electron microscopic examination reveals differences in the crystal structure of Rh particles that explain how the support influences the oxidation and reduction behavior of the metal. Edge-on views demonstrate that the metal oxide formed after oxidation of the metal remains three-dimensional in shape and does not spread on the silica support.