Atomic scale observations of the chemistry at the metal-oxide interface in heterogeneous catalysts

Here we present a preliminary analysis of the atomic scale interface chemistry in a model heterogeneous catalyst system, Pt/SiO2. We show that the combination of Z-contrast imaging and electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM) exhibits a sensitivity to surface oxidation and changes in the interfacial chemistry that is higher than that of conventional analytical methods such as energy-dispersive X-ray spectroscopy (EDS), chemisorption, and X-ray absorption near edge structure analysis (XANES). In particular, the presence of a few monolayers of platinum oxide can be clearly seen, and changes in the chemistry of the SiO2 support within similar to1 nm of the metaloxide interface can be characterized as a function of the catalyst preparation conditions. These results demonstrate that this combination of novel techniques can provide unparalleled information that is potentially the key to understanding the activity and selectivity of heterogeneous catalyst systems. (C) 2002 Elsevier Science.