Dispersion changes of platinum supported on silica glass during thermal treatment in oxygen and hydrogen atmospheres

Dispersion and chemical composition changes of thin platinum films supported on fused silica, caused by thermal treatment at temperatures of 773 and 823 K in hydrogen and oxygen atmospheres at pressures of 10−1 to 10−3 Pa, have been investigated by electron microscopy and electron diffraction. Heating the PtSiO2 system in hydrogen leads to an increase of the metal-support interaction, resulting in the flattening of the metal particles, formation of platinum-silicon intermetallic compounds, and generation of strain. During a subsequent heating in oxygen, redispersion of the platinum by splitting of the particles has been observed. Redispersion by spreading of platinum oxide over the support has been found after long (10 h) heating of the PtSiO2 system at 823 K in oxygen at a pressure of ~10−2 Pa. The mechanisms of platinum redispersion presented above are documented by electron micrographs.