REFLECTION ELECTRON-MICROSCOPY OF THE CATALYTIC ETCHING OF PT SINGLE-CRYSTAL SPHERES IN CO + O2

The influence of the catalytic oxidation of CO on structural changes of a Pt catalyst was studied with a Pt single-crystal sphere in the 10-4 Torr range at 200 °C sample temperature. Reflection electron microscopy (REM) served to follow the structural changes which are induced by the catalytic reaction on the Pt(100) and Pt(111) facets. Using an intensity-enhanced Bragg reflection for imaging the surface, the diffraction contrast allows one to resolve atomic steps. Both surfaces are homogeneously roughened by the catalytic reaction, but the Pt(100) surface is much more strongly attacked than Pt(111). Small positive islands develop on an initially flat (100) terrace which are preferentially oriented in the directions of the unit cell of the hex reconstruction. The mechanism of the roughening process on Pt(100) is traced back to the adsorbate-induced 1 × 1 ⇌ hex phase transition which can strongly enhance the mass transport of Pt atoms under reaction conditions. Oxide formation or mass transport via volatile Pt compounds is considered to play a negligible role under the conditions applied here. © 1990.