CO-induced structural changes of Pd particle surfaces

Abstract

The interaction of CO with Pd particle surfaces has been studied by means by field ion microscopy (FIM). CO-induced structural changes ranging from well defined reconstructions of individual surface planes to a reshaping of the apex crystal have been made visible with atomic resolution. For example, after reaction with CO at 1 hPa and at 300 K, the {011} and {113} surface planes, still covered by CO_ad, are found to exhibit the (1×2) missing row structure in which every second chain of atoms is removed. Other high index planes in the transition region between the low index {111} and {001} planes have dissolved in the presence of adsorbed CO and form facets, the terraces of which again contain the densely packed planes. The adsorbate-induced changes are explained on the basis of earlier mass spectrometric and kinetic investigations by means of atom-probe techniques according to which adsorbed subcarbonyl entities, Pd(CO)_2,3, liberated from kink site positions, diffuse across the surface until they decompose at favourable sites.