ИСТИНА

The phase composition and the element ratio at the surface and in the bulk are often differing from each other in case of bimetallic Pd-based catalytic systems, which is caused by surface segregation. The driving force of this process is the tendency to decrease the surface energy in bimetallic system. Surface rearrangement can be controlled by the adsorption of different adsorbate molecules (CO, O2, C2H2, etc), leading to enrichment of the catalyst surface with a component whose binding energy with the adsorbate molecule is higher. Since the structure of surface layers of bimetallic catalytic system depends on sample treatment conditions (temperature, exposure time), the surface segregation can be used as a simple and convenient method of controlling the surface structure of catalyst. It was shown earlier that configuration of active Pd sites at the surface of Pd-Ag system can be tuned by exposing the catalyst to CO-containing atmosphere [1]. Nevertheless, the existing experimental data dedicated to investigation of temperature and CO exposure time on the dynamics of surface changes of bimetallic Pd-Ag catalyst are incomplete. This work provides a thorough study of segregation process in Pd-Ag2/Al2O3 catalyst induced by CO at different temperatures and treatment durations. DRIFT spectroscopy of adsorbed CO and XPS were chosen as most appropriate methods for observation of surface changes during segregation.