Model bimetallic Pd-Co/HOPG catalysts: Preparation and XPS/STM study

Regularities of formation of bimetallic Pd–Co nanoparticles supported on the highly oriented pyrolytic graphite (HOPG) have been studied by a combination of STM and XPS techniques. Cobalt deposition on monometallic Pd/HOPG sample was determined to lead to formation of the bimetallic Pdcore–Coshell nanoparticles which then transformed into alloyed Pd–Co nanoparticles with homogeneous metal distribution resulting from sample heating at 400—500°C in ultrahigh vacuum. Heating of the Pd–Co/HOPG catalysts at temperatures higher than 500°C in ultrahigh vacuum was revealed to result in sintering of the nanoparticles. Under carbon monoxide environment in a range of temperatures 25—250°C, adsorption-induced segregation of palladium atoms on the surface of the bimetallic nanoparticles was shown to take place, with latter having volcano-shape temperature dependence with a maximum at 200°C. It was established that bimetallic Pd–Co nanoparticles in the model catalysts were stable against sintering up to 250°C in CO atmosphere.