III International Conference

PP-I-51RECONSTRUCTION OF THE Pd(poly) SURFACE IN VACUUM AND OXYGENATMOSPHERESuprun E.A., Serkova A.N., Salanov A.N.Boreskov Institute of Catalysis SB RAS, Novosibirsk, RussiaE-mail : salanov@catalysis.nsk.suThe microstructure of the surface of polycrystalline Pd foil was studied by scanningelectron microscopy at 600-1400 K under vacuum and in the O 2 atmosphere. The foiltemperature was found to determine the size of the grains, whereas the environment wasobserved to control the microstructure of their surface. Both under vacuum and in the O 2atmosphere the grains gradually grew from 0.5-1.0 to 10-50 μm with the temperatureincrease. A grains boundary separating the initial 0.5-1.0 μm grains was observed on theirsurface under vacuum. In O 2 atmosphere the surface of the grains was gradually covered withfacets having crystal faceting.The catalyst chemical composition and structure are known to determine its activity.Meanwhile, the environment interacting with the catalyst alters its composition and structure.To understand the mechanism how the environment affects the structure of catalysts, westudied microstructural reconstruction of the surface of 40 μm polycrystalline palladium foilunder vacuum and in the O 2 atmosphere at 600-1400 K by scanning electron microscopy.When temperature was increased, both under vacuum and in the O 2 atmosphere a grainboundary was found to appear and grow on the foil surface, which indicates the growth of thegrains from 0.5-1.0 to 10-50 μm. The surface structure of these grains was found to dependsignificantly on the environment. Under vacuum a grain boundary separating 0.5-1.0 μmgrains was observed when temperature was increased above 700 K. The outlines of thisboundary remained on the surface of 10-50 μm grains formed after heating to 1100-1300 K.In O 2 atmosphere PdO particles with dimensions ≤ 50 nm were formed on the surface atT ≥ 700 K. At Т ≥ 1100 K these particles were observed to decompose forming a grainboundary separating 10-20 μm grains on the surface. Structural elements with different shapes(facets) were observed on the surface of these grains. After heating to 1400 K the grains grewto 10-50 μm. Their surface was covered with facets having crystal faceting and definiteorientation. Thus, it was found that the sample temperature determines the size of grains onpolycrystalline Pd foil, whereas the environment controls the microstructure of their surface.100