Modifications in the morphological and chemical properties of copper supported on different allotropic forms of carbon

A combination of techniques including controlled atmosphere electron microscopy coupled with in situ electron diffraction has been used to follow the manner by which the nature of a carbonaceous support can impact both the chemistry and morphological properties of small copper particles when treated in various gas environments. We have found that the ease of reduction of CuO is dependent upon the nature of the carbon material and the strength of the interaction between the two components. It is suggested that an epitaxial relationship exists between copper and a diamond surface, which facilitates the reduction of copper oxide to the metallic state. In systems where copper species are supported on active carbon or graphite, attack on the substrate surface was observed to occur at low temperatures in the presence of hydrogen. This behavior is rationalized according to the notion that dissociation of molecular hydrogen takes place on Cu-0 sites at the surface of Cu2O particles and that the active atomic species "spill over" onto the graphitic support media and undergo reaction with the pi-electrons of the basal plane resulting in the creation of pits thus producing extensive modifications to the surface structure of these support media. Based on the data from in situ electron diffraction analysis it is tentatively concluded that at moderate temperatures under reducing conditions, Cu2O is the stable chemical state on amorphous and graphitic forms of carbon. (C) 1999 Academic Press.