Pd, Cu, and Au particles on Al2O3 thin films: An infrared reflection absorption spectroscopy study of monometallic and bimetallic planar model supported catalysts

The chemisorptive behavior of CO on several planar model monometallic and bimetallic Pd, Cu, and Au catalysts supported on thin film Al2O3 has been investigated using infrared reflection absorption spectroscopy (IRAS). For Pd and Cu monometallic catalysts, CO adsorption spectra indicate a high representation of low index planes, while the morphologies of smaller particles are characterized more by high densities of low coordinated step/edge defect sites. For Au particles, CO was observed to be present on the surface at conditions where low index Au single crystals have been observed to be inactive for CO adsorption, indicating the modified chemisorptive properties at step/edge sites. For the IRAS studies of supported Pd-Au and Pd-Cu catalysts, no conclusive indications of ligand effects were apparent in the CO stretching frequencies. The spectra for the bimetallics resemble combinations of both analogous monometallic catalysts, even though a significant degree of metal mixing is apparent from thermally induced changes in the IRAS, and from previous ion scattering spectroscopy studies. A peak possibly attributable to Pd diluted in the surface by the presence of a dissimilar metal is apparent for each of these bimetallic supported catalysts. (C) 1997 American Vacuum Society.