EVIDENCE FOR PD-X(CO)(Y) COMPOUND FORMATION ON AN ALUMINA SUBSTRATE

Although stable binary Pd carbonyls are unknown in the gas phase, we found strong evidence for a stable carbonyl-like Pd compound on an oxide surface: by in situ vapour deposition of Pd at a rate of 2 X 10(13) atoms s(-1) cm(-2) onto an alumina substrate (90 K) at a pressure of 2 X 10(-6) mbar CO, a binary compound of Pd and CO is formed which is stable up to 190 K. As substrate serves a well-ordered aluminium oxide film grown on a NiAl(110) single crystal surface. The system was characterized under UHV (ultrahigh vacuum) conditions by means of TDS, LEED, UPS and XPS in a coverage range between 1.4 X 10(14) Pd atoms cm(-2) and 1.4 X 10(16) Pd atoms cm(-2). The decomposition at 190 K results in the formation of metallic Pd particles and is accompanied by a sharp and dominant feature in the thermal desorption spectra.