STRUCTURE, THERMAL STABILITY, AND CO ADSORPTION PROPERTIES OF PD NANOPARTICLES SUPPORTED ON AN ULTRA-THIN SiO2 FILM

Abstract

Nucleation, growth, and thermal stability of Pd particles vapor-deposited on an ultra-thin crystalline silica film grown on Mo (112) have been studied by scanning tunneling microscopy, X-ray photoelectron spectroscopy, infrared reflection absorption spectroscopy, and temperature-programmed desorption of CO . No preferential nucleation of Pd on the silica film is found at room temperature deposition: the hemispherical Pd nanoparticles are homogenously dispersed on the support at all coverages studied (0.01 - 1 ML (mono layer)). The Pd particles are resistant toward sintering up to 700 K as judged by STM; however, CO adsorption studies have revealed surface chemical modification at temperatures as low as 550 K. Strong morphological changes are observed above 800 K (ultimately resulting in elongated rectangular islands at ~1000 K), which is accompanied by strong alterations of CO adsorption properties. The results are rationalized in terms of Pd and Mo substrate interdiffusion at elevated temperatures, while the silica film basically preserves its structure.