|
Abstract PHYSICAL AND CHEMICAL PHENOMENA IN MODEL THIN FILM CATALYSTS S. Ladas Department of Chemical Engineering, University of Patras and FORTH-ICEHT POB 1414, 26500 Rion , Patras Surface and interface phenomena in supported thin films play a central role in many technological applications, from microelectronics to heterogeneous catalysis [1-3]. Using modern surface science techniques it is possible to carry out qualitative and quantitative elemental analysis and chemical compound identification, as well as interfacial phenomena investigation in the first few atomic layers of a solid surface or through an ultra thin film prepared on the surface of an other solid. This information can be directly related with the behaviour of the films in various technologically important applications. The presentation will concentrate on the utilization of surface sensitive techniques, like X-ray and UV Photoelectron Spectroscopies (XPS or ESCA and UPS) in the surface and interface characterization of model thin film catalysts [4]. Commercial heterogeneous catalysts typically consist of a finely dispersed active phase (usually metallic) supported in the form of nanoparticles inside the porous structure of a carrier or support material. The carrier, as a rule , is some oxide or sulfide, more-or-less chemically inert, which however may influence the behaviour of the active phase via interfacial interactions. Model surface science research on these catalysts, aiming to elucidate microscopic aspects of their behaviour, involves two levels of complexity : the study of extended single crystals of the active phase metal or alloy , or the study of realistic model catalysts, which are nanoparticulate thin films of the active phase , prepared under controlled conditions onto a well-defined form of the carrier (often an extended oxide single crystal). Two case examples of realistic model catalyst studies will be discussed, based on recent work in our group. The first example concerns the behaviour of gold/nickel ultrathin bimetallic films on yttria-stabilized ZrO2 (100) [5]. The second example describes the interaction of metallic and oxidized nickel thin films with single-crystal yttria-stabilized -ZrO2 and Al2O3 surfaces [6]. |
||
|
References |
||