Energetics of oxide-supported noble metal particles

Fundamental knowledge on the atomic structure, the energetics and the sintering behaviour of oxide-supported metal nanoparticles and their relation to the observed adsorption and catalytic phenomena is indispensable as this family of catalysts is widely used in important chemical processes. However, despite the importance of these catalysts, little is known about the nature of the metal-support interface of the working catalyst and the reaction mechanisms on the molecular level. The interfacial region is the center of catalytic activity and the energetics are crucial factors in establishing reaction steps that may involve surface diffusion of metal atoms (i.e. sintering, particle redispersion, reaction of adsorbates). Selected oxide-supported noble metal model catalysts will be microcalorimetrically characterized concerning their metal adsorption and metal-oxide adhesion energies with parallel structural characterization by Scanning Tunnelling Microscopy (STM) and Temperature-dependent Ion Scattering Spectroscopy (TP-ISS) in order to elucidate the influence of both metal and support on the energetics of the catalysts. For two systems (Pd on different Al2O3 supports and CeO2 (111)), the influence of the energetic situation on the chemisorptive and catalytic properties in methane combustion will be investigated. Sintering in view of the pre-determined bonding energetics will be studied on the same model systems in order to reveal the influence of various internal (particle size, oxidation state) and external (presence of additives or promoters) parameters on the sintering kinetics. The main tools to accomplish this part of the project are again TP-ISS, STM, ARXPS (Angle-resolved Photoelectron Spectroscopy) but also AFM (Atomic Force Microscopy).