Adsorptions- und Reaktionseigenschaften planarer PtRu/Ru(0001)- und Au/TiO2/Ru(0001)-Modellkatalysatoren: Von der Oberflächenchemie zur Katalyse

Abstract

This work demonstrates how model catalyst studies can contribute to an improved understanding of the working principles in heterogeneous catalysis. The first part of this work focuses on the interaction of deuterium with PtRu surfaces, which have been prepared by deposition of platinum on a Ru(0001) single crystal substrate. TPD measurements evidence a significant weakening of D2 adsorption on PtRu/Ru(0001) surface alloys. This effect can be attributed to a combination of geometric strain and electronic ligand effects. Furthermore, mixed ensemble effects can explain the shape of the TPD spectra over the whole Pt concentration range. Coadsorption of CO leads to a further weakening of deuterium adsorption on the bimetallic surfaces. Additionally, the TPD spectra of bimetallic surfaces with Pt monolayer islands on a Ru(0001) substrate were reproduced by computer simulations. From these simulations, desorption energies of 100 and 40 kJ/mole are extracted for the pure Ru(0001) substrate and the Pt islands, respectively. The second part of this work is related to the adsorption and oxidation of CO on Au/TiO2 model catalysts under conditions relevant for heterogeneous catalysis. The activity of these model catalysts is approximately one order of magnitude below the results of more realistic Au/TiO2 powder catalysts under the same conditions. In contrast, the activation energy for the reaction and reaction orders are in good agreement, pointing to a similar or identical reaction mechanism for both types of catalyst materials. The addition of small water concentrations (100 - 3000 ppm) leads to a strong acceleration of the CO2 production rate. From a combination of in-situ IR and ex-situ XPS measurements, a change of the structural and electronic properties of the Au particles in the presence of pure CO (50 mbar) is evidenced. Finally, the CO adsorption energy on the Au particles is derived by quantitative IR measurements.