4.4 Model Systems in Catalysis for Energy Economy

Abstract

Harvesting, saving, and storing energy are key issues in today's general energy discussions [1]. Harvesting energy through photochemistry and storing energy in compounds using thermal energy-efficient processes are attractive solutions to some problems within the grand picture [2].Heterogeneous thermal and photocatalysis are bound to play a key role in those solutions. However, while thermal heterogeneous catalysis is widespread in chemical industries, and photocatalysis not yet, there is still a strong demand in both areas for research in order to understand the process and its elementary steps as well as to rationally design the catalytic material.Investigation of model catalysts can play a decisive role in a rational approach to understand heterogeneous catalysis, and this is the topic of this chapter [3][4][5][6].In the introduction, the model systems will be defined to familiarize the reader with the approach in order to appreciate the connection to real-world catalysis. Following the introduction, we will demonstrate via four case studies various fundamental aspects in thermal and photocatalysis whereby studies on model systems might become important to unravel the foundations of reaction mechanisms.The model systems have been created under the premises that it is possible to investigate them at the atomic scale using the toolbox that has been developed in surface science during the second half of the last century up to now [7].The model systems are based on the idea to grow well-ordered oxide layers or thin films, representing the bulk material, and as such the catalyst support, on singlecrystal metal surfaces using the concepts of epitaxial growth [8]. This, in turn, allows one to investigate bulk insulators without having to worry about charging when charged information carriers such as electrons or ions are used to investigate those systems. One thus avoids one of the key difficulties hampering the detailed study of real catalysts. Also the application of scanning probe techniques including electron tunneling is possible for thin-film systems. The fact that the oxides are grown on a metal support also ensures the easy applicability of infrared reflection absorption spectroscopy at such systems. Moreover, controlling the growth parameters of the oxide film also allows one to vary the density of defects at the surface of the oxide films, a factor of importance when nanoparticles are grown on the oxide support.

Formation and Evolution of Ultrathin Silica Polymorphs on Ru(0001) Studied with Combined in Situ, Real-Time Methods

“…Particularly in the area of catalysis, the development of silica-based model systems can provide a deeper understanding of the fundamental properties of the material in a controlled environment. In this sense, this approach opens the possibility of forging new concepts that can be later applied to real systems. , …”