Journalartikel

Jahr der Veröffentlichung: 2008

Seiten: 180302-180306

Zeitschrift: Journal of Physics: Condensed Matter

Bandnummer: 20

Heftnummer: 18

Open Access Status: Bronze

DOI Link: https://doi.org/10.1088/0953-8984/20/18/180302

Verlag: IOP Publishing

Abstract: 

This special issue is devoted to the application of in situ surface-sensitive techniques in the elucidation of catalysed reactions at (model) catalyst surfaces. Both reaction intermediates and the nature of the catalytically active phase are the targets of these investigations. In situ surface science techniques are also used to study the interaction of water with surfaces under realistic conditions. Since 80% of all technical chemicals are manufactured by utilizing (heterogeneous) catalysis, scientific understanding and technological development of catalysis are of central practical importance in modern society. Heterogeneously catalysed reactions take place at the gas/solid interface. Therefore one of the major topics in surface chemistry and physics is closely related to heterogeneous catalysis, with the aim of developing novel catalysts and to improve catalysts' performances on the basis of atomic scale based knowledge. Despite the economical and environmental rewards—if such a goal is achieved—and despite 40 years of intensive research, practical catalysis is still safely in a black box: the reactivity and selectivity of a catalyst are commercially still optimized on a trial and error basis, applying the high throughput screening approach.The reason for this discrepancy between ambition and reality lies in the inherent complexity of the catalytic system, consisting of the working catalyst and the interaction of the catalyst with the reactant mixture. Practical (solid) catalysts consist of metal or oxide nanoparticles which are dispersed and stabilized on a support and which may be promoted by means of additives. These particles catalyse a reaction in pressures as high as 100 bar. Practical catalysis is in general considered to be far too complex for gaining atomic-scale understanding of the mechanism of the catalysed reaction of an industrial catalyst during its operation. Therefore it has been necessary to introduce idealization and simplification of both the catalyst and the reaction conditions. For structural simplicity, single crystals of transition metals or oxides are typically used to mimic the catalyst's active surface. To avoid interfering 'dirt' effects, ultrapure reactants are introduced in ultrahigh vacuum (pressures better than 10-8 mbar) chamber systems. In order to gain an atomic-scale understanding of the reaction process, electron-based spectroscopic techniques, such as photoemission spectroscopy, LEED, etc, are applied, which need high vacuum environments due to the limited mean free path of the electrons. Simple model reactions, such as the CO oxidation reaction, have been chosen for trying to understand the microscopic reaction mechanism under these conditions. In this way, important, fundamental information on adsorption sites, dissociation processes and reaction pathways has been obtained over the past 40 years.Nevertheless, the large differences between these simple UHV model systems and more real-world non-single-crystal surfaces exposed to high pressures often prevent extrapolation of this atomic-scale knowledge to more realistic situations: a materials and pressure gap (cf figure 1) is introduced.

Harvard-Zitierstil: Lundgren, E. and Over, H. (2008) In situ gas–surface interactions: approaching realistic conditions, Journal of Physics: Condensed Matter, 20(18), pp. 180302-180306. https://doi.org/10.1088/0953-8984/20/18/180302

APA-Zitierstil: Lundgren, E., & Over, H. (2008). In situ gas–surface interactions: approaching realistic conditions. Journal of Physics: Condensed Matter. 20(18), 180302-180306. https://doi.org/10.1088/0953-8984/20/18/180302