Towards Realistic Surface Science Models of Heterogeneous Catalysts: Influence of Support Hydroxylation and Catalyst Pre
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PERSPECTIVE
Towards Realistic Surface Science Models of Heterogeneous Catalysts: Influence of Support Hydroxylation and Catalyst Preparation Method Martin Sterrer • Hans-Joachim Freund
Received: 19 February 2013 / Accepted: 25 February 2013 / Published online: 12 March 2013 Ó Springer Science+Business Media New York 2013
Abstract Surface science studies allow processes impor tant for heterogeneous catalysis to be investigated in greatest detail. Starting from the simplest model of a catalytic surface, a metal single-crystal surface under ultrahigh vacuum conditions, enormous progress has been made in the last decades towards extending the surface science of catalysis to technically more relevant dimensions. In this perspective, we highlight recent work, including our own, dealing with the influence of water on metal-support interactions in surface science studies of oxide-supported metal nanoparticle model catalysts. In particular, the effect of hydroxyl groups on nucleation and sintering of metal nanoparticles, and surface science investigations into catalyst preparation using wet-chemical procedures are addressed. Keywords Heterogeneous catalysis \ catalysis Oxide supports \ preparation and materials Metal-support interaction \ preparation and materials Characterization \ methodology and phenomena Thin films \ methodology and phenomena Spectroscopy and general characterisation
M. Sterrer (&) H.-J. Freund Department of Chemical Physics, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4–6, 14195 Berlin, Germany e-mail: [email protected] H.-J. Freund e-mail: [email protected]
1 Introduction Molecular level details are difficult to obtain from industrially applied heterogeneous catalyst materials because of their structural and chemical complexity. Instead, one must resort to simplified models such as ‘‘dispersed model systems’’ (powders), which will not be further discussed here, or planar model systems that allow sophisticated surface characterization techniques to be applied. The ‘‘classical’’ surface science approach, which also represents the simplest model approach in terms of surface structure, uses metal single-crystal surfaces in combination with the power of available ultrahigh vacuum (UHV)-based microscopic and spectroscopic techniques to gain detailed atomic and molecular level understanding of catalytically relevant processes such as adsorption, diffusion and reaction, and their structure sensitivity [1–3]. This approach has, however, two main limitations, which are commonly referred to as pressure gap and materials gap: first, adsorption structures and reaction pathways observed under UHV conditions may not necessarily be the same as those present under realistic pressure conditions. And second, single-crystal metal samples do not cover important materials aspects of a technical catalyst such as particle size effects and the influence of the support. Therefore, several approaches have in recent years been put forward in order to overcome these limitations [4–6]
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