Surface infrared spectroscopy

Nanoclusters open fascinating opportunities for quantum engineering because quantum-size effects become dominant in determining catalytic,1-3 optical,4 electronic,5 and magnetic6 properties. We succeeded in the controlled production of low-energy and high-flux monodispersed cluster beams, which allow for a systematic study of their reactivity after deposition onto a chemically inert substrate. We investigated the catalytic reaction that is the oxidation of CO on platinum and observed a distinct atom by atom size dependency for monodispersed platinum clusters on thin MgO(100) films. These results clearly show that the efficiency of a heterogeneous catalytic reaction can be tuned by the judicious choice of particle size.

Catalytic oxidation of carbon monoxide on monodispersed platinum clusters: Each atom counts

The parameters entering the kinetics for the mechanism of catalytic CO oxidation have been adapted for a Pt(110) surface, giving rise to a two‐variable model correctly predicting bistability. Oscillations are obtained when, in addition, the adsorbate‐driven 1×2–1×1 structural phase transition of Pt(110) is taken into account. Mixed‐mode oscillations can be qualitatively explained by including the faceting of the surface as a fourth variable. The limitations of the model essentially stem from the fact that only ordinary differential equations have been analyzed so far neglecting spatial pattern formation. It is discussed which dynamic phenomena observed experimentally in the CO oxidation on Pt(110) will probably not be adequately describable without taking spatial effects into account.

Oscillatory CO oxidation on Pt(110) : modeling of temporal self-organization

It is known that clean Pt(100) normally exists in a reconstructed (‘‘hex’’) phase, that a metastable clean unreconstructed phase [the (1×1)] can be prepared, and that during adsorption of CO the hex→(1×1) transition occurs. In this and the following paper, we describe an investigation of the CO/Pt(100) system which clarifies the mechanism of this adsorbate‐induced Pt phase transition. The experimental techniques included fast video‐LEED techniques, thermal desorption spectroscopy, electron energy loss spectroscopy, and work function measurements. Adsorption of CO at low temperature (T≲400 K) is discussed in this paper. CO on (1×1)‐Pt forms a c(2×2) overlayer near and at the ideal coverage of θ=0.5, in which the CO molecules occupy on‐top adsorption sites. Repulsive CO–CO interactions cause this structure to form. CO adsorption on hex‐Pt proceeds via formation of small areas with the same local structure, a c(2×2) layer of CO on (1×1)‐Pt, even when the total coverage of CO is low (0.05<θ<0.5). This compari...

The interaction of CO and Pt(100). I. Mechanism of adsorption and Pt phase transition

Experimental investigations on the catalytic oxidation of CO on well‐defined Pt(100) surfaces at low pressures (∼10−4 Torr) revealed under certain conditions the occurrence of kinetic oscillations which were associated with periodic transformations of the surface structure propagating wave‐like across the surface area. Based on experimental information about the various elementary steps involved (adsorption, desorption, surface reaction, adsorbate‐induced surface structural transformation) a set of coupled differential equations describing the kinetics of the various processes was established. A simplified version of these equations allows analytical treatment and provides qualitative insight into the occurrence of oscillations through linear stability analysis. Numerical solution of the full set of reaction‐diffusion equations reproduces the essential spatio‐temporal features of the experimental observations, although full quantitative agreement would still require better adjustment of the parameters inv...

Kinetic oscillations in the catalytic CO oxidation on Pt(100): Theory

Oscillations of the steady-state rate of catalytic CO oxidation on clean Pt surfaces were observed under low-pressure conditions and are related to the adsorption properties of the reactants. Evidence is presented for a model in which the reversible (5\ifmmode\times\else\texttimes\fi{}20)\ensuremath{\rightleftarrows}(1\ifmmode\times\else\texttimes\fi{}1) phase transition of the Pt(100) surface (which is associated with a marked variation of the oxygen sticking coefficient) is responsible for the oscillations.

J. Rüstig

Papers

Kinetic Oscillations in the Platinum-Catalyzed Oxidation of Co