Examples from recent studies in our laboratory are presented to illustrate the main tools available to surface scientists for the determination of the kinetics of surface reactions. Emphasis is given here to hydrocarbon conversions and studies that rely on the use of model systems, typically single crystals and controlled (ultrahigh vacuum) environments. A detailed discussion is provided on the use of temperature-programmed desorption for the determination of activation energies as well as for product identification and yield estimations. Isothermal kinetic measurements are addressed next by focusing on studies under vacuum using molecular beams and surface-sensitive spectroscopies. That is followed by a review of the usefulness of high-pressure cells and other reactor designs for the emulation of realistic catalytic conditions. Finally, an analysis of the power of isotope labeling and chemical substitutions in mechanistic research on surface reactions is presented.

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Field electron microscopy (FEM), high-resolution electron energy loss spectroscopy (HREELS), molecular beams (MB) and temperature-programmed reaction (TPR) have been applied to the study of the kinetics of CO oxidation at low temperature, and to determine the roles of subsurface atomic oxygen (O sub ) and surface reconstruction in self-oscillatory phenomena, on Pd(111), Pd(110) and Pt(100) single crystals and on Pd and Pt tip surfaces. It was found that high local concentrations of adsorbed CO during the transition from a Pt(100)-hex reconstructed surface to the unreconstructed 1·1 phase apparently prevents oxygen atoms from occupying hollow sites on the surface, and leads to the appearance of a weakly bound active adsorbed atomic oxygen (O ads ) state in an on-top or bridge position. It was also inferred that subsurface oxygen O sub on the Pd(110) surface may play an important role in the formation of new active sites for the weakly bound O ads atoms. Experiments with 18 O isotope labeling clearly show that the weakly bound atomic oxygen is the active form of oxygen that reacts with CO to form CO 2 at T~140-160 K. Sharp tips of Pd and Pt, several hundreds angstroms in diameter, were used to perform in situ investigations of dynamic surface processes. The principal conclusion from those studies was that non-linear reaction kinetics is not restricted to macroscopic planes since: (i) planes as small as~200 Å in diameter show the same non-linear kinetics as larger flat surfaces; (ii) regular waves appear under conditions leading to reaction rate oscillations; (iii) the propagation of reaction-diffusion waves involves the participation of different crystal nanoplanes via an effective coupling between adjacent planes.

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