Co-adsorption of CO and H(2) on a Rh(100) single crystal surface has been studied by a combination of temperature programmed desorption (TPD), reflection absorption infrared spectroscopy (RAIRS), low energy electron diffraction (LEED), and density functional theory (DFT) calculations. Exposure of CO to a hydrogen precovered surfaces at 150 K results in some displacement of adsorbed hydrogen and a layer with 0.67 ML H and 0.67 ML CO is obtained. A c(3 square root(2) x square root(2))R45 degree structure is formed with CO occupying bridge sites and hydrogen occupying partly bridge sites on the surface and partly octahedral subsurface sites, causing hydrogen to desorb at temperatures around 230 K.

The influence of carbon on the adsorption of CO from a Rh(100) single crystal has been studied by a combination of experimental techniques: Temperature Programmed Desorption (TPD), Low Energy Electron Diffraction (LEED), and High Resolution Electron Energy Loss Spectroscopy (HREELS). These experimental techniques were combined with a computational approach using Density Functional Theory (DFT). Using this combination of techniques, we have shown that surface carbon greatly influences adsorbed CO and we have determined the exact magnitude of this interaction. Furthermore, we have demonstrated that carbon does not remain fully on the surface; at higher coverage it diffuses partially to subsurface positions. The presence of these subsurface species significantly influences the adsorbates on the surface.

LEED, TPRS, and RAIRS experiments combined with DFT calculations have been used to study CO oxidation on Rh(100) from preadsorbed O and CO and to unravel how the reaction kinetics is influenced by the configuration of the adsorbed reactants. At least four different regimes are identified in increasing order of reactivity: near zero coverage, isolated CO and O species react with the highest activation energy observed in this work (105 ± 4 kJ/mol). In the second regime, oxygen is present in a p(2 × 2) structure and reacts with bridge bonded CO, with an activation energy of 77 ± 8 kJ/mol. In the third regime, the reactivity is associated with on-top CO in defects of a c(2 × 2) oxygen layer, at an estimated activation energy of 58 ± 10 kJ/mol. In the last and most reactive regime, the oxygen adlayer has (2 × 2)-pg order with the top metal layer reconstructed. According to DFT calculations, CO adsorption lifts the reconstruction. Oxygen occupies 4-fold hollow and bridge sites; the latter react with bridged CO. The general trend is that if the reactants become destabilized by repulsive lateral interactions, the rate of reaction to CO2 increases.

The adsorption and decomposition of ethylene glycol on Rh(100) have been studied with temperature-programmed reaction spectroscopy and reflection absorption infrared spectroscopy. Ethylene glycol adsorbs onto the surface via the hydroxyl groups. At 150 K, both hydroxyl bonds are broken, forming an ethylenedioxy intermediate. At high coverage, a portion of the ethylene glycol molecules dehydrogenate only one hydroxyl bond, forming a monodentate species. These intermediates decompose further, with complete dehydrogenation and simultaneous C--C bond breaking occurring at around 290 K. Hydrogen and carbon monoxide are formed, which desorb at 290 and 500 K, respectively.

The influence of nitrogen atoms on the adsorption of CO on a Rh(100) single crystal surface has been studied by a combination of experimental techniques: low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), temperature programmed desorption (TPD), and reflection absorption infrared spectroscopy (RAIRS). Dynamic Monte Carlo simulations have been used to model how the nitrogen atoms are distributed over the surface at different coverages. The nitrogen layer consists of small interconnected c(2 × 2)-N/Rh(100) islands with in between the islands well-defined sites for CO to adsorb onto. Two short-range ordered nitrogen geometries were identified with coadsorption sites binding CO less strongly. Nitrogen greatly influences adsorbed CO: a pairwise repulsive CO/N-interaction energy of ω N−C O = 21 kJ/mol was obtained.

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We present a kinetic Monte Carlo lattice gas model including top and bridge sites on a square lattice, with pairwise lateral interactions between the adsorbates. In addition to the pairwise lateral interactions we include an additional interaction: an adsorbate is forbidden to adsorb on a bridge site formed by two surface atoms when both surface atoms are already forming a bond with an adsorbate. This model is used to reproduce the low and high coverage adsorption behaviour of CO on Pt(100) and Rh(100). The parameter set used to simulate CO on Pt(100) produces the c(2 x 2)-2t ordered structure at 0.50 ML coverage, a one-dimensionally ordered structure similar to the experimentally observed (3 square root(2) x square root(2)) - 2t + 2b structure at 0.67 ML coverage, the c(4 x 2)-4t + 2b ordered structure at 0.75 ML coverage, and the recently reported c(6 x 2)-6t + 4b ordered structure at 0.83 ML coverage. The (5 square root(2) x square root(2)) ordered structure at 0.60 ML coverage is not reproduced by our model. The parameter set used to simulate CO on Rh(100) produces the c(2 x 2)-2t ordered structure at 0.50 ML coverage, a one-dimensionally ordered structure similar to the experimentally observed (4 square root(2) x square root(2)) - 2t + 4b structure at 0.75 ML coverage, and the c(6 x 2)-6t + 4b ordered structure at 0.83 ML coverage. Additionally, the simulated change of top and bridge site occupation as a function of coverage matches the trend in experimental vibrational peak intensities.

The decomposition of acetylene on a Rh(100) single crystal was studied by a combination of experimental techniques [static secondary ion mass spectrometry (SSIMS), temperature-programmed desorption (TPD), and low-energy electron diffraction (LEED)] to gain insight into the reaction pathway and the nature of the reaction intermediates. The experimental techniques were combined with a computational approach using density functional theory (DFT). Acetylene adsorbs irreversibly on the Rh(100) surface and eventually decomposes to atomic carbon and gas-phase hydrogen. The combination of experimental and computational results enabled us to determine the most likely reaction pathway for the decomposition process.