Anomalous hydrogen adsorption sites found for the c(2×2)-3H phases formed on the Re(101̄0) and Ru(101̄0) surfaces

Gas phase 1H NMR studies and kinetic modeling of dihydrogen isotope equilibration catalyzed by Ru-nanoparticles under normal conditions: dissociative vs. associative exchange

Exposure of surface H-containing Ru-nanoparticles to D₂ gas produces HD via associative adsorption, surface H-transfer and associative desorption.

Ligand Effect in Hydrogen Adsorption on Epitaxial Nickel Films

The adsorption structure of hydrogen on ultrathin epitaxial nickel films in pseudomorphic arrangement on the unreconstructed Ir(100) surface is investigated by quantitative low-energy electron diffraction (LEED). This is highly interesting in the light of the fact that on Ni(100) adsorption is in hollow sites whilst on unreconstructed Ir(100) it is exclusively in bridge sites. On Ni films thicker than 1 monolayer (ML) the adsorption is in 4-fold coordinated hollow sites as it is on Ni(100). This is in spite of the considerable tensile strain of the Ni film (+8.9%) and is interpreted by the dominance of ensemble effects in the hydrogen bonding. In contrast, on the 1 ML Ni film on Ir(100), with iridium atoms being nearest neighbours to nickel atoms, there is occupation of both bridge and hollow sites of the nickel layer – a clear indication for the presence of ligand effects.

2H-solid-state-NMR study of hydrogen adsorbed on catalytically active ruthenium coated mesoporous silica materials

(2)H solid-state NMR measurements were performed on three samples of ruthenium nanoparticles synthesized inside two different kinds of mesoporous silica, namely SBA-3 silica materials and SBA-15 functionalized with -COOH groups and loaded with deuterium gas. The line-shape analyses of the spectra reveal the different deuteron species. In all samples a strong -OD signal is found, which shows the catalytic activity of the metal, which activates the D-D bond and deuterates the -SiOH groups through the gas phase, corroborating their usability as catalysts for hydrogenation reactions. At room temperature the mobility of the -Si-OD groups depends on the sample preparation. In addition to the -Si-OD deuterons, the presence of different types of deuterons bound to the metal is revealed. The singly coordinated -Ru-D species exhibit several different quadrupolar couplings, which indicate the presence of several non-equivalent binding sites with differing binding strength. In addition to the dissociated hydrogen species there is also a dihydrogen species -Ru-D(2), which is attributed to defect sites on the surface. It exhibits a fast rotational dynamics at all temperatures. Finally there are also indications of three-fold coordinated surface deuterons and octahedrally coordinated deuterons inside the metal.

Growth and structure of gold films on a Re([Formula: see text]) surface

We have deposited Au films in ultra-high vacuum onto a rhenium ([Formula: see text]) surface in submonolayer and multilayer concentrations and studied them by means of low- and medium-energy electron diffraction in the temperature range between 300 and 800 K. In the submonolayer range, Au forms several low-energy electron diffraction (LEED) phases, namely, a (1 × 3), a (1 × 4), a (1 × 5) and a (1 × 6) phase, consisting of one-dimensionally ordered Au chains in the [[Formula: see text]] direction, until the formation of a complete pseudomorphic monolayer is indicated by a (1 × 1) LEED phase. In the multilayer regime, a (1 × 8) LEED phase appears over a surprisingly wide coverage range from about two to at least eight monolayers, which we interpret as a hexagonal uniaxially compressed reconstructed Au overlayer on pseudomorphically grown hexagonal close-packed gold layers. In order to get access to absolute Au coverages, we have performed LEED (I,V) measurements and carried out a LEED structure determination for the (1 × 1) phase. We propose the formation of a full Au monolayer in which both the Re trough and top-row sites are being covered by Au atoms. The data are discussed and compared with those from previous studies on related systems.

Atomic hydrogen interaction with Ru(101̄0)

The interaction of atomic hydrogen with clean and deuterium precovered Ru(1010) was studied by means of temperature-programmed desorption (TPD) spectroscopy. Compared to molecular hydrogen experiments, after exposure of the clean surface to gas-phase atomic hydrogen at 90 K, two additional peaks grow in the desorption spectra at 115 and 150 K. The surface saturation coverage, determined by equilibrium between abstraction and adsorption reactions, is 2.5 monolayers. Preadsorbed deuterium abstraction experiments with gas-phase atomic hydrogen show that a pure Eley-Rideal mechanism is not involved in the process, while a hot atom (HA) kinetics describes well the reaction. By least-squares fitting of the experimental data, a simplified HA kinetic model yields an abstraction cross section value of 0.5 +/- 0.2 angstroms2. The atomic hydrogen interaction with an oxygen precovered surface was also studied by means of both TPD and x-ray photoelectron spectroscopy: oxygen hydrogenation and water production take place already at very low temperature (90 K).

Anomalous Behavior of Atomic Hydrogen Interacting with Gold Clusters

The change in the electronic structure of Au(n)- clusters induced by the exchange of an Au atom by hydrogen is studied using photoelectron spectroscopy. Au anion clusters react with one hydrogen atom but not with molecular hydrogen. The spectra of Au(n)- and Au(n-1)H- clusters show almost identical features for n > 2 suggesting that hydrogen behaves as a protonated species by contributing one electron to the valence pool of the Au(n)- cluster. This behavior is in sharp contrast to that of the commonly understood electronic structure of hydrogen in metals; namely, it attracts an electron from the conduction band of the metal and remains in an "anionic" form or forms covalent bonding. We discuss the influence of the unique electronic structure of H on the unusual catalytic behavior of Au clusters.