Kinetic evidence for a non-Langmuir-Hinshelwood surface reaction: H/D exchange over Pd nanoparticles and Pd(111).

The mechanism of hydrogen recombination on a Pd(111) single crystal and well-defined Pd nanoparticles is studied using pulsed multi-molecular beam techniques and the H2/D2 isotope exchange reaction. The focus of this study is to obtain a microscopic understanding of the role of subsurface hydrogen in enhancing the associative desorption of molecular hydrogen. HD production from H2 and D2 over Pd is investigated using pulsed molecular beams, and the temperature dependence and reaction orders are obtained for the rate of HD production under various reaction conditions designed to modulate the amount of subsurface hydrogen present.

Tuning the surface chemistry of Pd by atomic C and H: a microscopic picture.

Palladium is crucial for industry-related applications such as heterogeneous catalysis, energy production, and hydrogen technologies. In many processes, atomic H and C species are proposed to be present in the surface/near-surface area of Pd, thus noticeably affecting its chemical activity. This study provides a detail and unified view on the interactions of the H and C species with Pd nanoparticles (NPs), which is indispensable for insight into their catalytic properties.

Toward Low-Temperature Dehydrogenation Catalysis: Isophorone Adsorbed on Pd(111).

Adsorbate geometry and reaction dynamics play essential roles in catalytic processes at surfaces. Here we present a theoretical and experimental study for a model functional organic/metal interface: isophorone (C9H14O) adsorbed on the Pd(111) surface. Density functional theory calculations with the Perdew-Burke-Ernzerhoff (PBE) functional including van der Waals (vdW) interactions, in combination with infrared spectroscopy and temperature-programmed desorption (TPD) experiments, reveal the reaction pathway between the weakly chemisorbed reactant (C9H14O) and the strongly chemisorbed product (C9H10O), which occurs by the cleavage of four C-H bonds below 250 K.

A kinetic study on the conversion of cis-2-butene with deuterium on a Pd/Fe3O4 model catalyst.

The conversion of cis-2-butene with deuterium over a well-defined Pd/Fe(3)O(4) model catalyst was studied by isothermal pulsed molecular beam (MB) experiments under ultra high vacuum conditions. This study focuses on the processes related to dissociative hydrogen adsorption and diffusion into the subsurface of Pd nanoparticles and their influence on the activity and selectivity toward competing cis-trans isomerization and hydrogenation pathways. The reactivity was studied both under steady state conditions and in the transient regime, in which the reaction takes place on a D-saturated catalyst, over a large range of reactant pressures and reaction temperatures.

Role of hydrogen in olefin isomerization and hydrogenation: a molecular beam study on Pd model supported catalysts.

The role of surface, and subsurface hydrogen species in olefin cis-trans isomerization and hydrogenation over a model Pd/Fe(3)O(4)/Pt(111) catalyst was investigated by pulsed molecular beam experiments and infrared reflection-absorption spectroscopy. We show that non-equivalent hydrogen species are involved in the two reaction pathways: whereas cis-trans isomerization proceeds with the surface hydrogen species, the presence of hydrogen absorbed in the subsurface region of Pd particles is required for the hydrogenation pathway. The activity and selectivity toward both reaction channels was found to significantly change on Pd particles when they are modified with strongly dehydrogenated carbonaceous deposits.

Ethanol adsorption, decomposition and oxidation on Ir(111): a high resolution XPS study.

Ethanol (C(2)H(5)OH) adsorption, decomposition and oxidation is studied on Ir(111) using high-energy resolution, fast XPS and temperature-programmed desorption. During heating of an adsorbed ethanol layer a part of the C(2)H(5)OH(ad) desorbs molecularly, and another part remains on the surface and decomposes around 200 K; these two decomposition pathways are identified, as via acetyl (H(3)C--C=O) and via CO(ad)+CH(3ad), respectively. Acetyl and CH(3ad) decompose around 300 K into CH(ad) (and CO(ad)).

Kinetics of the reaction C2H5 + HO2 by time-resolved mass spectrometry.

The overall rate constant for the radical-radical reaction C2H5 + HO2 --> products has been determined at room temperature by means of time-resolved mass spectrometry using a laser photolysis/flow reactor combination. Excimer laser photolysis of gas mixtures containing ethane, hydrogen peroxide, and oxalyl chloride was employed to generate controlled concentrations of C2H5 and HO2 radicals by the fast H abstraction reactions of the primary radicals Cl and OH with C2H6 and H2O2, respectively. By careful adjustments of the radical precursor concentrations, the title reaction could be measured under almost pseudo-first-order conditions with the concentration of HO2 in large excess over that of C2H5.