Rhenium substantially promotes the rate of Pt-catalyzed glycerol hydrogenolysis to propanediols and shifts the product selectivity from 1,2-propanediol to a mixture of 1,2 and 1,3-propanediols. This work presents experimental evidence for a tandem dehydration-hydrogenation mechanism that occurs over a bifunctional Pt-Re catalyst. Infrared spectroscopy of adsorbed pyridine and the rate of aqueous-phase hydrolysis of propyl acetate were used to identify and quantify Brønsted acid sites associated with the Re component. Near ambient pressure XPS revealed a range of Re oxidation states on the Pt-Re catalysts after reduction in H2 at 393 and 493 K, which accounts for the presence of Brønsted acidity. A mechanism involving acid-catalyzed dehydration followed by Pt-catalyzed hydrogenation was consistent with the negative influence of added base, a primary kinetic isotope effect with deuterated glycerol, an inverse isotope effect with dideuterium gas, and the observed orders of reaction

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The surface of a gold foil under ozone oxidation was examined by near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and scanning electron microscopy (SEM). Our in situ observations show that a surface oxide phase is formed during the exposure to ozone; however this phase decomposes under vacuum and even in the presence of ozone at temperatures higher than 300 °C. Assuming that an oxide overlayer completely covers the Au surface, the thickness of the oxide phase was estimated to be between 0.29 and 0.58 nm by energy-dependent XPS depth profiling. The surface oxidation led to structural modifications of the gold surface. These morphological changes do not disappear even under vacuum. In the Au 4f spectra, an additional component at low binding energy (83.3 eV), which appears during/after O3 treatment, is assigned to the presence of low-coordinated atoms which appear on the Au surface as a result of surface restructuring under oxidation. Ex situ SEM images demonstrate that only the region of the sample that was exposed to O3 shows the presence of ridges on the Au surface.

Rhenium is catalytically active for many valuable chemical reactions, and consequently has been the subject of scientific investigation for several decades. However, little is known about the chemical identity of the species present on rhenium surfaces during catalytic reactions because techniques for investigating catalyst surfaces in-situ -such as near-ambient-pressure X-ray photoemission spectroscopy (NAP-XPS) -have only recently become available. In the current work, we present an in-situ XPS study of rhenium catalysts. We examine the oxidized rhenium species that form on a metallic rhenium foil in an oxidizing atmosphere, a reducing atmosphere, and during a model catalytic reaction (i.e. the partial-oxidation of ethylene). We find that, in an oxidizing environment, a Re 2 O 7 film forms on the metal surface, with buried layers of sub-oxides that contain Re 4+ , Re 2+ and Re

Silver's unique ability to selectively oxidize ethylene to ethylene oxide under an oxygen atmosphere has long been known. Today it is the foundation of ethylene oxide manufacturing. Yet, the mechanism of selective epoxide production is unknown. Here we use a combination of UHV and in situ experimental methods along with theory to show that the only species that has been shown to produce ethylene oxide, the so-called electrophilic oxygen appearing at 530.2 eV in the O 1s spectrum, is the oxygen in adsorbed SO4 (SO4,ad). This adsorbate is part of a 2D Ag/SO4 phase, where the nonstoichiometric surface variant, with a formally S(V+) species, facilitates selective transfer of an oxygen atom to ethylene. Our results demonstrate the significant and surprising impact of a trace impurity on a well-studied heterogeneously catalyzed reaction.

We show atomic oxygen on an unreconstructed Ag(110) surface has a O 1s binding energy ≤ 528 eV and its stable at low coverages. Our findings point to the idea of multiple selective oxygen species in ethylene epoxidation on Ag.

Gold nanoparticles on transition-metal oxides were synthesized by two different methods: precipitation and photoinduced decomposition of an intermediate gold–azido complex. Only samples prepared by the precipitation method showed significant CO conversion at low temperature. XPS shows the formation of two Au species (Au0 and Auδ+) on the surface of active Au/TiO2 and Au/Fe2O3 samples. The energy shift of the Auδ+ peak depends on the support and is 0.6 and 0.9 eV for Au/TiO2 and Au/Fe2O3, respectively. TEM images indicate the formation of overlayer on Au particles. These results prove Au activation via a strong metal–support interaction, on the basis of the strong influence of the support on the electronic structure of the gold through charge transfer and stabilization of low-coordinated Au atoms.

The selective oxidation of ethanol to acetaldehyde and acetic acid over a monolayer V 2 O 5 /TiO 2 catalyst has been studied in situ using Fourier transform infrared spectroscopy and near-ambient pressure X-ray photoelectron spectroscopy (XPS) at temperatures ranging from 100 to 300 °C. The data were complemented with temperature-programmed reaction spectroscopy and kinetic measurements. It was found that at atmospheric pressure at low temperatures acetaldehyde is the major product formed with the selectivity of almost 100%. At higher temperatures, the reaction shifts toward acetic acid and at 200 °C its selectivity reaches 60%. Above 250 °C, the unselective oxidation to CO and CO 2 becomes dominant reaction. Infrared spectroscopy indicated that during the reaction at 100 °C, non-dissociatively adsorbed molecules of ethanol, ethoxide species, and adsorbed acetaldehyde are on the catalyst surface, while at higher temperatures the surface is mainly covered by acetate species. According to the XPS data, titanium cations remain in the Ti 4+ state, whereas V 5+ cations undergo a reversible reduction under reaction conditions. The presented data agree with the assumption that the selective oxidation of ethanol over vanadium oxide catalysts occurs at the redox V n+ sites via the redox mechanism involving the surface lattice oxygen species. A reaction scheme for the oxidation of ethanol over monolayer V 2 O 5 /TiO 2 catalysts is suggested.