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X-ray photoemission spectroscopy (XPS) measurements in near-ambient pressure (NAP) conditions result in a signal loss of the primary spectrum as a result of inelastic scattering of photoelectrons in the gas phase. The inelastic scattering of the primary electrons gives rise to a secondary signal that can result in additional and often unwanted features in the measured spectrum. In the present work, we derive equations that can be used to model the resulting signal and provide equations that can be used to simulate or remove the inelastic scattering signal from measured spectra. We demonstrate this process for photoemission spectra of a wide range of kinetic energies, measured from Au, Ag, and Cu, in a variety of gases (N2, He, H2, and O2). The work is supplemented with an open-source software in which the algorithms described here have been implemented and can be used to remove the gas phase inelastic scattering signal.

Single-atom alloys (SAAs) have recently gained considerable attention in the field of heterogeneous catalysis research due to their potential for novel catalytic properties. While SAAs are often examined in reactions of reductive atmospheres, such as hydrogenation reactions, in the present work, we change the focus to AgPd SAAs in oxidative environments since Pd has the highest catalytic activity of all metals for oxidative reactions. Here, we examine how the chemical reactivity of AgPd SAAs differs from its constituent Pd in an oxidative atmosphere. For this purpose, electronic structure changes in an Ag0.98Pd0.02 SAA foil in 1 mbar of O2 were studied by in situ x-ray photoemission spectroscopy and compared with the electronic structure of a Pd foil under the same conditions. When heated in an oxidative atmosphere, Pd in Ag0.98Pd0.02 partly oxidizes and forms a metastable PdOx surface oxide. By using a peak area modeling procedure, we conclude that PdOx on Ag0.98Pd0.02 is present as thin, possibly monolayer thick, PdOx islands on the surface. In comparison to the PdO formed on the Pd foil, the PdOx formed on AgPd is substantially less thermodynamically stable, decomposing at temperatures about 270 °C lower than the native oxide on Pd. Such behavior is an interesting property of oxides formed on dilute alloys, which could be potentially utilized in catalytic oxidative reactions such as methane oxidation.

Over the past decade, single-atom alloys (SAAs) have been a lively topic of research due to their potential for achieving novel catalytic properties and circumventing some known limitations of heterogeneous catalysts, such as scaling relationships. In researching SAAs, it is important to recognize experimental evidence of peculiarities in their electronic structure. When an isolated atom is embedded in a matrix of foreign atoms, it exhibits spectroscopic signatures that reflect its surrounding chemical environment. In the present work, using photoemission spectroscopy and computational chemistry, we discuss the experimental evidence from Ag0.98Pd0.02 SAAs that show free-atom-like characteristics in their electronic structure. In particular, the broad Pd4d valence band states of the bulk Pd metal become a narrow band in the alloy. The measured photoemission spectra were compared with the calculated photoemission signal of a free Pd atom in the gas phase with very good agreement, suggesting that the Pd4d states in the alloy exhibit very weak hybridization with their surroundings and are therefore electronically isolated. Since AgPd alloys are known for their superior performance in the industrially relevant semi-hydrogenation of acetylene, we considered whether it is worthwhile to drive the dilution of Pd in the inert Ag host to the single-atom level. We conclude that although site-isolation provides beneficial electronic structure changes to the Pd centers due to the difficulty in activating H2 on Ag, utilizing such SAAs in acetylene semi-hydrogenation would require either a higher Pd concentration to bring isolated sites sufficiently close together or an H2-activating support.

Metal alloy catalysts can develop complex surface structures when exposed to reactive atmospheres. The structures of the resulting surfaces have intricate relationships with a myriad of factors, such as the affinity of the individual alloying elements to the components of the gas atmosphere, and the bond strengths of the multitude of low-energy surface compounds that can be formed. Identifying the atomic structure of such surfaces is a prerequisite for establishing structure-property relationships, as well as for modeling such catalysts in ab initio calculations. Here we show that an alloy, consisting of an oxophilic metal (Cu) diluted into a noble metal (Ag), forms a meta-stable 2-dimensional oxide monolayer the more oxophilic metal, when the alloy is subjected to oxidative reaction conditions. The presence of this oxide is correlated with selectivity in the corresponding test reaction of ethylene epoxidation. In the present study, using a combination of in-situ, ex-situ and theoretical methods (NAP-XPS, XPEEM, LEED, and DFT) we determine the structure to be a 2-dimensional analogue of Cu2O, resembling a single lattice plane of Cu2O. The overlayer holds an pseudo-epitaxial relationship with the underlying noble metal. Spectroscopic evidence shows that the oxide’s electronic structure is qualitatively distinct from its 3-dimensional counterpart, and due to weak electronic coupling with the underlying noble metal, it exhibits metallic properties. These findings provide precise details of this peculiar structure, and valuable insights into how alloying can enhance catalytic properties.

Alloying provides a means by which to tune a metal catalyst’s electronic structure and thus tailor its performance; however, mean-field behaviour in metals imposes limits. To access unprecedented catalytic behaviour, materials must exhibit emergent properties that are not simply interpolations of the constituent components’ properties. Here we show an emergent electronic structure in single-atom alloys, whereby weak wavefunction mixing between minority and majority elements results in a free-atom-like electronic structure on the minority element. This unusual electronic structure alters the minority element’s adsorption properties such that the bonding with adsorbates resembles the bonding in molecular metal complexes. We demonstrate this phenomenon with AgCu alloys, dilute in Cu, where the Cu d states are nearly unperturbed from their free-atom state. In situ electron spectroscopy demonstrates that this unusual electronic structure persists in reaction conditions and exhibits a 0.1 eV smaller activation barrier than bulk Cu in methanol reforming. Theory predicts that several other dilute alloys exhibit this phenomenon, which offers a design approach that may lead to alloys with unprecedented catalytic properties. In solid metals, electron orbitals form broad bands and their binding of adsorbates depends on the bandwidth. Now, it is shown that a weak solute–matrix interaction in dilute alloys results in extremely narrow electronic bands on the solute, similar to a free-atom electronic structure. This structure affords unique adsorption properties important for catalysis.

Alloy catalysts under reaction conditions are complex entities. In oxidizing atmospheres, multiple phases can coexist on a catalyst s surface as a result of phase segregation and preferential oxidation. Such a scenario can result in unusual substoichiometric and metastable phases that could play important roles in catalytic processes. For instance, AgCu alloys known to exhibit enhanced epoxide selectivity in partial oxidation of ethylene form an oxide like surface structure under reaction conditions. Under these conditions, copper oxides are stable, while silver oxides are not. Consequently, copper segregates to the alloy s surface and forms an oxide overlayer. Little is known about the structure or function of such overlayers, and it is unknown whether they play an active role in the catalyst s enhanced selectivity. In order to develop a clearer picture of such catalysts, the current work utilizes several in situ spectroscopic and microscopic techniques to examine the copper oxide phases that form when AgCu is exposed to epoxidation conditions. It is found that several forms of oxidic Cu coexist simultaneously on the active catalyst s surface, namely, CuO, Cu2O, and some previously unreported form of oxidized Cu, referred to here as CuxOy. Online product analysis, performed during the in situ spectroscopic measurements, shows that increased epoxide selectivity is correlated with the presence of mixed copper oxidation states and the presence of the CuxOy species. These results support previous theoretical predictions that oxidic copper overlayers on silver play an active role in epoxidation. These results furthermore emphasize the need for in situ spectromicroscopic methods to understand the complexity of alloy catalysts

Es wurde ein Modellsystem realisiert, das mittels Elektronentransfer durch eine Metall-Isolator-Metall(MIM)-Struktur die Bildung eines CO2-Radikalanions von aus der Gasphase adsorbiertem Kohlendioxid induziert, welches anschliesend zu Oxalat weiterreagiert. Dieser reversible Prozess gestattet eine Studie der involvierten Elementarschritte auf atomarer Ebene. Die Oxalatspezies an der MIM-Grenzflache wurden mithilfe der Rastertunnelmikroskopie untersucht, chemisch mittels Infrarotspektroskopie identifiziert und ihre Bildung durch Dichtefunktionalrechnungen verifiziert.

This work reveals that the electrical conductivity σ of a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) film can be significantly increased by spin-coating multiple thin layers onto a substrate. Generally, σ can be improved by more than fourfold for multiple layers, as compared to a single thicker one. A gradual enhancement is observed for pristine PEDOT:PSS films (up to 2.10 ± 0.26 S cm–1 for five-layered films), while a plateau in σ at around 200 S cm–1 is reached after only three layers, when using a PEDOT:PSS solution with 5 vol% dimethyl sulfoxide. By contrast, only a small change in σ is observed for single layers of varying thickness. Accordingly, the thermoelectric power factor is also increased by up to 3.4 times for the multiple layers. Based on atomic force microscopy, X-ray photoelectron spectroscopy, UV–vis, and Raman spectroscopy measurements, two mechanisms are also proposed, involving an increase in percolation by inclusion of smaller grains within the existing ones, respectively, a reorganization of the PEDOT:PSS chains. These findings represent a direct strategy for enhancing the thermoelectric performance of conductive polymer films without additional reagents, while the mechanistic insights explain existing literature results.

By using a new type of lacunary tungstoselenite {Se(2)W(29)O(103)} (1), which contains a "defect" pentagonal {W(W)(4)} unit, we explored the assembly of clusters using this building block and demonstrate how this unit can give rise to gigantic nanomolecular species, using both a "one-pot" and "stepwise" synthetic assembly approach. Specifically, exploration of the one-pot synthetic parameter space lead to the discovery of {Co(2.5)(W(3.5)O(14))(SeW(9)O(33))(Se(2)W(30)O(107))} (2), {CoWO(H(2)O)(3)(Se(2)W(26)O(85))(Se(3)W(30)O(107))(2)} (3), and {Ni(2)W(2)O(2)Cl(H(2)O)(3)(Se(2)W(29)O(103)) (Se(3)W(30)O(107))(2)} (4), effectively demonstrating the potential of the {Se(2)W(29)} based building blocks, which was further extended by the isolation of a range of 3d transition metal doped tetramer family derivatives: {M(2)W(n)O(m)(H(2)O)(m)(Se(2)W(29)O(102))(4)} (M = Mn, Co, Ni or Zn, n = 2, m = 4; M = Cu, n = 3, m = 5) (5-9). To contrast the 'one-pot' approach, an optimized stepwise self-assembly investigation utilizing 1 as a precursor was performed showing that the high nuclearity clusters can condense in a more controllable way allowing the tetrameric clusters (5-8) to be synthesized with higher yield, but it was also shown that 1 can be used to construct a gigantic {W(174)} hexameric-cluster {Cu(9)Cl(3)(H(2)O)(18)(Se(2)W(29)O(102))(6)} (10). Further, 1 can also dimerize to {(Se(2)W(30)O(105))(2)} (11) by addition of extra tungstate under similar conditions. All the clusters were characterized by single-crystal X-ray crystallography, chemical analysis, infrared spectroscopy, thermogravimetric analysis, and electrospray ionization mass spectrometry, which remarkably showed that all the clusters, even the largest cluster, 10 (∼50 kD), could be observed as the intact cluster demonstrating the extraordinary potential of this approach to construct robust gigantic nanoscale polyoxotungstates.

The development of effective and precious‐metal‐free electrocatalysts for the oxygen evolution reaction (OER) represents a major bottleneck to unlock a renewable energy scenario based on water splitting technologies. Materials uniting the electrical conductivity of conjugated graphitic nanomaterials with the chemical regularity of metal‐organic‐framework (MOF) crystals are promising precursors for such electrocatalysts. Nanoscale integration of these two materials is challenging. A new synthesis route is developed that integrates 2D MOF nanocrystals and graphitic carbon nanolamellae into layered composites. The graphitic carrier contributes excellent charge–transport properties, and the 2D macromolecular MOF precursor provides a suitable shuttle for introducing highly dispersed metal species. Furthermore their direct chemical environment can be controlled via selection of organic linker. Thermal decomposition of 2D cobalt tetrafluoro benzene‐dicarboxylate MOF nanocrystals within such composites enables the stabilization of cobalt oxyhydroxyfluoride nanoparticles on the graphitic carrier, which display an extraordinary activity for the OER in alkaline media, with low onset overpotential (310 mVRHE) and current densities >104 mA cm−2 μmolCo−1 at an operating overpotential of 450 mV, alongside excellent operational stability. The wide compositional array of MOFs makes this synthesis approach versatile toward advanced (electro)catalysts and other functional materials for applications from sensing to energy storage and conversion.

By using a new type of lacunary tungstoselenite {Se2W29O103} (1), which contains a “defect” pentagonal {W(W)4} unit, we explored the assembly of clusters using this building block and demonstrate how this unit can give rise to gigantic nanomolecular species, using both a “one-pot” and “stepwise” synthetic assembly approach. Specifically, exploration of the one-pot synthetic parameter space lead to the discovery of {Co2.5(W3.5O14)(SeW9O33)(Se2W30O107)} (2), {CoWO(H2O)3(Se2W26O85)(Se3W30O107)2} (3), and {Ni2W2O2Cl(H2O)3(Se2W29O103) (Se3W30O107)2} (4), effectively demonstrating the potential of the {Se2W29} based building blocks, which was further extended by the isolation of a range of 3d transition metal doped tetramer family derivatives: {M2WnOm(H2O)m(Se2W29O102)4} (M = Mn, Co, Ni or Zn, n = 2, m = 4; M = Cu, n = 3, m = 5) (5 - 9). To contrast the ‘one-pot’ approach, an optimized stepwise self-assembly investigation utilizing 1 as a precursor was performed showing that the high nuclearity clusters can con...

A new family of TeIV-containing heteropolyoxometalate building blocks which consist of a {W3} top unit and one, two, and three layers of {TeW6} base units in [TeW9O33]8-, [Te2W15O54]10-, and [Te3W21O75]12-, respectively, is synthesized.

}; green spheres: Te; orange spheres: Pd.[*] J. Gao, Dr. J. Yan, S. Beeg, Dr. D. L. Long, Prof. L. CroninWestCHEM, School of Chemistry, The University of GlasgowUniversity Avenue, Glasgow G12 8QQ (UK)E-mail: deliang.long@glasgow.ac.uklee.cronin@glasgow.ac.ukHomepage: http://www.croninlab.com[**] We thank the EPSRC, the Chinese Scholarship Council, WestCHEM,and the University of Glasgow for supporting this work. L.C. thanksthe Wolfson Foundation & Royal Society of London for a meritaward.Supporting information for this article is available on the WWWunder http://dx.doi.org/10.1002/anie.201108428.