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The development of better catalysts is a passionate topic at the forefront of modern science, where operando techniques are necessary to identify the nature of the active sites. The surface of a solid catalyst is dynamic and dependent on the reaction environment and, therefore, the catalytic active sites may only be formed under specific reaction conditions and may not be stable either in air or under high vacuum conditions. The identification of the active sites and the understanding of their behaviour are essential information towards a rational catalyst design. One of the most powerful operando techniques for the study of active sites is near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS), which is particularly sensitive to the surface and sub-surface of solids. Here we review the use of NAP-XPS for the study of ceria-based catalysts, widely used in a large number of industrial processes due to their excellent oxygen storage capacity and well-established redox properties.

Emergent behaviors occur when simple interactions between a system's constituent elements produce properties that the individual elements do not exhibit in isolation. This article reports tunable emergent behaviors observed in domain wall (DW) populations of arrays of interconnected magnetic ring‐shaped nanowires under an applied rotating magnetic field. DWs interact stochastically at ring junctions to create mechanisms of DW population loss and gain. These combine to give a dynamic, field‐dependent equilibrium DW population that is a robust and emergent property of the array, despite highly varied local magnetic configurations. The magnetic ring arrays’ properties (e.g., non‐linear behavior, “fading memory” to changes in field, fabrication repeatability, and scalability) suggest they are an interesting candidate system for realizing reservoir computing (RC), a form of neuromorphic computing, in hardware. By way of example, simulations of ring arrays performing RC approaches 100% success in classifying spoken digits for single speakers.

The steam reforming of ethanol (ESR) has been studied by Near Ambient Pressure XPS (NAP-XPS), Extended X-ray Absorption Fine Structure (EXAFS) and X-ray Absorption Near Edge Structure (XANES) under in situ conditions in the ALBA synchrotron facility at 200-580ºC and S/C=3 over different cobalt-based catalysts that showed different catalytic performance: Co 3 [Si 2 O 5 ] 2 (OH) 2 (Co-talc), [Co 2 Mg 4 Al 2 (OH) 16 ]CO 3 •4H 2 O (Co-hydrotalcite shortened as Co-HT) calcined at 550ºC, and Co 3 O 4 (Co-spinel). Both, Co-spinel and Cotalc yield to a greater or lesser degree metallic cobalt under ESR conditions. While the Cospinel shows a complete reduction to metallic cobalt under the conditions used for the XANES measurements, more bulk-sensitive, the Co-talc sample exhibits only a partial reduction. On the other hand under the ESR conditions used with the NAP-XPS, a more surface sensitive technique, the results indicate a higher reduction degree for the Co-talc sample as compared to the Co-spinel. In contrast, the catalyst prepared from the Co-HT does not show metallic cobalt traces under the experimental conditions used with both techniques. Comparing these three cobalt-based catalysts, the stable operation exhibited by Co-HT under ESR reaction conditions is justified by the absence of metallic cobalt formation under in situ conditions, which is identified as responsible for the carbon deposition phenomena that triggers the deactivation suffered by most cobalt-based catalysts during ESR.

SynopsisThe electronic structure of water and methanol as vapours, liquids, as well as liquid mixture is determined using synchrotron-based X-ray photoemission spectroscopy on liquid μ-jets.These results together with density functional theory provide, among others, interesting insight into the hydration of these two molecules in the liquid phase mixture.Abstract The advent of liquid μ-jet setups as proposed by Faubel and Winter -in conjunction with X-ray Photoemission Spectroscopy (XPS) -has opened up a large variety of experimental possibilities in the field of atomic and molecular physics. In this study, we present first results from a synchrotron-based XPS core level and valence band electron spectroscopy study on water (10 -4 M aqueous NaCl solution) as well as a water/methanol mixture using the newly commissioned ALBA liquid μ-jet setup. The experimental results are compared with simulations from density functional theory (DFT) regarding the electronic structure of single molecules, pure molecular clusters, and mixed clusters configurations as well as previous experimental studies. We give a detailed interpretation of the core level and valence band spectra for the vapour and liquid phases of both sample systems. The resulting overall picture gives insight into the water/methanol concentrations of the vapour and liquid phases as well as into the local electronic structure of the pertinent molecular clusters under consideration, with a special emphasis on methanol as the simplest amphiphilic molecule capable of creating hydrogen bonds.