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Abstract: Hydrogen spillover is the phenomenon where a hydrogen atom, generated from the dissociative chemisorption of dihydrogen on the surface of a metal species, migrates from the metal to the catalytic support. This phenomenon is regarded as a promising avenue for hydrogen storage, yet the atomic mechanism for how the hydrogen atom can be transferred to the support has remained controversial for decades. As a result, the development of catalytic support for such a purpose is only limited to typical reducible oxide materials. Herein, by using a combination of in situ spectroscopic and imaging technique, we are able to visualize and observe the atomic pathway for which hydrogen travels via a frustrated Lewis pair that has been constructed on a nonreducible metal oxide. The interchangeable status between the hydrogen, proton, and hydride is carefully characterized and demonstrated. It is envisaged that this study has opened up new design criteria for hydrogen storage material.

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Abstract: The nature and evolution of FeNxCy moieties in Fe/C/N catalysts has been studied by analysing Fe and N environments. TEM and Fe-XAS reveal the presence of FeNx moieties and Fe3C particles in the fresh catalyst. NEXAFS reveals the presence of two groups of (Fe)NxCy ensembles, namely (Fe)Nx-pyridinic and (Fe)Nx-pyrrolic. The architecture of the FeNxCy ensembles and their evolution during the ORR has been analysed by XAS, NEXAFS, and identical locations TEM. NxCy, FeNxCy and Fe3C species are partially removed during the ORR, resulting in the formation of Fe2O3 and Fe3O4 particles with different morphologies. The process is more severe in acid electrolyte than in alkaline one. (Fe)Nx-pyrrolic moieties are the main ones in the fresh catalysts, but (Fe)Nx-pyridinic groups are more stable after the ORR. The correlation between the evolution of the ORR activity and that of the FeNxCy ensembles indicates that FeNx-pyridinic ensembles are responsible for the ORR activity.

Open Access

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Abstract: In-situ analysis of the TiO2 / water interface via NAP-XPS is demonstrated in both a lab based system (NAP-cell configuration) and synchrotron endstation (backfill configuration). Ultra-thin wetting layers (UTWL) of liquid water (~10 nm) are formed on a rutile TiO2 surface with minimal contamination present in addition to unique insight during the growth of the liquid films as indicated via NAP-XPS, in-situ sample temperature and background vapour pressure monitoring. Chemical changes at the solid / liquid interface are also demonstrated via healing of Ti3+ surface defect states. Photon depth profiling of the as grown liquid layers indicate that the formed films are ultra-thin (~10 nm) and likely to be continuous in nature. This work demonstrates a novel and flexible approach for studying the solid / liquid interface via NAP-XPS which is readily integrated with any form of NAP-XPS system, thereby making a critical interface of study available to a wide audience of researchers for use in operando electrochemical and photocatalytic research.

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Abstract: The reaction of ammonia oxidation over PtRh binary alloy has been studied with a surface science approach by operando techniques such as Near Ambient Pressure X-Ray Photoemission Spectroscopy (NAP-XPS) and Surface X-Ray Diffraction (SXRD) combined with mass spectrometry. The article will explore the surface evolution across five different oxygen to ammonia ratios in the millibar regime for two different temperatures. The presented data-set allows to link variations in the atomic structures measured by diffraction methods and surface species information from NAP-XPS to reaction products in the gas phase. We will show that NO production coincides with significant changes of the surface structure and the formation of a RhO2 surface oxide. It was also observed that the RhO2 surface oxide only fully forms when the nitrogen signal in the N1s has disappeared.

Open Access

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Abstract: The use of mechanochemistry to prepare catalytic materials is of significant interest; it offers an environmentally beneficial, solvent-free, route and produces highly complex structures of mixed amorphous and crystalline phases. This study reports on the effect of milling atmosphere, either air or argon, on mechanochemically prepared LaMnO3 and the catalytic performance towards N2O decomposition (deN2O). In this work, high energy resolution fluorescence detection (HERFD), X-ray absorption near edge structure (XANES), X-ray emission, and X-ray photoelectron spectroscopy (XPS) have been used to probe the electronic structural properties of the mechanochemically prepared materials. Moreover, in situ studies using near ambient pressure (NAP)-XPS, to follow the materials during catalysis, and high pressure energy dispersive EXAFS studies, to mimic the preparation conditions, have also been performed. The studies show that there are clear differences between the air and argon milled samples, with the most pronounced changes observed using NAP-XPS. The XPS results find increased levels of active adsorbed oxygen species, linked to the presence of surface oxide vacancies, for the sample prepared in argon. Furthermore, the argon milled LaMnO3 shows improved catalytic activity towards deN2O at lower temperatures compared to the air milled and sol–gel synthesised LaMnO3. Assessing this improved catalytic behaviour during deN2O of argon milled LaMnO3 by in situ NAP-XPS suggests increased interaction of N2O at room temperature within the O 1s region. This study further demonstrates the complexity of mechanochemically prepared materials and through careful choice of characterisation methods how their properties can be understood.