X-ray spectroscopy for chemistry in the 2-4 keV energy regime at the XMaS beamline: ionic liquids, Rh and Pd catalysts in gas and liquid environments, and Cl contamination in γ-Al2O3

In situ K-edge X-ray absorption spectroscopy of the ligand environment of single-site Au/C catalysts during acetylene hydrochlorination

The replacement of HgCl₂/C with Au/C as a catalyst for acetylene hydrochlorination represents a significant reduction in the environmental impact of this industrial process. Under reaction conditions atomically dispersed cationic Au species are the catalytic active site, representing a large-scale application of heterogeneous single-site catalysts. While the metal nuclearity and oxidation state under operating conditions has been investigated in catalysts prepared from aqua regia and thiosulphate, limited studies have focused on the ligand environment surrounding the metal centre. We now report K-edge soft X-ray absorption spectroscopy of the Cl and S ligand species used to stabilise these isolated cationic Au centres in the harsh reaction conditions. We demonstrate the presence of three distinct Cl species in the materials; inorganic Cl^-, Au-Cl, and C-Cl and how these species evolve during reaction. Direct evidence of Au-S interactions is confirmed in catalysts prepared using thiosulfate precursors which show high stability towards reduction to inactive metal nanoparticles. This stability was clear during gas switching experiments, where exposure to C₂H₂ alone did not dramatically alter the Au electronic structure and consequently did not deactivate the thiosulfate catalyst.

TEXS: in-vacuum tender X-ray emission spectrometer with 11 Johansson crystal analyzers

The design and first results of a large-solid-angle X-ray emission spectrometer that is optimized for energies between 1.5 keV and 5.5 keV are presented. The spectrometer is based on an array of 11 cylindrically bent Johansson crystal analyzers arranged in a non-dispersive Rowland circle geometry. The smallest achievable energy bandwidth is smaller than the core hole lifetime broadening of the absorption edges in this energy range. Energy scanning is achieved using an innovative design, maintaining the Rowland circle conditions for all crystals with only four motor motions. The entire spectrometer is encased in a high-vacuum chamber that allocates a liquid helium cryostat and provides sufficient space for in situ cells and operando catalysis reactors.

Soft XAS as an in situ technique for the study of heterogeneous catalysts

Soft X-ray absorption in situ studies of heterogeneous catalysts have been applied to areas such as copper methanol oxidation catalysts and cobalt Fischer-Tropsch type catalysts over a period of around two decades. The technique has the potential to offer several advantages for studying heterogeneous catalysts against hard X-ray XAS in: the systems that can be studied (includes elements such as C, N, O), the potential for surface sensitivity (crucial for catalysts, where reactions occur at surfaces) and the information content of the resulting spectra. Nevertheless, it is technically challenging and the necessary hardware has only been developed and evolved in a few specific groups worldwide. This perspective will introduce the technique in the context of other competing spectroscopies, summarise the development of hardware and the challenges that have been overcome in experimental terms, along with the outcome and impact on different fields within catalysis. Additionally, anticipated future trends and directions will be discussed.

Solubility, speciation and local environment of chlorine in zirconolite glass–ceramics for the immobilisation of plutonium residues

Understanding chlorine speciation and incorporation in glass ceramic wasteforms underpins future treatment of contaminated plutonium residues.

In situ study of metal leaching from Pd/Al2O3 induced by K2CO3

In situ quick extended X-ray absorption fine structure spectroscopy (QEXAFS) was employed to study temporally and spatially the leaching of Pd from a heterogeneous catalyst caused by K₂CO₃.

XMaS @ the ESRF

This paper describes the motivation for the design and construction of a beamline at the European Synchrotron Radiation Facility (ESRF) for the use of UK material scientists. Although originally focused on the study of magnetic materials, the beamline has been running for 20 years and currently supports a very broad range of science as evidenced by the research topics highlighted in this article. We describe how the beamline will adapt to align with the ESRF's upgrade to a diffraction limited storage ring. This article is part of the theme issue 'Fifty years of synchrotron science: achievements and opportunities'.

Atomic charges of sulfur in ionic liquids: experiments and calculations

A wide variety of experimental and computational methods are used to probe sulfur atomic charges in ionic liquids.

NEXAFS spectroscopy of ionic liquids: experiments versus calculations

Experimental N 1s and S 1s NEXAFS spectra are compared to TD-DFT calculated spectra for 12 ionic liquids.