Beamline K11 DIAD: a new instrument for dual imaging and diffraction at Diamond Light Source

The Dual Imaging and Diffraction (DIAD) beamline at Diamond Light Source is a new dual-beam instrument for full-field imaging/tomography and powder diffraction. This instrument provides the user community with the capability to dynamically image 2D and 3D complex structures and perform phase identification and/or strain mapping using micro-diffraction. The aim is to enable in situ and in operando experiments that require spatially correlated results from both techniques, by providing measurements from the same specimen location quasi-simultaneously. Using an unusual optical layout, DIAD has two independent beams originating from one source that operate in the medium energy range (7-38 keV) and are combined at one sample position. Here, either radiography or tomography can be performed using monochromatic or pink beam, with a 1.4 mm × 1.2 mm field of view and a feature resolution of 1.2 µm. Micro-diffraction is possible with a variable beam size between 13 µm × 4 µm and 50 µm × 50 µm. One key functionality of the beamline is image-guided diffraction, a setup in which the micro-diffraction beam can be scanned over the complete area of the imaging field-of-view. This moving beam setup enables the collection of location-specific information about the phase composition and/or strains at any given position within the image/tomography field of view. The dual beam design allows fast switching between imaging and diffraction mode without the need of complicated and time-consuming mode switches. Real-time selection of areas of interest for diffraction measurements as well as the simultaneous collection of both imaging and diffraction data of (irreversible) in situ and in operando experiments are possible.

Past, present and future-sample environments for materials research studies in scattering and spectroscopy; a UK perspective

Small angle x-ray scattering and x-ray absorption fine structure are two techniques that have been employed at synchrotron sources ever since their inception. Over the course of the development of the techniques, the introduction of sample environments for added value experiments has grown dramatically. This article reviews past successes, current developments and an exploration of future possibilities for these two x-ray techniques with an emphasis on the developments in the United Kingdom between 1980-2020.

Monitoring the process of formation of ZnO from ZnO2usingin situcombined XRD/XAS technique

Use ofin situcombined x-ray diffraction and x-ray absorption spectroscopy for the study of the thermal decomposition of zinc peroxide to zinc oxide is reported here. Comparison of data extracted from both x-ray diffraction (XRD) and x-ray absorption spectroscopy (XAS) with thermo gravimetric analysis (TGA) enabled us to follow the nature of the conversion of ZnO₂to ZnO. A temperature range between 230 °C and 350 °C appears to show that a very poorly crystalline ZnO is formed prior to the formation of an ordered ZnO material. Both the decrease in white line intensity in the Zn K-edge XANES and resulting lower coordination numbers estimated from analysis of the Zn K-edge data of ZnO heated at 500 °C, in comparison to bulk ZnO, suggest that the ZnO produced by this method has significant defects in the system.

Following the Formation of Silver Nanoparticles Using In Situ X-ray Absorption Spectroscopy

The formation of silver and Au@Ag core@shell nanoparticles via reduction of AgNO₃ by trisodium citrate was followed using in situ X-ray absorption near-edge structure (XANES) spectroscopy and time-resolved UV-visible (UV-vis) spectroscopy. The XANES data were analyzed through linear combination fitting, and the reaction kinetics were found to be consistent with first-order behavior with respect to silver cations. For the Au@Ag nanoparticles, the UV-vis data of a lab-scale reaction showed a gradual shift in dominance between the gold- and silver-localized surface plasmon absorbance bands. Notably, throughout much of the reaction, distinct gold and silver contributions to the UV-vis spectra were observed; however, in the final product, the contributions were not distinct.

Unraveling the H2 Promotional Effect on Palladium-Catalyzed CO Oxidation Using a Combination of Temporally and Spatially Resolved Investigations

The promotional effect of H₂ on the oxidation of CO is of topical interest, and there is debate over whether this promotion is due to either thermal or chemical effects. As yet there is no definitive consensus in the literature. Combining spatially resolved mass spectrometry and X-ray absorption spectroscopy (XAS), we observe a specific environment of the active catalyst during CO oxidation, having the same specific local coordination of the Pd in both the absence and presence of H₂. In combination with Temporal Analysis of Products (TAP), performed under isothermal conditions, a mechanistic insight into the promotional effect of H₂ was found, providing clear evidence of nonthermal effects in the hydrogen-promoted oxidation of carbon monoxide. We have identified that H₂ promotes the Langmuir–Hinshelwood mechanism, and we propose this is linked to the increased interaction of O with the Pd surface in the presence of H₂. This combination of spatially resolved MS and XAS and TAP studies has provided previously unobserved insights into the nature of this promotional effect.

Solid base catalysed 5-HMF oxidation to 2,5-FDCA over Au/hydrotalcites: fact or fiction?

Nanoparticulate gold has emerged as a promising catalyst for diverse mild and efficient selective aerobic oxidations. However, the mechanism of such atom-economical transformations, and synergy with functional supports, remains poorly understood. Alkali-free Mg-Al hydrotalcites are excellent solid base catalysts for the aerobic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furan dicarboxylic acid (FDCA), but only in concert with high concentrations of metallic gold nanoparticles. In the absence of soluble base, competitive adsorption between strongly-bound HMF and reactively-formed oxidation intermediates site-blocks gold. Aqueous NaOH dramatically promotes solution phase HMF activation, liberating free gold sites able to activate the alcohol function within the metastable 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) reactive intermediate. Synergistic effects between moderate strength base sites within alkali-free hydrotalcites and high gold surface concentrations can afford highly selective and entirely heterogeneous catalysts for aqueous phase aldehyde and alcohol cascade oxidations pertinent to biomass transformation.

Time-resolved, in situ DRIFTS/EDE/MS studies on alumina-supported rhodium catalysts: effects of ceriation and zirconiation on rhodium-CO interactions

The effects of ceria and zirconia on the structure-function properties of supported rhodium catalysts (1.6 and 4 wt % Rh/γ-Al2O3) during CO exposure are described. Ceria and zirconia are introduced through two preparation methods: 1) ceria is deposited on γ-Al2O3 from [Ce(acac)3] and rhodium metal is subsequently added, and 2) through the controlled surface modification (CSM) technique, which involves the decomposition of [M(acac)x] (M=Ce, x=3; M=Zr, x=4) on Rh/γ-Al2O3. The structure-function correlations of ceria and/or zirconia-doped rhodium catalysts are investigated by diffuse reflectance infrared Fourier-transform spectroscopy/energy-dispersive extended X-ray absorption spectroscopy/mass spectrometry (DRIFTS/EDE/MS) under time-resolved, in situ conditions. CeOx and ZrO2 facilitate the protection of Rh particles against extensive oxidation in air and CO. Larger Rh core particles of ceriated and zirconiated Rh catalysts prepared by CSM are observed and compared with Rh/γ-Al2O3 samples, whereas supported Rh particles are easily disrupted by CO forming mononuclear Rh geminal dicarbonyl species. DRIFTS results indicate that, through the interaction of CO with ceriated Rh particles, a significantly larger amount of linear CO species form; this suggests the predominance of a metallic Rh phase.

Structural characterization of alumina-supported Rh catalysts: effects of ceriation and zirconiation by using metal-organic precursors

The effects of the addition of ceria and zirconia on the structural properties of supported rhodium catalysts (1.6 and 4 wt % Rh/γ-Al₂O₃) are studied. Ceria and zirconia are deposited by using two preparation methods. Method I involves the deposition of ceria on γ-Al₂O₃ from Ce(acac)₃, and the rhodium metal is subsequently added, whereas method II is based on a controlled surface reaction technique, that is, the decomposition of metal–organic M(acac)_x (in which M=Ce, x=3 and M=Zr, x=4) on Rh/γ-Al₂O₃. The structures of the prepared catalyst materials are characterized ex situ by using N₂ physisorption, transmission electron microscopy, high-angle annular dark-field scanning transmission election microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine structure spectroscopy (XAFS). All supported rhodium systems readily oxidize in air at room temperature. By using ceriated and zirconiated precursors, a larger rhodium-based metallic core fraction is obtained in comparison to the undoped rhodium catalysts, suggesting that ceria and zirconia protect the rhodium particles against extensive oxidation. XPS results indicate that after the calcination and reduction treatments, a small amount of chlorine is retained on the support of all rhodium catalysts. EXAFS analysis shows significant Rh—Cl interactions for Rh/Al₂O₃ and Rh/CeO_x/Al₂O₃ (method I) catalysts. After reaction with H₂/He in situ, for series of samples with 1.6 wt % Rh, the EXAFS first shell analysis affords a mean size of approximately 30 atoms. A broader spread is evident with a 4 wt % rhodium loading (ca. 30–110 atoms), with the incorporation of zirconium providing the largest particle sizes.

Energy dispersive XAFS: characterization of electronically excited states of copper(I) complexes

Energy dispersive X-ray absorption spectroscopy (ED-XAS), in which the whole XAS spectrum is acquired simultaneously, has been applied to reduce the real-time for acquisition of spectra of photoinduced excited states by using a germanium microstrip detector gated around one X-ray bunch of the ESRF (100 ps). Cu K-edge XAS was used to investigate the MLCT states of [Cu(dmp)₂]⁺ (dmp =2,9-dimethyl-1,10-phenanthroline) and [Cu(dbtmp)₂]⁺ (dbtmp =2,9-di-n-butyl-3,4,7,8-tetramethyl-1,10-phenanthroline) with the excited states created by excitation at 450 nm (10 Hz). The decay of the longer lived complex with bulky ligands, was monitored for up to 100 ns. DFT calculations of the longer lived MLCT excited state of [Cu(dbp)₂]⁺ (dbp =2,9-di-n-butyl-1,10-phenanthroline) with the bulkier diimine ligands, indicated that the excited state behaves as a Jahn–Teller distorted Cu(II) site, with the interligand dihedral angle changing from 83 to 60° as the tetrahedral coordination geometry flattens and a reduction in the Cu–N distance of 0.03 Å.

I18--the microfocus spectroscopy beamline at the Diamond Light Source

The design and performance of the microfocus spectroscopy beamline at the Diamond Light Source are described. The beamline is based on a 27 mm-period undulator to give an operable energy range between 2 and 20.7 keV, enabling it to cover the K-edges of the elements from P to Mo and the L(3)-edges from Sr to Pu. Micro-X-ray fluorescence, micro-EXAFS and micro-X-ray diffraction have all been achieved on the beamline with a spot size of approximately 3 microm. The principal optical elements of the beamline consist of a toroid mirror, a liquid-nitrogen-cooled double-crystal monochromator and a pair of bimorph Kirkpatrick-Baez mirrors. The performance of the optics is compared with theoretical values and a few of the early experimental results are summarized.

Identification of the surface species responsible for N2O formation from the chemisorption of NO on Rh/alumina

Energy dispersive EXAFS (EDE) and diffuse reflectance infrared spectroscopy (DRIFTS) are combined synchronously at high time resolution (17 Hz) to probe how NO(g) reacts with gamma-Al(2)O(3) supported, metallic Rh nanoparticles of an average 11 A diameter; a bent nitrosyl species is considered to be the key to the formation of N(2)O.

Rapid Monitoring of the Nature and Interconversion of Supported Catalyst Phases and of Their Influence upon Performance: CO Oxidation to CO2 by γ-Al2O3 Supported Rh Catalysts

Spatially and temporally resolved energy-dispersive EXAFS (EDE) has been utilised in situ to study supported Rh nanoparticles during CO oxidation by O2 under plug-flow conditions. Three distinct phases of Rh supported upon Al2O3 were identified by using EDE at the Rh K-edge during CO oxidation. Their presence and interconversion are related to the efficiency of the catalysts in oxidising CO to CO2. A metallic phase is only found at higher temperatures (>450 K) and CO fractions (CO/O2 > 1); an oxidic phase resembling Rh2O3 dominates the active catalyst under oxygen-rich conditions. Below about 573 K, and in CO-rich environments, high proportions of isolated Rh(I)(CO)2 species are found to co-exist with metallic Rh nanoparticles. Alongside these discrete situations a large proportion of the active phase space comprises small Rh cores surrounded by layers of active oxide. Confinement of Rh to nanoscale domains induces structural lability that influences catalytic behaviour. For CO oxidation over Rh/Al2O3 there are two redox phase equilibria alongside the chemistry of CO and O adsorbed upon extended Rh surfaces.

A wide-aperture dynamically focusing sagittal monochromator for X-ray spectroscopy and diffraction

A scanning dynamically focusing sagittal X-ray monochromator accepting 7 mrad of the fan from a 6 T wiggler is in routine use on beamline 16.5 (ultra-dilute spectroscopy) of the SRS at CCLRC Daresbury Laboratory, UK. The energy range covered is 7-27 keV, with a horizontal spot size of <1.1 mm FWHM. Measured monochromatic flux from a Si 220 crystal pair is 1 x 10(11) photons s(-1) (100 mA)(-1) at 9 keV. This level of flux, usually associated with an insertion device on a third-generation source, permits collection of EXAFS data on concentrations at or below 10 ppm.

The new materials processing beamline at the SRS Daresbury, MPW6.2

A new beamline (MPW6.2) has been designed and built for the study of materials during processing where three synchrotron techniques, SAXS, WAXS and XAS, are available simultaneously. It has been demonstrated that Rietveld refinable data can be collected from silicon SRM 640b over a 60 degrees range in a time scale of 1 s. The data have been refined to a chi(2) of 2.4, the peaks fitting best to a Pearson VII function or with fundamental parameters. The peak halfwidths have been found to be approximately constant at 0.06 degrees over a 120 degrees angular range indicating that the instrumental resolution function has matched its design specification. A quantitative comparison of data sets collected on the same isotactic polypropylene system on MPW6.2 and DUBBLE at the ESRF shows a 17% improvement in angular resolution and a 1.8 improvement in peak-to-background ratio with the RAPID2 system; the ESRF data vary more smoothly across detector channels. The time-dependent wide-angle XRD was tested by comparing a hydration reaction of gypsum-bassanite-anhydrite with energy-dispersive data collected on the same system on the same time scale. Three sample data sets from the reaction were selected for analysis and gave an average chi(2) of 3.8. The Rietveld-refined lattice parameters are a good match with published values and the corresponding errors show a mean value of 3.3 x 10(-4). The data have also been analysed by the Pawley decomposition phase-modelling technique demonstrating the ability of the station to quickly and accurately identify new phases. The combined SAXS/WAXS capability of the station was tested with the crystallization and spinodal decomposition of a very dilute polymer system. Our measurements show that the crystallization of a high-density co-polymer (E76B38) as low as 0.5% by weight can be observed in solution in hexane. The WAXS and SAXS data sets were collected on the same time scale. The SAXS detector was calibrated using a collagen sample that gave 30 orders of diffraction in 1 s of data collection. The combined XRD and XAS measurement capability of the station was tested by observing the collapse and re-crystallization of zinc-exchanged zeolite A (zeolite Zn/Na-A). Previous studies of this material on station 9.3 at the SRS were compared with those from the new station. A time improvement of 38 was observed with better quality counting statistics. The improved angular resolution from the WAXS detector enabled new peaks to be identified.

Synchronous, time resolved, diffuse reflectance FT-IR, energy dispersive EXAFS (EDE) and mass spectrometric investigation of the behaviour of Rh catalysts during NO reduction by CO

Synchronous, time resolved, infra-red, XAFS, and mass spectroscopies are simultaneously applied in situ to the investigation of the dynamic behaviour of Rh/Al2O3 catalysts during NO reduction by CO; NO conversion, and its kinetic character are closely correlated to the conversion of Rh(I)(predominantly RhI(CO)2) to Rh(0).

Contrasting dynamic responses of supported Rh nanoparticles to H2S and SO2 and subsequent poisoning of NO reduction by H2

H2S induces rapid sulfidation of the Rh nanoparticles at room temperature and completely poisons NO reduction by H2; SO2 elicits an equally rapid but subtle modification of nanoparticle structure but has little effect upon NO reduction at 523 K.

Application of stopped flow techniques and energy dispersive EXAFS for investigation of the reactions of transition metal complexes in solution: activation of nickel beta-diketonates to form homogeneous catalysts, electron transfer reactions involving iron(III) and oxidative addition to iridium(I)

Stopped-flow techniques of rapid mixing have been combined with energy dispersive X-ray absorption spectroscopy to monitor the reaction of Ni(dpm)2 [dpm = Bu1C(O)CHC(O)Bu1] by aluminium alkyls (AlEt2X, X = OEt and Et) to form the active species for the catalytic di- and tri-merisation of hex-1-ene. Acquisition times down to ca. 30 ms were achieved on Station 9.3 of the SRS using a photodiode array detector. The EXAFS features of the resulting solution complexes are of the form [Ni(O-O)R)(alkene)]. In the presence of PPh3, [Ni(O-O)(R)(PPh3) appears to be the redominant type of species. The reduction of aqueous Fe(III) by hydroquinone was investigated on ID24 at the ESRF by Fe K-edge energy dispersive EXAFS with a CCD camera as detector, spectra were obtained in 1 ms or longer. No intermediate inner sphere complex was detected prior to the formation of aqueous Fe(II). Finally the oxidative addition of CH3SO3CF3 to [IrI2(CO)2]- was monitored on Station 9.3 with a silicon microstrip detector. A single acquisition of 400 micros was feasible, with spectra recorded in multiples of 1.2 ms. In that time, the first stage of the reaction had been completed, with a slower stage thereafter. The results are consistent with the two-stage ionic oxidative addition mechanism.

Bringing time resolution to EXAFS: recent developments and application to chemical systems

The currently available methodologies for applying extended X-ray absorption fine structure (EXAFS) spectroscopy to the interrogation of dynamic chemical systems are critically reviewed. Particular regard is paid to applicable experimental timescales, extraction of structural information, sample presentation, and simultaneous pairing with complementary techniques; the potential for further developments in this area is also assessed.

Susceptibility of a heterogeneous catalyst, Rh/gamma-alumina, to rapid structural change by exposure to NO

Metal particles in a Rh/gamma-Al2O3 catalyst of differing particle size are oxidised by NO/He within 5 seconds at 313 K; rapid, highly exothermic dissociative chemisorption of NO is the initial step.

Effect of Si(IV) substitution on the stability of microporous ZnAPSO-44 solid acid catalysts: a combined XAS/XRD study

The combined XAS/XRD technique has been used to investigate the stability of the microporous structure during calcination process for a series of ZnAPSO-44 materials. Incorporation of large amounts of Zn is found to produce materials that are unstable upon removal of the structure directing organic template molecule. However, simultaneous incorporation of Si is found to increase the thermal stability of the materials, yielding catalysts that are well suited for acid catalysed reactions.

In situ EXAFS, X-ray diffraction and photoluminescence for high-pressure studies

A new facility for simultaneous extended X-ray absorption of fine structure (EXAFS), X-ray diffraction and photoluminescence measurements under high pressures has been developed for use on station 9.3 at the Daresbury Laboratory Synchrotron Radiation Source. This high-pressure facility can be used at any suitable beamline at a synchrotron source. Full remote operation of the rig allows simultaneous collection of optical and structural data while varying the pressure. The set-up is very flexible and can be tailored for a particular experiment, such as time- or temperature-dependent measurements. A new approach to the collection of high-pressure EXAFS data is also presented. The approach significantly shortens the experimental times and allows a dramatic increase in the quality of EXAFS data collected. It also opens up the possibility for EXAFS data collection at any pressure which can be generated using a diamond cell. The high quality of data collected is demonstrated with a GaN case study. Particular attention will be paid to the use of energy-dispersive EXAFS and quick-scanning EXAFS techniques under pressure.

Initial data from the 30-element ORTEC HPGe detector array and the XSPRESS pulse-processing electronics at the SRS, Daresbury Laboratory

Following the completion of the collaborative project between CLRC Daresbury Laboratory and EG&G ORTEC to develop the world's first 30-element HPGe detector for fluorescence XAFS, it has now been tested and commissioned at the SRS. The system was commissioned with the XSPRESS digital pulse-processing electronics and this has demonstrated processed count rates in excess of 10 MHz. Initial data have been recorded and are presented.