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.

Monitoring the Formation and Reactivity of Organometallic Alkane and Fluoroalkane Complexes with Silanes and Xe Using Time-Resolved X-ray Absorption Fine Structure Spectroscopy.

Complexes with weakly coordinating ligands are often formed in chemical reactions and can play key roles in determining the reactivity, particularly in catalytic reactions. Using time-resolved X-ray absorption fine structure (XAFS) spectroscopy in combination with time-resolved IR (TRIR) spectroscopy and tungsten hexacarbonyl, W(CO)6, we are able to structurally characterize the formation of an organometallic alkane complex, determine the W-C distances, and monitor the reactivity with silane to form an organometallic silane complex. Experiments in perfluorosolvents doped with xenon afford initially the corresponding solvated complex, which is sufficiently reactive in the presence of Xe that we can then observe the coordination of Xe to the metal center, providing a unique insight into the metal-xenon bonding. These results offer a step toward elucidating the structure, bonding, and chemical reactivity of transient species by X-ray absorption spectroscopy, which has sensitivity to small structural changes. The XAFS results indicate that the bond lengths of metal-alkane (W-H-C) bond in W(CO)5(heptane) as 3.07 (±0.06) Å, which is longer than the calculated W-C (2.86 Å) for binding of the primary C-H, but shorter than the calculated W-C (3.12 Å) for the secondary C-H. A statistical average of the calculated W-C alkane bond lengths is 3.02 Å, and comparison of this value indicates that the value derived from the XAFS measurements is averaged over coordination of all C-H bonds consistent with alkane chain walking. Photolysis of W(CO)6 in the presence of HSiBu3 allows the conversion of W(CO)5(heptane) to W(CO)5(HSiBu3) with an estimated W-Si distance of 3.20 (±0.03) Å. Time-resolved TRIR and XAFS experiments following photolysis of W(CO)6 in perfluoromethylcyclohexane (PFMCH) allows the characterization of W(CO)5(PFMCH) with a W-F distance of 2.65 (±0.06) Å, and doping PFMCH with Xe allows the characterization of W(CO)5Xe with a W-Xe bond length of 3.10 (±0.02) Å.

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/CeOx /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.

Isomorphous substitution in a flexible metal-organic framework: mixed-metal, mixed-valent MIL-53 type materials.

Mixed-metal iron-vanadium analogues of the 1,4-benzenedicarboxylate (BDC) metal-organic framework MIL-53 have been synthesized solvothermally in N,N'-dimethylformamide (DMF) from metal chlorides using initial Fe:V ratios of 2:1 and 1:1. At 200 °C and short reaction time (1 h), materials (Fe,V)(II/III)BDC(DMF(1-x)F(x)) crystallize directly, whereas the use of longer reaction times (3 days) at 170 °C yields phases of composition [(Fe,V)(III)0.5(Fe,V)0.5(II)(BDC)(OH,F)](0.5-)·0.5DMA(+) (DMA = dimethylammonium). The identity of the materials is confirmed using high-resolution powder X-ray diffraction, with refined unit cell parameters compared to known pure iron analogues of the same phases. The oxidation states of iron and vanadium in all samples are verified using X-ray absorption near edge structure (XANES) spectroscopy at the metal K-edges. This shows that in the two sets of materials each of the vanadium and the iron centers are present in both +2 and +3 oxidation states. The local environment and oxidation state of iron is confirmed by (57)Fe Mössbauer spectrometry. Infrared and Raman spectroscopies as a function of temperature allowed the conditions for removal of extra-framework species to be identified, and the evolution of µ2-hydroxyls to be monitored. Thus calcination of the mixed-valent, mixed-metal phases [(Fe,V)(III)0.5(Fe,V)0.5(II)(BDC)(OH,F)](0.5-)·0.5DMA(+) yields single-phase MIL-53-type materials, (Fe,V)(III)(BDC)(OH,F). The iron-rich, mixed-metal MIL-53 shows structural flexibility that is distinct from either the pure Fe material or the pure V material, with a thermally induced pore opening upon heating that is reversible upon cooling. In contrast, the material with a Fe:V content of 1:1 shows an irreversible expansion upon heating, akin to the pure vanadium analogue, suggesting the presence of some domains of vanadium-rich regions that can be permanently oxidized to V(IV).

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.

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.

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.

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.

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.

Sc(III) complexes with neutral N3- and SNS-donor ligands--a spectroscopic study of the activation of ethene polymerisation catalysts.

Scandium trichloride complexes with tridentate N(3)- and S(2)N-donor ligands (L(3)) have been synthesised and characterised by IR, (1)H, (13)C{(1)H} and (45)Sc NMR spectroscopy, microanalysis, and solid state and solution XAFS spectroscopy. Catalytic testing of a subset of these complexes with ethene has been undertaken in chlorobenzene with MMAO-3A and PMAO-IP at 60 °C and 40 bar ethene, giving low activity ethene polymerisation. The reactions of these complexes with MeLi and AlMe(3) were studied by (1)H, (13)C{(1)H}, (27)Al and (45)Sc NMR spectroscopy and in situ via Sc K-edge XAFS spectroscopy. Three or four mol. equivalents of MeLi react with [ScCl(3)(Me(3)-tacn)] in THF solution to form [ScMe(3)(Me(3)-tacn)] cleanly, while complexes of type [ScCl(3)(R-SNS)] {R-SNS = HN(CH(2)CH(2)SC(10)H(21))(2)} form two different species proposed to be [ScMe(3)(R-SN(Li)S)] and [ScMe(2)(R-SN(-)S)]. In contrast, in situ(45)Sc NMR and Sc K-edge XAFS spectroscopic studies of the reaction of [ScCl(3)(Me(3)-tacn)] with 10 mol. equivalents of AlMe(3) strongly suggest that alkylation at the Sc(III) centre does not occur, instead retaining the Cl(3)N(3) coordination environment and most likely forming Sc-Cl-AlMe(3) bridging interactions. Similar studies on [ScCl(3)(decyl-SNS)] with 10 mol. equivalents of AlMe(3) are also consistent with this, indicating that alkylation at the Sc centre does not occur except in the presence of co-catalyst [Ph(3)C][Al{OC(CF(3))(3)}(4)] and the α-alkene, hex-1-ene.

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.

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 gamma-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.