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The extent of reduction of unsupported iron-based high-temperature water-gas shift catalysts with small (

In order to more deeply understand the mechanisms of catalytic reactions, improved methods are needed to monitor changes that occur in the electronic, structural, and chemical properties of catalytic systems under the conditions in which they work. We describe here a microreactor-based approach that integrates the capabilities of advanced X-ray, electron, optical, and gas-phase compositional analysis techniques under operando conditions. For several exemplary catalytic systems, we demonstrate how this approach enables the characterization of three of the major factors that contribute to structure–property correlations in heterogeneous catalysis. Specifically, we describe how this approach can be used to better understand the atomic structure and elemental composition of nanocatalysts, the physiochemical properties of the support and catalyst/support interfaces, and the gas- and surface-phase chemistry that occurs under operando conditions. We highlight the generality of the approach, as well as opportunities for future developments.

A low-cost optical feedback system using dynamic mirrors has been developed at the NSLS for stabilizing the position and direction of an infrared synchrotron beam against thermal drift and mechanical noise. The system design has some unique features that potentially simplify installation into an existing infrared beamline. We describe the system and its features along with some performance results.

Conductive metal sulfides are promising multi-functional additives for future lithium-sulfur (Li-S) batteries. These can increase the sulfur cathode’s electrical conductivity to improve the battery’s power capability, as well as contribute to the overall cell-discharge capacity. This multi-functional electrode design showed initial promise; however, complicated interactions at the system level are accompanied by some detrimental side effects. The metal sulfide additives with a chemical conversion as the reaction mechanism, e.g., CuS and FeS2, can increase the theoretical capacity of the Li-S system. However, these additives may cause undesired parasitic reactions, such as the dissolution of the additive in the electrolyte. Studying such complex reactions presents a challenge because it requires experimental methods that can track the chemical and structural evolution of the system during an electrochemical process. To address the fundamental mechanisms in these systems, we employed an operando multimodal x-ray characterization approach to study the structural and chemical evolution of the metal sulfide—utilizing powder diffraction and fluorescence imaging to resolve the former and absorption spectroscopy the latter—during lithiation and de-lithiation of a Li-S battery with CuS as the multi-functional cathode additive. The resulting elucidation of the structural and chemical evolution of the system leads to a new description of the reaction mechanism.

Realization of the hydrogen economy relies on effective hydrogen production, storage, and utilization. The slow kinetics of hydrogen evolution and oxidation reaction (HER/HOR) in alkaline media limits many practical applications involving hydrogen generation and utilization, and how to overcome this fundamental limitation remains debatable. Here we present a kinetic study of the HOR on representative catalytic systems in alkaline media. Electrochemical measurements show that the HOR rate of Pt-Ru/C and Ru/C systems is decoupled to their hydrogen binding energy (HBE), challenging the current prevailing HBE mechanism. The alternative bifunctional mechanism is verified by combined electrochemical and in situ spectroscopic data, which provide convincing evidence for the presence of hydroxy groups on surface Ru sites in the HOR potential region and its key role in promoting the rate-determining Volmer step. The conclusion presents important references for design and selection of HOR catalysts.

As promising high-capacity cathode materials for Na-ion batteries, O3-type Na-based metal oxides always suffer from their poor air stability originating from the spontaneous extraction of Na and oxidation of transition metals when exposed to air. Herein, a combined structure modulation is proposed to tackle concurrently the two handicaps via reducing Na layers spacing and simultaneously increasing valence state of transition metals. Guided by density functional theory calculations, we demonstrate such a modulation can be subtly realized through cosubstitution of one kind of heteroatom with comparable electronegativity and another one with substantially different Fermi level, by adjusting the structure of NaNi0.5Mn0.5O2 via Cu/Ti codoping. The as-obtained NaNi0.45Cu0.05Mn0.4Ti0.1O2 exhibits an increase of 20 times in stable air-exposure period and 9 times in capacity retention after 500 cycles, and even retains its structure and capacity after being soaked in water. Such a simple and effective structure mo...

The conversion of methane into alcohols under moderate reaction conditions is a promising technology for converting stranded methane reserves into liquids that can be transported in pipelines and upgraded to value-added chemicals. We demonstrate that a catalyst consisting of small nickel oxide clusters supported on ceria-zirconia (NiO/CZ) can convert methane to methanol and ethanol in a single, steady-state process at 723 K using O2 as an abundantly available oxidant. The presence of steam is required to obtain alcohols rather than CO2 as the product of catalytic combustion. The unusual activity of this catalyst is attributed to the synergy between the small Lewis acidic NiO clusters and the redox-active CZ support, which also stabilizes the small NiO clusters.

Ruthenium nanoparticles were immobilized onto an acidic supported ionic liquid phase (RuNPs@SILP) in the development of bifunctional catalysts for the selective deoxygenation of biomass substrates. RuNPs@SILPs possessed high catalytic activities, selectivities and recyclabilities in the hydrogenolytic deoxygenation and ring opening of C8- and C9-substrates derived from furfural or 5-hydroxymethylfurfural and acetone. Tailoring the acidity of the SILP through the ionic liquid loading provided a molecular parameter by which the catalytic activity and selectivity of the RuNPs@SILPs were controlled to provide a flexible catalyst system toward the formation of different classes of value-added products: cyclic ethers, primary alcohols or aliphatic ethers.

The production of value-added chemicals and fuels from CO2 and water by highly efficient, selective, robust electrocatalytic materials is of vital interest to address the energy challenges. In this work, we report a hierarchical CuO-derived inverse opal (CuO-HIO) electrocatalyst which demonstrated impressive CO selectivity and negligible H2 evolution at high current densities (achieved ~35 mA cm-2 at -1.2 V vs. RHE). Such a three-dimensional interconnected porous network with voids about 200 nm surprisingly exhibited a Faradaic efficiency (FE) of 72.5% for CO production at -0.6 V vs. RHE and was very stable during 24-hour CO2 electrolysis. The in situ Cu K-edge XANES and Fourier transformed EXAFS spectra dynamically revealed the direct transformation of Cu2+ to Cu0 species within few minutes at -0.6 V vs. RHE and CuO was entirely reduced to metallic copper after 60 min. Such an observation was well consistent with the in situ time-resolved XRD patterns which illustrated the gradual emergence of (111), (200), (220), (311), and (222) diffractions of cubic copper under the working condition. CO2-to-CO outperformance of CuO-HIO catalyst over typical oxidized copper catalysts could be ascribed to (i) the mass transport limitation and local pH effect induced by unique hierarchical morphology, (ii) highly roughened surface, and (iii) in situ reduction of Cu2+ to stabilized metallic Cu active sites during the CO2 electrolysis. Our findings may open an opportunity for rational design of promising, high-performance, less expensive electrocatalysts for renewable fuel production from fossil fuel-generated CO2 emission.

NH3 synthesis by the electrocatalytic N2 reduction reaction (NRR) under ambient conditions is regarded as an appealing alternative to the industrial method that requires high temperature and pressure. Finding a material that can efficiently catalyze electrochemical N2 fixation at ambient condition is a subject of considerable current interest. Atomically dispersed catalysts with mononuclear metal complexes or single metal atoms anchored on supports would be a promising candidate, because of their maximum atom efficiency, unique catalytic performances, and the similarity of the metal coordination environment to the ligand fields in molecular catalysts. A series of cost-effective and optimized atomically-dispersed eletrocatalysts for NRR will be reported. Our results show that the catalysts are featured with high density of single metal atoms supported on hierarchically porous carbon frameworks. They exhibited remarkable selectivity of NH3 formation and high NH3 yield rate at low applied potentials at room temperature. Moreover, the catalysts show negligible activity decay in an NRR electrolysis as long as 50,000 s. On the basis of our results and the previously reported work, a possible mechanism for NRR on the catalyst will be proposed to provide a fundamental insight into the high-efficiency NRR.

Ethanol is one of the most promising alternative fuels for fuel cells (FC). It is a renewable resource which can be produced on a large scale from biomass originating from agriculture, forestry and urban residues. The energy density of ethanol is as high as 8.01 kWh/kg, which is comparable to that of gasoline. Ethanol is easy to store, transfer and refuel owing to its non-toxicity and high boiling point in comparison with methanol and ammonia. [1] However, the sluggish kinetics and low energy efficiency for ethanol oxidation reaction (EOR) hinder the application of direct ethanol fuel cells (DEFCs). To address this issue, great effort has been made focusing on catalysts discovery as well as reaction mechanism understanding. [2] Here we report a systematic study on Pt-Ir modified Au/C electrocatalysts for efficient ethanol oxidation in alkaline media. In-situ electrochemical Infrared reflection absorption spectra (EC-IRRAS) reveals a high selectivity toward full oxidization to carbonate at low potentials, resulting in a high energy conversion efficiency. EC-IRRAS also indicate that the C-C bond splits upon ethanol interaction with the surface of PtIrAu/C ternary catalyst. More detailed discussion on this topic will be presented at the meeting. Acknowledgements This manuscript has been authored by employees of Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the U.S. Department of Energy. The publisher by accepting the manuscript for publication acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. [1] Liang An, Tianshou Zhao, Yinshi Li, Carbon-neutral sustainable energy technology: direct ethanol fuel cells. Renewable and Sustainable Energy Reviews 2015, 50: 1462- 1468 [2] Alexey Serov, Iryna V. Zenyuk, Christopher G Arges, Marian Chatenet. Hot topics in alkaline exchange membrane fuel cells. Journal of Power Sources 2018, 375: 149- 157

Since the first report of the inserting reaction of alkali metals in layered dichalcogenides in 1959, titanium disulfide (TiS2) has been widely studied as a model material of intercalation host compound in energy storage for Li-ion batteries. Due to its high electric conductivity, fast rate capability, good cycling performance and natural abundance, TiS2 electrode also became a promising candidate for the low-cost Na-ion battery system. However, the differences regarding the detailed chemical and structural evolutions and reaction mechanism of TiS2 in Li-ion and Na-ion batteries are not yet well understood. In this work, the chemical and structural evolutions of TiS2 in both Li-ion and Na-ion batteries are investigated via operando synchrotron absorption spectroscopy (XAS) at both the sulfur and titanium K-edges using complementary hard x-rays and tender x-rays at the National Synchrotron Light Source II. By combining X-ray diffraction and operando XAS with the Multivariate Curve Resolution - Alternating Least Squares (MCR-ALS) method, we reveal the chemical speciation during the electrochemical cycling. Our study also sheds light on the reaction mechanism of Na-TiS2, which is compared with that of the Li-TiS2 system. ACKNOWLEDGMENT We thank DOE Office of Energy Efficiency and Renewable Energy under the Advanced Battery Materials Research (BMR) program, Contract No. DE-SC0012704; we thank ISS, TES, and XPD beamlines of NSLS-II, supported by DOE Office of Science. This research used resources of the Center for Functional Nanomaterials, which is a U.S. DOE Office of Science Facility, at Brookhaven National Laboratory under Contract No. DE-SC0012704. Funding was supported by Stony Brook University and Brookhaven National Laboratory. Figure: An illustration of the structural and chemical evolutions during sodiaiton observed by operando XAS and ex situ XPD approaches. Figure 1

The biogeochemical cycle of Fe is intricately linked with that of organic matter. Cysteine represents an organic molecule with functionalities (O, S, N functional groups) and a C backbone that may mimic the functional groups present in organic matter from terrestrial and aquatic environments. In the present study we explore the redox speciation and coordination environment of Fe and the roles of the various ligand atoms of cysteine (C, N, S) in iron-organic redox coupling and transformations. The changes in oxidation state of Fe, C, N, and S in laboratory-synthesized Fe(II)–cysteine (synthesized from ferrous sulfate) and Fe(III)–cysteine (synthesized from ferric nitrate) complexes are monitored as a function of time using synchrotron X-ray absorption spectroscopy (Fe L2,3-edge XANES; C, N and S K-edge XANES; Fe K-edge EXAFS) and theoretical multiplet calculations using the program CTM4XAS (Charge Transfer Multiplet for X-ray Absorption Spectroscopy). CTM4XAS calculations show that 80% of the total Fe in both the Fe(II)–cysteine and the Fe(III)–cysteine complexes is present as Fe2+ initially (t = 0), thus indicating preservation of Fe(II) in Fe(II)–cysteine and reduction of Fe(III) in Fe(III)–cysteine at initial conditions, the latter caused by an internal electron transfer reaction from S of –SH on the cysteine molecule. After 12 months, however, ∼60% of the total Fe is present as Fe3+ in the Fe(II)–cysteine complex whereas ∼67% of the total Fe is present as Fe2+ in the Fe(III)–cysteine complex. The fact that a larger proportion of the Fe in the Fe(III)–cysteine complex remained reduced after 12 months than that in the Fe(II)–cysteine complex suggests that the reduced Fe in Fe(III)–cysteine after 12 months is further stabilized via preferential binding with the donor atoms of cysteine. Stabilization via preferential binding is supported by a coordination environment that changed from tetrahedral Fe2+ binding to S at a distance of 2.3 A at t = 0 for both Fe(II,III)–cysteine complexes, to Fe3+ in an octahedral coordination with O/N atoms at a distance of 2.05 A (most prevalent in Fe(II)–cysteine) and Fe2+ in tetrahedral coordination with S/O/N atoms at an average distance of 2.15 A (most prevalent in Fe(III)–cysteine) at t = 12 months. Redox changes in the –NH2 and –SH groups of cysteine accompanied the Fe redox changes thus reflecting the true potential of cysteine as a redox ligand. Our studies of the Fe(II,III)–cysteine complexes add valuable information to the existing literature on the redox chemistry of Fe–cysteine systems by shedding light on the electron exchange pathways that may occur within the complexes and by providing a detailed depiction of the iron-ligand structure and coordination. The presence and persistence of Fe(II) or Fe(III) in complexes with soluble organics have implications for Fe biological availability and Fe mobility and transport in terrestrial as well as in aquatic environments.

We present an in situ small- and wide-angle X-ray scattering (SAXS/WAXS) and quick-scanning extended X-ray absorption fine-structure (QEXAFS) spectroscopy study on the crystallization of the metal–organic framework ZIF-7. In combination with DFT calculations, the self-assembly and growth of ZIF-7 microrods together with the chemical function of the crystal growth modulator (diethylamine) are revealed at all relevant length scales, from the atomic to the full crystal size.

The structural and compositional changes of the partially reduced iron oxide Fe2O3 and 3% chromium oxide-modified iron oxide (3% Cr2O3/Fe2O3) catalysts before, during, and after the water gas shift (WGS) reaction are reported. The measurements were performed by collecting X-ray absorption fine structure, X-ray diffraction, and Raman spectroscopy data on the catalysts and the mass spectrometry data of reactants and products, all done in a single experiment. These materials demonstrated marked structural disorder and compositional heterogeneity that are peaked in their catalytically active states. The main findings revealed in the result of combining multiple techniques include the role of Cr in stabilizing the low-temperature γ-Fe2O3 phase, the nature of the disordered phase in the active state of the catalysts, and the possible deactivation mechanism.

A series of amino-functionalized MIL-53 with different metals as nodes has been synthesized. By determining adsorption properties and spectroscopic characterization, we unequivocally show that the interaction between the amines of the organic linker and bridging μ(2)-OH of the inorganic scaffold modulates metal organic framework (MOF) flexibility. The strength of the interaction has been found to correlate with the electropositivity of the metal.

A new post-functionalization method for metal–organic frameworks (MOFs) has been developed to introduce acidity for catalysis. Upon treatment with a mixture of triflic anhydride and sulfuric acid, chemically stable MOF structures MIL-101(Cr) and MIL-53(Al) can be sulfated, resulting in a Bronsted sulfoxy acid group attached to up to 50% of the aromatic terephthalate linkers of the structure. The sulfated samples have been extensively characterized by solid-state NMR, XANES, and FTIR spectroscopy. The functionalized acidic frameworks show catalytic activity similar to that of acidic polymers like Nafion® display in the esterification of n-butanol with acetic acid (TOF ∼ 1 min−1 @ 343 K). Water adsorbs strongly up to 4 molecules per sulfoxy acid group, and an additional 2 molecules are taken up at lower temperatures in the 1-D pore channels of S-MIL-53(Al). The high water content and Bronsted acidity provide the structure S-MIL-53(Al) a high proton conductivity up to moderate temperatures.

ZSM-58, having a DDR topology, is shown to be a very attractive catalyst for the direct formation of propylene and ethylene via conversion of methanol. A performance similar to the state of the art SAPO-34 catalysts is achieved, while no olefins longer than C4 are formed. In addition, ZSM-58 has a much higher thermostability than SAPO catalysts. Mainly propylene, ethylene and linear butenes (trans-but-2-ene and butadiene) are formed when materials with the DDR topology are used as catalysts during the MTO process. The ratio propylene/ethylene can be tuned by changing the reaction conditions or the degree of catalyst coking. An optimum in performance, in terms of stability and selectivity, is found for catalysts containing one acid site (one Al) per accessible cavity. Deactivation of the catalysts takes place due to formation of coke and homogeneous blocking of the catalysts porosity. Activity is fully recovered after regeneration in air.

The Lithium-Sulfur (Li-S) battery with metal sulfide additives attracts more interests in recent years due to its potential to provide higher energy density, to increase electric capacity, and to improve the electrical conductivity of the insulated sulfur electrode. This multi-functional design on cathode showed initial promise; however, complicated interactions at the system level are accompanied by some detrimental side effects. The metal sulfide additives that promote a chemical conversion as the reaction mechanism, e.g., CuS and FeS2, to increase the theoretical capacity of the Li-S system can cause undesired parasitic reactions, such as the dissolution of the additive in the electrolyte. Studying such complex reactions presents a challenge because it requires experimental methods that can track the chemical and structural evolution of the system during an electrochemical process. To address the fundamental mechanisms in these systems, structural and chemical evolution of CuS additive in Li-S battery was conducted via operando multi-modal synchrotron techniques in this work. Transformation of phase and chemical state in S-CuS hybrid electrode during cell discharge/charge was investigated by X-ray Powder Diffraction and X-ray Absorption Spectroscopy. The Cu ion dissolution and its migration from cathode to anode during battery reaction were monitored by X-ray Fluorescence Microscopy. With the combination of operando multi-modal synchrotron approach, a new reaction mechanism was understood and proposed in this study. Figure 1

Zeolites play a crucial part in acid–base heterogeneous catalysis. Fundamental insight into their internal architecture is of great importance for understanding their structure–function relationships. Here, we report on a new approach correlating confocal fluorescence microscopy with focused ion beam–electron backscatter diffraction, transmission electron microscopy lamelling and diffraction, atomic force microscopy and X-ray photoelectron spectroscopy to study a wide range of coffin-shaped MFI-type zeolite crystals differing in their morphology and chemical composition. This powerful combination demonstrates a unified view on the morphology-dependent MFI-type intergrowth structures and provides evidence for the presence and nature of internal and outer-surface barriers for molecular diffusion. It has been found that internal-surface barriers originate not only from a 90∘ mismatch in structure and pore alignment but also from small angle differences of 0.5∘–2∘ for particular crystal morphologies. Furthermore, outer-surface barriers seem to be composed of a silicalite outer crust with a thickness varying from 10 to 200 nm. Characterizing the internal architecture of zeolites is crucial for understanding their structure–function relationships, and for acid–base heterogeneous catalysis. Using a unique combination of diffraction and microscopy techniques provides a unified picture of the morphology of intergrowth structures and confirmation of surface barriers for molecular diffusion.

A combination of optical and fluorescence microscopy was used to study the morphology of micro- and mesoporous H-ZSM-5 zeolite crystals (17 x 4 x 4 microm) and to evaluate, in a spatially resolved manner, the effect of mesoporosity, introduced via desilication, on catalytic performance. For this purpose, the oligomerization of various styrene molecules was used as a model reaction, in which the carbocation intermediates formed in the zeolite pores act as reporter molecules. In situ confocal fluorescence measurements after the template removal process showed that the crystals generally consist of three different subunits that have pyramidal boundaries with each other. Examination of these crystals during styrene oligomerization revealed differences in the catalytic activity between the purely microporous and the combined micro- and mesoporous crystals. The introduction of intracrystalline mesoporosity limits the formation to dimeric carbocation intermediates and facilitates the transport of styrene molecules inside the zeolite volume. This leads to a more uniform coloration and fluorescence pattern of the crystals. Moreover, the oligomerization of various styrene compounds, which differ in their reactivity, provides a good way of estimating the Brønsted acid strength in a spatially resolved manner, showing a nonhomogeneously distributed Brønsted acidity over the volume of the crystals. More detailed information on the structure of the ZSM-5 crystals was revealed for mesoporous crystals during the oligomerization of 4-methoxystyrene. This reaction induced an "explosion" of the crystal leading to the formation of a complex system with at least eight different subunits. Finally, polarized-light microscopy was used to unravel the pore geometry in these individual building blocks. The observed differences in catalytic behavior between micro- and mesoporous ZSM-5 crystals are strengthened by the microspectroscopic techniques employed, which show that upon desilication the crystal morphology is affected, the product distribution is changed towards less conjugated carbocation intermediates, and that a gradient in Brønsted acid strength appears to be present.

Three photosensitizers based on tris-(pentafluorophenyl)antimony corroles that differ in oxidation state and axial ligands, namely, (pyridine) Sb (III)-, (oxo) Sb (V)- and (difluoro) Sb (V) complexes, were studied by time-resolved electron paramagnetic resonance spectroscopy and laser flash photolysis. The magnetic and orientational parameters of the corroles oriented in a nematic liquid crystal as well as their triplet lifetimes in liquid toluene were determined and interpreted in terms of their structure and geometry. The negative zero-field splitting parameter D assigned to all studied corroles is explained by the asymmetric π-electron withdrawal effect caused by perfluorinated peripheral aryl groups, which force the triplet electron spins to align in head-to-tail configuration. The effect of the axial ligands on the photoexcited triplet state properties of the corroles is correlated with their different efficiency to perform photoassisted aerobic oxygenation of some organic molecules. This is explained by the dependence of the main parameters of the photoexcited complexes on the interaction between the central ion and corrole π-system. This interaction is strongly influenced by axial ligands coordination, affecting the macrocycle symmetry, planarity, and rigidity.

A combination of in-situ optical and fluorescence microspectroscopy has been employed to investigate the oligomerization of styrene derivatives occurring in the micropores of coffin-shaped H-ZSM-5 zeolite crystals in a space- and time-resolved manner. The carbocationic intermediates in this reaction act as reporter molecules for catalytic activity, since they exhibit strong optical absorption and fluorescence. In this way, reactant selectivity and restricted transition-state selectivity for 14 substituted styrene molecules can be visualized and quantified. Based on a thorough analysis of the time- and space-resolved UV/Vis spectra, it has been revealed that two main parameters affect the reaction rates, namely, the carbocation stabilization effect and the diffusion hindrance. The stabilization effect was tested by comparison of the reaction rates for 4-methoxystyrene versus 4-methylstyrene and in the series 4-bromo-, 4-chloro and 4-fluorostyrene; in both cases less electronegative substituents were found to accelerate the reaction. As to the steric effect, bulkier chemical groups bring down the reaction rate, as evident from the observation that 4-methoxystyrene is more reactive than 4-ethoxystyrene due to differences in their diffusivity, while heavily substituted styrenes, such as 3,4-dichlorostyrene and 2,3,4,5,6-pentafluorostyrene, cannot enter the zeolite pore system and therefore do not display any reactivity. Furthermore, beta-methoxystyrene and trans-beta-methylstyrene show limited reactivity as well as restricted reaction-product formation due to steric constraints imposed by the H-ZSM-5 channel system. Finally, polarized-light optical microspectroscopy and fluorescence microscopy demonstrate that dimeric styrene compounds are predominantly formed and aligned within the straight channels at the edges of the crystals, whereas a large fraction of trimeric carbocations along with dimeric compounds are present in the straight channels of the main body of the H-ZSM-5 crystals. Our results reinforce the observation of a non-uniform catalytic behavior within zeolite crystals, with specific parts of the zeolite grains being less accessible and reactive towards reactant molecules. The prospects and potential of this combined in-situ approach for studying large zeolite crystals in the act will be discussed.

A new spectrometer design that will result in a highly efficient, easy to handle, low-cost, high-resolution spectroscopy system with excellent background suppression is being developed for the NSLS-II Inner-Shell Spectroscopy beamline. This system utilizes non-diffractive optics comprised of fused and directed glass capillary tubes that will be used to collect and pre-collimate fluorescence photons. There are several advantages enabled by this design; a large energy range is accessible without modifying the s-stem, a large collection angle is achieved per detection unit: 4-5% of the full solid angle, easy integration in complex and harsh environments is enabled due to the use of a pre-collimation system as a secondary source for the spectrometer, and background from a complex sample environment can be easily and efficiently suppressed. The polycapillary X-ray focusing optics segment of this application has been under development. This includes improvement in manufacturing methods of polycapillary structure for x-ray optics, forming the polycapillary structure to produce X-ray optics to achieve the required solid angle collection and transmission efficiency, and measurement of X-ray focusing properties of the optics using an X-ray source. Two promising advances are large open area ratios of 80% or more, and the possibility of adding coatings in the capillaries using Atomic Layer Deposition techniques to improve reflection efficiency.

Fourier-transform infrared (FTIR) spectroscopic imaging is a widely used method for studying the chemistry of proteins, lipids, and DNA in biological systems without the need for additional tagging or labeling. This technique can be especially powerful for spatially resolved, temporal studies of dynamic changes such as in vivo protein folding in cell culture models. However, FTIR imaging experiments have typically been limited to dry samples as a result of the significant spectral overlap between water and the protein Amide I band centered at 1650 cm(-1). Here, we demonstrate a method to rapidly obtain high quality FTIR spectral images at submicron pixel resolution in vivo over a duration of 18 h and longer through the development and use of a custom-built, demountable, microfluidic-incubator and a FTIR microscope coupled to a focal plane array (FPA) detector and a synchrotron light source. The combined system maximizes ease of use by allowing a user to perform standard cell culture techniques and experimental manipulation outside of the microfluidic-incubator, where assembly can be done just before the start of experimentation. The microfluidic-incubator provides an optimal path length of 6-8 μm and a submillimeter working distance in order to obtain FTIR images with 0.54-0.77 μm pixel resolution. In addition, we demonstrate a novel method for the correction of spectral distortions caused by varying concentrations of water over a subconfluent field of cells. Lastly, we use the microfluidic-incubator and time-lapsed FTIR imaging to determine the misfolding pathway of mutant copper-zinc superoxide dismutase (SOD1), the protein known to be a cause of familial amyotrophic lateral sclerosis (FALS).

The photoexcited triplet states of three 5,10, 15-tris(pentafluorophenyl)corroles (tpfc), hosting Sn(IV) and Al(III) in their core, namely, Sn(Cl)(tpfc), Al(pyr)2(tpfc) and Al(pyr)2(tpfc-Br8), were studied by time-resolved electron paramagnetic resonance (TREPR) spectroscopy in the nematic liquid crystal E7. Only two of these metallocorroles, namely, Sn(Cl)(tpfc) and Al(pyr)2(tpfc-Br8), exhibit TREPR spectra following pulsed laser excitation. This result is rationalized in terms of a very low quantum yield of triplet formation in Al(pyr)2(tpfc). Analysis of the spin polarized Q-band (34 GHz) EPR spectra of Sn(Cl)(tpfc) and Al(pyr)2(tpfc-Br8) provides detailed information on the magnetic and kinetic parameters of the triplet states as well as on the molecular ordering of the complexes in the liquid crystal. With the assignment of the zero-field splitting parameterD AX, AY, which is attributed to a large increase in the spin-orbit coupling strength arising from the peripheral bromine atoms on the corrole skeleton.

Light-driven multi-step intramolecular electron transfer in a rod-like triad, in which two of the three redox components are linked by three hydrogen bonds, was studied by time-resolved electron paramagnetic resonance (TREPR) and optical spectroscopies. One part of the molecule consists of a p-methoxyaniline primary electron donor (MeOAn) covalently linked to a 4-aminonaphthalene-1, 8-dicarboximide (6ANI) chromophoric electron acceptor (MeOAn-6ANI). The unsubstituted dicarboximide of 6ANI serves as one half of a hydrogen bonding receptor pair. The other half of the receptor pair consists of a melamine linked to a naphthalene-1,8:4,5-bis(dicarboximide) (NI) secondary electron acceptor (MEL-NI). TREPR spectroscopy is used to probe the electronic interaction between the radicals within the photogenerated, spin-correlated radical ion pair MeOAn +-6ANI/MEL-NI −. The results are compared to those obtained in earlier studies in which MeOAn-6ANI is covalently linked to NI through a 2,5-dimethylphenyl group (MeOAn-6ANI-Ph-NI). We show that the electronic coupling between the oxidized donor and reduced acceptor in the hydrogen-bonded radical ion pair MeOAn +-6ANI/MEL-NI − is very similar to that of MeOAn +-6ANI-Ph-NI −.

Time-resolved electron paramagnetic resonance (TREPR) spectroscopy was used to study two functionalized fullerenes consisting of a C60 moiety covalently linked to TEMPO radical via spacers of different length. Photoinduced electron spin polarization (ESP) reflecting a non-Boltzmann population within the energy levels of the spin system was observed in the electronic ground and excited states. Both fullerenes are characterized by a sign inversion of their TREPR spectra. A new mechanism of ESP generation was suggested to explain the experimental results. This mechanism, termed as the reversed quartet mechanism (RQM), includes the intersystem crossing process, which generates ESP in the excited trip-doublet and trip-quartet (2T1 and 4T1) states. This ISC is accompanied by ESP transfer to the ground state (2S0) by either electron-transfer reaction (in our case via charge transfer state, 2CT, i.e., 2T1 → 2CT → 2S0) or internal conversion, 2T1 → 2S0.

The magnetic field dependence of electron spin polarization (ESP), generated in free radicals when they encounter photoexcited triplets, was measured experimentally and analyzed theoretically. The time-resolved electron paramagnetic resonance measurements were performed with a microwave setup consisting of low-loss dielectric ring resonators with tunable microwave frequencies and the corresponding magnetic fields. The ESP of the radical was found in the magnetic field range of 170-370 mT, and the results of the calculation based on the numerical solution of the stochastic Liouville equation were found to be in line with the experimental data showing that ESP decreases when the magnetic field increases.

A novel miniature (∼2×2×1 mm) dielectric resonator for X-band electron paramagnetic resonance experiments is presented. The resonator is based on a single crystal of KTaO3, which is excited to its TE01δ resonance mode by means of a simple iris-screw coupling. Several configurations of resonators are considered and discussed with respect to their filling factor, power conversion ratio, and optical excitation efficiency. Our findings are presented in terms of both experimental and theoretical studies. For small samples, the high filling factor of this resonator results in a signal increase by a factor of 140–800 (assuming nonsaturating conditions) as compared to a rectangular X-band cavity. The high power conversion factor (∼40 G/W), should enable one to perform pulse experiments employing power amplifiers, with ∼100-fold less peak power used for rectangular cavities. With an antireflective layer, the crystal’s transparency enables efficient laser illumination of the sample in light-induced experiments.

We have synthesized a series of structurally related, covalently linked electron donor-acceptor triads having highly restricted conformations to study the effects of radical ion pair (RP) structure, energetics, and solvation on charge recombination. The chromophoric electron acceptor in these triads is a 4-aminonaphthalene-1,8-dicarboximide (6ANI), in which the 4-amine nitrogen atom is part of a piperazine ring. The second nitrogen atom of the piperazine ring is part of a para-substituted aniline donor, where the para substituents are X = H, OMe, and NMe(2). The imide group of 6ANI is linked to a naphthalene-1,8:4,5-bis(dicarboximide) (NI) electron acceptor across a phenyl spacer in a meta relationship. The triads undergo two-step photoinduced electron transfer to yield their respective XAn(*)(+)-6ANI-Ph-NI(*)(-) RP states, which undergo radical pair intersystem crossing followed by charge recombination to yield (3)NI. Time-resolved electron paramagnetic resonance experiments on the spin-polarized RPs and triplet states carried out in toluene and in E-7, a mixture of nematic liquid crystals (LCs), show that for all three triads, the XAn(*)(+)-6ANI-Ph-NI(*)(-) RPs are correlated radical pairs and directly yield values of the spin-spin exchange interaction, J, and the dipolar interaction, D. The values of J are all about -1 mT and show that the LC environment most likely enforces the chair conformation at the piperazine ring, for which the RP distance is larger than that for the corresponding boat conformation. The values of D yield effective RP distances that agree well with those calculated earlier from the spin distributions of the radical ions. Within the LC, changing the temperature shows that the CR mechanism can be changed significantly as the energy levels of the RPs change relative to that of the recombination triplet.

We report a series of powder X-ray diffraction experiments performed on the soft porous crystals MIL-53(Al) and NH2-MIL-53(Al) in a diamond anvil cell under different pressurization media. Systematic refinements of the obtained powder patterns demonstrate that these materials expand along a specific direction while undergoing total volume reduction under an increasing hydrostatic pressure. The results confirm for the first time the negative linear compressibility behaviour of this family of materials, recently predicted from quantum chemical calculations.

Using high time resolution Q-band EPR we have been able to identify three different radical pairs generated by pulsed laser excitation of the fixed distance triad consisting of a zinc-9-desoxo-meso-methylpyrochlorophyllide donor (ZC), a pyromellitimide primary acceptor (PI), and a naphthalene-1,8:4,5-diimide secondary acceptor (NI), i.e., ZC−PI−NI, oriented in a liquid crystal. Analysis of the transient EPR spectra provides direct evidence for sequential electron transfer from the primary to the secondary radical pair of the triplet channel. At room temperature, this process occurs with an exponential time constant of τT,2 = 50 ± 1 ns. In the singlet-initiated channel, the intramolecular electron-transfer rates are too fast for direct EPR detection. Thus, even the secondary singlet radical pair [ZC•+PINI•-]S is formed instantaneously on the time scale of the EPR experiment. The species decays with a time constant of τS,3 = 36 ± 1 ns by charge recombination to the singlet ground state. The time evolution o...

Microspectroscopic imaging in the infrared (IR) spectral region allows for the examination of spatially resolved chemical composition on the microscale. More than a decade ago, it was demonstrated that diffraction limited spatial resolution can be achieved when an apertured, single pixel IR microscope is coupled to the high brightness of a synchrotron light source. Nowadays, many IR microscopes are equipped with multi-pixel Focal Plane Array (FPA) detectors, which dramatically improve data acquisition times for imaging large areas. Recently, progress been made toward efficiently coupling synchrotron IR beamlines to multi-pixel detectors, but they utilize expensive and highly customized optical schemes. Here we demonstrate the development and application of a simple optical configuration that can be implemented on most existing synchrotron IR beamlines in order to achieve full-field IR imaging with diffraction-limited spatial resolution. Specifically, the synchrotron radiation fan is extracted from the bending magnet and split into four beams that are combined on the sample, allowing it to fill a large section of the FPA. With this optical configuration, we are able to oversample an image by more than a factor of two, even at the shortest wavelengths, making image restoration through deconvolution algorithms possible. High chemical sensitivity, rapid acquisition times, and superior signal-to-noise characteristics of the instrument are demonstrated. The unique characteristics of this setup enabled the real time study of heterogeneous chemical dynamics with diffraction-limited spatial resolution for the first time.

The NH{sub 2}-MIL-53(Al) metal-organic framework was studied for its use in the separation of CO{sub 2} from CH{sub 4}, H{sub 2}, N{sub 2} C{sub 2}H{sub 6} and C{sub 3}H{sub 8} mixtures. Isotherms of methane, ethane, propane, hydrogen, nitrogen, and CO{sub 2} were measured. The atypical shape of these isotherms is attributed to the breathing properties of the material, in which a transition from a very narrow pore form to a narrow pore form and from a narrow pore form to a large pore form occurs, depending on the total pressure and the nature of the adsorbate, as demonstrated by in-situ XRD patterns measured during adsorption. Apart from CO{sub 2}, all tested gases interacted weakly with the adsorbent. As a result, they are excluded from adsorption in the narrow pore form of the material at low pressure. CO{sub 2} interacted much more strongly and was adsorbed in significant amounts at low pressure. This gives the material excellent properties to separate CO{sub 2} from other gases. The separation of CO{sub 2} from methane, nitrogen, hydrogen, or a combination of these gases has been demonstrated by breakthrough experiments using pellets of NH{sub 2}-MIL-53(Al). The effect of total pressure (1-30 bar), gas composition, temperaturemore » (303-403 K) and contact time has been examined. In all cases, CO{sub 2} was selectively adsorbed, whereas methane, nitrogen, and hydrogen nearly did not adsorb at all. Regeneration of the adsorbent by thermal treatment, inert purge gas stripping, and pressure swing has been demonstrated. The NH{sub 2}-MIL-53(Al) pellets retained their selectivity and capacity for more than two years.« less

The miniaturization of in situ spectroscopic tools has been recognized as a forefront instrumental development for the characterization of heterogeneous catalysts. With the multitude of micro-spectroscopic methods available fundamental insight into the structure–function relationships of catalytic processes can be obtained. Among these techniques vibrational spectroscopy is one of the most versatile methods and capable to shed insight into the molecular structure of reaction intermediates and products, the chemical state of catalyst materials during reaction as well as the nature of interactions between reactants/intermediates/products and the catalyst surface. In this tutorial review we discuss the recent developments in the field of infrared (IR) and Raman micro-spectroscopy and illustrate their potential. Showcase examples include (1) chemical imaging of spatial heterogeneities during catalyst preparation, (2) high-throughput catalyst screening, (3) transport and adsorption phenomena within catalytic solids and (4) reactivity studies of porous oxides, such as zeolites. Finally, new in situ spectroscopy tools based on vibrational spectroscopy and their potential in the catalysis domain are discussed.

The study of catalysts under in-situ conditions enables the catalyst scientist to identify and understand the important steps, e.g., the formation of important reaction intermediates and active sites, and stages in a catalyst?s lifetime, such as activation/deactivation. The development of characterization methods as well as the design and construction of appropriate in-situ cells and reactor probes are inevitable in order to obtain such insight. Both spectroscopic and scattering techniques have been used in attempt to understand quantitative structure/composition-activity/selectivity relationships in catalysis. Armed with such detailed knowledge about the catalyst, it is then possible for scientists to design, in a more rational way, new and efficient catalysts for sustainable production of bulk and fine chemicals as well as for the removal of harmful compounds in industrial catalytic processes. This chapter provides an overview of the in-situ characterization techniques available for investigation of catalytic materials. The possibilities and limitations of the methods are discussed and illustrated with numerous case studies. Keywords: heterogeneous catalysis; in situ techniques; spectroscopy; diffraction; scattering; microspectroscopy; combined techniques

Large zeolite crystals have been used as model systems for the investigation of diffusion and catalytic reactivity phenomena in microporous host materials for at least two decades. However, their potential in assisting the detection of elusive reactive intermediates appears to have been underestimated. Herein, we show that a complementary use of vibrational and optical spectroscopy in combination with theoretical calculations allows for the unambiguous identification of transient carbocationic species generated upon the acid-catalyzed oligomerization of styrene derivatives within zeolite H-ZSM-5. Thanks to the mediated diffusion of the reactant in the large H-ZSM-5 crystals and minimal external surface the reaction intermediates can be accumulated within zeolite micropores in sufficient concentrations to allow their detection by synchrotron-based IR microspectroscopy. The UV/Vis and IR spectra display strong polarization dependence of on the molecular alignment of the dimeric styrene carbocations imposed by the zeolite channels and cages that can be rationalized in terms of the electronic and vibrational transitions of the intrazeolite carbocations. Based on these findings, a molecular-level picture of the macroscopic arrangement of the reaction intermediates confined within microporous zeolite matrices can be devised.