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Olefin metathesis is a broadly employed reaction with applications that range from fine chemicals to materials and petrochemicals. The design and investigation of olefin metathesis catalysts have b...

Organic cathode materials are promising for developing high-energy and high-power Li-ion batteries (LIBs). However, the energy storage of most organic cathodes relies on the electron transfer of a ...

Inspired by the gallstone formation mechanism, we report a fast one-pot synthesis of high-surface-area bimetallic hierarchical supra-nanostructures. As gallstones are generated from metal cholate complexes, cholate bile acid molecules with Au/Ag metal precursors formed stable nanocomplexes aggregated with metal Au ions and preformed ~2 nm silver halide nanoparticles before reduction. When a reducing agent was added, the metal cholate nanocomplexes quickly formed noble bimetallic hierarchical supra-nanostructures. The morphology of bimetallic supra-nanostructures could be tailored by changing the feeding ratio of each metal precursor. In situ synchrotron small-angle X-ray scattering measurement with a custom-designed reaction cell showed two-step growth and attachment behavior toward hierarchical supra-nanostructures from the gallstone-formation-inspired metal cholate nanocomplexes in a 60 s reaction. Additional wide-angle X-ray scattering, X-ray absorption near-edge structure, in situ Fourier transform infrared, and high-resolution scanning transmission electron microscopy investigations subsequently revealed the mechanism for the evolution of bimetallic hierarchical supra-nanostructures. The gallstone-formation-inspired synthesis mechanism can be universally applied to other metals, for example, Pt–Ag and Pd–Ag bimetallic nanostructures. Finally, the synthesized high-surface-area bimetallic supra-nanostructures demonstrated significantly enhanced X-ray computed tomography imaging contrast and radiosensitizing effect for a potential image-guided nanomedicine application. We believe that our synthetic method inspired by gallstone formation and understanding represents an important step toward the development of hierarchical nanoparticles for various applications.

Non-noble-metal, thin-film oxides are widely investigated as promising catalysts for oxygen evolution reactions (OER). Amorphous cobalt oxide films electrochemically formed in the presence of borate (CoBi) and phosphate (CoPi) share a common cobaltate domain building block, but differ significantly in OER performance that derives from different electron-proton charge transport properties. Here, we use a combination of L edge synchrotron X-ray absorption (XAS), resonant X-ray emission (RXES), resonant inelastic X-ray scattering (RIXS), resonant Raman (RR) scattering, and high-energy X-ray pair distribution function (PDF) analyses that identify electronic and structural factors correlated to the charge transport differences for CoPi and CoBi. The analyses show that CoBi is composed primarily of cobalt in octahedral coordination, whereas CoPi contains approximately 17% tetrahedral Co(II), with the remainder in octahedral coordination. Oxygen-mediated 4 p-3 d hybridization through Co-O-Co bonding was detected by RXES and the intersite dd excitation was observed by RIXS in CoBi, but not in CoPi. RR shows that CoBi resembles a disordered layered LiCoO

Cu-exchanged small-pore zeolites (CHA and AEI) form methanol from methane (>95% selectivity) using a 3-step cyclic procedure (Wulfers et al. Chem. Commun. 2015, 51, 4447−4450) with methanol amounts higher than Cu-ZSM-5 and Cu-mordenite on a per gram and per Cu basis. Here, the CuxOy species formed on Cu-SSZ-13 and Cu-SSZ-39 following O2 or He activation at 450 °C are identified as trans-μ-1,2-peroxo dicopper(II) ([Cu2O2]2+) and mono-(μ-oxo) dicopper(II) ([Cu2O]2+) using synchrotron X-ray diffraction, in situ UV–vis, and Raman spectroscopy and theory. [Cu2O2]2+ and [Cu2O]2+ formed on Cu-SSZ-13 showed ligand-to-metal charge transfer (LMCT) energies between 22,200 and 35,000 cm–1, Cu–O vibrations at 360, 510, 580, and 617 cm–1 and an O–O vibration at 837 cm–1. The vibrations at 360, 510, 580, and 837 cm–1 are assigned to the trans-μ-1,2-peroxo dicopper(II) species, whereas the Cu–O vibration at 617 cm–1 (Δ18O = 24 cm–1) is assigned to a stretching vibration of a thermodynamically favored mono-(μ-oxo) dicoppe...

Alpha-MnO2 is of interest as a cathode material for 3 V lithium batteries and as an electrode/electrocatalyst for higher energy, hybrid Li-ion/Li–O2 systems. It has a structure with large tunnels that contain stabilizing cations such as Ba2+, K+, NH4+, and H3O+ (or water, H2O). When stabilized by H3O+/H2O, the protons can be ion-exchanged with lithium to produce a Li2O-stabilized α-MnO2 structure. It has been speculated that the electrocatalytic process in Li–O2 cells may be linked to the removal of lithium and oxygen from the host α-MnO2 structure during charge, and their reintroduction during discharge. In this investigation, hydrated α-MnO2 was used, as a first step, to study the release and uptake of oxygen in α-MnO2. Temperature-resolved in situ synchrotron X-ray diffraction (XRD) revealed a nonlinear, two-stage, volume change profile, which with the aide of X-ray absorption near-edge spectroscopy (XANES), redox titration, and density functional theory (DFT) calculations, is interpreted as the releas...

Dimeric and monomeric supported single-site Fe(II) pre-catalysts on SiO2 have been prepared via organometallic grafting and characterized with advanced spectroscopic techniques. Manipulation of the surface hydroxyl concentration on the support influences monomer/dimer formation. While both pre-catalysts are highly active in liquid-phase hydrogenation, the dimeric pre-catalyst is ∼3× faster than the monomer. Preliminary XAS experiments on the H2-activated samples suggest the active species are isolated Fe(II) sites.

We report the synthesis, characterization, and catalytic performance for gas phase propane dehydrogenation of single-site Co2+ ions supported on silica. Spectroscopic characterization by resonance Raman, electron paramagnetic resonance, and X-ray near-edge and extended absorption fine structure revealed that tetrahedrally coordinated Co2+ ions are chemisorbed into the trisiloxane rings on the surface of amorphous silica. In situ XAS shows that Co is not oxidized by air nor reduced by hydrogen even at 650 °C. For catalytic propane dehydrogenation, single-site Co2+/SiO2 exhibits selectivities >95% at 550 °C and >90% at 650 °C with stable activity over 24 h. Calculations with hybrid density functional theory support a non-redox mechanism for activation of C–H and H–H bonds by Co2+ similar to that previously reported for single-site Zn2+/SiO2.

The effect of redox-active Cr substitution on the electrochemistry and voltage fade of a lithium-rich “layered–layered” composite cathode material has been investigated. A series of Cr-substituted 0.5Li2MnO3·0.5LiNi1/2Mn1/2O2 powder samples (i.e., Li1.2Ni0.2−2/xMn0.6−2/xCrxO2, where x = 0, 0.05, 0.1, and 0.2) was synthesized via the sol–gel method. X-ray diffraction data confirmed the incorporation of Cr ions into the lattice structure. While similar initial charge capacities (∼300 mA h g−1) were obtained for all of the cathode samples, the capacity contribution from the Li2MnO3 activation plateau (at 4.5 V vs. Li) decreased with increasing Cr content. This finding suggests suppressed oxygen loss that triggers cation migration and voltage fade in subsequent cycles. Continued investigation revealed that the Cr substitution mitigates the voltage fade on charge but not discharge. The resulting insignificant effect of Cr substitution on mitigating voltage fade, in spite of decreased Li2MnO3 activation, is attributed to the additional instability caused by Cr6+ migration to a tetrahedral site, as evidenced by ex situ X-ray absorption spectroscopy. Our results provide the framework for a future redox active cation substitution strategy by highlighting the importance of the structural stability of the substituent itself.

A well-defined, isolated, single-site organovanadium(III) catalyst on SiO2 [(SiO2)V(Mes)(THF)] was synthesized via surface organometallic chemistry, and fully characterized using a combination of analytical and spectroscopic techniques (EA, ICP, 1H NMR, TGA-MS, EPR, XPS, DR-UV/Vis, UV-Raman, DRIFTS, XAS). The catalyst exhibits unprecedented reactivity in liquid- and gas-phase alkene/alkyne hydrogenation. Kinetic poisoning experiments revealed that 100% of the V sites are active for hydrogenation.

The effect of alcohol as a solvent on the acid-catalyzed conversion of furfuryl alcohol ( FA ) into polymerized furfuryl alcohol ( PFA ) has been studied by UV Raman spectroscopy. The major peak intensity ratios were compared to gain quantitative information about the extent of polymerization in various solvents. The reaction rate of the polymerization has been found to significantly decrease with increasing concentrations of ethanol or butanol ( n -butanol and iso -butanol). Compared to ethanol, longer or branched chain alcohols such as n -butanol and iso -butanol can marginally reduce the acid-catalyzed polymerization at room temperature. The plot of reciprocal intensity of the characteristic Raman band of FA vs. the reaction time suggests that the polymerization reactions follow second-order kinetics.

Multimodal-imaging probes offer a novel approach, which can provide detail diagnostic information for the planning of image-guided therapies in clinical practice. Here we report targeted multimodal Nd3+-doped upconversion nanoparticle (UCNP) imaging reporters, integrating both magnetic resonance imaging (MRI) and real-time upconversion luminescence imaging (UCL) capabilities within a single platform. Nd3+-doped UCNPs were synthesized as a core-shell structure showing a bright visible emission upon excitation at the near infrared (minimizing biological overheating and increasing tissue penetration depth) as well as providing strong MRI T2 contrast (high r2/r1 ratio). Transcatheter intra-arterial infusion of Nd3+-doped UCNPs conjugated with anti-CD44-monoclonal antibody allowed for high performance in vivo multimodal UCL and MR imaging of hepatocellular carcinoma (HCC) in an orthotopic rat model. The resulted in vivo multimodal imaging of Nd3+ doped core-shell UCNPs combined with transcatheter intra-arterial targeting approaches successfully discriminated liver tumors from normal hepatic tissues in rats for surgical resection applications. The demonstrated multimodal UCL and MRI imaging capabilities of our multimodal UCNPs reporters suggest strong potential for in vivo visualization of tumors and precise surgical guidance to fill the gap between pre-procedural imaging and intraoperative reality.

Oxidative dehydrogenation (ODH) catalysts based on vanadium oxide are active for the production of alkenes, chemicals of great commercial importance. The current industrial practice for alkene production is based on energy-intensive, dehydrogenation reactions. UV resonance and visible Raman measurements, combined with density functional studies, are used to study for the first time the structure–reactivity relationships for alumina-supported monomeric vanadium oxide species. The relationship between the structure of three vanadium oxide monomeric surface species on a θ-alumina surface, and their reducibility by H2 was determined by following changes in the vanadia’s UV Raman and resonance Raman spectra after reaction with H2 at temperatures from 450 to 650 °C. The H2 reducibility sequence for the three monomeric species is bidentate > “molecular”> tridentate. The reaction pathways for H2 reduction on the three vanadium oxide monomeric structures on a θ-alumina surface were investigated using density funct...

Despite widespread importance in catalysis, the active and selective sites of supported vanadium oxide (VOx) catalysts are not well understood. Such catalysts are of great current interest because of their industrial significance and potential for selective oxidation processes.(1-4) However, the fact that the nature of the active and selective sites is ambiguous hinders molecular level understanding of catalytic reactions and the development of new catalysts. Furthermore, complete structural elucidation requires isolation and characterization of specific vanadium oxide surface species, the preparation of which presents a significant synthetic challenge. In this study, we utilize the structural uniformity inherent in organometallic precursors for the preparation of supported vanadium oxide catalysts. The resulting catalysts are characterized by UV−visible diffuse reflectance spectroscopy (UV−vis DRS), X-ray absorption spectroscopy (XAS), UV-Raman spectroscopy, and H2-temperature programmed reduction (H2-TP...

Copper oxide catalysts supported on KIT-6 silica were evaluated for cyclohexane oxidative dehydrogenation (ODH) to determine the effects of copper oxide domain size on ODH activity and selectivity. The catalysts were prepared by incipient wetness impregnation of KIT-6 at copper surface densities spanning 0.01–0.7 Cu/nm2 with carefully controlled drying and calcination conditions to systematically vary the average local copper oxide domain size. A distinct copper oxide active site exhibiting an order of magnitude higher activity than large copper oxide domains was identified by model cyclohexane ODH studies coupled with in situ X-ray absorption and UV–visible spectroscopies during reduction in H2. The structure of this site is experimentally identified by a combination of extended X-ray absorption fine structure analysis, resonant Raman studies, and modeling by density functional theory. All constraints imposed by these techniques indicate the active site is a mono(μ-oxo)dicopper(II) structure with copper ...

Supported vanadium oxide species are active catalysts for the selective, oxidative conversion of hydrocarbons to useful chemicals. Both the catalytic vanadium oxide and the supporting oxide were synthesized by ALD on high surface powders and anodic aluminum oxide (AAO) nanoliths. The nanoliths were prepared by anodic oxidation of aluminum. 1 nm of ALD aluminum oxide acts as the support for vanadium oxide loaded by 1 to 18 ALD cycles of vanadyltri-isopropoxide/H2O2. Ultraviolet-visible absorption edges red shift as the vanadia loading increases. The edge energy of 1-cycle ALD VOx corresponds to isolated, tetrahedral VO4 in agreement with Raman spectroscopy. V-O-V bonds form with additional cycles producing a gradual increase in VOx domain size. Reaction rate coefficients for the oxidative dehydrogenation of cyclohexane show increased overall activity in the high loading catalysts but a higher specific activity in the low loading catalysts for cyclohexene formation.

Raman spectroscopy was used to demonstrate that the lattice dynamics of SrTiO3 (STO) nanoparticles strongly depends on their microstructure, which is in turn determined by the synthetic approach employed. First-order Raman modes are observed at room temperature in STO single-crystalline nanocubes with average edge lengths of 60 and 120 nm, obtained via sol-precipitation coupled with hydrothermal synthesis and a molten salt procedure, respectively. First-order Raman scattering arises from local loss of inversion symmetry caused by surface frozen dipoles, oxygen vacancies, and impurities incorporated into the host lattice. The presence of polar domains is suggested by the pronounced Fano asymmetry of the peak corresponding to the TO2 polar phonon, which does not vanish at room temperature. These noncentrosymmetric domains will likely influence the dielectric response of these nanoparticles.

A solid solution was found to exist in the quaternary Li2O−MgO−V2O5−MoO3 system between the two phases Mg2.5VMoO8 and Li2Mg2(MoO4)3. Both Mg2.5VMoO8 and Li2Mg2(MoO4)3 are isostructural with the min...

Mg(2.56)V(1.12)W(0.88)O(8) crystals were grown from a MgO/V(2)O(5)/WO(3) melt. X-ray single-crystal diffraction studies revealed that it is orthorhombic with space group Pnma, a = 5.0658(5) A, b = 10.333(1) A, c = 17.421(2) A, Z = 6, and is isostructural with Mg(2.5)VMoO(8). Raman spectra are reported, and the assignment of the Raman bands is made by comparing the metal-oxygen vibrations of VO(4)/WO(4) tetrahedra in Mg(2.5)VWO(8) with the metal-oxygen vibrations of VO(4)/MoO(4) tetrahedra in Mg(2.5)VMoO(8). The stretching vibrations appearing at 1016 and 1035 cm(-)(1) are assigned to Mo=O and W=O double bonds, respectively, associated with the Mg(2+) cation vacancies.

UV Raman spectroscopic data measured at two distinct conditions, low and high laser power, establish that the manganese oxide (SP6-MnOx) produced by the freshwater bacterium (Leptothrix discophora SP-6) closely resembles the 3 × 3-tunnel todorokite among the MnO2 materials studied. Under the two conditions, the effect of hydration/cation and the phase transition of todorokite or SP6-MnOx to Mn3O4 or birnessite will be described. A higher concentration of Mg2+ incorporated in the framework of the SP6-MnOx than in todorokite is probably responsible for the formation of a new Raman band obtained at high laser powers, matching the most intense UV Raman band of synthetic birnessite. Also, we present the assignment of Raman bands for todorokite mineral and discuss the mutual exclusion principle that should hold for all the MnO2 materials studied. These experiments provide characterization of hydrous, poorly crystalline, or nanocrystalline metal oxides, which are frequently difficult to identify.

Fifteen distinct MgOV 2 O 5 , MgOMoO 3 , MgOV 2 O 5 MoO 3 , and V 2 O 5 MoO 3 compositions were prepared using sol–gel chemistry and their selectivities and conversions for propane oxidative dehydrogenation (ODH) to propylene were measured. The vanadates were more active than the molybdates at lower temperatures; however, the molybdates exhibited higher selectivities at similar conversions. An increase in both ODH conversion and selectivity with molybdenum substitution on vanadium sites was also observed. These results demonstrate the importance of the bulk structure on the ODH reaction. In general, propylene selectivities increased with increasing conversions at temperatures above 673 K when oxygen depletion in the reactant stream occurred. Visible and UV Raman spectroscopy corroborates this result and helps focus attention on critical surface-specific information. A new Raman peak was observed for the partially reduced MgMoO 4 and is associated with a three-coordinate surface oxygen.

We describe the design and performance of an electron-impact ion beam reflectron system coupled to our “single-photon infrared emission spectrometer” for measurement of infrared emission from excited gas-phase polycyclic aromatic hydrocarbon (PAH) cations. This experiment provides for direct comparison of laboratory infrared emission spectra of gaseous ionized PAHs with the “unidentified infrared emission bands,” the origin of which is still debated.

We describe the measurement of infrared emission from excited gas-phase polycyclic aromatic hydrocarbons (PAHs) cations by an electron-impact ion beam reflectron system coupled to our ‘‘ single-photon infrared emission ’’ (SPIRE) spectrometer. This experiment provides for direct comparison of laboratory infrared emission spectra of gaseous ionized PAHs with the ‘‘ unidentified infrared emission bands ’’ (UIRs), the origin of which is still debated. We present results for the pyrene cation (C16H10 þ ) and the dehydrogenated pyrene cations (C16H8 þ and C16H6 þ ) showing general agreement between the corresponding SPIRE bands and UIR features, although it is not a detailed match. We also discuss possible contributions from the pyrene dimer cation ðC16H10Þ2 þ . Subject headings: dust: extinction — infrared: ISM — ISM: lines and bands — methods: laboratory — molecular data — techniques: spectroscopic

Alpha manganese oxide (α-MnO2) is of interest as a cathode material for lithium-ion batteries and as an electrode/electrocatalyst for hybrid Li-ion/Li-O2 systems. It has a tunnel structure with large 2x2 channels that accommodate different species such as Ba2+, K+, NH4 +, or H3O+/H2O. Characterization and modeling of the insertion and removal of Li, oxygen, and H3O+/H2O species under electrochemical cycling and heating is important for understanding how MnO2 acts as a hybrid Li-ion/Li-O2 battery material. In this talk, we will discuss our work in using in-situ synchrotron X-ray diffraction (XRD), X-ray absorption near-edge spectroscopy (XANES), in-situ UV resonance Raman spectroscopy, and density functional theory (DFT) calculations, to unravel the changes in α-MnO2during electrochemical cycling as well as dehydration process. We found evidence of oxygen incorporation and partial removal during electrochemical cycling, as well as two-stage water removal during heating. Both processes involve facile oxygen diffusion through the center of 2x2 tunnels. Keywords: MnO2, in-situ XRD, DFT Reference: Z.-Z. Yang, D. Ford, J.-S. Park, Y. Ren, S. Kim, H. Kim, T. Fister, M. K. Y. Chan,# M. M. Thackeray,# “Probing the release and uptake of water in α-MnO2•xH2O,” Chemistry of Materials 29, 1507–1517 (2017). Z. Yang, L. Trahey, Y. Ren, M. K. Y. Chan,# C. Lin, J. Okasinski, and M. M. Thackeray, “In-Situ High-Energy Synchrotron X-ray Diffraction Studies and First Principles Modeling of α-MnO2 Electrodes in Li-O2 and Li-ion Coin Cells,” Journal of Materials Chemistry A 3, 7389-7398 (2015). Acknowledgements: This work was supported as a part of the Center for Electrochemical Energy Science, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Basic Energy Sciences under award number DE-AC02–06CH11. Use of the Advanced Photon Source, a US DOE Office of Science User Facility operated by Argonne National Laboratory, was supported by DOE under Contract No. DE-AC02-06CH11357. Use of the Center for Nanoscale Materials, an Office of Science user facility, was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. This research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Figure 1

The interaction of O2 with Fe supported on zeolite MFI has been investigated by the in situ UV Raman technique. Previously, the formation of adsorbed superoxide ions, O2-, on the Fe/MFI prepared by sublimation of FeCl3 vapor onto HMFI, was identified by ESR at 77 K. In situ Raman data indicate that adsorbed peroxide ions, O22-, are formed on the same catalysts with Fe/Al = 1 even at 300 K. A band at 730 cm-1, which was found to be sensitive to the partial pressure of O2, is tentatively assigned to the stretching vibration of peroxide ions. With the 18O2 isotope, a red shift of 32 cm-1 was observed for the 730 cm-1 band. Raman features of other catalyst samples show that the binuclear iron sites in the Fe/MFI are essential for the formation of peroxide ions. As proposed before, the same bridging sites between two Fe ions, that are occupied by O2- in the calcined catalyst, are also able to adsorb di-oxygen complexes.

Infrared emission spectra of five gas-phase UV laser-excited polycyclic aromatic hydrocarbons (PAHs) containing aliphatic hydrogens are compared with the main 3.3 microns and associated interstellar unidentified infrared emission bands (UIRs). We show that neutral PAHs can account for the majority of the 3 microns emission complex while making little contribution to the other UIR bands; peripherally hydrogenated PAHs produce a better match to astrophysical data than do those containing methyl side groups; 3.4 microns plateau emission is shown to be a general spectral feature of vibrationally excited PAHs containing aliphatic hydrogens, especially those containing methyl groups; and finally, hot-band and overtone emissions arising from aromatic C-H vibrations are not observed in laboratory emission spectra, and therefore, in contrast to current assignments, are not expected to be observed in the UIRs.

Highly isolated benzene molecules with near zero matrix shift have been prepared in the argon matrix at 9 K. By correlating the peak frequencies in the matrix state with those in other states, uncertainties could be resolved for the Fermi triad in the C-H stretching region of gas phase spectrum. The gas phase frequencies inferred from the matrix data were found in good agreement with those from the supersonic jet experiment. Based on the concentration and the temperature dependence, the peaks in the matrix spectra were classified in terms of monomeric, dimeric, and multimeric species.

An infrared matrix isolation study has been performed for sodium and benzene mixtures in solid argon at 9 K. In contrast with the earlier report, sodium was evidence to form complexes with benzene. Although the exact nature of the complexes is not certain, ab initio quantum mechanical calculation indicated clearly that the 1:1 NaC 6 H 6 complex should be as stable as the 1:1 LiC 6 H 6 complex. The tentatively assigned peak frequencies for the 1:1 NaC 6 H 6 complex were also inv fair agreement with the theoretical values.

Hollandite α-MnO2, with an open tunnel structure, is of interest as a cathode material for 3 V lithium batteries [1,2] and as an electrocatalyst for Li-O2 cells [3]. We recently proposed [4] that α-MnO2 belong to a class of materials that can be used as the cathode in hybrid Li-ion/Li-oxygen battery systems, which can incorporate/release both lithium and oxygen during cycling with redox reactions occurring on both the transition metal ions and oxygen ions of the electrode. In this talk, we will present in-situ and operando characterization and first principles modeling results of α-MnO2 during electrochemical cycling in conventional lithium cells and in Li-O2 cells [5,6]. Operando synchrotron x-ray diffraction (XRD) results, combined with first principles density functional theory (DFT) modeling, indicate insertion of lithium and oxygen into, as well as partial removal of these species from, the tunnel structure during cycling. On heating hydrated α-MnO2, in-situ XRD and Raman studies provide information about structural changes and diffusional properties of the oxygen species in the tunnel structure. DFT studies find low diffusion barriers for H2O and H3O+species in the tunnel. The implications of the results on other high-capacity, hybrid Li-ion/Li-oxygen materials will be discussed. Acknowledgements This work was supported as a part of the Center for Electrochemical Energy Science, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Basic Energy Sciences under award number DE-AC02–06CH11. Use of the Advanced Photon Source, a US DOE Office of Science User Facility operated by Argonne National Laboratory, was supported by DOE under Contract No. DE-AC02-06CH11357. Use of the Center for Nanoscale Materials, an Office of Science user facility, was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. References [1] M. H. Rossouw, D. C. Liles, M. M. Thackeray, W. I. F. David and S. Hull, Mater. Res. Bull., “a-Manganese Dioxide for Lithium Batteries: A Structural and Electrochemical Study,” Mater. Res. Bull., 27, 221 (1992). [2] C. S. Johnson, D. W. Dees, M. F. Mansuetto, M. M. Thackeray, D. R. Vissers, D. Argyriou, C.-K Loong and L. Christensen, “Structural and Electrochemical Studies of a-MnO2”, J. Power Sources, 68/2, 570 (1997). [3] A. Debart, A. J. Paterson, J. Bao and P. G. Bruce, “a-MnO2 Nanowires: A Catalyst for the O2 Electrode in Rechargeable Lithium Batteries,” Angew. Chem. Int. Ed., 47, 4521 (2008). [4] M. M. Thackeray, M. K. Y. Chan, L. Trahey, S. Kirklin, and C. Wolverton, “Vision for Designing High-Energy, Hybrid Li Ion/Li-O2 Cells,” Journal of Physical Chemistry Letters 4, 3607 (2013). [5] L. Trahey, N. Karan, M. K. Y. Chan, J. Lu, Y. Ren, J. P. Greeley, M. Balasubramanian, A. K. Burrell, and M. M. Thackeray, “Synthesis, Characterization and Structural Modeling of High Capacity, Dual-Functioning MnO2 Electrode/Electrocatalysts for Li-O2 Batteries,” Advanced Energy Materials 3, 75 (2013). [6] Yang, L. Trahey, Y. Ren, M. K. Y. Chan, C. Lin, J. Okasinski, and M. M. Thackeray, “In-Situ High-Energy Synchrotron X-ray Diffraction Studies and First Principles Modeling of α-MnO2 Electrodes in Li-O2 and Li-ion Coin Cells,” Journal of Materials Chemistry A 3, 7389 (2015). The submitted manuscript has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.

Resonance Raman (RR) spectroscopy has several advantages over the normal Raman spectroscopy (RS) widely used for in situ characterization of solid catalysts and catalytic reactions. Compared with RS, RR can provide much higher sensitivity and selectivity in detecting catalytically-significant surface metal oxides. RR can potentially give useful information on the nature of excited states relevant to photocatalysis and on the anharmonic potential of the ground state. In this critical review a detailed discussion is presented on several types of RR experimental systems, three distinct sources of so-called Raman (fluorescence) background, detection limits for RR compared to other techniques (EXAFS, PM-IRAS, SFG), and three well-known methods to assign UV-vis absorption bands and a band-specific unified method that is derived mainly from RR results. In addition, the virtues and challenges of surface-enhanced Raman spectroscopy (SERS) are discussed for detecting molecular adsorbates at catalytically relevant interfaces. Tip-enhanced Raman spectroscopy (TERS), which is a combination of SERS and near-field scanning probe microscopy and has the capability of probing molecular adsorbates at specific catalytic sites with an enormous surface sensitivity and nanometre spatial resolution, is also reviewed (300 references).

The vibrational spectrum of Mg2.5VMoO8 obtained by quantum mechanical simulation is compared with the experimentally observed Raman spectrum. This simulation suggests that the observed band at 1016 cm(-1) is attributed to the Mo=O-Mg stretching from two-coordinate oxygen atoms that are adjacent to Mg2+ cation vacancies. Extended X-ray absorption fine structure spectroscopy supports the structural model used to simulate the vibrational modes in Mg2.5VMoO8 that match the observed Raman data.

The vibrational spectrum of Mg2.5VMoO8 obtained by quantum mechanical simulation is compared with the experimentally observed Raman spectrum. This simulation suggests that the observed band at 1016 cm(-1) is attributed to the Mo=O-Mg stretching from two-coordinate oxygen atoms that are adjacent to Mg2+ cation vacancies. Extended X-ray absorption fine structure spectroscopy supports the structural model used to simulate the vibrational modes in Mg2.5VMoO8 that match the observed Raman data.

Vanadia species on aluminas (delta- and gamma-Al2O3) with surface VOx density in the range 0.01-14.2 V/nm2 have been characterized by UV and visible Raman spectroscopy, UV-visible diffuse reflectance spectroscopy (UV-Vis DRS), and temperature-programmed reduction in hydrogen. It is shown that the alumina phase has little influence on the structure and reducibility of surface VOx species under either dehydrated or hydrated conditions. Three similar types of dispersed VOx species, i.e., monovanadates, polyvanadates, and V2O5, are identified on both aluminas under dehydrated conditions. Upon hydration, polymerized VOx species dominate on the surfaces of the two aluminas. The broad Raman band at around 910 cm(-1), observed on dehydrated V/delta-, gamma-Al2O3 at all V loadings (0.01-14.2 V/nm2), is assigned to the interface mode (V-O-Al) instead of the conventionally assigned V-O-V bond. The direct observation of the interface bond is of significance for the understanding of redox catalysis because this bond has been considered to be the key site in oxidation reactions catalyzed by supported vanadia. Two types of frequency shifts of the V=O stretching band (1013-1035 cm(-1)) have been observed in the Raman spectra of V/Al2O3: a shift as a function of surface VOx density and a shift as a function of excitation wavelength. The shift of the V=O band to higher wavenumbers with increasing surface VOx density is due to the change of VOx structure. The V=O stretching band in dispersed vanadia always appears at lower wavenumber in UV Raman spectra than in visible Raman spectra for the same V/Al2O3 sample. This shift is explained by selective resonance enhancement according to the UV-Vis DRS results. It implies that UV Raman has higher sensitivity to isolated and less polymerized VOx species while visible Raman is more sensitive to highly polymerized VOx species and crystalline V2O5. These results show that a multiwavelength excitation approach provides a more complete structural characterization of supported VOx catalysts.

Mg(2.56)V(1.12)W(0.88)O(8) crystals were grown from a MgO/V(2)O(5)/WO(3) melt. X-ray single-crystal diffraction studies revealed that it is orthorhombic with space group Pnma, a = 5.0658(5) A, b = 10.333(1) A, c = 17.421(2) A, Z = 6, and is isostructural with Mg(2.5)VMoO(8). Raman spectra are reported, and the assignment of the Raman bands is made by comparing the metal-oxygen vibrations of VO(4)/WO(4) tetrahedra in Mg(2.5)VWO(8) with the metal-oxygen vibrations of VO(4)/MoO(4) tetrahedra in Mg(2.5)VMoO(8). The stretching vibrations appearing at 1016 and 1035 cm(-)(1) are assigned to Mo=O and W=O double bonds, respectively, associated with the Mg(2+) cation vacancies.

We describe the characterization of an unknown and difficult to identify but geochemically and environmentally significant MnOx structure produced by a freshwater bacterium, Leptothrix discophora SP-6, using combined transmission electron microscopy (TEM), extended X-ray absorption fine structure (EXAFS), and UV Raman spectroscopy. The large surface-to-volume ratio of the needle-shaped nanocrystalline MnO2 formed around the bacterial cells coupled to the porous, zeolite-like structure has the potential to catalyze reactions and oxidize and adsorb metals.

Resonance Raman (RR) spectroscopy has several advantages over the normal Raman spectroscopy (RS) widely used for in situ characterization of solid catalysts and catalytic reactions. Compared with RS, RR can provide much higher sensitivity and selectivity in detecting catalytically-significant surface metal oxides. RR can potentially give useful information on the nature of excited states relevant to photocatalysis and on the anharmonic potential of the ground state. In this critical review a detailed discussion is presented on several types of RR experimental systems, three distinct sources of so-called Raman (fluorescence) background, detection limits for RR compared to other techniques (EXAFS, PM-IRAS, SFG), and three well-known methods to assign UV-vis absorption bands and a band-specific unified method that is derived mainly from RR results. In addition, the virtues and challenges of surface-enhanced Raman spectroscopy (SERS) are discussed for detecting molecular adsorbates at catalytically relevant interfaces. Tip-enhanced Raman spectroscopy (TERS), which is a combination of SERS and near-field scanning probe microscopy and has the capability of probing molecular adsorbates at specific catalytic sites with an enormous surface sensitivity and nanometre spatial resolution, is also reviewed (300 references).