17 results on '"Hacksung Kim"'
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2. Activation of Low-Valent, Multiply M–M Bonded Group VI Dimers toward Catalytic Olefin Metathesis via Surface Organometallic Chemistry
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David M. Kaphan, Gokhan Celik, Jacob White, Prachi Sharma, A. Jeremy Kropf, Magali Ferrandon, Hacksung Kim, Alon Chapovetsky, Navneet Singh Khetrapal, Marek Pruski, Massimiliano Delferro, Alfred P. Sattelberger, Evan C. Wegener, Frédéric A. Perras, Jianguo Wen, Fulya Dogan, and Ryan R. Langeslay more...
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Olefin metathesis ,010405 organic chemistry ,Organic Chemistry ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Catalysis ,Inorganic Chemistry ,chemistry.chemical_compound ,Petrochemical ,chemistry ,Group (periodic table) ,Polymer chemistry ,Physical and Theoretical Chemistry ,Organometallic chemistry - Abstract
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... more...
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- 2020
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3. Resolution of Electronic and Structural Factors Underlying Oxygen-Evolving Performance in Amorphous Cobalt Oxide Catalysts
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Sarah R. Soltau, Hacksung Kim, Gihan Kwon, David M. Tiede, David J. Mandia, Alex B. F. Martinson, Hoyoung Jang, Jungho Kim, Anil U. Mane, Jun-Sik Lee, and Lisa M. Utschig
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X-ray absorption spectroscopy ,Oxygen evolution ,chemistry.chemical_element ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Biochemistry ,Catalysis ,0104 chemical sciences ,Amorphous solid ,symbols.namesake ,chemistry.chemical_compound ,Crystallography ,Colloid and Surface Chemistry ,chemistry ,Octahedron ,symbols ,0210 nano-technology ,Raman spectroscopy ,Cobalt oxide ,Cobalt ,Cobalt phosphate - Abstract
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 more...
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- 2018
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4. Formation of [Cu2O2]2+ and [Cu2O]2+ toward C–H Bond Activation in Cu-SSZ-13 and Cu-SSZ-39
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Bahar Ipek, Hacksung Kim, Florian Göltl, Raul F. Lobo, Ive Hermans, Karl S. Booksh, Joseph P. Smith, Matthew J. Wulfers, and Craig M. Brown
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biology ,010405 organic chemistry ,Inorganic chemistry ,Active site ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Catalysis ,Methane ,0104 chemical sciences ,SSZ-13 ,Crystallography ,chemistry.chemical_compound ,symbols.namesake ,chemistry ,biology.protein ,symbols ,Methanol ,Selectivity ,Zeolite ,Raman spectroscopy - Abstract
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... more...
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- 2017
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5. Nuclearity effects in supported, single-site Fe(ii) hydrogenation pre-catalysts
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Oleg G. Poluektov, Ryan R. Langeslay, E. Ercan Alp, Ce Yang, Adam S. Hock, Alfred P. Sattelberger, Bo Hu, Hacksung Kim, Magali Ferrandon, A. Jeremy Kropf, Patricia Anne A. Ignacio-de Leon, Jens Niklas, Cong Liu, Jacob S. Mohar, Massimiliano Delferro, and Hyuntae Sohn more...
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X-ray absorption spectroscopy ,010405 organic chemistry ,Dimer ,010402 general chemistry ,Grafting ,01 natural sciences ,0104 chemical sciences ,Catalysis ,Inorganic Chemistry ,chemistry.chemical_compound ,Monomer ,chemistry ,Single site ,Polymer chemistry - Abstract
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. more...
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- 2018
6. Selective propane dehydrogenation with single-site CoII on SiO2 by a non-redox mechanism
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Adam S. Hock, Ujjal Das, Jeffrey T. Miller, Hacksung Kim, Oleg G. Poluektov, Peter C. Stair, Andrew 'Bean' Getsoian, Bo Hu, Neil M. Schweitzer, Larry A. Curtiss, and Jens Niklas
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X-ray absorption spectroscopy ,Extended X-ray absorption fine structure ,Hydrogen ,Chemistry ,chemistry.chemical_element ,Photochemistry ,Resonance (chemistry) ,Redox ,Catalysis ,law.invention ,law ,Dehydrogenation ,Physical and Theoretical Chemistry ,Electron paramagnetic resonance - Abstract
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. more...
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- 2015
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7. Isolated, well-defined organovanadium(iii) on silica: single-site catalyst for hydrogenation of alkenes and alkynes
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Hacksung Kim, Jens Niklas, Oleg G. Poluektov, Magali Ferrandon, Massimiliano Delferro, Hyuntae Sohn, Cong Liu, Peter C. Stair, P. A. Ignacio-de Leon, Dali Yang, J. Kropf, Ryan R. Langeslay, Justin G. Connell, and Jeffrey Camacho-Bunquin more...
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Inorganic chemistry ,Alkyne ,010402 general chemistry ,01 natural sciences ,Catalysis ,law.invention ,chemistry.chemical_compound ,law ,Polymer chemistry ,Materials Chemistry ,Reactivity (chemistry) ,Electron paramagnetic resonance ,Organometallic chemistry ,chemistry.chemical_classification ,X-ray absorption spectroscopy ,010405 organic chemistry ,Chemistry ,Alkene ,Metals and Alloys ,General Chemistry ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Ceramics and Composites ,Proton NMR - Abstract
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. more...
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- 2017
8. Effects of solvent on the furfuryl alcohol polymerization reaction: UV Raman spectroscopy study
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Hacksung Kim, Peter C. Stair, Christopher L. Marshall, Rajeev S. Assary, Larry A. Curtiss, Taejin Kim, and David J. Gosztola
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Ethanol ,Butanol ,technology, industry, and agriculture ,Alcohol ,macromolecular substances ,General Chemistry ,equipment and supplies ,Photochemistry ,Catalysis ,Furfuryl alcohol ,Solvent ,chemistry.chemical_compound ,symbols.namesake ,chemistry ,Polymerization ,symbols ,lipids (amino acids, peptides, and proteins) ,Solvent effects ,Raman spectroscopy - Abstract
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. more...
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- 2013
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9. Structure-Specific Reactivity of Alumina-Supported Monomeric Vanadium Oxide Species
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Hacksung Kim, Glen Allen Ferguson, Lei Cheng, Larry A. Curtiss, Stan Zygmunt, and Peter C. Stair
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chemistry.chemical_classification ,Denticity ,Alkene ,Inorganic chemistry ,technology, industry, and agriculture ,Activation energy ,Photochemistry ,Vanadium oxide ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Catalysis ,chemistry.chemical_compound ,symbols.namesake ,General Energy ,Monomer ,chemistry ,symbols ,Dehydrogenation ,Physical and Theoretical Chemistry ,Raman spectroscopy - Abstract
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... more...
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- 2012
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10. Precursor Nuclearity Effects in Supported Vanadium Oxides Prepared by Organometallic Grafting
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Tobin J. Marks, Peter C. Stair, Hacksung Kim, and Staci L. Wegener
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X-ray absorption spectroscopy ,Absorption spectroscopy ,Diffuse reflectance infrared fourier transform ,Chemistry ,Vanadium ,chemistry.chemical_element ,General Materials Science ,Physical and Theoretical Chemistry ,Spectroscopy ,Photochemistry ,Grafting ,Vanadium oxide ,Catalysis - Abstract
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... more...
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- 2011
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11. Evidence for Copper Dimers in Low-Loaded CuOx/SiO2 Catalysts for Cyclohexane Oxidative Dehydrogenation
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Peter C. Stair, Hacksung Kim, Scott L. Nauert, Justin M. Notestein, Randall Q. Snurr, and Andrew S. Rosen
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Copper oxide ,Materials science ,Cyclohexane ,Inorganic chemistry ,Oxide ,chemistry.chemical_element ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Copper ,Catalysis ,0104 chemical sciences ,law.invention ,chemistry.chemical_compound ,chemistry ,law ,Dehydrogenation ,Calcination ,0210 nano-technology ,Incipient wetness impregnation - Abstract
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 ... more...
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- 2018
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12. Performance and Characterization of ALD Vanadium Oxide Catalytic Nanoliths
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Jeffrey W. Elam, Peter C. Stair, Joseph A. Libera, Hao Feng, Hacksung Kim, and Michael J. Pellin
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Materials science ,Chemical engineering ,Vanadium oxide ,Characterization (materials science) ,Catalysis - Abstract
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. more...
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- 2009
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13. Catalytic oxidative dehydrogenation of propane over Mg–V/Mo oxides
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Robin R. Hammond, Kenneth R. Poeppelmeier, Peter C. Stair, Donggeun Ko, Matthew T. Smith, Hacksung Kim, Jason D. Pless, and Billy B. Bardin
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Alkane ,chemistry.chemical_classification ,Inorganic chemistry ,chemistry.chemical_element ,Vanadium ,Photochemistry ,Catalysis ,chemistry.chemical_compound ,symbols.namesake ,Hydrocarbon ,chemistry ,Molybdenum ,Propane ,symbols ,Dehydrogenation ,Physical and Theoretical Chemistry ,Raman spectroscopy - Abstract
Fifteen distinct MgOV 2 O 5 , MgOMoO 3 , MgOV 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. more...
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- 2004
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14. UV−Raman Characterization of Iron Peroxo Adsorbates on Fe/MFI Catalyst with High Activity for NOx Reduction
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Qi Sun, Zhi Xian Gao, Peter C. Stair, Hacksung Kim, and Wolfgang M.H. Sachtler
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Chemistry ,Inorganic chemistry ,Photochemistry ,Peroxide ,Surfaces, Coatings and Films ,Catalysis ,law.invention ,Ion ,symbols.namesake ,chemistry.chemical_compound ,Adsorption ,law ,Materials Chemistry ,symbols ,Calcination ,Sublimation (phase transition) ,Physical and Theoretical Chemistry ,Zeolite ,Raman spectroscopy - Abstract
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. more...
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- 2001
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15. Resonance Raman Spectroscopy -Θ-Al2O3-Supported Vanadium Oxide Catalysts as an Illustrative Example
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Peter C. Stair, Hacksung Kim, and Zili Wu
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Materials science ,Resonance Raman spectroscopy ,Physical chemistry ,Vanadium oxide ,Catalysis - Published
- 2009
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16. On the structure of vanadium oxide supported on aluminas: UV and visible raman spectroscopy, UV-visible diffuse reflectance spectroscopy, and temperature-programmed reduction studies
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Sreekala Rugmini, Peter C. Stair, Hacksung Kim, S. David Jackson, and Zili Wu
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Diffuse reflectance infrared fourier transform ,Hydrogen ,Chemistry ,Analytical chemistry ,chemistry.chemical_element ,Resonance (chemistry) ,Vanadium oxide ,Surfaces, Coatings and Films ,Catalysis ,symbols.namesake ,Phase (matter) ,Materials Chemistry ,symbols ,Physical and Theoretical Chemistry ,Temperature-programmed reduction ,Raman spectroscopy - Abstract
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. more...
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- 2006
17. Nanocrystalline Todorokite-Like Manganese Oxide Produced by Bacterial Catalysis
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Hacksung Kim, Pablo A. Pastén, Peter C. Stair, and Jean François Gaillard
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Inorganic chemistry ,engineering.material ,Spectrum Analysis, Raman ,Biochemistry ,Catalysis ,symbols.namesake ,Colloid and Surface Chemistry ,Leptothrix ,Leptothrix discophora ,Fourier Analysis ,biology ,Extended X-ray absorption fine structure ,Chemistry ,Spectrometry, X-Ray Emission ,Oxides ,General Chemistry ,biology.organism_classification ,Nanocrystalline material ,Manganese Compounds ,Todorokite ,Transmission electron microscopy ,engineering ,symbols ,Spectrophotometry, Ultraviolet ,Crystallization ,Raman spectroscopy - Abstract
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. more...
- Published
- 2003
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