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Articles 1 - 11 of 11
Full-Text Articles in Physical Sciences and Mathematics
H2 Oxidation Over Supported Au Nanoparticle Catalysts: Evidence For Heterolytic H2 Activation At The Metal-Support Interface, Todd N. Whittaker, K. B. Sravan Kumar, Christine Peterson, Meagan N. Pollock, L. C. Grabow, Bert D. Chandler
H2 Oxidation Over Supported Au Nanoparticle Catalysts: Evidence For Heterolytic H2 Activation At The Metal-Support Interface, Todd N. Whittaker, K. B. Sravan Kumar, Christine Peterson, Meagan N. Pollock, L. C. Grabow, Bert D. Chandler
Chemistry Faculty Research
Water adsorbed at the metal-support interface (MSI) plays an important role in multiple reactions. Due to its importance in CO preferential oxidation (PrOx), we examined H2 oxidation kinetics in the presence of water over Au/TiO2 and Au/Al2O3 catalysts, reaching the following mechanistic conclusions: (i) O2 activation follows a similar mechanism to that proposed in CO oxidation catalysis; (ii) weakly adsorbed H2O is a strong reaction inhibitor; (iii) fast H2 activation occurs at the MSI, and (iv) H2 activation kinetics are inconsistent with traditional dissociative H2 chemisorption on metals. Density …
The Critical Role Of Water At The Gold-Titania Interface In Catalytic Co Oxidation, Johnny Saavedra, H. Doan, Christopher J. Pursell, L. C. Grabow, Bert D. Chandler
The Critical Role Of Water At The Gold-Titania Interface In Catalytic Co Oxidation, Johnny Saavedra, H. Doan, Christopher J. Pursell, L. C. Grabow, Bert D. Chandler
Chemistry Faculty Research
We provide direct evidence of a water-mediated reaction mechanism for room-temperature CO oxidation over Au/TiO2 catalysts. A hydrogen/deuterium kinetic isotope effect of nearly 2 implicates O-H(D) bond breaking in the rate-determining step. Kinetics and in situ infrared spectroscopy experiments showed that the coverage of weakly adsorbed water on TiO2 largely determines catalyst activity by changing the number of active sites. Density functional theory calculations indicated that proton transfer at the metal-support interface facilitates O2 binding and activation; the resulting Au-OOH species readily reacts with adsorbed Au-CO, yielding Au-COOH. Au-COOH decomposition involves proton transfer to water and was suggested to be …
Co Adsorption On Supported Gold Nanoparticle Catalysts: Application Of The Temkin Model, Christopher J. Pursell, Bert D. Chandler, M. Manzoli, F. Boccuzzi
Co Adsorption On Supported Gold Nanoparticle Catalysts: Application Of The Temkin Model, Christopher J. Pursell, Bert D. Chandler, M. Manzoli, F. Boccuzzi
Chemistry Faculty Research
The adsorption of CO on the supported gold nanoparticle catalysts Au/TiO2, Au/Fe2O3, and Au/ZrO2 was examined using infrared transmission spectroscopy to quantify the isobaric CO coverage as a function of temperature. The Temkin adsorbate interaction model was then applied to account for the adsorption behavior. To test the general applicability of the Temkin model, this treatment was also applied to three data sets from the literature. This included another real-world catalyst and two model catalysts. All data sets were accurately represented by the Temkin adsorbate interaction model. The resulting thermodynamic metrics are consistent with previous determinations and reflect a particle …
Dications Of Benzylidenefluorene And Diphenylmethylidene Fluorene: The Relationship Between Magnetic And Energetic Measures Of Antiaromaticity, Catherine Do, Julianne Hatfield, Shirali Patel, D Vasudevan, Cornelia Tirla, Nancy S. Mills
Dications Of Benzylidenefluorene And Diphenylmethylidene Fluorene: The Relationship Between Magnetic And Energetic Measures Of Antiaromaticity, Catherine Do, Julianne Hatfield, Shirali Patel, D Vasudevan, Cornelia Tirla, Nancy S. Mills
Chemistry Faculty Research
Oxidation of m- and p-substituted benzylidene fluorenes to antiaromatic dications was attempted by electrochemical and chemical means. Electrochemical oxidation to dications was successful for benzylidene fluorenes with p-methoxy, p-methyl, p-fluoro, and unsubstituted phenyl rings in the 3-position; attempts to oxidize the m-substituted derivatives via electrochemistry were unsuccessful. Chemical oxidation with SbF5/SO2ClF gave the dication of 9-[(4-methoxyphenyl)methylene]-9H-fluorene cleanly; oxidation of all other substituted benzylidene fluorenes resulted in mixtures of products. The excellent linear relationship between the chemical shifts calculated by the GIAO method and the experimental shifts for the p-methoxy-substituted benzylidene fluorene dication …
Antiaromatic Dianions: Dianions Of Dixanthylidene By Reduction And Attempted Excited-State Deprotonation, Mary Black, Clifford Woodford, Nancy S. Mills
Antiaromatic Dianions: Dianions Of Dixanthylidene By Reduction And Attempted Excited-State Deprotonation, Mary Black, Clifford Woodford, Nancy S. Mills
Chemistry Faculty Research
Reduction of dixanthylidene with potassium or lithium resulted in formation of the antiaromatic dianion in high yield. Attempts to form the dianion by excited-state deprotonation of dixanthene with n-butyllithium/TMEDA resulted in formation of the tetraanion from deprotonation ortho to the oxygen. Orientation of the sp3 hydrogens presumably allows preferential deprotonation of the xanthene rings.
Origin Of Enantioselection In Chiral Alcohol Oxidation Catalyzed By Pd[(–)-Sparteine]Cl2, J. A. Mueller, Anne Cowell, Bert D. Chandler, M. S. Sigman
Origin Of Enantioselection In Chiral Alcohol Oxidation Catalyzed By Pd[(–)-Sparteine]Cl2, J. A. Mueller, Anne Cowell, Bert D. Chandler, M. S. Sigman
Chemistry Faculty Research
A kinetic investigation into the origin of enantioselectivity for the Pd[(–)-sparteine]Cl2-catalyzed aerobic oxidative kinetic resolution (OKR) is reported. A mechanism to account for a newly discovered chloride dissociation from Pd[(–)-sparteine]Cl2 prior to alcohol binding is proposed. The mechanism includes (1) chloride dissociation from Pd[(–)-sparteine]Cl2 to form cationic Pd(–)-sparteine]Cl, (2) alcohol binding, (3) deprotonation of Pd-bound alcohol to form a Pd-alkoxide, and (4) β-hydride elimination of Pd–alkoxide to form ketone product and a Pd–hydride. Utilizing the addition of (–)-sparteine HCl to control the [Cl–] and [H+] and the resulting derived rate law, …
Low-Temperature Activation Conditions For Pamam Dendrimer Templated Pt Nanoparticles, Anil Singh, Bert D. Chandler
Low-Temperature Activation Conditions For Pamam Dendrimer Templated Pt Nanoparticles, Anil Singh, Bert D. Chandler
Chemistry Faculty Research
Surface immobilized polyamidoamine (PAMAM) dendrimer templated Pt nanoparticles were employed as precursors to heterogeneous catalysts. CO oxidation catalysis and in situ infrared spectroscopy were used to evaluate conditions for dendrimer removal. Infrared spectroscopy showed thatPAMAMdendrimer amide bonds begin decomposing at temperatures as low as 75 °C. Although the amide stretches are completely removed after 3 h of oxidation at 300 °C, 16 h were required to reach maximum catalytic activity. Further treatment under oxidizing or reducing atmospheres did not cause substantial changes in activity. Infrared spectroscopy of the activated materials indicated that organic residues, probably surface carboxylates, are formed during …
Synthesis And Characterization Of Dendrimer Templated Supported Bimetallic Pt-Au Nanoparticles, Huifang Lang, S. Maldonado, K. J. Stevenson, Bert D. Chandler
Synthesis And Characterization Of Dendrimer Templated Supported Bimetallic Pt-Au Nanoparticles, Huifang Lang, S. Maldonado, K. J. Stevenson, Bert D. Chandler
Chemistry Faculty Research
Bimetallic dendrimer-stabilized nanoparticles (DSNs) were used to prepare supported Pt-Au catalysts within the bulk miscibility gap for this binary system. Hydroxy-terminated generation 5 PAMAM dendrimers were used to prepare Cu0 nanoparticles (NPs). The Cu0 NPs were subsequently used to reduce K2PtCl4 and HAuCl4, preparing stabilized bimetallic Pt-Au NPs with a 1:1 stoichiometry. The stabilized NPs were adsorbed onto a high surface area silica support and thermally activated to remove the dendrimers. Transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and infrared spectroscopy of adsorbed CO showed that this preparation route resulted in NPs in …
Dendrimer-Encapsulated Nanoparticle Precursors To Supported Platinum Catalysts, Huifang Lang, R Alan May, Brianna L. Iversen, Bert D. Chandler
Dendrimer-Encapsulated Nanoparticle Precursors To Supported Platinum Catalysts, Huifang Lang, R Alan May, Brianna L. Iversen, Bert D. Chandler
Chemistry Faculty Research
In this contribution, we report the successful preparation of supported metal catalysts using dendrimer-encapsulated Pt nanoparticles as metal precursors. Polyamidoamine (PAMAM) dendrimers were first used to template and stabilize Pt nanoparticles prepared in solution. These dendrimer-encapsulated nanoparticles were then deposited onto a commercial high surface area silica support and thermally activated to remove the organic dendrimer. The resulting materials are active oxidation and hydrogenation catalysts. The effects of catalyst preparation and activation on activity for toluene hydrogenation and CO oxidation catalysis are discussed.
Synthesis, Characterization, And Molecular Structure Of Bis(Tetraphenylcyclopentdienyl)Rhodium(Ii)⊗, James E. Collins, Michael Castellani, Arnold L. Rheingold, Edward J. Miller, William E. Geiger, Anne L. Rieger, Philip H. Rieger
Synthesis, Characterization, And Molecular Structure Of Bis(Tetraphenylcyclopentdienyl)Rhodium(Ii)⊗, James E. Collins, Michael Castellani, Arnold L. Rheingold, Edward J. Miller, William E. Geiger, Anne L. Rieger, Philip H. Rieger
Chemistry Faculty Research
A 5 day diglyme reflux of Rh(acac)3 and K(C5HPh4), followed by treatment with aqueous HPF6, produces orange-yellow [(C5HPh4)2Rh]PF66 in 40 - 50% yield. Reduction of [(C5HPh4)2Rh]PF6 with sodium amalgam in THF yields olive green (C5HPh4)2Rh in 70% yield. (C5HPh4)2Rh crystallizes in the triclinic [Error : unloaded OLE object or mail attachment]space group with unit-cell parameters of a = 8.622 (3) Å, b = 10.778 (4) Å, c = 12.894 (5) Å, a = 65.58 (3)°, b = 72.66 (3)°, g = 83.52 (3)°, and Z = 1. The least squares data refined to RF = 7.63% and …
Synthesis, Characterization, And Crystal Structure Of The (Η5-C5ph5)Cr(Co)3 Radical, Ray J. Hoobler, Marc A. Hutton, Mills M. Dillard, Michael Castellani, Arnold L. Rheingold, Anne L. Rieger, Philip H. Rieger, Thomas C. Richards, William E. Geiger
Synthesis, Characterization, And Crystal Structure Of The (Η5-C5ph5)Cr(Co)3 Radical, Ray J. Hoobler, Marc A. Hutton, Mills M. Dillard, Michael Castellani, Arnold L. Rheingold, Anne L. Rieger, Philip H. Rieger, Thomas C. Richards, William E. Geiger
Chemistry Faculty Research
The reaction between Cr(CO)6 and Na(C5Ph5 ) in refluxing diglyme yields [Na(diglyme)3/2][(C5Ph5)Cr(CO)3], 1. Metathesis of 1 with [Ph3P=N=PPh3 ]Cl in CH2Cl2 yields [Ph3P=N=PPh3][(C5Ph5)Cr(CO)3], 2. Oxidation of 1 by AgBF4 in cold THF under an argon atmosphere produces (C5Ph5)Cr(CO)3, 3. Complexes 2 and 3 form a redox pair connected by a quasireversible one-electron process, E0 = -0.69 V vs ferrocene in CH2Cl2, …