Search results for "RIZ"
showing 10 items of 9613 documents
Acidic Co-Catalysts in Cationic Gold Catalysis.
2016
A systematic study on the effects of Lewis or Bronsted acid co-catalysts in gold-catalyzed reactions was undertaken using representative reactions (O-, N-, and C-nucleophilic additions to alkynes). Through these reactions, it was demonstrated that an acidic co-catalyst can increase the catalyst turnover significantly, enabling practical reaction rates at competitive catalyst loadings (<1 mol %). Further investigation is currently underway to improve the understanding of the subtle principles underlying these experimental observations.
Self-Assembled Molecular Rafts at Liquid|Liquid Interfaces for Four-Electron Oxygen Reduction
2011
The self-assembly of the oppositely charged water-soluble porphyrins, cobalt tetramethylpyridinium porphyrin (CoTMPyP(4+)) and cobalt tetrasulphonatophenyl porphyrin (CoTPPS(4-)), at the interface with an organic solvent to form molecular "rafts", provides an excellent catalyst to perform the interfacial four-electron reduction of oxygen by lipophilic electron donors such as tetrathiafulvalene (TTF). The catalytic activity and selectivity of the self-assembled catalyst toward the four-electron pathway was found to be as good as that of the Pacman type cofacial cobalt porphyrins. The assembly has been characterized by UV-visible spectroscopy, Surface Second Harmonic Generation, and Scanning …
Characterization of Cobalt Catalysts on Biomass-Derived Carbon Supports
2017
Cobalt catalysts are known to have a high activity and selectivity in the Fischer–Tropsch reaction converting synthesis gas to higher hydrocarbons (C5+). These catalysts have been supported by different porous materials. Porous carbon materials like activated carbon (AC) have physical and chemical surface properties that affect the preparation of supported metal catalysts and can easily be tailored. In this study, AC was produced by carbonization and steam activation of lignin, a waste fraction from the Kraft pulping process. A series of Co/AC-catalysts was produced and characterized by several techniques. According to the results, tailored properties (high surface area, mesoporosity) were …
Impact of Organoaluminum Compounds on Phenoxyimine Ligands in Coordinative Olefin Polymerization. A Theoretical Study
2013
The reduction of the phenoxyimine moiety in three individual species—namely free ligand, aluminum complex, and titanium complex—with aluminum alkyls and aluminum hydride has been studied by means of DFT. It was demonstrated that the free phenoxyimine ligand in an equimolar mixture with trimethylaluminum does not undergo reduction. Instead, experimentally observed formation of the six-membered cyclic aluminum–phenoxyimine complex, useful in the ring-opening polymerization of lactones, takes place as the kinetically and thermodynamically favored process. However, it is anticipated that a 2-fold excess of the aluminum compound, especially aluminum hydride, acting on the resulting cyclic comple…
Post-synthesis alumination of MCM-41: Effect of the acidity on the HDS activity of supported Pd catalysts
2010
Abstract Siliceous MCM-41 with different amount of alumina, from 0.25 up to 4.0 wt%, were prepared by impregnation of the MCM-41 with aqueous solution of Al(NO) 3 ·9H 2 O. The modified mesoporous silicas were then used as supports for Pd catalysts prepared by wet-impregnation from PdCl 2 precursor. Supports and corresponding Pd catalysts were characterized by XRD, XPS and NH 3 -TPD. The catalytic behavior was tested in the hydrodesulfurization (HDS) reaction of thiophene. An increase of the hydrodesulfurization activity with increasing alumina amount up to 0.5 wt% was observed. On the basis of the acidity change of the support and the structural modification underwent by the deposited palla…
Light-induced, site-selective isomerization of glyoxylic acid in solid xenon
2014
Abstract The isomerization of glyoxylic acid (GA) and its water complex was studied in a low temperature xenon matrix. The aim of these studies was to understand how xenon environment affects the cis-trans GA interconversion upon near infrared irradiation. In solid xenon, the GA conformers are embedded in two different matrix sites. These show up as different vibrational bands of GA that exhibit different kinetic rates of isomerization. Upon complexation with water, the isomerization process slows down. Xenon matrix appears not to affect energy relaxation process via intramolecular or intermolecular hydrogen bond as compared with previous experiments in an argon.
Characterization of high-temperature performance of cesium vapor cells with anti-relaxation coating
2017
© 2017 Author(s). Vapor cells with antirelaxation coating are widely used in modern atomic physics experiments due to the coating's ability to maintain the atoms' spin polarization during wall collisions. We characterize the performance of vapor cells with different coating materials by measuring longitudinal spin relaxation and vapor density at temperatures up to 95 °C. We infer that the spin-projection-noise-limited sensitivity for atomic magnetometers with such cells improves with temperature, which demonstrates the potential of antirelaxation coated cells in applications of future high-sensitivity magnetometers.
Vanadium-based Ziegler-Natta catalyst supported on MgCl2(THF)2 for ethylene polymerization
1996
A supported magnesium‐vanadium‐aluminium catalyst was prepared by depositing –with the use of a milling technique–VOCl3 on the MgCl2(THF)2 support and subsequent activation with diethylaluminium chloride. Catalytic activity of the obtained system for ethylene polymerization was evaluated as a function of Mg/V and Al/V ratios as well as catalyst ageing time and polymerization temperature. High concentrations of THF in the catalytic system and considerable excess of an organoaluminium co‐catalyst were found to have no deactivating action on vanadium active sites. The catalyst obtained is stable and its activity for ethylene polymerization is high. It yields polyethylene with higher molecular …
Hydrodesulfurization cobalt-based catalysts modified by gold
2007
Cobalt catalysts supported on amorphous SiO2 and ordered mesoporous silica (MCM-41) were prepared by incipient wetness impregnation. Gold was added by consecutive impregnation or by co-impregnation. The materials were characterised by XPS, XRD and TPR techniques and evaluated in the hydrodesulfurization (HDS) of thiophene in order to investigate the effect of the noble metal on the structure and on the catalytic behaviour of the supported cobalt. Co/MCM-41 exhibited higher HDS activity and higher stability than the Co/SiO2. Moreover, in contrast to silica case, the gold impregnated MCM-41, produced an enhancement of the cobalt catalytic activity, and this is likely to be related to an incre…
Amino-Acid-Based Polymerizable Surfactants for the Synthesis of Chiral Nanoparticles
2016
Amino-acid-based chiral surfactants with polymerizable moieties are synthesized, and a versatile approach to prepare particles thereof with a chiral surface functionality is presented. As an example of an application, the synthesized particles are tested for their ability as nucleating agents in the enantioselective crystallization of amino acid conglomerate systems, taking rac-asparagine as a model system. Particles resulting from chiral surfactants with different tail groups are compared and the results demonstrate that only the chiral nanoparticles made of the polymerizable surfactant are able to act efficiently as nucleation agent in enantioselective crystallization.