834 research outputs found

    Metal fluorides, metal chlorides and halogenated metal oxides as Lewis acidic heterogeneous catalysts. Providing some context for nanostructured metal fluorides

    Get PDF
    Aspects of the chemistry of selected metal fluorides, which are pertinent to their real or potential use as Lewis acidic, heterogeneous catalysts, are reviewed. Particular attention is paid to β-aluminum trifluoride, aluminum chlorofluoride and aluminas γ and η, whose surfaces become partially fluorinated or chlorinated, through pre-treatment with halogenating reagents or during a catalytic reaction. In these cases, direct comparisons with nanostructured metal fluorides are possible. In the second part of the review, attention is directed to iron(III) and copper(II) metal chlorides, whose Lewis acidity and potential redox function have had important catalytic implications in large-scale chlorohydrocarbons chemistry. Recent work, which highlights the complexity of reactions that can occur in the presence of supported copper(II) chloride as an oxychlorination catalyst, is featured. Although direct comparisons with nanostructured fluorides are not currently possible, the work could be relevant to possible future catalytic developments in nanostructured materials

    Structural and spectroscopic characterisation of C4 oxygenates relevant to structure/activity relationships of the hydrogenation of α,β-unsaturated carbonyls

    Get PDF
    In the present work, we have investigated the conformational isomerism and calculated the vibrational spectra of the C4 oxygenates: 3-butyne-2-one, 3-butene-2-one, 2-butanone and 2-butanol using density functional theory. The calculations are validated by comparison to structural data where available and new, experimental inelastic neutron scattering and infrared spectra of the compounds. We find that for 3-butene-2-one and 2-butanol the spectra show clear evidence for the presence of conformational isomerism and this is supported by the calculations. Complete vibrational assignments for all four molecules are provided and this provides the essential information needed to generate structure/activity relationships for the sequential catalytic hydrogenation of 3-butyne-2-one to 2-butanol

    Hydrogen partitioning as a function of time-on-stream for an unpromoted iron-based Fischer-Tropsch synthesis catalyst applied to CO hydrogenation

    Get PDF
    Sasol Ltd., the EPSRC (award reference EP/P505534/1), and the University of Glasgow are thanked for the provision of a postgraduate studentship (ALD). The STFC Rutherford Appleton Laboratory is thanked for access to neutron beam facilities. The Royal Society is thanked for the provision of an Industry Fellowship (PBW).Inelastic neutron scattering (INS) is employed to examine the evolution of a promoter-free iron-based Fischer-Tropsch synthesis catalyst (∼10 g catalyst charge) that is exposed to ambient pressure CO hydrogenation at 623 K for up to 10 days time-on-stream (T-o-S). The longer reaction time is selected to better understand how the formation of a previously described hydrocarbonaceous overlayer corresponds to the catalyst conditioning process. Although the onset of pseudo steady-state reactor performance is observed at approximately 9 h T-o-S, INS establishes that the intensity of the C-H stretching mode of the sp3-hybridized component of the hydrocarbonaceous overlayer saturates at about 24 h T-o-S, while the corresponding intensity of the C-H stretching mode of the sp2-hybridized component requires 100-200 h T-o-S to achieve saturation. This novel series of measurements reveal different aspects of the complex catalyst evolutionary process to be indirectly connected with catalytic turnover.Publisher PDFPeer reviewe

    Studies on casein kinase from the lactating rabbit mammary gland.

    Get PDF
    The mammary gland specific casein kinase is the enzyme responsible for the in vivo phosphorylation of caseins, the major class of milk proteins. It is distinct from other so-called "casein kinases", which are neither tissue specific nor catalyze the in vivo phosphorylation of caseins. The work here describes the identification, purification and characterization of a casein kinase from the lactating rabbit mammary gland. Initially localization studies, which involved centrifugation of mammary gland sub-cellular fractions through sucrose gradients, showed that whilst a small proportion of the rabbit casein kinase was associated with a golgi enriched fraction, the bulk was present in a fraction shown by electron microscopic analysis to be a homogeneous casein micelle fraction. In order to study further the enzyme from both sources, a sub-cellular fractionation procedure was developed for the co-isolatation of golgi and micelle fractions from mammary gland homogenates. Using these two fractions as starting sources, casein kinase was purified, essentially to homogeneity, by a combination of gel-filtration on Sephacryl-S-300 and affinity chromatography on casein-sepharose. Analysis of the purified material by SDS polyacrylamide gel electrophoresis followed by silver staining showed that in both cases the enzyme comprised a polypeptide doublet of apparent molecular weights 63 and 67 KDaltons. The enzyme was characterized with respect to a number of properties including assay parameters including: temperature, pH, substrate concentration, and the requirement for divalent cations and the effect of a number of activators and inhibitors was studied. It was planned to generate primary sequence data (10-20 amino acids only) which could be used to generate oligonucleotides which in turn could be used in future studies. It was found however that the purification procedure was unsuitable to isolate protein for sequencing since frequently low levels of contaminants were present. To over-come this the purification procedure was modified and an hplc step incorporated. This method was found to be suitable for the isolation of larger quantities (70-100 μg) of pure enzyme. The enzyme was not suceptible to direct sequencing, suggesting the presence of a blocked N-terminus. Treatment of the enzyme by chemical and enzymatic means did not generate any peptide fragments more suitable for sequencing

    Dreamer Technologies\u27 Home Automation System

    Get PDF
    The home automation market has been growing rapidly over the course of the last few years, and it is expected to grow by 143% between 2015 and 2022.1 In the next few years, the connected home automation system will come to fruition and there will be home automation systems for sale that allows users to control any home device seamlessly from an easy to use interface. While there are many home automation companies already in the market, none of them have truly captured the idea of the connected smart home. All of the systems are lacking in some area, whether it be dependence on internet connectivity, or slow response time. And to this date there is no consumer-friendly system that is regarded as the standard for home automation. This market is growing quickly and we hope to use our knowledge of computer systems and computer programing to change and advance the home automation market

    The application of inelastic neutron scattering to investigate the interaction of methyl propanoate with silica

    Get PDF
    A modern industrial route for the manufacture of methyl methacrylate involves the reaction of methyl propanoate and formaldehyde over a silica-supported Cs catalyst. Although the process has been successfully commercialised, little is known about the surface interactions responsible for the forward chemistry. This work concentrates upon the interaction of methyl propanoate over a representative silica. A combination of infrared spectroscopy, inelastic neutron scattering, DFT calculations, X-ray diffraction and temperature-programmed desorption is used to deduce how the ester interacts with the silica surface

    Structure/activity relationships applied to the hydrogenation of α,β-unsaturated carbonyls: The hydrogenation of 3-butyne-2-one over alumina-supported palladium catalysts

    Get PDF
    The gas phase hydrogenation of 3-butyne-2-one, an alkynic ketone, over two alumina-supported palladium catalysts is investigated using infrared spectroscopy in a batch reactor at 373 K. The mean particle size of the palladium crystallites of the two catalysts are comparable (2.4 ± 0.1 nm). One catalyst (Pd(NO3)2/Al2O3) is prepared from a palladium(II) nitrate precursor, whereas the other catalyst (PdCl2/Al2O3) is prepared using palladium(II) chloride as the Pd precursor compound. A three-stage sequential process is observed with the Pd(NO3)2/Al2O3 catalyst facilitating complete reduction all the way through to 2-butanol. However, hydrogenation stops at 2-butanone with the PdCl2/Al2O3 catalyst. The inability of the PdCl2/Al2O3 catalyst to reduce 2-butanone is attributed to the inaccessibility of edge sites on this catalyst, which are blocked by chlorine retention originating from the catalyst’s preparative process. The reaction profiles observed for the hydrogenation of this alkynic ketone are consistent with the site-selective chemistry recently reported for the hydrogenation of crotonaldehyde, an alkenic aldehyde, over the same two catalysts. Thus, it is suggested that a previously postulated structure/activity relationship may be generic for the hydrogenation of α,β-unsaturated carbonyl compounds over supported Pd catalysts

    Structural behaviour of copper chloride catalysts during the chlorination of CO to phosgene

    Get PDF
    The interaction of CO with an attapulgite-supported Cu(II)Cl2 catalyst has been examined in a micro-reactor arrangement. CO exposure to the dried, as-received catalyst at elevated temperatures leads to the formation of CO2 as the only identifiable product. However, phosgene production can be induced by a catalyst pre-treatment where the supported Cu(II)Cl2 sample is exposed to a diluted stream of chlorine. Subsequent CO exposure at ~ 370°C then leads to phosgene production. In order to investigate the origins of this atypical set of reaction characteristics, a series of x-ray absorption experiments were performed that were supplemented by DFT calculations. XANES measurements establish that at the elevated temperatures connected with phosgene formation, the catalyst is comprised of Cu+ and a small amount of Cu2+. Moreover, the data show that unique to the chlorine pre-treated sample, CO exposure at elevated temperature results in a short-lived oxidation of the copper. On the basis of calculated CO adsorption energies, DFT calculations indicate that a mixed Cu+/Cu2+ catalyst is required to support CO chemisorption

    Astronomical verification of a stabilized frequency reference transfer system for the Square Kilometre Array

    Full text link
    In order to meet its cutting-edge scientific objectives, the Square Kilometre Array (SKA) telescope requires high-precision frequency references to be distributed to each of its antennas. The frequency references are distributed via fiber-optic links and must be actively stabilized to compensate for phase-noise imposed on the signals by environmental perturbations on the links. SKA engineering requirements demand that any proposed frequency reference distribution system be proved in "astronomical verification" tests. We present results of the astronomical verification of a stabilized frequency reference transfer system proposed for SKA-mid. The dual-receiver architecture of the Australia Telescope Compact Array was exploited to subtract the phase-noise of the sky signal from the data, allowing the phase-noise of observations performed using a standard frequency reference, as well as the stabilized frequency reference transfer system transmitting over 77 km of fiber-optic cable, to be directly compared. Results are presented for the fractional frequency stability and phase-drift of the stabilized frequency reference transfer system for celestial calibrator observations at 5 GHz and 25 GHz. These observations plus additional laboratory results for the transferred signal stability over a 166 km metropolitan fiber-optic link are used to show that the stabilized transfer system under test exceeds all SKA phase-stability requirements under a broad range of observing conditions. Furthermore, we have shown that alternative reference dissemination systems that use multiple synthesizers to supply reference signals to sub-sections of an array may limit the imaging capability of the telescope.Comment: 12 pages, accepted to The Astronomical Journa