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  • X-ray lasersXFELsbiologystructuredynamics  (2)
  • perovskiteferroelectricpowder neutron diffraction  (2)
  • CHA zeolitescatalytic activitylocation of Cu2+synchrotron powder X-ray diffractionRietveld/maximum entropy method  (1)
  • International Union of Crystallography (IUCr)  (5)
  • Institute of Electrical and Electronics Engineers (IEEE)
Collection
Keywords
Publisher
  • International Union of Crystallography (IUCr)  (5)
  • Institute of Electrical and Electronics Engineers (IEEE)
Years
  • 1
    Publication Date: 2014-11-12
    Description: Accurate structural models of reaction centres in zeolite catalysts are a prerequisite for mechanistic studies and further improvements to the catalytic performance. The Rietveld/maximum entropy method is applied to synchrotron powder X-ray diffraction data on fully dehydrated CHA-type zeolites with and without loading of catalytically active Cu2+ for the selective catalytic reduction of NOx with NH3. The method identifies the known Cu2+ sites in the six-membered ring and a not previously observed site in the eight-membered ring. The sum of the refined Cu occupancies for these two sites matches the chemical analysis and thus all the Cu is accounted for. It is furthermore shown that approximately 80% of the Cu2+ is located in the new 8-ring site for an industrially relevant CHA zeolite with Si/Al = 15.5 and Cu/Al = 0.45. Density functional theory calculations are used to corroborate the positions and identity of the two Cu sites, leading to the most complete structural description of dehydrated silicoaluminate CHA loaded with catalytically active Cu2+ cations.
    Keywords: CHA zeolitescatalytic activitylocation of Cu2+synchrotron powder X-ray diffractionRietveld/maximum entropy method
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
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  • 2
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    International Union of Crystallography (IUCr)
    In: IUCrJ
    Publication Date: 2017-07-01
    Keywords: X-ray lasersXFELsbiologystructuredynamics
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
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  • 3
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    International Union of Crystallography (IUCr)
    In: IUCrJ
    Publication Date: 2017-05-11
    Description: The development and application of the free-electron X-ray laser (XFEL) to structure and dynamics in biology since its inception in 2009 are reviewed. The research opportunities which result from the ability to outrun most radiation-damage effects are outlined, and some grand challenges are suggested. By avoiding the need to cool samples to minimize damage, the XFEL has permitted atomic resolution imaging of molecular processes on the 100 fs timescale under near-physiological conditions and in the correct thermal bath in which molecular machines operate. Radiation damage, comparisons of XFEL and synchrotron work, single-particle diffraction, fast solution scattering, pump–probe studies on photosensitive proteins, mix-and-inject experiments, caged molecules, pH jump and other reaction-initiation methods, and the study of molecular machines are all discussed. Sample-delivery methods and data-analysis algorithms for the various modes, from serial femtosecond crystallography to fast solution scattering, fluctuation X-ray scattering, mixing jet experiments and single-particle diffraction, are also reviewed.
    Keywords: X-ray lasersXFELsbiologystructuredynamics
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
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  • 4
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    International Union of Crystallography (IUCr)
    In: IUCrJ
    Publication Date: 2017-04-27
    Keywords: perovskiteferroelectricpowder neutron diffraction
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
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  • 5
    Publication Date: 2017-03-09
    Description: The perovskite Li0.2Na0.8NbO3 is shown, by powder neutron diffraction, to display a unique sequence of phase transitions at elevated temperature. The ambient temperature polar phase (rhombohedral, space group R3c) transforms via a first-order transition to a polar tetragonal phase (space group P42mc) in the region 150–300°C; these two phases correspond to Glazer tilt systems a−a−a− and a+a+c−, respectively. At 500°C a ferroelectric–paraelectric transition takes place from P42mc to P42/nmc, retaining the a+a+c− tilt. Transformation to a single-tilt system, a0a0c+ (space group P4/mbm), occurs at 750°C, with the final transition to the aristotype cubic phase at 850°C. The P42mc and P42/nmc phases have each been seen only once and twice each, respectively, in perovskite crystallography, in each case in compositions prepared at high pressure.
    Keywords: perovskiteferroelectricpowder neutron diffraction
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
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