Measured selectivities and activities in isobutane conversion investigations on high-silica FAU materials prepared by different methods of dealumination indicate that the strong acidity exhibited by hydrothermally dealuminated (ultrastable) materials, while directly related to framework aluminum content, depends on a balance between aluminum in the framework and dislodged or nonframework aluminum that is entrained in the lattice during steam treatment. Isobutane conversions over ultrastable FAU materials containing low fractions of dislodged aluminum exhibit markedly enhanced activities, indicating that conventionally prepared ultrastable materials may contain a higher fraction of dislodged aluminum than is optimum.
Structural parameters for D2O ice VIII have been determined by Rietveld refinement of time-of-flight powder neutron diffraction data collected in situ at 28 kbar and −4 °C. The D2O molecule has a bond length of 0.973 (11) Å and a bond angle of 104(2)°. O–D⋅⋅⋅O bonds are slightly bent with an angle of 177(1)°. Thus, the D2O molecules in ice VIII are essentially identical to those observed in other high pressure ice structures for which accurate structural data are available.
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