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abstracts
Modern in situ synchrotron powder diffraction experiments can produce massive volumes of data which are of suitable quality for real structural information to be extracted. Parametric Rietveld refinement (Stinton, 2007) is an ideal method for dealing with such datasets as a huge number of diffraction patterns can be processed in parallel while the number of refined parameters is reduced by linking between scans. The time saving compared to earlier sequential methods of refinement using batch files is very significant with processing times being reduced from weeks to a few hours. The stability of the parametric method allows not only extraction of information from data with very weak trends but also refinement of entire slices of a tomographic map including the regions with zero diffraction. The power of the technique will be illustrated by examples from reactor scanning experiments with high time resolution (Wragg, 2012, 2013) as well as more conventional in situ powder diffraction and operando experiments combining diffraction with mass spectrometry. The extraction of structural information from complete tomographic datasets and reconstructions with real structural parameters will also be demonstrated. The figure shows time and space resolved c-axis data for the SAPO-34 catalyst during methanol to olefin conversion, together with mass spectrometry data collected during the experiment.
abstracts
Zeolites are widely used in the chemical industry for their catalytic properties and their ability to control the size and shape of both reactant and product molecules. In this presentation we will show unexpected catalytic properties of ZSM-57 and SUZ-4 during conversion of methanol to hydrocarbons (MTH). We have previously shown how analysis of anisotropic peak broadening in XRPD data [1] can reveal not only the average shape of the crystallites, but also how the zeolite channels are orientated relative to the morphology [2]. The same method was used to analyze the ZSM-57 and SUZ-4 samples revealing nano-sheet and -needle morphologies respectively. Electron imaging and diffraction furthermore revealed that the sheets of ZSM-57 are five-fold twinned with the 10-ring channel system perpendicular to the sheet. The 8-ring channel system would form a closed pentagon shape in defect free crystals. Based on these observations we will explain the remarkable MTH lifetime and selectivity displayed by the ZSM-57 and SUZ-4 samples respectively [3].
