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Publication Detail
Activation and local structural stability during the thermal decomposition of Mg/Al-hydrotalcite by total neutron scattering
  • Publication Type:
    Journal article
  • Publication Sub Type:
    Article
  • Authors:
    Mourad MCD, Mokhtar M, Tucker MG, Barney ER, Smith RI, Alyoubi AO, Basahel SN, Shaffer MSP, Skipper NT
  • Publisher:
    ROYAL SOC CHEMISTRY
  • Publication date:
    2011
  • Pagination:
    15479, 15485
  • Journal:
    J MATER CHEM
  • Volume:
    21
  • Issue:
    39
  • Print ISSN:
    0959-9428
  • Language:
    EN
  • Keywords:
    LAYERED DOUBLE HYDROXIDES, MG/AL/CO3-LAYERED DOUBLE HYDROXIDE, METASTABLE SOLID-PHASE, MG-AL HYDROTALCITES, SITU POWDER XRD, CATALYTIC-ACTIVITY, BASE CATALYSTS, MIXED OXIDES, RECONSTRUCTION, CONDENSATION
  • Addresses:
    Mourad, MCD
    UCL
    London Ctr Nanotechnol
    London
    WC1E 6BT
    England

    Bio Nano Consulting
    London
    NW1 3BT
    England
Abstract
The activation of synthetic hydrotalcite, the carbonated layered double hydroxide (LDH) with ratio Mg2+/Al3+ = 3 and structural formula [Mg6Al2(OH)(16)](2+)center dot CO(3)(2-)n(H2O), has been investigated using neutron and X-ray diffraction. In situ neutron diffraction was used to follow the structural phase transformations during the thermal decomposition (calcination) of hydrotalcite under vacuum in the temperature range 298-723 K, and during which the residual gas evolved by the sample was analysed by mass spectrometry. Detailed structural information of the LDH and mixed metal oxides (MMOs) was extracted from both the Bragg peaks and the total scattering. These two analysis techniques provide complementary insight into the relevant transition mechanisms, since Bragg diffraction originates from long-range periodicities within the samples while total scattering reveals the subtleties of the local atomic environment. This latter information is particularly important for our understanding of catalytic activity since it elucidates the local metal coordination. We find that, during the calcination process, the local environment around the metal centres is robust, as the various stages during the phase transition have identical local structures. The implications of these new results for the nature of the MMOs is discussed in relation to the well-studied, reverse, rehydration reaction, and the high propensity of trivalent Al ions to migrate to tetrahedrally-coordinated lattice sites.
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