title: Tracking the structural changes in pure and heteroatom substituted aluminophosphate, AIPO-18, using synchrotron based X-ray diffraction techniques.
abstract: We report the structural changes that occur during the thermal removal of organic template molecules that occlude the pores of small pore nanoporous zeolitic solids, AlPO-18, SAPO-18, CoAlPO-18, ZnAlPO-18 and CoSAPO-18. The calcination process is a necessary step in the formation of active catalysts. The studies performed using time-resolved High Resolution Powder Diffraction (HRPD) and High Energy X-ray Diffraction (HEXRD) techniques at various temperatures reveal that changes that take place are dependent on the type of heteroatom present in the nanoporous solids. While time-resolved HRPD shows clear changes in lattice parameters during the removal of physisorbed water molecules and subsequent removal of the organic template, HEXRD data show changes in various near neighbour distances in AlPO-18, SAPO-18, CoAlPO-18, CoSAPO-18 and ZnAlPO-18 during the calcination process. In particular HEXRD reveals the presence of water molecules coordinated to Al(III) ions in the as-synthesised materials. Upon removal of the template and water, these solids show contraction in the cell volume at elevated temperatures while first and second neighbour distances remained almost unchanged.
authors.affiliation: University College London, Department of Chemistry, 20 Gordon Street, London, WC1H 0AJ, UK.
authors.forename: Martin
authors.initials: M
authors.lastname: Martis
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Smith
authors.forename: Chiu
authors.initials: C
authors.lastname: Tang
authors.forename: Julia E
authors.initials: JE
authors.lastname: Parker
authors.forename: Timothy I
authors.initials: TI
authors.lastname: Hyde
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Watson
authors.forename: Xavier
authors.initials: X
authors.lastname: Baucherel
authors.forename: Shinji
authors.initials: S
authors.lastname: Kohara
authors.forename: Toru
authors.initials: T
authors.lastname: Wakihara
authors.forename: Gopinathan
authors.initials: G
authors.lastname: Sankar