Crystals morphology of AFO-type structure AlPO4-41 and SAPO-41 molecular sieves

Morphology of AFO-topology molecular sieves has been identified from the large individual crystals of AlPO4-41 and SAPO-41, which were synthesized from three routes: (1) using H3PO3 as the phosphorus source; (2) the mixture of H3PO3 and H3PO4 being used as the phosphorus source; (3) an aluminophosphite NKX-2 used as the aluminum and phosphorus source, respectively. Shape clear large individual crystals of AlPO4-41 with the aspect ratio being 3.0 have been obtained from the in situ transformation of NKX-2. It has been found that H3PO3-containing systems not only favor the formation of AFO-structure molecular sieves, but also promote the growth of their large crystals. The crystal morphology of AlPO4-41 has been identified as octagonal prisms. Furthermore, SAPO-41 crystals with lower aspect ratio (being 0.25) have been obtained. It is notable that if silicon is incorporated in the AFO framework, further crystallization may be hindered, resulting in the formation of plate-like crystals just similar to what happened in AFI-structure. Besides, as the aspect ratio decreases, the diffraction intensities of planes in XRD patterns such as (1 0 0), (0 2 0) (2 1 0), and (1 3 0) decrease, whereas the intensity of (0 0 2) increases remarkably.

Perfect single crystals of AlPO4-41 have been obtained from the transformation of phosphorus valence route. Veil vestured on AFO-structure crystals has been uncovered with the octahedral prism morphology of AlPO4-41 and SAPO-41 crystals being discriminated.Figure optionsDownload as PowerPoint slideResearch highlights
► Large individual crystals of AFO-type molecular sieves have been obtained.
► Octagonal prisms morphology of AlPO4-41 and SAPO-41 crystal is discriminated.
► The transformation of phosphorus valence favor the growth of AlPO4-41 crystals.