A comparison of the synthesis and properties of AlPO4-5 and AlPO4-STA-15, a new structure type from a well studied synthetic system

A. L. PICONE, Z. HAN, L. M. CLARK, S. E. ASHBROOK, P. A. WRIGHT

Sorrento

Conferencia; 16th International Zeolite Conference and 7th International Mesostructured Materials Symposium (IZC-IMMS 2010); 2010

Aluminophosphate molecular sieves are prepared in the presence of organic amines or alkylammonium cations that act as structure directing agents. As a result, there is much interest in materials that can be prepared using readily available organic species. The first syntheses concentrated on the use of tetraalkylammonium cations (NR4+, where R = CH3, C2H5, C3H7 and C4H9). The tetrapropylammonium cation (TPA+) has been reported to act as a structure directing agents for the aluminophosphates AlPO4-5 and AlPO4-40 and the silicoaluminophosphates SAPO-5 and SAPO-40, where the product phase depends on the reaction conditions and presence of additives that are not included in the crystals. Here we discuss the detailed synthesis of a novel large pore aluminophosphate, STA-15 (St. Andrews microporous material-15) using the TPA+  as a structure directing agent.  The new solid was prepared during an ongoing program of research in which combinations of organic bases are examined for their co-templating abilities: in the synthesis of STA-15, the addition of low concentrations of large charged molecules along with TPA+ results in the acceleration of crystallisation, without their incorporation. The structure of as-prepared STA-15 was solved by a combination of high resolution synchrotron powder diffraction and modelling, revealing a strongly elliptical pore shape.Original literature syntheses using the TPA+ cation were reported to give the AlPO4-5 structure. In this work we have investigated the synthetic factors that control crystallisation to AlPO4-5 or AlPO4-STA-15. We have also investigated the synthesis of STA-15 where transition metals (Mn, Fe, Co) have been introduced into the synthesis gels. To investigate the effect of this pore shape, the properties of STA-15 have been compared with those of AlPO-5.