Novel Large-Pore Aluminophosphate Molecular Sieve STA-15 Prepared Using the Tetrapropylammonium Cation As a Structure Directing Agent

Abstract

The novel aluminophosphate STA-15 (St Andrews microporous solid-15) is prepared by hydrothermal synthesis in the presence of tetrapropylammonium hydroxide (TPAOH), which acts as a structure directing agent. The crystallization is accelerated by the addition of low concentrations of tetraphenylphosphonium or other bulky organic cations, and the purity is improved by the addition of silica to the gel, but these additives are not included in the final crystalline product. The structure of STA-15 was solved by a combination of synchrotron X-ray powder diffraction and modeling. The as-prepared form of STA-15 (Iba2, a = 14.7953(1) Å, b = 27.3634(3) Å, c = 8.34464(6) Å at 100 K) has unit cell composition Al32P32O128(OH)1.8TPA1.8·3H2O. It has a system of one dimensional channels, limited by strongly elliptical 12-membered rings (12 tetrahedral cations and 12 oxygen atoms, 8.7 × 5.7 Å ) in which the TPA+ cations reside. The charge-balancing hydroxide ions are coordinated to framework Al, as shown by 27Al and 31P MAS NMR. STA-15 is stable to removal of the organic and hydroxyl species upon calcination in oxygen, leaving a microporous solid with a pore volume of 0.11 cm3 g-1 and showing uptakes of n-hexane and toluene (at 297 K, p/po = 0.10) of 0.48 and 0.69 mmol g−1, respectively.