Aluminophosphate-based Molecular Sieves Research Articles

A molecular sieve with eighteen-membered rings

In this letter we describe a novel family of aluminophosphate-based molecular sieves denoted as VPI-5. These molecular sieves are the first to contain rings consisting of greater than twelve tetrahedral atoms. The large pores of the VPI-5 materials are long channels circumscribed by rings containing eighteen tetrahedral atoms and possess free diameters of approximately 12-13 A.

Using X-ray Powder Diffraction to Determine the Structure of VPI-5 - A Molecular Sieve with the Largest Known Pores

The synthesis of a new family of aluminophosphate-based molecular sieves containing pores defined by 18 tetrahedrally linked atoms has been described by Davis et al at Virginia Polytechnic Institute (VPI). This development reprsents the first reposted synthesis of a moleoular sieve with pores larger than those defined by 12 tetrahedrally linked atoms. This material has been shown to readily absorb triisopropyl benzene and exhibits a pore size distribution, determined from, its argon adsorption isotherm, which suggests the existence of molecular sieve pores larger than those found in known molecular sieves. Confirmation of a pore defined by 18 tetrahedrally linked aluminum and phosphorus atoms was accomplished by crystallographic structure determination using X-ray powder diffraction data. Single crystal methods were impossible due to an inability to synthesize crystals of suitable size. Details of the structure determination are reported in this work.