An All-Silica Molecular Sieve That Is Isostructural with AlPO4-5

The aluminum phosphate molecular sieve AlPO4-5 has been the subject of much recent interest. Some substitution of Si for the tetrahedral Al and P has been accomplished leading to the SAPO-5 sieves. Now an all-silica sieve, SSZ-24, has been found which is isostructural with AlPO4-5. Syntheses, XRD patterns and unit cell parameters, IR spectra, SEM photos and adsorption properties of AlPO4-5 , SAPO-5 and SSZ-24 are compared. Although many organic templates and a wide variety of synthesis conditions lead to AlPO4-5, and many elements may be substituted for a significant portion of its tetrahedral Al or P, the conditions for synthesis of SSZ-24 are very restricted; only one type of organic template has proven successful, and substitution for the tetrahedral Si is very limited. Adsorption studies show that both AlPO4-5 and SSZ-24 have a preference for 2,2-dimethylbutane over n-hexane, in contrast to most large pore molecular sieves. IR spectra in the lattice vibration range are significantly different.