Formation of microporous material AlPO 4-18 under dry-gel conversion conditions

Abstract

The formation of microporous molecular sieve AlPO 4-18 under the dry gel conversion (DGC) conditions was examined. The evolution of the dry gel was monitored by powder XRD, SEM and, in particular, solid-state NMR techniques. The results show that the aluminophosphate (AlPO) amorphous dry gel is first converted to a layered AlPO phase. The layered intermediate has some resemblances to AlPO 4-18 and is held together by very weak non-bonding interactions. Continuous heating results in the transformation of this layered phase into AlPO 4-18 via reorganizations and condensations of P and Al sites. Three non-equivalent P sites of AlPO 4-18 develop at different rates during the evolution.