Synthesis and thermal stability of SOD-type SAPO-20 via interzeolite conversion of FAU-type SAPO-37 using tetramethylammonium hydroxide and piperidine

Abstract

Interzeolite conversion (IZC) of zeolites has attracted significant attention; however, research on silicoaluminophosphate zeolite system is still in its early stages. Herein, an IZC of an FAU-type silicoaluminophosphate zeolite (SAPO-37) is performed using tetramethylammonium hydroxide (TMAOH) and piperidine as organic additives. For comparison, conventional hydrothermal synthesis using an amorphous precursor instead of SAPO-37 is also performed. Using TMAOH, SOD-type silicoaluminophosphate zeolites (SAPO-20) are obtained from both parent SAPO-37 and the amorphous precursor. However, in the case of piperidine, SAPO zeolites with different topologies are obtained from parent SAPO-37 and the amorphous precursor; that is, SOD-type SAPO-20 is obtained from parent SAPO-37, and CHA-type silicoaluminophosphate (SAPO-34) is obtained from the amorphous precursor. Piperidine molecules, as organic additives, are observed to be occluded in the cages of the obtained SAPO-20. The characteristics and thermal stability of the as-synthesized SAPO-20 are analyzed in detail.