First synthesis of SAPO molecular sieve with LTL-type structure by hydrothermal conversion of SAPO-37 with FAU-type structure

Abstract

An interzeolite conversion method was applied to the synthesis of silicoaluminophosphate (SAPO) molecular sieves. In the interzeolite conversion process, a structural similarity between the starting zeolite and the final crystallized zeolite was the crucial factor for zeolite crystal growth. We succeeded in the first synthesis of a SAPO with LTL structure from SAPO-37 with FAU structure in the presence of KOH. The d6r unit was the common building unit between both SAPOs. The crystallization of the LTL-type SAPO was accomplished at 170 C and in only one day when tetramethylammonium hydroxide (TMAOH) was added to the starting materials. As the LTL-type SAPO could not be obtained from the amorphous hydrogel prepared from fumed silica, pseudoboehmite, and H 3PO4, even with prolonged reaction time, it was found that the SAPO formation process via such interzeolite conversion was more efficient, with an enhanced crystallization rate. The hydrothermal conversion of SAPO-37 into LTL-type SAPO was also found to depend significantly upon the synthesis parameters of H2O/T (T = Si + Al + P), KOH/T, and TMAOH/T, as well as the synthesis temperature. © 2013 Published by Elsevier Inc. All rights reserved.