Two-stage dual template alkali metal-free synthesis of micro-mesoporous aluminosilicates based on ZSM-5 zeolite precursors

Abstract

Carrying out the dual template synthesis (in the presence of molecular and micellar templates) in the alkali metal-free reaction media (pH 11.7-12) at a relatively lowtemperature hydrothermal treatment (100-120°C, duration 3-5 days) allowed to obtain micro-mesoporous aluminosilicates combining the properties of zeolite ZSM-5 and mesoporous molecular sieve AlSi-MCM-41. X-ray amorphous sol-precursors of ZSM-5 zeolite obtained by preliminary hydrothermal treatment of alkali metal-free reaction mixture at 160°C and containing secondary building units of zeolite were used as initial substances for synthesis of micro-mesoporous aluminosilicates. During the joint formation of the structure of zeolite and mesoporous molecular sieve in one reaction mixture and in contiguous conditions close to optimal for their individual formation, composites zeolite/mesoporous molecular sieve were formed. The structural and sorption characteristics and acidity of the obtained composites differ from mechanical mixture of two phases. X-ray amorphous micro-mesoporous aluminosilicate with secondary building units and precursors of ZSM-5 in mesostructure is characterized by higher concentration and strength of Brønsted and Lewis acid sites as well as a higher catalytic activity in the reaction of cracking of cumene compared to AlSi-MCM-41 of similar composition. This aluminosilicate also exhibits a higher total selectivity toward the major products of reaction, in comparison with ZSM-5.Keywords Micro-mesoporous aluminosilicates Á Dual template alkali metal-free synthesis Á Zeolite ZSM-5 precursors Á The degree of zeolitization Á Structure and sorption properties Á Acidity Á Catalytic cracking of cumene

Effect of the template on the hydrothermal synthesis of mixed molecular sieves for methanol dehydration

“…Similarly, to the low-angle XRD results, the absorbance of the peaks increased with the CTAB content up to 10% and decreased thereafter. The absorption band at 963 cm 21 was indicative of the existence of MCM-41 [24]. Thus, the FTIR spectra provided evidences of the formation of the catalyst.…”