Indexed by:期刊论文

Date of Publication:2014-07-15

Journal:MICROPOROUS AND MESOPOROUS MATERIALS

Included Journals:SCIE、EI、Scopus

Volume:193

Page Number:61-68

ISSN No.:1387-1811

Key Words:Polymerization degree; Si and Al sources; Morphology; Zeolite ZSM-5; Crystallization mechanism

Abstract:This study was focused on the regulation of the polymerization degree of silica sol and alumina with NaOH and H2SO4, and the role of the polymerization degree of Si and Al sources in determining the morphology of zeolite ZSM-5. Results show that, NaOH and H2SO4 were useful for decreasing the polymerization degree of silica sol and alumina, respectively. Micro-sized large ZSM-5 crystal can be obtained when the highly polymerized silica sal and alumina (slightly depolymerized by NaOH and H2SO4) were used. On the other hand, fine ZSM-5 crystal can be obtained when the highly depolymerized silica sol and alumina (deeply depolymerized by NaOH and H2SO4) were used. It is possible to fine tune the polymerization degree of silica sal and alumina by NaOH and H2SO4 dosage, and therefore to fine tune the crystal size of zeolite ZSM-5. Raman spectra disclosed that, there existed only very small amount of five-membered structure species in the gels formed by the highly polymerized Si and Al sources. However, monomeric silicate anions could be found in these gels. In contrary, in the gels formed by the deeply depolymerized Si and Al sources, abundant five-membered structure species were seen together with a small amount of monomeric aluminate anions. Such differences of the two kinds of gels accounted for the remarkable distinction of their crystallization processes and product morphologies. (C) 2014 Elsevier Inc. All rights reserved.