Phase transformation of MCM-41 in the mother liquid at moderate temperature

Chun Guey Wu, Yuh Twu Chang

Research output: Contribution to journalArticlepeer-review

Abstract

A new crystalline phase (via amorphous intermediate), NCUZ-1, was obtained when MCM-41 (Si/Al=9) was under prolonged heating in the mother liquid (which contains NaAlO2, [N(CH3)4]2SiO3, SiO2, and surfactant C16H33N(CH3)3OH(aq) at 105°C for more than two weeks. The largest d spacing of NCUZ-1 calculated from X-ray diffraction data is approx. 6 Å, indicating that the long-range order of the mesopores in MCM-41 was not present in NCUZ-1. Nitrogen absorption studies showed that NCUZ-1 contains both mesopores and micropores. The volume ratio of the mesopore to micropore is approx. 10 to 1 and the BET surface area is 400 m2/g. The TEM micrograph of NCUZ-1 revealed a homogenous phase with distorted mesopores. The 13C NMR spectrum of NCUZ-1 before calcination is similar to that of uncalcined MCM-41, indicating that the organic templates in both phases have a similar structure. In the phase transformation process, the counteranion (OH-) of the surfactant template played an important role. It increased the solubility of the aluminosilicate wall; the breaking and reforming the Si-O and Al-O bonds make the phase transformation possible, although the process is very slow. When C16H33N(CH3)3Cl, instead of C16H33N(CH3)3OH, was used as a template, no NCUZ-1 phase was obtained under the same reaction conditions. TEM micrograph, nitrogen absorption isothermal, and 13C NMR spectra of NCUZ-1 suggested that the mesopores were present in the NCUZ-1 phase, although there is no long-range order of these mesopores.

Original languageEnglish
Pages (from-to)311-316
Number of pages6
JournalJournal of Solid State Chemistry
Volume160
Issue number2
DOIs
StatePublished - 2001

Keywords

  • MCM-41
  • Mesoporous
  • Microporous
  • NCUZ-1
  • Phase transformation

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