Raman spectra of tetramethylammonium ion-containing molecular sieves

Abstract

Raman spectra of the tetramethylammonium (TMA) ions trapped inside the β- or gmelinite cages of molecular sieves with different framework compositions and structures are presented. Most skeletal Raman bands, especially the ν s(CN) and ν as(CN) bands of TMA in the β-cages of molecular sieves with SOD, LTA and FAU structures, are not sensitive to the framework composition, but are sensitive to the structure type of the molecular sieves. The ν s(CN) and ν as(CN) bands of TMA in the β-cages of these zeolites give a correlation with the average intertetrahedral TOT angles calculated using the ν s(TOT) vibration of the corresponding zeolites. However, such a correlation is not found in the Raman spectral changes of TMA with calculated TOT angles for non-zeolitic molecular sieves. Raman spectra of TMA in gmelinite cages show no significant effect from either the framework composition or the structure type of molecular sieves when compared to the spectra from TMA in the β-cages. The appearance of an intense structural Raman band at 1000–1200 cm −1 in the Raman spectra of non-zeolitic molecular sieves suggests that the technique can be useful to prove the substitution of heteroatoms other than Al or Si in the framework of molecular sieves.