Raman spectra of pyridine adsorbed on a series of ion-exchanged forms of zeolite Y

Abstract

As with other silicas and aluminas, it is shown that a broad general fluorescence from Y zeolite samples excited by irradiation with the 6328 Å line of a He/Ne laser can be greatly reduced by heating the zeolite in oxygen at 500 °C. This general fluorescence is attributed to the presence of traces of unsaturated hydrocarbon impurities which can be burned off by the oxygen treatment. A narrower residual fluorescence in the region of 14 000–14 500 cm−1 is attributed to the presence of Fe3+ impurities.Successful Raman spectra using He–Ne laser excitation have been obtained from pyridine adsorbed on oxygen-treated NaY zeolite, and on samples of this zeolite in which the majority of sodium ions have been replaced by Li+, K+, Co2+, Cu2+, Ce3+ or H+ (decationated Y zeolite). The position of the v1 Raman band from the ring-breathing mode of pyridine is found to give a linear correlation with q/r for the metal ions (where q is the charge and r the radius of an ion) strongly suggesting that the main adsorption is at cation sites. During adsorption of pyridine on CeY the spectrum changes as a function of time. Adsorption on Ce3+ appears to be the final situation and intermediate Raman spectra suggest that pyridine adsorbs and forms hydrogen bonds with surface OH groups; quite different Raman spectra are obtained from these two surface species. The Raman spectra of pyridine on HY zeolite is consistent with the coexistence of pyridinium ions and hydrogen-bonded pyridine molecules.

Pyridine adsorbed on Na-faujasite: a FT-Raman spectroscopic study

“…Egerton et a1. 6 also observed a shift of the same order of magnitude of the v1 mode of pyridine adsorbed onto faujasites, though they did not give an explanation for this phenomenon. As the effect is much smaller for the v12 than for the uI mode, we will not discuss the former band in detail.…”

Raman Spectroscopy

“…The zeolites have been much more successfully investigated. Angell,(38) Egerton et al, (39) and Buechler and Turkevich(40) have reported the Raman spectra of a large number of both natural and synthetic zeolites.…”

Resolving the Acid Site Distribution in Zn-Exchanged ZSM-5 with Stimulated Raman Scattering Microscopy

“…However, these data do not provide information about the location of active sites in the zeolite crystals. In a similar way to FTIR spectroscopy, the interactions of pyridine with different types of acid sites can be distinguished using the strong resonances of the ring breathing modes (900-1100 cm −1 ) in Raman spectroscopy [41][42][43][44]. The influence of different types of interactions on the ring breathing modes of pyridine can be illustrated with the Raman spectra of the molecule in different solutions ( Figure S4).…”