CHARACTERIZATION OF ACIDITY IN ZSM-5 ZEOLITES - AN X-RAY PHOTOELECTRON AND IR SPECTROSCOPY STUDY

An X-ray photoelectron spectroscopic (XPS) method is proposed for the identification and quantitation of Brønsted and Lewis acid sites in ZSM-5 zeolites. The method consists of deconvoluting the N1s XPS level of chemisorbed pyridine and measuring the relative intensities of the peak components. It was found that pyridine is chemisorbed in three different states on ZSM-5 zeolites corresponding to N1s binding energy of 398.7, 400.0, and 401.8 eV, respectively. The first peak at 398.7 eV was assigned to N1s level of pyridine adsorbed on Lewis sites, while the second and third were assigned to N1s levels of pyridine adsorbed on relatively weak and strong Brønsted acid sites, respectively. Comparison of the concentrations of the various acid sites as determined from the relative intensities of the N1s components with IR spectroscopic data showed that XPS has potential applications in the identification and the quantitative determination of Brønsted and Lewis acid sites in zeolites. © 1990 American Chemical Society.