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Mg Ka X-ray photoelectron spectroscopy (XPS) was used to establish the relative concentration and the chemical state of aluminum at the surface of dealuminated mordenites. A method for the binding energy calibration is proposed. Modified Auger parameters of AI have been determined for different zeolites and clay minerals as well as for dealuminated mordenites. The data are compared with those available in the literature. Ranges of values for modified Auger parameter of octahedral and tetrahedral aluminum are reported. The results obtained on highly dealuminated mordenites are consistent with the presence of surface tricoordinated AI. IntroductionMordenite is used in several industrial catalytic processes.'v2 Dealumination of mordenite is nowadays a common way to improve the catalytic performances as well as the catalyst life.3-4

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Chemisorption of ammonia on the acid sites located at the outer surface of dealuminated mordenites has been investigated by x-ray photoelectron spectroscopy. The N 1s level of chemisorbed ammonia results from the overlap ping of three components occurring near 402.4, 400.5 and 399.1 eV. From the N 1s binding energy of NH,+exchanged mordenite and values reported in the literature for pyridine adsorbed on Bronsted and Lewis acid sites, the components at 402.5 and 399.1 eV are assigned to ammonia in interaction with S i H -A 1 framework groups and with Lewis acid sites, respectively. Based on XPS N/Al ratios and infrared results, the component at 400.5 eV is attributed to ammonia chemisorbed on silanol groups. The surface concentration of the three types of acid sites is estimated from the decomposition of the N 1s peaks. Evidence for the presence of surface extra-framework Al in dealuminated mordenites is provided and the influence of these A1 species on the outer surface acidity is discussed.

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