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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The relative analyser trailsmission functions of two different XPS spectrometers (VG ESCA-3 Mk I1 and SSI X-F'robe of Fisons) have been determined experimentally by several methods presented in the literature. The transmission function of the VG ESCA-3 Mk I1 can be expressed as T cc En(E,/Ek)", where n is close to 0.8. The transmission function T of the SSI X-Probe cannot be presented as a separate function of En and Ek and it is expressed asThe possible influence of the efficiency D of the detector on the determined transmission functions is discussed. The advantages and disadvantages of the methods used are pointed out, together with their limitations and potential applications. The results show that some methods can only be applied to spectrometers such as the VG ESCA-3Mk I1 in which n is a constant or depends only on Ek . The method proposed by Hemminger et uf. [Surf. InterfaceAnal. 15, 323 (19%)) has been shown to be applicable to both spectrometers but a systematic error can be introduced when D is not constant. Such a systematic error can he reduced by another method but this method can only be applied to spectrometers in which the transmission function is known for a given analyser energy. t

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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.