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Infrared spectroscopy is used to characterize the hydroxyls of HEMT and the interactions with benzene of these hydroxyls and of Na+ cations in NaEMT. Benzene adsorption studies reveal that HEMT is a stronger solid acid than HY or HSAPO-37 and that ca. 5 5 6 5 % of the theoretical protons are still present after evacuation at 773 K. The changes with loading of the CH out-of-plane vibration of the adsorbed benzene give access to the number of interaction sites (H+ or Na+). In NaEMT all the cations are accessible to benzene. This may result from Na+ ion migration towards the large cages in the presence of the aromatic.EMT zeolite, the hexagonal analogue of faujasite, has been synthesized re~entlyl-~ using 18-crown-6 as the template. It contains Na+ cations which neutralize the charges on the framework. The EMT structure contains two different large cages4 owing to an arrangement of sodalite cages and hexagonal prisms different from that in faujasite. There are two non-equivalent hexagonal prisms, involving two different I sites inside this cage (I, and Ib) as well as two different I' (1; and I;) and I1 (11, and 11,) sites in the sodalite and large cages, re~pectively.~ At 723 K in a dehydrated NaEMT sample containing 25% of cubic faujasite domains, the cations are located, in the sites of a unit cell, as follows: I,( 1.9, Ib(o), 1:(4.5), 1;(4.6), II,(6) and IIb(2.9).5 The exchange of the alkali-metal cations with NH: is very easy.6 This generates a greater number of acid sites than in a faujasite with the same %:A1 ratio and a catalyst which is more active for the cracking of n-hexane.6 The infrared study of the protonic form in the hydroxyl range shows the presence of two hydroxyl bands at wavenumbers close to those observed in faujasi te. 7*8The aim of the present paper is to characterize the protonic acidity of HEMT (number of sites, strength and stability) and to locate the cations in NaEMT in the presence of benzene.

Two sets of WO x /SiO 2 -MCM-41 precatalysts (A and B) were prepared and compared. Tungsten-containing MCM-41 mesoporous molecular sieves have been synthesized with tetraethyl orthosilicate and tungsten precursors, tungstic acid, ``H 2 WO 4 '', or sodium tungstate, in the presence of cetyltrimethylammonium chloride (CTMACl) micelles as template in aqueous acid solution. In route A, H 2 O 2 was added to avoid the formation of iso-(or hetero-) polyoxometalates in the counter-ion-mediated S z X 2 I z pathway with oxo±peroxo species [S z ~quaternary ammonium ion surfactant, in this paper cetyltrimethylammonium (CTMA z ), X 2 ~Cl 2 and/ or anionic peroxo species, I z ~inorganic silicate precursor generating silanols or their protonated forms]. This procedure is compared with methods involving or generating polyoxometalates without peroxo moieties (route B) to determine whether the metal loading and/or dispersion is improved by H 2 O 2 . The native materials were calcined in air (1 K min 21 , isothermal at 920 K for 4 h) in order to decompose the organic template. The resulting molecular sieves have been characterized by chemical analysis, powder X-ray diffraction, UV-visible diffuse re¯ectance spectroscopy, nitrogen sorption isotherms, TEM and EDX analysis, and Raman spectrometry. High incorporation levels ((Si : W) exp molar ratio #30 : 1) with a nearly homogeneous distribution of the dopants can be obtained only by route A. The spectral differences between the materials are correlated with their catalytic reactivities for cyclooctene epoxidation with an anhydrous H 2 O 2 /t-BuOH mixture at room temperature. The results suggest that the novel preparation method (route A) has a marked effect on the dispersion of the WO x species on and into the silica matrix.