IR spectroscopy of probe molecules (pyridine, 2,6-dimethylpyridine, and CO) as well as high-resolution solid state NMR and especially double-resonance experiments give a new insight into the acidic sites of amorphous silica alumina (ASA). ASA samples are heterogeneous compounds that contain a silica alumina mixed phase as well as aluminum clusters and pure silica zones. The distribution of various forms depends both on the preparation method and on the Si/Al ratio. Formation of mixed phase leads to the creation of acidic hydroxyl groups of various strength, up to that present in dealuminated HY zeolite. Detailed spectroscopic analyses show that these acidic OH groups correspond to the silanol groups located in close vicinity to an Al atom in tetrahedral environment. The strength of the acidity of the OH species of ASA could be modified both by the location of the vicinal Al atom on the surface or in the bulk and by the number of aluminum atoms in the vicinity of silanol group. Cogelification of high silica-containing ASA appears as the best mean to prepare homogeneous amorphous aluminosilicate, which exhibits the strongest Brønsted acidity.

The structure and properties of glasses and melts in the MgO-Al 2 O 3 -SiO 2 (MAS) and CaO-MgOAl 2 O 3 -SiO 2 (CMAS) systems play an important role in Earth and material sciences. Aluminum has a crucial influence in these systems, and its environment is still questioned. In this paper, we present new results using Raman spectroscopy and 27 Al nuclear magnetic resonance on MAS and CMAS glasses. We propose an Al/Si tetrahedral distribution in the glass network in different Q n species for silicon and essentially in Q 4 and V Al for aluminum. For the CMAS glasses, an increase of V Al and VI Al is clearly visible as a function of the increase of Mg/Ca ratio in the (Ca,Mg) 3 Al 2 Si 3 O 12 (garnet) and (Ca,Mg)AlSi 2 O 8 (anorthite) glass compositions. In the MAS system, the proportion of V Al and VI Al increases with decreasing SiO 2 and, similarly with calcium aluminosilicate glasses, the maximum of V Al is located in the center of the ternary system.

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From one- to two- and three-dimensional MAS NMR solid-state experiments involving (31)P and (27)Al, we show that the structure of microporous alumino-phosphate AlPO(4)-40 contains at least four times more sites than expected, and we attribute two types of Al(IV) sites. The newly described (27)Al-(31)P MQ-HMQC opens new possibilities of describing details of three-dimensional bounded networks.