Arrangements associating three aluminium atoms in dealuminated Y zeolites are for the first time detected using a combination of multiple-quantum MAS (MQMAS) and 2D double-quantum homonuclear NMR correlation spectroscopy. From these results, we propose a model describing the enhanced Brønsted acid sites in dealuminated Y zeolite, consisting in a configuration where framework aluminium pairs are interacting with cationic extra-framework aluminium atoms.

Infrared and MAS NMR spectroscopies of a series of progressively sodium exchanged Y zeolites were used to study the influence of dealumination on Bronsted acidity. Dealumination of Y zeolite introduces extraframework phase in the structure of the zeolite. This extraframework phase can be located in the sodalite cages or in the supercages of the zeolite structure. Two types of extraframework phases can be observed, so-called amorphous and cationic. These two types of aluminium species in two different locations create four different perturbations of the Bronsted acid site. A new model is proposed for the Bronsted sites in the supercage of USY, explaining the influence of extraframework phase on Bronsted acidity.

Raman spectrometry has become a popular characterization technique for hydrotreatment catalysts: it provides important information on chemical structures along all the synthesis cycle, from the impregnation solution to the sulfided catalyst. Aspects of physico-chemical processes taking place on the catalyst surface can be monitored using this technique. This article describes some examples where Raman spectrometry has been used to evaluate the impact of experimental parameters (choice of metallic precursors, presence of impurity, influence of calcination temperature, coke deposit) on the catalyst structure.

Subnanometric cobalt metallic particles, with an average size of 0.8 nm and an estimated number of 50 atoms, have been stabilized in the confined spaces within the nanopores of crystalline molecular sieves. Remarkably, these clusters show a rapid vanishing of the magnetization as the temperature is increased from 10 to 20 K because of the ferromagnetic-paramagnetic transition together with thermal fluctuations of the remaining moment. This dramatic reduction of the transition temperature is due to strong finite size effects. Such behavior, predicted for very small metallic particles, was never observed before due to the inherent difficulty in achieving subnanometric stable metallic particles.