Characterization of nanocrystalline zeolite Beta

A thorough characterization of zeolite Beta materials with crystal sizes in the 200 to 10nm range has been done by using a combination of physicochemical techniques (N2 adsorption, XRD, multinuclear MAS NMR, pyridine adsorption, FTIR, thermal analysis). The micropore volume of the zeolite systematically decreases as a function of the decrease in crystal size. This decrease is apparent below 100nm and becomes dramatic for crystal sizes below 50nm. The nanocrystallinity does not affect much the thermal stability of the zeolite in terms of crystallinity, as measured by X-ray diffraction, but severely reduces the stability of Al in the framework during calcination in air. However, calcination in vacuum, and to a lesser extent in N2 followed by air, reduces the extent of the dealumination. The materials with crystal sizes below 50nm present a large mesopore volume (in the 20–300Å diameter range) with a narrow distribution of pore diameters, due to the interparticle space. The mesoporosity is retained after calcination, and the calcined materials combine a large mesoporosity (comparable to that of MCM-41 mesoporous materials) with microporosity, and they possess an acidity typical of zeolites.