Synthesis and characterization of core/shell Al-ZSM-5/silicalite-1 zeolite composites prepared in one step

A new synthesis way to form core/shell Al-ZSM-5/silicalite-1 zeolite composites in one step in fluoride medium is described. The effect of some parameters, such as Si/Al, H2O/SiO2 and F/SiO2 molar ratios, was investigated in order to understand their influence on the features of the products. These ones were systematically characterized by complementary techniques such as thermal analysis, X-ray emission mappings of silicon and aluminum, and in some cases by 27Al, 29Si and 19F MAS NMR.19F liquid state NMR was also performed to detect the presence of fluoro-metal complexes in order to get a better understanding of the crystal growth mechanism. The transposition of the reaction in an alkaline medium was also investigated and this method leads to smaller crystals with a reversed aluminum composition gradient.