Mingjin Zhang

W/HZSM-5 catalyst for methane dehydroaromatization: a multinuclear MAS NMR study

Detailed NMR investigations on fresh and coked Mo/HMCM-22 catalysts for methane dehydro-aromatization were presented. 27Al MAS and 29Si MAS as well as corresponding CP/MAS NMR experiments have proved that an interaction between molybdenum and the zeolite lattice occurs during the impregnation and calcination processes of the catalysts. With Bronsted acid sites serving as a powerful trap, molybdenum migrates into the internal channels of the zeolite and reacts preferentially with bridging hydroxyls groups. Thus, molybdenum is anchored to the framework aluminum through an oxygen bridge, which, in turn, modifies the acidic properties of the HMCM-22 and leads to a high dispersion of the molybdenum. If this kind of interaction becomes stronger, expelling of aluminum from the zeolite lattice would occur, with the forming of both octahedral nonframework aluminum and Al2(MoO4)3 crystallites. The latter can be hydrated to [Al(OH)n(H2O)6-n]n(MoO4) (n = 1 or 2) in a water-saturated desiccator and can give a line at ...

Solid state NMR study of acid sites formed by adsorption of SO3 onto γ-Al2O3

Detailed structure of Bronsted acid sites on the surface of SO3/Al2O3 catalyst has been proposed based on 1H/27Al TRAPDOR NMR results and the acidity of the catalyst has also been characterized by NMR probe molecules.