Study Mo/HZSM-5 catalysts by NMR

By using high-resolution solid state Nuclear Magnetic Resonance spectrometer with 27Al and 29Si probes, the interaction between Mo species and HZSM-5 of Mo/HZSM-5 catalysts has been studied. The results show that there is a strong interaction between Mo species and HZSM-5 zeolite. The framework aluminum in the zeolite can be easily extracted by the introduction of Mo species. The extract ability of framework aluminum by Mo species increases with increasing Mo loading and the calcination temperature. The extraction process leads to the formation of non-framework Al at first and then a new crystalline phase of Al2(MoO4)3. The catalyst, therefore, lost its catalytic activity for methane dehydrogenation and aromatization in the absence of oxygen. The MAS NMR results give us an evidence that Al2(MoO4)3 crystallites are much less active for the reaction.