METHANE DEHYDROGENATION AND AROMATIZATION IN THE ABSENCE OF OXYGEN ONMO HZSM-5 - A STUDY ON THE INTERACTION BETWEEN MO SPECIES AND HZSM-5 BY USING AL-27 AND SI-29 MAS NMR/

By using a high-resolution solid state nuclear magnetic resonance spec trometer with Al-27 and Si-29 probes, the interaction between Mo speci es and HZSM-5 of Mo/HZSM-5 catalysts has been studied. The results sho w that there is a strong interaction between Mo species and HZSM-5 zeo lite. The framework aluminum in the zeolite can be easily extracted by the introduction of Mo species. The extractability of framework alumi num by Mo species increases with increasing Mo loading and the calcina tion temperature, The extraction process leads to the formation of non -framework Al at first and then a new crystalline phase of Al-2(MoO4)( 3). The dealumination of the catalyst having a Mo loading of 15% and h ad been calcined at 973 K is so severe that all the aluminum in the fr amework are extracted and no framework Al could be detected by Al-27 M AS NMR. The catalyst, therefore, lost its catalytic activity for metha ne dehydrogenation and aromatization in the absence of oxygen, The Si/ Al ratio measured from Si-29 MAS NMR further confirms the dealuminatio n process observed by Al-27 MAS NMR. The MAS NMR results give us an ev idence that Al-2(MoO4)(3) crystallites are much less active for the re action.