27Al和29Si MAS-NMR对Mo/HZSM-5催化剂的研究

使用＾２９Ａｌ固体离分辨核磁技术对甲烷无氧芳构化催化剂Ｍｏ／ＨＺＳＭ－５分子筛进行了研究，发现ＨＺＳＭ－５分子筛本体中仅含有少量非骨架Ａｌ，Ｍｏ物种与分子筛骨架Ａｌ的相互作用随Ｍｏ担载量以及焙烧的温度的升高而增加，在高温焙烧下，Ｍｏ物种会使分子筛骨架严重脱铝，并且生成Ａｌ２（ＭｏＯ４）３新相，最终导致分子筛骨架塌陷，催化性能下降。

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-5zeolite. 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 nonframework 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.