FT－IR和程序升温热谱技术研究Mo／HZSM－5催化剂的制备过程

采用ＦＴ－ＩＲ和程序升温热谱技术研究了Ｍｏ／ＨＺＳＭ－５催化剂的制备过程．结果表明Ｍｏ／ＨＺＳＭ－５样品在合适的温度下焙烧一定时间，Ｍｏ物种与ＨＺＳＭ－５分子筛的酸中心（主要是强酸中心）起作用，并且一部分Ｍｏ物种会迁移到分子筛孔道内．在外表面的Ｍｏ物种和在孔道内强酸中心作用的Ｍｏ物种，可能是对甲烷活化起作用的

A STUDY OF THE PREPARATION OF Mo/HZSM 5 ZEOLITE CATALYSTS BY USING FT IR AND TEMPERATURE PROGRAMMED TECHNIQUES

Mo/HZSM 5 catalysts show high reactivity and selectivity in the activation of methane in the absence of oxygen. The catalytic performance of Mo/HZSM 5 catalysts is strongly dependent on the channel structure and acidity of the zeolite and the state and location of Mo species. Mo/HZSM 5 catalysts with Mo loading ranging from 0% to 10% were prepared by impregnation with an aqueous solution of ammonium heptamolybdate (AHM). The samples were dried at 393 K, and then calcined at different temperatures for 4 h. The interaction between Mo species and NH 4ZSM 5 zeolite was characterized by FT IR spectroscopy, differential thermal analysis (DTA), temperature programmed decomposition (TPDE) and NH 3 TPD at different stages of catalyst preparation. The results show that if Mo/HZSM 5 catalysts are calcined at a proper temperature, the Mo species will interact with strong acid sites (mainly with Brnsted acid sites) and part of Mo species will move into the channel. The Mo species in the form of small MoO 3 crystallites residing on the external surface and/or in the channel, and interacting with Brnsted acid sites may be responsible for the methane activation. The strong interaction between Mo species and the framework of HZSM 5 will occur if the catalyst is calcined at 973 K. This may lead to the formation of MoO 2- 4 species, which is much less active for, and detrimental to methane activation.