NH_4F改性MO/HZSM-5催化剂上的甲烷无氧芳构化反应:预处理温度影响的进一步研究

Dehydroaromatization of Methane over Mo/HZSM-5 Pretreated with NH_4F: Further Study on Effect of Pretreatment Temperature

进一步研究了HZSM-5分子筛的NH4F预处理温度对制得的MO/HZSM-5催化剂的影响.X射线衍射和魔角旋转固体核磁共振(27AL MAS NMR)的表征结果表明,NH4F预处理后的HZSM-5分子筛上发生了部分脱铝,在27AL MAS NMR谱中Δ=-12.7处出现了宽化峰,可归属为ALO6-XFX的特征峰.MO/HZSM-5样品的NH3程序升温脱附与27AL MAS NMR结果均表明,MOO3与经NH4F预处理的HZSM-5的相互作用增强,而且该作用随NH4F预处理温度的升高而加大.经NH4F预处理的MO/HZSM-5催化剂显示出良好的抗积碳性能,这不仅与载体B酸量的减少有关,而且与催化剂上MOCX/MOCXOY与载体B酸量的匹配有关.

Mo/HZSM-5 was prepared from HZSM-5 zeolite that was pretreated with NH4F at different temperatures. The results of 27Al magic angle spinning （MAS） NMR show that the pretreatment with NH4F at 623 K causes serious dealumination on HZSM-5, forming a new wide peak at around δ=-12.7, which is attributed to AlO6-xFx species. An enhanced interaction between MoO3 and HZSM-5 is confirmed by NH3 temperature-programmed desorption and 27Al MAS NMR characterization for Mo/HZSM-5 samples, and this interaction becomes more obvious when the pretreatment was carried out at a higher temperature. The coked Mo/HZSM-5 samples prepared with NH4F-pretreated HZSM-5 were characterized by thermogravimetry and temperature-programmed oxidation, and the results show that the NH4F pretreatment improves the catalyst resistance to the coke formation. This is related not only to the decrease in Broensted acid sites on Mo/HZSM-5, but also to the compatibility of the amounts of Broensted acid sites and the active molybdenum species.