在比较了纳米和微米HZSM-5分子筛催化甲醇制丙烯反应性能的基础上,对纳米HZSM-5分子筛进行了氟改性.利用透射电镜、N_2吸附、X射线衍射、氨程序升温脱附和吡啶吸附.红外光谱技术对改性前后的样品进行了表征,并在常压、500℃和甲醇空速(WHSV)为1.0h~(-1)的反应条件下,在连续流动固定床微型反应器上考察了其催化甲醇制丙烯的性能.结果表明,当氟含量<10%时,随氟含量的增加,改件纳米HZSM-5分子筛的酸量减少,酸强度降低,从而使丙烯选择性和催化剂稳定性不断提高.但过量(15%)氟的改性使纳米HZSM-5分子筛的酸量、比表面积和孔容均明显减小,致使其稳定性反而降低.在适量(10%)氟改性的纳米HZSM-5分了筛上.丙烯选择性和维持甲醇完全转化的反应时间分别由原来的30.1%和75h增加到46.7%和145h.
Based on the comparison of catalytic performance of nanosized and mierosized HZSM-5 zeolites for the conversion of methanol to propene.the fluorine-modified nanosized HZSM-5 zeolites were prepared by impregnation with NH4F aqueous solution.The parent and modified samples were characterized by transmission electron microscopy,N_2 adsorption,X-ray diffraction,temperature-programmed desorption ofammonia.and infrared spectroscopy ofadsorbed pyridine.Their performance for conversion of methanol to propene was tested in a continuous flow fixed-bed micro-reactor at atmospheric pressure,500℃,and methanol space velocity(WHSV) of 1.0 h~(-1).The results showed that when the content of fluorine was lower than 10％.the amount and intensity of acidic sites on the fluorinatednanosized HZSM-5 zeolites decreased continuously with fluorine content increasing,which resulted in the enhanced selectivity for propene and catalyst stability.However,the modification with too higher content(15％)of fluorine decreased the catalyst stability due to the distinctly reduced amount of acid sites,surface area,and pore volume.It Was concluded that after modification with appropriate amount(10％)of fluorine,the selectivity for propene and the reaction time that Can maintain toml conversion of methanol was increased significantly to 46.7％and 145 h from 30.1％ and 75 h Over the parent nanosized HZSM-5 zeolite.respectively.
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