Abstract:

The effect of particle size of silica sol on the acidity and MTO reaction performance of SAPO-34 was investigated. The synthesized molecular sieves were characterized by XRD, SEM, FTIR, NH₃-TPD and ²⁹Si MAS NMR, and their catalytic performance was evaluated on a fixed bed micro reactor at atmospheric pressure. The experimental results displayed that the particle size of silica sol had significantly affected the acidity of the prepared molecular sieves. The NH₃-TPD characterization results demonstrated that the strong and weak acidity of the molecular sieves decreased with the increase of the particle size of the silica sol. The ²⁹Si MAS NMR results indicated that the use of silica sol with large particles led to the formation of silicon island in the structure of SAPO-34 molecular sieve. From the results of MTO performance evaluation, it could be found that the silica sol with suitable particle size was more conducive to improve the selectivity of light olefins and the catalyst’s life.

Key words: silica sol, synthesis, molecular sieves, catalysis, methanol to olefin, acidity, particle size

摘要：

在合成SAPO-34的过程中加入不同粒径的硅溶胶来考察其对分子筛酸性和甲醇制烯烃（MTO）性能的影响。采用XRD、SEM、FTIR、NH₃-TPD和²⁹Si MAS NMR等表征手段对合成的分子筛进行表征，并通过固定床反应器对制备的SAPO-34分子筛进行MTO催化性能评价。实验结果表明，不同粒径的硅溶胶对合成的分子筛酸性有很大影响，通过NH₃-TPD表征结果可以看出，随着硅溶胶粒径的增大，分子筛的强酸量、弱酸量均降低。由分子筛的NMR表征结果发现，大颗粒硅溶胶合成的SAPO-34分子筛中存在硅岛。从MTO性能评价结果可以发现，适宜的硅溶胶粒径更有利于提高催化剂的双烯选择性和催化寿命。

关键词: 硅溶胶, 合成, 分子筛, 催化, 甲醇制烯烃, 酸性, 粒径