不同制备方法对AlOOH结构和甲醇脱水性能的影响

摘要

In this work, four different AlOOH catalysts prepared by complete liquid-phase technology, hydrothermal and precipitation method are investigated and the industrial AlOOH(SB)is used as a control. These catalysts are characterized by XRD, NH3-TPD-MS, FT-IR, N2 adsorption-desorption and TG-DTG, and evaluated in a fixed-bed reactor for methanol dehydration. The results show that significant differences exist in these catalysts of methanol dehydration. The AlOOH catalyst prepared by compete liquid-phase technology followed by calcination for removing deposited carbon on the surface displays the highest activity and good stability, especially the performance in low temperature. On the contrary, the AlOOH catalyst prepared by precipitation method shows the worst activity and bad stability. Combined characterization results with catalytic performance, it can be found that the AlOOH catalyst has weak and strong acid sites, whileγ-Al2O3 only has weak acid sites. When the content of weak acid sites is higher than its strong acid sites, the AlOOH catalyst shows better ability of methanol dehydration. On the other hand, more lattice defects and proper grain size of catalysts are beneficial to the improvement of the ability of methanol dehydration.%采用完全液相、水热和沉淀法制备了4种不同的AlOOH催化剂，选用工业AlOOH（SB粉）作为对照催化剂，分别用 XRD、NH3-TPD-MS、FT-IR、氮物理吸附和热重分析等方法对催化剂进行了表征并将其用于固定床甲醇脱水制二甲醚反应。活性评价结果显示，不同方法制备的 AlOOH 催化剂的甲醇脱水能力存在明显差异，完全液相法制备的催化剂经焙烧除炭后活性高，稳定性好，特别是有良好的低温催化活性，而沉淀法制备的催化剂活性低且稳定性差。表征结果发现，与γ-Al2O3不同，AlOOH表面拥有强、弱两种酸性中心，弱酸量相对较高的AlOOH催化剂具有强的甲醇脱水能力，较多晶格缺陷和晶粒度适中的催化剂有利于甲醇脱水能力的提高。