CeO2复合改性ZSM-5分子筛用于催化甲醇制丙烯研究

在甲醇制丙烯(MTP)反应中,ZSM-5分子筛较强的酸性易使甲醇与ZSM-5接触发生氢转移、芳构化等二次反应,堵塞孔道,使得其微孔结构更加不利于分子的扩散,加速催化剂积碳失活,导致丙烯选择性和丙烯/乙烯(P/E)比值下降。因此,本文利用催化活性较高的CeO₂对ZSM-5分子筛进行复合改性以达到有效降低其酸性并增大介孔的目的来提高丙烯选择性和P/E比。通过XRD、NH₃-TPD和N₂吸脱附技术表征,研究了不同ZSM-5硅铝比(摩尔比)、两相质量比(m(CeO₂)/m(ZSM-5))对CeO₂/ZSM-5复合催化剂物化性质的影响。在反应温度480 ℃、重时空速2.6 h^-1、N₂流量100 mL·min^-1、常压纯甲醇进料的条件下,考察了所制备的复合催化剂催化MTP的性能。结果表明,硅铝比为250、m(CeO₂)/m(ZSM-5)为1∶4的复合催化剂比以往研究结果具有更优异的MTP催化性能,甲醇转化率为99.9%,丙烯选择性为42.78%,P/E比为6.3。

CeO2 Composite Modified ZSM-5 Molecular Sieve for Catalyzing Methanol to Propylene

In methanol to propylene (MTP) reaction, due to the strong acidity of ZSM-5 molecular sieve, the secondary reactions such as hydrogen transfer and aromatization between methanol and ZSM-5 are easy to block the pores, making its microporous structure more unfavorable to the diffusion of molecules, accelerating the carbon deposition and deactivation of the catalyst, resulting in the decrease of propylene selectivity and propylene/ethylene (P/E) ratio. Therefore, in this paper, ZSM-5 molecular sieve was modified by CeO₂ with high catalytic activity to effectively reduce its acidity and increase mesoporous, so as to improve propylene selectivity and P/E ratio. The effects of different n(SiO₂)/n(Al₂O₃) and mass ratio of two phases (m(CeO₂)/m(ZSM-5)) on the physicochemical properties of CeO₂/ZSM-5 catalysts were investigated by XRD, XRF, NH₃-TPD and N₂ adsorption and desorption. When the reaction temperature was 480 ℃, the weight hourly space velocity was 2.6 h^-1, the nitrogen flow rate was 100 mL·min^-1, the pressure was atmospheric and pure methanol was fed, and the MTP catalytic performance of the prepared composite catalyst was investigated. The results indicate that the composite catalyst with n(SiO₂)/n(Al₂O₃) of 250 and m(CeO₂)/m(ZSM-5) of 1∶4 exhibits better MTP catalytic performance than the previous research results, with conversion of methanol of 99.9%, selectivity of propylene of 42.78%, and P/E ratio of 6.3.