多级孔ZSM-5/SAPO-34复合分子筛制备及催化MTO性能研究

Study on preparation of hierarchical ZSM-5/SAPO-34 composite molecular sieve and its MTO performance

为制备性能更加优异的甲醇制烯烃(MTO)催化剂及进一步探究多级孔道对MTO催化反应的影响,采用柠檬酸溶液(CA)运用后处理方法对复合分子筛进行刻蚀,成功制备了具有多级孔道结构的ZSM-5/SAPO-34复合分子筛(CA-Z-S)。对复合分子筛的晶相、骨架、孔结构等理化性质进行了表征;将复合分子筛用于催化MTO反应,考察了复合分子筛的催化性能。表征结果表明,使用CA处理对ZSM-5/SAPO-34复合分子筛的形貌、结构会产生影响,使CA-Z-S具有更紧密的复合结构、适量的弱酸中心和多级孔道复合结构。催化测试结果表明,甲醇转化率达到100%时,CA-Z-S的寿命为1200 min,较SAPO-34提高79%,较ZSM-5/SAPO-34提高30%;CA-Z-S对轻烯烃的选择性达到90.5%,较SAPO-34提高约3.7%。研究结果表明,利用CA对复合分子筛进行后处理,有利于复合分子筛催化MTO反应性能的提升。

In order to prepare MTO catalysts with better performance and further investigate the effect of multi-level pores on the catalytic reaction of MTO,ZSM-5/SAPO-34 composite molecular sieve(CA-Z-S)with multi-level pore structure was successfully prepared by etching the composite molecular sieve with citric acid solution(CA)using post-treatment method.The physicochemical properties of the composite molecular sieve,such as crystalline phase,skeleton and pore structure,were also characterized.The composite molecular sieve was used for catalytic methanol-to-olefin(MTO)reaction and its catalytic performance was investigated.The characterization results showed that the treatment with CA would have effect on the morphological structure of the ZSM-5/SAPO-34 composite molecular sieve,resulting in a more compact composite structure,a moderate amount of weak acid centers and a multi-level pore composite structure of CA-Z-S.The catalytic test results showed that the lifetime of CA-Z-S was 1200 min at 100%methanol conversion,which was 79%higher than that of SAPO-34 and 30%higher than that of ZSM-5/SAPO-34.The selectivity of CA-Z-S for light olefins reached 90.5%,which was about 3.7%higher than that of SAPO-34.The results indicated that the post-treatment of the composite molecular sieve with CA was beneficial to the performance of the composite molecular sieve catalyzed MTO reaction.