添加剂PVP和MTS对合成Beta分子筛结构与性能的影响

分别以铝酸钠和硅溶胶为铝源和硅源,四乙基氢氧化铵为模板剂,在水热条件下,考察了添加剂(聚乙烯吡咯烷酮(PVP)和甲基三乙氧基硅烷(MTS))对合成Beta分子筛结构与性能的影响,并通过XRD、TEM、BET、ICP、~(29)Si-NMR和NH_3-TPD等方法对合成样品进行了结构表征和作用机理讨论,同时以催化裂化异丙苯为模型反应评价其催化性能。结果表明,与传统Beta分子筛相比,加入PVP后所得样品具有更高结晶度和较高的硅铝物质的量比(25.68)以及较大的比表面积(772 m~2/g);而加入MTS后尽管具有较大比表面积(657 m~2/g)和较高硅铝物质的量比(25.76),但是结晶度却相对降低,且粒径减小(160-320 nm)。两种添加剂作用下所得样品均具有更多酸量,在催化裂化异丙苯的反应中表现出较高的催化活性。

Effect of the additives PVP and MTS on structural properties and synthesis mechanism of Beta zeolite

Beta zeolites were successfully synthesized via hydrothermal method using sodium aluminate as aluminium source, silica sol (Ludox) as silicon source and TEAOH as template, respectively. The effects of different additives polyvinyl pyrrolidone (PVP) and Methyltriethoxysilane (MTS) on their structural properties and synthesis mechanism were investigated in detail by various characterizations, such as XRD, TEM, BET, ICP, ²⁹Si-NMR and NH₃-TPD method. Also, their catalytic performances were evaluated through catalytic cracking of cumene. The results showed that the beta zeolite obtained in the PVP-added system presented a better crystallinity, higher Si/Al molar ratio (25.68), and larger surface area (772 m²/g). Comparably, the MTS-effected samples revealed a larger surface area (657 m²/g), higher Si/Al molar ratio (25.76), but lower crystallinity and smaller particle sizes(around 160-320 nm). Moreover, both of them exhibited a good catalytic activity for cumene cracking due to the existences of abundant and strong acid content.