ZSM-5分子筛酸性质对甲醛合成三聚甲醛催化性能的影响

ZSM-5分子筛是合成三聚甲醛的有效催化剂。本工作通过XRF、XRD、SEM、NH₃-TPD、Py-FTIR和²⁷Al MAS NMR等手段对一系列不同SiO₂/Al₂O₃物质的量比的ZSM-5分子筛催化剂进行了表征，研究了ZSM-5分子筛中Brønsted酸中心和Lewis酸中心对其甲醛合成三聚甲醛催化性能的影响。结果表明，SiO₂/Al₂O₃物质的量比为250的ZSM-5分子筛具有合适的Brønsted酸中心用于催化甲醛缩聚为三聚甲醛的反应，同时其Lewis酸中心量极少，可有效抑制Cannizzaro或Tishchenko等副反应，提高三聚甲醛的选择性，因而具有最佳的合成三聚甲醛催化性能。寿命实验评价结果显示，SiO₂/Al₂O₃物质的量比为250的ZSM-5分子筛具有良好的催化稳定性，单程寿命长达114 h，并且可通过550℃焙烧再生恢复其催化活性。

Effect of acidity on the catalytic performance of ZSM-5 zeolites in the synthesis of trioxane from formaldehyde

ZSM-5 zeolite is considered as an effective catalyst in the synthesis of trioxane from formaldehyde. In this work, a series of ZSM-5 zeolites with different SiO₂/Al₂O₃ molar ratios were used in the synthesis of trioxane from formaldehyde; through characterization by XRF, XRD, SEM, NH₃-TPD, Py-FTIR and ²⁷Al MAS NMR, the effect of acidity including the Brønsted and Lewis acid sites on the catalytic performance of ZSM-5 zeolites in the trioxane synthesis was investigated. The results indicate that the ZSM-5-250 zeolite with a SiO₂/Al₂O₃ molar ratio of 250 exhibits excellent catalytic performance in the synthesis of trioxane. The ZSM-5-250 zeolite owns sufficient amount of Brønsted acid sites which are active for the synthesis of formaldehyde to trioxane; meanwhile, it has few Lewis acid sites and can then effectively inhibit various side-reactions like the Cannizzaro or Tishchenko reactions. Moreover, the ZSM-5-250 zeolite displays high stability with a single-pass lifetime of 114 h and can be regenerated easily through calcination at 550℃.