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℃.