六氟硅酸铵后处理对H-ZSM-5分子筛酸性影响的固体NMR研究

The Effects of Ammonium Hexafluorosilicate Post-Treatment on the Acidity of H-ZSM-5 Zeolite Studied by Solid-State NMR Spectroscopy

本文利用固体核磁共振(NMR)实验对六氟硅酸铵(AHFS)溶液洗涤前后H-ZSM-5分子筛上铝物种变化引起的酸性改变进行了研究.结果显示经AHFS洗涤处理后,分子筛上构成Brønsted酸的骨架四配位铝物种会部分减少;具有Lewis酸性的骨架三配位铝量在经AHFS脱铝处理后少量降低;同时AHFS温和脱铝的方式主要会引起分子筛上另一类具有Lewis酸性且含Al-OH的铝物种大量减少,从而导致处理后分子筛整体酸性的显著改变.

In this study,solid-state nuclear magnetic resonance(NMR)spectroscopy was used to probe the changes of acidity of H-ZSM-5 zeolite caused by ammonium hexafluorosilicate(AHFS)washing-related changes of aluminium species.It was observed that the four-coordinate framework aluminum species with Brønsted acidity were partially reduced,while the tri-coordinated framework aluminum with Lewis acidity was slightly decreased after the AHFS treatment.However,AHFS washing was also found to induce mild dealumination and a significant reduction of aluminum species with Lewis acidity containing Al-OH group on zeolites,thus resulting in a remarkable change in the overall acidity of the zeolites.