HZSM-5沸石水热脱铝规律的研究

Study on the hydrothermal dealumination of HZSM-5 zeolite

高温条件下沸石骨架铝的迁脱是引起MTO过程催化剂不可逆失活的关键。应用XRD、IR、NH_3-TPD及^(27)AIMASNMR等谱学技术,表征研究了经水热处理后的HZSM-5(50)的失铝作用及表面酸度的变化。结果表明:在400～600℃经水热处理的HZSM-5(50),其骨架铝的迁脱并不显著影响晶格结构;酸度的变化几乎与骨架铝的迁脱呈平行关系;400℃时骨架铝的迁脱量为600℃时迁脱量的80%,表面强酸中心减少速率较弱酸中心快。认为HZSM-5(50)沸石骨架中可能有两种位置的铝;而对应于强酸中心的铝易于迁移。

The dealumination or zeolite catalyst is an unsolved problem for MTO process under the drastic condition at high temperatures. The dealumination of HZSM-5(50) and the change in surface acidity after hydrothermal treatment have been studied by using XRD, IR, NH_3-TPD and ^(27)Al MASNMR techniques. XRD analysis showed that the framework dealumination of HZSM-5 (50) by steaming at 400～600℃ does not influence the crystallinity. It was found that the variation of acidity is almost in parallel with the amount of Al migrated out of the framework. Steaming at 400℃, dealuminates of the framework Al is about 80%of the amount dealuminated by steaming at 600℃. It is noted that the strong acidity is less stable and lost more easily than the weak acidity. It is suggested that the HZSM-5 (50)consists of two kinds of framework Al in respect of the bonding strength. Steaming at 400℃, the less tightly bonded Al to a Significant extent can be removed more easily than the strongly bonded ones.