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本文报道关于HZSM-5分子筛中L酸的形成及其存在形式的研究。直接法合成的HZSM-5分子筛经系列温度培烧脱羟,B酸中心向L酸中心转化,并且在600-700℃有一突变温域。系列温度焙烧过的HZSM-5分子筛样品经乙酰丙酮浸泡后进行~(27)Al NMR检测,发现非骨架铝的数量极少;~(29)Si MAS NMR及X射线衍射实验则说明分子筛骨架上的铝量没有明显变化。没有迹象表明HZSM_5分子筛脱羟形成L酸与脱铝是同步发生的。从而可以否定L酸与脱铝是同步发生的。从而可以否定L酸与非骨架铝的必然联系。论证了与L酸中心所关系的铝离子仍处在HZSM-5分子筛的骨架之上。~(27)Al MAS NMR观测表明随着L酸的生成,与之关系的这一部分骨架铝的配位状态发生了重大的变化。
This article reports on the formation of L acid in HZSM-5 zeolite and its existing forms. Direct synthesis of HZSM-5 molecular sieve through a series of temperature and heat to take off the B, B acid center to L acid center transformation, and in 600-700 ℃ a mutation temperature. A series of samples of HZSM-5 zeolite calcined at elevated temperature were detected by ~ (27) Al NMR after being soaked in acetylacetone, and the amount of non-framework aluminum was found to be very small. The results of ~ (29) Si MAS NMR and XRD showed that the molecular sieve framework The amount of aluminum did not change significantly. There is no indication that the dehydroxylation of HZSM_5 zeolite to form L acid occurs synchronously with dealumination. It can be denied L acid and dealumination occurs simultaneously. Which can negate the inevitable link between L acid and non-framework aluminum. It is demonstrated that the aluminum ion associated with the L acid center is still above the framework of the HZSM-5 molecular sieve. ~ (27) Al MAS NMR observations show that with the formation of L acid, there is a significant change in the coordination state of aluminum in this part of the skeleton.