H-MCM-22沸石分子筛中Brφnsted/Lewis酸协同效应的1H和27Al双量子魔角旋转固体核磁共振研究

摘要

Bronsted/Lewis acid sites synergy in H-MCM-22 zeolite was studied by solid-state nuclear magnetic resonance (NMR). Two-dimensional 1H double quantum-magic angle spinning (DQ-MAS) NMR revealed the details of the spatial relationship between the Lewis and the Bφnsted acid sites in a dealuminated H-MCM-22 zeolite, which implied the existence of a Brensted/Lewis acid sites synergy. Two-dimensional 27A1 DQ-MAS NMR was used to give the details of the spatial proximities of various aluminum species. The Brensted/Lewis acid sites synergy occurred in the supercage of the H-MCM-22 zeolite between a T6 site A1 and extra-framework A1 species. 13C CP/MAS NMR of adsorbed acetone demonstrated that the spatial proximities of the Bransted and Lewis acid sites led to a synergy that enhanced the Brensted acid strength of the dealuminated zeolites. 1H MAS NMR of adsorbed deuterated pyridine confirmed that the Brφnsted/Lewis acid sites synergy occurred in the supercage of H-MCM-22. This finding is important for understanding the mechanism of acid-catalyzed reactions on H-MCM-22 zeolites.%采用各种固体核磁共振(NMR)技术详细研究了H-MCM-22分子筛中Brφnsted/Lewis酸的协同效应.二维1H双量子魔角旋转(DQ-MAS) NMR结果表明,在脱铝H-MCM-22分子筛中Brφnsted酸位(骨架桥式羟基)和Lewis酸位(非骨架铝羟基)之间是空间邻近的,暗示着可能存在B/L酸协同效应.二维27A1 DQ-MAS NMR结果揭示了各种铝物种之间的空间邻近性,表明B/L酸协同效应优先发生在H-MCM-22分子筛超笼中的骨架T6位铝和非骨架铝物种之间.2-13C-丙酮探针分子实验发现,因B/L酸协同效应而导致脱铝H-MCM-22分子筛酸性明显增强,氘代吡啶探针分子实验也证实在H-MCM-22分子筛的超笼中发生了B/L酸协同效应.上述结果将有助于我们理解在脱铝H-MCM-22分子筛上发生的多相催化机理.