Changes in Structural and Electronic Properties of the Zeolite Framework Induced by Extraframework Al and La in H-USY and La(x)NaY: A ~(29)Si and ~(27)Al MAS NMR and ~(27)Al MQ MAS NMR Study

摘要

A ~(27)Al 3Q MAS, a quantitative ~(27)Al MAS, and a ~(29)Si MAS NMR study has been carried out on La(x)NaY and H-USY, Assignment of the different types of Al coordinations has been done using the results of the MQ MAS experiments. The ~(29)Si MAS and ~(27)Al MAS NMR results obtained at high fields (14.1 T) and fast MAS up to 27 kHz made a quantitative assignment possible of the framework and nonframework Al coordinations. It is shown that highly charged octahedrally coordinated extraframework Al causes a polarization inducing a quadrupolar broadening of part of the framework Al in ultrastable Y. A similar interaction is found for the framework of La(x)NaY due to the La~(3+) cations. In both case, charged extraframework species polarize the framework Al. In La(x)NaY, La~(3+) in a cation position and in H-USY extraframework octahedral Al are the origin of the polarization. Besides this short-range polarization effect, an additional long-range effect is observed in La(x)NaY. This long-range geometrical effect causes an increase in both Si-O-Al and Si-O-Si angles depending on the La content.