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

By D.C. Koningsberger, J.A. van Bokhoven, A.L. Roest, J.T. Miller, G.H Nachtegaal and A. Kentgens


A 27Al 3Q MAS, a quantitative 27Al MAS, and a 29Si 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 29Si MAS and 27Al 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 La3+ cations. In both cases, charged extraframework species polarize the framework Al. In La(x)NaY, La3+ 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

Topics: Scheikunde
Year: 2000
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