On the acid-dealumination of USY zeolite: A solid state NMR investigation

State Key Laboratory of Catalysis, Chinese Academy of Sciences, Peping, Beijing, China
Journal of Molecular Catalysis A Chemical (Impact Factor: 3.62). 03/2003; 194(1-2):153-167. DOI: 10.1016/S1381-1169(02)00531-9


The dealumination of USY (ultrastable Y) zeolites by nitric acid and oxalic acid treatment was systematically investigated by multinuclear solid-state NMR and MQ MAS NMR experiments. The results show that both acids are very effective in removing non-framework Al as well as framework Al but that aluminum is extracted from the lattice at a higher rate by oxalic acid even at low concentrations. The presence of different species (e.g. silanol nest, Al–OH, four-coordinated framework Al, six-coordinated framework Al, six-coordinated non-framework Al and five-coordinated non-framework Al) was detected, and their changes were followed during the dealumination. The investigation gives evidence that the breakdown of the parent USY zeolite mainly depends on the degree of dealumination and that non-framework Al exerts a great effect on the acidity of the USY zeolite. Leaching-induced increase in the Brønsted acidity of the USY zeolite was also observed by 1 H MAS NMR spectroscopy. The different distribution of Al species in these samples accounted for the different catalytic performance of n-dodecane cracking. © 2002 Published by Elsevier Science B.V.

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    • "Their pore dimensions make them selective as to which hydrocarbon molecules diffuse where they are exposed to strong acid sites and converted. Steaming of Y zeolite is commonly used as the most preferred dealumination method for preparation of USY zeolites [6] [7] [8]. Dealumination of Y zeolite improves its thermal and hydrothermal stability, hydrophobicity and also modifies its hydrogen transfer activity. "
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