Acid Catalysis by Dealuminated Zeolite Y. 2. The Roles of Aluminum

摘要

Hexane cracking activity was determined for a series of dealuminated zeolites which were prepared both by treatment with Silicon Tetrachloride and by reaction with steam. Over a range of Silicon/Aluminum ratios from 4.7 to 255 the cracking activity increased in a linear manner with respect to the number of lattice Aluminum ions per unit cell. Thus, a constant turnover frequency is obtained, which is taken as evidence that the acid strength does not vary over this range of Si/Al ratios. By contrast, a zeolite prepared by deamination of Ammonium -Y was very much less active than expected on the basis of the protonic sites. The acidity of the protons in this material is clearly less than in the dealuminated zerolite. These results support a model of strong Bronsted acidity in which a structural aluminum atom has no next-nearest aluminum neighbors in a common 4-ring of the zeolite.