Journal of Catalysis, Vol.259, No.2, 203-210, 2008
Combined study of IRMS-TPD measurement and DFT calculation on Bronsted acidity and catalytic cracking activity of cation-exchanged Y zeolites
Ammonia infrared spectroscopy/mass spectroscopy-temperature programmed desorption was applied to Ba-, Ca-, and La-exchanged Y zeolites to measure the Bronsted acidity in detail and to gain insight into its relationship to catalytic cracking activity. It was found that the introduced cation located preferentially on sites I' and/or II replaced the OH in the sodalite cage and hexagonal prism, thereby activating the Bronsted OH in the super cage. The acid strength of Bronsted OH enhanced by the introduced metal cation due to the polarizing effect was confirmed theoretically by density functional calculations. The rate of octane cracking increased with increasing cation exchange, and the turnover frequency on the basis of the number of the active Bronsted OH in the supercage was correlated with the strength of the Bronsted acid site. Thus, the roles of metal cations in Bronsted acidity of Y zeolite was clearly revealed. (C) 2008 Elsevier Inc. All rights reserved.
Keywords:Zeolite;Bronsted acidity;Ammonia;TPD;IR;MS;Ba;Ca;La;Y zeolite;Catalytic cracking;Density functional theory