Combined study of IRMS-TPD measurement and DFT calculation on Brønsted 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 Brønsted 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 Brønsted OH in the super cage. The acid strength of Brønsted 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 Brønsted OH in the supercage was correlated with the strength of the Brønsted acid site. Thus, the roles of metal cations in Brønsted acidity of Y zeolite was clearly revealed.