Characterization of acid sites on Hf-Beta zeolite by CD3CN IR-TPD.

To identify Hf species and quantitatively evaluate their acid properties, combined measurement of infrared (IR) and temperature-programmed desorption (TPD) with deuterated acetonitrile (CD 3 CN) as probe molecule was performed on Hf-Beta and HfO 2 /Si-Beta. IR spectra of CD 3 CN adsorbed on Hf-Beta showed five types of Hf species including framework open and closed Hf sites, extra-framework HfO 2 , and two types of Hf species bearing hydroxy groups. IR measurement showed structural change in Hf-Beta upon exposing to water vapor with generation of the two types of Hf species bearing hydroxy groups. Integrated molar extinction coefficients for C N stretching vibration of CD 3 CN adsorbed on these Hf species were estimated and the number of each Hf acid site was calculated. Acid strength of these Hf species was estimated from CD 3 CN-TPD measurement in combination with IR; the acid strength of the open and closed Hf sites, extra-framework HfO 2 species, and the other Hf species was found to be strong, moderate, and weak, respectively. [Display omitted] • CD 3 CN IR-TPD can distinguish and quantify Hf species on Hf-Beta zeolite. • IR measurement distinguished five types of Hf species present on Hf-Beta. • Integrated molar extinction coefficients for adsorbed CD 3 CN were estimated. • The number of each Hf acid site was calculated. • Acid strength of these Hf species was estimated by TPD measurement of CD 3 CN. [ABSTRACT FROM AUTHOR]