title: Ammonia IRMS-TPD measurements and DFT calculation on acidic hydroxyl groups in CHA-type zeolites.
abstract: Brønsted acidity of H-chabazite (CHA) zeolites (Si : Al(2) = 4.2) was investigated by means of ammonia infrared-mass spectrometry/temperature-programmed desorption (IRMS-TPD) methods and density functional calculations. Four IR bands were observed at 3644, 3616, 3575 and 3538 cm(-1), and they were ascribable to the acidic OH groups on four nonequivalent oxygen sites in the CHA structure. The absorption band at 3538 cm(-1) was attributed to the O(4)H in the 6-membered ring (MR), and ammonia adsorption energy (DeltaU) of this OH group was the lowest among the 4 kinds of OH groups. The other 3 bands were assigned to the acidic OH groups in 8MR. It was observed that the DeltaU in 8 and 6MR were 131 (+/-3) and 101 kJ mol(-1), respectively. On the other hand, the density functional theory (DFT) calculations within periodic boundary conditions yielded the adsorption energies on these OH groups in 8 and 6MR to be ca. 130 and 110 kJ mol(-1), respectively, in good agreement with the experimentally-observed values.
authors.affiliation: Department of Materials Science, Faculty of Engineering, Tottori University, Tottori, Japan.
authors.forename: Katsuki
authors.initials: K
authors.lastname: Suzuki
authors.forename: German
authors.initials: G
authors.lastname: Sastre
authors.forename: Naonobu
authors.initials: N
authors.lastname: Katada
authors.forename: Miki
authors.initials: M
authors.lastname: Niwa
mesh_terms: D000465:Algorithms; D000641:Ammonia / Q000737:chemistry*; D017665:Hydroxyl Radical / Q000737:chemistry*; D008958:Models, Molecular; D010100:Oxygen / Q000737:chemistry; D013055:Spectrophotometry, Infrared / Q000379:methods*; D013696:Temperature; D013816:Thermodynamics; D017641:Zeolites / Q000032:analysis / Q000737:chemistry
chemical_list: D017641:Zeolites; D017665:Hydroxyl Radical; D000641:Ammonia; D010100:Oxygen