Chinese Journal of Catalysis ›› 2015, Vol. 36 ›› Issue (10): 1733-1741.DOI: 10.1016/S1872-2067(15)60900-7

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Structures and vibrational spectra of Ti-MWW zeolite upon adsorption of H2O and NH3: A density functional theory study

Yiming Qiaoa, Zhilin Fana, Yanjiao Jianga, Na Lia, Hao Donga, Ning Heb, Danhong Zhoua   

  1. a College of Chemistry and Chemical Engineering, Liaoning Normal University, Dalian 116029, Liaoning, China;
    b State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116024, Liaoning, China
  • Received:2015-04-08 Revised:2015-05-18 Online:2015-09-26 Published:2015-09-26
  • Supported by:

    This work was supported by the National Natural Science Foundation of China (21343010).

Abstract:

The structures and vibrational spectroscopic features of framework Ti(IV) species in Ti-MWW zeolite upon adsorption of H2O and NH3 were investigated by density functional theory. The calculations were carried out on cluster models up to 36 tetrahedra at the B3LYP/6-31G(d,p) level of theory. The calculated results indicate that both Ti(OSi)4 and Ti(OSi)3OH species can interact with H2O or NH3 molecules to form five-coordinated complexes. The Ti(OSi)3OH species has higher Lewis acidity and adsorbs the ligands more easily than Ti(OSi)4. The Ti-specific band is attributed to the collective vibration of the antisymmetric stretching of Ti-O-Si bonds. The vibrational frequencies of coordinated Ti species can be divided into two regions: the Ti-specific vibration region and the hydroxyl group vibration region. After adsorption of H2O, the Ti-specific band of the Ti(OSi)4 species shifted from 960 to 970 cm-1, and the Ti-specific bands of the Ti(OSi)3OH species shifted from 990 cm-1 (T1 site) and 970 cm-1 (T3 site) to 980 cm-1. The frequencies of the corresponding NH3 adducts were about 5 cm-1 higher. The Ti(OSi)3OH species can also form hydrogen bonded complexes with H2O and NH3 through Ti-OH, resulting in the hydroxyl stretching band of Ti-OH red shifting by 500-1100 cm-1 and appearing in the 2700-3200 cm-1 region.

Key words: Density functional theory, Titanosilicate, Coordination, Vibrational frequency, Infrared spectroscopy