Acta Phys. -Chim. Sin. ›› 2010, Vol. 26 ›› Issue (09): 2503-2509.doi: 10.3866/PKU.WHXB20100839

• QUANTUM CHEMISTRY AND COMPUTATION CHEMISTRY • Previous Articles     Next Articles

Adsorption of Linear C2-C5 Olefins on HYand H-ZSM-5 Zeolites

GUO Yu-Hua1, PU Min2, CHEN Biao-Hua2   

  1. 1. Huzhou Teachers College, Huzhou 313000, Zhejiang Province, P. R. China;
    2. State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, P. R. China
  • Received:2010-02-02 Revised:2010-05-09 Published:2010-09-02
  • Contact: GUO Yu-Hua E-mail:guoyuhua@hutc.zj.cn
  • Supported by:

    The project was supported by the National Key Basic Research Programof China (973) (2004CB217804).

Abstract:

The adsorption properties of linear C2-C5 olefins on HY and H-ZSM-5 zeolites were studied by the ONIOM(B3LYP/6-311++G(d,p):UFF)method. The results indicate that microcosmic interactions of the olefin molecules with the Br?nsted acid sites of the zeolites lead to the formation of π-complexes. The adsorption energies of olefins on zeolites increase with an increase in the number of carbon atoms, and the amount of increase is approximately constant (HY zeolites: ca 12 kJ·mol-1; H-ZSM-5 zeolites: ca 25 kJ·mol-1), which agrees well with the adsorption properties of alkanes on zeolites. The position of the double bond has a fairly large effect on the adsorption energies of olefins. The adsorption energies of 2-olefins are much higher than those of 1-olefins. The adsorption energies of olefins on the different types of zeolites also show a significant difference. The adsorption energies of olefins on small pore H-ZSM-5 zeolites are much larger than those on large pore HY zeolites. Furthermore, the confinement effect in the different types of zeolites is more obvious when the number of carbon atoms increase. From the microstructure, the distance between the adsorbent molecule and the acidic proton in the H-ZSM-5 zeolite is much bigger than that between the adsorbent molecule and the acidic proton in the HY zeolite. These are mainly attributed to differences in the van der Waals interactions for the different types of zeolites, and the small pore zeolites have much stronger van der Waals interactions. Frontier orbital calculations indicate that the catalytic activity of the large pore HY zeolite is similar for small olefins while the catalytic activity of the small pore H-ZSM-5 zeolite decreases slightly with increasing carbon number.

Key words: Adsorption, Olefin, Zeolite, ONIOM

MSC2000: 

  • O641