AB-INITIO MOLECULAR-ORBITAL CLUSTER STUDIES OF THE ZEOLITE ZSM-5 .1. PROTON AFFINITIES

被引:155
作者
BRAND, HV [1 ]
CURTISS, LA [1 ]
ITON, LE [1 ]
机构
[1] ARGONNE NATL LAB, 9700 S CASS AVE, ARGONNE, IL 60439 USA
关键词
D O I
10.1021/j100151a024
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
In this study we carried out ab initio molecular orbital calculations using the STO-3G, 3-21G, and 6-31G* basis sets on aluminosilicate clusters representing ZSM-5 containing up to 46 tetrahedrally coordinated tetravalent atoms and including (SiO)n rings. The proton affinity and OH stretching frequency of the central bridging oxygen site (O(24) site) are examined as a function of cluster size and shape. The proton affinity is found to depend significantly (5-15 kcal/mol) on the shape of the cluster. Calculation of the electrostatic potential in the region of the central bridging oxygen site for the clusters indicates that this dependence is largely due to electrostatic effects. The effects of geometry relaxation are studied with a constant-volume relaxation method in which a part of the cluster is optimized with the remaining being fixed in its crystal structure. Results indicate that relaxation increases the proton affinity by about 10-15 kcal/mol over the value from the rigid experimental structure. The final calculated proton affinity for the O(24) site in ZSM-5, including correction for zero-point effects, O:Si ratio, and higher level theory, is consistent with experiment. The OH stretching vibrational frequency is in good agreement with the experimental value.
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收藏
页码:12773 / 12782
页数:10
相关论文
共 52 条
  • [11] NON-EMPIRICAL QUANTUM CHEMICAL STUDY OF THE SITING AND PAIRING OF ALUMINUM IN THE MFI FRAMEWORK
    DEROUANE, EG
    FRIPIAT, JG
    [J]. ZEOLITES, 1985, 5 (03): : 165 - 172
  • [12] DWYER J, 1988, STUD SURF SCI CATAL, V35, P5
  • [13] NATURAL HYBRID ORBITALS
    FOSTER, JP
    WEINHOLD, F
    [J]. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 1980, 102 (24) : 7211 - 7218
  • [14] NON-EMPIRICAL QUANTUM-MECHANICAL CALCULATIONS ON PENTASIL-TYPE ZEOLITES
    FRIPIAT, JG
    BERGERANDRE, F
    ANDRE, JM
    DEROUANE, EG
    [J]. ZEOLITES, 1983, 3 (04): : 306 - 310
  • [15] FRISCH MJ, 1990, GAUSSIAN 9
  • [16] INTERACTION OF SURFACE HYDROXYLS WITH ADSORBED MOLECULES - A QUANTUM-CHEMICAL STUDY
    GEERLINGS, P
    TARIEL, N
    BOTREL, A
    LISSILLOUR, R
    MORTIER, WJ
    [J]. JOURNAL OF PHYSICAL CHEMISTRY, 1984, 88 (23) : 5752 - 5759
  • [17] A MOLECULAR-ORBITAL STUDY OF BOND LENGTH AND ANGLE VARIATIONS IN FRAMEWORK STRUCTURES
    GEISINGER, KL
    GIBBS, GV
    NAVROTSKY, A
    [J]. PHYSICS AND CHEMISTRY OF MINERALS, 1985, 11 (06) : 266 - 283
  • [18] PROTONATION OF 3-MEMBERED RING MOLECULES - AB-INITIO SCF VERSUS ELECTROSTATIC PICTURE OF PROTON APPROACH
    GHIO, C
    TOMASI, J
    [J]. THEORETICA CHIMICA ACTA, 1973, 30 (02): : 151 - 158
  • [19] STUDY OF THE MOLECULAR ELECTROSTATIC POTENTIALS OF ZEOLITES - THE ACIDITY IN OFFRETITE
    GOURSOT, A
    FAJULA, F
    DAUL, C
    WEBER, J
    [J]. JOURNAL OF PHYSICAL CHEMISTRY, 1988, 92 (15) : 4456 - 4461
  • [20] Hehre W.J., 1987, AB INITIO MOL ORBITA