Density functional studies of zeolites. 2. Structure and acidity of [T]-ZSM-5 models (T=B, Al, Ga, and Fe)

Journal Article · Thu Oct 12 00:00:00 EDT 1995 · Journal of Physical Chemistry

DOI:https://doi.org/10.1021/j100041a021· OSTI ID:136103

Stave, M S; Nicholas, J B ^[1]

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1. Pacific Northwest Lab., Richland, WA (United States)

We use local density functional theory/to study the structure an acidity of a series of molecules that model a catalytic site within zeolite ZSM-5. We consider models of the form (X){sub 3} Si-O(H)-T(X){sub 3} where X = OH, OSiH{sub 3}, and OSi(OH){sub 3} and T = Si, Al, B, Ga, or Fe. The theoretical predictions of the siliceous models agree well with the crystal structure of silicalite, the siliceous ZSM-5 analog. We show how increases in the size of the zeolite model affect the calculated results. In particular, internal coordinates converge quickly with increases in model size, while deprotonation energies do not converge within the range of models tested. We also show the effects on structure and acidity caused by replacing Si with trivalent metals. The most accurate calculations predict acidity increases in the order [B]-ZSM-5 << [Fe]-ZSM-5 < [Ga]-ZSM-5 < [Al]-ZSM-5, in agreement with experimental results. However, the correct prediction of the acidity trend requires both the largest models and extensive geometry relaxation. The calculations also elucidate the experimentally observed change from trigonal to tetrahedral coordination between the neutral and anionic forms of [B]-ZSM-5. This work demonstrates the great potential of density functional theory for the study of zeolite structure, reactivity, and the substitution of transition metals within the zeolite framework. 64 refs., 12 figs., 12 tabs.

• Sponsoring Organization: USDOE
• DOE Contract Number: FG06-89ER75522; AC06-76RL01830
• OSTI ID: 136103
• Journal Information: Journal of Physical Chemistry, Vol. 99, Issue 41; Other Information: PBD: 12 Oct 1995
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
40 CHEMISTRY
66 PHYSICS
99 MATHEMATICS
COMPUTERS
INFORMATION SCIENCE
MANAGEMENT
LAW
MISCELLANEOUS
ZEOLITES
ELECTRON DENSITY
PH VALUE
ACTIVATION ENERGY
CRYSTAL STRUCTURE
CALCULATION METHODS
BORON COMPOUNDS
NUMERICAL DATA
ALUMINIUM COMPOUNDS
GALLIUM COMPOUNDS
IRON COMPOUNDS
BOND ANGLE
BOND LENGTHS
CATALYSTS
PHYSICAL CHEMISTRY
CHEMICAL REACTIONS