X-RAY-POWDER DIFFRACTION DETERMINATION OF THE LOCATION OF THALLIUM CATIONS IN HYDRATED ZSM-5

Positions of thallium cations and adsorbed water molecules in zeolite ZSM-5 (Si/Al = 27/1) have been determined at room temperature by X-ray powder diffraction using CuK-alpha radiation. The Rietveld refinement was performed using the system developed at ETH in Zurich. Tl-ZSM-5 is found to be orthorhombic, Pnma, with a = 20.112, b = 19.993, and c = 13.426 angstrom. The Tl+ cations are located in partially occupied sites in the intersection between the straight and sinusoidal channels. The Tl+ cations are surrounded by a nest of coordinating water molecules that accounts for 6/7 of the water; the remaining 1/7 of the water is located in the sinusoidal channel. The profile intensity is very sensitive at low 2-theta angles to the contributions from the Tl+ and water. The final R values are R(F) = 0.10 and R(WP) = 0.204.