Using the thallous ion exchange method to exchange tin into high alumina zeolites. 1. Crystal structure of |Sn2+5.3Sn4+0.8Cl-1.8|[Si12Al12O48]-LTA

Abstract

Sn2+ and Sn4+ ions have replaced all of the Tl+ ions in the zeolite Tl12-A (|Tl12|[Si12Al12O48]-LTA) by thallous ion exchange (TIE), a vapor phase ion exchange method: SnCl2(g) was allowed to react with Tl12-A under anhydrous conditions at 723 K for 48 h. The tin content of the product, |Sn2+5.3Sn4+0.8Cl-1.8|[Si12Al12O48]-LTA, is 32.6 wt %, much higher than previously reported for any zeolite. Its structure was determined by single-crystal crystallography at 294 K using synchrotron X-radiation (Pm3¯m, a = 12.075(1) Å, R1 = 0.069, R2 = 0.224), and its composition was confirmed by scanning electron microscopy energy-dispersive X-ray analysis. Sn2+ is found at four crystallographic positions, Sn4+ at two, and Cl- at two. Among the 5.3 Sn2+ ions per unit cell, 2.7 (3-coordinate) lie opposite 6-rings in large cavities, 0.3 (4-coordinate) are opposite 6-rings in sodalite cavities, 1.5 are in 8-rings, and 0.7 approach a framework oxygen atom and two chloride ions in a trigonal planar manner. Among the 0.8 Sn4+ ions per unit cell (all 3-coordinate, from the disproportionation of Sn2+), 0.7 are opposite the intersection of a 4-, a 6-, and an 8-ring in large cavity, and 0.1 are in 6-rings. Most of the Cl- ions bridge between Sn2+ ions in the large cavity to form Sn3Cl24+. The rest, at the center of the sodalite cavity, bridge linearly between two Sn2+ ions to form Sn2Cl3+.