Effect of preparation conditions on the indium species in fully indium exchanged zeolite LTA

• Monatomic In+ and In3+ and polyatomic In32+, In57+, and In75+are found within zeolite LTA.
• Indium was present predominantly as monatomic In+ in 6- and 8-rings but also as In57+ in sodalite cavities.
• The number of In+ ions per unit cell increased with increasing preparation temperature from 623 to 673 K due to the disproportionation of In57+, but decreased at 723 K due to the greater disproportionation of In+.
• The number of In57+ ions decreased monotonically with increasing temperature due to its disproportionation to In and In3+.
• Post-treatment (hydration, washing with water, and redehydration) caused more In+ and In57+ ions to disproportionate to In atoms and In3+.

Three fully indium-exchanged zeolite A (LTA) crystals, In-A, were prepared by the reaction of fully dehydrated Tl-A with indium metal at 623, 673, and 723 K. Three additional crystals were prepared as above and then hydrated, washed with water, and redehydrated (post-treatment). All six structures were determined crystallographically with synchrotron X-radiation and refined in the space group Pm3¯m. Monatomic In+ ions predominate in all crystals: ca. 63–83 atomic % of the In atoms present are monatomic In+ at 6- and 8-ring positions. Tetrahedral In57+ clusters are always found in the sodalite cavities, occupying from 9% to 82% of them. Before post-treatment, only In+, In57+, and In3+ were found, and the In+ population was greatest after the 673 K reaction. The In57+ population decreases monotonically with increasing reaction temperature due to its disproportionation to In+ and In3+. Between 673 K and 723 K, In+ begins to disproportionate also, to In3+ and In0. Post-treatment continues the extent of these disproportionations to In3+ and In0. Some of the In0 atoms produced bridge between remaining In+ ions to form In32+ and In75+. The remainder have moved to the surface of the zeolite crystal.

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