Single-crystal structures of li+-exchanged zeolite X (FAU, Si/Al = 1.09) from aqueous solution depends on ion-exchange temperatures at 293 and 333 K

Abstract

Two single crystals of fully dehydrated partially Li+-exchanged zeolite X were prepared by the exchange of Na-X, Na 92Si 100Al 92O 384 (Si/Al = 1.09), with Li+ using aqueous 0.1 M LiNO 3 at 293 (crystal 1) and 333 K (crystal 2), followed by vacuum dehydration at 623 K and 1 × 10-6 Torr for 2 days. Their structures were determined by single-crystal synchrotron X-ray diffraction techniques in the cubic space group Fd3 at 100(1) K. Their structures were refined using all intensities to the final error indices (using the 1281 and 883 reflections for which (Fo > 4s(Fo)) R 1/R 2 = 0.075/0.244 and 0.074/0.223 for crystals 1 and 2, respectively. Their compositions are seen to be |Li 86Na6|[Si 100Al 92O 384]-FAU and |Li 87Na5|[Si 100Al 92O 384]-FAU, respectively. In crystal 1, 17 Li+ ions per unit cell are at site I′, 15 another site I′, 30 at site II, and the remaining 16 at site III; 2 Na+ ions are at site II and the remaining 4 at site III′. In crystal 2, 32 and 30 Li+ ions per unit cell fill sites I′ and II, respectively, and the remaining 25 at site III′; 2 and 3 Na+ ions are found at sites II and III′, respectively. The extent of Li+ exchange increases slightly with increasing ion exchange temperature from 93% to 95%. © 2005 KCSNET.