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제106회 대한화학회 학술발표회, 총회 및 기기전시회 안내 Investigation of the Imbibition Processes in Cd2+-exchanged Zeolites Y (FAU, Si/Al = 1.56) and Their Crystal Structures

2010년 8월 31일 11시 18분 48초
Ⅲ-PHYS.P-227 이곳을 클릭하시면 발표코드에 대한 설명을 보실 수 있습니다.
금 <발표Ⅲ>
저자 및
서성만, 임우택
안동대학교 응용화학과, Korea
Three single crystals of excessively Cd2+-exchanged zeolites Y were prepared by the exchange of Na-Y (|Na75|[Si117Al75O384]-FAU, Si/Al = 1.56) with aqueous Cd2+ concentration of 0.05 M to flow past the crystal for 3 days at 294 and 353 K for crystals 1 and 2 and crystal 3, followed by vacuum dehydration at 1 × 10-6 Torr and 423 K (crystal 1) and 723 K (crystals 2 and 3) for 2 days. They were ion exchanged and vacuum dehydrated to generate |Cd11.5(CdOH)12(CdOH2)20|[Si117Al75O384]-FAU (crystal 1, Cd43.5-Y), |Cd31.5(Cd8O4)1.25(CdOH)2)|[Si117Al75O384]-FAU (crystal 2, Cd43.5-Y), and |Cd26.5(Cd8O4)2.5(CdOH)2)|[Si117Al75O384]-FAU (crystal 3, Cd48.5-Y). Their crystal structures were determined crystallographically using synchrotron X-radiation in the cubic space group Fd3-m. They were refined to the final error indices R1/wR2 = 0.0482/01296, 0.0711/0.1846, and 0.0625/0.1640 using 577, 851, and 849 reflections with Fo > 4σ(Fo) for crystals 1, 2, and 3, respectively. The number of Cd2+, H2O, OH-, and O2- ions or molecules in the three crystal structures, respectively, are about 43.5, 28, 12, 0; 43.5, 0, 2, 5 and 48.5, 0, 2, 10 per unit cell. In all cases, over-exchange due to uptake of OH- occurred. In crystal 1, four Cd2+ ions per unit cell are at site I, 23 at site I’, 0.5 at site II’, 5, 4, and 3 at three different sites II, and remaining 4 at site III’ positions. Each of twelve OH- ions coordinates 7 site-I’ Cd2+ ions and 5 site-II Cd2+ ions to give CdOH+ and each 28 water molecules binds to 16 site-I’ Cd2+ ions and 4 site-III’ Cd2+ ions. In crystal 2, eight Cd2+ ions per unit cell fill at site I, 10.5 and 5 at two distinct sites I’, 3 at site II’, and 7, 9, and 1 at three different site II positions. In 1.25 of eight sodalite cavities, four Cd2+ ions at the second site-I’ and four Cd2+ ions at the first site-II bind to four non-framework oxide ions to give the larger cationic [Cd8O4]8+ cluster (symmetry 3m(Td)). Remaining two Cd2+ ions at the first site-II coordinate two hydroxide ions. Through crystals 1 and 2, zeoltie Y (Si/Al = 1.56) had apparently imbibed six Cd(OH)2 molecules per unit cell; these decomposed upon vacuum dehydration at 723 K to give, with five additional Cd2+ ions, two CdOH+, 1.25 [Cd8O4]8+ clusters. The extent of [Cd8O4]8+ cluster in zeolite framework, seen in crystals 2 and 3, increases with ion-exchange temperature from 293 K to 353 K; 1.25 to 2.5 [Cd8O4]8+ clusters per unit cell, respectively.