Single-crystal structures of highly NH_4~+-exchanged, fully deaminated, and fully Tl~+-exchanged zeolite Y (FAU, Si/Al = 1.56), all fully dehydrated

摘要

Single crystals of zeolite Y, |Na_(75)|[Si_(117)Al_(75)O_(384)]-FAU, with diameters up to 0.30 mm were grown from gels; Si/Al = 1.56. They were ion exchanged and fully dehydrated to generate |(NH4)_(67)H5Na3| [Si_(117)Al_(75)O_(384)]-FAU (crystal 1, partially deaminated), |H_(72)Na3|[Si_(117)Al_(75)O_(384)]-FAU (crystal 2, fully deaminated at 473 K) and |Tl_(75)|[Si_(117)Al_(75)O_(384)]-FAU (crystal 3). Their structures were determined crystallo-graphically at 294 K using synchrotron X-radiation in the cubic space group Fd3m. They were refined to the final error indices R_1/wR_2 = 0.037/0.126, 0.055/0.190, and 0.044/0.121 using 884, 723, and 851 reflections with F_o > 4σ(F_o) for crystals 1, 2, and 3, respectively. In crystal 1, 67 NHj and 3 Na~+ ions per unit cell are found at four different crystallographic sites. Six NHj ions were found at the centers of double 6-rings (site I; N...O = 2.888(3) A). Filling site I' are 32 NH_4~+ ions (N...O = 2.774(5) A); each is recessed 1.59 A into the sodalite cavity from the plane of the three oxygens to which it bonds. Filling site II in the supercages are 29 NH_4~+ and 3 Na~+ ions, each of which extends 1.69 A and 1.10A, respectively, into the supercage from its 3-oxygen plane (N...O = 2.818(5) A, Na...O= 2.512(19) A). The remaining 5 of the 72 NHj ions originally present per unit cell have apparently been deaminated by vacuum dehydration at 294 K. NH_4~+ ions simultaneously occupy sites 1 and I' as K~+ ions did in |K_(71)||[Si_(121)Al_(71)O_(384)]-FAU, |K_(72)|[Si_(100)Al_(92)O_(384)]-FAU, and |K_(96)|[Si_(96)Al_(96)O_(384)]-FAU; the internitrogen distance is 3.36 A. In crystal 2, three Na~+ ions per unit cell are found at site I' (Na-O = 2.207(13) A); no other cations were found so the deamination of NH_4~+ is complete at 473 K. In crystal 3, 30,30, 9,4, and 2 Tl~+ ions were found at sites I', II, and three sites III' per unit cell, respectively. The total, 75, agrees with the results of EDX analysis to establish the framework composition (the Si/Al ratio) of these crystals.