Determination of Si/Al Ratio of Faujasite-type Zeolite by Single-crystal X-ray Diffraction Technique. Single-crystal Structures of Fully Tl+- and Partially K+-exchanged Zeolites Y (FAU), |Tl71|[Si121Al71O384]-FAU and |K53Na18|[Si121Al71O384]-FAU

Abstract

Large colorless single crystals of faujasite-type zeolite with diameters up to 200 /an have been synthesized from gels with the composition of 3.58SiO 2 :2.08NaAlO 2 :7.59NaOH:455H 2 O:5.06TEA:1.23TCl. Two of these, colorless octahedron about 200 μm in cross-section have been treated with aqueous 0.1 M TlC 2 H 3 O 2 and KNO 3 in order to prepare Tl + - and K + -exchanged faujasite-type zeolites, respectively, and then determined the Si/Al ratio of the zeolite framework. The crystal structures of |Tl 71 |[Si 121 Al 71 O 384 ]-FAU and |K 53 Na 18 |[Si 121 Al 71 O 384 ]-FAU per unit cell, a = 24.9463(2) and 24.9211(16) A, respectively, dehydrated at 673 K and 1 x 10 -6 Torr, have been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd3 m at 294 K. The two single-crystal structures were refined using all intensities to the final error indices (using only the 905 and 429 reflections for which F o > 4σ(F o )) R 1 /R 2 = 0.059/0.153 and 0.066/0.290, respectively. In the structure of fully Tl + -exchanged faujasite-type zeolite, 71 Tl + ions per unit cell are located at four different crystallographic sites. Twenty-nine Tl + ions fill site I' in the sodalite cavities on 3-fold axes opposite double 6-rings (Tl-O = 2.631(12) A and O-Tl-O = 93.8(4)°). Another 31 Tl + ions fill site II opposite single 6-rings in the supercage (Tl-O = 2.782(12) A and O-Tl-O = 87.9(4)°). About 3 Tl + ions are found at site III in the supercage (Tl-O = 2.91(6) and 3.44(3) A), and the remaining 8 occupy another site III (Tl-O = 2.49(5) and 3.06(3) A). In the structure of partially K + -exchanged faujasite-type zeolite, 53 K + ions per unit cell are found at five different crystallographic sites and 18 Na + ions per unit cell are found at two different crystallographic sites. The 4 K + ions are located at site I, the center of the hexagonal prism (K-O = 2.796(8) A and O-K-O = 89.0(3)°). The 10 K + ions are found at site I' in the sodalite cavity (K-O = 2.570(19) A and O-KO = 99.4(9)°). Twenty-two K + ions are found at site II in the supercage (K-O = 2.711(9) A and O-K-O = 94.7(3)°). The 5 K + ions are found at site III deep in the supercage (K-O = 2.90(5) and 3.36(3) A), and 12 K + ions are found at another site III' (K-O = 2.55(3) and 2.968(18) A). Twelve Na + ions also lie at site I' (Na-O = 2.292(10) and O-Na-O = 117.5(5)°). The 6 Na + ions are found at site II in the supercage (Na-O = 2.390(17) A and O-Na-O = 113.1(11)°). The Si/Al ratio of synthetic faujasite-type zeolite is 1.70 determined by the occupations of cations, 71, in two single-crystal structures.