Synthesis and Characterization of the Large Single Crystal of Fully K+-exchanged Zeolite X (FAU),|K80|[Si112Al80O384]-FAU (Si/Al = 1.41)

摘要

Large colorless single crystals of sodium zeolite X,stoichiometry |Na80|[Si112Al80O384]-FAU,with diameters up to 200 mu m and Si/Al =1.41 have been synthesized from gels with the composition of 2.40SiO2:2.00NaAlO2:7.52NaOH:454H2O:5.00TEA.One of these,a colorless octahedron about 200 mu m in cross-section has been treated with aqueous 0.1 M KNO3 for the preparation of K+-exchanged zeolite X.The crystal structure of |K80|[Si112Al80O384]-FAU per unit cell,a = 24.838(4) A,dehydrated at 673 K and 1 x 10~(-6) Torr,has been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd3 at 294 K.The structure was refined using all intensities to the final error indices (using only the 707 reflections for which F_o > 4sigma(F_o)) R1 = 0.075 (based on F) and R2 = 0.236 (based on F2).About 80 K+ ions per unit cell are found at an unusually large number of crystallographically distinct positions,eight.Eleven K+ ions are at the centers of double 6-rings (D6Rs,site I;K-O = 2.492(6) A and O-K-O (octahedral) = 88.45(22)° and 91.55(22)°).Site-I' position (in the sodalite cavities opposite D6Rs) is occupied by five K+ ions per unit cell;these K+ ions are recessed 1.92 A into the sodalite cavities from their 3-oxygen planes (K-O = 2.820(19) A,and O-K-O = 78.6(6)°).Twety-three K+ ions are found at three nonequivalent site II (in the supercage) with occupancies of 5,9,and 9 ions;these K+ ions are recessed 0.43 A,0.75 A,and 1.55 A,respectively,into the supercage from the three oxygens to which it is bound (K-O = 2.36(13) A,2.45(13) A,and 2.710(13) A,O-K-O = 116.5(20)°,110.1(17)°,and 90.4(6)°,respectively).The remaining sixteen,thirteen,and twelve K+ ions occupy three sites III' near triple 4-rings in the supercage (K-O = 2.64(3) A,2.94(3) A,2.73(5) A,2.96(6) A,3.06(4) A,and 3.08(3) A).