Crystal Structures of Fully Indium-Exchanged ... - ACS Publications

Department of Industrial Chemistry, Kyungpook National UniVersity, Taegu ... Department of Chemistry, UniVersity of Hawaii at Manoa, Honolulu, Hawaii ...
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8372

J. Phys. Chem. B 2000, 104, 8372-8381

Crystal Structures of Fully Indium-Exchanged Zeolite X Nam Ho Heo,* Sung Wook Jung, Sung Wook Park, Man Park, and Woo Taik Lim Department of Industrial Chemistry, Kyungpook National UniVersity, Taegu 702-701, Korea

Karl Seff* Department of Chemistry, UniVersity of Hawaii at Manoa, Honolulu, Hawaii 96822-2275 ReceiVed: January 14, 2000; In Final Form: June 8, 2000

Fully indium-exchanged zeolite X has been prepared by solvent-free redox ion-exchange of fully dehydrated fully Tl+-exchanged zeolite X with In metal at 350 °C. Electron-probe microanalysis and single-crystal X-ray diffraction showed the product to be an indium aluminosilicate (ca. 47 wt % In) free of thallium. The crystal structure of the initial product (In88Si100Al92O384, Fd3h with a ) 24.913(2) Å, crystal 1) and that after washing and redehydration (In87Si100Al92O384, Fd3hm with a ) 24.916(3) Å, crystal 2) were determined by singlecrystal X-ray crystallography at 21 °C. They were refined with all measured reflections to the final error indices R1 ) 0.058 and 0.045 for the 615 and 337 reflections, respectively, with Fo > 4σ(Fo). In each unit cell of crystal 1, 88.0 indium atoms or ions are distributed over eight crystallographically distinct positions (for crystal 2, 87.0 and seven). Among those, 63.0 indium ions or atoms are found at four nonequivalent 3-fold axis equipoints: 29.0 In+ ions almost fill site II, 24.0 In+ and 8.0 “In2+” ions completely fill site I′, and 2.0 In0 atoms are found at sodalite unit centers. For crystal 2, the corresponding results are 66.5, 32.0 fill site II, 22.0 + 10.0 fill site I′, and 2.5. Each of the In0 atoms associates with four tetrahedrally arranged “In2+” ions to give “In58+”; In57+, an even species with an octet of electrons about the central In, is more likely. At four distinct site III′ (supercage) positions, 25.0 In+ ions are found in crystal 1 (20.5 at three positions for crystal 2).

Introduction Various formulations of elements from groups III, IV, and V have been the main, most widely used, semiconductor materials for several decades. This includes ions, atoms, and clusters of the group-III elements Ga and In. Perhaps regular arrays of quantum-sized clusters of these semiconductor materials1-11 could be prepared within the three-dimensional channels and cavities of zeolites. Such substances may have application in the area of material science. Clusters of GaP synthesized in the cavities of zeolite Y by chemical vapor deposition techniques have been extensively studied for their promising quantum size effect.3,4 InP synthesized in mordenite also shows this effect with a larger energy gap between valence and conduction bands.12 Such clusters may also be good catalysts for many potentially important chemical reactions. For example, gallium species in ZSM-5, introduced by ion-exchange13 or by impregnation14 of gallium salts, or by reducing mechanical mixtures of Ga2O3 and the zeolite,15,16 were found to be active for the aromatization of light alkanes13,17 and for hydrocarbon reduction.18,19 Indium species were also introduced into various zeolites during hydrothermal synthesis20 or by postsynthesis modification.21-23 Their catalytic activities were investigated for various reactions such as benzoylation of naphthalene,20 isomerization of mxylene,21 and reduction of NOx with CH4,22 showing that In+ and InO+ species within the zeolites are at or closely involved with the active sites for those reactions. Numerous attempts to ion-exchange In ions into zeolites with high Al content (low Si/Al ratios; high ion-exchange capacities), as routes to the formation of group III species in zeolite

frameworks, have failed. This is due primarily to the loss of zeolite crystallinity that occurs at the very low pH values required to keep the group III cations in solution.1,24 Other methods involving the use of melts of various anhydrous nitrates and halides have also failed for similar reasons.1 On the other hand, the physical inclusion of indium metal into the lattice of zeolite A was reported by Alekseev et al. at extreme conditions, such as 20 kbar of pressure.25,26 Just from a consideration of the geometry of the zeolite cavity and its contents, they suggested that Na12-A(8In) had formed, and they proposed some possible structures.25,26 Methods for introducing In species into zeolites of relatively high Si content (low ion-exchange capacities) involving ionexchange and subsequent reaction have also been reported. Uchida et al., by aqueous ion exchange of In3+ into mordenite (Si/Al ratio ca. 9.6), achieved nearly 71% (ca. 11.3 wt % of indium) exchange.12 Kanazirev et al. have reported the inclusion of relatively small amounts of In species (ca. 3.66 wt % as oxide), probably In+ as claimed, in zeolite ZSM-5 (Si/Al ratio in the composition of synthesis gel ca. 3.5) by mixing In2O3 and the zeolite, followed by reduction with hydrogen.16,23 Recently, a high concentration (ca. 44 wt %) of indium species was introduced into a zeolite of high Al content (zeolite A with Si/Al ratio probably ca. 1.0, although reported to be a bit greater, ca. 1.0427). It was accomplished by using a solventfree redox reaction28-30 between Tl+ ions and In metal in the zeolite.31 The expected redox reaction (Tl+ + In0 f In+ + Tl0, or Tl12-A + 12In0 f In12-A + 12Tl0) occurred in zeolite A to produce indium zeolite A free of Tl. However, the In+ ions in the product had disproportionationed32 to give In in various

10.1021/jp0001992 CCC: $19.00 © 2000 American Chemical Society Published on Web 08/09/2000

Fully Indium-Exchanged Zeolite X

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TABLE 1: Summary of Experimental and Crystallographic Data crystal number crystal cross-section (mm) ion exchange for Tl+ (days, mL, °C) dehydration of Tl-X (days, °C) reaction of Tl-X with In (days, °C) washing of In-X with deionized water (days, mL) redehydration of In-X (days, °C) temperature for data collection (°C) radiation (Mo KR) λ1 λ2 space group number unit cell constants, a0 (Å) No. of reflections for a0 scan technique scan width (deg) 2θ range for a0 (deg) 2θ range in data collection (deg) No. of reflections measured No. of unique reflections, m No. of reflections (Fo > 4σ(Fo)) No. of parameters, s data/parameter ratio, m/s weighting parameters: a/b R1 (Fo > 4σ(Fo))a wR2 (all unique data)b goodness of fitc

1 0.15 3, 10.0, 21 2, 400 4, 350 21 0.70930 0.71359 Fd3h, 203 24.913(2) 25 θ-2θ 0.49 + 0.60*tanθ 10-20 2-50 1299 1090 615 79 13.8 0.0997/759.272 0.0583 0.2012 1.062

2 0.15 3, 10.0, 21 2, 400 4, 350 1, 5.0 2, 400 21 0.70930 0.71359 Fd3hm, 227 24.916(3) 25 θ-2θ 0.47 + 0.62*tanθ 10-20 2-50 1277 685 337 53 12.9 0.0444/535.327 0.0452 0.1416 1.157

a R ) Σ(|F - |F ||)/ΣF is calculated using F > 4σ(F ), which corresponds to I > 2σ(I ). b wR ) [Σ{w(F 2 - F 2)2}/Σw(F 2)2]1/2 is calculated 1 o c o o o o o 2 o c o using all unique data. c [Σ{w(Fo2 - Fc2)2}/(m - s)]1/2, where m and s are the number of unique reflections and variables, respectively.

oxidation states (In0, In+, In2+, and In3+) and with various clusters.33,34 Later exposure to the atmosphere or to adsorbates such as H2O or sulfur modified the occupancies and distribution of oxidation states to a minor degree. The indium cations and clusters are stabilized by association with anionic oxygen atoms of the zeolite framework and with neutral In atoms (introduced during the reaction or produced by the disproportionation).31,35 In this work, the solvent-free redox reaction between In0 and Tl+ ions within fully Tl+-exchanged zeolite X (Tl92Si100Al92O384) was done with the hope that complete indiumexchange could be readily accomplished. Indium species in various oxidation states, the result of disproportionation as was seen with zeolite A, might be prepared, and clusters might again be found. Such zeolites may be immediately useful as catalysts or electronic materials, or may be precursors in the preparation of such materials. Experimental Section Large single crystals of sodium zeolite X, stoichiometry Na92Si100Al92O384 per unit cell (Na92-X or Na-X), were prepared in St. Petersburg, Russia.36 Colorless single crystals, octahedra about 0.15 mm in cross-section, were lodged in a fine Pyrex capillary. Fully Tl+-exchanged zeolite X (Tl92Si100Al92O384, Tl92-X, or Tl-X; sample A for electron-probe analysis) was prepared by dynamic ion-exchange (flow method) of the Na-X crystals with 0.1 M aqueous thallous acetate (pH ) 6.4, Aldrich Chemical Co., 99.99%); see Table 1. This and similar ionexchanges had been shown to be suitable for the preparation of stoichiometric Tl-X and Tl-A.31,37-39 Several crystals of colorless Tl-X were completely dehydrated (350 °C and 1 × 10-6 Torr for 48 h) and were brought into contact with In0 (Aldrich Chemical Co., 99.999%) in fine Pyrex capillaries at 350 °C for 96 h. This was achieved under vacuum as described and discussed before,31 by condensing In0 around the crystals whose temperature was somewhat lower than that of the metal in coaxially connected heating ovens. Although the vapor pressure of In(l) is reported to be very low at 350 °C

(ca. 2.92 × 10-10 N/m2 ) 2.19 × 10-12 Torr),40 droplets of In were seen to form very close to the zeolite crystals. At 350 °C the vapor pressure of Tl(s) is 1.22 × 10-6 Torr (1.63 × 10-4 N/m2);40 any elemental thallium produced could readily distill away from the crystal. Other experimental procedures for the reaction were similar in detail to those previously described for the preparation of In-A and for solvent-free ion-exchange, with the exception of the reversed temperature gradient to deliver In to the crystal during the reaction period.28-31 One of the resulting black crystals (crystal 1, sample B for microanalysis) was sealed off, still under vacuum in its capillary, from the reaction vessel by torch after cooling to room temperature. A second crystal was then exposed to the atmosphere and was washed with deionized water, hoping to remove any residual Tl or In species that might be present on the surface of the crystal, as was done in the preparation of In-A.31 This crystal, still black after washing, was in turn lodged in a fine Pyrex capillary and then dehydrated at 350 °C under 1 × 10-6 Torr for 48 h. The resulting crystal (crystal 2, sample C for microanalysis) was still black even after the redehydration, unlike that of similarly treated zeolite A crystals, which were pale yellow or colorless.31 Still under vacuum in its capillary, it was sealed off from the vacuum line for X-ray experiments, followed by electron-probe microanalysis. Electron-probe X-ray Microanalyses (EPXMA) of the above samples (A, B, and C) after exposure to the atmosphere were carried out with a Fisons KEVEX/SIGMA system, an energy dispersive spectrometer (EDS) system attached to a Hitachi S-4100 SEM. The resulting EDS spectra are presented in Figure 1. X-ray Data Collection. The space groups Fd3h and Fd3hm are consistent with the reflection conditions (hkl: h + k, k + l, l + h ) 2n; 0kl: k + l ) 4n). Of those two, Fd3h was used for crystal 1 because (a) this crystal does not have intensity symmetry across (110) and therefore lacks that mirror plane and (b) the diffraction data from this crystal refine successfully to error indices lower than with Fd3hm, with Si-O distances

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Figure 2. Stylized drawing of the framework structure of zeolite X. Near the center of the each line segment is an oxygen atom. The different oxygen atoms are indicated by the numbers 1-4. Silicon and aluminum atoms alternate at the tetrahedral intersections, with the exception that Si substitutes for Al at about 4% of the Al positions. Extraframework cation positions are labeled with Roman numerals.

Figure 1. EPXMA spectra of Tl-X and the products of its reaction with In metal: (A) after the consecutive treatments i-d-e (defined below), (B) after i-d-r-e, and (C) after i-d-r-e-w-d-e. (i, ionexchange with 0.1 M aqueous thallous acetate; d, dehydration at 350 °C and 1 × 10-6 Torr for 48 h; e, exposure to the atmosphere at ambient conditions; r, reaction with In metal at 350 °C for 96 h; and w, washing with deionized water at room temperature).

reasonably less than Al-O.41,42 However, the space group Fd3hm was used for crystal 2. It was justified by the obvious intensity equality observed for hkl and khl reflections and by the refinement results: the Si-O and Al-O distances are nearly the same in Fd3h, indicating that long-range Si/Al ordering has been lost,43 and the error indices are lower in Fd3hm (see the Results and Discussion section). A CAD4/Turbo diffractometer, equipped with a rotating anode generator and a graphite monochromator, was used for preliminary experiments and for the subsequent collection of diffraction intensities, all at 21(1) °C. Unit cell constants, determined by least-squares refinement of 25 intense reflections in diverse regions of reciprocal space, are given in Table 1. Finally, the absorption corrections (µ ) 3.53 and 3.60 mm-1 for crystals 1 and 2, respectively44) were calculated using semiempirical ψ-scan methods. The corrected data gave nearly the same final R indices, so these corrections were removed. Description of Zeolite X. Zeolite X is a synthetic Al-rich analogue of the naturally occurring mineral faujasite. The 14hedron with 24 vertices known as the sodalite cavity or β-cage may be viewed as the principal building block of the aluminosilicate framework of the zeolite (see Figure 2). These sodalite units are connected tetrahedrally at six-rings by bridging oxygens to give double six-rings (D6Rs, hexagonal prisms) and, concomitantly, to give an interconnected set of even larger cavities (supercages) accessible in three dimensions through 12-ring (24membered) windows. The Si and Al atoms occupy the vertices

of these polyhedra. The oxygen atoms lie approximately halfway between each pair of Si and Al atoms but are displaced from those points to give near tetrahedral angles about Si and Al. Exchangeable cations that balance the negative charge of the aluminosilicate framework are found within the zeolite’s cavities. They are usually found at the following sites shown in Figure 2: site I at the center of a D6R, I′ in the sodalite cavity on the opposite side of either of the D6R’s six-rings from site I, II′ inside the sodalite cavity near a single six-ring (S6R) entrance to the supercage, II opposite a S6R in the supercage, III on a 2-fold axis opposite an O(3)-O(4)-O(3)-O(4)- fourring (between two 12-rings) in the supercage, and III′ somewhat or substantially off the 2-fold axis but otherwise on the inner surface of the supercage or near a 12-ring.45,46 Structure Determination. Full-matrix least-squares refinements (SHELXL9747) were done on F2 using all reflections without an nσ cutoff. They were initiated with the atomic positions of the framework atoms [Si, Al, O(1), O(2), O(3), and O(4)] from Olson’s structure of dehydrated Na-X45 for crystal 1 and with those of [(Si,Al), O(1), O(2), O(3), and O(4)] from the structure of Ni-Y48 for crystal 2. Fixed weights were used initially; the final weights were assigned using the formula w ) 1/[σ2(Fo2) + (aP)2 + bP] where P ) [Max(Fo2,0) + 2Fc2]/3, with a and b as refined parameters (see Table 1). Atomic scattering factors for Si, Al, O-, In, In+, and In2+ were used.49,50 Oxidation states were assigned to the indium positions according to their distances to framework oxygens (vide infra). Scattering factors of In2+ and In+ were calculated from those of In3+ and In0 as follows, (2In3+ + In0)/3 and (In3+ + 2In0)/3, respectively. Other details of experimental and crystallographic data are given in Table 1. The final structural parameters are presented in Table 2, and selected interatomic distances and angles are in Table 3. In88-X (Crystal 1). Anisotropic refinement of the framework atoms with isotropic In+ ions at site II (In(II)) opposite sixrings on the 3-fold axes in the supercage (0.25, 0.25, 0.25), a most popular site for such moderately sized cations in zeolite

Fully Indium-Exchanged Zeolite X

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TABLE 2: Positional,a Thermal,a and Occupancy Parameters of Indium-Exchanged Zeolite X occupancyb atoms

Wyc pos site

Si Al O(1) O(2) O(3) O(4) In(II)c In(I′A)c In(I′B)c In(U)c In(III′A)c In(III′B)c In(III′C)c In(III′D)c

96(g) 96(g) 96(g) 96(g) 96(g) 96(g) 32(e) 32(e) 32(e) 8(a) 96(g) 96(g) 96(g) 96(g)

Si,Al O(1) O(2) O(3) O(4) In(II)c In(I′A)c In(I′B)c In(U)c In(III′A)c In(III′B)c In(III′C)c

192(i) 96(h) 96(g) 96(g) 96(g) 32(e) 32(e) 32(e) 8(a) 192(i) 192(i) 192(i)

x

y

z

U11 or Uiso

U22

II I′ I′ U III′ III′ III′ III′

-513(1) -526(1) -1052(4) -5(4) -262(4) -730(3) 2518(1) 751(1) 630(2) 1250d 715(8) 380(12) 634(14) 984(24)

1253(1) 370(1) 2(4) -19(4) 756(4) 762(4) 2518(1) 751(1) 630(2) 1250d 435(7) 686(11) 821(12) 701(25)

358(1) 1236(2) 1009(4) 1485(4) 710(4) 1760(4) 2518(1) 751(1) 630(2) 1250d 4186(7) 4171(11) 4213(12) 4232(24)

(a) In88-X, Crystal 1 133(18) 91(16) 126(19) 117(18) 222(50) 255(52) 174(44) 162(45) 256(52) 197(48) 169(46) 183(47) 329(6) 253(8) 184(19) 150(27) 797(44) 598(66) 477(70) 693(140)

II I′ I′ U III′ III′ III′

-519(1) -1020(3) -13(3) -256(4) 758(3) 2522(1) 750(1) 626(2) 1250d 689(11) 1033(21) 420(14)

1243(1) 0d -13(3) 730(3) 758(3) 2522(1) 750(1) 626(2) 1250d 897(11) 1284(21) 737(13)

365(1) 1020(3) 1474(4) 730(3) 3219(4) 2522(1) 750(1) 626(2) 1250d 4223(11) 4145(18) 4211(13)

(b) In87-X, Crystal 2 138(17) 127(16) 224(38) 254(62) 150(32) 150(32) 154(61) 299(42) 192(40) 192(40) 330(6) 267(11) 149(19) 90(27) 573(85) 778(203) 727(97)

U33

U23

U13

U12

fixed

varied

109(17) 92(17) 257(53) 243(49) 213(49) 178(47)

-11(14) -32(15) -21(47) -31(43) 30(42) -58(39)

-6(14) -31(15) -17(42) 5(42) -18(46) 16(42)

-16(14) -8(15) -132(45) 53(40) 9(44) 176(21)

96 96 96 96 96 96 29.0 24.0 8.0 2.0 11.0 6.0 5.0 3.0

28.8(4) 25.7(6) 6.0(5) 1.9(1) 10.6(9) 6.0(10) 5.1(10) 3.1(4)

192 96 96 96 96 32.0 22.0 10.0 2.5 8.0 4.5 8.0

33.1(3) 25.2(7) 8.7(7) 3.0(1) 7.4(12) 4.5(5) 7.9(12)

137(14) 224(38) 226(57) 299(42) 204(65)

-22(12) -99(37) 31(39) 27(54) 31(36)

0(12) -26(50) 31(39) 4(40) 31(36)

8(14) -99(37) 47(53) 4(40) 96(50)

a Positional and thermal parameters are given × 104. Numbers in parentheses are the estimated standard deviations in the units of the least significant figure given for the corresponding parameter. The anisotropic temperature factor is exp[-2π2a-2(U11h2 + U22k2 + U33l2 + 2U12hk + 2U13hl + 2U23kl)]. b Occupancy factors are given as the number of atoms or ions per unit cell. c The charges at the In positions are all 1+ except for (formally) 0 at In(U) and 1.75+ at In(I′B) where In5n+ clusters have formed (n is proposed to be 7). d Fixed by symmetry.

X, converged to R1/wR2 ) 0.44/0.82 with a resulting occupancy of 15.0(14) ions at In(II). (These error indices are defined in footnotes to Table 1.) A difference Fourier function revealed two large peaks at (0.0723, 0.0723, 0.0723) and (0.125, 0.125, 0.125) with electron densities of 25 and 8 eÅ-3, respectively. A subsequent refinement with these two peaks included as In+ and In0 at In(I′A) and In(U), respectively, quickly converged to R1/wR2 ) 0.14/0.42, with resulting occupancies of 29.0(8), 31.3(7), and 1.3(2) at In(II), In(I′A), and In(U), respectively. Inclusion of another strong peak (9 eÅ-3) at (0.057, 0.057, 0.057) from an ensuing Fourier function as In2+ at In(I′B) converged to R1/wR2 ) 0.11/0.37 with refined occupancies of 28.9(7), 25.6(8), 5.9(8), and 1.3(2) for In(II), In(I′A), In(I′B), and In(U), respectively. A subsequent Fourier function, based on the above model, revealed several other peaks in the vicinity of four-rings in the supercage. Inclusion of the two strongest peaks (5 and 4 eÅ-3 at (0.069,0.053,0.419) and (0.060,0.071,0.419), respectively) as In+ ions at In(III′A) and In(III′B) further reduced the error indices to R1/wR2 ) 0.071/0.28 with resulting occupancies of 29.8(5), 28.2(7), 7.3(8), 1.9(1), 9.6(11), and 11.8(11) for In(II), In(I′A), In(I′B), In(U), In(III′A), and In(III′B), respectively, with a rather large but stable thermal parameter for In(6), Uiso ) 0.10(1). Two more peaks (2.1 and 1.5 eÅ-3) nearly opposite four-rings on a subsequent Fourier function were included as In+ ions at In(III′C) and In(III′D). Refinement with this model converged to R1/wR2 ) 0.061/0.27 with resulting occupancies of 29.3(5), 27.6(6), 6.2(6), 2.4(1), 8.6(13), 5.1(10), 4.0(10), and 3.8(12) for In(II), In(I′A), In(I′B), In(U), In(III′A), In(III′B), In(III′C), and In(III′D), respectively. Refining the structure with both weighting-scheme parameters free to vary sharply reduced the error indices to R1/wR2 ) 0.058/

0.21; the resulting occupancies are given in the last column of Table 2(a). The final cycles of refinement with occupancies fixed at the values given in Table 2(a) (at their nearest or reasonable integers, considering their corresponding estimated standard deviations and the requirement that the total charge per unit cell sum to 92+) converged to R1/wR2 ) 0.059/0.20. Anisotropic refinement of the indium positions did not further improve the structure nor the crystallographic statistics, so these results were not included in the final model. All shifts in the final cycles of refinement were less than 0.01% of their corresponding esds. The largest peak (1.2 eÅ-3 at (0.070, 0.072, 0.097)) in the final difference Fourier function was not considered further because it was too close to the fully occupied I′ sites, In(I′A) (0.55 Å) and In(I′B) (0.88 Å). In87-X (Crystal 2). Anisotropic refinement of the framework atoms with isotropic In+ ions at site I′ (In(I′A)) opposite double six-rings on the 3-fold axes in the sodalite unit converged to R1/wR2 ) 0.42/0.77 with a resulting occupancy of 31.8(20) ions at In(I′A). A difference Fourier function revealed two large peaks at (0.256, 0.256, 0.256) and (0.125, 0.125, 0.125) with electron densities of 15 and 14 eÅ-3, respectively. A subsequent refinement including these peaks as In+ and In0 at In(II) and In(U), respectively, quickly converged to R1/wR2 ) 0.12/0.29, with occupancies of 31.8(6), 33.5(6), and 3.0(2) at In(II), In(I′A), and In(U), respectively. An ensuing Fourier function revealed another strong peak (7.4 eÅ-3) at (0.056, 0.056, 0.056) that refined as In2+ at In(3) to R1/wR2 ) 0.08/0.23 with resulting occupancies of 31.9(5), 25.0(1), 8.6(10), and 2.8(1) for In(II), In(I′A), In(I′B), and In(U), respectively. Another Fourier function, calculated on the basis of this model, revealed several other peaks in the vicinity of four-rings in the supercage. The inclusion of the strongest one (2.0 eÅ-3

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TABLE 3: Selected Interatomic Distances (Å) and Angles (deg)a In88-X (Crystal 1) Si-O(1) Si-O(2) Si-O(3) Si-O(4) mean of Si-O Al-O(1) Al-O(2) Al-O(3) Al-O(4) mean of Al-O In(II)-O(2) In(I′A)-O(3) In(I′B)-O(3) In(III′A)-O(4) In(III′A)-O(1) In(III′B)-O(4) In(III′B)-O(1) In(III′C)-O(4) In(III′C)-O(1) In(III′D)-O(4) In(III′D)-O(1) In(I′B)-In(U) O(1)-Si-O(2) O(1)-Si-O(3) O(1)-Si-O(4) O(2)-Si-O(3) O(2)-Si-O(4) O(3)-Si-O(4) O(1)-Al-O(2) O(1)-Al-O(3) O(1)-Al-O(4) O(2)-Al-O(3) O(2)-Al-O(4) O(3)-Al-O(4) Si-O(1)-Al Si-O(2)-Al Si-O(3)-Al Si-O(4)-Al O(2)-In(II)-O(2) O(3)-In(I′A)-O(3) O(3)-In(I′B)-O(3) O(1)-In(III′A)-O(4) O(1)-In(III′B)-O(4) O(4)-In(III′B)-O(4) O(1)-In(III′C)-O(4) O(1)-In(III′D)-O(4) In(I′B)-In(U)-In(I′B)

1.606(9) 1.634(9) 1.642(9) 1.632(9) 1.629(9) 1.696(9) 1.735(10) 1.754(9) 1.706(9) 1.723(9) 2.574(9) 2.526(9) 2.253(10) 2.50(2) 2.71(2) 2.53(3) 2.70(3) 2.48(3) 2.82(3) 2.56(6) 2.77(6) 2.674(9) 112.4(5) 110.9(5) 107.6(5) 105.9(5) 108.1(5) 111.9(5) 113.4(5) 109.6(5) 109.5(5) 107.0(4) 105.6(4) 111.7(5) 143.1(6) 135.2(6) 132.0(6) 140.5(6) 89.3(3) 87.9(3) 102.2(4) 60.0(5) 64.1(7)

In87-X (Crystal 2) (Si,Al)-O(1) (Si,Al)-O(2) (Si,Al)-O(3) (Si,Al)-O(4) mean of (Si,Al)-O

1.641(4) 1.675(5) 1.699(5) 1.660(4) 1.669(5)

2.610(9) 2.508(9) 2.228(11) 2.53(3) 2.85(3) 2.74(5), 3.12(5) 2.61(3) 2.74(3)

O(1)-(Si,Al)-O(2) O(1)-(Si,Al)-O(3) O(1)-(Si,Al)-O(4) O(2)-(Si,Al)-O(3) O(2)-(Si,Al)-O(4) O(3)-(Si,Al)-O(4)

(Si,Al)-O(1)-(Si,Al) (Si,Al)-O(2)-(Si,Al) (Si,Al)-O(3)-(Si,Al) (Si,Al)-O(4)-(Si,Al)

2.694(8) 112.1(4) 109.6(5) 110.6(5) 105.7(5) 107.4(5) 111.3(5)

145.2(7) 136.7(6) 131.0(6) 142.5(7) 89.1(3) 87.7(4) 102.5.(4) 60.3(5) 72.2(7) 60.9(7)

62.8(8) 58.6(13) 109.47b

109.47b

a

b

Numbers in parentheses are the estimated standard deviations in the units of the least significant digit given for the corresponding parameter. Exactly the tetrahedral angle by symmetry.

at (0.045, 0.072, 0.419)) as In+ at In(III′A) further reduced the error indices to R1/wR2 ) 0.059/0.16 with resulting occupancies of 33.3(4), 24.4(8), 9.9(8), 3.0(1), and 15.4(8) for In(II), In(I′A), In(I′B), In(U), and In(III′A), respectively, with an unusually large but stable thermal parameter for In(III′A), Uiso ) 0.12(1). Refinement including the second strongest peak, which appeared again near In(III′A) at (0.103, 0.147, 0.412) on a subsequent Fourier function, as In+ at In(III′B) converged to R1/wR2 ) 0.053/0.15 with refined occupancies of 33.4(3), 25.4(8), 8.9(7), 3.0(1), 12.2(8), and 4.5(3) for In(II), In(I′A), In(I′B), In(U), In(III′A), and In(III′B), respectively. Another peak in the vicinity of four-rings from the subsequent Fourier function was included as In+ ions at In(III′C). Refinement with this model and anisotropic framework atoms converged to R1/ wR2 ) 0.048/0.14 with resulting occupancies of 33.1(3), 25.2(7), 8.7(7), 3.0(1), 7.4(13), 4.3(4), and 8.2(13) for In(II), In(I′A), In(I′B), In(U), In(III′A), In(III′B), and In(III′C), respectively. The final cycles of refinement, with anisotropic refinement of framework atoms and isotropic refinement at all indium

positions with weighting-scheme parameters refining and occupancies fixed at values given in Table 2(b) for reasons described above for crystal 1, converged to R1/wR2 ) 0.045/ 0.14. Anisotropic refinement of indium species did not improve the structure nor the crystallographic statistics any further, so they were dismissed. All of the shifts in the final cycles of refinement were less than 0.01% of their corresponding esds. The largest peak (1.0 eÅ-3 at (0.246, 0.246, 0.272)) in the final difference Fourier function was too close (0.55 Å) to the fully occupied In(II) position, so it was not considered further. Results and Discussion Electron-Probe X-ray Microanalyses. Spectrum A in Figure 1 shows several peaks corresponding to Si and Al of the zeolite framework and to Tl,51 indicating that this zeolite X sample is a thallium aluminosilicate free of other guest cations and that Tl-X has been successfully prepared by the ion-exchange procedure used. Spectrum B (of a crystal after reaction of Tl-X with In metal) shows the presence of a large amount of indium,

Fully Indium-Exchanged Zeolite X but also indicates that a reasonable amount of thallium has remained, perhaps only on the surface (EPXMA is a surface sensitive technique) because Tl is not seen in the structure of crystal 1. Spectrum C (of a crystal after washing and redehydration) shows that the final product is an indium aluminosilicate free of Tl. Further EPXMA experiments using the fresh surface of an intentionally broken crystal of sample C confirmed that In is the only nonframework element present in the product. In all three spectra in Figure 1, the KR lines of Al and Si appear consistently with almost the same relative intensities, indicating that the composition of the zeolite framework was not significantly altered by the solvent-free redox ion-exchange reaction. The strong MR and Mβ lines (overlapping) of Tl in spectrum A (without those of In) and the LR and Lβ lines of In in spectrum C (without those of Tl)51 indicate that the replacement of Tl+ by In species is complete, confirming that fully indiumexchanged zeolite X, perhaps with the retention of additional atoms of In, has been successfully prepared. Space Group Considerations. If the Si and Al atoms alternate in the zeolite X framework in obeyance of Loewenstein’s rule,52 then the space group of zeolite X is Fd3h. This is true even though about 4% of the Al sites are occupied by Si atoms to accommodate the excess Si atoms in Na92Si100Al92O384.36 This ordering of Si and Al atoms is confirmed by the average values of the Si-O (1.63 Å) and Al-O (1.72 Å) distances in crystal 1 (see Table 3). These values are the same as those in Mg46-, Ca46-, and Ba46-X,41 1.63 and 1.73 Å, respectively, and very close to the best mean values for zeolites in general, ca. 1.61 and 1.72 Å. This indicates that crystal 1, like all other crystals that had not been subjected to harsh chemical treatment,41-43,53-55 retained the long-range Si/Al order initially present. Crystal 2, however, was refined with space group Fd3hm, due to the obvious mirror planes at (110). The experimentally observed intensity equality between hkl and khl pairs of reflections indicate that the tetrahedra of Si and Al atoms are no longer distinguishable in the framework structure of crystal 2. Furthermore, when crystal 2 was refined with Fd3h, the averaged Si-O and Al-O distances, 1.67 and 1.66 Å, respectively, are almost same, indicating that the Si and Al atoms of crystal 2 are entirely or nearly entirely disordered. The longrange Si/Al ordering presumed to be uniformly present in the batch supply36 of Na-X56 used and therefore initially present in crystal 2, as found in crystal 1, has therefore been lost. This change of space group has presumably been caused by the chemical treatment given to crystal 2 and might have happened during the additional steps of exposure to the atmosphere, washing, and dehydration at elevated temperature. This treatment probably produced additional In3+ and/or In2+ ions by the further disproportionation of In+ (vide infra). These higher oxidation states of In may have hydrolyzed to some degree within the zeolite to produce protons which can attack the zeolite X framework, especially at elevated temperatures.43,56-60 Crystal Structures of In-X. The oxidation state at each indium position in the two In-X structures is identified on the basis of its approach distance to framework atoms and to each other (vide infra), with the general expectation that indium ions nearest to framework oxygens should have the largest cationic charges. In addition, the final assignment must give a structure that is electrically neutral. The latter consideration was also used to select the fixed occupancies in Table 2. This reasoning has been used before with In-A31 and In-A(S2).35 The charge of the zeolite framework is 92- per unit cell. With 88 or 87 In atoms or ions per unit cell, it is clear that they do

J. Phys. Chem. B, Vol. 104, No. 35, 2000 8377 TABLE 4: Deviations of Guest Ions and Atoms (Å) from (111) Planes of Six-Rings deviation ions or atoms

site

charge

In88-X, Crystal 1

In87-X, Crystal 2

S6Ra

In(II) In(I′A) In(I′B) In(U)c

II

At O(2)s of +1 1.51

1.53

I′ I′ U

At O(3)s of D6Rb +1 1.51 +2 0.99 0 3.66

1.51 0.97 3.66

a A positive deviation indicates that the ion lies in the supercage. bA positive deviation indicates that the ion or atom lies in the sodalite unit. c At the very center of the sodalite unit.

not all have the same oxidation state. All of the In atoms or ions occupy cationic sites except those few at In(U). It follows that most In atoms or ions are In+ with some at a higher oxidation state (the 2+ and 3+ states are common). With a formal charge of ca. 0.25- at each framework oxygen, In+ would provide better local charge balance than In2+, with In2+ better than In3+. All high-occupancy In positions should be populated by In+. (a) The Indium Ions at Sites I′ and II. The ions at In(II) fill the 32-fold site II position almost completely (29) and completely (32) in crystals 1 and 2, respectively. Each of these ions lies relatively far inside the supercage, 1.51 and 1.53 Å for crystals 1 and 2, respectively, from the (111) plane of three O(2) framework oxygens of the S6R to which it is bound (see Table 4). They are 2.574(9) and 2.610(9) Å, respectively for crystals 1 and 2, from their nearest neighbors, the O(2) framework oxygens (see Table 3). Considering the ionic radii of the framework oxygens to be 1.32 Å,61,62 the radii of these indium ions must be ca. 2.57 (2.61 for crystal 2) - 1.32 ) 1.25 (1.29 for crystal 2) Å, almost identical to those, 1.25 Å, in In11-A.31 This is somewhat shorter than those found for In+ in various indium halides, which range from 1.32 to 1.51 Å.63-65 However, similarly shortened radii have been found for Tl+ ions in zeolites; ca. 1.30 vs ca. 1.47 Å in various thallium halides, respectively,38,39,66 probably due to the low coordination number of these ions in the dehydrated zeolite. An even smaller radius, 1.17 Å, was suggested for In+ by a theoretical calculation using the numerical HF method.67 Accordingly, considering the argument in the previous paragraph and the high occupancy at In(II), the oxidation state of the cations at In(II) appears to be 1+. Therefore, all supercages in crystal 2 and most supercages in crystal 1 have four tetrahedrally arranged In+ ions at In(II). A stereoview of their arrangement in the supercage of crystal 2 is shown in Figure 3. The remaining supercages in crystal 1 can be expected to have three such In+ ions. In each crystal, site I′ is filled with cations at In(I′A) and In(I′B): the sum of their occupancies is 32.0 (see Table 2). Each of the 24.0 and 22.0 cations at In(I′A) is 2.526(9) and 2.508(9) Å, respectively for crystals 1 and 2, from their nearest framework oxygens, three O(3)s. The ionic radii of these cations must be ca. 2.53 (2.51 for crystal 2) - 1.32 ) 1.21 (1.19 for crystal 2) Å, indicating that the ions at In(I′A) must also be In+ by the same reasoning used above. These In+ ions at In(I′A) extend 1.51 Å for both crystals into the sodalite unit from their nearest framework oxygens, three O(2)s. The In+ ions at In(II) extend into the supercage by about the same amount (see Table 4), again affirming that the ions at In(I′A) must be In+. The remaining site I′ cations, 8.0 and 10.0 per unit cell at In(I′B) in crystals 1 and 2, respectively, are 2.253(10) and 2.228(11) Å from three six-ring oxygens at O(3) (see Table 3). The radii of these cations, ca. 2.25 (or 2.23) - 1.32 ) 0.93 (or 0.91)

8378 J. Phys. Chem. B, Vol. 104, No. 35, 2000

Figure 3. A stereoview of a supercage in In87-X (crystal 2). Four In+ ions are tetrahedrally arranged at In(II). The three site III′ In+ positions at In(III′A), In(III′B), and In(III′C) are shown. Other supercages may have other numbers and arrangements of site III′ ions. The zeolite framework is drawn with heavy solid bonds. The coordination about In+ cations is indicated by fine solid lines. Ellipsoids of 50% probability are shown. For the purposes of this and following drawings, some of atom names have been abbreviated, e.g., In(III′B) is shown as In3′B.

Figure 4. A stereoview of a sodalite unit in In87-X (crystal 2) with an In5n+ cluster, most likely In57+, in its center. In57+, shown with solid white bonds, may be viewed as an In atom at In(U) surrounded by four tetrahedrally arranged “In2+” ions (actually In1.75+) at In(I′B). Each ion at In(I′B) further coordinates to three six-ring oxygens at O(3). Only two or three sodalite units per unit cell have such In5n+ clusters in them. See the caption of Figure 3 for other details.

Å, is sharply less than those of the In+ ions at sites I and II, indicating a higher oxidation state, probably In2+. The mean of the two values, 0.92 Å, is close enough to the average value, 0.95 Å, of the ionic radii of the adjacent cations in the periodic table, Cd2+ (0.97 Å) and Sn2+ (0.93 Å).61,62 These In2+ ions may have been produced by the disproportionation reaction of In+ ions,32 i.e., 2In+ f In2+ + In0. Such In2+ ions had been seen before only in fully indium-exchanged zeolite A,31 its sorption complex,35 and in some indium trihalide dimers68,69 such as [In2Cl6]2-. These In2+ ions at In(I′B) are recessed, 0.99 and 0.97 Å for crystals 1 and 2, respectively, into the sodalite units from the (111) planes of three O(3) oxygens (see Table 4). The O(3)In(I′B)-O(3) angles (102.2(4)o and 102.5(4)o, respectively, in two crystals) are somewhat close to 109.47°, indicating that these In2+ ions with an additional atom may have tetrahedral environments. Furthermore, In2+ has an odd number of electrons and is an unstable oxidation state; it might be stabilized by further coordination. The 2 and 2.5 In0 atoms per unit cell at site U in crystals 1 and 2, respectively, can complete these tetrahedra in that many sodalite units to give tetrahedral clusters of (In2+)4In0, alternatively written In58+. Further electronic considerations (Vide infra, Section c) suggest that In57+ is more likely. The remaining 6 and 5.5 sodalite units, respectively, per unit cell would each have four tetrahedrally arranged In+ ions at In(I′A). Stereoviews of these two kinds of sodalite units in crystal 2 are shown in Figures 4 and 5. (b) Indium Ions at III′ Sites. In crystal 1, 25 indium ions per unit cell are found at four different III′ sites. At In(III′A),

Heo et al.

Figure 5. A stereoview of a sodalite unit in In87-X (crystal 2) with four In+ ions at In(I′A) tetrahedrally arranged opposite the D6Rs. Only five or six sodalite units per unit cell have four such In+ ions; the others have the arrangement shown in Figure 4. See the caption of Figure 3 for other details.

In(III′B), In(III′C), and In(III′D), respectively, 11.0, 6.0, 5.0, and 3.0 indium ions per unit cell are found. Their approach distances to nearest framework oxygen atoms, O(4)s, are 2.50(2), 2.53(3), 2.48(3), and 2.56(6) Å, respectively. The ionic radii of these ions therefore range narrowly from 1.17 to 1.21 Å, indicating that they are all In+ ions (vide supra). In crystal 2, 20.5 indium ions per unit cell are found at three different III′ sites with somewhat different distributions of occupancies. At In(III′A), In(III′B), and In(III′C), respectively, 8.0, 4.5, and 8.0 indium ions are found. Their respective approach distances to nearest oxygen atoms, O(4)s, are 2.54(3), 2.74(5), and 2.61(3) Å. Again, all indium ions at these positions must be In+, including those at In(III′B) that are somewhat further from O(4) but still within range (2.57 to 2.83 Å for In+-O, vide supra). The site-III′ positions can be seen in Figure 3. Their occupancies vary from supercage to supercage and some may not exist in some supercages. Close-up stereoviews of the III′ sites are given in Figure 6. It is surprising that In+ ions occupy so many III′ sites, as opposed to a single lowest energy III′ site. Although Na+ ions in dehydrated Na-X have been found at only one III′ site by powder diffraction methods at 5K,70 two56 or three45 III′ sites are found at ambient temperatures by single-crystal diffraction. In dehydrated Tl-X, Tl+ ions are found at two (or more) III′ sites.37 It seems that there are multiple sites of similarly low energy and that intercationic repulsions are important. The substitution of Si into some Al positions must have some effect and is likely to play a role. The greater number of III′ positions seen here may be associated with the lower symmetry in the supercages due to the placements of other cations: in crystal 1, site II is not full, and in both crystals there are two I′ positions. In dehydrated Na-X and Tl-X, these two sites may be considered full. A simulated annealing calculation71 indicates that there is no basis for the proposal that there is ordering of the Si atoms within the Al equipoint.72 (c) Clustering of Atoms at Site U with Ions at Site I′. That indium atoms are located at In(U) in both crystals, at the very center of the sodalite unit (site U), is unambiguous. Such indium atoms have been found in the sodalite units of In-A.31,35 No other chemically possible atom or ion, such as Si, Al, or O, could account for the electron density found at this position. The failure of In(U) to approach the negatively charged framework oxygens indicates, as before,31,35 that In(U) is occupied by atoms. As such, they may preferentially approach cations rather than framework oxygens because the cations have a higher absolute charge and are therefore more polarizing and because there is more opportunity for delocalization. Indeed, they are reasonably close to the indium cations at In(I′A) and In(I′B) in the sodalite unit. These In0 atoms might have been

Fully Indium-Exchanged Zeolite X

J. Phys. Chem. B, Vol. 104, No. 35, 2000 8379

Figure 6. Close-up stereoviews of the three site III′ In+ positions in In87-X (crystal 2). Each shows three consecutively connected four-rings and an adjacent six-ring with an In+ ion at In(II) in it. All In(III′)-oxygen distances less than 3.8 Å are indicated by fine solid lines. The distances shown are 2.53, 2.85, and 3.46 Å to In(III′A), 2.74 and 3.12 Å to In(III′B), and 2.61, 2.74, and 3.65 Å to In(III′C). See the caption of Figure 3 for other details.

retained during the reaction between In0 and Tl-X or may be the product of the ‘in-situ’ disproportionation of In+, i.e., 2In+ f In2+ + In0 (vide supra). Some of the In0 atoms in crystal 2 might also have been produced by further disproportionation upon later exposure to the atmosphere or to deionized water, or both: the In0 and In2+ occupancies both increased after the treatments, from 2.0 and 8.0 for crystal 1 to 2.5 and 10.0 for crystal 2, at In(U) and In(I′B), respectively. The possible In(U) to In(I′A) approach distances (ca. 2.151(3) and 2.158(5) Å for crystals 1 and 2, respectively) are unreasonably short when compared to 2.92 Å, the sum of the atomic radius of In0 (1.67 Å)73 and the ionic radius of In+ (ca. 1.25 Å); it can readily be avoided by not putting an atom at In(U) and one or more ions at In(I′A) in the same sodalite unit. However, the In(U)-In(I′B) distance (2.674(9) and 2.694(8) Å for crystals 1 and 2, respectively) is reasonable, comparable to

2.60 Å, the sum of the atomic radius of In0 and the ionic radius of In2+ (0.92 Å). Some coordination of In0 is needed to support it in space at its position far from the zeolite framework, and In(I′B) is the obvious “ligand” position. Furthermore, In0 should coordinate to In2+ rather than In+ because In2+ is more electrophillic and because In2+ is the less stable oxidation state. Clusters such as (In2)2+, (In3)4+ (bent), (In4)6+, or “(In5)8+” (four In2+ ions tetrahedrally arranged in the sodalite unit with an In0 at their center) must exist. The ratio of the occupancies at In(I′B) and In(U), In(I′B)/ In(U) ) 8.0/2.0 ) 4.0 for crystal 1 and 10.0/2.5 ) 4.0 for crystal 2 indicate that the clusters are (In2+)4In0 or In58+. (The next paragraph argues that this is an In57+ cluster.) The “In58+” cluster had been found in fully indium-exchanged zeolite A,31 and this ratio is always a constant for various structures in this system.31,35 Also, the other clusters given at the end of the

8380 J. Phys. Chem. B, Vol. 104, No. 35, 2000 previous paragraph would not support In0 symmetrically at the centers of the sodalite cavities, except by chance. The thermal parameter at In(U) is small (see Table 2), showing no evidence of being an average of several off-center positions. The highly symmetric “In58+” cluster, with four In2+ ions at In(I′B) placed tetrahedrally (precisely so, by symmetry) about an In atom at In(U), is present in 2.0 of the eight sodalite units per unit cell in crystal 1 and 2.5 in crystal 2. Some delocalization of electron density from In0 to the In2+ ions must occur in the cluster, so these oxidation states are only approximate. Stereoviews of the sodalite units in crystal 2 are shown in Figures 4 and 5, respectively. Each of the other 6.0 and 5.5 sodalite units for crystals 1 and 2, respectively, contains four In+ ions at In(I′A). “In58+” contains an odd number of electrons, a total of seven electrons, beyond the filled 4d10 shells of its five atoms. This is inconsistent with the apparent stability of this cluster. Accordingly, to complete a stable octet of electrons about the central atom, the actual charge of In5n+ cluster is proposed to be 7+. Together with 78 In+ ions at In(II), In(I′A), In(III′A), In(III′B), In(III′C), and In(III′D), per unit cell of crystal 1, this assignment of charge to 2.0 In57+ clusters balances the anionic charge (92-) of the zeolite framework. For crystal 2, the corresponding quantities are 74.5 In+ ions at In(II), In(I′A), In(III′A), In(III′B), and In(III′C) with 2.5 In57+. For the same reason, the corresponding sodalite unit clusters in In-A31,35 are likely to be In57+ also; it is within the precision of that work. Summary All Tl+ ions in fully dehydrated, fully Tl+ exchanged zeolite X were reduced to atoms that vaporized away from the zeolite by exposure to In vapor at 623 K. In their place, In+ and In2+ ions are found at a variety of 3-fold axis and supercage sites, and tetrahedral In5n+ clusters, n likely equals 7, are seen at the centers of some sodalite cavities. Exposure to the atmosphere, washing with H2O, and redehydration caused the unit-cell formula to change little, from (In+)78(In57+)2Si100Al92O384 to (In+)74.5(In57+)2.5Si100Al92O384. However, the space group changed from Fd3h to Fd3hm due to a loss of long-range order. Acknowledgment. N. H. Heo gratefully acknowledges the support of the Central Laboratory of Kyungpook National University for the diffractometer and computing facilities. This work was supported in part by the Ministry of Education of Korea (Grant No. 01-D-0048) and in part by the Research Fund at Kyungpook National University. Supporting Information Available: Observed and calculated structure factors squared with esds for In88-X and In87X. This material is available free of charge via the Internet at http://pubs.acs.org. References and Notes (1) Srdanov, V. I.; Blake, N. P.; Markgraber, D.; Metiu, H.; Stucky, G. D. AdVanced Zeolite Science and Applications, Studies in Surface Science and Catalysis; Jansen, J. C., Stocker, M., Karge, H. G., Weitkamp, J., Eds.; Elsevier Science: Amsterdam, 1994; Vol. 85, pp 115-144. (2) Terasaki, O.; Yamazaki, K.; Thomas, J. M.; Ohsuna, T.; Watanabe, D.; Sanders, J. V.; Barry, J. C. Nature (London) 1987, 330, 58-60. (3) Stucky, G. D.; MacDougall, J. E. Science 1990, 247, 669-678. (4) Moller, K.; Bein, T.; Herron, N.; Mahler, W.; Macdougall, J. E.; Stucky, G. D. Mol. Cryst. Liq. Cryst. 1990, 181, 305-314. (5) Ozin, G. A.; Ozkar, S.; Prokopowicz, R. A. Acc. Chem. Res. 1992, 25, 553-560. (6) Alekseev, Yu. A.; Bogomolov, V. N.; Zhukova, T. B.; Petranovskii, V. P.; Romanov, S. G.; Kholodkevich, S. V. IzV. Akad. Nauk SSSR, Ser. Fiz. 1986, 50, 418-423. (7) Marques, F.; Fornes, V. Solid State Commun. 1999, 112, 17-20.

Heo et al. (8) Stramel, R. D.; Thomas, J. K. J. Chem. Soc., Faraday Trans. 1, 1988, 84, 1287-1300. (9) Chen, W.; Lin, Z. J.; Wang, Z. G.; Lin, L. Y. Solid State Commun. 1996, 100, 101-104. (10) Nozue, Y.; Tang, Z. K.; Toto, T. Solid State Commun. 1990, 73, 531-534. (11) Herron, N. J.; Wang, Y.; Eddy, M. M.; Stucky, G. D.; Cox, D. E.; Moller, K.; Bein, T. J. Am. Chem. Soc. 1989, 111, 530-540. (12) Uchida, H.; Ogata, T.; Yoneyama, H. Chem. Phys. Lett. 1990, 173(1), 103-106. (13) Kitagawa, H.; Sendoda, Y.; Ono, Y. J. Catal. 1986, 101, 12-18. (14) Gnep, N. S.; Doyemet, J. Y.; Seco, A. M.; Famoa, R. F.; Guisnet, M. Appl. Catal. 1988, 43, 155-166. (15) Kanazirev, V.; Price, G. L.; Dooley, K. M. Zeolite Chemistry and Catalysis; Jacobs, P. A., Ed.; Elsevier: Amsterdam, 1991; pp 227-285. (16) Kanazirev, V.; Valtchev, V.; Tarassov, M. P. J. Chem. Soc. Chem. Commun. 1994, 1043-1044. (17) Mowry, J. R.; Anderson, R. F.; Johnson, J. A. Oil Gas J. 1985, 128-131. (18) Kanazirev. V.; Price, G. L.; Dooley, K. M. J. Chem. Soc., Chem. Commun. 1990, 712-713. (19) Price, G. L.; Kanazirev, V. J. Catal. 1990, 126, 267-278. (20) Chatterjee, M.; Bhattcharya, D. Hayashi, H.; Ebina. T.; Onodera, Y.; Nagase, T.; Sivasanker, S.; Iwasaki, T. Micro. Meso. Mater. 1998, 20, 87-91. (21) Mihalyi, R. M.; Beyer, H. K.; Mavrodinova, V.; Minchev, Ch.; Neinska, Y. Micro. Meso. Mater. 1998, 24, 143-151. (22) Ogura, M.; Ohaski, T.; Kikuchi, E. Micro. Meso. Mater. 1998, 21, 533-540. (23) Kanazirev, V.; Neinska, Y.; Tsoncheva, T.; Kosova, L. Proceedings of the Ninth International Zeolite Conference; van Ballmoos, R., Higgins, J. B., Tracy, M. M. J., Eds.; Butterworth-Heinemann, New York, 1993; pp 461-468. (24) Heo, N. H.; Choi, H. C., Unpublished results. (25) Alekseev, Yu. A.; Bogomolov, V. N.; Egorov, V. A.; Petranovskii, V. P.; Kholodkevich, S. V. JETP Lett. 1982, 36, 463-465. (26) Alekseev, Yu. A.; Bogomolov, V. N.; Zhukova, T. B.; Petranovskii, V. P.; Kholodkevich, S. V. SoV. Phys. Solid State 1982, 24(8), 1384-1388. (27) Blackwell, C. S.; Pluth, J. J.; Smith, J. V. J. Phys. Chem. 1985, 89, 4420-4423. (28) Heo, N. H.; Seff, K. J. Am. Chem. Soc. 1987, 109, 7986-7992. (29) Heo, N. H.; Seff, K. PerspectiVes in Molecular SieVe Science; ACS Symposium Series 368; Flank, W. H., Whyte, T. E., Jr., Eds.; American Chemical Society: Washington, DC, 1988; pp 177-193. (30) Sun, T.; Seff, K. J. Phys. Chem. 1993, 97, 5213-5214. (31) Heo, N. H.; Choi, H. C.; Jung, S. W.; Park, M.; Seff, K. J. Phys. Chem. B 1997, 101, 5531-5539. (32) Thiel, A. Z. Anorg. Chem. 1904, 40, 280. (33) Ashraf, M.; Aziz-Alrahmam, A. M.; Headbridge, J. B. J. Chem. Soc., Dalton Trans. 1977, 170-173. (34) Biedermann, G.; Wallin, T. Acta Chem. Scand. 1960, 14, 594608. (35) Heo, N. H.; Kim, S. H.; Choi, H. C.; Jung, S. W.; Seff, K. J. Phys. Chem. B 1998, 102, 17-23. (36) Bogomolov, V. N.; Petranovskii, V. P. Zeolites 1986, 6, 418-419. (37) Kim, Y.; Han, Y. W.; Seff, K. Zeolites 1997, 18, 325-333. (38) Firor, R. L.; Seff, K. J. Am. Chem. Soc. 1977, 99, 4039-4044. (39) Riley, P. E.; Seff, K.; Shoemaker, D. P. J. Phys. Chem. 1972, 76, 2593-2597. (40) Wade, K.; Banister, A. J. ComprehensiVe Inorganic Chemistry; Bailar, J. C., Jr., Ed.; Pergamon Press: Oxford, 1973; Vol. 1, pp 9971000. (41) Yeom, Y. H.; Jang, S. B.; Kim, Y.; Song, S. H.; Seff, K. J. Phys. Chem. B 1997, 101, 6914-6920. (42) Jang, S. B.; Jeong, M. S.; Kim, Y.; Seff, K. J. Phys. Chem. B 1997, 101, 9041-9045. (43) Bae, D.; Seff, K. Micro. Meso. Mater., accepted for publication. (44) International Tables for X-ray Crystallography; Ibers, J. A., Hamilton, W. C., Eds.; Kynoch Press: Birmingham, England, 1974; Vol. IV, pp 61-66. (45) Olson, D. H. Zeolites 1995, 15, 439-443. (46) Sun, T.; Seff, K. Chem. ReV. 1994, 94, 859. (47) Sheldrick, G. M., SHELXL97, Program for the Refinement of Crystal Structures, University of Gottingen, Germany, 1997. (48) Haniffa, R. M.; Seff, K. J. Phys. Chem. B 1998, 102, 2688-2698. (49) Doyle, P. A.; Turner, P. S. Acta Crystallogr., Sect. A 1968, 24, 390-397. (50) Reference 44, pp 71-98. (51) Handbook of Chemistry and Physics, 74th ed.; Chemical Rubber Co.; Cleveland, 1993; pp 10-258. (52) Loewenstein, W. Am. Mineral. 1954, 39, 92-96. (53) Seff, K. Studies in Surface Science and Catalysis 102, Elsevier: New York, 1996, pp 267-293.

Fully Indium-Exchanged Zeolite X (54) Kim, M. J.; Jeong, M. S.; Kim, Y.; Seff, K. Micro. Meso. Mater. 1999, 30, 233-241. (55) Kwon, J. H.; Jang, S. B.; Kim, Y.; Seff, K. J. Phys. Chem. 1996, 100, 13 720-13 724. (56) Zhu, L.; Seff, K. J. Phys. Chem. B 1999, 103, 9512-9518. (57) Bae, D.; Zhen, S.; Seff, K. J. Phys. Chem. B 1999, 103, 56315636. (58) Zhu, L.; Seff, K.; Olson, D. H.; Cohen, B. J.; Von Dreele, R. B. J. Phys. Chem. B 1999, 103, 10 365-10 372. (59) Bae, D.; Seff, K. Micro. Meso. Mater. 1999, 33, 265-280. (60) Bae, D.; Seff, K. Micro. Meso. Mater., in press. (61) Shannon, R. D.; Prewitt, C. T. Acta Crystallogr., Sect. B 1969, 25, 925-946. (62) Handbook of Chemistry and Physics, 64th ed.; Chemical Rubber Co.; Cleveland, 1983; p F-187. (63) Brode, H. Ann. Phys. 1940, 37, 344.

J. Phys. Chem. B, Vol. 104, No. 35, 2000 8381 (64) Barrett, A. H.; Mandel, M. Phys. ReV. 1955, 99, 666. (65) Barrow, R. F.; Glaser, D. V.; Zeeman, P. B. Proc. Phys. Soc., London, Sect. A 1955, 68, 962-968. (66) Kim, Y.; Seff, K. J. Phys. Chem. 1978, 82, 1307-1311. (67) Fraga, S.; Saxeua, K. M. S.; Karwowski, J. Handbook of Atomic Data; Elsevier Scientific: Amsterdam, 1976; p 465. (68) Stevenson, D. P.; Schomaker, V. J. Am. Chem. Soc. 1942, 64, 2514-2514. (69) Cotton, F. A.; Wilkinson, G. AdVanced Inorganic Chemistry, 5th ed.; John Wiley & Sons: New York, 1988; pp 209-233. (70) Vitale, G.; Mellot, C. F.; Bull, L. M.; Cheetham, A. K. J. Phys. Chem. B 1997, 101, 4559-4564. (71) Peterson, B. K. J. Phys. Chem. B 1999, 103, 3145-3150. (72) Takaishi, T. J. Phys. Chem. 1995, 99, 10 982-10 987. (73) Tyzack, G.; Raynor, G. V. Trans. Faraday Soc. 1954, 50, 675680.