Method. Preparation of Fully Indium-Exchanged Zeolite Y (FAU, Si

Sep 29, 2014 - prepared by thallous ion exchange (TIE), a vapor phase ion exchange method .... TIE reaction (eq 2), which may have already begun durin...
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First Successful Application of the Thallous Ion Exchange (TIE) Method. Preparation of Fully Indium-Exchanged Zeolite Y (FAU, Si/Al = 1.69) Joon Young Kim,† Cheol Woong Kim,† Yong-Ki Park,‡ Na Young Kang,‡ Nam Ho Heo,*,† and Karl Seff*,§ †

Laboratory of Structural Chemistry, Department of Applied Chemistry, College of Engineering, Kyungpook National University, Daegu 702-701, Korea ‡ Korea Research Institute of Chemical Technology, Yuseong, Daejeon 305-600, Korea § Department of Chemistry, University of Hawaii, 2545 The Mall, Honolulu, Hawaii 96822-2275, United States S Supporting Information *

ABSTRACT: Fully indium-exchanged zeolite Y, |In+62.6(In57+)1.2|[Si121Al71O384], was prepared by thallous ion exchange (TIE), a vapor phase ion exchange method. InCl(g, 510 Pa) was allowed to react with a single crystal of Tl71−Y under anhydrous conditions at 623 K. A second crystal prepared as above was washed with deionized water and redehydrated to give |In+39.7 (In57+)4.5|[Si121Al71O384]. The structures of fully dehydrated Tl71−Y and these two forms of In−Y were determined by single-crystal crystallography using synchrotron X-radiation. Then the two In−Y crystals were subjected to scanning electron microscopy energy-dispersive X-ray (SEM-EDX) analysis. Both methods indicated that no Tl remained in the In−Y crystals. The additional steps of washing and redehydration caused some of the In+ ions in the first In−Y crystal to disproportionate to give additional In57+ clusters in the sodalite cavities and In0 atoms on the crystal surface. Most of the In+ ions in both forms of In−Y are easily accessible to guest molecules via the 12-ring channel system.

1. INTRODUCTION

The concentration of trace amounts of unwanted cations from the exchange medium into the zeolite can usually be avoided by employing TIE.4 1.3. Catalysis by Indium Zeolites. Indium containing zeolites are important catalysts with high activity and selectivity for a number of industrial reactions, and new processes involving indium zeolites are under development.1,5−15 In these, the intrazeolitic indium species are at least closely involved with the active sites. 1.4. Objectives of this Work. Because the vapor pressure of InCl(g) is appreciable at a moderate temperature, 510 Pa at 623 K,16 it was hoped that In+ could be introduced into zeolites in their dehydrated Tl+ forms by TIE. Accordingly, this work was done with this two-step reaction sequence in mind,

1.1. Vapor Phase Ion Exchange (VPIE) of Indium. The difficulties associated with the aqueous exchange of In+ into high-Al zeolites may sometimes be overcome by VPIE.1−3 In VPIE, an anhydrous zeolite is exposed to a volatile compound of the incoming cation, either a salt or a covalent compound. VPIE has been used to introduce indium cations into the native forms, Na−Z, of the high-Al zeolite Na−X (Si/Al = 1.09) using InCl(g) at 623 K.1,3 Similarly, it has been used to introduce indium ions into the lower-Al zeolite Na−Y (Si/Al = 1.69).2 These one-step VPIE reactions, however, did not go to completion, and sometimes chloride ions were retained.2,3 1.2. Thallous Ion Exchange (TIE). TIE4 is a two-step VPIE method. It has the same purpose as VPIE, to avoid the difficulties seen in conventional aqueous exchange, but it opens many additional possibilities. In TIE, an anhydrous Tl+exchanged zeolite is allowed to react with a volatile compound as in VPIE, but here the product is also volatile, so it is easily and quantitatively removed. TIE is a simple metathesis reaction that can be driven to completion by mass action. The volatile compound used is often an anhydrous halide, MmXn, with 623 K < T < 723 K; the product is then TlX(g). TIE can be expected to have general utility in producing cationic forms of zeolites and other materials that have heretofore, for various chemical reasons, been difficult or impossible to prepare. © 2014 American Chemical Society

Na−Y + Tl(C2H3O2 )(aq) → Tl−Y + Na(C2H3O2 )(aq) (aqueous ion exchange)

(1)

followed by the complete dehydration of Tl−Y and Tl−Y + InCl(g ) → In−Y + TlCl(g ) (TIE ).

(2)

Reaction 1 had been seen to go easily to completion many times before,16,17 and dehydration had proceeded without Received: August 26, 2014 Revised: September 25, 2014 Published: September 29, 2014 24655

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Table 1. Experimental Conditions and Crystallographic Data crystal 1 (Tl71−Y) crystal cross-section (mm) ion exchange for Tl+ (T (K), h, mL) dehydration of Tl−Y (T (K), h, P (Pa)) reaction of Tl−Y with InCl (T (K), h, P (Pa)) exposure to atmosphere (T (K)) wash with deionized water (T (K), h, mL) redehydration (T (K), h, P (Pa)) X-ray source wavelength (Å) detector crystal-to-detector distance (mm) data collection temperature (T (K)) space group, No. unit cell constant, a (Å) maximum 2θ for data collection (deg) no. of reflections measured no. of unique reflections measured, m no. of reflections with Fo > 4σ(Fo) no. of variables, s data/parameter ratio, m/s weighting parameters: a, b final error indices: R1b, R2c goodness of fitd

crystal 2 (In69−Y)

0.085 294, 48, 10 673, 48, 1 × 10−4

0.085 294, 48, 10 623, 48, 1 × 10−4 623, 120, 510

PF(BL-5A)a 0.9000 ADSC Quantum-315r 60 294(1) Fd3̅m, 227 24.980(1) 69.14 48,143 830 763 57 14.6 0.0166, 950.2 0.035, 0.077 1.18

PF(BL-5A)a 0.9000 ADSC Quantum-315r 60 294(1) Fd3̅m, 227 24.856(1) 69.18 43,564 823 792 56 14.7 0.0525, 440.6 0.041, 0.130 1.32

crystal 3 (In62−Y) 0.085 294, 48, 10 623, 48, 1 × 10−4 623, 120, 510 294 294, 24, 5 623, 48, 1 × 10−4 PF(BL-5A)a 0.9000 ADSC Quantum-315r 60 294(1) Fd3̅m, 227 24.890(1) 69.10 43,046 823 775 56 14.7 0.0323, 518.9 0.042, 0.114 1.25

Beamline BL-5A at the Photon Factory, Japan. bR1 = Σ|Fo − |Fc||/ΣFo; R1 is calculated using only those reflections for which Fo > 4σ(Fo). cR2 = [Σw(Fo2 − Fc2)2/Σw(Fo2)2]1/2 is calculated using all unique reflections measured. dGoodness of fit = (Σw(Fo2 − Fc2)2/(m − s))1/2. a

Another Tl−Y crystal treated similarly in flowing oxygen gas was colorless, suggesting that the black color of the crystal studied is a consequence of the decomposition of the template, bis(2-hydroxyethyl)dimethylammonium chloride (in aqueous triethanolamine), used to synthesize these large single crystals.19 Despite the apparent presence of some amount of organic material after Tl+ exchange, that exchange appears to have gone to completion. 2.1.2. Crystal 2 (In69−Y). A single crystal of In69−Y was prepared from Tl71−Y by TIE. About 14 mg of InCl (SigmaAldrich, 99.999%), a 105 excess for the complete replacement of Tl+ with In+, was placed in a small Pyrex test tube which was then put into the reaction vessel (a Pyrex tube) above the capillary (a continuation of the capillary) containing the Tl71−Y crystal. The crystal and the InCl were then dehydrated at 673 K at 1 × 10−4 Pa for 48 h. As the temperature was increased (25 K/h) toward 673 K, InCl began to vaporize and condense higher up within the reaction vessel (outside the heater). The initial green color of the indium monochloride changed to both white and red at the bottom, black in middle, and bright yellow at the top. (InCl is bright yellow below about 393 K and red above that temperature.26) The white and black colors are attributed to the formation of InCl3 and In, respectively:

complication.17,18 It had been proposed that reaction 2 could also proceed without complication.4 The extra-framework indium species that formed would easily be identified crystallographically, including their relative abundances and positioning within the zeolite, their geometry and coordination environments, and their oxidation states. Some of these chemically and thermally stable species may be responsible for the catalytic activity of In-exchanged zeolites.

2. EXPERIMENTAL SECTION 2.1. Synthesis and Composition. Single crystals of sodium zeolite Y (|Na71(H2O)x|[Si121Al71O384]−FAU, Na71− Y, or Na−Y; Si/Al = 1.69) were prepared in this laboratory by the synthetic method of Ferchiche et al.19 Because their procedure was followed without variation, it is expected that the composition of the product crystals would be the same as theirs. Least-squares refinement (paragraph 3 of Section 1.1 in the Supporting Information) supports this expectation. 2.1.1. Crystal 1 (Tl71−Y). A single crystal of Na−Y, a colorless octahedron about 0.085 mm in cross-section, was selected and loaded into a fine Pyrex capillary. Fully Tl+exchanged zeolite Y (|Tl71(H2O)y|[Si121Al71O384]−FAU, Tl71− Y, or Tl−Y) was prepared by dynamic ion exchange (the flow method) with 0.10 M aqueous (pH = 6.4) thallous acetate (TlC2H3O2, Aldrich, 99.99%) at 294 K for 48 h. This and similar procedures had been shown to be suitable for the preparation of fully Tl+-exchanged Tl−Y,18,20 Tl−X,21,22 and Tl−A.23−25 The resulting colorless Tl−Y crystal was dehydrated by heating (rate = 25 K/h) in its capillary under dynamic vacuum to 673 K and 1 × 10−4 Pa. These conditions were maintained for 48 h. The crystal, now black, was sealed under vacuum in its capillary by torch.

3InCl(bright yellow) → InCl3(white) + 2In(black)

(3)

After cooling to room temperature (−50 K/h), the reaction vessel containing dry InCl above the crystal-containing capillary was sealed off under vacuum from the vacuum line. To do the TIE reaction (eq 2), which may have already begun during the dehydration step, the isolated reaction vessel was maintained at 623 K for 120 h. At 623 K, the vapor pressures of InCl and TlCl are 510 and 8 Pa, respectively. Finally, only the crystal was heated at 623 K for 24 h to distill away any excess InCl and TlCl that might be in or near it. After cooling (−50 K/h), the 24656

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24657

192(i) 96(h) 96(g) 96(g) 96(g) 32(e) 32(e) 192(i) 48(f)

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

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

T O1 O2 O3 O4 Tl1 Tl2 Tl31 Tl32

T O1 O2 O3 O4 InU In11 In12 In2 In31

T O1 O2 O3 O4 InU In11 In12 In2 In31

U I′ I′ II III′

U I′ I′ II III′

I′ II III′ III

cation site y 3617(6) 0d −157(18) −7619(17) 17910(17) 7291(2) 25305(2) 19688(81) 12500d 3662(4) 0d −91(13) −7463(13) 17615(14) 12500d 6354(38) 7503(8) 25244(3) 20405(80) 3637(4) 0d −94(13) −7319(13) 17460(14) 12500d 6278(9) 7533(21) 25270(3) 19367(125)

x

−5386(6) −10491(16) −157(18) −7619(17) 17910(17) 7291(2) 25305(2) 17690(67) 12500d

−5243(4) −10291(13) −91(13) −7463(13) 17615(14) 12500d 6354(38) 7503(8) 25244(3) 17626(71)

−5246(4) −10316(12) −94(13) −7319(13) 17460(14) 12500d 6278(9) 7533(21) 25270(3) 16962(114) 12465(4) 10316(12) 14554(18) 2666(18) 32117(17) 12500d 6278(9) 7533(21) 25270(3) 41999(66)

12477(4) 10291(13) 14663(19) 2670(19) 32218(18) 12500d 6354(38) 7503(8) 25244(3) 42104(49)

12532(6) 10491(16) 14322(23) 3178(24) 32135(23) 7291(2) 25305(2) 42243(32) 40922(50)

z U22

crystal 1 (Tl71−Y) 136(8) 104(8) 217(20) 236(32) 212(18) 212(18) 213(20) 213(20) 212(20) 212(20) 276(3) 276(3) 304(3) 304(3) 1328(107) 3251(297) 2752(217) 2752(217) crystal 2 (In69−Y) 71(6) 53(6) 169(14) 168(23) 153(14) 153(14) 161(14) 161(14) 165(14) 165(14) 149(39) 149(39) 117(23) 117(23) 234(6) 234(6) 298(5) 298(5) 1095(118) 1612(162) crystal 3 (In62−Y) 87(6) 73(6) 175(13) 208(22) 187(13) 187(13) 179(14) 179(14) 234(15) 234(15) 147(10) 147(10) 165(6) 165(6) 281(15) 281(15) 345(5) 345(5) 2093(256) 2825(327)

U11 or Uisob

75(6) 175(13) 209(22) 209(23) 155(22) 147(10) 165(6) 281(15) 345(5) 421(78)

55(6) 169(14) 175(23) 205(24) 146(22) 149(39) 117(23) 234(6) 298(5) 331(54)

116(8) 217(20) 218(31) 240(33) 200(31) 276(3) 304(3) 353(37) 265(64)

U33

−28(4) −41(12) −33(13) −25(13) −3(13) 0 −1(5) −54(12) −46(3) −167(130)

−22(4) −48(12) −7(13) 4(13) −21(13) 0 30(22) −37(4) −42(3) −130(74)

−22(6) −32(18) −17(18) −4(18) −39(18) −47(2) −42(2) 34(72) 0

U23

−12(4) 19(17) −33(13) −25(13) −3(13) 0 −1(5) −54(12) −46(3) −207(119)

−14(4) −4(17) −7(13) 4(13) −21(13) 0 30(22) −37(4) −42(3) −241(66)

−14(6) 24(25) −17(18) −4(18) −39(18) −47(2) −42(2) −217(52) 0

U13

3(4) −41(12) 78(18) 37(17) 98(19) 0 −1(5) −54(12) −46(3) 1833(253)

0(4) −48(12) 59(18) 25(17) 67(18) 0 30(22) −37(4) −42(3) 432(114)

−3(6) −32(18) 65(25) 11(25) 68(24) −47(2) −42(2) 565(141) −1111(234)

U12

4.56(7) 18.1(3) 8.7(5) 22.88(17) 6.3(4)

1.10(7) 4.2(5) 25.8(5) 27.34(22) 7.6(4)

27.66(19) 28.24(19) 11.5(3) 4.35(21)

varied

4.48(7)e 17.9(3)e 8.7(3) 22.77(16) 8.2(3)

1.19(7)e 4.8(3)e 25.1(4) 27.70(22) 9.8(3)

27.63(19) 28.18(19) 11.03(17) 4.16(17)

constrained

occupancyc

192 96 96 96 96

192 96 96 96 96

192 96 96 96 96

fixed

Positional parameters × 105 and thermal parameters × 104 are given. Numbers in parentheses are the estimated standard deviations (esds) in the units of the least significant figure given for the corresponding parameter. bThe anisotropic temperature factor is exp[−2π2a−2(U11h2 + U22k2 + U33l2 + 2U12hk + 2U13hl + 2U23kl)]. cOccupancy factors are given as the number of atoms or ions per unit cell. Occupancy constraints requiring that the charge of the Tl+ ions (crystal 1) and indium ions (crystals 2 and 3) sum to 71+ were applied, respectively. dExactly, by symmetry. eThe constraint, occupancy at In11 = 4 x occupancy at InU, was applied to the In57+ cluster.

a

Wyckoff position

atom position

Table 2. Positional, Thermal, and Occupancy Parametersa

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Figure 1. EDX spectrum of partially hydrated |In+39.7(In57+)4.5|[Si121Al71O384]−FAU (crystal 3). The three largest Tl peaks would be Tl Lα1 at 10.267 eV, Tl Lβ1 at 12.212 eV, and Tl Lβ2 at 12.269 eV. Note that they are absent. The EDX spectrum for crystal 2 is essentially identical to that of crystal 3.

thallium. They are in general agreement with the composition determined crystallographically (Table 3).

resulting crystal, still black, was sealed off under vacuum in its capillary by torch. Similar VPIE procedures had been used successfully to prepare In−A,23−25 In−X,21,22 and In−Y.2,17 2.1.3. Crystal 3 (In62−Y). Another single crystal of In69−Y, prepared as described in Section 2.1.2, was exposed to the atmosphere and washed with deionized water. This was done to possibly remove any residual Tl or In species that might be present on the surface of the crystal. It was expected to produce more In57+ clusters within the zeolite by the disproportionation of In+, as had been seen in the preparation of In−A,23−25 In− X,21,22 and In−Y.2,17 This crystal, still black after washing, was redehydrated (25 K/h) at 673 K and 1 × 10−4 Pa for 48 h. After cooling to room temperature (−50 K/h), the resulting crystal, showing no change in appearance, was sealed under vacuum in its capillary by torch. 2.2. X-ray Diffraction and Structure Determination. The diffraction intensities for the three crystals were measured with synchrotron X-radiation via a silicon (111) double crystal monochromator. The ADSC Q315 ADX program was used for data collection by the omega scan method. Highly redundant data sets were harvested by collecting 72 sets of frames for each crystal with a 5° scan and an exposure time of 1 s per frame. The basic data files were prepared using the program HKL2000.27 The reflections were successfully indexed by the automated indexing routine of the DENZO program.27 These were corrected for Lorentz and polarization effects; negligible corrections for crystal decay were also applied. The space group Fd3̅m, standard for zeolite Y, was determined by the program XPREP.28 Additional experimental data are presented in Table 1. The structures of the three crystals were determined using full matrix least-squares refinements in the space group Fd3̅m. Additional crystallographic information is given in Table 1, and the final structural parameters are presented in Table 2. The detailed procedures for the determination of all three structures are given in the Supporting Information. 2.3. Scanning Electron Microscopy Energy-Dispersive X-ray (SEM-EDX) Analysis. After diffraction data collection, crystals 2 and 3 were removed from their capillaries (exposed to the atmosphere). Each was attached to a sample holder with carbon tape for SEM-EDX analysis. The composition of the crystals was determined using a Versa 3D FIB (focused ion beam) within an Ametek EDX spectrometer and a FE (field emission) scanning electron microscope at 294 K and 1 × 10−3 Pa with a beam energy of 20 keV and current of 1 nA. The SEM-EDX results (Figure 1) show that they are free of

Table 3. Crystal Composition (Atomic %) by Crystallographic (SXRD) and SEM-EDX Analysesa crystal 2

crystal 3

element

SXRD

SEM-EDX

SXRD

SEM-EDX

Si Al O In Tl

18.8 11.0 59.6 10.6 0

17.0(10) 12.1(7) 63(6) 7.46(12) 0.45(14)

19.0 11.1 60.2 9.7 0

18.3(10) 12.8(8) 60(6) 8.42(13) 0.44(15)

a

The zeolite crystal can be expected to have suffered some decomposition under the action of the electron beam. This can be a significant source of error.

3. THE THREE CRYSTAL STRUCTURES The three crystal structures are unremarkable, similar to those already reported for Tl−Y18,20 and In−Y.8,17 They were determined only to show that crystal 1 was fully Tl+ exchanged and that crystals 2 and 3 contained no residual Tl+, not at the Tl+ positions seen in crystal 1 nor elsewhere (Tables 2 and 4). This is seen more precisely by single-crystal crystallography than by SEM-EDX. Additional description of the structures (e.g., stereodrawings and bond distances and angles) is available in the Supporting Information. 3.1. Structure of Crystal 1 (Tl71−Y). The 71 Tl+ ions per unit cell distribute themselves over four sites, I′, II, III, and site III′. On the 3-fold axes, 27.6 of the 32 D6Rs (site I′) and 28.2 of the 32 S6Rs (site II) are occupied per unit cell. Rather than filling these sites fully, some Tl+ ions were found at sites III and III′, perhaps avoiding 6-rings with only one Al3+.29 The distribution of Tl+ ions among these cationic sites is similar to those previously reported in Tl−Y structures.18,20 This is summarized in Table 5. 3.2. Structures of Crystals 2 (In69−Y) and 3 (In62−Y). About 62.6 In+ ions were found at three crystallographically distinct positions per unit cell of In69−Y (crystal 2), but only about 39.7 were present in In62−Y (crystal 3). Most of this difference can be seen at In12 (Tables 2 or 4), where 25.1(3) In+ ions were found in In69−Y, but only 8.7(3) in In62−Y. Additional In+ ions are present at In2 in both In−Y structures, 27.7 in In69−Y and 22.8 in In62−Y. The remaining In+ ions are found in 12-rings at In31, 9.8 in In69−Y and 8.2 in In62−Y. In2+ ions (from a consideration of formal charges, In57+ may be 24658

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Table 4. Unit Cell Charge Budget cation sites

occ.a

atom position

I′ II III′

Tl1 Tl2 Tl31 Tl32 Σ Tl

27.63(19) 28.18(19) 11.03(17) 4.16(17) 71.00e,f

I′

In11 In12 In2 In31 InU Σ In

4.8(3) 25.1(4) 27.70(22) 9.8(3) 1.19(7) 68.6f

In11 In12 In2 In31 InU Σ In

17.9(3) 8.7(3) 22.77(16) 8.2(3) 4.48(7) 62.1f

II III′ U

I′ II III′ U

M−O,b Å

r,c Å

NCd

charge

charge × occ.

crystal 1 (Tl71−Y) 2.618(6) 2.744(6) 2.566(10) 2.910(11)

1.30 1.42 1.25 1.59

3 3 2 2

+1 +1 +1 +1

27.6 28.2 11.0 4.2 Σ Charges 71.0

crystal 2 (In69−Y) 2.277(8) 2.529(5) 2.631(5) 2.553(13)

0.96 1.21 1.31 1.23

4 3 3 2 4

+2h +1 +1 +1 −1h

9.6 25.1 27.7 9.8 −1.2 Σ Charges 71.0g

crystal 3 (In62−Y) 2.256(5) 2.540(7) 2.668(4) 2.508(17)

0.94 1.22 1.35 1.19

4 3 3 2 4

+2h +1 +1 +1 −1h

35.8 8.7 22.8 8.2 −4.5 Σ Charges 71.0g

a

Occupancy, ions per unit cell. bShortest M−O (metal ion to framework oxygen) bond lengths. cRadii of M ions obtained by subtracting 1.32 Å (the conventional radius of the oxide ion, reference 38) from the shortest M−O bond lengths. dCoordination numbers. eThe constraint, occupancy at Tl1 + Tl2 + Tl31 + Tl32 = 71, was applied to crystal 1. fNumbers of M atoms per unit cell. gConstrained in least-squares refinement to be 71.0. hFormal charges.

Table 5. Distribution of Tl+ Ions in Fully Tl+-Exchanged FAU Zeolites

The distribution of indium ions among these cationic sites are similar to those previously reported in In−Y structures.8,17 This is summarized in Table 6.

site and occupancy crystal Tl92.0-X Tl71.1-Y Tl71.1-Y Tl71.0-Y

Si/Al 1.09 1.69 1.69 1.69

I′ 32.0 30.4 28.9 27.6

II a

IIIb

III′1b

III′2b

reference

12.0 3.0

2.7 4.2

16.0 5.7 8.3 11.0

Y. Kim20 Y. Kim20 W. T. Lim18 this work

a

32.0 32.0a 31.2 28.2

4. DISCUSSION 4.1. TIE Was Entirely Successful. No Tl+ was found in either of the two In−Y crystals. Tl+ is easily characterizable crystallographically because of its distinctively high scattering power and large size, and the positions it might occupy are wellknown from crystal 1 and previously reported Tl+-exchanged FAU zeolites (Table 5). It is thus clear that the TIE reaction being tested in this work, Tl−Y + InCl(g) → In−Y + TlCl(g), went to completion. 4.2. In−Y Structures. The contents and distributions of indium ions in the two products are similar to those prepared by the anhydrous VPIE reaction Tl−Y + In0 → In−Y + Tl0

a

Fixed at 32.0 in refinement. bThe variations in the occupancies might be attributed to differing Al population distributions in 6-rings.

viewed as (In2+)4(In−)) were found at In11 in both structures. In69−Y has 4.8 In2+ ions per unit cell at this position. This occupancy is much higher in In62−Y, 17.9.

Table 6. Placement and Charge Budget for Extra-Framework Atoms in Fully Indium-Exchanged FAU Zeolitesa In ions I′ ion exchange method

crystal/site

VPIE

In88-Xb

VPIE

In87-Xb

VPIE

In67−Yd

TIE

In69−Ye

TIE

In62−Ye

occ. charge occ. charge occ. charge occ. charge occ. charge

II

In11

In12

In21

24.0 1+ 22.0 1+ 7.1 2+c 4.8 2+c 17.9 2+c

8.0 2+c 10.0 2+c 22.1 1+ 25.1 1+ 8.7 1+

29.0 1+ 32.0 1+ 23.9 1+ 27.7 1+ 22.8 1+

In22

0.5 2+

III & III′

U

In23

In31

In32

In33

In34

InU

∑ In+

6.0 1+ 4.5 1+ 3.0 1+

5.0 1+ 8.0 1+

3.0 1+

3.8 1+

11.0 1+ 8.0 1+ 4.6 1+ 9.8 1+ 8.2 1+

2.0 1−c 2.5 1−c 1.8 1−c 1.2 1−c 4.5 1−c

In57+

∑ In

78.0

2.0

88.0

74.5

2.5

87.0

1.8

66.8

62.6

1.2

68.6

39.7

4.5

62.1

57.4

In2+

0.5

a

Occupancies are given as the numbers of atoms or ions per unit cell. bReference 22. cFormal charge at this position. The terminal atoms of the In57+ cation (a centered tetrahedron) carry a 2+ formal charge and its central atom 1-. dReference 17. eThis work. 24659

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Notes

(Table 6). This method had been used to prepare numerous fully In-exchanged zeolites, In−A (Si/Al = 1.0),23−25 In−X (Si/ Al = 1.07),21,22 and In−Y (Si/Al = 1.69).8,17 There, as in this report, In57+ clusters were found in sodalite cavities. Their numbers increased upon subsequent treatment, exposure of In−Z (Z = zeolite) to water or to the atmosphere, followed by redehydration.17,22,23 Treatment with H2S caused the number of In57+ clusters to increase substantially,24 sometimes to fill all sodalite cavities.8 However, when In−Y was allowed to react at elevated temperatures with NO, air, or oxygen, all In57+ clusters disappeared; most In atoms were oxidized to form In3+ ions as members of InNO32+ 8 or In4O44+ clusters.8,17 The number of In57+ clusters in crystal 3 is more than 2.5 times that in In−Y previously prepared by VPIE,17 and the number of In+ ions in other sodalite cavities is considerably reduced (Table 6). However, the number of In+ ions in the supercages remained almost the same in both In−Y structures. If it is these In+ ions, which are readily accessible to incoming guest molecules, that participate in catalysis, then In−Y prepared by either method would be expected to have similar activity. As discussed in Section 1.1, the various VPIE methods have unique advantages over aqueous and SSIE methods. One-step VPIE reactions involving Na-Z, however, have not been found to go to completion. This was seen when Na-Z was allowed to react with the vapors of elements, salts, or covalent compounds under anhydrous conditions at 623 K.1,2 VPIE has also been used to introduce Cu+ into acid zeolites, H−Z. Guidry30 and Spoto et al.31 used VPIE to introduce Cu+ into H-ZSM-5. Afterward, Yang et al. prepared fully Cu(I)exchanged zeolite Y32−37 by reacting H−Y (Si/Al = 2.40) with CuCl vapor at 703 K. TIE is a more general two-step method because it does require that the zeolite be acid stable.

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We gratefully acknowledge the Photon Factory, High Energy Accelerator Research Organization, KEK, Tsukuba, Japan for the use of their diffractometer and computing facilities. This work was supported by the National Research Foundation of Korea (2011-0006652). This research was performed in cooperation with Project No. KK-1401-G0 and thus was further supported by the Korea Research Institute of Chemical Technology (KRICT).

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5. SUMMARY Fully indium-exchanged zeolite Y, In69−Y, |In+62.6(In57+)1.2| [Si121Al71O384], was prepared by thallous ion exchange (TIE), a vapor phase ion exchange method. It was then washed with deionized water and redehydrated to give In62−Y, |In+39.7 (In57+)4.5|[Si121Al71O384]. TIE caused all of the Tl+ ions in Tl71−Y to be replaced, thereby demonstrating the utility of the method. Washing and redehydration caused some In+ ions to disproportionate to give additional In57+ clusters and In0 atoms on the crystal surface. Most In+ ions in both In69−Y and In62−Y are easily accessible to guest molecules via the 12-ring channel system.

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ASSOCIATED CONTENT

S Supporting Information *

Structure description with stereodrawings and bond distances and angles. Observed and calculated structure factors squared with esds for Tl71−Y and the two forms of In−Y. This material is available free of charge via the Internet at http://pubs.acs.org.

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*Tel.: +82 53 950 5589; Fax: +82 53 950 6594; E-mail address: [email protected] (N.H.H.). *Tel: +1 808 226 7917; Fax: +1 808 956 5908; E-mail address: seff@hawaii.edu (K.S.). 24660

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