1837
J. Phys. Chem. 1995, 99, 1837-1839
Use of 13C CP NMR Spectroscopy for the Quantification of FAU/EMT Zeolite Intergrowths Synthesized with 15-Crown-5 and 18-Crown-6 Ethers Eddy J. P. Feijen,* Reinoud A. Reynders, Hilde Geerts, Johan A. Martens, Piet J. Grobet, and Pierre A. Jacobs Centrum voor Oppervlaktechemie en Katalyse, KU Leuven, Kardinaal Mercierlaan 92, B-3001 Heverlee, Belgium Received: September 30, 1994; In Final Form: January 5, 1995@
The I3C C P NMR envelope of as-synthesized crown ether containing intergrown faujasite polytype zeolites can be used to determine their FAU and EMT content. The method is calibrated with multiphase Rietveld refinement of X-ray patterns that are not broadened too much compared to those of the phase pure samples.
Introduction The developments in the field of zeolite synthesis led to the preparation of different kinds of faujasite zeolites, containing various amounts of the cubic and hexagonal polytype.'-I2 Successful characterization of such materials, in terms of quantification of the two polytypes, has been rather limited. This can be attributed to the different stacking modes of the FAU and EMT zones in the intergrowth zeolites, resulting in different X-ray diffraction patterns, which often impose major difficulties in determining the FAU and EMT amount. Furthermore, these diffraction pattern based techniques are rather complex and time consuming. Recently, however, a new method became available that allows to quantify these materials. The method is based on the splitting of at least part of the 29SiMAS NMR spectrum for FAU and EMT in their Li exchanged form.I3 Unfortunately, the method only applies to Al-rich frameworks. The recent discovery that the presence of 15-crown-5 and 18-crown-6 ethers in the synthesis hydrogel directed the crystallization toward the cubic and the hexagonal polytype, respectively, offered a new way for preparing FAU and EMT as well as the total range of intergrowth zeolite^.'^-^^ These intergrowths have been characterized by multiphase Rietveld refinement of the X-ray diffraction profiles.21 In the present work, a new method for determining the FAU and EMT amount of as-synthesized faujasite polytypes is presented, based on the I3C CP NMR spectra of occluded crown ethers. It is calibrated with the help of X-ray Rietveld refinement data.
Results and Discussion The synthesis procedure for the FAU and the EMT as well as for the intergrowth faujasite polytypes used in this study has been described elsewhere.21 The 18-crown-6 ether fraction (18crown-6/15-crown-5 18-crown-6) used to prepare the synthesis hydrogel was 0.6, 0.8, and 0.9 for sample MIX40/60, MIX20/80, and MIX10/90, respectively. The I3C CP NMR spectra were recorded on a Bruker 400MSL spectrometer under static conditions, after in vacuo dehydration of the samples at 393 K, to avoid decomposition of the crown ethers. The measurements were performed at a resonance frequency of 100.6 MHz with a contact time of 1 ms and a delay time of 5 s. The spectra were referenced to TMS. The I3C CP NMR spectrum of the as-synthesized EMT sample exhibits a broad shoulder at 75 ppm (Figure lB, curve
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* To whom correspondence should be addressed. @
Abstract published in Advance ACS Abstrucrs, February 1, 1995.
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shift (ppm) Figure 1. I3C static CP NMR spectra of dehydrated, as-synthesized faujasite polytype materials, containing crown ethers. Parts A, B, and C display the deconvolution of the MIX40160,MIX20180,and MIX101 90 spectrum, respectively. Curve a shows the spectrum for the pure EMT sample, curve b for the pure FAU sample, and curve c for the linear combination of FAU and EMT,used to fit the experimental envelope of the intergrowth sample (curve d). Curve e shows the difference spectrum between curves c and d.
a) This shoulder is absent in the spectrum of the FAU sample, which is only slightly asymmetric (Figure lB, curve b). Note that I3C CP NMR spectra, recorded under MAS conditions, are narrow and highly symmetric for EMT as well as for FAU.*' Therefore, the observed asymmetric resonance envelopes under static conditions should stem from anisotropic shielding. The I3C CP NMR spectra of the intergrowth samples MIX40/60, MIX20/80, and MIX10/90 displayed in Figure lA, B, and C, respectively, show resonance profiles (trace d) which are intermediate between those of FAU (trace b) and EMT (trace a). The origin of this anisotropic shielding is clarified by examining the I3C static spectra of crown ethers occluded in
0022-3654/95/2099-1837$09.00/0 0 1995 American Chemical Society
Letters
1838 J. Phys. Chem., Vol. 99, No. 7, 1995 TABLE 1: Overview of the Shape of the Resonance Profile of the Static I3C CP NMR Spectra of Dehydrated Faujasite SamDles. Containing Different TvDes of Crown Ethers crown ether\topology 15-crown-5 18-crown-6
FAU
15
EMT
isotropic i~otropic’~
12
ani~otropic’~ anisotropic h
different topologies. An overview of the shape of the recorded resonance envelopes is given in Table 1. This overview clearly demonstrates that the observed anisotropic shielding of the C nucleus originates from the EMT topology in which the crown ether is occluded. The nature of the crown ether itself seems of no importance for the anisotropic signal. The exact nature of the crown ether carbon anisotropic shielding inside the hypoand/or hypercages is not quite clear yet. As the plane of the crown ethers in the hypo- and hypercages21,22is perpendicular to the c axis, this unique orientation of the crown ethers may play an important role. As it is clear now that the observed anisotropy is caused only by the EMT polytype, and not by the FAU structure, it was examined whether this anisotropic effect could be used to quantitatively determine the FAU and EMT amounts of the as-synthesized intergrowth type materials. For comparison, the FAUEMT quantification from Rietveld refinement of XRD pattems was used. The use of the Rietveld refinement technique to quantitatively determine the cubic and hexagonal polytype in the faujasite intergrowth samples, synthesized using crown ethers, as applied earlier,*’ is justified. Indeed, the intergrowth samples consist of altemating FAU and EMT zones, infinitely prolonged in 2 dimensions.I8 These individual FAU and EMT “2-dimensional crystals” are sufficiently large to give a full diffraction pattern, as no line broadening at all is observed. Even if there would be some line broadening, which for these type of samples then would be expected to be index-dependent, the Rietveld refinement program slightly compensates for this feature as the whole diffraction profile is used. Furthermore, the Rietveld refinement procedure has already proven its use in quantifying these types of material^.*^ Note that it is even possible to determine up to seven phases simultaneously during a Rietveld refinement.24 Accidental stacking faults in crystal lattices will not be observed by X-ray powder diffraction measurements or by Rietveld refinements techniques based on these data.23 This means that accidental FAU stacking faults in EMT23and accidental EMT stacking faults in FAU, as present in zeolite Y,25-26are not detected by XRD. However, such “faults” are expected to more or less compensate each other in calculating the FAU and EMT content from XRD pattems of intergrowth samples. If line broadening, as a result of abundant stacking faults or small diffraction domains in 3 dimensions (such as zeolite ZSM-20 which “comprises faulted block intergrowths of cubic and hexagonal stackings of faujasite sheet@), is present, a much more complex method such as DIFFaX27is preferred to quantify the different phases present. The I3C CP NMR profiles of the pure FAU and pure EMT samples were linearly combined in order to fit the spectra of the MIX, Le., intergrowth samples.28 To do so, the spectra of FAU and EMT were scaled until their sum matched the spectra of the MIX samples. To obtain an optimal fit, the spectra of FAU and EMT were slightly relaxed on the chemical shift axis. The goodness-of-fit ( R ) parameter was evaluated by the sum of the quadratic differences between the MIX and (FAU EMT) profile. The EMT content was then determined by the area (Ai) of both profiles
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% EMT = A,,,/(A,,lJ
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Figure 2. Evolution of the goodness-of-fit parameter R as a function of the EMT content (determined by AEMT/(AFAU AEMT))for sample MIX 40/60 (a), MIX 20180 (b), and MIX 10190 (c).
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0
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EMT 96 (XRD) Figure 3. Correlation between the EMT content determined by Rietveld refinement of X-ray diffraction patterns (from ref 21) and the EMT content derived from the deconvolution of the I3C CP NMR spectra.
In Figure 1A-C, the deconvolution is shown for intergrowth samples MIX60/40, MIX20/80, and MIX10/90. The EMT content determined for these samples is 11, 48, and 83%, respectively. Curve e in these figures shows the difference spectra of the MIX samples and the sum of FAU and EMT. These difference plots are essentially flat, indicative of a satisfactory fit. Furthermore, the fit of the FAU and EMT profile in the experimental MIX profile is unique as indicated by the R versus % EMT plots in Figure 2, which exhibit only one minimum. From these plots, the accuracy in the determination of the EMT content is estimated at f 3 % based on a 1% deviation from &in. During the fitting of the MIX spectra, the FAU and EMT profiles were shifted on the chemical shift axis by -1.7 to 3.7 ppm with respect to the original positions. In Figure 3, the EMT content derived from the 13CCP NMR spectra and determined by Rietveld refinement of the X-ray pattemsZ1is compared. It is clear from this figure that the data obtained by both methods correlate very well. This new and simple method based on deconvolution of static I3C NMR spectra allows to determine quickly the FAU and EMT amount of faujasite intergrowth polytypes, synthesized in the presence of crown ethers. Work is in progress to expand the method to all faujasite polytypes, by introducing crown ethers in the void space via a postsynthesis treatment. This
Letters method is only sensitive to the presence of crown ethers in a constraint environment (micropores) and will therefore be independent of the stacking mode of the different FAU and EMT zones in the intergrowth materials. When suitable probes are used, it will be applicable to the characterizationof other zeolite intergrowths as well.
Acknowledgment. This work was sponsored in the frame of an NAP-PAI Federal Programme. E.J.P.F. acknowledges the Belgian IWONL for a research grant. J.A.M. and P.J.G. acknowledge the Flemish NFWO for a position as Senior Research Associate.
References and Notes (1) Barrer, R. M.; Sieber, W. J. Chem. Soc., Dalton Trans. 1976, 1020. (2) Kokotailo, G. T.; Ciric, J. Adv. Chem. Ser. 1971, 101, 109. (3) Perez-Pariente, J.; Fomes, V.; Martens, J. A.; Martens, P. A. In Innovation in Zeolite Marerials Science; Grobet, P. J., Mortier, W. J., Vansant, E. F., Schulz-Ekloff, G., Eds.; Elsevier Science Publishers B. V.: Amsterdam, 1988; p 123. (4) Emst, S.; Kokotailo, G. T.; Weitkamp, J. Zeolites 1987, 7, 180. (5) Vaughan, D. E. W.; Treacy, M. M. J.; Newsam, J. M.; Strohmaier, K. G.; Mortier, W. J. In Zeolite Synthesis; Occelli, M. L., Robson, H. E., Eds.; ACS Symp. Ser. No. 398; American Chemical Society: Washington, DC, 1989; p 545. (6) Dwyer, J.; Millward, D.; O’Malley, P. J.; Araya, A.; Coma, A.; Fomes, V. Martinez, A. J. Chem Soc., Faraday Trans. 1990, 86, 1001. (7) Gabelica, 2.;Dewaele, N.; Maistriau, L.; Nagy, J. B.; Derouane, E. G. In Zeolite Synthesis; Occelli, M. L., Robson, H. E.Eds.;ACS Symp. Ser. No. 398; American Chemical Society: Washington, DC,1989; p 519. (8) Newsam, J. M.; Treacy, M. M. J.; Vaughan, D. E. W.; Strohmaier, K. G. Mortier, W. J. J. Chem Soc., Chem. Commun. 1989, 493. (9) Vaughan, D. E. W. Eur. Pat. Appl. 0,315,461, 1989. (10) Vaughan, D. E. W.; Strohmaier, K. G.; Treacy, M. M. J.; Newsam, J. M. U.S. Pat. 5,116,590, 1992. (11) Cotteman, R. L.; Hickson, D. A.; Cartlidge, S.; Dybowski, C.; Tsiao, C.; Venero, A. F. Zeolites 1991, 11, 27.
J. Phys. Chem., Vol. 99, No. 7, 1995 1839 (12) Cartlidge, S.; Nissen, H.-U.; Shatlock, M. P.; Wessicken, R. Zeolites 1992, 12, 889. (13) Martens, J. A.; Xiong, Y. L.; Feijen, E. J. P.; Grobet, P. 3.; Jacobs, P. A. J. Phvs. Chem. 1993, 97, 5132. (14) Deiprato, F.; Delmotte, L.; Guth, J. L.; Huve, L. Zeolites 1990, 10, 546. (15) Annen, M. J.; Young, D.; Arhancet, J. P.; Davis, M. E.; Schramm, S. Zeolires 1991, 11, 98. (16) Anderson, M. W.; Pachis, K. S.: Prtbin, F.; Can, S. W.; Terasaki, 0.;Ohsuna, T.; Alfreddson, V. J. Chem. Soc., Chem. Commun. 1991, 1660. (17) Dougnier, F.; Patarin, J.; Guth, J. L.; Anglerot, D. Zeolites 1992, 12, 160. (18) Terasaki, 0.;Ohsuna, T.; Alfredsson, V.; Bovin, J.-0.; Watanabe, D.; Can, S. W.; Anderson, M. W. Chem Mater. 1993, 5, 452. (19) Burkett, S. L.; Davis, M. E. Microporous Mater. 1993, 1, 265. (20) Skeels, G. W.; Blackwell, C. S . ; Reuter, K. B.; McGuire, N. K.; Bateman, C. A. In Proceedings of the 9th International Zeolite Conference, Montreal, 1992; von Ballmoos, R., Higgins, J. B., Treacy, M. M. J. Ed.; Buttenvorth Heinemann: London, 1993; p 415. (21) Feijen, E. J. P.; De Vadder, K.; Bosschaerts, M. H.; Lievens, J. L.; Martens, J. A.; Grobet, P. J.; Jacobs, P. A. J. Am. Chem. SOC. 1994, 116, 2950. (22) Baerlocher, C.; McCusker, L. B.; Chiapetta, R. Microporous Mater. 1994,2, 269-280. (23) Bons, A. J.; Lievens, J. L.; Verduijn, J. P.; Mortier, W. J. Microsc. Res. Tech. 1993, 25, 175-176. (24) Snyder, R. L; Bish, D. L. Rev. Mineral. 1989, 20, 101-144. (25) Audier, M.; Thomas, J. M.; Klinowski, J.; Jefferson, D. A.; Bursill, L. A. J. Phys. Chem. 1982, 86, 581-584. (26) Thomas, J. M.; Ramdas, S.; Millward, G. R.; Klinowski, J.; Audier, M.; Conzalec-Calbet, J.; Fyfe, C. A. J. Solid State Chem. 1982, 45, 368380. (27) Treacy, M. M. J.; Newsam, J. M.; Deem, M. W. In Disorder in Crystalline Materials (MRS Symp. Proc.); Materials Research Society: Pittsburgh, PA, 1989; Vol. 138, pp 497-502. (28) To allow application of the method, software (written in Microsoft QBasic ver. 4.00, running on an IBM or compatible PC, 486SX or DX processor), including spectra of pure FAU and EMT samples, is available from the authors upon E-mail request (
[email protected]). JP942649U
