J . Phys. Chem. 1991,95, 6654-6656
6654
Correlatlon of Raman Spectra of Zeolltes wlth Framework Archltecture Prabir K. Dutta,* K. Mohana Rao, and Jong Yul Parkt Department of Chemistry, The Ohio State University, 120 West 18th Avenue, Columbus, Ohio 43210 (Received: February 21, 1991)
The prominent band in the Raman spectra of a zeolitic framework in the 300-600-cm-~region is found to be sensitive to the ring structures present in the framework. In the case of zeolites with even-membered rings such as 4,6,8,10, and 12 rings, the band is around 500 cm-l. The presence of five-membered rings leads to a lowering of this frequency to 390-450 cm-I. For the ferrierite family of zeolites with 5-, 6-, 8-, and IO-membered rings, this band is at 430 cm-I. The absence of eight-membered rings in this set increases the frequency to 450 cm-I, as in ZSM-23 and NU-10.The presence of 4-, 5-, 6-, 8-, IO-, or 12-memberedrings, as in ZSM-5, mordenite, and ZSM-48 leads to bands at 390 and 460 an-'.This empirical correlation could be of considerable value in determining zeolitic framework structure.
Introduction
Zeolites are complex three-dimensionalaluminosilicatecrystals with channels and cavities of molecular dimensions.' Synthesis of a new family of zeolites offers opportunities for new chemistry within its pores, as exemplified by the discovery of the ZSM-5 family of zeolites? Synthesis of new zeolitic structures is therefore a very active area of research, especially considering the fact that only a few percent of the possible frameworks have been synthesized. Since the structures of these zeolites are critical to their function, extensive research over the past decades has focused on this problem. The most definitive structural information comes from single-crystalX-ray diffraction studies.' However, it is very difficult to grow large enough single crystals of zeolites for such studies. Therefore, most structure determinations are made from powder diffraction data.4-7 Spectroscopic studies also provide important bonding information. Two of the most commonly used methods are infrared and solid-state NMR spectro~copy.~,~ Raman spectroscopy, based on vibrational motions of the framework, can also provide structural information. However, its use in studying zeolites has been limited due to the low scattering cross section as well as the presence of strong emission bands that obscure the Raman spectra.'O Careful treatment and handling of samples alleviates this problem to some degree, and both spontaneous Raman and resonance Raman spectra of molecules in zeolites has been reported.ll-Is In this report, we examine the Raman spectra of a series of pentasil zeolite frameworks and find that the frequency of the most prominent v , ( T U T ) band provides information about the specific ring sizes present in the zeolites. This information can be particularly helpful in determining the framework structure of new zeolites as well as in the model building necessary for simulating the diffraction data. Experimental Section
The zeolites discussed in this study were synthesized from published procedures in both the open and patent literature. The following zeolites were synthesized: ZSM-35, ZSM-38,I6inorganic ferrierite,I7 ZSM-23,18 NU-IO,l9 inorganic ZSM-5 and morVarious chemicals denite>O organic ZSM-5:' and zST~f-48.~~ were obtained from Aldrich, Alfa, Nalco, Du Pont, and Baker Chemicals. Pretreatment of the zeolites in order to obtain the Raman spectra has been described in the literature." Raman spectra of the zeolites were obtained with the 406.7-nm radiation from a Kr ion laser (Coherent K100) or 457.9-nm radiation from a Ar ion laser (Spectra Physics 171). The backgrounds in the spectra were corrected, if necessary, with Spectracalc using a base-line fitting routine. Powder diffraction studies and infrared spectra were obtained from a Rigaku (D Max/2B) diffractometer with Ni-filtered Cu Ka radiation and a Mattson Cygnus FTIR spectrometer. 'Permanent address: Department of Chemistry, Pusan National University, Pusan 609-735, Korea.
0022-3654/91/2095-6654S02.50/0
Results and Discussion Figure 1 shows the X-ray diffraction powder patterns of the different zeolites whose vibrational spectra have been examined in this study. The first group consists of the ferrierite family, represented by ZSM-35 and ZSM-38. The structures of these two zeolites are very similar, as manifested in almost identical diffraction patterns, except for the 28 = 11O reflection, in the case of ZSM-38. This is consistent with the patent literature on these materials.I6 However, we would like to point out that this is a subtle difference and the two zeolites could indeed have very similar structures. The ferrierite structure consists of chains of 5-membered rings interconnected via 6- and IO-membered rings to produce channels enclosed by 8- and IO-membered rings.23 Besides ZSM-35 and ZSM-38, which have been referred to as the ZSM-21 group, FU-9 also belongs to this family.24 In the second group, we have included ZSM-23 and NU-10, which belong to the M'IT and TON families of zeolite^.'.^ The building blocks for these frameworks are similar, the different connectivities giving rise to different structures.% The fram'kwork in both cases is generated by chains of 5-membered rings connected (1) Szostak, R. Molecular Sieues; Nostrand Reinhold: New York, 1989. (2) Ward, J. W. Appl. Ind. Caral. 1984, 3, 271. (3) Pluth, J. J.; Smith, J. V. ACS Sympo. Ser. 1983, No. 3, 271.
(4) Rohrman, A. C.; Lapierre, R. B.; Schlenker, J. L.;Wood, J. D.; Valyocsik, E. W.; Rubin, M. K.; Higgins, J. B.; Rohrbaugh, W. J. Zeolires 1985, 5, 352. (5) Barri, S.A. I.; Smith, G. W.; White, D.; Young, D. Narure 1984,312, 533. ( 6 ) Kokotailo, G. T.; Schleuker, J. L.; Dwyer, F. G.; Valywik, E. W. Zeolites 1985. 5. 349. . .(7) Schlenkei, J. L.; Rohrbaugh, W. J.; Chu, P.; Valyocsik, E. W.; Kokotailo, G. T. Zeolires 1985, 5, 355. (8) Ranigen. E. M. In Zeolire Chemistry and Catalysis; Rabo, J. A,, Ed.; ACS'Monogr. Ser. 1976, No. 171, 80. (9) Fyfe, C. A. Solid Srare NMR for Chemists; CFC Press: 1983. (10) Angell, C. L. J. Phys. Chem. 1973, 77, 222. (11) Dutta, P. K.; Zaykoski, R. Zeolires 1988, 8, 179. (12) Dutta, P. K.; DelBarco, B. J. Chem. Soc., Chem. Commun. 1985, 1297. (13) Dutta, P. K.; DelBarco. B. J . Phys. Chem. 1988, 92, 354. (14) Dutta, P. K.; Shieh, D. C.; Puri, M.Zeolires 1988, 8, 306. (15) Dutta, P. K.; Incavo, J. J . Phys. Chem. 1990, 91,3075. (16) Plank, C. J.; Rosinski, E. J.; Rubin, M.K. U S . Patent 4,046,859, 1977. (17) Belussi, G.; Penegro, G.; Carati, A,; Cornaro, L.; Fattore, V. In Innovation in Zeolife Materials Science; Grobet, P. J., Mortier, W. J., Vansant, E. F.,Schultz-Ekloff, G., Eds.; Elsevier: Amsterdam, 1988. (18) Plank, C. J.; Rosinski, E. J.; Rubin, M. K. US.Patent 4,076,842, 1978. (19) Araya, A,; Lowe, B. M. Zeolifes 1984, 4, 280. (20) Shiralkar, V. P.; Clearfield, A. Zeolires 1989, 9, 363. (21) Rollman, L.D.; Valyocsik, E. W.; Shannon, R.D. Inorg. Synth. 1983. 22, 61. (22) Chu, P. US. Patent 4,397,827, 1983. (23) Vaughn, P. A. Acfa Crysrallogr. 1966, 21, 983. (24) Jacobs, P. A.; Martens, J. A. Synthesis of High-Silica Aluminosilicate Zeolites; Elsevier: Amsterdam, 1987.
0 1991 American Chemical Society
Framework Architecture of Zeolites
The Journal of Physical Chemistry, Vol. 95, No. 17, 1991 6655
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2 Theta Figure 1. Powder X-ray diffraction patterns of (a) ZSM-35, (b) ZSM(d) NU-IO,(e) ZSM-5, and (f) ZSM-48. 38, (c) ZSM-23,
through 6-membered rings and enclosing channels of 10-membered rings. Zeolites that belong to the TON family, besides NU-10 are theta-1, ISI-1, KZ-2, and ZSM-22.5vs.24 The MTT family includes besides ZSM-23, ISI-4, KZ-1 ,EU- 1, EU-4, and EU- 13.24 In the last group, we have included zeolites that also contain four-membered rings and include ZSM-525and ZSM-48.' These structures are composed of 4-, 5-, 6-, and 10-membered rings. Zeolites similar in structure to ZSM-48 include EU-2, EU-11, and ZBM-30.24 Zeolites that are related to ZSM-5 include pentad-like ZSM-11, zeta-1, zeta-3, NU-4, NU-5, and ZBM-
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Figure 2. Comparison of the Raman spectra of various zeolitic frameworks.
ZSM-5 leads to a shift of the prominent band to -390 cm-1,28 This trend of lowering of frequency of the u,(T-O-T) band in zeolites containing five-membered rings is supported by the data 10.24 shown in Figure 2. The frequency range for these frameworks Figure 2 compares the Raman spectra of these frameworks. spans the region between 380 and 450 cm-I. Moreover, it is also In addition, we have included in this figure spectra of zeolites A of particular interest to note that structures with similar ring and Y,ferrierite, mordenite, and ZSM-5, all of which have been systems also have comparable frequencies. For example, ferprepared via a completely inorganic system. There have only been rieritelike structures with 5-, &, 8-, and 10-membered rings exhibit a few reports on the Raman spectra of zeolitic f r a m e ~ o r k s , ~ ~ J ~the - ~band ~ ~ at -430 cm-l, whereas in the absence of 8-membered beginning with the work of Angell.Io This is primarily due to rings, such as in ZSM-23 and NU-10. the band is a t 450 cm-'. experimental problems associated with a large luminescent The presence of four-membered rings in the pentad framework background that obscures the weak Raman signal. Ways of leads to a considerable lowering in frequency; e.g., in ZSM-5, minimizing the background have also been discussed." However, mordenite, and ZSM-48, bands at 384, 396, and 386 cm-' are it is clear from all the published Raman data of zeolitic frameobserved, respectively. There is also a group of bands observed works, that the most prominent band occurs in the region between around 460 cm-I, with intensities increasing in the order ZSM-5, 300 and 550 cm-I, followed by weaker bands in the 7W900- and mordenite, and ZSM-48. For the same framework, changes in 1000-1200-cm-' regions. In this paper, we will focus only on the the Si/AI ratio result in a slight shift of the u,(T-O-T) band, 300-550-cm-' region, though the other regions of the spectrum as exemplified by comparison of "inorganic" ferrierite and ZSM-5 have also been shown to have important structural informawith their high-silica analogues, synthesized in the presence of ti~n.'~-"*~' The prominent low-frequency band of interest in this organic structure-directing agents. study is assigned to u,(T-0-T) mode, involving primarily the It is quite clear from Figure 2 that the frequency of the u,(Tmotion of the oxygen atom. In an earlier study of zeolites A, 0-T) band is indicative of the ring systems present in the zeolite faujasite (X,Y),chabazite (R), gismondine (P), and edingtonite frameworks. Though this correlation is presently empirical in (D),"we noted that the u,(T-O-T) mode occurred in the frenature and, along with our earlier study, is based on a total of quency range of 486-521 cm-I. These frameworks are charac12 or so frameworks, its value in determining structural inforterized by combinations of 4-, 6-, 8-, IO-, and 12-membered rings. mation of zeolites can be significant. To the best of our knowledge, The presence of five-membered rings in the framework as in this is the first spectroscopic technique that can provide such information. There are another 50 frameworks and it will be of interest to obtain the Raman spectra of these materials in order (25) Kokotailo, 0.T.; Lawton, S. L.; Olson, D. H.; Meier, W. M. Nurure 1978, 272,437. to establish firmly this correlation. (26) Buckley, R. G.;Dcckman, H. W.; Witzke, H.; McHenry, J. A. J . Phys. Chem. 1990, 94,8384. (27) Dutta, P. K.; Twu, J. J . Phys. Chem. 1991, 95, 2498.
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(28) Dutta, P. K.; Puri, M. J . Phys. Chem. 1987, 91, 4329.
6656 The Journal of Physical Chemistry, Vol. 95, No. 17, 1991
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Figure 3, Infrared spectra of five-membered ring containing zeolitic frameworks.
In our study of zeolites with even-membered rings, it was noted that the frequency of the u,(T-O-T) mode had an inverse dependence on the magnitude of the average T U T angle.I4 This was rationalized based on the decreased bending force constant as the T43-T angle increases. The trends observed in Figure 2 are in overall agreement with such a picture. The average T U T angle in zeolites Na-A and Na-Y is between 142.2 and 148.3O,I4 whereas for femerite, ZSM-5, and mordenite, this angle is between 152 and 158°.23*29*30 This empirical correlation between the (29) Ito, M.; Saito, Y. Bull. Chem. Soc. Jpn. 1985, 50, 3035.
Dutta et al. Raman frequency of the u,(T-0-T) band and the T U T angle has been used recently to examine framework changes in zeolite ZK-5 upon dehydration.26 Calculations of the nature of normal modes of zeolites, as are being increasingly reported in the literature, should lead to a more quantitative picture of this correlati~n.~l,~~ Unlike the Raman spectra, the infrared spectra of these frameworks do not provide an unambiguous pattern that can distinguish between different zeolites. Figure 3 shows the infrared spectra of the five-memberedzeolites included in this study. Some of these spectra have been reported before and are included here for comparison with the Raman spectra (Figure 2). All the frameworks exhibit a prominent band between 455 and 470 cm-I. This band is also present in zeolites with even-membered rings, such as in zeolite A, faujasite, and chabazite, and is assigned to a T - O bend.8 Many of these frameworks also exhibit a band between 550 and 560 cm-', as is evident in Figure 3 and in the infrared spectra of zeolites A and faujasite. This band has been assigned to motion involving double The strongest band in the infrared spectrum occurs at 1 100 cm-' and is broad and not of much diagnostic value. However, the shoulder around 1225 cm-' in the infrared spectrum is specific to zeolites that contain high %/A1 ratios,37 as is typical of most zeolites with five-membered rings, and has been pointed out in the l i t e r a t ~ r e .Even ~ ~ though the similiarity of infrared spectra of very different framework geometries makes it of limited value in identifying framework structures, the dependence of the framework frequencies for a particular framework on Si/Al ratio?>' ion-exchangeable cations,'* hydration! and other physical parameters makes it a powerful structure probe. In combination with the possibility of Raman spectroscopy identifying framework structure as shown in this study and infrared spectroscopy of the framework providing specific structural information, vibrational spectroscopy of zeolites can be expected to continue to play an important role in studies of zeolites.
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(30) Lermer, H.; Draeger, M.; Steffen, J.; Unger, K. K. Zeolites 1985,5, 131. (31) No, K. T.; Bae, D. H.; Jhon, M. S. J . Phys. Chem. 1986,90, 1772. (32) de Man, A. J. M.; van Beest, B. H. W.; Leslie, M.; van Santen, R. A. J . Phys. Chem. 1990, 94,2524. (33) Blackwell, C. S. J . Phys. Chem. 1979,83, 3251, 3257. (34) Coudurier, G.; Naccache, C.; Vedrine, J. C. J . Chem. Soc., Chem. Commun. 1982, 1413. (35) Jacobs, P. A.; Beyer, H. K.; Valyon, J. Zeolites 1981, I , 161. (36) Jansen, J. C.; vander Gaag, F. J.; van Bekkum, H. Zeolites 1984,4, 369. (37) Pichat, P.; Beaumont, R.; Barthomeuf, D. C.R. Acad. Sci. Ser. C 1971,272,612. (38) Godber, J.; Ozin, G. A. J . Phys. Chem. 1988, 92, 2861.
