J . Phys. Chem. 1989, 93, 3240-3243
3240
changes of ordering between columns b and d, and the large reduction of the extra stability of configuration 6 in the periodic calculation (d) as opposed to the individual absorption calculation as given by the moments method (b) calls for caution regarding the use of periodic models in the theory of absorption. Interactions mediated by the surface are not a d d i t i ~ e . ~ (8) It seems that various forms of approaches based on periodic boundary conditions have been invented independently by several groups. These differ in the number of k points used (if more than one k point is used, this is essentially a "large unit cell" crystal orbital method), in the way the lattice summations are carried to convergency, and in the manner the Hamiltonian is approximated. For selected references, see: (a) Zunger, A. J. Chem. Phys. 1975,62, 1981. Zunger, A. J. Chem. Phys. 1975.63, 1713. (b) Kertesz, M.; Koller, J.; Azmann, A. Chem. Phys. Lett. 1978, 53, 446. Evarestov, R. A.; Lovchikov, V. A,; Tupitsin, I. I. Phys. Status Solidi B 1983, 117, 417. (c) Messmer, R. P. Phys. Rev. B 1977, 15, 1811. Skala, L. Phys. Status Solidi B 1982, 109, 733. Salem, L. J . Phys. Chem. 1985, 89, 5576. (d) Burdett, J. K. In Structure and Bonding in Crystals; OKeefe, M., Navrotsky, A., Eds.; Academic: New York, 1981. (e) Baetzold, R. C.; Mason, M. G.; Hamilton, J. F. J . Chem. Phys. 1980, 72, 366, 6820. S e d , M.; Bagus, P. S.; Ladik, J. J . Chem. Phys. 1982, 77, 3123. Deilley, B.; Ellis, D. E.; Freeman, A. J.; Baerends, E. F.; Post, D. Phys. Reu. B 1983, 27, 2132. Mason, M. G. J . Chem. Phys. 1983,27,748. (f) Saillard, J.-Y.;Hoffmann, R. J . Am. Chem. SOC.1984, 106, 2006. (9) Deik, P., Snyder, L. C. Phys. Rev.B 1987, 36, 9619.
We would like to point out that the effects of Friedel oscillationsZ on adatoms-adatom interactions are following from the present method of moments approach to chemisorption but should be also obtainable from very large cluster calculations (periodic or properly terminated finite) as well. In choosing properly sized clusters or repeat units, such that V, has decayed sufficiently, one may be able to use any of the more convenient approaches4,* based on periodic boundary conditions as advocated by many groups to extract useful adatom-adatom interaction information. It is advisable that the clusters or repeat units be chosen large enough to allow a sufficient decay of V, for intercell interactions. We recommend that at least 4-5 sites should separate the adatoms within the unit cell from the ones in neighboring cells in every direction.
Acknowledgment. We thank Prof. A. Graovac for useful discussions in an early stage of this project. This work has been supported by the Camille and Henry Dreyfus Foundation and by N S F Grant DMR8702148. Registry No. H,, 1333-74-0; graphite, 7782-42-5. (9) Burdett, J. K. (private communication), also finds that adatom-adatom interactions are not additive.
Improved Method for Dealumination of Faujasite-Type Zeolites with Sllicon TetrachlorMe B. Sulikowski: Gabriela BorbBly, Hermann K. Beyer, Central Research Institute of Chemistry of the Hungarian Academy of Sciences, Pusztaszeri ut 59-67, 1025 Budapest, Hungary
Hellmut G . Karge,* Fritz- Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 1000 Berlin 33, Federal Republic of Germany
and I. W. Mishin Zelinsky Institute of Organic Chemistry of the Academy of Sciences of the USSR, Leninski Prospekt 47 Moscow 117913, USSR (Received: June 3, 1988)
The dealumination of Na-Y zeolite with silicon tetrachloride vapor is a product-inhibited reaction because of the formation of sodium tetrachloroaluminate, which is nonvolatile at the reaction temperature. However, starting from Li,Na-Y prepared by ion exchange in aqueous solution, a nearly complete substitution of framework aluminum by silicon proceeds as evidenced by magic-angle spinning NMR and IR spectrometry. Also after contact-induced ion exchange performed by grinding a mechanical mixture of hydrated Na-Y and crystalline LiCI, the framework dealumination is not prematurely stopped by product inhibition. In contrast to Na[AICI,], the corresponding Li compound dissociates at the reaction temperature, the decomposition product (AQ) volatilizes, and only minor amounts of solid products not affecting the progression of the dealumination reaction are deposited in the zeolite pores.
Introduction Zeolites with high Si/Al ratios and especially crystalline silica isostructural with zeolites are known to be adsorbents with predominant hydrophobic properties. The S i 0 2 variety of faujasite is of special interest because this structure shows the largest pore space and, consequently, the highest potential adsorption capacity among all known zeolites. The removal of lattice aluminum from the framework of Y zeolite by treatment with H4EDTA1 (EDTA = ethylenediaminetetraacetic acid) gives products maintaining much of the crystallinity. High-crystalline Y-zeolite with Si/Al ratios over 100 could be obtained by repeated alternating hy'On leave from Institute of Organic Chemistry and Technology, Krakdw Technical University, 31-155 Krakbw, Poland.
0022-3654/89/2093-3240$01.50/0
drothermal treatment and acid leachingz These procedures, however, create lattice vacancies or even a secondary mesopore system inside the zeolite crystallites, first reported by Ciembroniewicz et al.,3 and result in the formation of hydrophilic sites. In 1980 a new method for dealuminating zeolites by reaction with silicon tetrachloride was reported4 that involves, in contrast to the methods mentioned above, the direct substitution of framework aluminum by silicon atoms. However, the dealumi( I ) Kerr, G. T. J . Phys. Chem. 1968, 72,2594. (2) Scherzer, J. J. J. Catal. 1978, 54, 285. (3) Ciembroniewicz, A,; Zolcinska-Jezierska, J.; Sulikowski, B. Pol. J . Chem. 1979, 53, 1325. (4) Beyer, H. K.; Belenykaja, I. Stud. Surf. Sci. Cutal. 1980, 5 , 203.
0 1989 American Chemical Society
The Journal of Physical Chemistry, Vol. 93, No. 8, 1989 3241
Dealumination of Faujasite-Type Zeolites TABLE I: Chemical Composition of Zeolites Used in This Study' sample Na-Y Na,Lio.,2-Y Na-Y deal. Na,Li-Y deal. Na/LiCl deal.
AIb 4.43 4.67 0.73 0.85 1.16
Nab 4.25 1.58
2.58
0.10 0.07 0.10
0.12 0.05
Sib
Lib
10.70 1 1.24 16.05 15.86 15.61
AIC 0.07 0.07 ndg nd nd
Si/AI, bulk" 2.42 2.41 22.0 18.7 13.5
AI/Si, frameworke 2.45 2.44
f 2.2 2.2 62
> 1000 >loo0
"All data in mmol/g of zeolite fired a t 1000 OC bFrom chemical analysis by atomic absorption spectroscopy. eExtraframework AI from 27AI MAS N M R data. "From chemical analysis. eFrom chemical analysis and 27Al MAS N M R data. /From 29SiMAS N M R data. gn.d. = nondetectable.
'AI M A S - N M R S P E C T R U M O F THE PARENT ZEOLITE N a - Y
'si M A S - N M R S P E C T R U M O F THE PARENT ZEOLITE Na-Y I
l ' " ' 1 " " 1 " " /
I
L
i
A l
l
~
#
150
!
6.7
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I
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~
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,
