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Murday, Patterson, Resing, Thompson, and Turner
In the zeolite heat treated above 500°C the surface must be so much altered by the heat treatment that no methyl radical can be stabilized on the zeolite. Hence, no ESR spectrum was observed for this experimental condition.
(8) T. Katsu, M. Yanagita, and Y. Fujita, J. Phys. Chem., 75, 4064 (1971). (9) S. Kudo, A. Hasegawa, T. Komatsu, M. Shiotani, and J. Sohma, Chem. Lett., 705 (1973). (10) R. Lefebvre and J. Maruani, J. Cbem. Phys., 42, 1480 (1965). (11) J. Maruani, program rewritten and extended (1970): version of program described in ref 10. (12) J. Adrian, E. L. Cochran, and V. A. Bowers, J. Chem. Phys., 36, 1661 (1962). (13) P. W. Atkins and M. C. R. Symons, “The Structure of Inorganic Radicals”, Elsevier, Amsterdam, 1972, p 21. (14) Y. Fujlta, T. Katsu. and M. Sato, J. Chem. Phys., 61,4307 (1974). (15) S. A. Goidman, G. V. Bruno, and J. H. Freed, J. Phys. Chem., 78, 1858 (1972). (16) S.P. Mishra and M. C. R. Symons, J. Chem. Soc., Perkin Trans. 2, 391 (1973). (17) H. M. McConnell, C. Heller, T. Cole, and R. W. Fessenden, J. Am. Chem. Soc., 82, 766 (1960). (18) T. Shiga, and A. Lund, J. Phys. Chem., 77, 453 (1973). (19) Y. Suzuno, M. Shiotani. and J. Sohma, unpublishedresults,
References and Notes (1) Author to whom correspondence should be addressed. (2) J. Turkevich and Y. Fujita, Science, 152, 1619 (1966). (3) M. Fujimoto, H. D. Gesser, B. Carbutt, and A. Cohen, Science, 154, 381 (1966). (4) N. Shimamoto, Y. Fujita, and T. Kwan, Bull. Chem. SOC.Jpn., 43, 580 (1970). (5) T. Katsu, M. Yanagita, and Y. Fujita, J. Phys. Chem., 75, 4064 (1971). (6) G. B. Garbutt and H. D. Gesser, Can. J. Chem., 48, 2685 (1970). (7) S. Kubota, M. Iwaizumi, and T. Isobe, Bull. Chem. SOC.Jpn., 114, 2684 ( 1971).
Kinetics of Surface Reactions from Nuclear Magnetic Resonance Relaxation Times. II. Reaction of Water with Surface Complex in Zeolite 13-X J. S. Murday, R. L. Patterson, H. A. Resing,‘ J. K. Thompson, and N. H. Turner Naval Research Laboratory, Washington, D.C. 20375 (Received January 6, 1975) Publication costs assistedby the Na Val Research Laboratory
Proton NMR relaxation times have been measured as a function of temperature for water adsorbed on zeolite 13-X a t various coverages of water, various deuteration levels, and various degrees of hydrolysis. Hydrolysis produces a new surface proton site, which exchanges protons with the adsorbed water. The three limiting cases of rapid exchange, slow exchange, and exchange rate limited relaxation, as predicted by the theory of Zimmerman and Britten are observed; a quantitative fit of this theory to the relaxation data was carried out. The exchange reaction is half order with respect to water and first order with respect to the proton surface complex. Proton second moment data indicate an Al(OH), structure for the proton surface complex. A new view of zeolite hydrolysis is proposed, in which it is shown that the removal of Na+ ions is not necessary in order for the structural aluminum to be hydrolyzed.
I. Introduction
The rates of heterogeneously catalyzed reactions are often supposed to be limited by the rates of molecular transfers between physisorbed and chemisorbed species.1*2 In order to maximize rates of chemical production it should be helpful to understand the details of the relevant rate processes.’ Important among these details may be (a) reaction orders with respect to participating chemical species, (b) identities, (c) concentrations, and (d) activities of the various participating species. It has been known for some time, according to the ideas of Zimmerman-Britten3 (ZB theory), that NMR relaxation times in surface systems may provide a direct measure of the probability per unit time of nuclear transfer from one “environment” to another. Recently, this theory has been extended4 by expressing this probability in terms of those details of the rate process which are listed above. In this work are reported NMR relaxation time measurements for water adsorbed to various
* To
whom correspondence should be addressed a t Code 6173, U S . Naval Research Laboratory, Washington, D.C. 20375.
The Journal of Physical Chemistry, Vol. 79, No. 24, 1975
loadings and at various hydrogenldeuterium ratios on zeolite 13-X. It is shown that these data quantitatively verify in the greatest detail the predictions of the ZB theory and its recent extension. It is hoped that this example will prompt the application of these NMR techniques to reaction systems of more direct interest in industrial catalysis. The stability of the zeolitic lattices is of considerable importance in their use as catalysts and supports, and the 13-X zeolites have shown especial problems in this regard.5-s Herein we show that washing of zeolite 13-X with water can cause an interior hydrolysis which leaves the external shape of the crystal unchanged. Analysis of the proton NMR data presented here according to the ZB theory shows that in these hydrolyzed specimens 17% of the protons are present in a relatively immobile surface complex and that the most likely structure of this complex involves two protons (as hydroxyl) and one aluminum atom. (The deuterium enriched specimen was most helpful in this structure assignment.) On this basis about half of the structural A104 tetrahedra or 25% of the structural elements O f the Zeolite lattice are involved; yet the CryStaIS remain perfect cubooctahedra. In the ideal zeolite structure
Kinetics of Surface Reactions from NMR Relaxation Times there is one sodium atom per aluminum atom; the process of hydrolysis has been viewed as the replacement of a sodium ion by a proton, with the eventual structural fate of the proton not specified.6.8In this work, sodium NMR intensity measurements show that the involvement, described above, of as many as half of the aluminum atoms in proton containing complexes has not led to an equivalent loss of sodium ions; that is, we show that the lattice can be “attacked” even in the presence of a near full complement of sodium ions. This is thus a basic change in the accepted notions concerning zeolite hydrolysis. Further, we propose here a simple method for estimation of the number of hydroxyl groups resulting from such hydrolysis, a new measure of the degree of hydrolysis; all that is required is the measurement of the NMR transverse relaxation time Tz at a given temperature and relative humidity. Since zeolite hydroxyl groups figure prominently in the use of zeolite catalyst^,^^^ the information gained here as to the origin, structure, and demise of these hydroxyl groups should prove useful in catalyst design. It is important to note that before hydrolysis there is also present a surface proton site which differs in kinetic properties from the new site produced by hydrolysis; there is insufficient data a t present to determine all of the parameters necessary to describe this prehydrolysis surface proton site? and therefore it is not treated quantitatively herein, but is only the subject of mild speculation. It has been shown previouslyg that water in the zeolite cavities is not uniform with respect to its motional properties; a broad distribution of motional correlation times was necessary to describe the NMR relaxation times. The new NMR relaxation time data reported here for hydrolyzed and unhydrolyzed zeolite 13-X indicate that this distribution may originate with non uniformities in (a) the zeolite structure andlor (b) cavity occupancy caused by hydrolysis products. The plan of the paper is as follows. First, the experimental methods and the zeolite samples are discussed. Second, the experiments (NMR, adsorption, and hydrolysis) and their results are presented. Next a detailed theoretical model is constructed to fit the NMR relaxation data for protons in the hydrolyzed specimens: this model takes into account the effects of temperature, relative pressure of water, effects of deuteration, and relative concentration of the surface complex. Finally, the parameters and necessary concepts of the model are analyzed in terms of the structure, motions, and reactions of the surface complex.
11. Experimental Arrangements A. NMR Spectrometers and Methods. The pulsed NMR spectrometer has been described previously;1° the only change is the use of a signal average+ to improve signalto-noise ratio. The residual proton content of the probe was about 20% of the zeolite proton signal a t room temperature, and the probe protons had a transverse relaxation time of 17 psec. When necessary this signal could be subtracted from that of the specimen protons. Most proton relaxation times were measured at 11.5 MHz; some a t 29 MHz. Transverse relaxation times were measured by the CarrPurcell-Meiboom-Gill technique,12 with the purpose of avoiding complications due to chemical shifts in the two (or more) phase ~ i t u a t i 0 n . Measurements l~ of the intensities of sodium NMR signals and of deuterium relaxation times were made with a Bruker SXP spectrometer. B. Adsorption Isotherms. The quartz spring balance
2675
used for gravimetric adsorption isotherm determination has been described previ0us1y.l~ C . Zeolite 13-X Crystals. The 75-p diameter crystals were prepared by the method of Charnell.15J6 The unit cell composition of these crystals is estimated as Nass[AlssSi10403~41 220H20 from x-ray measurements.17 After crystallization, the crystals were washed with alcohol to remove mother liquor; the alcohol was used to prevent hydrolysis.16 As prepared the crystals were fairly uniformly sized cubooctahedra, but the preparation contained about 20% Na-A zeolite cubes, some smaller NaX crystals and some apparently noncrystalline material. Colorimetric analysis showed less than 6 ppm by weight of iron. An NMR specimen of this as received material was prepared by sealing about 0.5 cm3 of solid in a tube at a relative humidity of about 50%, which corresponds to a coverage of 0 = 0.96. This is the prehydrolysis specimen. After elutriation or hydrolysis (described below in IIIC), NMR specimens were prepared by first immersing the crystals in enough water to cover them and then removing the excess water by equilibration a t a given pressure of water vapor. The specimen isotopically enriched in DzO was prepared by loading with an excess of 66.6% DzO water. (An NMR relative intensity measurement gave a D/H atom ratio of 1.94 f 0.04.) A sample summary is presented in Table I.
111. Experiments and Results For ease of reference in discussion the separate subexperiments are listed below and the salient results obtained are described for each. A. Water Adsorption Isotherms. The gravimetrically determined adsorption isotherms for water on various Na-X specimens are compiled in Figure 1. The specimens are (a) the 75-p crystals before hydrolysis; (b) Linde 13-X powder; and (c) a special NRL preparation which is low in paramagnetic impurities. Note that there is not a great dependence of the isotherm on specimen origin. (Both Linde and NRL preparations had a crystal size of about 3 p . ) The adsorption isotherm is required for estimation of reaction order as described in IVB below. B. NMR Proton Relaxation Times. Prehydrolysis. In Figure 2 are presented the relaxation times for the 75-p crystal preparation as received, i.e., before elutriation. The T1 minima and frequency dependence are as expected from the theory of Bloembergen, Purcell, and Pound (BPP).la There is a hint of some underlying T1 minimum a t 103/T 2.7. The maximum in Tz and subsequent decrease as the temperature is raised are indications of exchange with some slow moving proton specie^.^^*^^ Not indicated in Figure 2 are the effects of a small amount (ca. 20% of the total proton signal) of a “second phase” which was apparent in the decay of the transverse magnetization for W / T less than 2.5; the Tz for this phase became as large as 8 msec at room temperature. This second phase is most likely the water in the zeolite 5-A cubes present in the Charnel1 preparation.21 Also included in Figure 2 for comparison are some of the T2 values reported previouslyg for the NRL 3 - crystals ~ of Na-X. For this study the specimen used for that work9 was reinvestigated for two-phase effects; there was found to be 9.6 f 1.0% of a second phase with a very short Tz of 45 f 10 psec. It is not clear for this prehydrolysis specimen that this second phase of 9.6% abundance (i.e., ca. 6 protons per supercage) (a) represents the proton site responsible for the
-
The Journal of PhysicalChemistry, Vol. 79, No.24, 1975
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Turner
TABLE I: Relative HzO Pressures, Fractional H2O Coverages, and Relative Sodium Contents of the NMR Specimens SCUll-
Ple no.
Sample
1 Prehydrolysis 2 Post-hydrolysis high P/PQ 3 Post-hydrolysis low P/PQ 4 Post-hydrolysis deuterated, 67%D
P/P,"
ob
0.5d 0.809'
0.96' 0.9gd
0.247'
0.9ld
0.876'
0.9gd
0.0756 rt 0.007 0.0572,f0.049V (rt0.006)
a PIP0 is the actual pressure of H2O vapor divided by the saturated vapor pressure of HzO at 25°C. * 0 is the fraction of filling of the intracrystalline space. This quantity was directly determined. This quantity was estimated from the isotherm. e The ratio of the sodium density observable via NMR to the proton density determined by NMR; see text/footnote h. f Only long 2'2 protons included; see text. g All protons included. For a zeolite of composithis ratio is 0.2 if the total 23Na tion Nasa[A1a~Si~0~0~a4]2ZoH~o intensity is seen, or 0.08 if only the central transition is seen.
-
Figure 2. Relaxation times for water in the Mobile 75-p crystals at 6 0.96 before hydrolysis. The circles represent T2 data previously reported for the NRL 3-p crystals; in this work a short T2 component has been found for this specimen, as Indicated.
0 05
-4
2 PIPo
k
Flgure 1. Adsorption isotherms for various zeolite 13-X specimens. The intercept at 19 = 1 corresponds to (a) 0.32 g/g for the Mobile 75-p crystals: (b) 0.30 gig for the Linde 3-1.1 crystals: and (c) to 0.31 g/g for the NRL 3-1 crystals.
exchange effects seen in the main phase T2, (b) represents protons on some extraneous, non-zeolite X matter in the 3-c~crystal preparation, or (c) represents yet another proton or water molecule site, such as perhaps water molecules in sodalite cages. It is curious that both of these specimens, prepared by radically different have the same relaxation effect due to exchange a t high temperatures (Figure 2); this suggests that there is an inherent structural entity in the zeolite lattice which contains a tightly bound proton and/or water molecule. The assembly of a more complete data set for the prehydrolysis 13-X zeolite structure is work for the future;4c a t present the data set is underdetermined with respect to the number of parameters necessary to describe the system. As will be seen this is in marked contrast to the situation for the hydrolyzed specimens, in which an overdetermined data set exists. Note that both of these prehydrolyzed specimens are essentially The Journal of Physical Chemistry, Vol. 79, No. 24, 1975
iron free20(-6 ppm Fe) and that therefore all relaxation effects are due to proton motions in the nuclear fields of protons, deuterons, sodium ions, and aluminum atoms. C. Crystal Sizing. Elutriation and Hydrolysis. In order to obtain crystals of uniform dimensions for diffusion23 experiments the product from the Charnell15recipe was elutriated with water in a velocity gradient device.24 This procedure resulted in a specimen of relatively uniform crystal size (75 f 10 1)and purity ( 3.6) each “phase” shows its own relaxation time;19*20here the long T2 is characteristic only of the rotational and translalo-’k 1 tional motions of the “free” intracrystalline water moleIRREVERSIBLE cules; the ratios of the proton relaxation times for the parHIGH TEMP. ANNEAL tially deuterated specimen to those of the nondeuterated specimen is about 3 in comparison to a predicted ratio of -2.5 (see Appendix and Table VI). The fact that a t higher temperatures both T1 and T2 ratios are much less than 2.5 indicates that some nonproton nuclear field is dominating the relaxation, most likely27A1 (see part IV). In the intermediate temperature region (3.0 I 103/T < c I 3.5),the0ry’~.~~ indicates that T2 is the mean lifetime of a proton in a water molecule; a first approximation is that this should not depend strongly on the degree of deuteration, and should even be roughly the same for a deuteron as well as a proton. In the second approximation, some measure of isotope effects for the exchange reaction should be manifested, and there is some evidence for this (Figure 3). 2 3 4 5 F. Deuterium Relaxation Times. Post Hydrolysis. In order to determine the effect of isotopic species on ex103 T change lifetime, the deuterium relaxation times were meaFlgure 4. Relaxation tlmes vs. temperature for protons In the hydrosured a t room temperature: T1 = 11.8 msec; T2 = 3.75 lyzed Mob11 75-p crystals. In the upper set of data the undeuterated msec. This will be discussed in part V. The temperature despecimen at B = 0.99 was carried to the hlghest temperature and pendence of the deuterium relaxation times has also been back down, showing an irreversible change. In the lower set of data, reiaxatlon tlmes for protons at 0 = 0.91, P/Po 3: 0.25 are compared determined and will be published separately;26but in the with those at 0 = 0.99, PIP, = 0.81. vicinity of room temperature, T2 decreases as the temperature is raised just as for the protons. G. NMR Relaxation. Post-Hydrolysis. Effect of High tightly bound proton sites. At temperatures below that of Temperature Anneal on Relaxation. As indicated in Figthe T2 minimum, theory predicts two-phase relaxation beure 4, specimen 2 of Table I was heated to almost 170DC, havior in T2, i.e., the decay of the transverse magnetization, and on returning to lower temperatures was not completely should be describable as the sum of two exponential^;^^*^^ reversible in relaxation time behavior. Evidently some of this is indeed the case, as is shown in Figure 3. The fraction the tightly bound proton sites were destroyed in the heatof the magnetization associated with the short relaxation ing. This will be used below to estimate the effect of tightly times is about 17%, as indicated in Figure 5 for slower exbound proton concentration on relaxation and proton lifechange regions. At temperatures above that of the T2 minimum the transverse relaxation should be single ~ h a s e , ~ ~time. .~~ H. Effect of High Temperature Treatment on Hydrogen and it is. E. NMR Relaxation-Post Hydrolysis. Effects of Partial ’ Content, NMR Two-Phase Behavior, and Crystallinity. The answera to two questions are sought here: (a) is there a Deuteration a t High Relative Pressure. Relaxation times The Jouml of Physlcal Chernlsby, Vol. 79, No. 24, 1975
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Murday, Patterson, Resing, Thompson, and Turner
TABLE 11: Effect of Heat Treatments on Zeolite Properties
Specimen NRL 3 p
hr
3 3
Time at Temp “C llOC 220d Room temp P/P, 1 llOC 22od
SF, capacity,“ cc3 Proton (STP)content (NMR), SF,/g g H20/g Na-X NaX
T 2 b,
Phb
psec
Tzo,
msec
78
0.005 0.31e
0.75
0
N
Mobil 7 5 p
3 3
48
22OC
72 0.1 0.01
57
0.25f
24
0.33
17
(0.54613fh) 0.25”3.9 0.81
As determined from isotherms a t the CO2 solid-vapor equilibrium point at 1 atm. P b is here the fraction of the protons, Le., transverse proton magnetization having the shortest relaxation time. Heated in adsorption pan of quartz spring balance under evacuation. d Heated in -1 cm3 narrow-necked tube under evacuation. e Determined gravimetrically. f If p b is estimated on the basis that only “free”, i.e., long 2’2 water molecules were lost, a value of Pb = 0.23 is obtained at this total proton content. The long 2’2 relaxation was itself two phase; these are fractions of total proton content associated with each. These are the relaxation times of the “phases” referred to in g
suitable heat treatment that will remove only adsorbed “free” water molecules and leave the tightly bound protons behind so that they can be studied via NMR without interference from, or exchange with, the “free” water molecules; and (b) are the tightly bound protons, which are the products of hydrolysis, the eventual cause of lattice instability and collapse? The effects of various heat treatment on the Mobil 75-jt crystals are compared with similar treatments of the NRL 3-jt crystals in Table 11. The llO°C heat treatments were carried out under vacuum on the pan of the quartz spring adsorption balance. The 22OOC heat treatments were carried out in narrow necked, 1-cm 0.d. NMR sample tubes, also under vacuum. For the 3-jt crystals a 3-hr 22OOC heat treatment removes 98% of the protons; there is no longer any trace of the short Tz phase (see section B). The crystallinity of the 3-jt crystals, as estimated from the SF6 capacity, is comparable to that reported for other Na-X preparation^.'^.^' In contrast, for the hydrolyzed Mobil 75-jt crystals, a 3-hr 22OOC treatment removes only 2/3 of the protons, and those removed are only “long Tz” protons presumably corresponding to “free” adsorbed water. However, a longer treatment at 22OOC (-48 hr) removes both sorts of protons so that only 3 4 % of the protons remain; thus, in agreement with section G, the short T2 proton phase is not stable to this relatively mild heat treatment. Moreover crystallinity has been reduced by -25%, on the basis of loss in SF6 capacity (Table 11); this suggests a relation between the hydrolysis product and zeolite lattice instability. I. NMR Relaxation-Post Hydrolysis. Proton Relaxation at PIP0 = 0.25. The second set of data in Figure 4 refers to the specimen with P/Po = 0.25. As Table I shows, the water activity, P , is down by a factor of -113 in comparison to the other specimens, but the fractional filling has changed by > ~ 1 and T~ < ( UoH2)-1’2, ( UOD2)-1’2.
The relaxation rate T ~ Hdue - ~to like spins is50 T2H-l =
YH4h21(1
+ 1)x
try, through certain- lattice sums, and on the correlation time T ~ Now . the geometry of the sums changes on deuteration only to the extent that the sites become occupied by different magnetic ingredients, i.e., certain sites (‘switch” from T ~ Hto- T~z ~ - l . Suppose the high-energy proton sites are clustered in groups of N , each site of the cluster being at a distance r from the other sites of the cluster. For a cluster in which all N sites are protons we have, if only terms involving Jo(0) are retained 3 T ~ H N -=’ r4h21(1 1 ) - ( N - 1 ) ~ ~(A4)
+
8
For a cluster in which n of N sites are occupied by protons and N - n by deuterons, the proton relaxation times T2Hn-l and T z D ~are - ~respectively
where R21 is identically the relaxation rate ratio a t low temperatures, i.e., in the motional narrowing region (indicated by subscript 1: the extreme narrowing region in which Y H H O TY~D, H O T>>~ 1 will be indicated by the second subscript equal to 2). Clearly N cannot be unity for then there would be no other magnetic ingredients in the cluster. It is also clear that T ~ B =~ T2Hn-l - ~ -!- T2Dn-l is a strong function of n , with an especially sharp decrease as n goes from one to two; thus there arises a distribution of relaxation rates for the clusters on deuteration. Fortunately we are interested only in the fast exchange region where the observed relaxation rate is the weighted average. To calculate this weighted average we need the fraction qn of protons in clusters having n protons (Znqn= PB, the fraction of protons and deuterons in high-energy sites). The relaxation rate to be observed is then
+
T2-l = P A T ~ A - ~P B T ~ A I - ~ + n
where Pa = 1 - PB is the fraction of protons and deuterons in the free water. Let f D be the deuterium fraction in the specimen and f~ = 1 - f D be the hydrogen fraction. Then the probability p n that there exists a cluster containing n protons and N - n deuterons is given by the binomial distribution
-
p n = fHnfDN-”N![(N n)!n!]-l
(A81
The fraction of all the protons in the system which are in n type clusters is then 4n = PBnPn ( N f d - ’
(A91
and the relaxation rate becomes
+
+
T2-l = P A T ~ A - ~ P~T2al-l P B T z H N -~ fD(1[~
Here the spectral densities Jo,etc. depend only on geomeThe Journalof Physical Chemistry, Vol. 79, No. 24, 1975
R2l)I
(A101
The only parameter in (A10) which depends on the cluster size N is T ~ H Nand - ~ since , this parameter is not itself also a function of the degree of deuteration f D , the isotopic substitution experiment gives no additional information about
Kinetics of Surface Reactions from NMR Relaxation Times
TABLE VI: Relaxation Rate Ratios RIJand Relaxation Time Ratios
Relaxation time Tl Ti T2 T2
Ti (fD = 0.75)/Ti (fD = 0)
Condition
Rijb
Calcd
Obsd"
Narrowing, R,, Extreme narrowing, Ri2 Narrowing, R 2 , Extreme narrowing, Rz2
(5/3)Ri, 0.0629
2.50 2.69
3.0
(4/9)Ri2 (2/3)R1,
2.87 2.79
3.6
a Observed for the free water in the zeolite cages. See text for definition of i and j .
cluster size. An important point which emerges from the above is that isotopic substitution gives rise to a distribution of magnetic environments (over and above that which may already exist), and it is only the fast averaging which allows characterization of the high-energy sites by a single parameter T2" = T ~ BIn . (A10) T2.4 is also a function of the degree of deuteration; T2.4 and T ~ for A the "free" intracrystalline water are evaluated next. The exchange of protons between "free" water molecules occurs many times in a relaxation time;b2 therefore it is not necessary to calculate relaxation times for the species H2O and HDO, as the weighted average relaxation rate will suffice. For pure water the dependence on deuteration of the relaxation rates is simply where T1(2)0 is the relaxation time with f~ = 0, and Ri, is defined above. These various Rij are required to take into account the variation of the various spectral density functions appearing in (A2) and (A3) (and similar equations for TI) with the value of the correlation times T ~the ; exponential correlation function is presupposed, The various R;j are given in Table VI. To calculate the relaxation rates for the intracrystalline free water T Lof ~(A7) terms must of course be added for any other magnetic ingredients contributing to the relaxation. References and Notes (1) P. 8. Venuto, Adv. Chem. Ser., No. 101, 260 (1971). (2) A. L. Dent and R. J. Kokes, J. Phys. Chem.. 73, 3781 (1969); 74, 3653 (1970), J. Am. Chem. Soc., 92, 1092, 6709 (1970). (3) J. R. Zimmerman and W. E. Brltten, J. Phys. Chem., 61, 1328 (1957). (4) (a) H. A. Resing, J. Phys. Chem., 78, 1279 (1974): (b) H. A. Resing and J. S.Murday, Adv. Chem. Ser., No. 121, 414 (1973). Certain tentative and not entirely correct ideas regarding surface kinetics expressed in (b) are corrected In (a). (c) H. A. Resing, Adv. Mol. Relaxation Processes, 3, 199 (1972): in (c) NMR relaxation in the rotating frame Is used to infer additional Information about prehydrolysis surface sites. (5) A. P. Bolton and M. A. Lanewala, J. Catal., 18, 154 (1970). (6) A. Maes and A. Cremers. Adv. Chem. Ser., 121,230 (1973). (7) R. Beaumont, D. Barthomeuf, and Y. Trambouze, Adv. Chem. Ser., No. 102, 327 (1971). (6) H. S. Sherry, Adv. Chem. Ser., No. 101, 350 (1971). (9) H. A. Resing and J. K. Thompson, Adv. Chem. Ser., No. 101, 473 (1971).
(IO) H. A. Resing and R. A. Neihof, J. Colloid. lnterface Sci., 34, 480 (1970). (11) Nicoiet Model 1074. (12) H. Y. Carr and E. M. Purceli, Phys. Rev., 94, 630 (1954). (13) J. P. Carver and R. E. Richards, J. Magn. Reson., 6, 89 (1972). (14) J. K. Thompson and H. A. Resing, J. Collokj lnferface Sci., 26, 279 (1988). (15) J. F. Charneii, J. Crysf. Growth, 8, 291 (1971). (16) The crystals were grown by Dr. L. F. Brown (at the Mobil Research Laboratory, Pennlngton, N.J.) who described the method of preparation to us. (17) D. H. Olson, J. Phys. Chem., 74, 2756 (1970). (18) N. Bloembergen, E. M. Purcell, and R. V. Pound, Phys. Rev., 73, 679 (1948). (19) D. E. Woessner and J. R. Zimmerman, J. Phys. Chem., 67, 1590 (1983). (20) D. E. Woessner, J. Chem. Phys., 39, 2783 (1963). (21) This conclusion was reached by comparing the T2 values for the second phase with those measured for NaA; see I. V. Matyash, M. A. Piontkovskaya, L. M. Tarasenko, and I. M. Tyutyunik, J. Struct. Chem. (USSR) (fngl. Trans.), 3, 214 (1962). This conclusion cannot be considered rlgorous. (22) H. A. Resing and R. L. Patterson, to be submitted for publication. (23) J. Karger, Ann. Phys. (Leipzig). 27, 107 (1971); Z.Phys. Chem. (Leipzjg), 248, 27 (1971). (24) H. F. Aly and R. M. Latimer, J. lnorg. Nucl. Chem., 29, 2041 (1967). (25) H. A. Resing, Adv. Mol. RelaxafionProcesses, 1, 109 (1967-1968). (26) H. A. Resing, J. Phys. Chem., submitted for publication. (27) R. M. Barrer and P. J. Reucroft, Proc. R. Soc. (London), Ser. A, 256, 431, 449 (1960). (28) A. Abragam, "The Principles of Nuclear Magnetism," Oxford University Press, London, 1961, p 239. (29) H. Lechert, Adv. Chem. Ser., No. 121, 74 (1973). (30) For an example of the use of this program see H. A. Resing, G. Belfort, and S.H. Dairymple, In press. (31) CDC Program Library, E-2, UOMD-GLSWS: or see N. E. Daniels, Jr., Technical Report No. 579, Department of Physics and Astronomy, University of Maryland. (32) J. A. Van Vleck, Phys. Rev., 74, 1168 (1948). (33) Actually, there are partially compensating errors in this procedure. Experimentally, below the T2 maximum, T, has not quite reached T, (see Figure 2 for example) as the BPP theory requires for isotropic motlon; thus the assumption that TZa = TI under-allows for the effects of the ath phase. On the other hand, the approximate eq 7 does not properly account for Pa in the vicinity of the T2 maximum: this has the effect of promoting Pa to unity in this region and thus over-allowing for the effects of the ath phase. (34) For a discussion of activities of adsorbed species see C. Wagner in "Heterogeneous Kinetics at Elevated Temperatures", Vol. 21, G. R. Belton and W. R. Worrell, Ed., 1970, p 323. (35) A. Gutsze, D. Delninger, H. Pfeifer. W. Schirmer, and H. Stach, Z.Phys. Chem. (Leipzig),248, 383 (1972). (36) H. Pfeifer in "Proceedings of the Third International Conference on Molecular Sieves", J. B. Uyterhoeven, Ed., Leuven Unlversity Press, Lenven, p 53. See also comment there by H. A. Resing, ibM., p 54. Pfeifer gave values of cb, which have been converted via eq 6 to C.. For the least-squares fit values of C, were estimated directly from ref 35. (37) W. A. Van Hook ACS Monogr., 167, 13 (1970). (38) It is possible that spin flips of the AI nucleus may also be effective in motional narrowing. See ref 28, p 565. (39) The AI-0 distance in X zeolites is -1.65 A; see D. H. Olson and E. Dempsey, J. Catal., 13,221 (1969). (40) The 0-H bond distance in ice is 1.01 A; S. W. Peterson and H. A. Levy, Acta Crystallogr., 10, 553 (1957). (41) The 0-H bond distance In AIO-OH is 0.99 A; W. R. Busing and H. A. Levy, Acta. Crysfallogr.. 11, 798 (1957). (42) E. R. Andrew, "The Principles of Nuclear Magnetlsm", Cambridge University Press, Cambridge, 1955, p 17t. (43) The Important effect of "Intramolecular" proton-proton interactions in decationated zeolites has been demonstrated by R. L. Stevenson, J. Catal., 21, 113 (1971). (44) J. W. Akitt, J. Chem. Soc., Dalton Trans.. 1177 (1973); 604 (1972): also C. Canet, J. J. Delpeuch, M. R. Khoddar, and P. Rubini, J. Magn. Resort., 9, 329 (1973). (45) D. Freude, D. Muller, and H. Schmiedel. J. ColloM lnferface Sci.. 36, 320 (197 1). (46) V. J. Shiner, ACSMonogr., No. 167, 90 (1970). (47) H. Pfeifer, NMR, 7, 53 (1972). (48) R. M. Barrer, Ber. Bunsenges. Phys. Chem., 69, 786 (1965). (49) H. Pfeifer, private communication. (50)A. Abragam, "Principles of Nuclear Magnetism", Oxford Unlversity Press, London, 1961, p 292. (51) Reference 50, p 295. (52) 2. Luz and S.Meiboom, J. Chem. Phys., 39,366 (1963).
The Journal of Physical Chemistry, Vol. 79, No. 24, 1975
