2752
The Journal of Physical Chemistry, Vol. 83, No. 21, 1979
Yang et al.
Mean Molal Activity of NaCI, KCI, and CsCl in Ethanol-Water Mixtures R. Yang," J. DemIrglan,lbJ. F. Solsky,lc E. J. Klkta, Jr.,ld and J. A. Marinsky" Chemistry Department, State University of New York at Buffalo, Buffalo, New York 14214 (Received June 30, 1977; Revised Manuscript Received June 29, 1979)
The partial pressure of ethanol and water in mixtures ranging in composition from 10 to 90% by weight ethanol and containing variable amounts of dissolved salt (NaC1, KC1, or CsC1) to provide a range of salt molalities (based on 1000 g of each mixture) from zero to saturation has been measured. Compilation of these data has been facilitated by vapor chromatographicmeasurements. The mean molal activity coefficients of these chlorides in the various ethanol-water mixtures have been deduced from these measurements. In the case of NaCl and KC1, the mean molal activity coefficients in the mixed media have also been determined directly in cells without a liquid junction. The cross-differential terms in the Gibbs-Duhem equation have been employed to show that both kinds of measurements (vapor phase chromatographic and potentiometric) yield equivalent results.
Introduction Application of the Gibbs-Donnan model to interpretation of ion exchange in zeolites leads to the following expression for the thermodynamic representation of uni-univalent exchange reactions in 1:l electrolyte solutions; with the A zeolite in the M+ form and the exchange carried out in solutions of NX and MX
In this expression K is the experimentally determined selectivity coefficient, m is the molal concentration of the species, y is the activity coefficient of the ion in the zeolite phase, and ya is the mean molal activity coefficient of the electrolyte in the external phase. This expression has been shown to provide a quantitative description of the ionexchange process in the A zeolite equilibrated in aqueous median2Subsequent studies of the ion-exchange process in alcohol-water media3,4 have indicated that the Gibbs-Donnan model may provide a valid basis for the anticipation of equilibria in mixed media as well. To examine this possibility further it was necessary to compile accurate measurements of the colligative properties of each component in such solutions. A complete analysis of the colligative properties of ethanol-water-MC1 solutions was made for this purpose. Experimental Section Vapor Pressure Measurements. The partial pressure of the volatile components in the systems investigated was determined in the following way: The total pressure of each solution was measured first. The vapor pressure of the alcohol was then determined directly and subtracted from the total pressure to obtain the partial pressure of the water component. The vapor chromatographic method of Arnikar, Rao, and Bodhe5 was used to measure the partial pressure of the alcohol component in the experimental mixtures. With this method the chromatographic behavior of a known volume of the saturated vapor of pure solvent is injected and compared under identical conditions with the chromatographic pattern of the same volume of vapor in equilibrium with the mixed solvent media of known composition. The presence of the second component does not hinder the measurement, since it is effectively sepa0022-3654/79/2083-2752$0 l .oo/o
rated either by the column or by its lack of response to the detector. From the ratio of the signals for the given component in the solution and in the pure state, and from earlier calibration of the column, the ratio ( p / p o )of the partial pressure of the component over the solution (p)and in the pure state (po)can be computed. This ratio, by Raoult's law, defines the activity of the solvent in the mixture. The accuracy and reliability of the measurements were demonstrated first with the two component alcohol-water systems. Results obtained were shown to agree with the literature to assure the accuracy and reliability of the techniques and instrumentation employed. Measurements in three-component systems were then shown to be valid by demonstrating the identity, within experimental error, of the Gibbs-Duhem based cross-differential terms ( a In Ya/ams)n,,m, measured chromatographically and ( a In ys/ am,),,?, measured electrochemicallyin this program. The subscripts a, w, and s refer, respectively, to ethanol, water, and neutral salt. Total Vapor Pressure Measurement. Ethanol-water mixtures of varying composition (10-90% by weight water) were prepared with triply distilled water. Sodium chloride, potassium chloride, or cesium chloride (dried to constant weight) of varying amounts (moles per 100 g of liquid) was dissolved in each mixture scheduled for vapor pressure measurement. The variation of total vapor pressure with salt composition of each alcohol-water mixture was measured as a function of the salt molality until saturation. During a measurement, a chamber consisting of a 50-mL Erlenmeyer flask with a 19/38 female fitting connected to a V-2 vacuum stopcock was filled with 10 mL of solution. This sample was degassed by repeating the following cycle of operations three times: the sample was frozen in liquid N2, the system was evacuated, and subsequently the sample was melted. At the evacuation stage of the third cycle the chamber pressure was reduced to mmHg. The chamber was then attached to one part of a 77 H-100 pressure head which was connected to a MKS Baratron pressure meter, Type 77, which measured directly the pressure differential across a diaphragm. The reference chamber separated by the diaphragm was attached to a source of high vacuum (lo-' mmHg). The sample was maintained at constant temperature with a Precision Scientific 154 Lo Temptrol circulating water bath with temperature control to f0.005 "C provided by a Precision Scientific 62541 mercury temperature probe connected to a Precision Scientific electronic relay. A Hewlett-Packard H P 2850 C quartz thermometer was used to define this 0 1979 American Chemical Society
Mean Molal Activity of NaCI, KCI, and CsCl in EtOH-H,O
range of temperature fluctuation. Such preparation for a measurement yielded a constant pressure reading reproducible to f0.02 mmHg; an experimental error of f0.04 mmHg in the measurements was due to temperature fluctuation in the room. Measurement of the Partial Pressure of Ethanol. The gas chromatograph used to measure the vapor pressure of ethanol in these mixtures was a modified HewlettiPackard 5750 research chromatograph. A Fisher proportional temperature controller was used for accurate control of the oven temperature (f0.02 "C). The injection system was modified by the addition of a Seiscore gas sampling valve, Model VIII, which was actuated by a solenoid valve. Samples were injected by allowing the sample carrier gas (helium) to bubble through a liquid sample chamber, become saturated with the vapor of the liquid sample, and then pass through the sampling valve. The valve was thermostated outside the oven in the Precision Scientific Model 154 constant temperature bath at 25.0 f 0.05 OC. The instrument was equipped with a Beckman GC-4 ionization detector. The potential across the plates was held at 350 V by a power supply in the Hewlett-Packard 5750. The signal from the detector was amplified by the electrometer on the 5750. The output from the electrometer was displayed on an Esterline-Angus Model 5-6014 Speedservo 5-in. strip-chart recorder. A 2.00-m, 0.25411. i.d. copper tube was packed with 10% Carbowax 1540 coated on 80/lOO mesh silanized Chromosorb W. This column was used for all determinations carried out at a temperature of 120 "C. Peak areas were determined by the peak height method. Each data point was the average of at least ten runs. Pure ethanol was used as the standard for comparison. Stability of performance during the analysis period was assured by the reproducibility of periodic runs with absolute ethanol.12 In order to minimize bias, if present, in these measurements,a series of at least ten injections for each solution was made, and the mean-square method was employed to obtain precise numbers. The standard deviation showed the variation of each series of measurements to be no greater than 3 % . Before each series of runs, the sample chamber was washed thoroughly with acetone and dried. The chamber was then connected to a vacuum pump and evacuated for 30 min. The samples were then introduced and the chamber closed by means of a valve connected to the sample carrier line. The sample chamber immersed as described above in a constant temperature bath maintained at 25.0 f 0.05 "C was pressurized to 18 psi with helium. A constrictor was used at the output of the sampling valve to restrict the flow rate of the He to approximately 0.25 mL/min. The system was then allowed to come to equilibrium for at least 30 min before making any vapor injections. An automatic injection sequence was used6 to make each injection time exactly 1.00 s. Chromatographic runs after 15 min of equilibration showed a constant peak height to indicate that equilibriumhad truly been reached. The vapor pressure of the pure ethanol component7was used to obtain the vapor pressure of the alcohol in each mixture studied by multiplying this absolute pressure value by the ratio of the chromatographic areas observed for the mixture and the pure alcohol, respectively. Electrochemical Studies. Preparation of Salt Solutions. Ethanol-water mixtures of varying composition (10-90% by weight water) were prepared in liter quantity, and the prescribed amounts (moles per 100 g of liquid) of sodium chloride or potassium chloride, previously dried to constant weight, were dissolved in an aliquot portion of alcohol-
The Journal of Physical Chemistry, Vol. 83, No. 21, 1979 2753
water mixture to constitute the most concentrated solution of each series scheduled for measurement. In order to minimize error in the alcohol-water compositions of each particular series of solutions, the more dilute salt solutions were derived from the most concentrated salt solutions so obtained for a particular series by dilution with the primary solution. Potentiometric Measurements. A cell without liquid junction potential was used to measure the mean molal activity of NaCl and KC1 as a function of concentration (0.001-1.0 m or the lower saturated concentrations in the alcohol-rich mixtures) in the ethanol-water mixtures studied in this program. In the assembly of the cell a Corning sodium-ion-selective electrode (catalog no. 476210) for the Na', a Corning monovalent cation electrode (catalog no. 476220) for the K+, and a silver-silver chloride electrode were employed. The silver-silver chloride electrodes were prepared by using the general procedure described by Brown8 Because some modifications to this procedure were made to obtain reliable electrodes more rapidly and simply, the method of preparation is described below. 1. Platinum wire, 0.15 cm in diameter, was used (VWR Scientific catalog no. 66269-181) in place of the smaller gauge prescribed by Brown. It was found that the greater Ag-AgC1 electrode surface in solution provided faster and more stable response. 2. A pair of platinum wire strands of equal length (-3.0 cm) were, after smoothing the surface, inserted into a size 10 rubber stopper. a single stranded wire was attached to the end of the platinum and approximately 2.5 cm of the platinum protruded from the stopper. 3. After cleaning the platinum wire in boiling concentrated nitric acid, the pair of platinum wires were transferred to a polyethylene cell containing potassium silver cyanide solution (prepared as described by Brown) by inserting the stopper. Approximately 1.8 cm of the platinum wire was covered by the solution. Exposure of the surface of the rubber stopper to HN03 vapor was avoided by a parafilm cover. 4. During the silver-platingstep of the electrolysis, argon gas was constantly and gently bubbled through the solution (at a rate of 30 mL/min). Care was taken to avoid ingestion of vapor (the possibility of HCN gas evolution exists during the electrolysis) by working in a well-ventilated hood. A constant current of about 0.5 mA was maintained for 6 h. 5. At the end of the silver-plating process, the electrodes were flushed with warm, deaerated, triply distilled water for at least 30 min to remove all traces of cyanide ion from the surface. This washing procedure was found to prolong the life of the Ag-AgC1 electrodes that were produced. Insufficient washing resulted in a poorly plated electrode. 6. The washed electrodes were then chloridized by electrolysis for 1 h in 0.1 N HC1 at a current of about 1 mA. During this time, argon was used to expel any O2 dissolved in the solution. Electrodes prepared in this manner were purplish-brown in color as described by Brown.8 7. The electrodes were then carefully rinsed and stored in triply-distilled water free of dissolved 02. Under normal usage, a silver-silver chloride electrode lasted about 8 weeks before slow oxidation of the surface of the electrode significantly influenced potential readings. During the emf measurements, the Precision Scientific Model 154 constant temperature bath was used to maintain the temperature of the cell at 25.0 f 0.05 "C. The potential measurement was made with a Radiometer
2754
The Journal of Physical Chemistry, Vol. 83, No. 21,
1979
Model 4 potentiometer. Readings, reproducible to f0.2 mV, were obtained. Overnight conditioning of the electrodes in each solvent medium employed in the study was required prior to a series of measurements in that medium. In the absence of such pretreatment of the electrodes the response was slow and erratic. After completion of a set of measurements reproducibility of cell performance was always checked by monitoring the potential of standard aqueous NaCl (KC1) solutions. The Nernstian response of the cell was maintained over a concentration range of >lo3; only the Eo shifted several millivolts. The value of Eo derived in this manner was used in eq 2 to compute the mean molal
Yang et al.
;
A Demirgian 0
F3ote
0
Dabsor
vang
81d
end Soholes
9
-0
2C
33
,
,
,
,
,
,
,
40
23
4i
7C
63
90
13C
P e ~ e e nETisnol ~
activity coefficient of the NaCl (KC1) in every alcoholwater mixture examined. For each alcohol-water-salt system the measurement of at least one solution in each alcohol-water series (Le., 10% ethanol, 0.5 m NaC1, 20% ethanol 0.1 m NaC1, etc.) was repeated to ensure electrode reproducibility. In the compilation of data it was necessary to keep each system free of dissolved O2 during the course of measurement, the presence of O2 reducing the effective life of the silversilver chloride electrode! For this purpose argon gas, purified by passing through Carbowax and sodium hydroxide packed columns, was bubbled through the cell at a rate of 30 mL/min. To prevent evaporation of the solution the argon was presaturated by passing it through the salt-free solution prior to its introduction to the cell. A 30-min interval prior to each measurement was provided to assure removal of dissolved O2 in the sample. After each measurement the electrodes covered with argon gas were first rinsed thoroughly with triply distilled, deionized water; they were then rinsed with the solution to be examined next. The Ag-AgC1 electrodes were never allowed to dry to reduce the possibility of oxidation. Pairs of AgCl electrodes used in these studies were constantly checked against each other to ensure equivalent response. Chemicals. The sodium chloride and potassium chloride used were either Baker Analyzed or Fisher Certified Reagent grade. Cesium chloride (99.9% pure) was purchased from Ventron Alfa Co., Beverly, Mass. All salts were used without further purification; in solutions any insoluble matter was filtered. Anhydrous ethanol from Commercial Solvent Corp. was used as received. Gas chromatographic analysis indicated a purity of 99.9%. Earlier analysis by Karl-Fisher titration3i4 had shown 0.06 wt % water present in the ethanol.
Results Vapor Pressure Measurements. The partial pressure data obtained for ethanol and water in the various proportions as a function of NaCl and KC1 content are presented in Table I together with the total vapor pressure data obtained for these systems. Each subheading designates the alcohol-water composition of the system under investigation. Under column 1, the salt concentration of the mixed medium is listed. The total vapor pressure of each system, the vapor pressure of alcohol, and the computed vapor pressure of water are given in the next three columns. The activity (ai = pi/p:) of the alcohol and water are presented in the last two columns of the table. For this computation the values of pioassigned to water and ethanol at 25 "C were 23.76 and 59.78 mmHg.7 The partial pressure of the water and its listed activity in Table I are least reliable since they are based on the small
Flgure 1. Comparison of ethanol-water vapor pressure data compiled at 25 OC.
difference between two measurements susceptible to a small error range. The data obtained from chromatographic study of the various mixtures of ethanol and water containing CsC1 are presented in Table I1 as (a log aa/amJm,m, values. Potentiometric Measurements. Electrode response, prior to use in the alcohol-water-salt systems, was Nernstian. The change in E with log m(S) was 117.5 f 0.50 and 117.86 f 0.74, respectively, in NaCl and KC1. For NaCl the Eo was 68.5 f 1.5, and for KCl the Eo was 81.0 f 1.1. The small shifts in Eo prior to each series of measurements in the three-component systems are believed to arise from variability of the assymmetry potential of the glass electrode over the time interval of the measurement program. The potentiometric data that were obtained for the ethanol-water-NaC1 and the ethanol-water-KC1 systems are presented in Tables I11 and IV. The experimental S value was substituted for 2.303RTIF in eq 2 to compute the mean molal activity coefficient of the salts that is listed in the tables for the alcohol-water mixtures examined. The percentage of each alcohol-water mixture for a particular salt is designated at the head of each subdivision of Tables 111and IV. The first column of each table lists the salt concentrations in molality (based on 1000 g of water). The second column lists the emf data in millivolts. In the third column, the E -Eo values are presented. The fourth, fifth, and sixth columns report the logarithm of the mean molal activity, the mean molal activity, and the mean molal activity coefficient based on the molality as defined in column 1 of the tables. In the seventh column, salt concentration is based on 1000 g of solvent. The mean molal activity coefficient values listed in the final column are based on this definition of the salt molality.
Discussion Vapor Pressure Data. The vapor pressure data for the two component system (ethanol-water) are compared in Figure 1 with literature values reported for this system. The data are in excellent agreement with the earlier work of Foote and Scholes and of Dobson reported by Timmermann,' deviations not exceeding experimental error. Further evidence for the reliability of the vapor pressure data presented for the ternary mixtures has been provided from the independent emf measurements of the activity of NaCl and KCl in these mixtures with a cell consisting of a cation selective electrode and an Ag-AgC1 electrode. This aspect is discussed fully later. With the data listed above isotherms can be constructed to describe the activity or partial pressure of each volatile component in ethanol-water media at any specified
Mean Molal Activity of
NaCI, KCI, and CsCl in EtOH-H,O
The Journal of Physical Chemistry, Vol. 83, No. 21, 1979 2755
TABLE I: Total and Partial Vapor Pressures of Three-Component Systems mNaCl
Ptot
Pa
Pw
aa
aw
mKCl
Ptot
Ethanol- Water-Na c1 10% EtOH
Pa
Pw
aa
a,
Ethanol- Water-KC1 10% EtOH
0.0 0.3 0.5 1.0 satd
31.03 31.40 31.70 32.40 39.00
8.43 9.03 9.51 10.52 21.70
22.60 22.37 22.19 21.88 17.30
0.141 0.151 0.159 0.176 0.360
0.951 0.942 0.933 0.921 0.730
0.0 0.3 0.5 1.0 satd
31.03 31.40 31.64 32.23 34.73
8.43 9.11 9.59 10.89 16.92
22.60 22.29 22.05 21.34 17.81
0.141 0.152 0.160 0.182 0.283
0.951 0.938 0.828 0.898 0.750
0.0 0.3 0.5 1.0
38.15 38.82 39.20 40.45 47.08
20% EtOH 16.88 21.27 17.93 20.89 18.53 20.67 20.25 20.20 30.69 16.39
0.282 0.300 0.310 0.339 0.513
0.895 0.879 0.870 0.850 0.690
0.0 0.3 0.5 1.0 satd
38.15 38.77 39.23 40.55 43.95
20% EtOH 16.88 21.27 17.98 20.79 18.75 20.48 20.92 19.63 26.61 17.34
0.282 0.301 0.314 0.350 0.445
0.895 0.875 0.862 0.826 0.730
satd
43.48 44.21 44.77 45.86 50.15
30% EtOH 23.52 19.96 24.63 19.58 25.41 19.36 27.09 18.77 34.12 16.03
0.393 0.412 0.425 0.435 0.571
0.840 0.824 0.815 0.790 0.675
0.0 0.3 0.5 1.0 satd
43.48 44.23 44.83 45.87 47.83
30% EtOH 23.52 19.96 24.77 19.46 25.73 19.10 27.69 18.18 31.08 16.75
0.393 0.418 0.430 0.463 0.520
0.840 0.819 0.804 0.765 0.705
0.0 0.3 0.5 1.o satd
47 * 54 48.14 48:44 49.15 51.30
40% EtOH 28.73 18.81 29.64 18.50 30.25 18.19 31.77 17.38 35.78 15.52
0.481 0.496 0.506 0.531 0.599
0.792 0.779 0.766 0.730 0.653
0.0 0.3 0.5 satd
47.54 48.19 48.63 50.17
40% EtOH 28.73 18.81 29.94 18.25 30.81 17.82 33.78 16.39
0.481 0.501 0.51 5 0.565
0.792 0.768 0.750 0.690
0.0 0.2 0.3 0.5 1.0 satd
49.95 50.28 50.35 50.63 51.20 52.20
50% EtOH 32.38 17.57 33.14 17.14 33.44 16.91 33.95 16.68 35.33 15.87 37.60 14.60
0.542 0.554 0.559 0.568 0.591 0.629
0.739 0.721 0.712 0.702 0.668 0.614
0.0 0.3 0.5 satd
49.94 50.54 50.82 51.48
50% EtOH 32.38 17.59 33.53 17.01 34.43 16.39 35.56 15.92
0.542 0.561 0.576 0.595
0.739 0.716 0.690 0.671
51.72 52.40 52.76
60% EtOH 35.33 16.39 36.65 15.75 37.48 15.28
0.590 0.613 0.627
0.690 0.663 0.643
0.0 0.3 0.5 0.7
51.72 52.20 52.51 52.70 53.12
60% EtOH 35.33 16.39 36.33 15.87 36.99 15.52 37.54 15.16 38.70 14.42
0.0 0.3 satd
0.590 0.608 0.619 0.628 0.647
0.690 0.668 0.653 0.638 0.607
0.0 satd
53.42 54.14
70% EtOH 37.89 15.53 39.30 14.84
0.634 0.657
0.654 0.625
0.00 0.15 0.30 0.50 satd
53.42 53.64 53.81 54.08 54.18
70% EtOH 37.89 15.53 38.64 15.00 39.41 14.40 40.26 13.82 40.97 13.21
0.643 0.646 0.659 0.674 0.685
0.654 0.631 0.606 0.582 0.556
0.0 satd
55.80 55.81
80% EtOH 42.56 13.24 42.99 12.82
0.711 0.719
0.557 0.540
0.0
57.80 58.11
90% EtOH 48.78 9.02 48.90 9.21
0.816 0.818
0.380 0.388
0.00 satd
55.80 55.72
80% EtOH 42.56 13.24 44.01 11.71
0.711 0.736
0.557 0.493
0.00 satd
57.80 57.77
90% EtOH 48.78 9.02 48.94 8.83
0.816 0.819
0.380 0.372
satd 0.0 0.3 0.5 1.0
satd
TABLE 11: The Value of ( a log aa/amS), ,m Derived from Vapor Chromatographic Measuremen& f& Ethanol-H,O-CsCl ma
( a log d a m s )m a, m
0.00 2.41 5.43 9.31 14.50 21.70 32.60 50.72 86.95
0.1512 0.1166 0.0690 0.0400 0.0312 0.0158 0.0174 0.0128 0.0108
concentration of NaCl or KC1 as a function of the relative alcohol and water content of these ternary systems. This is illustrated in Figure 2 which provides such an isotherm for the ethanol-water system containing NaCl a t its
satd
saturation concentration over the complete composition range of the mixed media from 0 to 100% by weight ethanol. The ethanol and water vapor pressure values for &lo% and 90-100% by weight ethanol of this figure were obtained by interpolation of points based on an extrapolation from the 10 and 90% points measured in this research to the literature values for the pure salt-saturated components. These interpolated values are presented in Table V. Isotherms a t any specified salt concentration can be easily resolved by interpolation of the vapor pressure data over the complete salt concentration range (zero to saturated) measured. The solvent composition range of each isotherm is only limited by the decreasing solubility of the salt with enrichment of the medium by the alcohol. Comparison of Potentiometric and Vapor Phase Chromatographic Measurements. The mean molal ac-
2756
The Journal of
Physical Chemistry, Vol. 83,No. 21,
Yang et al.
1979
Figure 4. A plot of (a log a,/ama)m,,mw (m, = 0.1) vs. NaCI-ethanol-water system.
ma for
0.08,
10
20
30
40 50
60
70
80
90
100
Percent E t h a n o l
Figure 2. Total and partial pressures of the ethanol-water-NaCI (saturated) system. 1.1
(+$
Figure 5. A plot of (a log NaCI-ethanol-water system.
as/ama)m,,mw (m, =
0.1) vs.
ma for
O'OBI
0
I
10
20
I ii0
00
60
ma
Figure 6. A plot of (a log CsCi-ethanol-water system.
a,/ama),8,mw( m , =
0.1) vs.
ma for
to ( a log a,/ama)mB,mT and are plotted vs. ma in Figure 6. Only the points obtained in 50 and 60% ethanol fail to lie on the smooth curve drawn to describe best these data. With these data and the literature value for the mean molal activity of CsCl dissolved in pure water at m, = O.lg as the reference point a least-squares program leads to values of log a,, at this fixed m,, as maincreases from 0 to 80. The results of these computations are presented in Table VIII. The ( a log as/ama)mp,m, values derived from the vapor phase chromatographic data at different fixed m, values (0.3, 0.5, and 1.0 m as well as 0.1 m) as described above were in good agreement with each other except that the
The Journal of Physical Chemistry, Vol. 83, No. 21, 1979 2757
Mean Molal Activity of NaCI, KCI, and CsCl in EtOH-H,O
TABLE 111: Mean Molal Activity Coefficient of NaCl for NaC1-EtOH-H,O Mixtures
m,
E
E - E,
0.0111 0.0222 0.0556 0.1111 0.2222 0.3333 0.5556 1.1111
-150.0 -117.3 - 74.0 -42.0 - 9.5 9.5 33.8 66.5
- 219.0 - 186.3 - 143.0 - 111.0 - 78.5 - 59.5 - 35.2 - 2.5
0.0125 0.0250 0.0625 0.1250 0.2500 0.3750 0.6250 1.2500
-130.4 - 97.8 - 54.0 - 21.8 12.0 30.0 53.5 85.4
- 199.4
0.0143 0.0286 0.0715 0.1430 0.2860 0.4286 0.7150 1.4300
log as 1 0 % EtOH
a,
YS
ms’
YS
- 1.8607 -1.5828 -1.2150 -0.9431 -0.6669 -0.5055 -0.2991 -0.0212
0.0138 0.0261 0.0610 0.1140 0.2153 0.3122 0.5023 0.9523
1.2417 1.1771 1.0964 1.0261 0.9690 0.9368 0.9040 0.8571
0.01 0.02 0.05 0.10 0.20 0.30 0.50 1.00
1.3783 1.3066 1.2192 1.1401 1.0765 1.0408 1.0045 0.9523
-166.8 - 123.0 - 90.8 -57.0 - 39.0 -15.5 16.4
20% EtOH -1.6941 -1.4172 -1.0450 -0.7715 -0.4843 -0.3314 -0.1317 0.1393
0.0202 0.0383 0.0902 0.1693 0.3279 0.4663 0.7384 1.3783
1.6179 1.5307 1.4424 1.3541 1.3115 1.2434 1.1815 1.1026
0.01 0.02 0.05 0.10 0.20 0.30 0.50 1.00
2.0224 1.9134 1.8030 1.6926 1.6394 1.5543 1.4769 1.3783
-107.2 - 75.8 - 33.1 -2.0 30.0 47.2 71.0 102.8
- 176.2 -144.8 -102.1 -71.0 - 39.0 - 21.8 2.0 33.8
30% EtOH -1.4970 - 1.2302 - 0.8675 - 0.6032 -0.3314 -0.1852 0.0170 0.2872
0.0318 0.0589 0.1357 0.2493 0.4663 0.6528 1.0399 1.9372
2.2266 2.0577 1.8977 1.7436 1.6304 1.5231 1.4544 1.3547
0.01 0.02 0.05 0.10 0.20 0.30 0.50 1.00
3.1840 2.9425 2.7138 2.4933 2.3314 2.1760 2.0798 1.9372
0.0167 0.0333 0.0833 0.1667 0.3333 0.5000 0.8333 1.6667
-85.2 - 55.0 -12.5 19.0 48.5 66.2 89.5 120.4
- 154.4 -124.2 -81.7 - 50.2 - 20.7 - 3.0 20.3 51.2
40% EtOH - 1.3096 -1.0534 -0.6930 -0.4258 -0.1756 - 0.0254 0.1722 0.4343
0.0490 0.0884 0.2020 0.3752 0.6675 0.9431 1.4866 2.7181
2.9355 2.6553 2.4344 2.2505 2.0026 1.8862 1.7839 1.6308
0.01 0.02 0.05 0.10 0.20 0.30 0.50 1.00
4.9023 4.4211 4.0557 3.7516 3.3373 3.1436 2.9731 2.7181
0.02 0.04 0.10 0.20 0.40 0.60 1.00 2.00
-64.2 - 32.3 9.2 38.9 69.0 86.2 108.6 138.7
-133.2 - 101.3 - 59.8 - 30.1 0.0 17.2 39.6 69.7
50% EtOH -1.1317 -0.8607 -0.5081 -0.2557 0.0000 0.1461 0.3364 0.5922
0.0738 0.1378 0.3104 0.5550 1.0000 1.4000 2.1699 3.9101
3.6921 3.4457 3.1040 2.7748 2.5000 2.3334 2.1699 1.9550
0.01 0.02 0.05 0.10 0.20 0.30 0.50 1.00
7.3843 6.8914 6.2081 5.5496 5.0000 4.6667 4.3399 3.9101
0.025 0.050 0.125 0.250 0.500 0.750 1.250 2.500
- 38.2 - 7.6 33.0 62.3 90.5 107.0 129.6 158.2
- 107.20 - 76.60 - 36.0 - 6.7 21.5 38.0 60.6 89.2
60% EtOH -0.9108 - 0.6508 -0.3059 -0.0569 0.1827 0.3229 0.5149 0.7579
0.1228 0.2235 0.4945 0.8772 1.5229 2.1031 3.2724 5.7261
4.9121 4.4691 3.9557 3.5086 3.0458 2.8041 2.6179 2.2904
0.01 0.02 0.05 0.10 0.20 0.30 0.50 1.00
12.2803 11.1728 9.8893 8.7715 7.6144 7.0102 6.5448 5.7261
0.0333 0.0667 0.1667 0.3333 0.6667 1.0000 1.6667
-4.3 26.3 63.7 89.0 120.0 136.1 148.0
- 73.1 - 42.5 - 5.1 20.2 51.2 67.3 79.2
70% EtOH - 0.6221 -0.3617 - 0.0434 0.1719 0.4357 0.5728 0.6740
0.2387 0.4348 0.9049 1.4856 2.7274 3.7391 4.7211
7.1685 6.5189 5.4283 4.4574 4.0909 3.7391 2.8326
0.01 0.02 0.05 0.10 0.20 0.30 0.50
23.8711 21.7404 18.0978 7.4.8 5 64 3.3.63 69 12.4636 9,4422
0.05 0.10 0.25 0.50 1.00
35.2 63.8 100.1 128.0 155.2
- 33.6
-0.2860
0.5177 0.9067 1.8466 3.1903 5.4365
10.3532 9.0666 7.3866 6.3806 5.4365
0.01
0.02 0.05 0.10 0.20
51.7658 45.3332 36.9329 31.9029 27.1825
0.05
90.00 118.10 154.2
1.5150 2.6277 5.3310
30.3009 26.2769 21.3240
0.005 0.010 0.025
303.0090 262.7692 213.2399
80% EtOH
0.10
0.25
- 5.0 31.3 59.2 86.4 21.2 49.3 85.4
-0.0426 0.2664 0.5038 0.7353 90% EtOH 0.1804 0.4196 0.7268
2758
The Journal of Physical Chemistry, Vol. 83, No. 21, 1979
Yang et al.
TABLE IV: Mean Molal Activity Coefficient Measurements o f KCl for EtOH-H,O-KCl Mixtures 10% EtOH 0.0111 0.0222 0.0556 0.1111 0.2222 0.3333 0.5556 1.1111
-135.7 -105.2 - 62.5 -31.3 0.1 17.5 40.7 72.7
- 215.7 - 185.2 -142.5 -111.3 -79.9 - 62.5 - 39.3 - 7.3
- 1.8436 -1.5829 -1.2179 -0.9513 - 0.6829 -0.5342 - 0.3359 - 0.0624
0.0143 0.0261 0.0605 0.1119 0.2075 0.2923 0.4614 0.8662
1.2915 1.1769 1.0889 1.0069 0.9340 0.8769 0.8305 0.7796
0.01 0.02 0.05 0.10 0.20 0.30 0.50 1.00
1.4335 1.3064 1.2108 1.1187 1.0377 0.9743 0.9229 0.8662
0.0125 0.0250 0.0625 0.1250 0.2500 0.3750 0.6250 1.2500
-117.9 - 85.9 -43.6 - 11.8 19.0 37.0 60.3 90.5
-197.9 - 165.9 -123.6 -91.8 - 61.0 - 43.0 - 19.7 10.5
20% EtOH -1.6915 -1.4179 - 1.0564 - 0.7846 -0.5214 - 0.3675 -0.1684 0.0897
0.0203 0.0382 0.0878 0.1642 0.3010 0.4290 0.6786 1.2295
1.6279 1.5280 1.4051 1.3136 1.2042 1.1441 1.0858 0.9836
0.01 0.02 0.05 0.10 0.20 0.30 0.50 1.00
2.0349 1.9099 1.7564 1.6420 1.5052 1.4301 1.3572 1.2295
0.0143 0.0286 0.0715 0.1430 0.2860 0.4286 0.7150 1.4300
-98.7 -67.2 -23.5 8.3 37.9 54.3 77.1 107.2
- 178.9 -147.4 - 103.7 - 71.9 -42.3 - 25.9 - 3.1 27.0
30% EtOH - 1.5265 - 1.2577 - 0.8848 -0.6135 - 0.3609 -0.2210 - 0.0265 0.2304
0.0298 0.0552 0.1304 0.2435 0.4356 0.6012 0.9409 1.6997
2.0807 1.9318 1.8234 1.7029 1.5230 1.4026 1.3160 1.1886
0.01 0.02 0.05 0.10 0.20 0.30 0.50 1.00
2.9754 2.7624 2.6075 2.4351 2.1780 2.0040 1.8818 1.6997
0.0167 0.0333 0.0833 0.1667 0.3333 0.5000 0.8333 1.6667
- 78.0
-46.1 - 4.1 26.9 55.8 72.2 94.2 121.3
- 158.2 -126.3 - 84.3 - 53.3 - 24.4 -8.0 14.0 41.1
40% EtOH - 1.3498 -1.0776 -0.7193 - 0.4548 -0.2082 -0.0683 0.1195 0.3507
0.0447 0.0836 0.1909 0.3509 0.6192 0.8546 1.3166 2.2422
2.6758 2.5114 2.2912 2.1052 1.8577 1.7090 1.5800 1.3453
0.01 0.02 0.05 0.10 0.20 0.30 0.50
1.00
4.4686 4.1814 3.8172 3.5093 3.0958 2.8485 2.6332 2.2422
0.0200 0.0400 0.1000 0.2000 0.4000 0.6000 1.0000
- 54.9 - 24.5 16.0 46.9 73.8 90.5 113.0
-135.2 -104.8 - 64.3 - 33.4 - 6.5 10.2 32.7
- 0.8934 - 0.5482 - 0.2847 -0.0554 0.0870 0.2788
0.0704 0.1278 0.2830 0.5191 0.8802 1.2217 1.9001
3.5186 3.1952 2.8303 2.5956 2.2005 2.0361 1.9001
0.01 0.02 0.05 0.10 0.20 0.30 0.50
7.0372 6.3905 5.6606 5.1911 4.4011 4.0723 3.8002
0.025 0.050 0.125 0.250 0.500 0.750 1.250
- 30.3 0.0 39.1 67.8 94.4 110.0 133.0
- 110.4 - 80.1 -41.0 - 12.3 14.3 29.9 52.9
60% EtOH -0.9428 -0.6840 -0.3501 -0.1050 0.1221 0.2553 0.4517
0.1141 0.2070 0.4466 0.7852 1.3247 1.8003 2.8298
4.5633 4.1400 3.5724 3.1407 2.6494 2.4004 2.2638
0.01 0.02 0.05 0.10 0.20 0.30 0.50
11.4082 10.3500 8.9310 7.8517 6.6235 6.0009 5.6600
0.0333 0.0667 0.1667 0.3333 0.6667
0.3 30.0 68.0 95.0 120.0
- 79.80 -50.10 - 12.10 14.90 39.90
70% EtOH - 0.6815 - 0.4278 -0.1033 0.1272 0.3407
0.2082 0.3734 0.7883 1.3404 2.1915
6.2530 5.5980 4.7286 4.0217 3.2870
0.01 0.02 0.05 0.10 0.20
20.8224 18.6694 15.7652 13.4042 10.9573
0.05 0.10 0.25 0.50
43.7 68.9 100.5 123.2
- 36.50 - 11.30 20.30 43.00
80% EtOH -0.3114 - 0.0964 0.1732 0.3669
0.4882 0.8009 1.4901 2.3275
9.7633 8.0091 5.9603 4.6550
0.01 0.02 0.05 0.10
48.8165 40.0455 29.8015 23.2752
0.05 0.10 0.20
73.1 97.0 119.2
-7.00 16.90 39.10
90% EtOH - 0.0598 0.1443 0.3339
0.8714 1.3942 2.1573
17.4282 13.9419 1'0.7 863
0.005 0.010 0.020
174.2818 139.4187 107.8630
50% EtOH
- 1.1526
alcohol molality range of applicability dropped from 80% a t 0.1 m to 70% a t 0.3 m, to 60% at 0.5 m, and to 40% a t 1.0 m.
Analysis of these data to obtain log a, as a function of ma at these fixed m, values over the alcohol concentration range specified above yield log a, vs. ma plots that parallel
TABLE V : Interpolated Values of a, and a, for the Ethanol-Water-NaC1 Mixtures (Saturated NaC1) %EtOH Ptot 22.5 29.3 33.4 33.8 36.6 58.3 58.7 59.1 59.4 59.6
1.0 2.9 4.8 5.0 7.0 93.5 95.2 97.2 98.6 99.1
Pa
4.8 11.7 15.9 16.3 19.2 51.5 53.0 55.0 56.7 57.4
a,
aa
PW
17.7 17.6 17.5 17.5 17.4 6.8 5.7 4.1 2.7 1.8
0,080 0.196 0.266 0.272 0.321 0.861 0.887 0.920 0.948 0.960
a
The Journal of Physical Chemistry, Vol. 83, No. 21, 1979 2759
Mean Molal Activity of NaCI, KCI, and CsCl in EtOH-H,O
-
0.745 0.741 0.737 0.737 0.732 0.286 0.240 0.173 0.114 0.076
1.0
P
1
0.8
I\
TABLE VI: Potentiometric Determination of Mean Molal Activity Coefficient of 0.1 m (Based on 1000 g of Water) Salt as a Function of Ethanol Content of Liquid Medium
_____-____
0.00 2.41 5.43 9.31 14.50 21.74 32.60 50.72 86.95 195.70
-(E - flo), E, mV mV Ethanol-H,O-NaC1 -62.2 131.2 -46.5 115.5 - 32.0 101.0 -18.1 87.1 73.4 -4.2 78.2 9.2 46.0 23.0 28.3 40.5 5.0 63.8 118.1 -49.3
1.1092 0.9813 0.8581 0.7400 0.6226 0.5081 0.3908 0.2409 0.0426 -0.4196
0.00 2.41 5.43 9.31 14.50 21.74 32.60 50.72 86.95 195.70
Ethanol-H,O-KC1 -49.7 129.7 -35.9 115.9 - 21.9 101.9 - 8.9 89.1 4.2 76.0 16.0 64.3 31.0 49.1 47.3 32.8 68.9 11.3 97.0 - 16.9
1.1134 0.9906 0.8709 0.7602 0.6485 0.5482 0.4193 0.2801 0.0964 - 0.1443
ma
-log a,
TABLE VII: Computation of (a log a,lam,)ma,m, from the Plot of log a, Vs. ma at 0.1 m MCl ma
ams.)ma,mw
ma
0.00 2.41 5.43 9.31 14.50
Ethanol-H,O-NaC1 0.1556 21.70 0.0866 32.60 0.0640 50.72 0.0438 86.95 0.0258 195.70
0.00 2.41 5.43 9.31 14.50
Ethanol-H,O-KCI 0.1540 21.70 0.0940 32.60 0.0716 50.72 0.0508 86.95 0.0346
ams)ma,mw
0.0118 0.0160 0.0128 0.0114 -0.0026 0.0250 0.0192 0.0178 0.0096
TABLE VIII: Computed log a, Values from Vapor Phase Chromatographic Data for the CsCl-EtOH-H,O ma
0 5 10
20 30
log a, -1.121 -0.911 - 0.808 -0.675 - 0.582
ma
40 50 60
70 80
log a, -0.511 - 0.459 - 0.418 - 0.394 - 0.383
each other and differ only by the difference in the mean molal activity of the salt in pure water at the respective m, value^.^ The mean molal activity coefficient values resolved for these systems are presented in Table IX. They are based upon a molality unit that refers to 1000
Figure 7. A plot of log a, vs. ma at m, = 0.1 for CsCI-ethanol-water system as derived from vapor pressure measurements.
TABLE IX: Mean Molal Activity Coefficients of CsCl in Various Alcohol-Water Mixed Media % EtOH
10 20 30 40 50 60 70 80
ma
m s = 0.1 m 2.41 5.43 9.31 14.59 21.70 32.60 50.72 86.95
Y i CsCl
1.0965 1.5136 2.0749 2.8249 4.4058 6.0954 9.7724 16.5196
m s =0.3 m 10 20 30 40 50 60 70
2.41 5.43 9.31 14.50 21.70 32.60 50.72
0.9503 1.317.8 1.7737 2.4148 3.3953 5.0568 8.3345
10 20 30 40 50 60
m s = 0.5 m 2.41 5.43 9.31 14.50 21.70 32.60
0.8791 1.2051 1.6445 2.2440 3.1552 4.6885
10 20 30 40
ms= 1.0 m 2.41 5.43 9.31 14.50
0.7907 1.0864 1.4689 2.009 1
g of mixed solvent rather than to 1000 g of water.
Observations and Conclusions It was found that the values of the ethanol activity varied linearly with the salt molality in a particular ethanol-water mixture (see Figure 8). This behavior was noted at all ethanol and salt molalities with the salts employed. In other words, for a given molality of alcohol-water mixture, a unique (a log ua/amB)ma,hvalue was obtained. On the other hand, plots of (a log ua/ama)m,,m, vs. ma at various salt molalities are curved, each curve paralleling the other, the distance between each curve being dependent on the activity of the salt in water (Le.) the intercept of each curve at ma = 0). This behavior, however, is believed to occur only in dilute salt (say, up to 1 mol/kg) since salting out effects do occurlo at the higher salt concentrations of the alcohol-water mixed media. The same effect occurs when vapor measurements
2760
Yang et al.
The Journal of Physical Chemistry, Vol. 83, No. 21, 1979
Most of the subsequent equations can be expressed conveniently in terms of activities (ai) by substituting d log ai for dui; dui = R T d In ai and the constant 2.303RT cancel out of the equations. Equation A3 can be expressed in general form as
or
1
0
I
1
I
0.3
0.3
0.9
ms (m)
Flgure 8. A representative plot of a, vs. m, for NaCI-ethanol-water system (40 % by weight ethanol-vapor pressure measured).
are made at higher salt concentrations. The thermodynamic soundness of the electrochemical measurements of NaCl and KC1 dissolved in alcohol-water mixtures with glass Na+ and K+ ion selective electrodes, in conjunction with Ag-AgCl electrodes in this research program, has been verified by demonstrating the identity of two cross-differential terms in the Gibbs-Duhem equation for ternary systems. The (a log a,/am,), m, term, measured electrochemically, has been shown to be equal term, evaluated by the chroto the (a log aa/am,)ma,mw matographically based method. The good correspondence of these cross-differential terms obtained by independent experimental approaches provides a meaningful substantiation (Figures 4 and 5) of the validity of the two kinds of measurements. With the mean molal activity data that have been measured in this phase of the research program all information essential to proper examination of the utility of the Gibbs-Donnan model for interpretation of ionexchange equilibria between zeolite A and uni-univalent alkali halides in ethanol-water mixtures has been obtained.
Appendix The Gibbs-Duhem Equation and Its Application to Ternary Systems. The complete differential of the Gibbs free energy for a system of three components a t constant pressure and temperature can be written as d F = u1 dnl
+ u2 dn2 + u3 dn3
and
u2 = (aF/an2)nl,n3
(E)ms,mw
2.303RTv, A log ys =-
esF
(
r ) m B , m w
('5)
If the measured ratio (left-hand side of eq A5) varies linearly with nonelectrolyte molality, the ratio of the finite differences given on the right-hand side of eq A5 may be replaced by a partial derivative. Spink and SchrierlO and Wilcox and Schrierll have shown that, in alcoholwater-salt systems, this is the case. Equation A5 may therefore be written
and, using the cross-differentiation relationship from eq A4b, the above equation becomes (A71 so that from eq A4a,b
(AI)
where nl, n2, and n3 represent the number of moles of components 1, 2, and 3 in a ternary system, F is the corresponding Gibbs free energy, and ul, u2, and us are the chemical potentials of the components. Then u1 = (aF/anl),,,,,
where e is the number of moles of electrons involved in the reaction, yi is the activity coefficient for component i, and u is the number of species constituting each component of a particular system. Equation 4 is the basic Gibbs-Duhem cross-differentiation equation for ternary systems. With it the activity of all components can be detailed with the experimental measurement of the activity of one component. It has been used in this study to compute the activity of NaCl and KC1 from the ethanol activity measurements obtained in the chromatographic studies of the salt-ethanol-water systems for comparison with the values obtained directly from these components in the potentiometric measurements detailed above. To facilitate this analysis the activity computations have been based on 1000 g of water. The emf data are interpolated to yield constant salt molality during the variation of ethanol molality. The change in potential E with alcohol concentration (ma) a t constant water (m,) and electrolyte (m,) is
a log a,
a log a,
(Ma)
and
(A21
The quantity on the right-hand side of eq A8a is the slope of a plot of log a, vs. ma (at constant ma, m,), readily available from the direct emf measurements. By the same token, the left-hand side of the same equation is also the slope of a plot of log a, vs. m, (at constant ma, mJ, which
Reduction of Ni Ions in X-Type Zeolite
is obtained from the vapor phase chromatographic measurements.
References and Notes (1) (a) Warner Lambert Company, Research Institute, Chemical Research Department, Morris Plains, N.J. 07950. (b) Christopher Newport College, Chemistry Department, Newport News, Va. 23606. (c) Chemistry Department, Creighton College, Omaha, Nebr. (d) FMC Corporation, Agricuttural Chemical Division, Middleport, N.Y. 14105. (2) S. Bukata and J. A. Marinsky, J. fhys. Cbem., 68, 994 (1964). (3) R. B. Barrett and J. A. Marinsky, J . fhys. Cbem., 75, 85 (1971). (4) R. 6.Barrett, J. A. Marinsky, and P. Pavelich, Adv. Chem. Ser., No. 101, 414 (1971).
The Journal of Physical Chemistry, Vol. 83, No. 21, 1979
2761
(5) H. J. Arnikar, T. S. Rao, and A. A. Bodhe, J. Chem. Educ., 47, 826 (1970). (6) P. Schnipelsky, J. F. Solsky, and E. Grushka, J . Chromatog. Sci., 12, 45 (1974). (7) J. Timmerman, Ed., “PhysicoChemical Constants of Binary System”, Vol. 3, Interscience, New York, 1960. (8) A. S . Brown, J. Am. Chem. Soc., 56, 646 (1934). (9) R. A. Robinson and R. M. Stokes, “Electrolyte Solutions”, 2nd ed, Butterworth, London, 1959. (10) M. Y. Spink and E. S. Schrier, J . Chem. Thermodyn., 2,821 (1970). (1 1) F. L. Wilcox and E. E. Schrier, J . fhys. Cbem., 75, 3757 (1971). (12) With the CsCl containing systems stability of chromatographic performance was checked much more frequently (after each measurement) with the anhydrous ethanol standard.
X-ray Diffraction Study of the Reduction of Nickel Ions in X-Type Zeolite J. Jeanjean,
D. Delafosse,”
Laboratolre de Chimie des Solides, Universit6 Pierre et Marie Curie, 75230 Paris, Cedex 05, France
and P. Gallerot Institut de Recherches sur la Catalyse, 69626 Villeurbanne Cedex, France (Received March 16, 1979)
The crystal structure of NiNaPt-X zeolite has been determined to locate the nickel cations before and after hydrogen reduction. In the zeolite activated at 733 K under vacuum, 12 Ni2+out of 17 present in the unit cell occupy SI sites (hexagonal prisms) and 3 Ni2+occupy SIIsites (supercages). On hydrogen reduction at 633 K only the Ni2+ions from SIIsites are reduced and well-dispersed nickel is formed. On reduction at 788 K there are only 5 Ni2+left on SI sites; the other cations are reduced and agglomerate into large particles. a Lindemann glass capillary where the treated zeolite was Introduction transferred for the X-ray investigation. Three samples In recent years the preparation of very small metal have been prepared: sample A is the activated zeolite, particles has been a subject of growing interest. Easily samples B and C have been reduced at 633 and 788 K, reducible cations of refractory metals can lead to highly respectively. dispersed metal encaged in the zeolite; this holds for Crystal Structure Determination. Crystal structures platinum1 and for most other noble metals of group VIII. were determined from powder data as previously deOn the other hand, stabilization in a zeolite matrix of metal scribed: The overlapping of X-ray diffraction lines at high of the first transition row is more difficult to obtain. Thus, Bragg angles was more severe for NiNa-X zeolites, esthe reduction by molecular hydrogen of nickel in faujapecially after high temperature reduction, than for NiNa-Y site-type zeolites is complete only at 873 K and large zeolites. The crystal structures of samples A and B were particles are formed. Even at lower reduction temperarefined with only hkl reflections with N = h2 + k2 + l2 < tures a broad size distribution of metal particles is gen299 and, in the case of sample C, N < 243. Due to the erally observed. Systematic studies have been undertaken limited set of data available the temperature factors of the to analyze the factors governing the reducibility of Ni2+ atoms were not allowed to vary during the least-squares ions in faujasite-type zeolites and the optimum conditions for obtaining well-dispersed nickel have been establi~hed.~,~ refinement. One of these conditions is the introduction of traces of Results and Discussion platinum in the zeolite which favors the reduction and can The limitations of the method have been previously lead to nickel particles of 20 A diameter. In this work discu~sed.~ Even if more accurate diffraction data were the reduction process of a NiNaPt-X zeolite has been available (e.g., from single crystal) extraframework species studied by X-ray diffraction. Location of Ni2+ cations sited outside the symmetry axes could not be located before and after reduction should indicate from what sites because the occupancy factors of atoms in general positions the Ni2+cations are removed first and why other cations are too small. Moreover, two cations of a different nature are less easily reduced. cannot be easily distinguished from each other because of Experimental Section the fractional occupancy of cations sites unless one of them Materials. The nickel zeolite was prepared from Linde exhibits an overwhelming preference for a given site. The Na-X zeolite by ion exchange in nickel nitrate water standard errors given by the least-squares refinement are solution (0.05 mol dm-3). The zeolite was subsequently ion therefore greatly underestimated. exchanged in Pt(NH3)4C12solution. The unit cell comIn the three samples investigated, scattering matter was position determined by chemical analysis of nickel, found mostly on SI (hexagonalprisms), SI,(sodalites), and platinum, and sodium is Ni17Pt0.5Na40Hll-X. After SII (supercages) sites. Assigning these sites to nickel or washing and drying the zeolite was activated by heating sodium was based on the distance from sites to framework at 733 K for 16 h under vacuum, then reduction was oxygen atoms and on the evolution of site occupancy after carried out under 6650 Pa (N m-2) hydrogen pressure for hydrogen reduction treatments. The platinum (0.5 atom 25 h. Treatments were performed in a cell connected to per unit cell) is probably in metallic form because the
-
0022-3654/79/2083-2761$01 .OO/O
0 1979 American
Chemical Society
