NOTES
412
lower valence states' and the reduced oxide has a different color from that of the unreduced oxide. Thus, WOShas a yellow color and reduces initially to blue WrOll and then to brown WOZ. Hydrogen molecules accomplish the reduction above 200°, but not a t room temperature.2 The Pt-A1203 catalyst used in this work is a reforming catalyst prepared as described in the literature. The catalysts mere made by impregnation of the support with aqueous chloroplatinic acid followed by drying a t 550' for 1 hr. The support is a y A & 0 3 and is commercially available. The pure hydrogen was passed over 1lr03 or mixtures of WO, with either -?.1203 or Pt-hlzO3 a t room temperature in a 1 X 5 in. glass tube. Table I shows the results for equal volumes of the various mixtures.
H . or H + as a two-dimensional gas on the surface and diffusion through interparticle contacts from particle to particle. One possible mechanipm would be Pt
Ha --+ 2 F . AlzOs
2H. 2H.
(1)
Table I
A B
c
Vol. % FOs
Vnl. AlzOa
Vol. % Pt-AlzOs
100 50 50
..
, ,
50
, ,
, ,
50
Initial color
Time, min.
Final
Yellow Yellow Yellow
300 300
Yellow Yellow Blue
1
(4) (5)
H. R. Melville and J. C. Robb, Proc. R o y . Soc. (London), A196, 445 (1956). L. G. Austin, I n d . Eng. Chem., 53, 660 (1961). F. G. Ciapetta and C. J. Plank, "Catalysis," Vol. 1, Reinnold Publishing Corp., K'ew York, N. Y . , 1954, p. 316. L. Spenadel and M.Boudart, J . P h y s . Chem., 64, 204 (1960). S. Khoobiar, P. J. Lucchesi, and J. L. Carter, to be published.
color
All the powders were dried a t 150" in drying ovens prior to use and had a grain size of 500-800 M. The powders were thoroughly mixed a t room temperature manually.
These results demonstrate directly that Hz a t room temperature does not reduce W03when it is alone or mixed with A1203,but does reduce W03 readily in the presence of Pt-d1903. When the temperature is increased to 50°, mixture C converts instantaneously to a blue color, but in order to change the color of h and B, higher temperatures are required (200-500°). The effectiveness of Pt-A1203 in bringing about the color change is attributed to dissociation of the hydrogen on Pt, followed by migration of H atoms to was.
Discussion of Results The dissociation of Hz on Pt-A1203 can be inferred from Hz chemisorpt,ion studies4 and from various related studies including the known ability of these systems to catalyze reactions such as H2-D2 exchange. The present experiments offer direct and conclusive evidence for this dissociation even a t room temperature and, more important, for a subsequent migration of the dissociated products. Unpublished data from this laboratory5 based on electrical conductivity measurements have shown that hydrogen can exist as H + on AlzO,q. Although the details of the migration are of course unknown, one can postulate migration of either T h e Journal of Physical Chemistry
+ 4\4-03 -+- W4011 + H,O H . + H. +H,
This finding is very important since it sheds some light on the more elusive steps involved in catalytic reactions involving Hzon supported metal catalyst systems.
(2) (3)
MixtureQ
2H+ 2(e) -
Hartlep Band Extinction Coefficients of Ozone in the Gas Phase and in Liquid Nitrogen,
Carbon Monoxide, and Argon
by William B. DekIore and Ode11 Raper Calijornia Institute o j Technology Jet Propulsion Laboratory, Pasadena, California (Receiced September 6 , 1965)
I n the course of work on the photolysis of 03, we have determined the 03 extinction coefficients in the region 2000-3100 A. in liquid Sz and CO at 77.4"K. and in liquid Ar a t 87.5'K. Previously, 03 extinction coefficients have been reported in aqueous s o l v e n t ~ l -and ~ in CC14,j but the only data for low temperature solvents are those of Kirshenbaum and Strengs for the visible absorption of O3 in liquid 0 2 . In the gas phase, differing extinction coefficients in the Hartley band were reported by Ny and Choong,' (1) (2)
(3) (4)
(5) (6)
(7)
H. Taube, Trans. Faraday S O C . ,53, 656 (1957). J. Weiss, i b i d . , 31, 668 (1935). 11. G. Alder and 0. R. Hill, J , Am. Chem. SOC.,72, 1884 (1950). M . L. Kilpatrick, C. C. Herrick, and 1t.Kilpatrick, i b i d , 78, 1784 (1956). G. W. Robinson, M.S. Thesis, Georgia Institute of Technology, 1949. A. 0 . Kirshenbaum and A. G. Streng, J . Cham. Phys., 35, 1440 (1961). T.-2. Ny and S.-P. Choong, Chinese J. Phys., 1, 38 (1933).
NOTES
Vigroux,8 and Inn and Tanaka.9 The Inn and Tanaka results have subsequently been verified closely by Hearng a t six wave lengths and are considered to be the most reliable vaJues available. We have measured the gas phase extinction coefficients throughout the region 2000-3100 A. and our results are in close agreement with those of Inn and Tanaka.
Experimental Reagents. Ozone was prepared by a Tesla coil discharge in purified O2 and stored at 77°K. Transfer of O3 to the absorption cells was accomplished by distillation from a liquid argon bath and collection at 77°K. Following the transfer, residual tracles of O2 were removed by pumping on the O3 under high vacuum. The solvents (Xz, Linde high purity dry; CO, Matheson C.P.; Ar, Linde tank grade) were passed through a Drierite-Ascarite column, liquefied, and further purified by two distillations, taking the center fraction in each case. Argon was handled using liquid argon as a coolant. Apparatus. Spectra were recorded on a Cary Model 11 spectrophotometer. The wave length scale wa,s calibrated by means of a low pressure mercury arc, and the wave lengths reported in this work are considered reliable to A2 A. Gas phase spectra were taken in a 5-cm. cylindrical quartz cell, the 0 3 being sealed off in the cell under vacuum. The liquid cell was a 1-cm. cylindrical quartz cell, with an annular quartz jacket for the coolant, suspended in a vacuum canister with quartz windows. The entire unit could be placed in the spectrophotometer. Since the light path did not pass through the coolant and the solution was free of turbulence, the quality of the spectra was comparable to that of ordinary room temperature solvents. Optical densities of aqueous solutions of chromium nitrate were found to be identicstl within 0.59;b in the above cell and in standard I-cm. cylindrical cells, with an appropriate zero correction. Measurement of gaseous 02,from decomposed 03, was done by means of a calibrated gas buret which was similar in consitruction to a nlcLeod gage, witjh the exception that the measuring stem had a stopcock to permit the O2 to be collected by Toepler pump action. Calibration of the gas buret was checked by measurement of known samples in a standard volume a t a pressure measured on a 0-20 mm. Walllace and Tiernan gage which was calibrated by means of a JIcLeod gage. The gas buret is considered accurate to 2% or better. Methods. Ozone concentrations in the low temperature solvents wclre determined by separately measuring
413
the amount of O3 spectrophotometrically in gas cells, using the relation [O3Isolvent
=
[03]gasVgas/Vsolvent
The volumes, Vgas and Vsolvent,were determined b!r filling the cells with water from a buret or by weighing the water. To ensure against errors due to loss of O3 in transfer, the following three separate methods were employed in the initial experiments with solvent. Method 1 . The O3 peak optical density (2553 A.) was measured in a sealed-off gas cell and the O3 was then transferred to the liquid cell at 77"K., using glass blown connections and break-off seals exclusively. In transfers of this type all glassware in contact with the O3 sample was pre-exposed to O3 a t higher pressures. The solvent was then condensed into the cell and the spectrum was recorded. Zero corrections for the liquid spectra were made by taking the spectrum of the cell containing solvent only. Afethod 2 . The spectrum was first recorded in solution, followed by removal of the solvent by pumping a t 77OK. and subsequent transfer of the O3 to the gas cell. Although more difficult than method 1, this technique gave results which were within 1% of those of method 1. Since methods 1 and 2 give upper and lower limits, respectively, for O3 concentrations in solution, convergence of the results eliminates the possibility of error due to 0 3 loss in transfer. Method 3. I n this method, which was the simplest experimentally, gaseous O3 was placed in the low temperature cell and the spectrum was recorded. The O3 was then condensed by addition of coolant to the annular jacket and the solvent was condensed into the cell, and the spectrum was then taken. Although this method suffered somewhat from an unfavorable volume ratio (the volume of O3 in the light path was about the total gaseous volume), the results were equal to within 1% of those from methods 1 and 2. Therefore, method 3 was used exclusively for the solvents Ar and
co.
Ozone concentrations in the gas phase were determined by converting the O3 to 02,by means of heat or ti Tesla spark coil, and then measuring the O2 in the gas buret. The technique was as follows: a sample of pure O3 was sealed off in the (well-baked out) 5-cm. cell, with two break-off seals attached, and the peak (2653 A.) was measured. The cell was immediately placed in liquid X2to quench O3 decomposition, and the ~~
~
~
~~~~~~~~~~~~
(8) E. Vigroux, Ann. phys., 8 , 709 (1953). (9) E. C. Y. Inn and T. Tanaka, "Ozone Chemistry and Technology," Advances in Chemistry Series, No. 21, American Chemical Society, Wmhington, D. c., 1959, p. 263; J . Opt. SOC.Am., 43, 870 (1953).
Volume 68, Number 23
February, 196.4
NOTES
414
cell was then opened to high vacuum by means of one of the break-off seals. After removal of any 0, or other volatile gases, the cell was resealed (while pumping) and the 0 3 was decomposed. The cell was then placed in a Dry Ice bath and attached to the gas buret, and the O2 was admitted to the gas buret through the second break-off seal. Extinction coefficients a t other wave lengths in the region 2000-3100 A. were then determined relative to the peak value by taking the spectrum of O3 with about 10 cm. added O2 (no pressure effect was noted). This method has the advantage that 0 3 decomposition is sufficiently inhibited so that no corrections are necessary.
200 I80
I60
-
I40
I
a 120
I-
z E
100
9
k-
80 60
40 20 0
2000
2200
2400
2600 WAVELENGTH,
2800
3000
1
Figure 1. Extinction coefficients of zone. (To obtain K values for N2, Ar, or CO, subtract 20, 40, or 60, respectively, from the value indicated on the ordinate.)
Table I : Ozone Extinction Coefficients Obtained by Different Workers (em. P;ITP)-' Wave length,
A.
Inn and Tanaka
Presenl
2102 2152 2202 2252 2302 2352 2362 2372 2382 2392 2402 2412 2422 2432 2452 2478 2500 2519 2537 2539 2553 2587 2604 2624 2643 2675 2702 2752 2802 2852 2894 2902 2052 2RCi7
6.39 11.7 21 .o 34.3 52.8 73.6 78.2 83 2 86.2 90.1 95.3 98.9 103 107 116 124 130 133 (133.1)" 134 135 133 128 123 118 103 89.1 66.6 43.6 27.5 (17. I )" I 3 ,5 8 33 (6.72)"
6 33 12 1 21 4 34 8 53 5 74 6 79 8 84 1 88 9 93 1 97 3 102 105 5 110 118 125 130 134 5 135 135 137 134 5 129 123 5 117 5 103 91 1 66 9 45 6 28 0 17 3 15 6 8 5 6 85
work
A P inic:rpol:it,c:d by ITcarn, ref. 9.
Results and Discussion
Hearn
The extinction coefficients of 0 3 in liquid Kz,CO, and Ar, and in the gas phase, are shown in Fig. 1. The concentration ratios were determined to within 2% and therefore, coupled with a 2% uncertainty in the gas phase extinction coefficients, the solvent values are believed to be reliable to within 4%. Values for the gas phase extinction coefficients obtained by Inn and Tanaka, Hearn, and in the present study are listed a t several wave lengths in Table 1. Our results are for the most part 1 or 2% higher than the Inn and Tanaka values, and near the maximum seem to be in better agreement with the values found by Hearn. Agreement with the Inn and Tanaka reeults is poorest in the region from about 2375 to 2450 A., where the Inn and Tanaka values fall as much as 374 below ours. We have rechecked out data in this region and find no error.
133 9
Concerning the Densities and Temperature Coefficients of Liquid Barium and Calcium
by h. T'. Grosse and P. J. AlcGonigal' The Research Instttute of Temple University, Philadelphza, Pennsylvania (Received June 14, 196'3)
17 2
6 97
The density of liquid barium has been measured recently by =\ddison and Pulhani2 and the density of liquid calcium mas measured previously by Culpin3 in connection with his viscosity studies. KO other data are available. The present authors have had
