NOTES
3003
of these results, it is important to consider factors such as differences in the crystallite size and reducibility of the nickel in the catalysts. Useful information of this type can be obtained from magnetic Therefore, it was decided to obtain magnetic data on these particular catalysts, which include nickel supported on alumina, silica, and silica-alumina at concentrations of 1 and 10% nickel. I n this report, the catalytic properties of these samples are considered in the light of the information obtained from the magnetic studies.
I 19
I 20
I 22
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21 X
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23
lo-’ ( *K)
Figure 4. Equilibrium distribution of the nitrogen isotopes in the ambient of a flow system as a function of the temperature of the ion gauge filament.
that of IC or 56.5 kcal, which compares well with the 58 kcal observed. The ambient distribution of nitrogen isotopes is shown as a function of ion gauge filament temperature in Figure 4. The increase in 14N15Nand decrease in 14N2 and lSN2(the input gases) above 2100°K is apparent; part of the decrease is attributed to pumping by the glass walls.
Catalysis over Supported Metals. VI.
The
Application of Magnetic Studies in the Interpretation of the Catalytic Properties of Nickel
Experimental Section Apparatus and Procedure. The Faraday method was used to determine the magnetic properties of the supported nickel catalysts. The apparatus is similar to others described in the l i t e r a t ~ r e . ~ The ~ ’ ~ sample, in a quartz bucket, was suspended from a Cahn electrobalance which was used to measure the force on the sample. A Varian 4-in. magnet with “constant gradient” pole pieces and a 2-in. gap provided magnetic fields up to 6500 gauss. The vacuum system was arranged so that samples could be reduced in situ in flowing hydrogen. Pressures of low6 torr were readily attainable in the apparatus. The standard procedure included reduction of the catalyst overnight at 370” in a hydrogen flow of 500 cc/min. The sample was then outgassed at the same temperature for 30 min. The magnetic measurements were made either in vacuo or in helium. If the measurements were made in vacuo, the approach to liquid nitrogen temperature was very slow, with a temperature of 85 to 90°K being the practical lower limit. In most cases a small amount of helium was added to facilitate the cooling to 80°K. The catalysts used in these studies have been described previously.’!
Results by J. L. Carter and J. H. Sinfelt Esao Research and Enuineering Company, Linden, New Jersey (Received March 8, 1966)
I n previously reported studies from this laboratory, it was shown that the catalytic activity of nickel for ethane hydrogenolysis varied markedly when the nickel was supported on different oxide carriers.’I2 From hydrogen chemisorption measurements it was concluded that the variations in nickel surface areas on the different supports were small compared to the variations in catalytic activity. In other words, the specific catalytic activity of the nickel varied with the support. It was also shown that the specific catalytic On a given support varied activity Of with the nickel concentration. In the interpretation
Typical data on t h e effect of field strength on specific (1) W. F. Taylor, D. J. C. Yates, and J. H. Sinfelt, J . Phys. Chem., 68, 2962 (1964). (2) W. F. Taylor, J. H. Sinfelt, and D. J. C. Yates, ibid.,69, 3857 (1965). (3) P. W. Selwood in “Catalysis,” Vol. I, Reinhold Publishing Corp., New York, N. Y., 1954, p 353. (4) P. W. Selwood, “Adsorption and Collective Paramagnetism,” Academic Press Inc., New York, N. Y., 1962. ( 5 ) P. W. Selwood, T. R. Phillips, and S. Adler, J . Am. Chem. SOC., 76, 2281 (1954). (6) P. W. Selwood, S. Adler, and T. R. Phillips, ibid., 77, 1462 (1955). (7) P. W. Selwood, ibid., 78, 3893 (1956). (8) D. Reinen and P. W. Selwood, J . Catdyaia, 2 , 109 (1963). (9) P. W. Selwood, “Magnetochemistry,” 2nd ed, Interscience Publishers, Inc., New York, N. Y., 1956, pp 11-13. (10) P. E. Jacobson and P. W. Selwood, J . Am. Chem. Soc., 7 6 , 2641 (1954).
Volume 70, Number 9 September 1968
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3004
60 REDUCED A T 37OoC., SINTERED A T 800'C.
REDUCED 1 6 HR. AT 370%.
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Figure 1. Specific magnetization of nickel on different supports.
magnetization at 80°K are given in Figures 1 and 2. I n Figure 1, the data were obtained on the catalysts after reduction in hydrogen for 16 hr a t 370", followed by evacuation at 370". The specific magnetization increases with increasing field strength and is higher when the nickel is supported on silica-alumina than when it is supported on alumina or silica. Furthermore, for a given support, the specific magnetization increases with increasing nickel concentration. It should be noted that the specific magnetization does not approach that of bulk nickel for any of the nickel catalysts shown. At 80"I
