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1470
that were not exposed to oxygen. Therefore, the soluble platinum(1V)-alumina complex postulated by McHenry, et al., does not exist under reforming conditions, i.e., after reduction with hydrogen. Upon intentional oxygen exposure of the reduced catalyst, considerable amounts of platinum appeared as the soluble form. Because soluble platinum was obtained in the absence of alumina and in the absence of chloride, there is no evidence for a specific soluble platinum complex. A possible alternative for the species dissolved by H F may be metal upon which oxygen is chemisorbed. Both hydrogen3 and carbon monoxide2 chemisorption studies 011 reduced catalysts have been interpreted to indicate that the platinum is a very highly dispersed form. Thus, a large fraction of the platinum atoms is on the surface and available for chemisorption of oxygen. These particles, because of their small size, have exceptionally high surface energies. The very low value for soluble platinum in Experiment !3 shows that the chemisorbed oxygen is removed readily by hydrogen a t room temperature. This is consistent with recent work by Chon, Fisher and Aston,6 which showed by a calorimetric technique that chemisorbed oxygen (or hydrogen) on platinum can be quantitatively titrated at room temperature with hydrogen (or oxygen). CALIFORXI& RESEARCH CORP. RICHMOND. ClLIFORNI.4
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Vol. 65
typical specimen, together with the spacings4 for Fe304,are shown in the table. hkl
d FesOd
d
I
hlcl
dFeaO4
I
m v \v IllW
v\v mw ms mw mrv ms ms
inci-
The agreement is excellent; t’he value of the lat’tice constant (a = 8.39 A,) is quite differpt from the value quoted by Shishakov ( a = 8.97 A). That the spinel pattern is not due to an oxide of gold is shown by its absence from the diffraction pattern .of oxidised S.S. gold and by its remaining unchanged on the surface of “fine” gold after electrochemical reduction under conditions which Tyould have been expected to reduce gold oxides.
ROYAL AIRCRAFTESTABLISHXENT FARNBOROUGH, HAMPSHIRE HARRIS E. KLUKSDAHLE X G L a S D ROBERT J. HOUSTOX RECEIVED JULY 5 , 1961
( 6 ) H. Chon, R. A,. Fisher, and J. G. Aston, 1055 (1960).
d
111 4.86 a 533 1.279 1.282 622 1.266 220 2.97 2.99 R 311 2.53 2.54 vs 444 1.209 1.211 222 2.425 2.439 w 711 1.174 400 2.097 2.107 s 642 1.120 1.123 33 1 1.937 w 553,731 1.091 1.093 422 1,714 1.716 ms 800 1.048 1.050 333,511 1.615 1.622 s 660,882 0.988 0 989 440 1.484 1.485 s 751,555 0.968 0 969 531 1.421 V K 840 0.938 0 939 620 1.326 1.328 w 5 S o t observed owing to heavy background close t o dent beam.
D. CLARK T. DICKINSON IT. N. MAIR
J. Am. Chem. Soc., 8%
OX T H E OXIDATION OF GOLD Sir: The evidence for base-metal oxides on the surface of oxidisecl gold’ has been questioned recently by Tu‘. A. Shisbakov,Z but the evidence appears to us to be conclusive. Samples of Spectroscopically sta,ndardised (S.S.) gold (Pb, 3 ppm.; Cu, Ag, Na, Ca, Fe and Mg, each less than 1 ppm.) and “fine” gold (0.05% impurity, mainly Ag) behaved differently on oxidation. We found no evidence for the exist’enceof oxides of gold on the surfaces of bulk samples which ha,d been heated to 900’ either in air at atmospheric pressure or in oxygen a t 3 X mm., although their existence in thin gold films heated to 300--500° has been r e p ~ r t e d . ~Fe, Sn a,nd P b were detected spectrographically in the “fine” gold and their presence on the surface of oxidised “fine” gold Jvas demonstrated conclusively by X-ray emission analysis; the presence of Fe was supported by electrochemical evidence.’ 1 spinel pattern usually was obtained, by electron-diffraction, from t~hesurface of oxidised “fine” gold, but never from the surface of the much purer S.S. gold subjected to the same treatment. The lattice parameter varied from yecimen to specimen within the range 8.34 t>o8.39 A. The observed line intensities ( I ) and interplanar spacings ( d ) for ;I (1) D. Clark, T. Dickinson and 1%’.N. &fair, Trans. I+’araday Soc., 55, 1937 (1959). (2) N. A . Shisliakov, J . P h g s . Chem., 64, 1880 (1960). (3) Moodie, -4cta Cryst., 9, 998,(1956).
(4) H. P. Rooksby, “Identification of Clay Minerals.”
GAh‘IMA-IRRADIATION OF ISOPROI’YLBEXZENE ADSORBED OY RIICROPOROUS SILICA-ALUMINA
Sir: A study is in progress at this laboratory of the gamma irradiation of isopropylbenzene adsorbed on various solids. Isopropylbenzene has been irradiated with cobalt-60 gamma rays in the presence of a microporous silica-alumina (10% alumina) with a surface area of 400 m.2/g., pore volume of 0.43 ml./g. and particle density of 1.15 g./ml. This heterogeneous system has been studied at 36’ over a range of composition expressed in terms of the electron fraction, F , of isopropylbenzene from 0.0017 to 1.0. For comparison purposes the radiolysis of pure isopropylbenzene has been studied over a wide range of conditions (from liquid a t 36’ to gas a t 400’ and a t 0.5 and 1.0 atm.) and will be reported in a subsequent paper. I n Table I some typical results selected from these studies are compared. SignificantJy, t h t benzene yield is increased relative to the yields of all other products in the heterogeneous system, and the yields for isopropylbenzene cwiversion and benzene formation are higher in the presence of t h c solid than in the pure liquid at the same temperature even though the radiation is absorbed overwhelmingly in the solid. Plots of produrt yields as a function of electroii fraction, F , of isopropylbenzene are similar in nature to those recently reported by Sutherland and Allen’ for most products; however, the results for hydrogen for-
