NOTES
655
Table I : Refractive Iindex of Anhydrous HF a t 25" x
n
4358.3 4861.3 5892,6 6862.8
1,1598
1,1586 1.1574 1.1567
on the basis of a molecular weight of 20.01 using the sodium D-line index is 2.13 cc. The refractive index as a function of the wave length can be represented within *0.0001 unit through the visible region by the simple Cauchy type equation 0.001025 _ A
n = 1.15436 -I- _
~
The temperature coefficient of the refractive index is -0.0004.
Acknowledgments. The continued encouragement of H. H. Hyman and the staff a t Argonne National Laboratory is gratef Ltlly acknowledged.
prior to testing was carried out a t 400' for 6 hr. a t a flow rate of 100 cc. (STP) Hz/min. The hydrogen was purified bv passage through a "Deoxo" unit and over Linde 5A Molecular Sieves. The catalyst supports were commercial grades of Davison 11-alumina and Davison silica gel. They were calcined for 3 hr. at 500' prior to impregnation from aqueous solutions of nickel nitrate as described prev i o u ~ l y . ~The samples were oven-dried at 100' for 2 hr., then calcined a t 500' overnight. Supported cobalt, tungsten, and platinum catalysts were prepared in a similar manner using solutions of cobaltous nitrate and ammonium metatungstate, and a 10% solution of platinum chloride. The compositions and surface areas of these catalysts are listed in Tahle I. The decomposition of ammonia was determined by collecting portions of the desorbed gas and submitting for gas analysis.
Table I : Surface Area of the Metal-Promoted Alumina.
Metal
co
Ammonia A'dsorption on Rletal-.Promoted Nf
0 4 1 3 5 9
by R. T. Barth and R. N. Pinchok Gulf Research d% Development Company, Pittsburgh, Pennsylvania (Received October 14,1968)
W
Experimental The ammonia adsorption technique was identical with that, described previously' except that reductioln
0 5 1 0 2 2 4 1
Catalyst Systems
The surface acidity of acid catalysts such as silicaalumina has been characterized by means of ammonia adsorption-desorption measurements.' Here the volume of ammonia adsorbed was measured as a function of the catalyst temperature, and the acid strength of the surface was determined from the relationship between catalyst temperature and the volume of adsorbed ammonia.2 This measurement has now been extended to include a series of supported metal catalysts. Alumina and silica were selected as the catalyst supports because of the distinct difference in their acid properties. The silica surface has approximately one-fifth the capacity for ammonia adsorption as the alumina surface. The metals used in this study included nickel, cobalt, platinum, and tungsten.
Wt. 70 metal
6 8 5 5
1 0
20 1 199 199 194 206 200
200 193 178
13 3
186 184 179 167 169
0 8
200
18
196
3 5 5 5
10 3
Pt
Surface area, m.a/g.
Results The ammonia data obtained from met,al-alumina systems are presented in Fig. 1 and 2. The amount of ammonia chemisorbed a t 175' (the initial adsorption temperature) and 515' (the final desorption temperature) is plotted as a function of metal concentration. The results in Fig. 1 show the effect of nickel and co(1) R. T. Barth and E. V. Ballou, Anal. Chem., 33, 1080 (1961). (2) A. N. Webb, I n d . Eng. Chem., 49, 261 (1959). (3) G. T. Rymer, J. M . Bridges, and J. R. Tomlinson, J . Phus. Chem., 65,2152 (1961).
Volume 68, AVumber S March, 1864
Koms
656
o' Y
b
o ,'
2 -_--___-io io
5'0
0-0 XNI
XCO
Figure I . ZiH3adsorption on metal-promoted alurnins supports: -U, pretreated under vacuum; -e-, pretreated with hydrogen.
001 [
1
121203 are prescnted in Ia'ig. 2 . The increased ammonia adsorption with increasing metal conceiltration is again evident, particularly at the lower concentration of tungsten and platiiium. The reduction of these catalysts appeared to have little cffcct on the ammonia data; however, \\-
