P L A T I N J M BLACK CATALYSTS
I. Physical Properties and Catalytic Activity* BY GUY B. TAYLOR, GEORGE B. KISTIAKOWSKY AND JOHN H. PERRY
Introduction Platinum is among the oldest known contact catalytic agents. It is widely used for a variety of chemical reactions both in the plant and laboratory. The present investigation is an attempt to correlate the catalytic activity of three samples of platinum black prepared by different methods with other properties of the preparations such as particle size and adsorptive characteristics. I n these studies several members of the staff of this laboratory have participated. Part I is concerned with physical properties and catalytic activity. Part 11, to follow, is a study of heats of adsorption. Preparation of Samples No. I was prepared by heating precipitated ammonium chloroplatinate in a stream of hydrogen a t zoo°C. followed by a stream of nitrogen a t 250300OC. for 2 4 hours. The sample contained a little ammonium chloride. No. z was prepared by pouring an aqueous solution of platinic chloride and formaldehyde into boiling sodium hydroxide solution. The precipitated platinum was washed with dilute hydrochloric acid followed by hot and cold water for several days. Sodium could still be detected spectroscopically. No. 3 was prepared by reducing platinic chloride solution with hot hydrazine hydrate solution and washing the precipitate free of the chloride ion. Structure of Samples The X-ray diffraction patterns of the three samples were obtained by the standard procedure with the General Electric Multiple X-ray Diffraction Apparatus, which uses filtered molybdenum radiation. The lines in all cases corresponded to pure platinum. The pattern of sample No. I was characterized by clear, sharp lines extending the entire length of the film. Nos. z and j gave patterns with broad, diffuse lines which faded out for the larger angles of diffraction. These differences indicate that the crystallites in No. I were considerably larger than those in the other two samples. They were, in fact, outside the range of measurement by the X-ray method, Le., larger than Io-ssm. Kos. 2 and 3 could not be differentiated by X-ray methods, and their crystallites, as calculated by the Debye-Scherrer formula for line breadths, were of the order of 30 A.U. The X-ray photographs are shown in Fig. I .
* Contribution No. z z from the Experimental Station of E. I. du Pont do Semours and Company.
... .
.. I 11 Ill
. .
. . -.
.
..
.. ..-
.. . . .
750
G. B. TAYLOR, G. B. KISTIAKOWSKY AND J. H. PERRY
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Reaction ~ H Z0 2 = SHZO Electrolytic gas equivalent to 15 mg. € 1 2 0 per 5 min. interval' was added to either zoo cc. hydrogen or 115 cc. oxygen flowing per minute over 0.2 g. of the samples, unheated. The efficiency of reaction was in every case 100% for catalysts Nos. I and 2. KO.3 was not tested.
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Reaction S N O 5 H 2 = BNH3 2 H 2 0 Hydrogen containing 370 nitric oxide was passed over o.jg. platinum. At rates of 2 0 0 cc. per minute the conversions to NH3 without heating the catalysts were high. Addition of carbon monoxide, 2 to 3 7 c J definitely poisoned the reduction a t temperatures up to 28j0, but not 400' (tests with No. 3). The carbon monoxide was not changed to methane by platinum under any conditions. A nickel catalyst in the same apparatus was not poisoned by carbon monoxide whether the temperature was high enough to convert carbon monoxide to methane or not.
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Reaction C2H4 H2 = C z H s This reaction was studied thoroughly with all three samples at Zj'C., using a static method. Two grams of the sample were placed in a tube connected with a manometer. The platinum was first heated to z50°C. in hydrogen and then out-gassed. A mixture of ethylene and hydrogen was then admitted after cooling to 25'C., and the reaction followed by pressure change. Ratios of hydrogen to ethylene of 0.5, I , and 2 were used. The results were reproducible and consistent but no kinetic reaction-order could be established. Table I for equimolar mixtures sufficiently fixes the order of activity as 3, 2, I . The initial partial pressure of each gas was 33 j mm.
TABLE I Hydrogenation of Ethylene Time Minutes.
0.5 I
3 5 IO
Pressure decrease in mm. No. 3 I No. 2
KO.
50 60
85 93
IO1
93
IO0
125
131
"7
140
162
I80
146 185
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Reaction 2 C O O2 = 2 COz The apparatus consisted of a short Pyrex laboratory condenser supported vertically. The inside tube contained a plug of glass wool on which the catalyst was supported. Projecting 2 or 3 mm. through the plug from below was a narrow glass tube carrying a fine wire chromel-alumel thermocouple. Heating the catalyst was accomplished by boiling water or aniline in the condenser jacket. The effluent gases were analyzed volumetrically for carbon For general method see Pease and Taylor: J. Am. Chem. SOC., 44, 1637-47 (1922); or Larson and Smith: 47, 346-55 (1925).
PLATINUM BLACK CATALYSTS
751
dioxide with a Burrell-Haldane apparatus before and after passage over red-hot platinum gauze. In the following experiments (Table 11) the oxygen flow was 110-120 cc. per minute.
TABLE I1 Oxidation of Carbon Monoxide Catalyst No.
Heating T.C. % co, %Cog Medium “C. after cat. Total Combus-
Remarks
Wt. g.
tion
I
1.2
I .2 0.2 2
1.0
As made 11
0.1
JJ
11
11
11
11
11
11
J1
11
11
JJ
11
11
11
1J
J’
J1
11
11
1J
11
”
”
”
”
675’
I
11
11
JJ
11
J1
11
11
11
17
1J
11
1J
11
11
o,
11
J1
J1
1J
1J
11
1.2
hr.
”
”
Barely covered glass wool support
0.2 0.2
62 35 150
2.80
2.85
0.15
3.15
2.55
2.45
0.00
3.50 4 .oo
0.00
4.00 4 .oo
JJ
As made
1.2 0 .2
Steam None Steam Aniline
11
11
1.95 I,95 I,95
0.1
3
11
Barely covered glass wool support Heated in air a t 490’ 24 hr.
I .o
2
Steam 92 0.00 2 . 7 5 Aniline 180 2.10 2 . 1 0 Steam 25 0.00 3 . j o None 65 3.40 3 . 3 0
11
Jf
JJ
11
I1
11
1J
11
11
1)
2.55
0.00 Kone Steam 3.55 0.00 None Steam 97 0.10 Aniline 203 3 .os
2.85 2.90
3.55 3.60 3.60 3 .oo
From Table I1 it is evident that the order of activity is 2 , 3 , I. The best criterion is the temperature a t which quantitative conversion occurs. Sample KO.2 withstood a rather high temperature without becoming thermally inactivated.
TABLE I11 Conversion of SO2 to SO3 KO. I
Vol. catalyst cc. (0.976 g.) Space velocity Temp. max. conversion Maximum conversion Conversion a t 300’ ”
”
400’
Tests after operation a t Temp. max. conversion Maximum conversion Conversion a t 300’~ ”
”
4o0°
0.75 36,000 445’ 85%
71% 83% 585’ 500’
75% 0%
61%
No.
2
No. 3
I .2
I.2
22,000
22,000
340’
412’
98.5% 98% 98% 545’ 460’ 85% 69% 84%
92470 74%
91% 575’ 500’
82YG 0%
66%
752
G. B. TAYLOR, G . B. KIYTIAKOWSKY A S D J. H. PERRY
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Reactioii 2 SO? 0 2 = 2 SOS. X mixture of air and sulfur dioxide, 85; by volume, was passed through the catalysts a t a rate of 450 cc. per minute. The samples were contained in a glass tube heated in an electric resistance furnace. Temperatures were measured by a thermocouple in a small glass tube, the tip of which rested against the catalyst on the upstream side. Conversion efficiencies were determined by analysis of the exit gases by a modified Reich test. After operation a t about 2ooOC. for several hours, a series of conversion tests at increasing temperatures were made and curves constructed of conversion vs. temperature. Operation was then continued for several hours a t a temperature above 54oDC~, the temperature lowered, and a second series of tests made. The results are given in Table 111. It is quite clear from the data that the order of activity is 2 , 3 , I . Just as in the oxidation of carbon monoxide, No. z mas remarkable in resisting thermal deactivation. summary Particle size and catalytic activity have been measured for three samples of platinum black prepared by different methods. The two samples showing the smaller ultimate particle size show the greater catalytic activity. One of these is superior in oxidation reactions and the other is slightly better for hydrogenation. Further discussion is reserved for Part 11. Acknowledgments are made to A. IT. Kcnney and G . €1. Cameron for the X-ray studies, to H. B. DeVore for photomicrographs, to J. B. Sichols for sedimentation measurements and to P. W.Bachman and TT. T. Harvey for some of the catalytic meaeurements.
