CATALYTIC ACTIVITY OF CADMIUM* BY R. J.
HART MAN^ AND
0.w. BROWN?
Introduction Many metals commonly not considered as hydrogenation catalysts in the vapor phase have been quantitatively studied in this laboratory by one of the writers and his co-workers. Of the catalysts studied, lead, thallium, bismuth, and the lower oxides of titanium, tin, molybdenum, and vanadium, were found to give high yields of anilin from nitrobenzene. Thallium, bismuth and lead gave very good yields of azobenzene when operated under proper conditions. Previous work on the use of cadmium as a hydrogenation catalyst in the vapor phase, conducted in this laboratory, indicated that cadmium had possibilities of making an excellent catalyst for the reduction of nitrocompounds to amines. This investigation was undertaken t o thoroughly study the conditions under which cadmium as a catalyst would best promote this reaction in the vapor phase. The following factors were studied in an effort to obtain the maximum conversion of nitrobenzene to anilin; the temperature of ignition in the preparation of the catalyst, the temperature of reduction of nitrobenzene, the rate of flow of hydrogen, rate of flow of nitrobenzene, effect of catalyst supports, effect of the amount of catalyst used and the coalescence of the catalyst when used above its melting point.
Apparatus The apparatus shown in the sketch, Fig. I., was used in all of the following experiments. A, Fig. 2, is a T-tube bent as shown in the diagram. C is a short piece of glass capillary tubing through which the hydrogen gas is passed. The U-tube, D, bent from ordinary glass tubing, is made from 3 j to 40 cm. high. Rubber tubing (B) is used to connect the separate pieces. The flowmeter is assembled as shown in the diagram and then mounted on a suitable wooden support on which cross-section paper (E) has been pasted. This enables one to read the differences of water levels in the two arms of the U-tube. In the calibration of the flowmeter hydrogen from a tank of commercial electrolytic hydrogen was used. The gas was first passed over heated copper wire or fillings in a 1 / 2 inch iron pipe fitted with a cork and a glass tube at each end for the inlet and the outlet of the hydrogen. From * This paper is constructed from a dissertation presented by Robert J. Hartman to the Faculty of the Graduate School of Indiana University in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemistry. Instructor of Chemistry, Indiana University. Professor of Chemistry, Indiana University.
2652
R. J. HARTYAN A S D 0. Vi. BROWN
the pipe the gas was passed into a flask of concentrated sulphuric acid. The gas should bubble through a glass tube drawn to a fine point and just dipping into the acid. Otherwise each bubble of gas causes a deflection on the flow-meter. From the acid the hydrogen entered a U-tube full of glass wool and then passed through a caustic soda tower into the flowmeter. I n this way the hot copper removed the traces of oxygen if present, the sulphuric acid removed the water vapor, the glass wool removed the particles of the sulphuric
FIG.I A-Flowmeter. B-Glass tube into which the nitrobenzene is placed. &Capillary tubing which is welded t o the glass tubing and which conveys the nitrobenzene into the catalyst chamber. D-Rubber tubing. E-Mercury leveling bulbs which furnish pressure for the injection of the nitrobenzene. F-Iron nipple, 1/4 inch diameter and 3 inches long. &Iron pipe, 3/8 inch diameter. H-Iron pipe reducer, from I inch to 3/8 inch. I-Catalyst chamber, I inch inside diameter and 30 inches long. J-Iron heating jacket (pipe), 2 inch inside diameter and 23 inches long. K-Large iron washers gas welded to the catalyst chamber and jacket. &Layer of asbestos paper. M-Layer of alundum cement. N-Heating element, 0-Layer of alundum cement. P-Four layers of asbestos paper. &-Eutectic alloy of tin and lead. R-Iron pipe, 5/8 inch inside diameter and 3 inches long. S-Asbestos cord wrapped around the thermocouple and coated with concentrated sodium silicate solution. T-Copper-advance (constantan) thermocouple. U-Catalyst, V-Cork. W-Glass condenser. X-Glass tubing. Y-One liter graduated flask. Z-100 CC. HC1 ( I : I ) . The flowmeter, A, was used to determine the rate at which the hydrogen was admitted into the furnace. It was constructed as shown in Fig. 2.
acid carried over with the gas and the caustic soda neutralized any acid still present in the gas. The above purification apparatus was connected with red rubber hose. The apparatus used in the calibration of the flowmeter is shown in Fig. 3. Bottle X is large enough to hold about 20 lbs. of water. Bottle Z is about three times as large as X. The red rubber hose B, connecting them, should be sufficiently long to allow bottle X to be lowered from the table to the floor
CATALYTIC ACTIVITY OF CADMIUM
2653
without moving bottle Z. The flowmeter must have a proper capillary tube with a certain bore. This tube should be cleaned with hot chromic and sulphuric acid mixture, washed with water and a stream of air drawn or blown through it until it is dry. If the capillary tube is too large, a considerable back pressure occurs in the bottle Z and the flowmeter does not register correctly as it leaks gas. On the other hand if the capillary t ! ? is too small, not sufficient gas is permitted to pass through it to be of any use. Attention is called to Fig. 3 for the procedure in calibration. To start, bottle Z is full of water and X is empty. Water is siphoned out so that the tubes connecting the two bottles are full of water. X is now weighed with rubber tube and --E clamp attached. The clamp C is closed while h remains open. E is also closed and D is opened. - t D The gas is then turned on and the flowmeter read. For example, let the difference of level be 3 . -
FIG.3 3. Bottle X must no\+ be continually raised or lowered in order to keep the flowmeter reading the same. The hydrogen gauge must never be changed in an attempt to keep the flowmeter reading the same. After the bottle S i i half to three-fourths full, take the exact time and close E quickly, imniediately opening D. Quickly lift X until its water level is even with that in Z in order to adjust the pressure and then close C and Remove S and weigh as before. Take the temperature of the water and also the barometric pressure. Then fill out the table in B manner similar to the following:
R. J. HARTMAH AND 0 . W. BROWK
2654
Column
I
Water displaced in pounds
3
2
4
Flowmeter reading
Time in Minutes
I
io
I1
15
8 6
3
I3
Liters
1% 26.52 41.67 56.56 13 08
5 Liters per hour corrected to standard conditions of temperature and pressure
23.62 3;. IO 49.47 11.6j
The results are then plotted with liters per hour as ordinate and flowmeter readings as abscissa. In calculating column 4, it must be recalled that one pound is equal to 453.6 g. Multiplying pounds by this figure gives grams or cubic centimeters of water or cubic centimeters of hydrogen for so many minutes. To get column j the laws of Boyle and Gay-Lussac are applied thus:
V‘ = 26.52 P’ T’
=
74.86
= 29
+
273
1-1’= x P” = 76 T” = 273
Referring to Fig. I,showing the complete apparatus, the glass tube, B, is welded to the capillary tube, C, and holds the nitrobenzene which has been placed in B by means of a calibrated pipette (holding about 2.3 g.). By raising E, which is a bulb containing mercury, sufficient pressure is put on the nitrobenzene to cause its gradual expulsion into the catalyst chamber. Two cubic centimeters of nitrobenzene will flow through the capillary in about thirty-five or forty minutes when from four to twelve centimeters of mercury pressure is used. The amount of pressure actually needed, of course, depends upon the size of the capillary. Even though the volume of nitrobenzene steadily decreases, the pressure will remain nearly constant because the pressure due to the nitrobenzene is so slight in comparison with that due to the mercury that it can be considered negligible for practical purposes. The time required for 2 cc. of nitrobenzene to pass through the capillary was found to be practically constant for a certain pressure of mercury. The heating jacket, J, Fig. I, was covered with one layer of asbestos paper over its whole length. It was pasted to the jacket with sodium silicate solution. A layer of alundum cement mixed with water and about 3/8 inch thick was applied on top of the asbestos paper. Thirty feet of chrome1 wire, size 16 B Br S gauge, was then wound evenly on top of the alundum cement. Special care was taken not to place the wire too near the protruding iron tubes R. I n starting the winding the end of the wire is doubled for about two feet. This doubled end is brought around one end of the pipe and twisted tightly on the heating jacket, the end sticking out several inches for
CATALYTIC ACTIVITY O F CADMIUM
265s
electrical connection. This first round of doubled wire does not do any of the heating but holds the wire in place and the winding is continued with less difficulty. When the ot'her end of the heating jacket is reached the wire is again doubled for about two feet and inst'ead of going around the jacket in the same direction as before, the last round is bent back and brought around the jacket in the opposite direction. This bending back of the wire for the last round forms a loop and after bringing the wire around the jacket it is brought through this loop, bent back and twisted tightly with one side of the loop, the end again sticking out several inches for electrical connection. On top of the wire, another layer of alundum cement, 0, is placed. This layer of alundum cement is about 114 inch thick. Water is the only ingredient used in mixing the cement. Sodium silicate solution, if added to the cement, will tend to corrode the heating element. Several layers of asbestos, P, are then wrapped around the last layer of cement to insure more perfect heat insulation. One hundred ten volt direct current was used. The catalyst chamber consists of an iron pipe one inch in diameter (inside) and thirty inches long. The heating jacket, J, Fig. I , is placed equidistant from each end of the catalyst chamber and held in place by gas welding to iron washers at either end. The space between the catalyst chamber and the heating jacket was filled with the eutectic alloy of tin and lead, 7 j atomic per cent of tin, melting point, 180°C.This low-melting alloy is an excellent conductor of heat' and permits one to maintain very constant temperatures, IIOC. The thermocouple is wrapped well with asbestos cord and coated by dipping in a concentrated solution of sodium silicate and allowed to dry. The thermocouple extends down into the molten alloy through the pipe It. The entire furnace is set' up on a slant so that the exit is about three inches lower than the feed end. The small pipes, R, enable one to entirely fill the space between the catalyst chamber and the heating jacket with the heat conducting alloy, and, at the same time, prevents the alloy from spilling out of the slanting furnace. The open pipe, R, at the loaer end of the furnace, is wrapped well with asbestos paper in order to prevent sir currents from cooling the alloy that' is standing in the pipe, and, accordingly, lowering the thermocouple reading. Shredded asbestos is then stuffed in around the top opening t o assure further insulation. These pipes are threaded and screw into the heating jacket. To keep the alloy from seeping out around the threads, a lute, consisting of 90 parts by volume of glycerine and I O parts by rolume of water made into a stiff paste with a mixture of 90 parts by weight of litharge and I O parts by weight of red lead, was used. White lead and oil was used in making all other threaded pipe connections gas tight. Since the molten alloy is a very good conductor, it can be assumed that the temperature of the catalyst chamber is that of the alloy. Experiments verifying this mere performed. The catalyst column was twelve inches long and was placed in the furnace about six inches from the exit end of the catalyst tube. The iron pipe reducer at the condenser end of the furnace was removed in order to insert the catalyst. The catalyst was then put in place by means of a boat conveyor
2656
R. J. HARTMAPU' AXD 0 . W. BROTYN
made of tin bent into the shape of a trough. By so placing the catalyst, ample space is afforded where the vaporized nitrobenzene and hydrogen may become well mixed before coming in contact with the catalyst. The cork, V, was pasted to the pipe, G, with sodium silicate solution in order to make it gas tight. The condenser, IT, fits tightly over the cork. The temperature was measured by means of a copper-constantan (advance) thermocouple, the voltage being read by a high resistance millivoltmeter. The thermocouple was made by wrapping copper and constantan wire (gauge 16) separately and then wrapping them together with asbestos cord. The bare ends were twisted and welded. This was calibrated by using the freezing points of tin, lead and zinc. The constant temperature junction used was boiling water, and can he considered for practical purposes 100°C. Therefore, when both junctions reach IOO'C.,the millivoltmeter should 300 read o and this point, o millivolt,, ioo"C, L should fall on the curve. The calibra$ tion curve obtained and used by the writers is shown in Fig. 4. =O0 1: Between 225°C. and 3zsoC. the 7 00 4 8 /2 curve takes the form of practically a .w,LuvoLrs straight line but for higher or lower FIG.4 temperatures the slope of the curve becomes more prominent. This calibration curve can not, therefore, be considered entirely as a straight line.
2400'37 !i
Materials used The hydrogen passed into the furnace was commercial electrolytic hydrogen and was purified in the same manner as described above when used to calibrate the flowmeter. The nitrobenzene was purified by first shaking with sodium carbonate solution and then steam distilling. After drying with calcium chloride, it was simple distilled two times. The cadmium nitrate, from which all catalysts used in this investigation were prepared, was obtained from .J. T. Baker Chemical Company and its label bore the following analysis: F e , , . O O I ~ ~Zn. , . . .none, As. . . .none and C1. . . . 00 I %. The shredded asbestos used for catalyst support was Powminco Asbestos from Powhatan Mining Corporation, Woodlawn, Baltimore, Md., Grade "A" long, acid washed. This asbestos was boiled for three hours in concentrated hydrochloric acid and then washed free from acid with distilled water on a Buchner funnel. It was then dried in an ovenat 105°C.for eight hours. The pumice stone used for catalyst support was treated in the following manner. Lump pumice stone was ground in a Blake crusher and sizes ranging from 3/16 to 1 / 2 inch were used for treatment. The crushed material was ,
CATALYTIC ACTIVITY O F CADXITJM
2657
boiled for four hours in 1:s nitric acid. I t was then washed free from acid and dried in the same manner as the asbestos. I t was later sorted into various sizes and that which passed through a 1,’2 inch sieve was used for support. Procedure The experiments were carried out at various temperatures which were regulated by means of a variable external chrome1 wire resistance. With the aid of the excellent heat conducting alloy bath, the temperature was fairly easily kept within one degree of that desired. Before each experiment the furnace was brought to the required temperature while a stream of hydrogen was being continually passed through the furnace, preventing oxidation of the catalyst. (Hydrogen was also passed over the catalyst while the furnace was cooling.) As soon as the temperature a t which the experiment was to be carried out had been reached, two cubic centimeters of nitrobenzene was placed in the tube B, Fig. I . The rubber tube, D, was then placed on B and the mercury bulb, E, was raised to generate pressure on the nitrobenzene in order to force it, through the capillary into the catalyst chamber. The rate of flow of the nitrobenzene was adjusted by lowering or raising the bulb E. From the time required and the weight in grams of nitrobenzene delivered by means of the pipette, the grams per hour of nitrobenzene admitted into the furnace could easily be calculated. dfter all the nitrobenzene had passed into the furnace, the same temperature as that of the experiment was maintained and hydrogen was let flow at 1 4 liters per hour for the same length of time as that required to pass all the nitrobenzene into the furnace, in order to make certain the catalyst chamber was completely washed free from reduction products. Kot until then was the condenser removed for washing. I n this manner all of the products of the furnace were sure to have been washed out of the furnace into the condenser. Determination of Yield of Anilin The product was run into the flask in which was previously placed IOO cc. of I : I hydrochloric acid. The condenser was washed well with I : I O hydrochloric acid, the washings flowing into the flask. The sample was then diluted with water to the graduated mark on the liter flask. From this, one hundred cc. samples were pipetted out, 2 5 cc. conc. hydrochloric acid added to each, and titrated with standard tenth molar sodium nitrite solution. Starch iodide paper was used as an external indicator. The reaction involved in the titration is a diazotization. This reaction is rapid a t first but as the end point is reached it becomes slow. Therefore, the end point is not attained until the solution will turn the starch iodide paper blue after standing several minutes. This reaction involves all amines, but, since amines other than anilin were not present, this factor need not be considered. The sodium nitrite solution was standardized against weighed samples of pure catalytic ortho amido phenol.
2658
R. J. HARTHAN A S D 0 . W. BROWS'
Preparation of Cadmium Catalyst from Cadmium Oxalate One part by weight of cadmium nitrate, Cd(N03)2.4H20,was dissolved in four parts of water and cadmium oxalate precipitated with five per cent by weight oxalic acid solution. The precipitate was washed with distilled water, five times by decantation, and four times through a Buchner funnel. The oxalate was then dried at room temperature for several hours. Forty-two grams of the cadmium oxalate was placed directly into the furnace and reduced a t 3ooOC. for one and one-half hours with a rate of flow of hydrogen of 14 liters per hour. The figures of column A, Table I , represent the yield of anilin in per cent of theory obtained with this catalyst at the corresponding temperatures. Column B, Table I , represents the yield of anilin in per cent of theory obtained over a catalyst where forty-two grams of the previously prepared cadmium oxalate was roasted at 25oOC. for two hours in an electric muffle with a stream of air passing over it and then reduced in the same manner as described above. I n each case 18.gj g. of reduced cadmium catalyst was finally produced and used. Effect of Variation of Temperature on the Yield of Anilin The two catalysts prepared in the above described manner were used simultaneously a t various temperatures in order to determine at which temperature the reduction of nitrobenzene to anilin was best carried out. In each experiment the furnace was washed with hydrogen for sixty minutes after all the nitrobenzene had been injected into the catalyst chamber. Table I shows the results obtained.
TABLE I Rate of flow of nitrobenzene: 2.3462 g. per hour. Rate of flow of hydrogen: 14 liters per hour. Temperature degrees Centigrade
'A Per cent anilin over reduced cadmium oxalate catalyst
*B Per cent anilin over previously roasted and then reduced cadmium oxalate catalyst
2 90
40.00
37.70
305
87.22
66.45
315
94.10
319
95.12
92 ' 70 98 .oo
325
94.12
96 ' I 9
335
90.71
91.72
350
79.12
80.35
* Each figure in this column represents an average of the results of from four to twelve consecutive experiments.
CATALYTIC ACTITITY O F CADMIUM
2659
The following curves, Fig. 5 , show the temperature plotted as abscissa and the yield of anilin as ordinates. Curve I represents the yields obtained a t various temperatures with the cadmium catalyst which was previously roasted at z50°C while curve z shows the yields obtained with the cadmium catalyst reduced directly from the oxalate and not previously roasted. From the curves it is seen that both catalysts give the best yields of anilin at 319'C ~tI O , although the roasted catalyst gives about 2 . j ( J c better yield a t that temperature. The unroasted catalyst will give a higher per cent yield at a lower temperature than the roasted catalyst,. I t is also seen that the
FIG.5
roasted catalyst produces a curve having a sharp maximum while that of the unroasted is a more smooth and rounded curve a t its maximum. These facts tend to indicate that the physical properties of the catalyst are changed by roasting. Previously roasting the oxalate in air and then reducing seems to produce a more finely divided catalyst which will enable the vapors tomore readily and more completely come in contact with it since there is, accordingly, more catalyst surface. I t is noted here that several experiments were performed a t temperatures above that of the melting point of cadmium, jz0.9'C. Fairly good yields are obtained at these high temperatures and shows clearly that the catalyst is still active to a high degree even above its melting point. This fact places cadmium in a class with lead with respect t o its catalytic activity above its melting point as shown in this laboratory by F. A. Madenwald, C. 0. Henke and 0. W. Brown.' J. Phys. Chem., 31, 862-866 (1927).
2660
R. J. HARTMAK AND 0. W. B R O W S
Effect of Temperature of Roasting of Cadmium Hydroxide One part by weight of cadmium nitrate was dissolved in four parts of water and cadmium hydroxide precipitated with a zo% sodium hydroxide solution. The precipitate was washed free from alkali on a Buchner funnel. Before reducing, two quantities of this cadmium hydroxide were roasted separately a t zjo°C. and a t 350°C. in a stream of air for two hours. Experiments a t various temperatures were made with these two catalysts to check the temperature of maximum yield with that found using the catalysts made from the oxalate. In each case 21.19 g. of cadmium oxide were placed in the catalyst chamber which on reduction would yield 18.55 g. of cadmium catalyst. Following in Table I1 are the results obtained with the two catalysts.
TABLE I1 Rate of flow of nitrobenzene: 2.3462 g. per hour Rate of flow of hydrogen: 14 liters per hour. Temperature degrees Centigrade
300 310 315 3'9 325 330 3 50 400
*Per cent anilin over catalyst previously roasted a t 250°C.
68.6 92 4 95 . o 98.3 9s . o 93.5 87 .o 65.2
*Per cent anilin over catalyst previously roasted a t 350°C.
53.7 81 . o 89.6 92.8 90.5 90.2 83.5 60.3
* Each figure in this column represents an average of the results of from two to six experiments. The temperature 3 I 9°C. a t which the maximum yield of anilin was obtained agrees substantially with that previously found with the catalysts prepared from cadmium oxalate. Curve I, Fig. 6, represents the yield of anilin in per cent of theory obtained a t the various temperatures with the catalyst previously roasted a t z50°C. while curve 2 represents that of the catalyst roasted a t 350°C. It is obvious that z50°C. is a much better roasting temperature than 350°C. as the yields of anilin are considerably lower in the latter case. It is also noted that the catalyst made from the hydroxide roasted a t z50°C. gives slightly better yields a t 31g'C. than that made from the oxalate also roasted a t 250°C. Before any data could be used for the above graphs, Fig. 6, it was unnecessary to perform ten experiments in each case before the catalysts had reached a point where they would give consistent results, Le., until two con-
CATALYTIC ACTIVITY O F CADMIUM
2661
secutive experiments would yield the same per cent of anilin under similar conditions. I n the first three or four of these experiments better yields were obtained with the catalyst roasted at 3 jo"C., but, after ten experiments, better yields were obtained with the catalyst roasted at z jo"C. This seems to indicate that roasting at 3 jo°C. gives the catalyst a high initial activity which decreases with use.
A
300
34 0
380
T€,wP€,?/7TUIPE
FIG.6
Effect of Presence of Nitrobenzene on Coalescence of the Catalyst Again it will be noted that several of the above experiments were carried out above the melting point of the metal, 32o.goC., and, that the catalysts were still active to a marked degree at these higher temperatures. This is probably due to the fact that the metal does not fuse or coalesce as rapidly while the vapors of nitrobenzene and hydrogen are both present over the catalyst, Le., while the nitrobenzene is being passed into the furnace. To verify this two furnaces were each charged with 21.19 g. cadmium hydroxide previously roasted in a stream of air at 2 jo°C. They were both reduced a t 3oo'C. inastream of hydrogen of 1 4 liters per hour. .Ifter the catalysts mere completely reduced, nitrobenzene was passed into one of the furnaces a t the rate of 2.3462 g. per hour along with the hydrogen. ilt the same time the temperature was raised to 32g3C., 7 . 1 O C . above the melting point of the catalyst, and maintained there for one hour. The furnace was then permitted to cool to room temperature, being careful t o continue the flow of nitrobenzene until the temperature had fallen to 3oo0C'., zo"C. below the melting point of the catalyst. Hydrogen was left flowing until the furnace reached room temperature. The other catalyst was treated in exactly t,he same manner except that no nitrobenzene as introduced into the furnace at any time.
2662
R. J. HARTMAN AND 0. W. BROWN
The two catalysts were carefully removed and examined for apparent differences in physical properties. It was found in the case where nitrobenzene had not been passed over the catalyst that the volume of the catalyst had shrunk to one-half of that over which nitrobenzene had been passed, indicating considerable coalescence. The catalyst over which nitrobenzene had been passed was still finely divided and appeared not to have coalesced to any marked degree while the other catalyst contained many small balls of metal I to 3 mm. in diameter and had a general metallic luster which was not noticeable in the case where nitrobenzene had been kept in contact with the catalyst. These facts indicate that cadmium might be used above its melting point and still remain quite active as long as nitrobenzene is continually passed into the furnace. Effect of Rate of Flow of Hydrogen on Production of Anilin The catalyst used was supported on shredded asbestos. Cadmium nitrate was dissolved in water as before and enough shredded asbestos added so that when reduced there would be twice the weight of cadmium catalyst as support. The cadmium nitrate solution was boiled well with the support in order that the support might become thoroughly impregnated with the solution. Cadmium hydroxide was then precipitated, roasted a t 2 5o°C. and reduced in the same manner as before. I n studying the rate of flow of hydrogen all other factors were kept constant. The results obtained are given in Table 111. TABLE 111 Weight of catalyst: 18.j5 g. cadmium supported on 9.28 g. of shredded asbestos. Rate of flow of nitrobenzene: 2.3462 g. per hour. Temperature of reduction of nitrobenzene: 3 19°C.
Hydrogen passed in per cent of theory
I094 587 5'4
44 I 294 I25
Hydrogen passed in liters per hour 14.0 7 .o 6.2
5.3
3.5
*Yield of anilin in per cent of theory
97 . o 97 . o 100.0
95.9 94.0
I .6 90.8 * Each figure in this column represents an average of results of from two to six experi-
ments.
It is seen from the above results that, when 6.2 liters of hydrogen per hour or 5 14% of theory were passed, complete conversion of nitrobenzene to anilin took place. Effect of Rate of Flow of Nitrobenzene on Production of Anilin Two catalysts were used in this study. One consisted of 18.55 g. cadmium supported on 9.28 g. shredded asbestos, or twice the weight of cadmium as support. The other catalyst cbnsisted of 37.1 g. cadmium supported on
2663
CATALYTIC ACTIVITY O F CADMIEM
9.28 g. shredded asbestos, or four times the weight of catalyst as support. They were both prepared in the same manner as that used in the study on the effect of the rate of flow of hydrogen. All factors except the rate of flow of nitrobenzene were kept constant in this study: Following in Table IV are the results obtained.
TABLE IV Hydrogen passed in per cent of theory: 514. Temperature of reduction of nitrobenzene: 3 19°C. Time in minutes required to paas 2.3462 g. nitrobenzene
60 30
Rate of flow of nitrobenzene in grams per hour
Rate of flow of hydrogen in liters per hour
Yield of anilin in per cent of theory over cstalyst consisting of: *18.j5g.Cd, *37.1g.Cd, 9.28g. aa9.28g. asbestos bestos
6.20
100.0
100.0
12.40
100.0
100.0
20
2.3462 4.6924 7.0386
18.60
100.0
18
j ,8128
20.65
98.4 97 , I
I5 IO
8
9.3848 14.0772 17.5965
24.80 37.20 46.50
-
-
__
100.0 100.0
94.6
* Each figure in this column represents an average of results of three consecutive experiments.
From the above data it is shown that 7.0386 g. nitrobenzene per hour can be passed over 18.55 g. of catalyst with quantitative reduction to anilin. When 37.1 g. of catalyst or twice the former amount were used, it was found that twice the weight of nitrobenzene, or 14.07j 2 g. per hour could be passed without lowering the yield of anilin. This confirms the fact that a definite amount of catalyst will permit a definite amount of conversion to take place.
Effect of Supports A catalyst consisting of 18.55 g. cadmium supported on 9.28 g. pumice stone was used along with one of the same weight of cadmium supported on the same weight of shredded asbestos. They were both prepared in the same manner as those used in the study of the rate of flow of nitrobenzene. I t was found that each gave quantitative yields of anilin when used at a temperature of 319'C., with 5 1 4 y ~hydrogen and nitrobenzene passing a t 7.0286 g. per hour. On examination of the catalysts the pumice stone appeared to be thoroughly saturated with cadmium while the asbestos did not. It is noted here that, in the study of the rate of flow of nitrobenzene, 9.28 g. shredded asbestos will support 37.1 g. of catalyst and still give quantitative yields when the rate of flow of nitrobenzene is doubled. This indicates that asbestos will support a larger weight of catalyst than an equal weight of pumice stone. Several experiments were performed using 18.55 g. unsupported cadmium catalyst also prepared in an identical manner to the supported catalysts.
2664
R. J. NARTMAN AND 0. W. BROWN
The same temperature and rate of flow of hydrogen and nitrobenzene as used with the supported catalysts were maintained. It was found that the yields of anilin obtained under these conditions was only an average of 42. j%, showing a decided decrease. This indicates that supporting the catalyst permits the passage of a greater flow of nitrobenzene without decreasing the yields of anilin. The use of supports permits more material to come in contact with the catalyst. Supporting evidently retards to a great extent the coalescence of the catalyst when used so near its melting point, keeping it more finely divided, hence more active. Nature of Products In every experiment where the temperature of reduction of nitrobenzene to anilin was 319'C., the anilin obtained was colorless. At temperatures below 3 19°C. the products were contaminated with traces of isonitrile which made the anilin appear colored as is the case with most catalysts when used a t too low a temperature. Above 319'C., the products again became slightly colored. I n no instance in this investigation was ammonia detected as a product. This fact shows that cadmium is a very suitable catalyst for the reduction of nitrocompounds to amines since the extent of the reduction is the production of the amine, the reaction not proceeding far enough to split' off ammonia.
Conclusion Cadmium was shown to be an active catalyst for the reduction of nitrobenzene to anilin. The most active catalyst used in this investigation was prepared from 2. the hydroxide precipitated on asbestos support, roasted at 2 jo"C., and reduced with hydrogen at 300OC. 3 . 'The temperature of reduction of nitrobenzene to anilin found to give the highest yields was 319'C. &IO('. 4. Cadmium when used above its melting point as a catalyst gives high yields of anilin from nitrobenzene. j . Cadmium catalyst when heated above its melting point has a less tendency to coalesce in the presence of nitrobenzene and hydrogen than when in the presence of hydrogen alone. 6. The catalyst prepared from cadmium oxalate roasted at z jo°C. was found to be more active for the production of anilin than that prepared from the unroasted oxalate. 7. The catalyst prepared from cadmium hydroxide roasted at z j o T . was found to be more active for the reduction of nitrobenzene to anilin than that prepared from cadmium hydroxide roasted at 3 jo°C, 8. Cadmium hydroxide roasted at zjo'C. was found to give a slightly better catalyst for the production of anilin than cadmium oxalate roasted at zj0"C. 9. The hydrogen in per cent of theory which gave the highest yield of nnilin was jI 4 . I.
CATALYTIC ACTIVITY O F CADMICM
266 j
The rate of flow of nitrobenzene in grams per hour found to give IO. quantitative yields of anilin was ,3794 g. per gram of catalyst when supported on shredded asbestos. Without the aid of a support the catalyst will not give quantitative yields at this rate. The use of shredded asbestos and pumice stone as supports did not II, improve the yield of anilin to any great extent but enabled the same quantity of catalyst to reduce more nitrobenzene per hour. 12. Shredded asbestos was found to be a more suitable support fbr the cadmium catalyst than vias the pumice stone. 13. The anilin produced at 319Y'. was colorless in every instance. 14. Ammonia was not detected as a product in any experiment' in this investigation. I j. The writers prefer the type of furnace used in this investigation to that previously used in this laboratory. The molten alloy which surrounds the catalyst chamber in this apparatus affords more easy control than the one previously used where hot air surrounded the catalyst chamber. L a b o r d o r y of Physical Chemistry, I n d i a n a Uniuersity, Bloomington.
