964
BERNARD BERIC AND OLIVER W. BROWN
CATALYTIC ACTIVITY OF INTERMETALLIC COMPOUNDS IN T H E VAPOR-PHASE REDUCTION OF NITROBENZENE. 11’ BERNARD BERK
AND
OLIVER W . BROWN
Department of Chemistry, Indiana University, Bloomington, Indiana Received Apral 10, l$&
This paper is a continuation of the work previously published (1) covering the intermetallic compounds ThBi as catalysts in the vapor-phase reduction of nitrobenzene. The present work includes mixtures of copper and zinc, copper and tin, and copper and antimony, the oxides of which were coprecipitated in such ratios as to give CuzZns, CusSn, and CusSb after reduction in a current of hydrogen. For the sake of brevity these mixtures will hereinafter be referred to as CuzZns, CusSn, and CusSb, even though no evidence has been obtained as to whether such intermetallic compounds were present. The object in the present study was to obtain as high a yield of aniline as possible, rather than azobenzene. The yield of aniline throughout this paper is derived as follows: Grams aniline produced X molecular weight nitrobenzene Grams nitrobenzene entering furnace X molecular weight aniline
x
100
The expression “per cent hydrogen in excess of theory” is obtained from: Actual molecules of hydrogen entering furnace X 100 Theoretical molecules of hydrogen required for 100 per cent conversion The materials and general procedure were essentially the same as those used by Brown and Henke (2), with the exception that in the present work a short vertical furnace R ~ employed, S rather than the usual long horizontal furnace. The construction of the furnace is shown in figure 1; it has a catalytic chamber capacity of 63 cc. and is 30 cm. high. From the figure it is evident that the lower half of the furnace can be unscrewed to receive the catalyst. The first catalyst to be studied was Cu2Zna. Copper and zinc nitrates, in the amounts calculated to give the intermetallic compound Cu~Znawith possibly a slight excess of copper, not exceeding 1 per cent, were precipitated as the carbonates, ignited to the oxides at 31OoC., and reduced at 210°C. in a current of hydrogen. At this loiv temperature of reduction it is highly probable that the zinc oxide was not fully reduced to the metal; under such conditions the catalyst is more nearly a pure copper catalyst supported on zinc oxide. The effect of change of temperature on the catalytic reduction of nitrobenzene to aniline over catalyst S o . 1 is the variable studied in table 1. The results given in the table indicate that the most favorable temperature for the reduction 1 This paper is constructed from a dissertation presented by Bernard Berk t o the Faculty of the Graduate School of Indiana University in partial fulfillment of the requirements for the degree of Doctoi of Philosophy, January, 1941.
VAPOR-PHASE REDL'CTIOX OF NITROBENZESE
965
of nitrobenzene to aniline is between 250" and 260°C. This is also the temperature at which pure copper is most active. At a temperature of 250OC. and a rate of flow of nitrobenzene of 3.5885 g. per hour, the yield of aniline decreased when the rate of flow of hydrogen was reduced to 7 liters per hour (323 per cent of hydrogen in excess of theory). Doubling the rate of flow of nitrobenzene at 250°C. with a hydrogen flow of 14 liters per hour decreased the yield of aniline about 5 per cent. The next catalyst to be studied was Cu$n, prepared by precipitating the mixed hydroxides of copper and tin from a solution of copper nitrate and stannous chloride contained in such a ratio as to give the desired compound with a
F N
G H I J
K
L
FIG.1. Detailed drawing of the catalytic furnace. A, I#-in. iron cap; B, supplementary heating well; C, heat insulation; D, iron pipe, 14 x 6 in.; E, If-in. iron coupling; F, iron nipple, 1) x 2 in.; G , catalytic chamber; H , iron gauze; I, thermocouple well; J, iron reducer 1) x If in.; K, S o . 20 chrome1 wire; L, 120 volts A S . ; M, +-in. iron pipe; N, 120 vols .4.c.; 0, capillary.
very slight excess of copper. The hydroxides were dried at 110°C. and reduced in a current of hydrogen a t 236°C. Only after eight runs over this catalyst at temperatures between 210" and 25OoC.,with a rate of flow of hydrogen of 14 liters per hour and a nitrobenzene flow of 3.5885 g. per hour, were exact data collected. With these rates of flow of hydrogen and nitrobenzene, ten runs in the temperature range of 250-290OC. inclusive gave an average yield of aniline of 92.5 per cent of theory. The yields of the ten individual runs were within a range of 1 per cent of the average value. At 240°C. the yield of aniline was 87.7 per cent, whereas at 300°C. the yield wm 88.25 per cent of theory. The temperatures of maximum activity for copper and tin are 250-260OC.
966
BERNARD BERK AND OLIVER W. BROWN
and 274494°C. The range for this particular catalyst, CusSn, is 250-290°C.; it evidently shows the properties of each individual metal irrespective of the other. In table 2 the effects of variations in the rates of flow of hydrogen and nitrobenzene are summarized. A fresh sample of catalyst was treated in the same manner as described above. The temperature of reduction waa 250°C. It is seen from data given in this table that the rate of flow of nitrobenzene of 3.5885 g. per hour and of 14 liters of hydrogen per hour resulted in the highest yield of TABLE 1 The effect of temperature on the yield of aniEine Weight of catalyst before reduction, 30 g . ; rate of flow of hydrogen, 14 liters per hour; rate of flow of nitrobenzene, 3.5886g. per hour TKMPKRATUPE OF OPKBAIION
YlUD O? -E'
T.
pa cent
225
89.12 95.12 98.70 94.25 93.80 87.50 84.50
250 260 275
292 310 320
* Each yield of aniline is expressed as the average of
the given number of runs.
TABLE 2 The effect of rate of flow of hydrogen and nitrobenzene on the yield of aniline Catalyst: CurSn with a very slight excess of copper I E X P K M R T P K OF CAIALYBT, 250'c.
Rate of Bow of hvdronen 1R.k of Eow of nitrobenzene in pama p r hour in liters per hour -
7 14
21 14 21
3.5886 3.5886 3.5885 7.1710 7.1770
PEP CENT OF BYDlOOKN W U(CESs OF wopy
323.6 647.0 970.0 323.8 485.4
n E L D OF A N I L I N E I N P K I CENT OF IgKOPY
76.3 92.8 85.9 66.9 57.3
aniline obtained over the catalyst CusSn. Both lower and higher rates of flow of hydrogen reduced the yield. Doubling the rate of flow of nitrobenzene reduced the aniline yield. When the catalyst was heated for 2 hr. to 360'C. in a current of hydrogen and then used a t 250°C.,the yields decreased to 45.7 and 33 per cent for the first two runs; the product was highly colored, with evidence of a large proportion of nnreacted nitrobenzene. The CusSb catalyst was prepared by treating antimonous oxide with 18 per cent hydrochloric acid and adding copper nitrate in sufficient amount to give
967
VAPOR-PHASE REDCCTIOS OF SITROBESZENE
the calculated intermetallic compound. The precipitated hydroxides were dried at 110°C. and reduced in a current of hydrogen at 325°C. In table 3 is shoun the effect of an increase cf temperature on the yield of aniline. The catalyst soon lcses its activity uhen used a t temperatures below 225OC.; however, the activity of the catalyst is restored when re-reduced or used at higher temperatures. A trace of azobenzene vas obtained up to and including 275°C. An examination cf the data in the table indicates that the maximum yield of aniline was obtained a t 345°C. It appears that the CurSb catalyst is quite different in properties from either of its constituent metals, since the temperatures of maximum activity for pure copper and antimony are 255°C. and 320°C., respectively, whereas water-white aniline I! as obtained at 345°C. over this catalyst. TABLE 3 The efecect o j lrmprralure on ihe yieId o j aniline Weight of catalyst before reduction, 30 g.; rate of flow of hydrogen, 14 liters per hour: rate of flow of nitrobenzene, 3.5885 E. per hour NMIIIEP OF PUNS MADE
T E U 3 W I U L E 01 O P W I I O N
%.
2 3 2 2 2 3 1
200 225 250 275
290 315 330 345
2
2 1
* Each yield of
355 360
YIEW) or AmLINE.
per csrl
18.8 55.0t 75.5 82.5 85.5 89.0 92.5 96.2 95.0 95.0
aniline is expressed as the average of the given number of runs.
t A t 225'C., in addition t o a 55 per cent yield of aniline, there is also obtained a 14.7 per cent yield of azobenzene.
An average of two runs, made over Cu3Sb a t 345°C. and at a hydrogen rate of flow of 14 liters per hour with the rate of flow of nitrobenzene reduced to 2.3923 g. per hour, gave an aniline yield of 97.5 per cent. Under the same conditions of temperature and hydrogen flow, but with a nitrobenzene flow of 7.1770 g. per hour, the aniline yield \vas reduced to 92.5 per cent. An increased rate of flow of hydrogen with the rate of flow of nitrobenzene at 7.1770 g. per hour further reduced the yield of aniline. CusSb is unique among the catalysts reported in this paper in that it is the only one over which there was obtained any azobenzene, and also for the fact that it has a higher catalytic activity than either of the other catalysts. Although increasing the rates of flow of hydrogen and nitrobenzene either independently or simultaneously resulted in a decrease of catalytic activity, the decrease was much less marked than with the other catalysts.
968
BERNARD BERK AND OLIVER W. BROWN
It has been reported in the literature (3) that antimony is active only above 320"C., and that below this temperature the activity decreases rapidly. The present work shows the same tendencies but not to the same degree. While a pure antimony catalyst at 300'C. will give 85 per cent yields only after being heated in hydrogen to 450OC. for 30 min., the CuaSb catalyst will give yields of 89 per cent at 300'C. with continued use. CONCLUSIONS
1. The copper on zinc oxide catalyst exhibited the same general properties as does a pure copper catalyst. The temperature of maximum activity was 250-26OoC.; with 3.5885 g. of nitrobenzene per hour and a rate of flow of hydrogen of 14 liters per hour, the maximum material yield of aniline was 98.7 per cent. 2. The Guan catalyst appeared to have the properties of both metals. The temperature range of maximum activity was 250-29O0C., and the average yield of aniline in this range was 92.5 per cent. 3. Heating the CusSn catalyst in hydrogen for 2 hr. at 360°C. decreased the activity of the catalyst more than 60 per cent. 4. The temperature of maximum activity for the Cu&b catalyst is higher than that of either of the constituent metals, being at 345OC. while that for pure antimony is 320°C. At 345OC., with a rate of flow of nitrobenzene of 2.3923 g. per hour and a rate of flow of hydrogen of 14 liters per hour, the yield of aniline is 97.5 per cent. 5. At lower temperatures, below 290°C., there is also formed with the CuaSb catalyst small amounts of azobenzene; at 225°C. there is formed 14.7 per cent of azobenzene. 6. At lower temperatures the activity of the C u a b catalyst can be restored by heating it in hydrogen at temperatures above 320°C. REFERENCES
(1) BROWN, 0. W . , BORLAND, J. B., JOHNSTON, R. A., AND GRILLS, R . C.: J. Phys. Chem. 43,805 (1939). (2) BROWN, 0.W . , AND HENKE,C. 0.:J. Phys. Chem. 26,161 (1922). (3) Reference 2, page 279.
