CATALYTIC ACTIVITY OF INTERMETALLIC COMPOUNDS I N T H E GAS PHASE REDUCTION OF NITROBENZENE 0. W. BROWN, J. B. BORLAND, R. A. JOHNSTON, AND R. C. GRILLS Laboratory of Physical Chemistry, Indiana University, Bloomington, Indiana Received January 18, 1980
Upon investigation of the literature the authors found no published data on the use of definite intermetallic compounds as reduction catalysts in the vapor phase. Mixed catalysts have been studied but not definite intermetallic compounds. Thallium, bismuth, and lead have been used by Brown and Henke (2) as catalysts for the vapor phase reduction of nitrobenzene to azobenzene and aniline. Yields of azobenzene as high as 90 per cent were obtained with thallium under specific conditions. This paper deals with the use of the intermetallic compounds of thallium, bismuth, and lead as catalysts in the vapor phase reduction of nitrobenzene to azobenzene and aniline. A large yield of azobenzene is preferred to one of aniline. The catalysts used were all supported on asbestos, t h e ratio of catalyst to asbestos being 60:40. The materials used and general procedure were essentially the same as those used by Brown and Henke (1). Any variations will be discussed with the description of the catalysts. The electric furnaces used were of two types,--one a short vertical furnace and the other horizontal. The horizontal furnace has been described by Brown and Henke (1). The vertical furnace was 30 cm. in height and had a catalytic chamber volume of 63 cc. It was heated by chrome1 resistance wire and was constructed in a manner similar to the horizontal furnace. The essential difTerence in the two furnaces is the time of contact of the reactants with the catalysts. I n the horizontal type the reactants are in contact with the catalyst for a longer period of time than in the vertical furnace. Most of the work done was on a TlpPb catalyst. Samples were prepared by two different procedures. The first procedure was to mix Hammond litharge with thallium oxide (on asbestos) in the ratio to make TlpPb and then to reduce in hydrogen a t 265°C. This catalyst will be referred to as catalyst A'. The second procedure was to use C.P. lead nitrate in place of litharge, and to precipitate the hydroxides of the metals together in the 806
806
BROWN, BORLAND, JOHNSTON AND GRILLS
presence of the asbestos support. The hydroxides were reduced in hydrogen a t 265OC. to give catalyst A*. Catalyst B1,consisting of TlzPb with 10 per cent excess lead, was prepared by procedure No. 1. Catalyst B2 consisted of TlzPb with 20 per cent excess thallium; it was prepared by procedure No. 2. Catalyst C1 was TLBi with 10 per cent excess thallium. Catalyst C2 was pure TLBi. These catalysts were prepared by mixing bismuth nitrate and thallium oxide in the correct ratio, precipitating the hydroxides together, and reducing a t 265OC. Some of the experiments tried and results obtained are listed in table 1. TABLE 1 Vapor phase reduction of nitrobenzene CATALYBT
NITROBEN-
COKPOUlTION OF CATALYBT
ZBNE
___
~
B' C' C'
10 g. TlzPb 3.5 g. TlzPb 3.5 g. TlzPb 3.5 g . TlzPb; 10 per cent excess Pb 10 g. TI2Pb; 20 per cent excess T1 10 g. TlsBi ; 10 per cent excess T1 10 g. TlrBi
* H = horizontal; V = vertisal.
litsrs
oc.
hwr
FVRIACEB'
__
~
#ram8 pcr
A' A2 AS B1
YDRO OEN
TEYPXRATURE
pcr hour
~
Asobensene ~
Aniline
__
par cant
pcr u n t
8 20 20 23
265 3.6 265 3.5 4.75 260 3 . 5 !57-271
7 14 14 14
H H
H
8l.lt 57.6$ 53.6s 68.8s
Mo-247
14
H
Trace 99-100
7
14
H
None
44-72
2 . s ?60-3307
14
H
None
2o-m -
3.5
2 . G MI-287
V
TBLD I N P B R CBNT OF TEBORET%CAL
t Average of six experiments. More than 96 per cent of azobenzene was obtained in some runs. 2 Average of six experiments. Average of three experiments. Maximum yield at 255°C. 8U M M A R Y
1. The intermetallic compounds of thallium and lead, under the conditions studied, possess the same catalytic power as that of the components; however, their behavior is more like that of lead than that of thallium. 2. The TlnPb made with Hammond litharge gave better yields of azobenzene than that made with lead nitrate. 3. Both the vertical furnace, which gives a short time of contact of reactant with the catalyst, and a low rate of flow of hydrogen are favorable to the production of azobenzene. 4. The experiments show that only slight changes in the method of
REDUCTION OF NITROBENZENE
807
preparation of the catalyst and in the procedure of reduction give entirely different results. 5. The catalytic activity of TbBi, with and without excess thallium,. is similar to that of the metals themselves. However, the activity is not as great as the activity of the individual components when used alone. REFERENCES (1) BROWN, 0. W.,AND HENKE, C. 0.: J. Phys. Chem. 26, 161 (1922). (2) BROWN, 0.W.,AND HENKE, C.0.:J. Phye. Chem. 26,631-8 (1922).
