Liquid phase hydrogenation of nitrobenzene to para-aminophenol over Pt/ZrO2 Catalyst and SO4 2-/ZrO 2-Al2O3 solid acid

Article abstract of DOI:10.1007/s10562-010-0427-8

ZrO₂-Al₂O₃ binary oxide was prepared by homogeneous coprecipitation method. SO₄ ^2-/ZrO₂ and SO₄ ^2-/ZrO₂-Al₂O₃ were prepared by impregnation method and were characterized by BET, XRD and TPD. Pt/ZrO₂ was prepared by incipient wetness impregnation of ZrO ₂ with an aqueous solution of H₂PtCl₆. Subsequently, hydrogenation of nitrobenzene to para-aminophenol over Pt/ZrO ₂ catalyst and SO₄ ^2-/ZrO₂-Al ₂O₃ solid acid using water as solvent was performed. The results indicate that para-aminophenol as well as a small quantity of aniline and ortho-aminophenol are obtained without using any environmentally undesirable liquid acid. The para-aminophenol selectivity reaches to 74.9% with 44.8% of nitrobenzene conversion under the optimal reaction conditions. And the amount of Al₂O₃ in SO₄ ^2-/ZrO ₂-Al₂O₃ has great influence on the selectivity to para-aminophenol. Graphical Abstract: Hydrogenation of nitrobenzene to para-aminophenol over Pt/ZrO2 catalyst andSO₄ ^2-/ZrO ₂-Al₂O₃ solid acid was developed. The results indicate that para-aminophenol as well as a small quantity of aniline and ortho-aminophenol are obtained without using any environmentally undesirable liquid acid. The para-aminophenol selectivity reaches to 74.9 with 44.8% of nitrobenzene conversion under the optimal reaction conditions. And the amount of Al₂O₃ in SO₄ ^2-/ZrO ₂-Al₂O₃ has great influence on the selectivity to para-aminophenol.[Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-010-0427-8

Catal Lett (2010) 140:65–68
DOI 10.1007/s10562-010-0427-8
Liquid Phase Hydrogenation of Nitrobenzene
to Para-Aminophenol over Pt/ZrO2 Catalyst
and SO4 /ZrO2–Al2O3 Solid Acid
22
•
Pingle Liu Yaohua Hu Min Ni
•
•
•
Kuiyi You Hean Luo
Received: 8 July 2010 / Accepted: 3 August 2010 / Published online: 21 August 2010
Ó Springer Science+Business Media, LLC 2010
Abstract ZrO2–Al2O3 binary oxide was prepared by
homogeneous coprecipitation method. SO42-/ZrO2 and
SO42-/ZrO2–Al2O3 were prepared by impregnation method
and were characterized by BET, XRD and TPD. Pt/ZrO2 was
prepared by incipient wetness impregnation of ZrO2 with an
aqueous solution of H2PtCl6. Subsequently, hydrogenation of
nitrobenzene to para-aminophenol over Pt/ZrO2 catalyst and
SO42-/ZrO2–Al2O3 solid acid using water as solvent was
performed. The results indicate that para-aminophenol as well
as a small quantity of aniline and ortho-aminophenol are
obtained without using any environmentally undesirable liquid
acid. The para-aminophenol selectivity reaches to 74.9% with
44.8% of nitrobenzene conversion under the optimal reaction
conditions. And the amount of Al2O3 in SO42-/ZrO2–Al2O3
has great influence on the selectivity to para-aminophenol.
the Pt-catalyzed hydrogenation of nitrobenzene and the acid-
catalyzed Bamberger rearrangement of the hydrogenation
intermediate product, N-phenylhydroxylamine (PHA) (see
Scheme 1). The first hydrogenation reaction is catalyzed by
metal catalysts and the rearrangement process is catalyzed by
acid catalysts. By-products are aniline through the successive
hydrogenation of PHA intermediate and ortho-aminophenol
(OAP) through the Bamberger rearrangement into ortho
position [2]. The shortcomings of this route mainly involve
the corrosion problems due to the necessary use of mineral
acid and the loss of expensive active component of the
catalyst. Hydrogenation of nitrobenzene to PHA has been
studied with various metal catalysts [3–7], and the Bamberger
rearrangement of PHA to PAP using a solid acid catalyst
instead of sulfuric acid has seldom been studied. Wang et al.
[8] used metal–solid acid bifunctional catalyst to synthesize
PAP directly from nitrobenzene hydrogenation and the PAP
yield was 23.9% with a selectivity of 46.6%. Chaudhari et al.
[9] reported that ion-exchange resin and Pt–S/C were simul-
taneously used to synthesize PAP from nitrobenzene and the
PAP yield was 13.9%. A series of Pt-solid acid bifunctional
catalysts using HF-SiO2, H-ZSM5 and supported heteropoly
acid as support were prepared by Chu et al. [10]. Unfortu-
nately, these catalysts showed very low activity in a non-acid
medium. In this work, a single-step synthesis of PAP from
nitrobenzene over Pt/ZrO2 and SO42-/ZrO2–Al2O3 using
water as solvent was carried out.
Keywords Nitrobenzene hydrogenation Á Para-
aminophenol Á Bamberger rearrangement Á SO42-/ZrO2–
Al2O3 solid acid
1 Introduction
Para-aminophenol (PAP) is a commercially important inter-
mediate for the production of analgesic and antipyretic drugs,
such as paracetamol and acetaminophen [1]. The commercial
manufacture of PAP is typically carried out in stirred tank
reactors in which a four-phase system is used to accomplish
2 Experimental
P. Liu (&) Á Y. Hu Á M. Ni Á K. You Á H. Luo (&)
College of Chemical Engineering, Xiangtan University,
Xiangtan, Hunan 411105, China
2.1 Catalyst Preparation
e-mail: liupingle@xtu.edu.cn
Zr(OH)4 was prepared by precipitation of aqueous solution
of ZrOCl2 with 28 wt% ammonia. ZrO2 support was
H. Luo
e-mail: heanLuo@126.com
123

66
P. Liu et al.
radiation. Scanning speed was 3.6° min-1 and scanning
range was over 10°–70°.
Temperature programmed desorption (TPD) of NH3 was
performed on chem BET 3000. The catalysts were swept
by N2 flow at 573 K for 1 h and then cooled to 353 K. Pure
NH3 was introduced for about 20 min, followed by purging
with N2 for 30 min at 353 K, then the samples were purged
further with He flow (50 ml/min) for 2 h at 373 K. And the
samples were heated at a ramp of 10 K/min up to 973 K.
2.3 Typical Experimental Procedure
Scheme 1 Schematic of hydrogenation of nitrobenzene
The reaction of hydrogenation of nitrobenzene to PAP was
carried out in a 50 ml stainless steel autoclave with a
magnetic stirrer. 0.02 g Pt/ZrO2, 0.6 g SO42-/ZrO2–Al2O3,
2.4 g nitrobenzene and 0.01 g hexadecyl trimethyl
ammonium bromide (CTAB) along with 30 ml H2O as
solvent were added into the autoclave. The autoclave was
then purged with nitrogen. The reaction was carried out at
353 K and 0.3 Mpa H2 pressure for 3 h. The reaction
products were analyzed using a high performance liquid
chromatograph equipped with a 4.6 mm 9 250 mm C18
column, with 30:70 of CH3OH:H2O as eluent.
prepared by calcination of Zr(OH)4 at 873 K for 3 h under
air flow. Pt/ZrO2 was prepared by incipient wetness
impregnation of the obtained ZrO2 with an aqueous solu-
tion of H2PtCl6. Then the sample Pt/ZrO2 was dried at
393 K for 2 h, calcinated under air flow at 633 K for 2 h
and reduced at 723 K for 3 h.
The ZrO2–Al2O3 binary oxide was prepared by homo-
geneous coprecipitation method. For this purpose, aqueous
solutions of ZrOCl2ÁxH2O and Al(NO3)3ÁxH2O were mixed
together. Then the mixture was hydrolyzed with dilute
ammonium hydroxide under vigorous stirring until the pH
reached to 9–10. A white precipitate was formed and the
precipitate was allowed to age at 353 K for 12 h. After
filtration, the samples were washed with deionized water
for several times and dried at 393 K for 12 h. The prepared
hydrous alumina–zirconia was immersed in 1 M H2SO4 for
30 min to incorporate sulfate ions. The excess water was
evaporated and the obtained samples were dried at 393 K
for 12 h, calcinated at 923 K for 4 h. The SO42-/ZrO2
solid acid catalyst was labeled as SZ. The SO42-/ZrO2–
Al2O3 samples were labeled as SZA-1, SZA-2, SZA-3,
SZA-4 and SZA-5 according to the Zr:Al molar ratio of
9:1, 7:3, 1:1, 3:7, and 1:9, respectively. The particle size of
the catalyst used for the catalytic tests was between 100 to
120 mesh.
3 Results and Discussion
3.1 The Characterizations of Catalysts
BET surface areas and pore volume of various samples are
shown in Table 1. BET surface areas of all the catalysts are
little lower than those reported in the literatures [11]. This
may be attributed to the influence of preparation parame-
ters such as the calcination temperature, sulfating agents
and the concentration [12, 13]. As can be seen from
Table 1, BET surface area increases when Zr:Al molar
ratio decrease from 9:1 to7:3. And BET surface area
increases greatly when Zr:Al molar ratio varies from 1:1 to
1:9. BET surface area reaches to the maximum of
177.59 m2/g when Zr:Al molar ratio is 1:9, which indicates
that the introduction of Al2O3 contributes to the increase of
BET surface area.
2.2 Catalyst Characterization
BET surface areas and pore volume distributions of the
catalysts were measured on a Quantachrome NOVA 2200e
by N2 adsorption at 77 K. Prior to the analysis, each
sample was degassed at 573 K for 3 h in vacuum under
10-3 Torr. BET nitrogen porosimetry analysis was done
with multipoint calibration curves. The pore volume was
calculated from the adsorption isotherms using Barrett–
Joyner–Halenda (BJH) method.
Table 1 BET surface areas and pore volume of SZ and SZA
Materials
Specific
area (m2/g)
Pore volume
(cm3/g)
Pore diameter
(nm)
SZ
74.11
71.08
90.29
71.35
87.53
177.59
0.07
0.15
0.26
0.24
0.16
0.19
1.42
6.57
6.60
7.89
3.82
3.84
SZA-1
SZA-2
SZA-3
SZA-4
SZA-5
X-ray diffraction (XRD) patterns of the solid catalysts
were recorded on a DX-1000 diffractometer, operating at
40 kV and 25 mA and using nickel-filtered Cu Ka
123

Liquid Phase Hydrogenation of Nitrobenzene to Para-Aminophenol
67
sites are artificially divided into weak, middle and strong
acidic centers [16, 17]. SZA-1 with small amount of Al2O3
has the largest amount of acid sites. It has been reported
that the increase of acid strength was caused by the for-
mation of Al–O–Zr [14]. And the acid strength of the SZA
samples decrease gradually with the increased content of
Al. There is a strong acid site on SZA-3 and SZA-5,
respectively, which give NH3-TPD peaks about at 870 K.
Combined with the results of XRD, the enhanced acid
strength on the SZA-3 sample might be related to the
formation of the tetragonal ZrO2 phase [12].
3.2 Catalytic Performance
The influence of different solid acid on the reaction is
shown in Table 2. As can be seen from Table 2, the
selectivity to PAP is only 0.33% in the absence of solid
acid catalyst. The selectivity to PAP is enhanced signifi-
cantly with the action of SZ or SZA solid acid catalysts.
And the SZA catalysts give better results, especially, the
SZA-5 with the Zr:Al molar ratio of 1:9 gives the best
result with the selectivity of 74.9%.
Fig. 1 X-ray powder diffraction patterns of SZ and SZA
XRD patterns of the samples are shown in Fig. 1. The
tetragonal ZrO2 and monoclinic ZrO2 phase are observed in
SO42-/ZrO2. The Al2(SO4)3 crystalline phase emerges in
SO42-/ZrO2–Al2O3 in addition to zirconium species. It can
be seen from Fig. 1 that the tetragonal phase increases
slightly and the monoclinic phase reduces with the increase
of the content of Al. It might be due to the interaction of
Al, Zr and sulfating agents resulting in the formation of
Al–O–Zr bands [14]. It is shown that the Al2O3 plays an
important role in stabilizing tetragonal ZrO2, and the
introduction of Al prevents the tetragonal ZrO2 from
transforming to the monoclinic ZrO2. Among all these
catalysts, no diffraction pattern for Al2O3 is observed,
which indicates that the Al2O3 is uniformly distributed in
ZrO2 [15].
From the results of the catalytic test, it shows that acidic
sites on the catalyst are necessary for Bamberger rear-
rangement process. However, SZA-1 catalyst with the
strongest and the largest amount of acidic site does not give
the best result. On the contrary, SZA-4 and SZA-5 with
less acidic site give better performance. It might be an
integrated effect of suitable amounts of acidic sites and
BET surface area on the performance of nitrobenzene
hydrogenation to PAP.
The effect of reaction temperature on the nitrobenzene
conversion and PAP selectivity is reported in Table 3.
From the results reported in Table 3, it can be noted that
both nitrobenzene conversion and PAP selectivity increase
as the reaction temperature increases from 333 to 353 K.
And nitrobenzene conversion is found to increase from
44.82 to 68.77% with further increase in temperature from
353 to 373 K. However, the selectivity to PAP decreases
sharply from 74.91 to 43.5%.
TPD of NH3 spectra of SZA are shown in Fig. 2. It can
be seen that all the catalysts afford a broad desorption
profiles over the range from 373 to 973 K, suggesting a
broad distribution of heterogeneous acid sites. The acidic
Table 2 Conversion of nitrobenzene to PAP over different catalysts
Catalyst
Conversion (%)
Selectivity (%)
Pt (1%)/ZrO2
48.66
49.86
50.13
46.83
47.71
46.64
44.82
0.33
12.38
15.65
21.33
37.93
60.19
74.91
Pt (1%)/ZrO2 and SZ
Pt (1%)/ZrO2 and SZA-1
Pt (1%)/ZrO2 and SZA-2
Pt (1%)/ZrO2 and SZA-3
Pt (1%)/ZrO2 and SZA-4
Pt (1%)/ZrO2 and SZA-5
Reaction conditions: temperature: 353 K, pressure: 0.3 Mpa, reaction
time: 3 h
Fig. 2 NH3-TPD profiles of the catalysts
123

68
P. Liu et al.
hydrogenation of nitrobenzene with solid acid over Pt/ZrO2
is proposed. Firstly, nitrobenzene is adsorbed on the active
center of Pt/ZrO2 catalyst and reacts with the adsorbed
activated hydrogen molecule to form PHA intermediate.
The formed PHA desorbs from Pt/ZrO2 and adsorbs on the
acid sites of SO42-/ZrO2–Al2O3 and then rearranges to
PAP with the aid of water molecules as a nucleophilic
reagent. And the undesorbed PHA will further react with
hydrogen to obtain aniline.
Table 3 Effect of reaction temperature
Temperature(K)
Conversion (%)
Selectivity (%)
333
343
353
363
373
32.21
37.88
44.82
54.13
68.77
50.63
66.03
74.91
62.42
43.50
Reaction conditions: catalyst: Pt (1%)/ZrO2 and SZA-5, pressure:
0.3 Mpa, reaction time: 3 h
4 Conclusions
Table 4 Effect of platinum loading
In conclusion, the hydrogenation of nitrobenzene to para-
aminophenol over Pt/ZrO2 and SO42-/ZrO2–Al2O3 was
developed in this work. The prepared catalysts were
characterized by BET, XRD and TPD. The results indicate
that the amount of Al2O3 in SO42-/ZrO2–Al2O3 solid acid
catalyst has remarkable influence on the selectivity to para-
Catalyst
Conversion (%)
Selectivity (%)
Pt (0.5%)/ZrO2 and SZA-5
Pt (1%)/ZrO2 and SZA-5
Pt (2%)/ZrO2 and SZA-5
19.77
44.82
78.89
79.44
74.91
37.67
Reaction conditions: temperature: 353 K, pressure: 0.3 Mpa, reaction
time: 3 h
aminophenol. And an optimized para-aminophenol selec-
2-
tivity of 74.9% was obtained over Pt/ZrO2 and SO4
ZrO2–Al2O3 with Zr:Al molar ratio of 1:9.
/
Table 5 Stability and reusability of catalyst
Run
Conversion (%)
Selectivity (%)
Acknowledgments This work was supported by the NSFC
(20976148), Scientific Research Fund of Hunan provincial Educa-
tion Department (09A090, 09CY007) and Project (2009LC004,
09HJYH03).
1
2
3
44.82
41.77
43.25
74.91
65.12
63.69
Reaction conditions: catalyst: Pt (1%)/ZrO2 and SZA-5, the catalyst
used in the first run was used in the second and third run after simple
treatment, temperature: 353 K, pressure: 0.3 Mpa, reaction time: 3 h
References
1. Kirk-Othmer Mitchell S (1992) Encyclopedia of Chemical
Technology, 4th edn. Wiley, New York
The influence of platinum loading was studied for the
catalyst prepared with H2PtCl6Á6 (H2O) within the range of
0.5–2% (w/w) platinum. As can be seen from Table 4,
increasing platinum loading increases nitrobenzene con-
version and decreases the selectivity towards PAP. It may
because the increasing platinum loading helps to promote
over hydrogenation of PHA intermediate to byproduct
aniline.
2. Komatsu T, Hirose T (2004) Appl Catal A 276:95
3. Rylander PN, Karpenko IM, Pond GR (1970) Ann N Y Acad Sci
172:266
4. Karwa SL, Rajadhyaksha RA (1987) Ind Eng Chem Res 26:1746
5. Pernoud L, Candy JP, Didillon B, Jacquot R, Basset JM (2000)
Stud Surf Sci Catal 130:2057
6. Gao Y, Wang FD, Liao SJ, Yu DR (1998) React Kinet Catal Lett
64:351
7. Perez MCM, de Lecea CSM, Solano AL (1997) Appl Catal A
151:461
The Pt (1%)/ZrO2 and SZA-5 were selected to test the
stability and reusability (Table 5). After reaction, the cat-
alysts were separated by filtration, washed with ethanol and
calcined at 923 K. The results of reusability of the catalysts
are shown in Table 5. It can be seen from Table 5 that the
selectivity to PAP decreases from 74.9 to 65.1% in the
second run and almost keeps the value of about 60–64%.
We find that the deactivation of the catalysts is mainly
caused by the adsorbed species on the surface of the cat-
alysts and removal of these species is helpful to restore the
activity of the catalyst.
8. Wang SF, Ma YH, Wang YJ, Xue W, Zhao XQ (2008) J Chem
Technol Biotechnol 83:1466
9. Chaudhari RV, Diveher SS, Vaidya MJ, Rode CV (2000) US
Patent 6028227
10. Chu W, Wu XT, Cui MQ (2004) CN Patent 1562464
11. Escalona Platero E, Pen˜arroya Mentruit M, Otero Aredn C,
Zecchina A (1996) J Catal 162:268
12. Yadav GD, Murkute AD (2004) J Catal 224:218
13. Vishwanathan V, Balakrishna G, Rajesh B, Jayasri V, Coville NJ
(2008) Catal Commun 9:2422
14. Hua WM, Xia YD, Yue YH, Gao Z (2000) J Catal 196:104
15. Reddy BM, Sreekanth PM, Yamada Y, Kobayashi T (2005) J Mol
Catal A 227:81
16. Yadav GD, Murkute AD (2004) Adv Synth Catal 346:389
17. Kirumakki SR, Shpeizer BG, Sagar GV, Chary KVR, Clearfield
A (2006) J Catal 242:319
On the basis of the results in this work and the reported
findings [2, 8], the possible reaction mechanism of liquid
123