Room-temperature heterogeneous hydroxylation of phenol with hydrogen peroxide over Fe2+, Co2+ ion-exchanged Naβ zeolite

Article abstract of DOI:10.1039/b212296k

Ion-exchanged Naβ zeolite with Fe²⁺ and Co²⁺ cations shows high catalytic activity at room temperature in phenol hydroxylation with H₂0₂, where the conversion of phenol is ca. 21% and the selectivity of benzoquinone is below 3% at a molar ratio of phenol to H₂0₂ of 3 in the starting aqueous reaction medium.

Full text of DOI:10.1039/b212296k

Room-temperature heterogeneous hydroxylation of phenol with
2
+
2+
hydrogen peroxide over Fe , Co ion-exchanged Nab zeolite
Jun Wang, Jung-Nam Park, Xian-Yong Wei and Chul Wee Lee*a
ab
a
ac
a
Advanced Chemical Technology Division, Korea Research Institute of Chemical Technology, P.O.Box 107,
Yusung, Daejeon 305-600, Korea. E-mail: chulwee@pado.krict.re.kr; Fax: 82 42 860 7388; Tel: 82 42 860
7381
b
c
Department of Chemical Engineering, Nanjing University of Technology, Nanjing 210009, China
School of Chemical Engineering, China University of Mining and Technology, Xuzhou 221008, China
Received (in Cambridge, UK) 13th December 2002, Accepted 27th January 2003
First published as an Advance Article on the web 6th February 2003
Ion-exchanged Nab zeolite with Fe2+ and Co2+ cations
stirrer, a reflux condenser and a temperature controllable oil-
shows high catalytic activity at room temperature in phenol
bath. 2.0 g Phenol (Kumho P&B Chem., Inc.) was dissolved in
60 ml water and 0.2 g catalyst was added. After the reaction
temperature reached a desired value (20–70 °C), 0.48 ml of
2 2
hydroxylation with H O , where the conversion of phenol is
ca. 21% and the selectivity of benzoquinone is below 3% at a
molar ratio of phenol to H
reaction medium.
2
O
2
of 3 in the starting aqueous
2 2
H O aqueous solution (50 wt%, DC Chem. Co., Ltd) was
charged dropwise into the reaction system using a syringe pump
at the beginning of the reaction. To avoid any photocatalytic
effect on the reaction, the reactor was wrapped in aluminum foil
during the reaction. The reaction mixture was sampled
periodically and filtered to remove catalyst particles, followed
by HPLC (Shimadzu, LC-10ADVP, equipped with a PR, C18
column) analysis using 4-fluorophenol as the external standard,
and UV/Vis as the detector (wavelength = 265 nm, ICI,
LC1200). Besides the target products, CAT and HQ, 1,4-benzo-
quinone (BQ) and by-products (BPs), including maleic acid,
acrylic acid, acetic acid and oligomerization products, were also
detected.
The dihydroxybenzenes, such as catechol (CAT) and hydro-
quinone (HQ), are high value chemicals. They are widely used
as photography chemicals, antioxidants and polymerization
inhibitors, and also used in pesticides, flavoring agents and
medicines. The most desirable method for producing dihydrox-
ybenzenes is the direct hydroxylation of phenol with hydrogen
2 2
peroxide (H O ), an environmentally-friendly catalytic process.
1,2
Homogeneous catalysts such as mineral acids, metal ions and
metal complexes are difficult to be separated and recovered
from the reaction mixture, which prevents their practical
utilization. Therefore, numerous heterogeneous catalysts such
Table 1 compares the catalytic performance of the employed
catalysts at 30 °C. No products are detected without catalyst.
Nab alone gives only a small amount of BPs, indicating that the
zeolite itself without transition metal is not active for the
reaction. Over FeCoNab, the conversion of phenol and the
3
,4
5
as metal oxides, supported metal complexes, metallosilica-
lites,6
–12
hydrotalcite-like compounds, metal-bearing me-
13
14
15
soporous materials, metal hydroxylphosphates and heterop-
oly compounds16 have been attracting research interest recently.
Among them, titanosilicalites have proved to be the most
important catalysts for commercial production of dihydrox-
ybenzenes.6 However, most of the above catalysts either are
high cost and complicated to prepare or show unsatisfied
catalytic activity. Moreover, to our knowledge, no heteroge-
neous catalysts have been found to exhibit high activity in
phenol hydroxylation at room temperature.
2 2
effective conversion of H O increase with the reaction time
while the selectivity of BQ and the molar ratio of CAT to HQ
decrease, which is in good agreement with previous results over
TS-1 catalysts.6 It is proposed that at early stages of the
reaction a fast over-oxidation of HQ by the large concentration
–10
,7
2 2
of H O could cause the formation of BQ in a large amount. The
subsequent disappearance of BQ could arise from the decom-
position of BQ into deep oxidation or degradation BPs, and/or
In contrast with the extensive studies on transition metal
framework-substituted zeolites for phenol hydroxylation,6
ion-exchanged zeolites have not been paid much attention. The
fact that the well-known oxidative Fenton’s reagents are low-
–12
2 2
the oxidation of H O by BQ with the formation of HQ and
oxygen.19 Moreover, phenol conversion attains constant values
around 21% after 2 h of reaction, and the BQ selectivity drops
to a very low level of < 4%, with CAT/HQ being 2.9 after 4 h
of reaction. On the other hand, no further reaction can be
observed in the absence of catalyst for 48 h after filtering
FeCoNab from the sample of 0.5 h of reaction, as shown in
Table 1, confirming the non-leaching of metal ions from the ion-
exchanged zeolite during the reaction. In addition, FeNab is
found to be very active with the same phenol conversion at
21.4% as FeCoNab at 3 h of reaction, however, higher
selectivities of BQ (18.7 vs. 7.0%) and BPs (32.7 vs. 26.9%) are
found over FeNab than those over FeCoNab, even if CoNab
itself is inactive. This observation indicates that cobalt could act
as an effective catalytic promoter in FeCoNab for the
hydroxylation of phenol into dihydroxybenzenes while inhibit-
ing the formation of the undesirable BQ and BPs. Compared
valence transition metal ions such as Fe2 and Cu ,
together with the simplicity of the synthesis of ion-exchanged
zeolites, prompted us to investigate the activity of transition
metal ion-exchanged zeolites in phenol hydroxylation with
+
2+ 17,18
2+
2+
2 2
H O . Here we initiate our investigation on the Fe , Co ion-
exchanged Nab zeolite catalyst, observing that the catalyst is
very active even at room temperature in phenol hydroxylation in
aqueous medium.
FeNab was prepared by the ion exchange of Nab (PQ, SiO
Al = 25) with a 0.005 M aqueous solution of FeSO ·7H
Aldrich, A.C.S. reagent) at 25 °C for 8 h with the liquid/solid
2
/
2
O
2
O
3
4
(
weight ratio being 100, followed by filtration, washing with
water until the filtrate became free from metal ions, drying at
1
00 °C for 8 h and calcination at 450 °C for 5 h in air. CoNab
7
and FeCoNab were prepared from Nab and FeNab, re-
with TS-2 in Table 1, FeCoNab is found to exhibit much higher
spectively, via ion exchange with a 0.005 M aqueous solution of
conversion of phenol (21.3 vs. 9.3%) and effective conversion
Co(NO
3
)
2
·6H
2
O (Aldrich, A.C.S. reagent) at the same reaction
2 2
of H O (48.2 vs. 35.4%), as well as much lower BQ selectivity
conditions as those for FeNab. ICP-AES analysis shows a very
similar iron or cobalt concentration level in the three catalysts,
i.e., 1.15 wt% of Fe in FeNab, 1.14 wt% of Co in CoNab, and
(2.7 vs. 57.2%). Furthermore, the activity of FeCoNab at 30 °C
is comparable to that of TS-1 at a high temperature of 57 °C, as
shown in Table 1, except that a much lower CAT/HQ ratio (1.2)
is observed over TS-1 than that (2.9) over FeCoNab. Although
1
.12 wt% of Fe and 1.26 wt% of Co in FeCoNab.
6
7
Phenol hydroxylation with H
2
O
2
was carried out in a 100 ml
the BPs have not been measured over TS-1 and TS-2, it has
been revealed that titanosilicalite catalysts also generate
three-necked round-bottom flask equipped with a magnetic
6
28
CHEM. COMMUN., 2003, 628–629
This journal is © The Royal Society of Chemistry 2003

2 2
Table 1 Activities of various ion-exchanged zeolite catalysts in phenol hydroxylation with H O at a reaction temperature of 30 °C
Product selectivity (%)
Reaction time
(h)
a
b
2
CAT/HQc
Catalyst
X
phenol (%)
X
H O (%)
CAT
HQ
BQ
BPs
2
No catalyst
Nab
5
5
0.17
0
0
0
1
2
3
4
5
3
3
24
6
0
0.4
0.5
1.4
3.5
3.8
17.9
21.9
21.4
20.4
21.3
21.4
0.5
0
0
0
—
0
0
0
0
0
35.9
47.3
49.4
51.6
52.1
41.5
0
—
0
0
0
0
—
0
0
—
100
100
—
—
—
—
—
—
5.1
3.2
3.0
2.9
2.9
5.9
—
FeCoNab
.34
.5
.5 + 48
3.9
12.3
12.9
52.6
56.8
51.4
47.1
48.2
55.2
0
46.9
58.0
57.2
27.4
11.8
7.0
3.9
2.7
18.7
0
53.1
42.0
42.8
29.5
d
0
7.1
15.0
16.7
17.6
18.0
7.1
0
25.0
26.9
27.0
27.2
32.7
100
?
?
FeNab
CoNab
e
TS-2
9.3
19.8
35.4
55
34.3
55
8.5
45
57.2
0
4.0
1.2
f
TS-1
a
b
2 2
Phenol conversion = 100 3 (phenol before reaction (moles) phenol after reaction (moles))/phenol before reaction (moles). Effective conversion of H O
2 2
100 3 products (moles, HQ + CAT + 2BQ)/total H O
(moles) added. Molar ratio of CAT to HQ. d Analyzed after an additional 48 h when the sample
c
=
e
of 0.5 h of reaction time was filtered from catalyst particles. From ref. 7, reaction temperature 37 °C, phenol/H
ratio) = 9.4, acetone as a solvent. f From ref. 6, reaction temperature 57 °C, phenol/H
O
2 2
(molar ratio) = 3, phenol/catalyst (weight
2 2
O (molar ratio) = 3, phenol/catalyst (weight ratio) = 10, acetone
as a solvent.
considerable deep oxidative tarry by-products.10
of which is even lower than that of FeCoNab at 20 °C in this
work.6
Fig. 1 compares the conversion of phenol over FeCoNab at
various reaction temperatures. It is found that FeCoNab is very
active in the reaction temperature range 20–70 °C. As expected,
raising the reaction temperature accelerates the reaction. For
example, phenol conversion reaches a plateau value of ca. 21%
after 4 h at 20 °C; by contrast, only 10 min is needed at 70 °C.
On the other hand, a maximum conversion of phenol at ca. 24%,
and then a slight decrease of conversion could be observed at
Overall, the results discussed above demonstrate that the
FeCoNab catalyst is very active and selective for dihydrox-
2 2
ybenzenes in phenol hydroxylation with H O in aqueous
reaction medium at room temperature. Metal ions exchanged
into supercages and/or channels of b zeolite are supposed to act
as active centers for the reaction. The results described herein
are believed to be very important for industrial production of
dihydroxybenzenes. Further studies on the reaction mechanism
and the promoter role of cobalt are being undertaken.
0.17–1 h at above 50 °C. This could possibly be ascribed to the
4
more rapid formation of a significant amount of tar products, or
the easier decomposition of H in a non-productive manner at
2
O
2
J. W. acknowledges the financial support of the Foreign
Scientist Invitation Program sponsored by KISTEP (Korea
Institute of S&T Evaluation and Planning).
higher reaction temperatures. This phenomenon is not found at
room reaction temperature. At all reaction temperatures in Fig.
1, both conversion and selectivity reach a steady state within 5
h; when the phenol conversion is ca. 20%, the selectivity of BQ
is < 3%, the selectivity of BPs is ca. 27% and the effective
Notes and references
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Fig. 1 Effect of reaction temperature on phenol conversion over the
FeCoNab catalyst in phenol hydroxylation with H
2 2
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CHEM. COMMUN., 2003, 628–629
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