A novel catalyst of Cu-Bi-V-O complex in phenol hydroxylation with hydrogen peroxide

Article abstract of DOI:10.1006/jcat.2000.2901

A new catalyst of Cu-Bi-V-O complex oxide was hydrothermally synthesized in a Bi₂O₃-V₂O₅-CuO-H₂O system, and its was found that this compound is very active for phenol hydroxylation by H₂O₂, which was comparable to titanium silicalite (TS-1). Investigation using the ESR spin-trapping technique on the catalyst indicated that Cu²⁺ species are major active sites, and hydroxyl radicals are the major active intermediates in phenol hydroxylation. The key factors for phenol conversion and product selectivity were reaction temperature, solvent, phenol/H₂O₂ molar ratio, reaction time, catalyst amount, and method of H₂O₂ addition.

Full text of DOI:10.1006/jcat.2000.2901

Journal of Catalysis 193, 199–206 (2000)
doi:10.1006/jcat.2000.2901, available online at http://www.idealibrary.com on
A Novel Catalyst of Cu–Bi–V–O Complex in Phenol Hydroxylation
with Hydrogen Peroxide
Jianmin Sun, Xiangju Meng, Yanhui Shi, Runwei Wang, Shouhua Feng, Dazhen Jiang,
Ruren Xu, and Feng-Shou Xiao1
Department of Chemistry & Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University,
Changchun 130023, People’s Republic of China
E-mail: fsxiao@mail.jlu.edu.cn
Received September 7, 1999; revised April 7, 2000; accepted April 24, 2000
since it allows simple separation and recovery of the cata-
lyst from the reaction mixture. Therefore, heterogeneous
catalysis over pure metal oxides or supported oxides has
been studied extensively, e.g., MoO3 (10), CuO/SiO2 (11),
Fe2O3 (12), Fe2O3/Al2O3 (13), Co3O4 (14), V2O5, and TiO2
colloidal particles (15). However, these oxides show either
low catalytic activity or undesirable product selectivity.
Microporous titanosilicalites, due to their high activity
in a wide range of oxidation reactions, minimal nonpro-
ductive hydrogen peroxide decomposition, and high cata-
lyst stability, have opened an important catalysis area in
zeolite research (16–19). The first commercial process uti-
lizing titanium silicalite (TS-1) as a catalyst was the hy-
droxylation of phenol introduced by Enichem (20, 21).
After that, a series of microporous and mesoporous mate-
rials containing framework titanium and vanadium species
were investigated intensively, such as TS-2 (22, 23), Ti-
(24), Ti-MCM-41 (25), Ti-ZSM-48 (26), TAPO-5, TAPO-11
(27), zirconotitanosilicates (28), and VS-2 (29). Despite
the obvious attractiveness of these transition metal sub-
stituted molecular sieves, their somewhat complicated syn-
thesis and low reaction rates will limit their application as
popular catalysts for catalytic oxidation in organic chem-
istry. It has been reported that vanadium and copper sites
are active in phenol hydroxylation separately, for example,
VS-2 (29, 30), V2O5–SiO2 xerogels (31), V–Zr–O complex
(32, 33), and CuAlCO3-HTLcs (HTLcs: hydrotalcite-like
compounds) (34). However, catalysis on a complex with the
two transition metals copper and vanadium has not been re-
ported yet. Here we report the catalytic performance of a
novel catalyst (Cu–Bi–V–O) with both vanadium and cop-
per species.
A novel complex oxide of Cu–Bi–V–O was hydrothermally syn-
thesized in a Bi2O3–V2O5–CuO–H2O system, and it was found that
this compound is catalytically active for phenol hydroxylation by
H2O2, which is comparable to TS-1. Reaction temperature, solvent,
the molar ratio of phenol to H2O2, reaction time, catalyst amount,
and method ofH2O2 addition werefound tobemajor factorsfor phe-
nol conversion and product selectivity. Furthermore, electron spin
resonance (ESR) was used to characterize the reaction intermedi-
ates, two species assigned to hydroxyl radicals and hydroperoxyl
radicals were observed, and the hydroxyl radicals are proposed to
play important roles in the formation of products in catalytic phenol
c
hydroxylation by H2O2.
2000 Academic Press
Key Words: complex oxide of Cu–Bi–V–O; catalytic phenol
hydroxylation; hydrogen peroxide; novel catalyst for oxidation
reactions.
INTRODUCTION
Diphenols are important chemical materials; their pro-
duction from hydroxylation of aromatic compounds is al-
ways of great interest to chemists, in particular for phenol
direct hydroxylation by H2O2 (1). Of the environmentally
benign materials, hydrogen peroxide (H2O2) is the most at-
tractive for organic laboratory and small-scale procedures
because H2O2 offers many advantages such as high active
oxygen content and the absence of by-products. These reac-
tions, due to absence of by-products, are considered “clean
reactions,” which are one of the present urgent goals of re-
search in chemistry. Historically, phenol hydroxylation has
been widely investigated over various catalysts such as min-
eral acids (2–4), simple metal ions (5, 6), and metal com-
plexes (7–9). Although some of these catalysts have shown
potential catalytic activities, the obvious disadvantages of
homogeneous reactions are too distinct to prevent their
wide use in phenol catalytic oxidation. A heterogeneous
catalytic system has advantages over homogeneous systems
EXPERIMENTAL
Materials
Bi(NO2)3 6H2O, NaVO3 2H2O, NaOH, CuCl2, H2O2,
and phenol with A.R. purity were supplied from Beijing
1 To whom correspondence should be addressed.
199
0021-9517/00 $35.00
c
Copyright
2000 by Academic Press
All rights of reproduction in any form reserved.

200
SUN ET AL.
Chemical Co. Spin trapping reagent of 5,5-dimethyl-1- 9.77 GHz, a microwave power of 6.5 mW, a modulation fre-
pyrroline N-oxide (DMPO) with G.R. purity was purchased quencyof100KHz, a field modulation intensityof1.25Gpp,
from Aldrich Chemical Co.
a time constant of 500 ms, a scan range of 100 G, and a mild
range of 3480 G.
Synthesis of Samples
Catalytic Hydroxylation of Phenol
Bi(NO3)3 6H2O, NaVO3 2H2O, and CuCl2 were used
as the starting materials in the synthesis, and NaOH
was employed as a mineralizer. The preparation of
Cu2Bi4V2O13 3H2O (Cu–Bi–V–O) with starting molar ra-
tio in the reaction was 0.45 Bi2O3 : 0.45 V2O5 : 0.5 CuO : 5
Na2O : 550 H2O (35). A typical synthesis procedure was as
follows: (1) 0.426 g NaVO3 2H2O was first dissolved in
30 ml NaOH (1.0 M) to form a solution, followed by addi-
tion of 1.308 g Bi(NO3)3 6H2O and 0.255 g CuCl2, forming
the reaction mixture; (2) after stirring for 1 h at room tem-
perature, homogeneous gel was formed, which was then
sealed in a Teflon-lined stainless steel autoclave; (3) the
gel was crystallized at 240 C for 3 days; (4) after crystal-
lization, the product was filtered, washed with deionized
water, and dried in air at ambient temperature. Greenish
crystalline products were obtained. Furthermore, the sam-
ple was characterized by various techniques.
Phenol hydroxylation experiments were run in a 50-ml
glass reactor equipped with a reflux condenser and a mag-
netic stirrer. In a typical experimental procedure, 80 mg
catalyst was mixed with 1.67 g phenol in the glass reactor,
followed by addition of 15 ml water as a solvent, which was
heated to the reaction temperature. Then, 0.60 ml H2O2
(30% aqueous solution) was added into the reaction mix-
ture dropwise using a syringe pump for 40 min. The reac-
tion temperature was in the range 60–90 C. After the reac-
tion, the products including catechol (CAT), hydroquinone
(HQ), and benzoquinone (BQ) were taken out periodically
and analyzed on gas chromatography (Shimadzu GC-9A)
with a flexible quartz capillary column coated with OV-17.
The initially programmed temperature was 140 C, and the
final temperature was 186 C. The H2O2 conversion was de-
termined by two methods: (1) The efficiency conversion of
H2O2 wascalculated asfollows:H2O2 eff. conv. = 100 H2O2
(mol) consumed in formation of diphenols and benzo-
quinone/total H2O2 (mol) added. (2) The H2O2 conversion
was determined by decomposition of H2O2 experimentally.
Similarly, the preparation of Bi16V4O39 (Bi–V–O) and
Bi2CuO4 (Bi–Cu–O) was also synthesized with the hy-
drothermal method, and their starting molar ratios were at
0.5 Bi2O3 : 0.5 V2O5 : 7.5 Na2O : 550 H2O and 0.5 Bi2O3 : 0.5
CuO :25 Na2O : 550 H2O, respectively. The products were
both crystallized at 240 C for 3 days.
ESR Spin-Trapping Measurements
Electron spin resonance (ESR) spectra were recorded
at room temperature and DMPO (5,5-dimethyl-1-pyrroline
N-oxide) was used as the spin trapping reagent. In a typical
run, 24.6mgsample wasmixed with 25 l DMPO;then 45 l
aqueous H2O2 solution was added. Finally, the mixture was
fed into the ESR tube, which was inserted into the cavity of
an ESR spectrometer. At the same time, the ESR spectra
were measured. In order to measure the intensity of radicals
quantitatively, a quartz tube of 1 mm diameter was used in
all the experiments.
Characterization Method
X-ray diffraction (XRD) data were collected on Rigaku
D/Max IIIA diffractometer with Cu K radiation, 40 KV,
and 30 mA in the range 4–70 at room temperature. Ther-
mal analysis including differential thermal analysis (DTA)
and thermogravimetric analysis (TGA) was made with a
Perkin–Elmer DTA-1700 and TGA-7PC analyzer with a
heating rate of 10 C/min, respectively. X-ray photoelectron
spectroscopy(XPS) wasmeasured on an ESCA-LAB MKII
spectrometer (VG Co.) with monochromatic light using
7
RESULTS AND DISCUSSION
Al K radiation, and the base pressure was 10 Pa. The
C1s signal at 284.3 eV was used as the internal standard.
The scanning electron micrograph (SEM) investigation was
performed with a Hitachi X-650B electron microscope. The
Characterization of Various Catalysts
Figure 1showsthe XRD patternsofthe Cu–Bi–V–O sam-
sample compositions were determined by inductively cou- ple, which indicates a novel phase with a monoclinic system
pled plasma (ICP) with a Perkin–Elmer plasma 40 emission with cell parameters of a = 1.497(2) nm, b = 0.3692(1) nm,
spectrometer. The surface area ofthe catalyst wasmeasured c = 1.1168(3) nm, = 107.32(2), and V = 0.6153(1) nm3.
with nitrogen adsorption methods (BET) by using a Micro Similarly, the samples of Bi–Cu–O and Bi–V–O also show
ASAP 2010 M at 77 K, and the adsorption isotherms, for, new peaks of XRD patterns, indicating that Bi–Cu–O and
e.g., water and hexane, were carried out with the Cahn-2000 Bi–V–O are also novel phases.
microbalance at room temperature (298 K). The sensitiv-
The molecular formula of the Cu–Bi–V–O sample was in-
ity of the microbalance was 0.1 g. Electron spin reso- vestigated by ICP analysis, which showed that the percent-
nance (ESR) spectra were recorded at room temperature ages of Bi, V, Cu, and O were at 63.2, 7.7, 9.7, and 19.4% ,
with a Brucker ER 200D-SRC instrument at a frequency of respectively, indicating that the molar ratio of the product

Cu–Bi–V–O CATALYST IN PHENOL HYDROXYLATION BY H2O2
201
Isotherms for N2 at 77 K over the samples of Cu–Bi–V–O,
Bi–Cu–O, and Bi–V–O show that there is little adsorption
of nitrogen, indicating that they do not have micropores
and mesopores. The surface areas of these samples were
measured at 1.5–3.6 m2/g by N2 adsorption, and little ad-
sorption resulted from the outer surface of these catalysts.
Furthermore, the adsorption of H2O over Cu–Bi–V–O ex-
hibited a low adsorption amount 1.4% , which was due to
the small surface area of the sample. In contrast, we could
not, observe the adsorption of n-hexane on this sample. The
samples of Bi–Cu–O and Bi–V–O showed similar adsorp-
tion properties. Moreover, the adsorption of ammonia on
these samples showed that there was no chemical adsorp-
tion, suggesting that these materials are not acidic, which is
similar to TS-1.
The characterization data on surface area, crystal size,
chemical adsorption, and elemental composition of various
catalysts are summarized in Table 1.
Catalytic Phenol Hydroxylation
Catalytic activities over various catalysts. Catalytic ac-
tivities in phenol hydroxylation over various catalysts such
as CuO, V2O5, Bi2O3, CuO + V2O5, Bi–Cu–O, Bi–V–O,
and Cu–Bi–V–O are presented in Table 2. V2O5 is almost
inactive, giving a phenol conversion of only 1.4% . Bi2O3
and CuO show low conversions, 4.5 and 9.8% , respectively.
FIG. 1. X-ray powder diffractions for (a) Bi–V–O, (b) Bi–Cu–O, and
(c) Cu–Bi–V–O samples.
was at 2Bi : 1V : 1Cu : 8O. Furthermore, the Bi–Cu–O and The catalytic activity over the mechanical mixture of CuO
Bi–V–O samples showed molar ratios at 2Bi : 1Cu : 4O and and V2O5 gives low conversion, at 6.7% . Furthermore, the
16Bi : 6V : 39O, respectively.
samples of Bi–V–O and Bi–Cu–O catalysts also exhibit
Chemical states on the surface of various elements were low conversions (5.5 and 8.7% ). It is very interesting to
analyzed by the XPS technique. The spectra of Bi4f7/2 and note that the Cu–Bi–V–O catalyst shows relatively high
Bi4f5/2, V2P3/2 and V2P1/2, Cu2P3/2 and Cu2P1/2 over the catalytic activity, giving conversion at 23.1% with diphenols
Cu–Bi–V–O sample exhibit at 158.6 and 163.9 eV, 516.7 selectivity at 97.7% . This activity is comparable with those
and 524.3 eV, 934.0 and 954.0 eV, respectively. These re- of TS-1 which is well known as one of the best catalysts for
sults suggest that the bismuth, vanadium, and copper in the catalytic oxidation by H2O2 (39). Since the surface area is
chemical state are at Bi3+ (36), V5+ (37), and Cu2+ (38), small (3.6 m2/g) and only the sites in the surface can interact
respectively. Similarly, XPS spectra show that the chemical with reactants in catalysis, a very high turnover number of
states of bismuth, vanadium, and copper in the samples of Cu–Bi–V–O is achieved. At 80 C, the turnover frequency
Bi–Cu–O and Bi–V–O samples are the same as those of (446 h 1) of the Cu–Bi–V–O is much higher than that
Cu–Bi–V–O.
(7.2 h 1) of TS-1 catalyst. Considering the low activities
The stability of the samples is investigated by thermal for Bi–V–O and Bi–Cu–O catalysts, the high activity
analysis, and DTA and TG curves show that all samples are for Cu–Bi–V–O catalyst may be related to its unique
stable below 500 C.
structure.
TABLE 1
Characterization of Various Catalysts
Average
particle size
Elemental
analysis
Cu/Bi/V/O
Adsorption of
Surface area
(m2/g)
Ammonia
adsorption
Sample
(
m)
n-Hexane (% )
Water (% )
Cu–Bi–V–O
Bi–V–O
Bi–Cu–O
25
60
35
3.6
1.5
2.5
no
no
no
1.4
0.5
0.8
2/4/2/16
16/6/39
2/1/4
no
no
no

202
SUN ET AL.
TABLE 2
TABLE 4
Catalytic Performance in Phenol Hydroxylation
over Various Catalystsa
Influence of Temperature in Phenol Hydroxylationa
Phenol
conv.
(% )
H2O2 eff.
conv.
(% )
Product selectivity (% )
Temperature
Phenol
conv.
(% )
H2O2 eff.
conv.
(% )
Product selectivity (% )
( C)
BQ
CAT
HQ
Catalyst
BQ
CAT
HQ
60
70
80
90
13.2
18.9
23.1
20.2
42.9
59.4
70.9
61.2
8.4
4.8
2.3
0.8
52.9
55.9
55.0
54.3
38.7
39.3
42.7
44.9
V2O5
Bi2O3
CuO
Bi–V–O
Bi–Cu–O
CuO + V2O5
Cu–Bi–V–O
TS-1b
1.4
4.5
9.8
5.5
8.7
6.7
23.1
26.4
4.0
14.1
32.7
19.4
30.1
25.2
70.9
75.0
—
4.6
100
—
18.3
20.7
65.4
62.0
73.2
55.0
52.0
77.1
68.0
17.3
22.8
1.7
11.3
17.3
15.2
25.1
2.3
a Reaction conditions are the same as those in Table 2.
42.7
46.0
ple was inactive; however, both are the best solvents over
TS-1 (39, 41). In contrast, over Cu–Bi–V–O catalyst the best
solvent is water, which is considerably safer, cheaper, and
more environmentally benign than organic solvents in in-
dustrialuse. Wu etal. (34, 42, 43) reported that over the cata-
lysts of CuAlCO3-LTLcs and Iron(II)-8-quinolinol/MCM-
41 the change in solvents resulted in large differences in
conversion, suggesting that the free radicals were important
intermediates in the catalysis. The results for solvent influ-
ence may suggest that the mechanism over the Cu–Bi–V–O
sample might be different from that over titanosilicalites
(20, 22).
2.0
a Reaction conditions: water as solvent; reaction temperature 80 C; re-
action time 4 h; phenol/H2O2 (molar ratio) = 3; catalyst/phenol (weight
ratio) = 0.05.
b Reaction conditions (39): TS-1 with Ti/(Ti + Si) = 0.091; acetone as
solvent;reaction temperature 57 C; reaction time 6h; phenol/H2O2 (molar
ratio) = 3; catalyst/phenol (weight ratio) = 0.1.
Because the highest activity is found on the Cu–Bi–V–O
sample, catalytic investigation of various influencing fac-
tors for phenol hydroxylation is mainly focused on this
catalyst.
Effect of reaction temperature. In order to choose the
optimum reaction temperature at which phenol conversion
and selectivity are most desirable, we performed this re-
action in the temperature range 60–90 C, as presented in
Table 4. It is observed that phenol conversion increases
with temperature from 13.2 to 23.1% from 60–80 C. Mean-
while, H2O2 efficiency also increases with temperature from
42.9% at 60 C to 70.9% at 80 C. However, when the tem-
perature is enhanced to 90 C, phenol conversion decreases
to 20.2% , and H2O2 efficiency reduces to 61.2% . In ad-
dition, benzoquinone selectivity decreases with increasing
temperature from 8.4% at 60 C to 0.8% at 90 C. To explain
the decrease of conversion at higher temperature, it is pro-
posed that benzoquinone was further oxidized to tar, and
similar phenomena have been observed in the literature
(44). Therefore, the suitable temperature for this catalytic
reaction is 80 C.
Effect of the solvent. It has been reported that the sol-
vent has profound influences on the phenol conversion
and the ratio of catechol to hydroquinone over titanosil-
icalites (40, 41), VS-2 (29), and vanadium silicate xero-
gels (31). Table 3 presents the effect of various solvents
in phenol hydroxylation over Cu–Bi–V–O catalyst. We ob-
served that the sample of Cu–Bi–V–O was almost inactive
in the organic solvents of acetone, acetonitrile, and 1,2-
dichloroethane. Changing the solvent from organic solvents
to water resulted in a significant increase of conversion. Ob-
viously, phenol conversion increased with increasing polar-
ity of the solvents (the conversions at 0, 1.1, 1.8, and 12.5%
for acetone, acetonitrile, 1,2-dichloroethane, and water, re-
spectively). In methanol and acetone, the Cu–Bi–V–O sam-
TABLE 3
Effect of reaction time. Table 5 presents the dependence
of the reaction conversion and selectivity on reaction time.
Obviously, relatively short reaction time results in incom-
plete conversion of phenol and H2O2. Moreover, the selec-
tivity of benzoquinone in the product is very high at the
beginning of the reaction. These phenomena are very sim-
ilar to those on TS-1 (39). When phenol conversion gives
a maximum conversion of 23.1% at 4 h, benzoquinone se-
lectivity is only at 2.3% . When reaction time is prolonged
beyond 4 h, phenol conversion and H2O2 efficiency reduce
remarkably, exhibiting 9.8 and 29.5% at 8 h, respectively.
This is assigned to the formation of a large amount of tar
Influence of Various Solvents in Phenol Hydroxylationa
Phenol
conv.
Product selectivity (% )
Solvent
Methanol
(% )
BQ
CAT
HQ
inactive
inactive
1.1
1.8
12.5
—
—
—
—
26.8
—
—
79.3
35.2
56.1
—
—
20.7
64.8
17.1
Acetone
Acetonitrile
1,2-Dichloroethane
Water
a Reaction conditions: temperature at 60 C; other conditions are the
same as those in Table 2.

Cu–Bi–V–O CATALYST IN PHENOL HYDROXYLATION BY H2O2
203
TABLE 5
Influence of Reaction Time in Phenol Hydroxylationa
TABLE 7
Influence of Phenol/H2O2 Molar Ratio in Phenol Hydroxylationa
Reaction
time
Phenol
conv.
(% )
H2O2 eff.
conv.
(% )
Molar ratio
of phenol
to H2O2
Phenol
conv.
(% )
H2O2 eff.
conv.
(% )
Product selectivity (% )
Product selectivity (% )
(h)
BQ
CAT
HQ
BQ
CAT
HQ
1
2
3
4
6
8
12.9
16.7
20.3
23.1
13.2
9.8
50.2
56.4
65.8
70.9
40.3
29.5
29.7
12.6
8.1
2.3
1.7
54.8
57.9
55.3
55.0
55.1
56.2
15.5
29.5
37.6
42.7
42.2
41.3
3 : 1
2 : 1
1 : 1
1 : 2
1 : 3
23.1
29.6
38.9
40.7
51.2
70.9
59.2
38.9
20.4
17.1
2.3
—
—
—
—
55.0
56.3
65.2
62.9
67.6
42.7
43.7
34.8
37.1
32.4
0.5
a Reaction conditions are the same as those in Table 2.
a Reaction conditions are the same as those in Table 2.
product for a longer reaction time. The product of benzo-
quinone is generally considered as the oxidation product of
hydroquinone, and benzoquinone is further oxidized to tar
(45).
phenol conversion is 23.1% and H2O2 efficiency is 70.9% .
When the molar ratio is 3/1, phenol conversion is 51.2% , but
H2O2 efficiency reduces to 17.1% . Keeping industrial pro-
cesses in mind, we performed the experiments at a molar
ratio of 3 : 1 (phenol/H2O2).
Effect of catalyst amount. Table 6 presents the effect of
catalyst amount on catalytic activity and selectivity. Cata-
lytic phenol hydroxylation does not occur in the absence
of the catalyst. Phenol conversion increases with catalyst
amount in the range 0–5% (weight ratio of catalyst to phe-
nol); however, when the ratio is over 5% , the conversion re-
duces remarkably. For example, phenol conversion is 23.1%
at the ratio 5% , and the conversion is only 13.1% at the ratio
10% . Additionally, we observe that H2O2 decomposition in
the reaction increases with catalyst amount. When the cata-
lyst amount is at 80 mg, 9.2% of total H2O2 is decomposed
(2.4% of total H2O2 is decomposed over TS-1 catalyst un-
der the same reaction conditions), and when the catalyst
amount is 320 mg, 14.5% of H2O2 is decomposed. There-
fore, having the ratio of catalyst to phenol at 5% is suitable
for obtaining higher phenol conversion.
Effect of addition method for H2O2. The method of
H2O2 addition has a large effect on conversion and prod-
uct selectivity. The catalytic results of two methods of H2O2
addition are shown in Table 8. In the first method, H2O2
is completely added into the reaction mixture in one lot at
room temperature, and the system is then slowly warmed
to the reaction temperature (80 C). In the second method,
the phenol-catalyst mixture is first heated to 80 C, and then
H2O2 isadded dropwise at 80 C over a period of40min. Ob-
viously, phenol conversion and H2O2 efficiency are higher,
and benzoquinone selectivity is lower, in the latter case.
When H2O2 was added at room temperature, 12.4% of the
H2O2 was decomposed. When H2O2 was added at 80 C,
9.2% of the H2O2 was decomposed. It is well known that
when H2O2 is added into the reaction mixture in one lot,
Effect of molar ratio of phenol to H2O2. Table 7 presents the effective concentration of H2O2 in the reaction is much
the effect of molar ratio of phenol to H2O2. We observe higher than that achieved by dropwise addition, leading to
that phenol conversion increases with increasing molar ra- formation of a large amount of benzoquinone, which is the
tio of H2O2/phenol, but H2O2 efficiency displays the op- product of further oxidation of hydroquinone. Similar phe-
posite trend. When the molar ratio of H2O2/phenol is 1/3, nomena have been reported in the literature (39).
TABLE 8
TABLE 6
Influence of Catalyst Amount in Phenol Hydroxylationa
Influence of the Method of Addition of H2O2
in Phenol Hydroxylationa
Catalyst
amount
(wt% )
Phenol
conv.
(% )
H2O2 eff.
conv.
(% )
Product selectivity (% )
Phenol
conv.
(% )
H2O2 eff.
conv.
(% )
Product selectivity (% )
BQ
CAT
HQ
Method of H2O2
addition
BQ
3.9
CAT
55.9
HQ
0
1
2.5
5
10
20
0
0
0
0
0
10.5
18.7
23.1
13.1
9.9
33.5
57.2
70.9
40.6
31.2
6.5
1.9
2.3
3.4
4.9
52.8
55.3
55.0
50.1
52.9
40.7
42.8
42.7
46.5
42.2
H2O2 addition in one
lot at room
temperature
H2O2 addition
dropwise at 80 C
15.2
47.4
70.9
40.2
23.1
2.3
55.0
42.7
a Reaction conditions are the same as those in Table 2.
a Reaction conditions are the same as those in Table 2.

204
SUN ET AL.
TABLE 9
Regeneration of the Catalyst in Phenol Hydroxylationa
Phenol
conv.
(% )
Product selectivity (% )
Catalytic reaction
BQ
CAT
HQ
First run (fresh sample)
23.1
18.4
11.3
6.2
2.3
2.2
4.5
3.9
1.4
55.0
55.8
50.3
51.8
51.4
42.7
42.0
45.2
44.3
47.2
Second run (used sample from run 1)
Third run (used sample from run 2)
Fourth run (used sample from run 3)
Fifth run (regeneration by calcining
used sample from run 4 at
22.5
500 C for 2h)
Tenth run (regeneration 5 times)
22.2
1.8
51.1
47.1
a Reaction conditions are the same as those in Table 2.
Regeneration of the catalyst. Phenol conversion reduces
drastically from 23.1 to 6.2% after four runs over the Cu–
Bi–V–O catalyst (see Table 9); it is proposed that the cat-
alyst surface is poisoned by tar formed by deep oxidation
of benzoquinone, preventing its further reaction with phe-
nol. TG analysis on spent catalyst in oxygen atmosphere
indicates the weight loss in the region 350–500 C is close
to 25% , suggesting that the catalyst surface is partially cov-
ered with tar. However, when used Cu–Bi–V–O catalyst is
calcined at 500 C for 2 h, its catalytic activity is maintained
at the initial level, 22.5% , because the deposited tar on the
catalyst surface is burned out. Moreover, the XRD and IR
spectra show that the structure of the Cu–Bi–V–O catalyst
remains unchanged after calcination, suggesting that it has
high stability. Therefore, the catalyst can be regenerated
easily without any significant loss in activity.
FIG. 2. ESR spectra of DMPO with H2O2 on the samples of (a) Bi–
V–O, (b) Bi–Cu–O, (c) CuO, and (d) Cu–Bi–V–O.
and VS-2(29, 30). Because the intensityofthe hydroperoxyl
radical was relatively low, the catalytic activity of Bi–V–O
was also low.
Hydroxyl radicals were observed in the reaction of Bi–
Cu–O and CuO with H2O2, which resulted from interaction
of H2O2 with Cu2+ species in these catalysts. These hydroxyl
radicals are possibly intermediates in the catalysis on CuO
and Bi–Cu–O (34, 42, 43). Notably, both hydroxyl radicals
and hydroperoxyl radicals were observed in the mixture
of Cu–Bi–V–O with H2O2, but the intensity of hydroxyl
radicals was much stronger than that of hydroperoxyl rad-
icals. Relating to the large difference in catalytic activity
on various catalysts, we suggest that the higher activity in
the Cu–Bi–V–O catalyst is mainly from a larger amount of
hydroxyl radicals, which result from the unique structure
of the sample. As shown in Fig. 3, the dependence of the
ESR Investigation for Various Samples
The ESR spectra of the DMPO with H2O2 on various
samples are shown in Fig. 2. On the Bi–V–O sample, the
spectrum shows signals at aN = 1.41 mT, aH = 1.13 mT, and
aH = 0.13 mT, which are assigned to the adduct of DMPO
with hydroperoxyl radical (46). The spectrum on the CuO
sample shows signals at aN = aH = 1.49 mT, which are typi-
cally assigned to the adduct of DMPO with hydroxyl radical
(47). The Bi–Cu–O sample also shows the same signals at
aN = aH = 1.49 mT, but the intensity is slightly weaker. The
spectrum on the Cu–Bi–V–O sample exhibits both very
strong signals at aN = aH = 1.49 mT and weak signals at
aN = 1.41 mT, aH = 1.13 mT, and aH = 0.13 mT, which are
assigned to hydroxyl radicals and hydroperoxyl radicals,
respectively.
ESR spin trapping experiments showed that hydroper-
oxyl radicals were formed in the reaction of Bi–V–O with
H2O2, and hydroperoxyl radicals might be the intermedi-
ates in the phenol hydroxylation on Bi–V–O catalyst. Sim-
ilar phenomena have been observed on the catalysts VS-1
FIG. 3. Catalytic activity as a function of the relative intensity of hy-
droxyl radicals characterized by ESR.

Cu–Bi–V–O CATALYST IN PHENOL HYDROXYLATION BY H2O2
ACKNOWLEDGMENTS
205
This work was supported by the National Natural Science Founda-
tion of China (grant numbers 29825108 and 29733070), the Outstanding
Junior Faculty of the Education Committee of China, and the National
Advanced Materials Committee of China (NAMMC, grant number 863-
715-004-0210).
REFERENCES
1. Taramasso, M., Pereg, G., and Notari, B., U.S. Patent 4,410,501 (1983).
2. Skepalik, C., Ger. Offen. 2,138,735 (1973).
3. Uohama, M., Japan Patent 0,334,948 [91 34948] (1991).
4. Brown, S. W., Br. Patent Appl. 913,323 (1991).
5. Brook, M. A., Catle, L., and Lindsay, I. R., J. Chem. Soc. Perkin Trans.
2, 687 (1982).
FIG. 4. ESR spectra of (Cu–Bi–V–O)–H2O2–DMPO mixture (a) af-
ter addition of phenol and (b) without addition of phenol.
6. Hoching, M. B., and Intihom, D., J .Chem. Technol. Biotechnol. 35, 365
(1985).
7. Litvintsv, L. Y., Kinet. Catal. 34, 71 (1993).
8. Hytbrechts, D. R. C., Catal. Lett. 8, 273 (1991).
9. Danopoulos, A. A., Paraskevas, S. M., and Savogias, S., Erdoel Kohle.
Erdgas. Petrochem. 47, 240 (1994).
10. Tatarinova, T. A., Katal. Katal. 23, 54 (1985).
11. Njnibeako, A., Prepr. Can. Symp. Catal. 5, 170 (1977).
12. Imamura, S. M., Gjjutsu 22, 201 (1981).
intensity of hydroxyl radicals on the catalytic activity over
Cu–Bi–V–O, Bi–Cu–O, and CuO is plotted, and a linear re-
lationship between hydroxyl radical intensity with catalytic
activity is observed, confirming that the hydroxyl radicals
are important intermediates for the phenol hydroxylation
by H2O2.
13. Al-Hayck, N., Water Res. 19, 657 (1985).
Furthermore, when phenol was added into the reac- 14. Ai, M., J. Catal. 54, 223 (1978).
15. Goldstein, S., Czapski, G., and Robani, J., J. Phys. Chem. 98, 6586
tion mixture of the Cu–Bi–V–O catalyst system (catalyst +
H2O2 + DMPO), the signals assigned to hydroxyl and hy-
droperoxyl radicals disappeared very quickly (Fig. 4), and
the products of diphenols were observed by the character-
ization of mass spectroscopy technique. These results sug-
gest that these radicals are important intermediates in the
catalytic reactions.
(1994).
16. Thangaray, A., Kumar, R., and Ratnasamy, P., Appl. Catal. 57, L1
(1990).
17. Neri, C., Esposito, A., Anfossi, B., and Buonomo, F., Eur. Patent
100,119 (1984).
18. Zecchina, A., Spoto, G., Bordig, S., Geobaldo, F., Petrini, G., Leofanti,
G., Padovan, M., Mantegazza, M., and Roffia, P., Stud. Surf. Sci. Catal.
75, 719 (1995).
19. Esposito, A., Neri, C., and Buonomo, F., U.S. Patent 4,480,135 (1984).
20. Bellusti, G., and Fattore, V., Stud. Surf. Sci. Catal. 69, 79 (1991).
Because hydroxyl radicals and hydroperoxyl radicals are
electrophile, and tend to allow electrophilic attack at the
ortho and para positions of phenol to form catechol and 21. Zecchina, A., Spoto, G., Bordiga, S., Ferrero, A., and Petrini, G., Stud.
Surf Sci. Catal. 69, 251 (1991).
22. Reddy, J. S., Kumar, R., and Ratnasamy, P., Appl. Catal. 58, L1 (1990).
23. Reddy, J. S., and Sivasanker, S., Catal. Lett. 11, 241 (1994).
24. Camblor, M. A., Corma, A., Martinez, A., and Perez-Pariente, J.,
hydroquinone (48, 49), no resorcinol is detected in this re-
action.
As presented in Table 3, it was observed that over Cu–
Bi–V–O catalyst phenol hydroxylation in water proceeded
J. Chem. Soc. Chem. Commun. 589 (1992).
better than in the other organic solvents. This phenomenon 25. Jiri, K. R., Amost, Z., and Jiri, H., Collect Czech, Chem. Commun. 60,
451 (1995).
is possibly explained by these active radicals being more
easily formed and dispersed in water than those in the other
organic solvents, in good agreement with the literatures
(42, 43).
26. Serrano, D. P., Li, H.-X., and Davis, M. E., J. Chem. Soc. Chem. Com-
mun. 745 (1992).
27. Vlagappan, N., and Rishasany, V., J. Chem. Soc. Chem. Commun. 374
(1995).
28. Kondo, O., Sugsi, T., and Yoshida, S., Japan Kokai Tokkyo Koho, Japan
Patent 1,640,978 (94 40978) (1994).
29. Hari, P. R., Rao, P., and Ramaswamy, A. V., Appl. Catal. A 93, 123
(1993).
CONCLUSIONS
30. Hari, P. R., Rao, P., Ramaswamy, A. V., and Ratnasamy, P., J. Catal.
137, 225 (1992).
31. Neumann, R., and Levin-Elad, M., Appl. Catal. A 122, 85 (1995).
A novel catalyst of Cu–Bi–V–O complex oxide has been
hydrothermally synthesized, and its catalytic data in phenol
hydroxylation byhydrogen peroxide showthat Cu–Bi–V–O 32. Yu, R. B., Xiao, F. S., Wang, D., and Xu, R., Catal. Lett. 49, 49 (1997).
33. Yu, R. B., Xiao, F. S., Wang, D., Sun, J. M., and Xu, R., Catal. Today
complexoxide isveryactive, which iscomparable with TS-1.
51, 39 (1999).
Moreover, investigation using the ESR spin-trapping tech-
34. Zhu, K. Z., Liu, C. B., Ye, X. K., and Wu, Y., Appl. Catal. A 168, 365
nique on the catalyst has suggested that Cu2+ species are
(1998).
major active sites, and hydroxyl radicals are proposed to be
major active intermediates in phenol hydroxylation.
35. Shi, Y. H., Ph.D. thesis, Jilin University, China, 1999.
36. Debies, T. P., and Rabalais, J. W., Chem. Phys. 20, 277 (1977).

206
SUN ET AL.
37. Larsson, R., Fockesson, B., and Schon, G., Chem. Scr. 3, 88 (1973).
38. Mcintyre, N. S., Rummery, T. E., Cook, M. G., and Owen, D., J. Elec- 44. Martens, J. A., Buskens, Ph., and Jacobs, P. A., Appl. Catal. A 99, 7
trochem. Soc. 123, 1165 (1976). (1993).
39. Thangaraj, A., Kumar, R., and Ratnasamy, P., J. Catal. 131, 294 (1991). 45. Reddy, J. S., Sivasanker, S., and Ratnasamy, P., J. Mol. Catal. 71, 373
43. Liu, C. B., Shan, Y. K., Yang, X. G., and Wu, Y., J. Catal. 168, 35 (1997).
40. Romano, U., Esposiito, A., Maspero, F., Neri, C., and Clerici, M. G.,
(1992).
Chem. Ind. (Milan) 72, 610 (1990).
46. Harbour, J. R., and Hair, M. L., J. Phys. Chem. 81, 1791 (1977).
41. Toel, A., Moussa-Khou Zami, S., Ben. Tarit, Y., and Naccache, C., 47. Finkelstein, E., Rosen, G. M., and Ranckman, E. J., J. Am. Chem. Soc.
J. Mol. Catal. 68, 45 (1991).
102, 4994 (1980).
42. Liu, C. B., Zhao, Z., Yang, X. G., and Wu, Y., Chem. Commun., 1019
48. Metelitsa, D. I., Russ. Chem. Rev. 40, 563 (1971).
49. Walling, C., Actas Chem. Rsch. 8, 125 (1975).
(1996).