Study on the formation and role of copper chloride hydroxide in the oxidative carbonylation of methanol to dimethyl carbonate

Article abstract of DOI:10.1134/S0023158410020138

The synthesis of dimethyl carbonate by oxidative carbonylation of methanol over CuCl/SiO₂-TiO₂ catalysts has been investigated in a slurry reaction system. The γ-Cu₂(OH)₃Cl crystals were detected by X-ray diffraction on the catalysts after reaction. It was revealed that γ-Cu₂(OH)₃Cl was formed by CuCl reacting with O₂ and by-product water. The catalytic tests showed that γ-Cu₂(OH)₃Cl was largely inactive for this reaction, may be attributed to its high stability that resisted the Cu ⁺/Cu²⁺ redox cycle.

Full text of DOI:10.1134/S0023158410020138

ISSN 0023ꢀ1584, Kinetics and Catalysis, 2010, Vol. 51, No. 2, pp. 250–254. © Pleiades Publishing, Ltd., 2010.
Published in Russian in Kinetika i Kataliz, 2010, Vol. 51, No. 2, pp. 265–269.
Study on the Formation and Role of Copper Chloride Hydroxide
in the Oxidative Carbonylation of Methanol to Dimethyl Carbonate1
Jun Ren*, Zhong Li, Shusen Liu, Xinglu Lu, and Kechang Xie
Key Laboratory of Coal Science and Technology (Taiyuan University of Technology),
Ministry of Education and Shanxi Province, 030024 Taiyuan, China
*eꢀmail: renjun@tyut.edu.cn
Received December 29, 2008
Abstract—The synthesis of dimethyl carbonate by oxidative carbonylation of methanol over CuCl/SiO2–
TiO2 catalysts has been investigated in a slurry reaction system. The
Xꢀray diffraction on the catalysts after reaction. It was revealed that
reacting with O2 and byꢀproduct water. The catalytic tests showed that
this reaction, may be attributed to its high stability that resisted the Cu+/Cu2+ redox cycle.
γ
ꢀCu2(OH)3Cl crystals were detected by
ꢀCu2(OH)3Cl was formed by CuCl
ꢀCu2(OH)3Cl was largely inactive for
γ
γ
DOI: 10.1134/S0023158410020138
1
1. INTRODUCTION
was reported that two different crystal habits of
Cu2(OH)3Cl ꢀtype and ꢀtype were observed during
the preparation of CuCl2/NaOH/AC catalysts, the
Cu2(OH)3Cl phase changed from ꢀtype to ꢀtype
with increasing OH/Cl molar ratios [8]. The improved
performance of the catalysts was related with the existꢀ
,
α
γ
Dimethyl carbonate (DMC) is an environmentally
benign chemical product and unique intermediate
with versatile chemical reactivity [1]. The direct oxiꢀ
dative carbonylation of methanol with CO and О2 to
DMC in a liquidꢀphase slurry process has been indusꢀ
trially employed by using cuprous chloride as catalyst
[2]. The existence of Cl– in aqueous media, under the
condition of the redox of Cu, was revealed to induce
severe corrosion to metallic materials along with cataꢀ
lyst deactivation. Attempts have been made to develop
alternative catalyst systems, mainly including supꢀ
ported CuCl or CuCl2 catalysts [3, 4]. On the other
hand, a oneꢀstep vapor phase process was subseꢀ
quently developed and considered to be more desirꢀ
able because it has been found almost free from corroꢀ
sion [5], However, the CuCl2/AC catalyst suffered
deactivation due to loss of chloride [6]. The catalyst
structure changed together with the removal of chloꢀ
ride anions during the catalytic reaction, CuCl2 and
α
γ
ence of Cu2(OH)3Cl, the
ered to be more favorable to DMC synthesis than the
ꢀtype catalyst [9]. Together, these previous studies
indicated that there might be a correlation between the
remarkable compound Cu2(OH)3Cl and DMC proꢀ
ductivity. However, the mechanism of Cu2(OH)3Cl
formation has not been clarified. Moreover, the correꢀ
lation between Cu2(OH)3Cl and intrinsic catalytic
γꢀtype catalyst was considꢀ
α
γꢀ
γꢀ
γꢀ
performance remains ambiguous.
We have recently studied the interaction between
CuCl and the oxide support of CuCl/SiO2–TiO2 cataꢀ
lysts for the synthesis of DMC using quantum
mechanical methods (DFT). The calculation results
show that supporting CuCl on silicaꢀtitania mixed
oxides surface can lead to enhanced methanol oxidaꢀ
tive carbonylation activity and improved catalyst staꢀ
bility due to the formation of Cu–O coordination
bonds [10]. In the present work, in order to elucidate
the above two problems, the SiO2–TiO2 supported
CuCl catalysts along with the compound
CuCl species seemed to be converted to Cu–Cl–OH
compounds. It was found that maintaining these comꢀ
pounds on the surface of activated carbon appeared to
be helpful to selective DMC synthesis.
Supported Wackerꢀtype catalyst PdCl2–CuCl2–
CH3COOK/AC was recently investigated, it was found
that the activated carbon supports pretreated with
H2O and KOH or H2 reduction could promote the forꢀ
mation of Cu2(OH)3Cl, which was recognized as the
active phase over the catalysts [7]. An excellent correꢀ
lation was further observed between the intensity of
Xꢀray diffraction (XRD) reflections of Cu2(OH)3Cl
and the space—time yield for DMC production. It
γꢀCu2(OH)3Cl were prepared and their catalytic perꢀ
formances for the oxidative carbonylation of methanol
have been investigated in the liquidꢀphase reaction.
The influence of
formance of CuCl/SiO2ꢀTiO2 was discussed, and the
formation mechanism and role of Cu2(OH)3Cl in
γꢀCu2(OH)3Cl on the catalytic perꢀ
γꢀ
this reaction was proposed and confirmed by experiꢀ
ment.
1
The article is published in the original.
250

STUDY ON THE FORMATION AND ROLE OF COPPER CHLORIDE HYDROXIDE
251
Table 1. Catalytic activities of the CuCl/SiO2–TiO2 catalysta
STYd
,
Grain size
Sample
Fresh
DMC, wt % DMM, wt % MF, wt % Cmb Smc , mol %
, mol %
gDMC g–1 h–1
of
γ
ꢀCu2(OH)3Cle, nm
Cat
8.79
6.88
5.71
4.64
0.93
1.34
1.28
1.28
0.07
0.15
0.12
0.13
7.68
6.85
5.87
5.10
83.35
72.61
69.99
65.36
1.17
0.92
0.76
0.62
–
1st recycle
2nd recycle
21
46
56
3rd recycle
a
Note: Reaction conditions: MeOH/CO/O = 19.13/2/1(mol/mol/mol), W = 2.0 g, Temperature = 140°C. Pressure = 2.4 MPa. Reaction
2
cat.
b
c
time (t) = 1.5 h. MeOH conversion = Produced (DMC + DMM + MF)/MeOH. DMC selectivity (based on MeOH) = DMC/(DMC +
DMM + MF). DMC spaceꢀtime yield = (MeOH conversion)(DMC selectivity)/(tW ). Calculated from the Scherrer equation.
d
e
cat.
2. EXPERIMENTAL
2.4. XRD Analysis
Xꢀray diffraction (XRD) data were recorded on a
2.1. Preparation of CuCl/SiO2ꢀTiO2 Catalysts
Rigaku D/max 2500 diffractometer using Cu
K radiaꢀ
α
tion (40 kV and 100 mA) over a
a scanning rate of 1 deg/min.
2θ range of 10°–65° at
The silicaꢀtitania support with a Si/Ti ratio of 10
was prepared by following the method described in the
previous paper [11]. The support was mixed with CuCl
(weight ratio: 80/20) and calcined at 550оС in a tube
oven under N2 atmosphere for 3 h followed by cooling
to room temperature, then the CuCl/SiO2–TiO2 cataꢀ
lyst was obtained.
3. RESULTS AND DISCUSSION
3.1. Catalytic Activity of CuCl/SiO2ꢀTiO2
Table 1 gives the results of catalytic tests on the
CuCl/SiO2ꢀTiO2 catalyst through three successive
recycle runs after filtration and washing with methaꢀ
nol. The products derived from methanol included
DMC, DMM and MF. The freshly prepared catalyst
gave a methanol conversion of 7.68% and DMC selecꢀ
tivity of 83.35%, and an obvious decrease in activity
and selectivity was observed after successive recycling
of the catalyst. In its first recycling use, methanol conꢀ
version and DMC selectivity dropped to 6.85 and
72.61%, respectively. During the second and third
recycling, DMC selectivity eventually decreased to
69.99 and 65.36% with further decline in methanol
conversion.
2.2. Preparation of
γ
ꢀCu2(OH)3Cl
γꢀCu2(OH)3Cl was synthesized by two separate
routes. Route 1: Treating CuO and CuCl2 2H2O in a
⋅
hydrothermal process [12], the slurry was mixed using
a magnetic stirrer in a round bottomed flask for 24 h.
The precipitate was collected, washed and dried at
80°С for 1.5 h and the resulting powder was repreꢀ
sented as sample “A.” Route 2: A saturated solution
was prepared with 30 g NaCl dissolving in 100 ml
water, and then CuCl was immersed. The solution was
transferred into a threeꢀnecked bottle when its color
had become yellow, then air was introduced and the
system was kept in a hotꢀbath of 70°С for 7–8 h under
stirring conditions. The product was washed, filtered
and dried at 90°С overnight; the resultant powder was
represented as sample “B.”
3.2. Crystalline Structure of CuCl/SiO2
before and after Reaction
–TiO2
Figure 1 presents XRD patterns of the fresh and the
recycled CuCl/SiO2–TiO2 catalysts. In all cases, a
broad diffraction peak at approximately 23° was
obtained, which was believed to be due to amorphous
supports, SiO2–TiO2 mixed oxide. For the fresh cataꢀ
lyst, regardless of the broad diffraction peak, very weak
diffraction peaks corresponding to CuCl were
detected, revealing that CuCl was well dispersed on
the surface of SiO2–TiO2 support through heat treatꢀ
ment under N2 atmosphere. The elemental analysis
results showed that the asꢀprepared CuCl/SiO2–TiO2
catalyst contained 5.85 wt % Cu and 2.93 wt % Cl,
suggesting that a great part of CuCl was lost by subliꢀ
mation during the procedure of catalyst preparation
(The theoretical concentrations of Cu and CI were
12.83 wt % and 7.17 wt %, respectively). The Cu/Cl
2.3. Catalytic Reaction and Analytical Procedures
The catalytic reaction was performed in a 250 ml
autoclave according to the following procedure: 50 ml
of methanol, which served as the substrate and solvent,
and catalyst powders (2.0 g) were added in the autoꢀ
clave. Then, CO (1.6 MPa) and О2 (0.8 MPa) were
introduced. After reaction at 140°С for 1.5 h, concenꢀ
trations of DMC, methanol, dimethoxymethane
(DMM) and methyl formate (MF) were analyzed by
gas chromatography. The blank test was also perꢀ
formed under catalystꢀfree condition for comparison. mol ratio in the catalyst was 1.12. It was therefore
KINETICS AND CATALYSIS Vol. 51
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252
JUN REN et al.
CuCl
ꢀCu2(OH)3Cl
γ
ꢀCu2(OH)3Cl
αꢀCu2(OH)3Cl
γ
A
4
3
B
10
20
30
40
, deg
50
60
2θ
2
1
Fig. 2. XRD patterns of
by two separate routes: (
) CuCl + H O + O .
γ
ꢀCu (OH) Cl samples prepared
2 3
A
) CuCl + CuO + H O;
2
2
(
B
2
2
respectively. Whereas, the grain size of
crystals increased from 46 to 56 nm.
γꢀCu2(OH)3Cl
10
20
30
40
, deg
50
60
2θ
3.3. Characterization and Catalytic Performance
of Cu2(OH)3Cl
γ
ꢀ
Fig. 1. XRD patterns of the fresh and the recycled
CuCl/SiO ꢀTiO catalysts. ( ) Fresh, ( ) 1st recycle, (3)
2nd recycle, (4) 3rd recycle.
Figure 2 shows XRD patterns of two
samples, and . The characteristic diffraction peaks
of Cu2(OH)3Cl crystals were clearly observed in both
samples. In addition, very weak reflections correꢀ
sponding to the Cu2(OH)3Cl phase were also
detected, showing that the resulting powders were preꢀ
dominantly in the form of Cu2(OH)3Cl crystal with a
thimbleful of ꢀCu2(OH)3Cl crystal concomitant.
γ
ꢀCu2(OH)3Cl
1
2
2
2
A
B
γ
ꢀ
believed that most of copper was presented in the form
of CuCl crystalline phase. As can be seen from Fig. 1,
the diffraction peaks of CuCl disappeared after reacꢀ
tion, but weak diffraction peaks corresponding to
α
ꢀ
γ
ꢀ
α
γ
ꢀ
Cu2(OH)3Cl were clearly observed. One possible
explanation is that CuCl has been partly converted
into Cu2(OH)3Cl during the catalytic reaction. Simꢀ
Previous studies have shown that the Cu2(OH)3Cl
phase was perhaps formed during the catalytic reacꢀ
tion [6]. Furthermore, it could also be generated in the
procedures of catalyst preparation. Yang [7] and Han
[8, 9] reported that Cu2(OH)3Cl was detected on the
surface of freshly prepared Wackerꢀtype catalysts and
CuCl2/NaOH/AC catalysts. For supported Wackerꢀ
type catalysts, proper treatment of the carbon supports
γ
ꢀ
ilar results were reported for the CuCl2/AC catalysts by
Tomishige [6], in which methanol was suggested to
promote the structural change of the catalyst. It can be
further observed that the diffraction peaks attributed
to ꢀCu2(OH)3Cl became higher with increasing recyꢀ
γ
cling of the catalyst, which may be related to the could promote the formation of Cu2(OH)3Cl, which
was believed to be responsible for the improved cataꢀ
lytic performance for DMC synthesis [7]. The surface
growth of crystals.
The grain size of
based on the Scherrer equation and given in Table 1.
As can be seen, DMC spaceꢀtime yield became lower
and the grain size of
larger as recycling increased. For the fresh catalyst,
γ
ꢀCu2(OH)3Cl were calculated
phase was revealed to change from
Cu2(OH)3Cl with increase of OH/Cu molar ratio in
CuCl2/NaOH/AC catalysts and Cu2(OH)3Cl was
considered to more favorable to DMC synthesis than
α
ꢀCu2(OH)3Cl to
γ
ꢀ
γ
ꢀ
γ
ꢀCu2(OH)3Cl crystals became
α
ꢀCu2(OH)3Cl [8, 9].
−1
DMC spaceꢀtime yield reached 117
−1. In
h
Cat
In order to gain further insight into the intrinsic
gDMC
g
properties, the catalytic performance of the
Cu2(OH)3Cl crystals for the oxidative carbonylation of
methanol was studied. Table 2 gives the results of cataꢀ
lytic tests on Cu2(OH)3Cl, together with the data
obtained in the blank test. Both Cu2(OH)3Cl sample
and exhibited very poor catalytic performance and
its first recycling use, DMC spaceꢀtime yield
γ
ꢀ
−1
decreased to 0.92
−1 and the
ꢀCu2(OH)3Cl
γ
gDMC
g
h
Cat
crystal with an average grain size of about 21 nm was
γ
ꢀ
formed. In the second and third recycling, DMC spaceꢀ
γ
ꢀ
A
−1
h−1
,
Cat
time yield dropped from 0.76 to 0.62
B
gDMC
g
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STUDY ON THE FORMATION AND ROLE OF COPPER CHLORIDE HYDROXIDE
253
Table 2. Catalytic performance of γꢀCu2(OH)3Cl in DMC synthesisa
Cmb
,
mol
%
Smb , mol % STYb gDMC g–1 h–1
,
Sample
Blank
DMC, wt %
DMM, wt %
MF, wt %
Cat
0.43
0.40
0.23
0.26
0.07
0.41
0.30
0.30
1.00
0.92
0.82
30.65
31.16
52.42
0.06
0.05
0.08
A
B
0.61
b
a
Note: As in Table 1. As in Table 1.
were nearly inert to the reaction. As can be seen, the was perhaps partly converted into
CH3OH conversion was not more than 1.0% with the ing the reaction.
γ
ꢀCu2(OH)3Cl durꢀ
DMC selectivity below 53%, and the spaceꢀtime yield
DMC is catalytically synthesized by the reaction of
oxidative carbonylation of methanol as shown in
Eq. (1):
of DMC maintained between 0.05 and
−1
0.08
−1, almost the same activity as the
h
Cat
gDMC
g
blank test. These results strongly suggested that
. (1)
2
2CH OH + CO + 0.5O → CH O CO + H O
(
)
3
2
3
2
γ
ꢀ
Cu2(OH)3Cl was carbonylation inactive. In this case,
As displayed in Eq. (1), formation of DMC moleꢀ
cule from СН3ОН and CO gives equimolar amounts
of water. If the byꢀproduct water can not be removed
from the reaction system, water is always present in
increasing amounts as the reaction proceeds. It has
been reported that when CuCl is placed at a situation
with the existence of О2 and H2O, the following reacꢀ
tion perhaps takes place and results in the formation of
it becomes difficult to explain the improved catalytic
performance of Wackerꢀtype catalysts [7] and
CuCl2/NaOH/AC catalysts [8, 9].
The redox capability of Cu species between Cu2+
and Cu+ was considered to be important for the
enhancement in reaction rate in the oxidative carbonꢀ
ylation of methanol to DMC [2, 13], and the factors
that could accelerate the redox cycle of the active cenꢀ
ters would be beneficial for the reaction rate. In the
γ
ꢀ
Cu2(OH)3Cl [15], as indicated by Eq. (2):
4CuCl + O2 + 4H2O
+
present work, the ꢀCu2(OH)3Cl crystals were found
γ
(2)
almost completely insoluble in the reaction mixture
and only presented as a suspension. In addition, no
weight loss could be detected after reaction.
In order to better understand its stability in the
reaction system, the crystal structures and textural
−
→ 2Cu OH Cl + 2H + 2Cl .
(
)
2
3
This finding has been confirmed by Bell et al. [16] in
the preparation of CuꢀZSMꢀ5 catalysts for the syntheꢀ
sis of DMC by Solidꢀstate ion exchange of HꢀZSMꢀ5
with CuCl.
properties of
γ
ꢀCu2(OH)3Cl powder were studied
before and after reaction. Almost the same XRD patꢀ
terns were obtained before and after reaction, suggestꢀ
ing that the crystal structure was not transformed
through catalytic reaction. From these results, it was
In the oxidative carbonylation of methanol, CuCl
serves as active species, and O2 is the reagent gas. Since
byꢀproduct water is produced during the reaction, it
can be concluded that side reaction may be induced as
shown in Eq. (2) and lead to the formation of
obvious that the ꢀCu2(OH)3Cl crystal was highly staꢀ
γ
ble in the reaction system at 140оС and 2.4 MPa under
γ
ꢀCu2(OH)3Cl. In order to confirm this inference,
vigorous stirring. These findings provided further conꢀ
experiments might also be operative and were carried
out as described in route 2. The XRD patterns shown
in Fig. 2 displayed that the resulting compound, samꢀ
firmation for high stability of ꢀCu2(OH)3Cl under the
γ
reaction conditions. The synthesis of DMC from
methanol, CO and О2 mainly relied on the redox reacꢀ
tions between Cu+/Cu2+ [2]. Therefore, it is conꢀ
ple
this result has provided a powerful confirmation for
the formation of Cu2(OH)3Cl
From the Eq. (2), we can see that active species
CuCl is transformed into inactive Cu2(OH)3Cl phase
B
was mainly in the form of
γ
ꢀCu2(OH)3Cl. Thus,
cluded that the compound ꢀCu2(OH)3Cl having limꢀ
γ
γ
ꢀ
.
ited or no activity may be attributed to the high stabilꢀ
ity of Cu2+, which resisted the reduction under the
reaction conditions and could not form active interꢀ
mediate responsible for the CO insertion [14].
γ
ꢀ
for methanol oxidative carbonylation associated with
loss of chloride. Accordingly, it is believed that the forꢀ
mation of ꢀCu2(OH)3Cl must be the intrinsic factor
γ
leading to catalyst deactivation. Moreover, according
to Eq. (2), the higher the DMC yield is achieved, the
more water is produced and kept in the reactor. As a
result, higher water content means more significant
3.4. Formation and role of
γ
ꢀCu2(OH)3Cl
The
γ
ꢀ
Cu2(OH)3Cl crystals were formed over
CuCl/SiO2–TiO2 catalysts after being used in the oxiꢀ
dative carbonylation of methanol; moreover, catalyst
recycling led to a significant loss of catalytic activity.
formation of
γ
ꢀCu2(OH)3Cl [17].
From above discussion, the water formation and
These results suggested that the active species, CuCl the loss of chlorides may be the intrinsic reasons for
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254
JUN REN et al.
2. Romano, U., Tese, R., Mauri, M.M., and Rebora, P.,
Ind. Eng. Chem. Res., 1980, vol. 19, no. 3, p. 396.
3. Cao, Y., Hu, J.C., Yang, P., Dai, W.L., and Fan, K.N.,
Chem. Commun., 2003, no. 7, p. 908.
4. Sato, Y., Kagotani, M., Yamamoto, T., and Souma, Y.,
Appl. Catal., A, 1999, vol. 185, no. 2, p. 219.
5. Itoh, H., Watanabe, Y., Mori, K., and Umino, H.,
the catalyst deactivation. This conclusion has been
supported by the results of previous studies, that an
improved catalytic activity and decreased deactivation
rate of the catalyst could be attained by adding chloꢀ
ride sources (R4NC) [18] and chloride ionic liquids
[19] to the reaction system. In addition, we think that
perhaps this problem can also be solved by adding
water removing solids (zeolites and others). The dried
zeolite is suggested to efficiently protect the catalyst
from the fast deactivation.
Green Chem., 2003, vol. 10, no. 5, p. 558.
6. Tomishige, K., Sakaihori, T., Sakai, S.I., and
Fujimoto, K., Appl. Catal., A, 1999, vol. 181, no. 1,
p. 95.
7. Yang, P., Cao, Y., Dai, W.L., Deng, J.F., and Fan, K.N.,
4. CONCLUSIONS
Appl. Catal., A, 2003, vol. 243, no. 2, p. 323.
8. Han, M.S., Lee, B.G., Suh, I., Kim, H.S., Ahn, B.S.,
and Hong, S.I., J. Mol. Catal. A: Chem., 2001, vol. 170,
nos. 1–2, p. 225.
The
γ
ꢀCu2(OH)3Cl crystals were formed on
CuCl/SiO2–TiO2 catalysts in the synthesis of DMC by
liquid phase oxidative carbonylation of methanol. It
was revealed that the formation of
due to active CuCl reacting with О2 and byꢀproduct
water. The catalytic tests indicated that Cu2(OH)3Cl
was essentially inactive for this reaction. It could be
attributed to its high stability that resisted the reducꢀ
tion of Cu2+ under the reaction conditions and could
not form active intermediate.
9. Han, M.S., Lee, B.G., Ahn, B.S., Kim, H.S.,
γ
ꢀCu2(OH)3Cl was
Moon, D.J., and Hong, S.I., J. Mol. Catal. A: Chem.
,
2003, vol. 203, nos. 1–2, p. 137.
γ
ꢀ
10. Ren, J., Li, Z., Liu, S.S., and Xie, K.C. (in press).
11. Ren, J., Li, Z., Liu, S.S., Xing, Y.L., and Xie, K.C.,
Catal. Lett., 2008, vol. 124, nos. 3–4, p. 185.
12. Strandberg, H., Atmos. Environ., 1998, vol. 32, no. 20,
p. 3511.
13. Yuan, Y.Z., Cao, W., and Weng, W.Z., J. Catal., 2004,
vol. 228, no. 2, p. 311.
14. King, S.T., Catal. Today, 1997, vol. 33, nos. 1–3, p. 173.
ACKNOWLEDGMENT
We are grateful for the financial support from the
National Natural Science Foundation of China
(20606022), the National Basic Research Program of
China (2005 CB221204) and the Natural Science
Foundation for Young Scientists of Shanxi Province,
China (20051008).
15. Scott, D.A. and Dodd, L.S., J. Cult. Herit, 2002, vol. 3,
no. 4, p. 333.
16. Zhang, Y.H., Drake, I.J., and Bell, A.T., Chem. Mater.
2006, vol. 18, no. 9, p. 2347.
,
17. Kricsfalussy, Z., Waldmann, H., and Traenckner, H.J.,
Ind. Eng. Chem. Res., 1998, vol. 37, no. 3, p. 865.
18. Raab, V., Merz, M., and Sundermeyer, J., J. Mol. Catal.
A: Chem., 2001, vol. 175, nos. 1–2, p. 51.
19. Dong, W.S., Zhou, X.S., Xin, C.S., Liu, C.L., and
Liu, Z.T., Appl. Catal., A, 2008, vol. 334, nos. 1–2,
p. 100.
REFERENCES
1. Delledonne, D., Rivetti, F., and Romano, U., Appl.
Catal., A, 2001, vol. 221, nos. 1–2, p. 241.
KINETICS AND CATALYSIS Vol. 51
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