Water-improved heterogeneous transfer hydrogenation using methanol as hydrogen donor over Pd-based catalyst

Article abstract of DOI:10.1016/j.apcata.2010.01.004

The heterogeneous catalytic transfer hydrogenation (CTH) of styrene and nitrobenzene over Pd-based catalyst using methanol as hydrogen donor was investigated in a fixed-bed reactor. With the increase of the molar ratio of water to methanol from 0 to 1, the conversions of styrene and nitrobenzene are increased from 26.3% and 7.1% to 100% and 31.9%, respectively, and the selectivity of aniline is increased from 22.0 to 94.5 mol%. The presence of water improves the hydrogen transfer from methanol to styrene or nitrobenzene through the quick reaction of water with formaldehyde, formed from the dehydrogenation of methanol, into formic acid, which is an excellent hydrogen donor for the CTH of unsaturated organics. In the presence of water, methanol is a better hydrogen donor than isopropanol, n-propanol and ethanol, because water cannot easily react with acetone, propionaldehyde, and acetaldehyde formed from isopropanol, n-propanol, and ethanol, respectively. Additionally, the hydrogen atom utilization of the methanol donor in the presence of water is higher than the other donors, hydrogen atom in a part of water can also be utilized for the reduction of unsaturated organics.

Full text of DOI:10.1016/j.apcata.2010.01.004

Applied Catalysis A: General 375 (2010) 289–294
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Water-improved heterogeneous transfer hydrogenation using methanol as
hydrogen donor over Pd-based catalyst
Yizhi Xiang, Xiaonian Li *, Chunshan Lu, Lei Ma, Qunfeng Zhang
State Key Laboratory Breeding Base of Green Chemistry-Synthesis Technology, Institute of Industrial Catalysis, Zhejiang University of Technology, Hangzhou, P.O. Box 310014, PR China
A R T I C L E I N F O
A B S T R A C T
Article history:
The heterogeneous catalytic transfer hydrogenation (CTH) of styrene and nitrobenzene over Pd-based
catalyst using methanol as hydrogen donor was investigated in a fixed-bed reactor. With the increase of
the molar ratio of water to methanol from 0 to 1, the conversions of styrene and nitrobenzene are
increased from 26.3% and 7.1% to 100% and 31.9%, respectively, and the selectivity of aniline is increased
from 22.0 to 94.5 mol%. The presence of water improves the hydrogen transfer from methanol to styrene
or nitrobenzene through the quick reaction of water with formaldehyde, formed from the
dehydrogenation of methanol, into formic acid, which is an excellent hydrogen donor for the CTH of
unsaturated organics. In the presence of water, methanol is a better hydrogen donor than isopropanol, n-
propanol and ethanol, because water cannot easily react with acetone, propionaldehyde, and
acetaldehyde formed from isopropanol, n-propanol, and ethanol, respectively. Additionally, the
hydrogen atom utilization of the methanol donor in the presence of water is higher than the other
donors, hydrogen atom in a part of water can also be utilized for the reduction of unsaturated organics.
ß 2010 Elsevier B.V. All rights reserved.
Received 16 August 2009
Received in revised form 19 December 2009
Accepted 6 January 2010
Available online 11 January 2010
Keywords:
Water
Transfer hydrogenation
Methanol
Heterogeneous catalysis
1
. Introduction
Reduction of unsaturated organics by catalytic transfer
Additionally, methanol is also a widely used solvent for many
reactions including the catalytic hydrogenation of unsaturated
organics. Recently, we reported a novel catalytic in situ hydro-
genation system by coupling the endothermic APR of alcohols
(methanol, etc.) for hydrogen production with the exothermic
liquid phase hydrogenation of unsaturated organics [11]. However,
the reduction of organics by the catalytic in situ hydrogenation
method cannot be realized at low temperature, because the APR of
alcohols for hydrogen production is kinetically inhibited due to the
high activation barrier [10]. Therefore, the reduction of unsaturat-
ed organics by the CTH using methanol as hydrogen donor is quite
important [12–14]. However, the CTH of unsaturated organics
using methanol as the hydrogen donor is difficult to achieve,
hydrogenation (CTH) using hydrogen containing compounds as
hydrogen donor is an important synthetical methodology in both
laboratory and industry [1–5]. In contrast to the catalytic
2
hydrogenation using H , the CTH using hydrogen donor has the
advantages of convenience and safety. Furthermore, the CTH could
also potentially afford enhanced activity and/or selectivity in
reduction because the properties of hydrogen donor could affect
the reductions highly [1]. Palladium has usually been regarded as
the most active catalyst [2], and hydrazine, formic acid or formates,
and cyclohexene, etc., are normally the effective hydrogen donor
for the heterogeneous CTH. Although the alcohols can also be
served as the hydrogen donor [1], the primary alcohol is generally
less active than the secondary alcohol due to the smaller electron-
releasing inductive effect of one alkyl group as against two.
Therefore, the primary alcohols (in particular methanol) were
rarely used as the hydrogen donor for the heterogeneous CTH [1].
Dumesic and coworkers have introduced a catalytic pathway
for hydrogen production from biomass-derivated hydrocarbons,
such as methanol, ethylene glycol, and glycerol, by aqueous-phase
reforming (APR) over a Pd-, Pt-, and Ni-based catalyst [6–10].
ꢀ
1
because the bond energies of the a-C–H (401.9 kJ mol ) and O–H
ꢀ
1
(437.7 kJ mol ) in methanol are the highest among the aliphatic
alcohols [15], and the dehydrogenation of methanol to formalde-
hyde and hydrogen is thermodynamically inhibited because the
reaction is a highly endothermic reversible process [16].
In this paper, we reported that the heterogeneous CTH of
unsaturated organics (e.g. nitrobenzene and styrene) using
methanol as hydrogen donor can be efficiently achieved in the
presence of water under moderate conditions. Pd–Ba/Al
2 3
O and
Pd–Fe/Al were used as the catalysts to investigate the effect of
2 3
O
the presence of water on the CTH of styrene and nitrobenzene
using methanol as hydrogen donor, because the two catalysts
*
Corresponding author. Tel.: +86 571 88320409; fax: +86 571 88320409.
were found to be more active than the Pd/Al
2 3
O catalyst for the
E-mail address: xnli@zjut.edu.cn (X. Li).
catalytic in situ hydrogenation of phenol into cyclohexanone [17].
0926-860X/$ – see front matter ß 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2010.01.004

2
90
Y. Xiang et al. / Applied Catalysis A: General 375 (2010) 289–294
Additionally, the reaction mechanism has been proposed based on
the intermediates observed in the reaction and the deuterium
tracer experiments.
for 5 h in air. BaO and Fe
The nominal loading of Fe
respectively. A second impregnation was then carried out on the
modified -Al support with an aqueous solution of H PdCl
4
2
O
3
were formed during the calcination.
2 3
O
and BaO are 8 and 2 wt%,
g
2
O
3
2
2
. Experimental
(0.05 g/ml, Pd nominal loading 3 wt%), followed by drying at 383 K
for 5 h and calcining at 533 K for 5 h in air.
The Pd–Fe/Al
step-wise incipient wetness impregnation. The commercial
Al (80–120 mesh, Zibo Boyang Chemical Co. Ltd.) was
impregnated with an aqueous solution of Fe(NO
ꢁ9H
>98.5 wt%) or Ba(NO (>99 wt%). The impregnation was
followed by drying at 383 K for 5 h, and then calcining at 623 K
2
O
3
and Pd–Ba/Al
2
O
3
catalysts were prepared by
The morphology and Pd particle size distribution of the reduced
g
-
2 3 2 3
Pd–Fe/Al O and Pd–Ba/Al O catalysts were determined by a JEM-
2
O
3
2100F TEM at an operating voltage of 200 kV. The BET surface areas
of the catalysts were determined by nitrogen physical adsorption
at 77 K under vacuum condition by using a NOVA 1000e surface
area analyzer (Quantachrome Instruments Corp.).
3
)
3
2
O
(
3 2
)
0
0
Fig. 1. TEM micrographs of (A) Pd–Ba/Al
2
O
3
and (B) Pd–Fe/Al
2
O
3
catalysts and (A and B ) Pd particle size distribution, (C) HRTEM micrographs of Pd–Ba/Al
2
O
3
.

Y. Xiang et al. / Applied Catalysis A: General 375 (2010) 289–294
291
Table 2
The catalytic transfer hydrogenation (CTH) of unsaturated
compounds (styrene, etc.) using methanol as hydrogen donor was
carried out in a fixed-bed reactor (a stainless-steel tube with an
inner diameter of 8 mm). The typical procedure of the CTH of
Effect of water on the CTH of nitrobenzene into aniline using methanol as hydrogen
donor.
a
Entry
Water/
Nitrobenzene
conversion
(%)
Selectivity (mol%)
methanol
styrene was described as follows. 1 g of Pd–Fe/Al
2 3
O catalyst was
(mol/mol)
Aniline
NMA
NMEA
NFA
loaded in the isothermal region of the reactor, and then was
ꢀ1
1
2
3
4
5
0
7.1
13.6
22.9
25.8
31.9
22.0
75.1
86.7
93.8
94.5
3.4
2.9
1.5
1.0
0.6
74.6
22.0
11.8
4.7
0.0
0.0
0.0
0.5
4.2
reduced in H (99.999 vol%) stream with a flow rate of 30 ml min
2
0.1
0.25
0.5
1
at 553 K for 2 h. The reactor pressure was then increased by adding
Ar (99.999 vol%) to 2.0 MPa to maintain reaction in liquid phase at
ꢀ
1
3
73 or 393 K. The mixed solution of styrene (0.35 mol L ) and
0.7
ꢀ1
methanol (with or without water) at 0.1 ml min was co-fed into
the reactor using a high-performance liquid chromatography
pump (PK564AN-TG10-A2). The gases and condensates were
separated in a stainless-steel vessel (about 40 ml) at the system
pressure. The liquid effluent was collected and analyzed by a GC–
MS instrument (Agilent-6890 GC-5973 MS equipped with 30 m
HP-5 capillary) with the external standard method. The gas
effluent was analyzed by an on-line GC instrument (Fuli 9790,
Porapak Q & 13X molecular sieves columns) equipped with thermo
conductive detector (TCD).
2 3
Reactions were carried out over the Pd-Ba/Al O (1 g) at 393 K while other
conditions were the same as Table 1.
a
NMA: N-methylaniline, NMEA: N-methyleneaniline, and NFA: N-formylaniline.
using isopropanol as hydrogen donor instead of methanol. These
results suggest that methanol becomes a more effective hydrogen
donor than isopropanol for the CTH of styrene in the presence of
water, although the reactivity of isopropanol is generally consid-
ered to be higher than methanol for the CTH in the anhydrous
system [1].
3
. Results and discussion
The effect of water on the CTH of nitrobenzene using
methanol as hydrogen donor was also investigated over the Pd–
3.1. Catalysts characterization
2 3
Ba/Al O catalyst at 393 K and 2.0 MPa. The experimental results
are shown in Table 2. With the increase of the molar ratio of
water to methanol from 0 to 1, the conversion of nitrobenzene
and the selectivity of aniline are increased from 7.1% to 31.9%
and 22.0 to 94.5 mol%, respectively, and the selectivity of N-
methyleneaniline produced from the condensation of formalde-
hyde and aniline is decreased from 74.6 to 0.7 mol%. The
experimental results indicate that formation of by-products,
such as N-methyleneaniline and N-methylaniline, can be
effectively inhibited with the presence of water, because the
2 3 2 3
The BET surface areas of the Pd–Ba/Al O and Pd–Fe/Al O
2
ꢀ1
catalysts are 254.5 and 199.4 m g , respectively. The correspond-
ꢀ
1
ing pore volumes and pore diameters are 0.29 and 0.25 ml g , and
.96 and 4.50 nm, respectively. The TEM micrographs of the two
catalysts are shown in Fig. 1. The Pd particle sizes of the Pd–Ba/
Al and Pd–Fe/Al catalysts are mainly distributed in 1–3 nm
Fig. 1A ) and 2–5 nm (Fig. 1B ), respectively. The HRTEM of the
Pd–Ba/Al catalyst exhibit that the interplanar spacing of the Pd
4
2
O
3
2 3
O
0
0
(
2 3
O
particle is 0.225 nm (consistent with the interplanar distance of
the Pd (1 1 1) plane), indicating the presence of metallic Pd instead
reaction of formaldehyde with water to form CO
easily over the catalyst (the conversions of nitrobenzene and
styrene as a function of the yield of CO are shown in Fig. 2).
2
will take place
of PdO
x
on support.
2
Otherwise, small amounts of N-formylaniline (from the reaction
of formic acid with aniline) were detected in the CTH of
nitrobenzene using methanol as hydrogen donor with the
presence of water, which indicates the presence of formic acid,
as an intermediate, in the system.
3
.2. Effect of water on the CTH using methanol as hydrogen donor
The effect of the presence of water on the CTH of styrene over
the Pd–Fe/Al catalyst using methanol as hydrogen donor was
2 3
O
investigated at 373 K and 2.0 MPa. The experimental results are
shown in the entries 1–5 of Table 1. With the increase of molar
ratio of water to methanol from 0 to 0.25, the conversion of styrene
raises from 26.3% to 100% in the maintenance of 100 mol%
selectivity to ethylbenzene. But when the molar ratio of water to
methanol is greater than 0.5, the selectivity of ethylbenzene is
decreased slightly. As shown in the entries 6 and 7 of Table 1, the
improvement of water on the CTH of styrene has not been observed
To extend the application of the current idea, the CTH of other
unsaturated organics like acetophenone, benzaldehyde, and
cyclohexanone using methanol (with or without water) as
hydrogen donor were also investigated. The experimental results
Table 1
Effect of water on the CTH of styrene into ethylbenzene using methanol as hydrogen
donor.
Entry
Water/
Styrene
conversion
(%)
Ethylbenzene
selectivity
(mol%)
CO
2
yield
ꢀ
1
methanol
(
mmol min
)
(mol/mol)
1
2
3
4
5
0
26.3
74.4
100
100
100
100
100
97.6
100
100
0
0.1
0.25
0.5
1
5.1
7.5
7.2
6.7
0
100
100
a
6
0
57.4
56.6
a
7
0.1
0
2 3
Reactions were carried out in a fixed-bed reactor over the Pd–Fe/Al O (1 g) at 373 K
ꢀ
1
ꢀ1
and 2.0 MPa with a liquid flow rate of 0.1 ml min (LHSV = 4 h ), the styrene
ꢀ1
concentration was 0.35 mol L
.
Fig. 2. Effect of styrene or nitrobenzene conversion on the yield of CO
phase. (&) Nitrobenzene and (*) styrene.
2
in the gas
a
Isopropanol instead of methanol was used as the donor.

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92
Y. Xiang et al. / Applied Catalysis A: General 375 (2010) 289–294
Table 3
the hydrogenation of phenol and its derivatives [19]. Additionally,
Xiao and coworkers have done a lot of works on the homogeneous
CTH using formates as hydrogen donor in water solvent [20–22].
Water for the improved heterogeneous CTH of nitroarenes [23],
C 55 C double bond [24], and aryl halides [25] using formates as
hydrogen donor was also proposed early. Second, the reaction of
water with formaldehyde (generated from the dehydrogenation of
methanol during the CTH reaction) will form formic acid as
Experimental results of the CTH of organics using methanol or other alcohols (with
or without water) as hydrogen donor.
Substrates
Products
Alcohols
MeOH
Water/Alcohols
mol/mol)
Yield
(
(mol%)
0
2.56
MeOH
MeOH
0.5
0
12.88
.07
2
excellent hydrogen donor and finally to form CO , which could
overcome the thermodynamic limitation during the CTH of
organics using methanol as hydrogen donor. In our experimental,
5
2
CO was detected in the gaseous products, and the presence of N-
methyleneaniline and N-formylaniline in the liquid products
indicates the formation of formaldehyde and formic acid,
MeOH
MeOH
0.5
0
20.12
1.31
2
respectively. The yield of CO as a function of the conversions of
nitrobenzene and styrene is increased linearly with the slopes of
0.4 and 0.1, respectively (Fig. 2).
MeOH
MeOH
0.5
0
5.07
.65
4
3.3. Reaction mechanism
MeOH
EtOH
EtOH
PrOH
PrOH
0.5
0
51.45
5.10
The stoichiometric reactions and the schematic representation
of the CTH of nitrobenzene using methanol as hydrogen donor are
shown in Schemes 1 and 2, respectively. First, the hydrogen
transfer from methanol to nitrobenzene causes the formation of
formaldehyde and aniline, respectively (Scheme 1 rec. 1a, Scheme
2 step I: this reaction is both kinetically and thermodynamically
inhibited as mentioned above). In the presence of water, the
formaldehyde is converted into formic acid over the catalyst
quickly (Scheme 1 rec. 2, Scheme 2 step III), which accelerates the
CTH using methanol as the donor, and additionally, the formic acid
is also an effective hydrogen donor for the CTH (Scheme 1 rec. 1b,
Scheme 2 step IV) [1]. Moreover, the condensation of aniline and
formaldehyde, which leads to the formation of by-products N-
methyleneaniline (Scheme 2 step II), is also highly suppressed with
the presence of water. The conversion of formaldehyde into formic
acid is supported by the fact that the steam and aqueous-phase
0.5
0
12.50
6.66
0.5
14.43
Reactions were carried out over the Pd–Fe/Al
2
O
3
(1 g) at 393 K and 2.0 MPa with a
ꢀ1
ꢀ1
liquid flow rate of 0.1 ml min , the concentration of the substrate was 0.35 mol L
.
are shown in Table 3. The improvements of water (water/
methanol = 0.5 mol/mol) on the CTH of those unsaturated organics
using methanol as hydrogen donor have been observed. The ideal
yields of the desired products should be realized through the
modification of the catalyst and optimization of the reaction
conditions in the future. The effect of water on the CTH of
nitrobenzene using other primary aliphatic alcohols, such as
ethanol and n-propanol, as hydrogen donors was also investigated.
The yield of aniline is also increased in the presence of water. But
methanol is a more active hydrogen donor than ethanol and n-
propanol in the CTH of nitrobenzene in the presence of water.
The main reasons for the improvement of water on the activity
and/or selectivity of the heterogeneous CTH of unsaturated
organics by using methanol as hydrogen donor are as follows.
First, the presence of water in methanol could favor the hydrogen
transfer from methanol to unsaturated organics (i.e. improved the
dehydrogenation of methanol into hydrogen and formaldehyde)
due to the hydrophobic and aqueous solvation effects [18].
Recently, we also proposed that an aqueous system could improve
reforming of methanol for H
place according to the following mechanism: CH
CH + H [26,27]. Additionally, N-formylaniline
2
production are generally taking
3
OH ! CH O !
3
2
O ! HCOOH ! CO
2
2
is produced from the dehydration of aniline and formic acid
(formed from formaldehyde), Scheme 2 step V. Furthermore, this
mechanism is supported by the experimental observation of CO
2
(Fig. 2), N-methyleneaniline, and N-formylaniline.
To confirm the proposed mechanism, the decomposition of
methanol, and the APR of methanol/water mixture for hydrogen
production over the Pd–Fe/Al
2.0 MPa were investigated. The results suggest that these two
reactions could not occur under those conditions, because H , CO,
2 3
O catalyst under 393 K and
2
Scheme 1. Stoichiometric reactions of the water improved catalytic transfer hydrogenation of nitrobenzene using methanol as hydrogen donor.

Y. Xiang et al. / Applied Catalysis A: General 375 (2010) 289–294
293
Scheme 2. Schematic representation of the catalytic transfer hydrogenation of nitrobenzene using methanol as hydrogen donor.
Scheme 3. Stoichiometric reaction and experimental results for the reaction of nitrobenzene with formaldehyde and water.
and CO
by gas-chromatographs), and CO
liquid effluent (determined by clarification limewater,
2
were not detected in the gaseous products (determined
The reaction of formaldehyde, water, and nitrobenzene over
the Pd–Fe/Al catalyst under 393 K and 2.0 MPa was also
2
was also not observed in the
2 3
O
K
sp
investigated to make sure the proposed mechanism. In this
reaction (Scheme 3), the conversion of nitrobenzene was 100%,
and the selectivity of N,N-dimethylaniline, N,N-dimethyl-4-
methylaniline, N-formylaniline, N-formyl-N-methylaniline, and
ꢀ9
(
CaCO
3
) = 2.9 ꢂ 10 ); additionally, liquid products like formal-
dehyde and formic acid were also not observed. These results
indicate that the catalytic in situ hydrogenation process could not
occur over the Pd-based catalyst under the conditions of 393 K and
0
benzenamine, 4,4 -methylenebis[N,N-dimethyl-] were 41.0,
2
.0 MPa.
The deuterium tracer experiments were performed to gain an
insight into the CTH of styrene using methanol as hydrogen
donor improved by D O. The results indicate that the H/D
exchange was existed between D O and methanol at the
hydroxyl position (reaction 1) as detected by GC–MS. Fig.
40.6, 6.9, 2.0, and 9.5 mol%, respectively. Additionally, the yield
ꢀ
1
of CO
2
on the gaseous products is 54
m
mol min
. The
observation of N-formylaniline and CO
2
indicate the occurrence
2
of the steps III, IV, and V in Scheme 2, i.e. the nitrobenzene can
be reduced into aniline by formaldehyde and water through the
conversion of formaldehyde with water into formic acid as the
reducing reagent.
2
3
shows the mass spectrum of ethylbenzene produced from the
CTH of styrene using methanol as hydrogen donor with the
presence of D
observed in the molecules of Ph–C
D (m/z = 107). The Ph–C D (m/z = 107) was produced
from the CTH of styrene using CH OD as the hydrogen donor
reaction 2), while Ph–C (m/z = 108) was generated
through the successive occurrence of reactions 3 and 4. These
results also suggest that the H/D exchange occurs between D
2
O. As shown in Fig. 3, the deuterium was
3.4. Comparison between methanol and the other hydrogen donor
2
3 2
H D
(m/z = 108) and Ph–
C
2
H
4
2
H
4
In comparison with the CTH using other primary aliphatic
alcohols, such as isopropanol, as hydrogen donor, the use of
methanol as hydrogen donor for the CTH has several advantages.
Water is used as the promoter for the CTH using methanol as
hydrogen donor. The CTH using methanol as hydrogen donor has a
3
(
2 3 2
H D
2
O
and methanol. Additionally, the reaction of formaldehyde with
water to form formic acid (Scheme 1 rec. 2, Scheme 2 step III) is
further confirmed. Therefore, hydrogen atom in molecular water
can be utilized for the reduction of organics.
Reaction 1.
Reaction 2.
Reaction 3.
Fig. 3. Mass spectrum of ethylbenzene produced from the CTH of styrene using
Reaction 4.
2
methanol as hydrogen donor improved by D O.

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94
Y. Xiang et al. / Applied Catalysis A: General 375 (2010) 289–294
higher hydrogen atom utilization than the CTH using isopropanol
as the donor. All hydrogen atoms in methanol molecular can be
used for the reduction of unsaturated organics, but only 25% of
hydrogen atoms in isopropanol molecular can be utilized.
Additionally, hydrogen atom in a part of water can be utilized
for the reduction of unsaturated organics, 2 mol hydrogen atoms in
water can be utilized with the consumption of 1 mol methanol.
Meanwhile, the CTH using methanol as hydrogen source in the
presence of water also has higher hydrogen atom utilization than
our previous reported catalytic in situ hydrogenation process with
hydrogen from the APR of methanol [11], because at high
temperature, hydrogen generated from the APR of methanol
cannot be fully used for the hydrogenation of unsaturated organics,
Acknowledgements
This work was supported by the Nation Nature Science
Foundation of China (NSFC-20976164), the Specialized Research
Fund for The Doctoral Program of High Education of China (SRFDP-
20060337001).
References
[1] R.A.W. Johnstone, A.H. Wilby, I.D. Entwistle, Chem. Rev. 85 (1985) 129–170.
[2] G. Brieger, T.J. Nestrick, Chem. Rev. 74 (1974) 567–580.
[
[
3] F.Z. Su, L. He, J. Ni, Y. Cao, H.Y. He, K.N. Fan, Chem. Commun. (2008) 3531–3533.
4] J. Li, Y.M. Zhang, D.F. Han, G.Q. Jia, J.B. Gao, L. Zhong, C. Li, Green Chem. 10 (2008)
6
08–611.
[5] P. Selvam, S.K. Mohapatra, S.U. Sonavane, R.V. Jayaram, Appl. Catal. B: Environ. 49
2004) 251–255.
2
but molecular H was not detected in the gaseous products in the
(
CTH using methanol as hydrogen donor.
[6] R.R. Davda, J.W. Shabaker, G.W. Huber, R.D. Cortright, J.A. Dumesic, Appl. Catal. B:
Environ. 56 (2005) 171–186.
4
. Conclusions
[7] R.D. Cortright, R.R. Davda, J.A. Dumesic, Nature 418 (2002) 964–967.
[
[
8] G.W. Huber, J.W. Shabaker, J.A. Dumesic, Science 300 (2003) 2075–2077.
9] R.R. Davda, J.A. Dumesic, Angew. Chem. Int. Ed. 42 (2003) 4068–4071.
The heterogeneous CTH of unsaturated organics over Pd-based
[
10] J.W. Shabaker, J.A. Dumesic, Ind. Eng. Chem. Res. 43 (2004) 3105–3112.
[11] X.N. Li, Y.Z. Xiang, Sci. China B: Chem. 50 (2007) 746–753.
12] H. Itatani, J.C. Bailar, J. Am. Chem. Soc. 89 (1967) 1600–1602.
13] J.C. Bailar, H. Itatani, J. Am. Chem. Soc. 89 (1967) 1592–1599.
14] K. Tani, A. Iseki, T. Yamagata, Chem. Commun. (1999) 1821–1822.
[15] Y.R. Luo, Hand Book of Bond Dissociation Energies in Organic Compounds, CRC
Press, 2005, 22 & 189.
16] S. Ruf, A. May, G. Emig, Appl. Catal. A: Gen. 213 (2001) 203–215.
17] H.J.Wang,Y.Z.Xiang,T.Y.Xu,H.J.Zhou,L.Ma,X.N.Li,Chin.J.Catal.30(2009)933–938.
[18] M.C. Pirrung, Chem. Eur. J. 12 (2006) 1312–1317.
[19] Y.Z. Xiang, L. Ma, C.S. Lu, Q.F. Zhang, X.N. Li, Green Chem. 10 (2008) 939–943.
20] X.F. Wu, X.G. Li, W. Hems, F. King, J. Xiao, Org. Biomol. Chem. 2 (2004) 1818–1821.
21] X.F. Wu, X.G. Li, F. King, J. Xiao, Angew. Chem. Int. Ed. 44 (2005) 3407–3411.
22] X.F. Wu, D. Vinci, T. Ikariya, J. Xiao, Chem. Commun. (2005) 4447–4449.
catalyst using methanol as hydrogen donor can be achieved
efficiently in the presence of water. Appropriate amounts of water
in methanol could increase the conversions of styrene and
nitrobenzene and/or selectivity of the desired products in the
CTH using methanol as hydrogen donor highly. The deuterium
tracer experiments and the mechanistic discussion suggest that
the presence of water could improve the CTH using methanol as
hydrogen donor through the fast conversion of formaldehyde into
formic acid. The hydrogen atom utilization of the CTH using
methanol as hydrogen donor in the presence of water is as high as
[
[
[
[
[
[
[
[
1
00%, which is significantly higher than the CTH using other
[23] H. Wiener, J. Blum, Y. Sasson, J. Org. Chem. 56 (1991) 4481–4486.
[
[
[
24] G. Cavinato, L. Toniolo, J. Mol. Catal. A: Chem. 106 (1996) 25–30.
25] H. Wiener, J. Blum, Y. Sasson, J. Org. Chem. 56 (1991) 6145–6148.
26] E. Jeroro, J.M. Vohs, J. Am. Chem. Soc. 130 (2008) 10199–10207.
hydrogen donors. Additionally, 2 mol hydrogen atoms in molecu-
lar water can also be utilized for the reduction of unsaturated
organics with the consumption of 1 mol methanol.
[27] N. Takezawa, N. Iwasa, Catal. Today 36 (1997) 45–56.