N-Methylation of N-Methylaniline with Carbon Dioxide and Molecular Hydrogen over a Heterogeneous Non-Noble Metal Cu/TiO2 Catalyst

Article abstract of DOI:10.1002/cctc.201900582

A non-noble heterogeneous catalyst of Cu/TiO₂ was prepared for N-methylation of N-methylaniline (MA) with CO₂ and H₂. 5 wt.–% Cu loaded TiO₂ (P25) catalyst exhibited a high performance, with 82 % MA conversion and 98 % N,N-dimethylaniline (DMA) selectivity under the reaction conditions used (4 MPa H₂, 2 MPa CO₂, 180 °C, 36 h). The Cu/TiO₂ catalyst was more effective with respective to the total conversion and the DMA selectivity as compared to 5 wt.–% Cu loaded catalysts on CeO₂, ZnO and activated carbon materials. The possible active species of Cu/TiO₂ catalyst should be both Cu⁺ and Cu⁰ which contributed to the high activity as the reaction conversion increased linearly with them exposed on the surface of catalyst. Moreover, the reaction pathways involved were studied; it was likely that the reaction took place via an intermediate of formaldehyde that was formed from CO₂ and H₂, as confirmed by in situ diffuse reflectance Fourier-transform infrared spectroscopy, then it reacted with MA to give N-methylformanilide (MFA), and finally MFA was hydrogenated to DMA.

Full text of DOI:10.1002/cctc.201900582

Accepted Article
Title: N-methylation of N-methylaniline with Carbon Dioxide and
Molecular Hydrogen over a heterogeneous non-noble metal Cu/
TiO2 catalyst
Authors: Ke Liu, Zhenbo Zhao, Weiwei Lin, Qiang Liu, Qifan Wu,
Ruhui Shi, Chao Zhang, Haiyang Cheng, Masahiko Arai, and
Fengyu Zhao
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10.1002/cctc.201900582
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N-methylation of N-methylaniline with Carbon Dioxide and
Molecular Hydrogen over a Heterogeneous Non-noble Metal
Cu/TiO2 catalyst
Ke Liu,[a,b] Zhenbo Zhao,[a] Weiwei Lin,*[b,c] Qiang Liu,[a,b] Qifan Wu,[ b,c] Ruhui Shi,[b,c] Chao Zhang,[b,c]
Haiyang Cheng,[b,c] Masahiko Arai,[b,c] and Fengyu Zhao*[b,c]
Dedication ((optional))
Abstract: A non-noble heterogeneous catalyst of Cu/TiO2 was
prepared for N-methylation of N-methylaniline (MA) with CO2 and H2.
5 wt.-% Cu loaded TiO2 (P25) catalyst exhibited a high performance,
with 82% MA conversion and 98% N,N-dimethylaniline (DMA)
selectivity under the reaction conditions used (4 MPa H2, 2 MPa CO2, Previously Cantat et al.
dimethyl ether, higher alcohols, formates, CO, methane, and
[2]
light alkanes by using different catalysts.
In addition, a
breakthrough development in this area is a new catalytic method
[3]
using CO2 as a carbon source of N-methylation reaction.
[4]
[5]
and Beller et al.
reported the
180 ºC, 36 h). The Cu/TiO2 catalyst was more effective with
respective to the total conversion and the DMA selectivity as
compared to 5 wt.-% Cu loaded catalysts on CeO2, ZnO and
activated carbon materials. The possible active species of Cu/TiO2
catalyst should be both Cu+ and Cu0 which contributed to the high
activity as the reaction conversion increased linearly with them
exposed on the surface of catalyst. Moreover, the reaction pathways
involved were studied; it was likely that the reaction took place via an
intermediate of formaldehyde that was formed from CO2 and H2, as
confirmed by in situ diffuse reflectance Fourier-transform infrared
spectroscopy, then it reacted with MA to give N-methylformanilide
(MFA), and finally MFA was hydrogenated to DMA.
methylation of amines with hydrosilanes and CO2 by
homogeneous catalysts in 2013. Unfortunately, the methods
were not practical due to the use of hydrosilanes as the reducing
agents. At the same time, they reported a possible utilization of
CO2 as N-methylation reagent. Subsequently, a more practical
method for the direct N-methylation of aromatic amines with CO2
and H2 by a homogeneous Ru catalyst of Ru(triphos)(tmm) was
reported by Klankermayer and co-workers. [6] Beller et al. [7] also
found an improved catalyst with extended scope, in which
aliphatic and aromatic amines as well as primary and secondary
amines were tolerated by an in situ formed homogeneous Ru
catalyst with LiCl or acid additives. However, homogeneous
catalysts suffer from problems of catalyst/product separation,
reusability, and the necessity of additives (acids, ligands, and
salts) in the reaction system. Therefore, high-efficiency
Introduction
heterogeneous catalysts are required from the view of practical
[8]
utilization. Shi and co-workers
reported that Pd/CuZrOx was
Carbon dioxide (CO2) is a renewable, low-cost, abundant, and
nontoxic C1 resource and, therefore, the transformation of CO2
to value-added chemicals has attracted extensive attention in
both green and synthetic chemistry fields.[1] Because of the
thermodynamic stability of CO2, a strong thermodynamic driving
power is required for the effective transformation of CO2. Great
efforts have been concentrated on fixation of CO2 into methanol,
effective for the methylation of amines with CO2 and H2 and a
high product yield of about 97% was achieved. Shimizu et al.
utilized Pt-MoOx/TiO2 catalyst to transform aliphatic and
aromatic secondary amines to tertiary amines with CO2 and H2
in solvent-free system and proposed
a plausible reaction
mechanism. [9] This catalyst was also effective in direct synthesis
of trimethylamine from N-Methylation of ammonia with CO2 and
H2. [10] In addition, Au/Al2O3 and Re/TiO2 catalysts were reported
to be active for the N-methylation of aromatic and aliphatic
second amines with CO2 and H2, yielding tertiary amines with
excellent yields. [11] In addition, supported Cu catalysts were also
[a]
[b]
K. Liu, Prof. Z. Zhao, Q. Liu
School of Chemistry and Life Science
Changchun University of Technology
Changchun, 130012, P. R. China.
K. Liu, Dr W. Lin, Q. Liu, Q. Wu, R. Shi, Dr C. Zhang, Dr. H.
Cheng, Prof.Dr. M. Arai, Prof. Dr. F. Zhao
State Key Laboratory of Electroanalytical Chemistry
Changchun Institute of Applied Chemistry
Chinese Academy of Sciences
[12]
used in the N-methylation reactions. Shi and co-workers
applied a simple CuAlOx catalyst to transform primary and
secondary amines into the corresponding N-methyl or N,N-
dimethyl products with CO2 and H2. In this system, however, a
large amount (38 mol%) Cu with respect to amine was required.
More recently, Tomishige et al. reported that Cu/CeO2 catalyst
was high efficent for the synthesis of N-methylaniline by N-
methylation of aniline with CO2 and H2. [13]
Changchun, 130022, P. R. China.
E-mail: linwei@ciac.ac.cn, zhaofy@ciac.ac.cn
K. Liu, Dr W. Lin, Q. Liu, Q. Wu, R. Shi, Dr C. Zhang, Dr. H.
Cheng, Prof.Dr. M. Arai, Prof. Dr. F. Zhao
Jilin Province Key Laboratory of Green Chemistry and Process,
Changchun Institute of Applied Chemistry,
Chinese Academy of Sciences,
[c]
Cu-based catalysts were widely used for the
hydrogenation reactions for its inexpensive price and remarkable
hydrogenation activity. [14] Many years ago, it was demonstrated
Changchun, 130022, P. R. China.
[15]
that Cu catalysts were active in the hydrogenation of CO2.
Baiker and co-workers found that active Cu species was mainly
Supporting information for this article is given via a link at the end
of the document.
[16]
present as Cu0 over Cu/ZrO2.
In contrast, Cu+ was proposed
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10.1002/cctc.201900582
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to be the active species for Cu/ZnO/SiO2 catalyst. [17] Liu and co-
The results of the relative amounts of anatase and rutile
phases estimated are shown in Table S2. WR was 10% for
Cu/TiO2 sample using un-calcined TiO2 and it increased to 17%,
85%, and 100% on the calcination at 600, 700, 800 ºC,
respectively. Such a change of the crystal phase from anatase
to rutile with the calcination temperature was also confirmed by
Raman spectroscopy (Figure S2).
workers reported
a
direct comparison in the catalytic
performances between ZnCu and ZnO/Cu model catalysts for
methanol synthesis. [18] The results emphasize a synergy of Cu
and ZnO at the interface that facilitates methanol synthesis via
formate intermediates. Recently, Cu/TiO2 catalyst was reported
to be effective for photocatalytic CO2 reduction, in which the Cu+
and Cu0 species formed by H2-reduction was confirmed to be
[19]
more active in charge separation than Cu+ species alone.
Cu/TiO2 was also used in the photocatalytic hydrogenation of
CO2 into CH4 and the coexistence of Cu0 and Cu+ was beneficial
to enhance the activity by prolonging the lifetime of electrons. [20]
Considering the above-mentioned results, we have
investigated the feasibility of Cu catalyst for direct N-methylation
of N-methylaniline (MA) with CO2 and H2. In the present work,
TiO2 (P25) was employed as a support to disperse Cu species
and Cu/TiO2 samples were prepared by deposition-precipitation
method and tested for the target reaction in n-octane. It is
important to note here that Cu/TiO2 is more effective with
respect to the total MA conversion and the DMA selectivity than
those Cu catalysts on CeO2, ZnO, and activated carbon. The
bulk and surface properties of Cu/TiO2 catalysts were
characterized by XRD, TEM, XPS, and TPR and possible
reaction intermediates were examined by controlled reaction
runs and in situ high-pressure FTIR for the reaction system in
the presence of CO2 and H2 under reaction conditions. From
those results, discussion was given on Cu species effective for
the selective production of DMA from MA and possible reaction
pathways concerned.
Cu/TiO2-800
Cu/TiO2-700
Cu/TiO2-600
Cu/TiO2
10 20 30 40 50 60 70 80 90
2 theta (degree)
Figure 1 XRD patterns of Cu/TiO2-T (Cu loading is 5%) samples using TiO2
supports pretreated at different calcination temperatures.
The dispersion of Cu particles in those samples was
examined by transmission electron microscope (TEM). As
shown in Figure 2, Cu was finely dispersed in the form of
nanoparticles on the TiO2 supports. The average Cu particle size
was 2.3, 3.6, 4.6 and 6.1 nm for Cu/TiO2, Cu/TiO2-600, Cu/TiO2-
700, and Cu/TiO2-800, respectively. The size of Cu
nanoparticles was increased by a factor of 3 on the calcination
at 800 ºC. The pre-calcination of TiO2 decreased the degree of
Cu dispersion thereon. The reducibility of the above-mentioned
Cu/TiO2-T samples was investigated by H2-TPR measurements
Results and Discussion
3.1. Catalyst characterization
The BET surface area, pore size and pore volume of 5 wt.-% Cu
catalysts on TiO2 supports pre-calcined at different temperatures
were determined by N2 sorption (as shown in Figure S1). The
results obtained with the samples reduced in H2 at 250 ºC were
shown in Table S1. The calcination temperature was observed
to have a remarkable impact on these textural properties. For
example, the BET surface area was 47.4 m2/g for Cu/TiO2 at
250 ºC and it decreased to 42.5, 20.7, and 9.4 m2/g, respectively,
by the pre-calcination of TiO2 support at 600, 700, and 800 ºC.
The bulk structure of those catalysts was examined by XRD
and Raman spectroscopy measurements. Figure 1 gives the
XRD patterns and there is no diffraction peaks of Cu species,
probably due to the small metal loading and/or the fine
dispersion of Cu species on TiO2 supports. Figure 1 indicates
the presence of anatase and rutile crystal phases in the samples.
The relative contents of these two phases changed on the
calcination of TiO2 and were calculated by the following equation
(1), where WR is the weight fraction of rutile phase in the sample
and AA and AR represent the integral XRD intensities of the
anatase (101) at 2 = 25.2º and the rutile (110) at 2 = 27.4º
(Figure 3). TiO2 did not show any reduction peak in the range of
[21]
temperature range of 50-600 ºC
and the Cu/TiO2 samples
showed two or more reduction peaks, in which larger or
crystallized CuO particles were reduced at higher temperature
than that of smaller CuO particles or highly dispersed Cu2+
[22]
species.
Figure 3 showed two reduction peaks at 114 and
128 ºC for Cu/TiO2 and Cu/TiO2-600, in which the former
corresponded to the reduction of smaller CuO particles and/or
highly dispersed Cu2+ species while the latter to that of larger
CuO particles and/or Cu2+ species in strong interaction with TiO2.
For Cu/TiO2-700 and Cu/TiO2-800 samples, three peaks were
observed at around 101, 113, and 158 ºC. The first two peaks
may be attributable to the highly dispersed copper oxides and
the third one presented at a wide range of temperature to the
[23]
crystalline copper oxides.
The large difference between the
samples on TiO2 supports pre-calcined at 600 and 700 ºC was in
accordance with the differences in the structure of TiO2 supports
measured, respectively.
퐴푅
푊푅 =
(1)
0.884퐴퐴 + 퐴푅
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in BE between Cu+ and Cu0 is only 0.1 eV and so these Cu
species cannot be distinguished by XPS. [19] Thus, the peaks at
933.8 and 953.8 eV were assigned to Cu0 and/or Cu+ species.
a
b
d
[24]
The relative amounts of those Cu species and the BE values
35
30
25
20
15
10
5
D = 3.6 nm
25
20
15
10
5
D = 2.3 nm
in the samples examined indicated that the relative amount of
Cu0 and Cu+ decreased with an increase in the calcination
temperature of TiO2 support (Table S3). In addition, Cu0 and Cu+
was distinguished by using Cu (LMM) Auger photoelectron
spectroscopy (Figure S3); A peak at 916.5 eV was ascribed to
0
0
1.5 1.8 2.1 2.4 2.7 3.0 3.3 3.6
Diameter (nm)
2.4 3.2 4.0 4.8 5.6
Diameter (nm)
[25]
Cu+ and a peak at 921.5 eV to transition state of Cu LMM.
c
While, the peak of Cu0 at 918.3 eV was not detected due to
surface oxidation when the sample exposed to air in the
handling. In addition to Cu+ and Cu2+, some amount of Cu0
species might also exist on the surface of Cu nanoparticles of
Cu/TiO2-T catalysts.
35
25
D = 4.6 nm
D = 6.1 nm
30
25
20
15
10
5
20
15
10
5
0
0
2
3
4
5
6
7
8
3
4
5
6
7
8
9 10
Cu 2p3/2
Cu 2p1/2
Diameter (nm)
Diameter (nm)
Figure 2 TEM images of (a) Cu/TiO2, (b) Cu/TiO2-600, (c) Cu/TiO2-700, (d)
Cu/TiO2-800
Cu/TiO2-800 samples.
Cu/TiO2-700
Cu/TiO2-600
(Figure 1) and in the size of dispersed Cu nanoparticles thereon
(Figure 2).Figure 3 shows, however, that all Cu species loaded
on those TiO2 supports could be reduced at a temperature of
250 ºC. Thus, for the following activity test in the N-methylation
of MA with CO2 and H2, all the catalysts were reduced at 250 ºC.
Cu/TiO2
966 960 954 948 942 936 930
Binding Energy (eV)
128
Figure 4 XPS results of Cu/TiO2-T (Cu loading is 5%) with the supports
calcined at different temperatures.
114
Cu/TiO2
3.2 Catalytic performance
Cu/TiO2-600
The catalytic performances of the Cu/TiO2 catalysts
prepared were investigated for the N-methylation of MA with
CO2 and H2. Under the conditions used, DMA, MFA, aniline (AN),
N-phenylformamide, N,N-dimethylcyclohexylamine, and other
condensation products were detected to form and the product
distribution depended on the catalysts used (Scheme 1).
158
Cu/TiO2-700
Cu/TiO2-800
100
200
300
400
500
600
Temperature (oC)
H
NH2
N
N
H
N
Cat.
Cat.
Cat.
Figure 3 TPR profiles of Cu/TiO2-T (Cu loading is 5%) catalysts with the
supports calcined at different temperatures.
O
2H2,-H2O
-CH4
H2,CO2,-H2O
AN
MA
DMA
MFA
Scheme
1 N-methylation of N-methylaniline (MA) to N,N-dimethylaniline
(DMA) with CO2 and H2.
Furthermore, the chemical state of Cu species exposed on
Cu/TiO2-T samples reduced at 250 ºC was examined by XPS
measurements (Figure 4). For Cu/TiO2 (un-calcined), there
appeared peaks at binding energies (BE) of 935.7, 955.7 eV and
942.9, 963.7 eV, which were attributed to Cu2+ and the shake-up
satellite peak of Cu2+, respectively, indicating that there was
Cu2+ species on the surface even after reduction. The difference
Initially, we compared the catalytic performance of 5 wt.-%
Cu catalysts using different support materials, which were
loaded and reduced in the same manners as described in
Experimental. The results obtained are summarized in Table 1.
The most active catalyst was Cu/TiO2 (P25), giving a conversion
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of 55.7% and a DMA selectivity of 95.9% (entry 1). When CeO2,
ZnO, and C were used as supports, the conversion and the
DMA selectivity became decreased significantly (entries 2 - 4),
among which the DMA selectivity was good (81%) with Cu/ZnO
catalyst (entry 3). The results indicated that Cu/TiO2 (P25) was
the most efficient catalyst with respect to the total conversion
and the DMA selectivity.
obtained are shown in Table 2. The conversion simply
decreased from 56% to 18% with an increase in the calcination
temperature up to 800 ºC while DMA was produced in a
selectivity of > 95% with all these catalysts. As above-mentioned,
the size of Cu nanoparticles and the relative fraction of Cu+ and
Cu0 were reduced by the pre-calcination of TiO2 and the amount
of Cu+ was even larger than that of Cu0. As seen in Figure 5，
the total MA conversion increased linearly with the amount of the
exposed Cu+ and Cu0 species, which was estimated by the XPS
results (Table S3) and Cu particle size as described in
experimental part. Therefore, the surface Cu+ and Cu0 species
exposed on the catalysts should be the active sites for the
present methylation reaction.
Table 1 N-Methylation of N-methylaniline with CO2 and H2 over Cu
catalysts on various supports.
Selectivity (%)
Conversion
(%)
Entry
Catalyst a
DMA
95.9
38.1
81.0
20.9
MFA
0.1
AN
0.3
Others b
3.7
1
2
3
4
Cu/TiO2
Cu/CeO2
Cu/ZnO
Cu/C
55.7
1.4
1.1
59.2
13.1
53.0
1.6
9.6
0.3
5.6
60
9.6
0.5
2.6
Reaction conditions: Catalyst (Cu loading is 5%) 100 mg, MA 1 mmol, n-
octane 10 mL, 4 MPa H2, 2 MPa CO2, 180 ºC, 8 h.
[a] Reduced in H2 at 250 ºC for 2 h. Cu loading 5 wt.-%.
[b] The others were N-phenylformamide, N,N-dimethylcyclohexylamine and
condensation products.
Cu/TiO2
50
Cu/TiO2-600
40
30
Cu/TiO2-700
The influence of Cu loading on the performance of Cu/TiO2
(un-calcined) was then studied. The results obtained (Table S4)
shows that TiO2 itself was inactive, the total conversion became
increased by loading Cu, and it was maximized at a Cu loading
of 5 % in weight in the range of Cu loading up to 15%. In
contrast, the selectivity to DMA was large (> 90%) irrespective of
the Cu loading. So, a Cu/TiO2 with 5% loading was used for
further experiments. The catalytic performance (activity and
selectivity) was examined at different reaction temperatures
(Table S5). The total conversion was 20, 56, 52, and 51% and
the DMA selectivity was 83, 96, 94, and 86% at 160, 180, 200,
and 220 ºC, respectively. These results indicate that the
optimum reaction temperature was 180 ºC.
20
Cu/TiO2-800
10
0
0
5
10
15
20
+
0
Amount of Cu and Cu (mol)
Figure 5 Relation between total conversion and the amount of Cu+ and Cu0
species exposed on the surface of catalyst.
100
80
60
40
20
0
Table 2 The catalytic performance of Cu/TiO2 catalysts with TiO2 supports pre-
calcined at different temperatures.
Selectivity(%)
Conversion
Entry
Catalyst a
(%)
DMA
MFA AN Others b
1
2
3
Cu/TiO2
55.7
51.2
25.4
95.9
97.0
94.9
0
0
0.3
0.4
1.4
3.8
2.6
0
Cu/TiO2-600
Cu/TiO2-700
3.7
4
Cu/TiO2-800
17.7
94.3
0
4.4
1.3
0
5
10
15
20
25
30
35
40
Reaction conditions: Catalyst (Cu loading is 5%)100 mg, N-Methylaniline 1
mmol, n-octane 10 mL, H2 4 MPa, CO2 2 MPa, 180oC, 8 h.
[a] Reduced in H2 at 250 ºC for 2 h.
[b] The others were N-phenylformamide, N,N-dimethylcyclohexylamine and
condensation products.
Time (h)
Figure 6 Variation of MA conversion (■), DMA selectivity (□) and AN
selectivity (○) with the reaction time in the N-methylation of MA over Cu/TiO2
(Cu loading is 5%). Reaction conditions: Cu/TiO2 100 mg, MA 1 mmol, n-
octane 10 mL, H2 4 MPa, CO2 2 MPa, 180oC.
Then, the catalytic performance of a series of Cu/TiO2
samples different in the pre-calcination temperature of TiO2 was
examined, for which the results of structural and surface
characterization are given in the above section, and the results
Figure 6 showed the variation of MA conversion and DMA
selectivity as a function of reaction time over Cu/TiO2 (un-
calcined) catalyst. The selectivity to DMA was larger than 96%
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at an early stage of reaction and this high DMA selectivity
remained unchanged during the reaction. A large MA conversion
of 82% was achieved with a DMA selectivity of 96%, which is
one of the best results reported to date with copper-based
catalysts for N-methylation reaction.
The spent catalyst after used four runs was characterized
by ICP, TEM, TGA, and XRD. No leaching of Cu species from
the catalyst was detected by ICP but the growth of Cu
nanoparticles was observed by TEM, in which the average
particle size increased to 3.6 nm from 1.9 nm of the fresh
catalyst (Figure 2a, Figure 8a). TGA (Figure S4) indicated a few
stage of the reduction of catalyst weight at different
temperatures. The first stage below 170 ºC was ascribable to the
removal of moisture residue and trapped CO2 [26], while the
gradual weight decrease at temperatures of 170 to 270 ºC to the
loss of organic solvent and/or adsorbed substance. A major
weight loss occurred between 370 and 570 ºC, which should be
due to the removal of coke. The deposition of carbon materials
was also confirmed by XRD (Figure S5); the spent Cu/TiO2
catalyst showed diffraction peaks at 2Ѳ of 18.1º, 32.1º attributed
to carbon deposits. The amount of carbon deposited was about
8 wt.-% to the total weight of the catalyst estimated from TGA.
Thus, the factors causing a loss of catalytic activity during
recycles should be the deposition of carbon materials, which
covered the surface active sites on the Cu particles. As
described above, the spent catalyst was regenerated by a
simple calcination in air and reduction in H2, which should
remove the carbon deposits from the surface of Cu
nanoparticles. The TEM image of regenerated catalyst was
shown in Figure 8b. The average particle size decreased to 2.4
nm, close to the fresh one of Cu/TiO2, which should be ascribed
to the removal of the surface carbon deposit during the heat
treatment.
Finally, the reusability of the most active Cu/TiO2 catalyst
was examined. After the first run, the catalyst was collected from
the reaction mixture by centrifugation, washed with ethanol and
n-octane for several times, and used for the subsequent run. As
shown in Figure 7, the conversion was around 55% and the
selectivity to DMA was > 97% for the first two runs. However, the
conversion decreased to 35% and 29% for the third and fourth
runs, respectively. That was, the loss of catalytic activity
occurred to some extent during the repeated runs. However,
when the spent catalyst used for four runs was thermal treated
in air at 450 ºC for 4 h followed by reduction in H2 at 250 ºC for 2
h, the MA conversion recovered to 56%, indicating that the spent
Cu/TiO2 could be regenerated through such a simple calcination
and reduction process.
100
80
60
40
20
0
Table 3 Results of N-methylation of MA with various carbon sources over
Cu/TiO2.
Conversion
(%)
Selectivity (%)
Entry
Additive
DMA
MFA
AN
Othersf
1
2
3
4
5
1a
2b
3c
4d
5e
CO2
HCOOH
CH3OH
HCHO
CO
55.7
95.7
31.5
69.2
14.2
95.9
0.9
95.8
86.3
95.1
0.1
98.9
0
0
0
0.3
0.1
4.2
0.3
3.8
3.7
0.1
0
13.4
1.1
Usage count
Figure 7 Results of repeated reaction runs. Reaction conditions: Cu/TiO2 (Cu
loading is 5%) 100 mg, MA 1 mmol, n-octane 10 mL, H2 4 MPa, CO2 2 MPa,
180oC, time 8 h. For the fifth run, the spent catalyst used for four times was
pretreated in air at 450 ºC for 4 h and reduced in H2 at 250 ºC for 2 h.
Reaction conditions: Catalyst (Cu loading is 5%) 100 mg, MA 1 mmol, n-
octane 10 mL, H2 4 MPa, 180 ºC, 8 h. [a] CO2 2 MPa, [b] HCOOH 2 mmol, [c]
CH3OH 16 mmol, [d] HCHO 2 mmol, [e] CO 1 MPa, [f] The others were N-
phenylformamide, N,N-dimethylcyclohexylamine and condensation products.
a
b
3.3 Possible reaction pathways
40
35
30
25
20
15
10
5
As described in Scheme 1, MA will transform to DMA
through MFA or to AN in the N-methylation of MA with CO2 and
H2. Further control experiments were carried out to explore
reaction intermediates and mechanisms involved. Initially
several carbon sources were tested, including HCOOH, CH3OH,
HCHO, and CO that were possible species produced from CO2
and H2 during the reaction. [2e, 27] Table 3 gives the results of N-
methylation reactions using these compounds over the most
active Cu/TiO2 catalyst, with which a MA conversion of 56% and
a DMA selectivity of 96% were obtained in the presence of CO2
and H2 (entry 1). When HCOOH was used instead of CO2, the
MA conversion was increased to 96% but MFA was exclusively
produced in a selectivity of 99% (entry 2). CH3OH gave a
30
25
20
15
10
5
D = 2.4 nm
D = 3.6 nm
0
0
1.5 1.8 2.1 2.4 2.7 3.0 3.3
Diameter (nm)
2.5 3.0 3.5 4.0 4.5 5.0 5.5
Diameter (nm)
20 nm
20 nm
Figure 8. TEM images of Cu/TiO2 (Cu loading is 5%) after (a) 4 runs and (b)
regeneration.
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10.1002/cctc.201900582
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smaller conversion of 32% with a high DMA selectivity of 96%
(entry 3) similar to that with CO2 (entry 1), and medium
conversion (69%) and DMA selectivity (86%) were obtained with
HCHO (entry 4), while a small conversion (14%) and a high
DMA selectivity (95%) with CO (entry 6). Those results indicate
that CH3OH and/or HCHO should be intermediate formed in the
target reaction with CO2 and H2.
Besides, the catalyst was also subjected to in-situ ATR-
FTIR to further examine the existence of intermediate species.
As shown in Figure 9, there appeared three new bands at 1677,
1109 and 990 cm-1 at 43 min, and these bands became intense
with time, which are assigned to the carbonyl (C=O) vibration of
HCHO as they are similar to the spectrum of pure HCHO (Figure
S6). Therefore, it was more likely that CHO* species was the
main reaction intermediate in the N-methylation reaction. Based
on the above results, the reaction pathways were proposed, as
shown in Scheme 2. First, CO2 reacts with H2 to form CHO*
species on the surface of Cu+ and Cu0 active species, CHO*
species formed reacts with MA to yield intermediate MFA, and
then MFA was hydrogenated to DMA, which was in agreement
with the case of the reaction with homogeneous copper catalyst
[27c]. In the present catalysis system, the Cu+ and Cu0 are active
species, as the reaction conversion increased linearly with the
amount of Cu+ and Cu0 species exposed on the surface of catalyst
(Figure 5).
Next, an intermediate of MFA (Scheme 1) was used as a
starting reactant, with which control reactions were conducted in
the absence or presence of different methyl reagents under the
same conditions as used for the above-mentioned reactions with
MA. The results obtained are shown in Table 4. With no methyl
reagent, a MFA conversion of 96% was obtained and DMA and
MA were produced in comparable amounts (entry 1). When 2
MPa CO2 was added, the product selectivity was significantly
changed and DMA was obtained in a selectivity of 80% being
larger by a factor of 4 compared to MA (entry 2). As described
above, the reaction with MA gave a larger DMA selectivity of
96% (Table 1). Therefore, it is assumed for the target
methylation reaction of MA that MFA was produced from MA
and some fraction of MFA molecules produced converted back
to MA; however, the rate of MFA transformation to DMA is faster
than that to MA (Table 4) and so MFA can finally change to DMA
after repeated transformation between MFA and AM during the
course of reaction. When either HCOOH or CH3OH was used,
the major product was MA with a selectivity of 79% (entry 3) or
70% (entry 4). In contrast, for the case of HCHO, DMA was
1109
990
0.2
1677
120 min
101 min
80 min
70 min
60 min
53 min
43 min
exclusively obtained in
a selectivity of 93% at a 100%
34 min
conversion (entry 5). The results of Tables 3 and 4 indicate that
HCHO is a possible intermediate and it is of significance in the
selective N-methylation of MA to DMA compared to CH3OH.
18 min
10 min
5 min
0 min
1950 1800 1650 1500 1350 1200 1050 900
Table 4 Results of hydrogenation of MFA with different carbon sources
over Cu/TiO2 catalyst.
-1
Wavenumber (cm )
Selectivity (%)
Conversion
(%)
Entry
additive
DMA
48.5
79.5
20.2
28.6
92.9
MA
51.2
19.4
78.6
70.0
6.5
AN
0.3
0
1.2
0.3
0.1
Others e
Figure 9 In-situ ATR-FTIR spectra recorded at different times in H2 and CO2
atmosphere over Cu/TiO2. Conditions: Cu/TiO2 (Cu loading is 5%) 50 mg, CO2
2 MPa, H2 4 MPa, n-octane 4.4 mL, 180 ºC.
1
-
95.7
100
83.3
100
100
0
1.1
0
1.1
0.5
2a
3b
4c
5d
CO2
HCOOH
CH3OH
HCHO
CO2+H2
5Cu/TiO2
H
Reaction conditions: Catalyst (Cu loading is 5%) 100 mg, MFA 1 mmol,
n-octane 10 mL, H2 4 MPa, 180 ºC, 8 h. [a] CO2 2 MPa, [b] HCOOH 2
mmol, [c] CH3OH 16 mmol, [d] HCHO 2 mmol, [e] The others were N-
phenylformamide, N,N-dimethylcyclohexylamine and condensation
products.
N
N
H
N
H2, -H2O
5Cu/TiO2
CHO*
O
5Cu/TiO2
Furthermore, FTIR was used to examine intermediate
species formed from CO2 and H2 on Cu/TiO2 (Cu loading is 5%)
catalyst under the reaction conditions. The Cu/TiO2 catalyst was
exposed to CO2 and H2 at 180 ºC for 4 h in the reactor and then
subjected to FTIR measurement. Figure S6 gives a FTIR
spectrum collected, indicating absorption bands at 2935 and
2861 cm-1 assignable to CHO* species. The bands at 1648 and
1446 cm-1 correspond to the carbonyl vibration and C-H
stretching in the CHO group, respectively. [28] It is suggested that
the CHO* species are generated on Cu/TiO2 catalyst during the
process.
MA
DMA
MFA
Scheme 2 Possible reaction pathways for N-methylation of MA with CO2 and
H2 over Cu/TiO2 catalyst (Cu loading is 5%).
Conclusions
In summary, a non-noble metal catalyst of Cu/TiO2 is effective
for the heterogeneous N-methylation of MA with CO2 and H2.
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10.1002/cctc.201900582
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the deconvolution of overlapped XPS peaks. Visible Raman spectra
Under the optimum reaction conditions, the desired product of
DMA was obtained in a high selectivity of 96% at 82%
conversion. It is likely that CO2 reacts with H2 to form CHO*
species, CHO* formed reacts with MA to give intermediate MFA,
and finally MFA is hydrogenated to DMA. These processes
occur on the active species of Cu+ and Cu0. While, the
were recorded on
a
Jobin–Yvon U1000 scanning double
monochromator with a spectral resolution of 4 cm-1. The line at 514
nm from a DPSS 532 Model 200 532-nm single-frequency laser was
used as excitation source. Thermo-Gravimetric Analysis (TGA)
measurements were performed on a TA-Q50 system under air
atmosphere at a heating rate of 10 °C min-1. Thermograms were
recorded in the temperature range of 50 to 800 °C.
deactivated catalyst can be recovered by
a simple heat
treatment of calcination at 450 ºC in air and reduction at 250 ºC
in hydrogen, through which the activity of the regenerated
Cu/TiO2 is similar to its original activity.
In order to examine possible intermediate species produced
from CO2 and H2, Fourier-transform infrared (FTIR) spectra of
Cu/TiO2 pretreated with CO2 and H2 were recorded at room
temperature with a NICOLET iS50 infrared spectrometer in the
region of 400–4000 cm-1. A Cu/TiO2 sample was exposed to CO2 (2
MPa) and H2 (4 MPa) at 180 ºC for 4 h in a 50 mL stainless steel
autoclave reactor, the gases were vented to ambient pressure, the
catalyst was put into the infrared instrument, and then the FTIR
spectra were collected. In addition, in-situ total reflectance Fourier-
transform infrared spectroscopy (ATR-FTIR) measurements were
performed in a 22 mL high-pressure cell with a transparent diamond
prism window on the bottom plate using a Nicolet iS50 spectrometer
equipped with a MCT detector. First, a background spectrum was
collected under air and 4.4 mL octane, and 50 mg Cu/TiO2 were
added to the cell. It was sealed and flushed with H2 a few times and
introduced with 4 MPa H2 and 2 MPa CO2. Then, FTIR spectra were
collected for a period of 2 h while stirring.
Experimental Section
2.1. Preparation of catalysts
All chemicals used in this work were analytic grade and used
without further purification. A commercial TiO2 (P25) (Acros) was
selected as support and a Cu/TiO2 catalyst with Cu 5 wt.-% loading
was prepared by deposition-precipitation method. The support TiO2
powder and a certain amount of Cu(NO3)2·3H2O were dissolved in
100 mL of deionized water while stirring and the suspension was put
into a water bath at 50 ºC. Then, a Na2CO3 solution was added
dropwise into the suspension until the pH value became to 9.5. The
mixture was aged for 2 h and the precipitate obtained was filtered
and washed with deionized water and ethanol several times,
followed by drying at 80 ºC overnight and calcination in static air at
350 ºC for 4 h. The Cu/TiO2 catalysts with different Cu loadings of 1,
3, 10, and 15 wt.-% were also prepared, and they are herein named
as 1%Cu/TiO2, for example. For comparison, several catalysts with
5% Cu supported on other supports of ZnO (Aladdin), CeO2
(Sinopharm Chemical Reagent Co., Ltd.) and active carbon (Sigma-
aldrich) were prepared by the same procedures described above,
and they are named as Cu/ZnO, Cu/CeO2 and Cu/AC, respectively.
In addition, the TiO2 (P25) powder was calcined at different
temperatures (600, 700, 800 ºC) in air for 4 h and these calcined
TiO2 materials were also used as supports for 5 wt.-% Cu catalysts.
These catalysts are denoted as Cu/TiO2-T, where T stands for the
TiO2 calcination temperature. If no otherwise specified, Cu/TiO2
stands for a catalyst with Cu loading of 5% in weight. All the catalyst
2.3. Activity test
N-methylation of N-methylaniline (MA) with CO2 and H2 was
performed in a 50 mL stainless steel autoclave reactor at 180 ºC.
Prior to the catalytic test, all the catalysts were reduced in a quartz
tube with a H2 flow (30 mL min-1) at 250 ºC for 2 h. Measured
amounts of MA (1 mmol), solvent (n-octane 10 mL) and catalyst (100
mg) were added into the reactor and it was sealed and flushed with
1 MPa H2 at least three times to remove the air. The reactor was
then heated to 180 ºC and pressurized with 4 MPa H2 and 2 MPa
CO2. The reaction was started under stirring. After the reaction
finished, the reactor was cooled and the gas mixture was then
vented to ambient pressure. The liquid products obtained were
analyzed by gas chromatograph (Shimadzu GC-2010, Rtx-5
capillary column) using a flame ionization detector and identified by
gas chromatography/mass spectrometry (GC/MS, Agilent 5890). The
conversion and selectivity to N,N-dimethylaniline (DMA) were
calculated using the following equations.
samples were reduced in H2 at 250 ºC for
characterization and reaction runs.
2 h prior to
2.2. Characterization of catalysts
MA conversion (%) = (1 − Amount of MA unreacted) × 100 (2)
Initial amount of MA
Powder X-ray diffraction (XRD) was performed using a Bruker
D8 Advance X-ray diffractometer with a Cu K source at 40 kV and
40 mA for a 2θ range from 10 o to 90 o with a scan speed of 4 º/min.
Transmission electron microscopy (TEM) was carried out on a JEOL
JEM-2010 instrument at an accelerating voltage of 187 kV.
Temperature programmed reduction (TPR) profiles were measured
on Micromeritics AutoChem II 2920. For TPR, a catalyst sample (50
mg) was pretreated in Ar at 120 °C for 1 h to remove physically
adsorbed H2O and other impurities. After cooling to 50 ºC, the
sample was flushed in Ar for an additional 0.5 h and then heated to
800 °C at a rate of 10 °C min−1 in a flow of 10% H2/Ar (30 mL min-1).
Nitrogen adsorption-desorption experiments were conducted with a
Micromeritics ASAP 2020 surface area and porosity analyzer. X-ray
photoelectron spectroscopy (XPS) measurements were carried on
VG Microtech 3000 Multilab equipped with an Al Kα X-ray exciting
source (1486.6 eV). The C1s peak at 248.6 eV (accuracy within ±0.3
eV) was used as reference. XPSPEAK fitting software was used for
Amount of DMA produced
(
)
DMA selectivity % =
× 100 (3)
Total amount of all products
The catalyst reusability was also examined. The catalyst was
collected by centrifugation after the first run, washed with ethanol
and then n-octane several times each, and reused for the next run
under the same reaction conditions as described above.
In order to exmaine the active species, the ralation between
total conversion and the amount of Cu+ and Cu0 species exposed on
the surface of catalyst was examined, The amount of Cu+ and Cu0
species was calculated based on the Cu particle size and XPS
results. The Cu dispersion (D) was calculated from the following
equation: D = 6(vm/am)/d. The calculation method was obtained from
the hand book of heterogeneous catalysis, vm = the volume of a Cu
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atom, am = the area of a Cu atom, where vm and am is 11.83 Å3 and
6.85 Å2, respectively. The average diameter (d) of Cu particles was
determined by TEM. Moles of the exposed of Cu0 and Cu+ was
calcuated by [(the mole of Cu used) × (the dispersion D) × (the
relative amount of Cu+ and Cu0)]. The relative amount of Cu+ and
Cu0 species was calculated by (Cu+ + Cu0)/( Cu2+ + Cu+ + Cu0) from
the XPS results (Table S3).
[9]
K. Kon, S. Siddiki, W. Onodera, K. Shimizu, Chem.-Eur. J. 2014, 20,
6264-6267.
[10] T. Toyao, S. Siddiki, K. Ishihara, K. Kon, W. Onodera, K. Shimizu,
Chem. Lett. 2017, 46, 68-70.
[11] a) X. L. Du, G. Tang, H. L. Bao, Z. Jiang, X. H. Zhong, D. S. Su, J. Q.
Wang, ChemSusChem 2015, 8, 3489-3496; b) G. Tang, H. L. Bao, C.
Jin, X. H. Zhong, X. L. Du, RSC Adv. 2015, 5, 99678-99687; c) T.
Toyao, S. Siddiki, Y. Morita, T. Kamachi, A. S. Touchy, W. Onodera, K.
Kon, S. Furukawa, H. Ariga, K. Asakura, K. Yoshizawa, K. I. Shimizu,
Chem. Eur. J. 2017, 23, 14848-14859.
Acknowledgements
[12] X. Cui, X. Dai, Y. Zhang, Y. Deng, F. Shi, Chem. Sci. 2014, 5, 649-655.
[13] M. Tamura, A. Miura, Y. Gu, Y. Nakagawa, K. Tomishige, Chem. Lett.
2017, 46, 1243-1246.
The authors gratefully acknowledge the financial support from
the National Key Research and Development Program of China
(2016YFA0602900), Natural Science Fund Council of China
(NSFC 21603212, 21672204), and Chinese Academy of
Sciences President’s International Fellowship Initiative
(2018VCA0012).
[14] L. F. Chen, P. J. Guo, M. H. Qiao, S. R. Yan, H. X. Li, W. Shen, H. L.
Xu, K. N. Fan, J. Catal. 2008, 257, 172-180.
[15] a) M. Behrens, F. Studt, I. Kasatkin, S. Kuhl, M. Havecker, F. Abild-
Pedersen, S. Zander, F. Girgsdies, P. Kurr, B. L. Kniep, M. Tovar, R. W.
Fischer, J. K. Norskov, R. Schlogl, Science 2012, 336, 893-897; b) F.
Studt, M. Behrens, E. L. Kunkes, N. Thomas, S. Zander, A. Tarasov, J.
Schumann, E. Frei, J. B. Varley, F. Abild-Pedersen, J. K. Norskov, R.
Schlogl, Chemcatchem 2015, 7, 1105-1111.
Keywords: N-Methylation • N-methylaniline • CO2 • Copper •
[16] R. A. Koeppel, A. Baiker, A. Wokaun, Appl. Catal. A-Gen. 1992, 84, 77-
102.
Heterogeneous catalysis
[17] W. P. A. Jansen, J. Beckers, J. C. Van der Heuvel, A. W. D. Van der
Gon, A. Bliek, H. H. Brongersma, J. Catal. 2002, 210, 229-236.
[18] S. Kattel, P. J. Ramirez, J. G. Chen, J. A. Rodriguez, P. Liu, Science
2017, 355, 1296-1299.
[1]
[2]
a) M. Aresta, A. Dibenedetto, A. Angelini, Chem. Rev. 2014, 114, 1709-
1742; b) S. G. Jadhav, P. D. Vaidya, B. M. Bhanage, J. B. Joshi, Chem.
Eng. Res. Des. 2014, 92, 2557-2567; c) R. Sun, Y. Xu, J. Liu, J. Mu, S.
Ji, Sci. China-Chem 2018, 48, 547-561.
[19] L. J. Liu, F. Gao, H. L. Zhao, Y. Li, Appl. Catal. B-Environ. 2013, 134,
349-358.
a) Z. H. He, Q. L. Qian, J. Ma, Q. L. Meng, H. C. Zhou, J. L. Song, Z. M.
Liu, B. X. Han, Angew. Chem. Int. Ed. 2016, 55, 737-741; b) P. Gao, S.
G. Li, X. N. Bu, S. S. Dang, Z. Y. Liu, H. Wang, L. S. Zhong, M. H. Qiu,
C. G. Yang, J. Cai, W. Wei, Y. H. Sun, Nat. Chem. 2017, 9, 1019-1024;
c) X. H. Zhou, T. M. Su, Y. X. Jiang, Z. Z. Qin, H. B. Ji, Z. H. Guo,
Chem. Eng. Sci. 2016, 153, 10-20; d) G. A. Filonenko, W. L. Vrijburg, E.
J. M. Hensen, E. A. Pidko, J. Catal. 2016, 343, 97-105; e) A. Alvarez, A.
Bansode, A. Urakawa, A. V. Bavykina, T. A. Wezendonk, M. Makkee, J.
Gascon, F. Kapteijn, Chem. Rev. 2017; f) A. Behr, K. Nowakowski, in
CO2 Chemistry, Vol. 66 (Eds.: M. Aresta, R. V. Eldik), Elsevier
Academic Press Inc, San Diego, 2014, pp. 223-258; g) G. Centi, S.
Perathoner, Catal. Today 2009, 148, 191-205; h) B. Liu, S. S. Geng, J.
Zheng, X. L. Jia, F. Jiang, X. H. Liu, Chemcatchem 2018, 10, 4718-
4732.
[20] B. R. Chen, V. H. Nguyen, J. C. S. Wu, R. Martin, K. Koci, Phys. Chem.
Chem. Phys. 2016, 18, 4942-4951.
[21] M. L. Lan, B. Zhang, H. Y. Cheng, X. R. Li, Q. F. Wu, Z. Ying, Y. X. Zhu,
Y. Li, X. Meng, F. Y. Zhao, Mol. Catal. 2017, 432, 23-30.
[22] a) W. P. Dow, Y. P. Wang, T. J. Huang, J. Catal. 1996, 160, 155-170; b)
G. Fierro, M. LoJacono, M. Inversi, P. Porta, F. Cioci, R. Lavecchia,
Appl. Catal. A: Gen. 1996, 137, 327-348; c) J.-N. Nian, S.-A. Chen, C.-
C. Tsai, H. Teng, J. Phys.Chem. B 2006, 110, 25817-25824; d) F. S.
Delk, A. Vavere, J. Catal. 1984, 85, 380-388.
[23] X. F. Yu, N. Z. Wu, Y. C. Xie, Y. Q. Tang, J. Mater. Chem. 2000, 10,
1629-1634.
[24] R. Morrish, A. J. Muscat, Chem. Mater. 2009, 21, 3865-3870.
[25] N. Boreriboon, X. Jiang, C. Song, P. Prasassarakich, J. CO2 Util. 2018,
25, 330-337.
[3]
a) A. Tlili, E. Blondiaux, X. Frogneux, T. Cantat, Green Chem. 2015, 17,
157-168. b) K. Beydoun, K. Thenert, E. S. Streng, S. Brosinski, W.
Leitner, J. Klankermayer, ChemCatChem 2016, 8, 135-138.
O. Jacquet, X. Frogneux, C. D. Gomes, T. Cantat, Chem. Sci. 2013, 4,
2127-2131.
[26] S. Luo, L. Barrio, N.-P. Thuy-Duong, D. Vovchok, A. C. Johnston-Peck,
W. Xu, E. A. Stach, J. A. Rodriguez, S. D. Senanayake, J. Phys. Chem.
C 2017, 121, 6635-6642.
[4]
[5]
[6]
[7]
[8]
[27] a) F. L. Chan, G. Altinkaya, N. Fung, A. Tanksale, Catal. Today 2018,
309, 242-247; b) X.F. Liu, X.Y. Li, L.N. He, Eur. J. Org. Chem. 2019,
2019, 2437-2447. c) X. D. Li, S. M. Xia, K. H. Chen, X. F. Liu, H. R. Li,
Y. H. Li, X. J. Fang, K. Junge, M. Beller, Angew. Chem. Int. Ed. 2013,
52, 9568-9571.
K. Beydoun, G. Ghattas, K. Thenert, J. Klankermayer, W. Leitner,
Angew. Chem. Int. Ed. 2014, 53, 11010-11014.
L. N. He, Green Chem. 2018, 20, 4853-4858.
[28] M. C. Arevalo, J. L. Rodriguez, A. M. Castro-Luna, E. Pastor,
Electrochim. Acta 2006, 51, 5365-5375.
Y. H. Li, I. Sorribes, T. Yan, K. Junge, M. Beller, Angew. Chem. Int. Ed.
2013, 52, 12156-12160.
X. J. Cui, Y. Zhang, Y. Q. Deng, F. Shi, Chem. Commun. 2014, 50,
13521-13524.
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Entry for the Table of Contents
FULL PAPER
Ke Liu, Zhenbo Zhao, Weiwei Lin,*
H2 + CO2
CHO*
Qiang Liu, Qifan Wu, Ruhui Shi, Chao
Zhang, Haiyang Cheng, Masahiko Arai,
and Fengyu Zhao*
H2
Cu
Cu
TiO2
Cu
Page No. – Page No.
N-methylation of N-methylaniline with
Carbon Dioxide and Molecular
Hydrogen over a Heterogeneous Non-
noble Metal Cu/TiO2 catalyst
A non-noble metal catalyst of Cu/TiO2 is effective for the heterogeneous N-
methylation of N-methylaniline with CO2 and H2, in which CHO* is formed as methyl
reagent, and it reacts with N-methylaniline to produce intermediate N-
methylformanilide followed by its hydrogenation to N,N-dimethylaniline.
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