Direct Methylation of Amines with Carbon Dioxide and Molecular Hydrogen using Supported Gold Catalysts

Article abstract of DOI:10.1002/cssc.201500486

The N-methylation of amines with CO₂ and H₂ is an important step in the synthesis of bioactive compounds and chemical intermediates. The first heterogeneous Au catalyst is reported for this methylation reaction with good to excellent yields. The average turnover frequency (TOF) based on surface Au atoms is 45 h^-1, which is the highest TOF value ever reported for the methylation of aniline with CO₂ and H₂. Furthermore, the catalyst is tolerant toward a variety of amines, which includes aromatic, aliphatic, secondary, and primary amines. Preliminary mechanistic studies suggest that the N-alkyl formamide might be an intermediate in the N-methylation of amine process. Moreover, through a one-pot process, it is possible to convert primary amines, aldehydes, and CO₂ into unsymmetrical tertiary amines with H₂ as a reductant in the presence of the Au catalyst.

Full text of DOI:10.1002/cssc.201500486

DOI: 10.1002/cssc.201500486
Full Papers
Direct Methylation of Amines with Carbon Dioxide and
Molecular Hydrogen using Supported Gold Catalysts
Xian-Long Du,[a] Gao Tang,[b] Hong-Liang Bao,[a] Zheng Jiang,[a] Xin-Hua Zhong,[b]
Dang Sheng Su,*[c] and Jian-Qiang Wang*[a]
The N-methylation of amines with CO2 and H2 is an important
step in the synthesis of bioactive compounds and chemical in-
termediates. The first heterogeneous Au catalyst is reported
for this methylation reaction with good to excellent yields. The
average turnover frequency (TOF) based on surface Au atoms
is 45 hÀ1, which is the highest TOF value ever reported for the
methylation of aniline with CO2 and H2. Furthermore, the cata-
lyst is tolerant toward a variety of amines, which includes aro-
matic, aliphatic, secondary, and primary amines. Preliminary
mechanistic studies suggest that the N-alkyl formamide might
be an intermediate in the N-methylation of amine process.
Moreover, through a one-pot process, it is possible to convert
primary amines, aldehydes, and CO2 into unsymmetrical terti-
ary amines with H2 as a reductant in the presence of the Au
catalyst.
Introduction
The use of CO2 as a renewable and nontoxic C1 source is of in-
creasing interest for the production of value-added chemi-
cals.[1] As a result of its thermodynamic stability, the highly effi-
cient activation of CO2 and a strong thermodynamic driving
force are required for efficient transformation. In this respect,
only a handful of industrial processes have been realized for
CO2 utilization, such as the production of urea, salicylic acid,
and carbonates.[2] In recent years, the catalytic hydrogenation
of CO2 to methanol, formic acid, or its derivatives have been
reported using different catalysts.[3] In addition to these trans-
formations, a recent advance in this area is the discovery of
the catalytic reduction of CO2 to methylamines. This is a green
method for the production of N-methylated compounds as it
bypasses the classical methodologies that involve formalde-
hyde or hazardous alkylating agents, such as methyl iodide, di-
methyl sulfate, or dimethyl carbonate.[4a]
The methylation of amines using CO2 in the presence of hy-
drosilane or hydroborane with a homogeneous catalyst was
first reported by Cantat et al. and Beller et al., respectively.[4]
Subsequently, Dyson et al. reported a metal-free homogeneous
catalyst for the methylation of amines using CO2 as a C1 source
combined with hydrosilane as the reducing agent.[5] From both
economic and engineering perspectives, the development of
efficient methods for the methylation of amines using CO2
and H2 with H2O as the only byproduct is needed. In this con-
text, a breakthrough in the methylation of amines using CO2
and H2 in the presence of the triphos-based Ru catalyst
[Ru(triphos)(tmm)] (triphos: 1,1,1-tris(diphenylphosphinome-
thyl)ethane, tmm: trimethylene methane) has been reported.[6]
Beller et al. extended the scope of this reaction to a wide varie-
ty of substrates, in which aliphatic amines and aromatic
amines were tolerated by an in situ generated catalyst system
composed of the triphos ligand, a homogeneous Ru precursor,
and LiCl.[7]
Despite the significant progress that was made in the area
of amine methylation using CO2/H2 with homogeneous sys-
tems, there are few available reports on the methylation of
amines with CO2/H2 catalyzed heterogeneously. Recently, Shi
et al. reported a greener method using heterogeneous CuAlOx
and Pd/CuZrO2 catalysts.[8] Very recently, the solvent-free meth-
ylation of aliphatic and aromatic secondary amines by CO2 and
H2 with a Pt-MoOx/TiO2 catalyst was also reported.[9] However,
these heterogeneous systems are limited by their low turnover
frequencies (TOF; less than 3.3 hÀ1) and prolonged reaction
times (24–48 h) to achieve high product yields (greater than
75%).
[a] Dr. X.-L. Du, Dr. H.-L. Bao, Prof. Z. Jiang, Prof. J.-Q. Wang
Key Laboratory of Interfacial Physics and Technology
Shanghai Institute of Applied Physics
Chinese Academy of Sciences
Jialuo Road 2019, Shanghai 201800 (P.R. China)
E-mail: wangjianqiang@sinap.ac.cn
[b] G. Tang, Prof. X.-H. Zhong
Key Laboratory for Advanced Materials
Institute of Applied Chemistry
East China University of Science and Technology
Shanghai 200237 (P.R. China)
[c] Prof. D. S. Su
Shenyang National Laboratory for Materials Science
Institute of Metal Research
Chinese Academy of Sciences
Wenhua Road 72, Shenyang 110016 (P.R. China)
E-mail: dssu@imr.ac.cn
Recently, supported Au nanoparticles (NPs) have attracted
considerable attention because of their extraordinarily high ac-
tivity and selectivity for a broad array of organic transforma-
tions.[10] Although much attention has been focused on several
Supporting Information for this article is available on the WWW under
http://dx.doi.org/10.1002/cssc.201500486.
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classical chemical reactions for green and atom-efficient organ-
ic synthesis, the potential offered by supported Au for catalytic
CO2 conversion, especially toward the synthesis of high-value-
added fine chemicals, remains largely unexplored.[11] Deng
et al. showed that polymer-immobilized Au NPs displayed un-
precedented catalytic activity in the activation of CO2 in the
synthesis of cyclic carbonates and substituted ureas.[11a] Recent-
ly, Liu et al. reported the synthesis of benzimidazoles from 2-ni-
troanilines and CO2/H2 using a supported Au catalyst.[11b] The
superior performance of Au catalysts for CO2 activation led us
to investigate the possibilities offered by Au catalysts for the
methylation of amines with CO2 and H2. Herein, we describe
a general and highly effective Au-catalyzed methylation of
both aromatic and aliphatic amines using CO2/H2 to N-methy-
lated products. Moreover, through a one-pot process, it is pos-
sible to convert primary amines, aldehydes, and CO2 to unsym-
metrical tertiary amines with H2 as the reductant.
Table 1. Direct methylation of 1a with CO2 and H2 using various catalyst-
s.[a]
Entry
Catalyst
t
[h]
Conversion[b]
[%]
Yield[b] [%]
1b
1c
1
2[c]
3[d]
4
5
6
7
8
9
Au/Al2O3-VS
Au/Al2O3-VS
Au/Al2O3-VS
Au/Al2O3
Au/TiO2
Au/ZrO2
Au/CeO2
Au/ZnO
7
7
15
7
7
7
7
7
7
100
100
100
86
33
31
35
10
2
8
15
24
21
18
18
26
10
2
92
85
76
65
15
13
9
0
0
Au/SiO2
10
11
12
13
14
15
Pt/Al2O3
Ir/Al2O3
Rh/Al2O3
Al2O3
HAuCl4
Au0 power
7
7
7
7
7
7
3
3
n.r.
n.r.
n.r.
n.r.
2
3
–
–
–
–
1
0
–
–
–
–
Results and Discussion
Methylation of aniline with CO2 and H2
[a] Reaction conditions: 1a (1 mmol), CO2 (2 MPa), H2 (6 MPa), metal
(0.5 mol%), hexane (10 mL), 1408C; n.r.=no reaction. [b] Conversions and
yields were determined by means of GC using n-octane as the internal
standard. [c] Results for the third run using a recycled catalyst. [d] Reac-
tion conditions: 1a (1 mmol), CO2 (1 MPa), H2 (3 MPa), metal (0.5 mol%),
hexane (10 mL), 1408C.
Through exploratory research, the direct methylation of aniline
(1a) to yield N-methylaniline (1b) and N,N-dimethylaniline (1c)
was used as a model reaction to investigate the catalytic activi-
ty of various solid catalysts. The preparation of this series of
catalysts and the relevant characterization data are provided in
the Supporting Information. Initially, we studied the methyla-
tion of 1a with CO2 and H2 over a catalyst derived from very
small Au NPs (ꢀ2.0 nm; Figure 1 and Figure S4) supported on
g-Al2O3 (this catalyst system is denoted as Au/Al2O3-VS
(0.7 wt%); see details in the Supporting Information). The time
course plot for the reaction of aniline with CO2 and H2 in the
presence of Au/Al2O3-VS is provided in Figure S1, and the re-
sults obtained after a reaction time of 7 h were compared with
those obtained with other catalysts (Table 1). Interestingly, if
the Au/Al2O3-VS catalyst was used, a complete conversion of
1a with a 92% yield of 1c and an 8% yield of 1b was ob-
served after a reaction time of 7 h at 1408C (Table 1, entry 1).
We also tested the repeated use of the Au/Al2O3-VS catalyst for
the methylation of 1a. To our delight, the conversion of 1a de-
creased only slightly after three repeated uses (Table 1, entry 2
and Table S2, entry 2). The average TOF (the number of mole-
cules of 1c formed per hour per Au atom) based on surface
Au atoms is 45 hÀ1, which is the highest TOF value ever report-
ed for the methylation of 1a with CO2 and H2 (Table S1). Nota-
bly, the reaction also proceeded efficiently under relatively
mild conditions with a higher proportion of the monomethy-
lated product, although a longer reaction time was required
(Table 1, entry 3). This result may be ascribed to a slow reaction
rate for the second methylation under low pressures of CO2/H2
(Table S2, entries 4 and 5). Importantly, if we used the Au/Al2O3
catalyst (supplied by Mintek), which has a larger average Au
particle size (ꢀ3.0 nm; Figure S4), the catalytic activity and
product yield were slightly lower (Table 1, entry 4).
A comparison with Pt, Ir, and Rh NPs supported on alumina
as reference catalysts showed Au to be far superior to other
noble metals for the methylation of 1a (Table 1, entries 10–12).
As the nature of the support plays an important role in Au cat-
alysis,[12] we also evaluated Au supported on other oxide sup-
ports. The use of Au/TiO2, Au/ZrO2, and Au/CeO2 catalysts re-
sulted in the formation of the desired products 1b and 1c in
moderate yields (Table 1, entries 5–7). In contrast, Au support-
ed on silica (Au/SiO2) and zinc oxide (Au/ZnO) was less effec-
Figure 1. Representative HAADF-STEM image of the Au/Al2O3-VS catalyst.
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tive for the methylation of 1a under similar reaction conditions
(Table 1, entries 8 and 9). These results indicate that both the
noble metal and the nature of the support play important
roles in the methylation of 1a with CO2 and H2. However, the
reaction did not proceed if we used Au-free Al2O3; thus, the
presence of Au was essential for the high activity observed in
the methylation of 1a with CO2 and H2 (Table 1, entry 13). In
addition, the use of the catalyst precursor HAuCl4 and Au0
powder did not promote the reaction at all (Table 1, entries 14
and 15).
To verify whether the observed catalysis was truly heteroge-
neous, we performed the methylation of 1a with CO2 and H2
under the conditions described in entry 1 of Table 1 and re-
moved the Au/Al2O3-VS catalyst from the reaction mixture by
filtration at approximately 40% conversion of 1a. Further stir-
ring of the filtrate under the reaction conditions for 7 h did
not yield any additional product. It was confirmed by induc-
tively coupled plasma (ICP) analysis that no Au was present in
the filtrate (below 0.10 ppm). These results rule out any possi-
ble contribution to the observed catalysis from homogeneous
Au species that may have leached into the reaction solution,
which thus confirms that the observed catalysis was intrinsical-
ly heterogeneous.
Figure 2. XANES at the Au L3 absorption edge of (a) HAuCl4, (b) Au2O3, (c) Au
foil, and (d) Au/Al2O3-VS.
parison to the Au foil, Au/Al2O3-VS has a lower coordination
number (7.8Æ2.1) for the AuÀAu bond, which results primarily
from the size effect of the Au nanoparticles.[13]
Methylation of amines with different structures using CO2
and H2
After we established that Au/Al2O3-VS is an excellent catalyst
for the methylation of 1a with CO2 and H2 we extended our
studies to include different types of amines, and the results are
listed in Table 2. Various amines (aromatic and aliphatic) react
with CO2 and H2 to produce the corresponding tertiary amines
in good yields. Anilines with electron-donating groups, such as
methyl and methoxy, react smoothly (Table 2, entries 2–5),
whereas substitution with electron-withdrawing groups on the
benzene ring decreases the reactivity (Table 2, entry 6). The re-
action was also successful for the methylation of benzylamine
with a yield of 87% (Table 2, entry 7). Unfortunately, under sim-
ilar reaction conditions, the reactivity of aliphatic amines,
which include cyclohexylamine, hexylamine, and cyclopentyl-
amine, was strongly suppressed. Surprisingly, this problem was
resolved successfully by performing the reaction at a relatively
high temperature (1708C; Table 2, entries 8–10).
Catalyst characterization
Next, a typical characterization of the representative Au/Al2O3-
VS sample was performed. The XRD patterns of the alumina
support (Figure S3) show that all of the reflection peaks were
identified as cubic g-Al2O3 (JCPDS Card no. 10-0425). If Au NPs
were deposited onto this material, no Au diffraction line was
detected, which thus indicates that the deposited Au particles
were small in size. High-angle annular dark-field scanning
transmission electron microscopy (HAADF-STEM) of the re-
duced catalysts showed that the Au NPs were highly dispersed
onto the alumina surface and the average size of the Au NPs
was approximately 2 nm (the size distribution of the metal NPs
was determined by measuring ꢀ200 random particles on the
images shown in Figure 1 and S4).
Inspired by the promising results for the methylation of pri-
mary amines to tertiary amines with CO2 and H2 using the Au/
Al2O3-VS catalyst, we investigated whether tertiary amines can
be produced from secondary amines. Both 1b and substituted
N-methylaniline with a methyl group were converted into their
corresponding tertiary amines with yields of 96 and 98%
within 7 h at 1408C (Table 2, entries 11 and 12). If N-ethylani-
line (13a) was used, the corresponding N-methylated product
13c was obtained in a moderate yield (Table 2, entry 13). In
the transformation of dibenzylamine (14a), diphenylamine
(15a), and 4,4’-dimethoxydiphenylamine (16a), the lower reac-
tion rates of 15a and 16a than 14a indicate a steric effect
that may block N-methylation and prevent the formation of
the corresponding tertiary amines. Next, we were interested in
the reaction of heterocyclic amines. Pyrrolidine was chosen as
the starting amine as it is one of the simplest alkaloid struc-
tures[14] present in many important natural products. The
methylation of this cyclic amine with CO2 and H2 gave the de-
sired tertiary amine in an excellent yield after 7 h at 1408C
The structure of Au in Au/Al2O3-VS was investigated by X-ray
photoelectron spectroscopy (XPS) and X-ray absorption fine
structure spectroscopy (XAFS). Only metallic Au was identified
on the surface Au species of the Au/Al2O3-VS catalyst from the
XPS data (Figure S5). Au L3-edge X-ray absorption near-edge
structure (XANES) analysis was performed to confirm the state
of Au in the Au/Al2O3-VS sample (Figure 2). The intensity of the
white line at a binding energy (BE) of approximately 11 922 eV
caused by the 2p3/2!5d transition increases with increasing
oxidation state. In contrast to HAuCl4 and Au2O3, the Au/Al2O3-
VS sample is similar to Au foil without the white line in the
XANES spectrum, which indicated that Au in the Au/Al2O3-VS
sample exists in the elemental state. Moreover, the Fourier
transform (FT) of the extended X-ray absorption fine structure
(EXAFS) data (Figure S6) has a main peak in the range of 2.2–
3.2 Š, which arises from the AuÀAu scattering contribution.
The structural parameters of Au in Au/Al2O3-VS were obtained
by fitting the EXAFS data (Table S3, Figures S7 and S8). In com-
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(Table 2, entry 17). In addition, the catalyst is
also tolerant toward other heterocyclic
amines, such as indoline and 1,2,3,4-tetrahy-
droquinoline (Table 2, entries 18 and 19).
Finally, the methylation of some unique
functional N-containing compounds can
progress well with excellent yields to the
desired products (Table 2, entries 20–23).
Thus, the Au/Al2O3-VS catalyst exhibits ex-
cellent generality in the N-methylation of
secondary amines.
Table 2. Methylation of amines with CO2 and H2 catalyzed by Au/Al2O3-VS.[a]
Entry Substrate
Product
Yield [%][b,c]
1
1a
2a
3a
4a
5a
1c
2c
3c
4c
5c
92
2
3
4
5
96
94
98
99
Reaction pathway for the methylation of
aniline with CO2/H2
To understand the reaction pathways in-
volved in the methylation of 1a with CO2/H2
as the alkylation reagent, control experi-
ments were used to identify the possible
mechanism (Scheme S1). As it is known that
CO2 can be hydrogenated to form formic
acid in the presence of a heterogeneous Au
catalyst,[3c] the hydrogenation of N-phenyl-
formamide (1d) and N-phenyl-N-methylfor-
mamide (1e) was investigated. Compound
1d was converted fully under 6 MPa of H2
under otherwise standard reaction condi-
tions, and 1b was the major product
formed in 51% yield (Scheme S1). However,
a major byproduct of this reaction was 1a
(30%), which resulted from decarbonyla-
tion.[6,15] In addition, 1c was also produced
with a yield of 16% in this process. Under
the same conditions, if 1e was used as the
substrate, 1c was the major product with
a yield of 61%. Meanwhile, the decarbonyla-
tion product of the monoalkylated product
1b was also formed (36%). During the
methylation of 1a with CO2/H2 under stan-
dard reaction conditions, neither 1d nor 1e
was detected as an intermediate. In con-
trast, under relatively mild reaction condi-
tions, 1d and 1e were detected in low
yields (Scheme S1). These results are consis-
tent with those of previous studies that in-
volve the methylation of amines with CO2/
H2 using homogeneous Ru catalysts.[6,7]
Based on the above discussions, a plausible
reaction pathway is proposed (Scheme 1).
First, 1a is carbonylated with CO2/H2 to pro-
duce N-phenylformamide, which is reduced
rapidly into 1b or decarbonylates into 1a.
Next, 1b is again carbonylated with CO2/H2
to generate 1e following a similar hydroge-
nation and decarbonylation process as de-
scribed above to produce the correspond-
ing products.
6
6a
7a
8a
6c
7c
8c
78
7
87
8[c]
43 (93)
9[c]
9a
9c
51 (95)
40 (92)
10[c]
10a
10c
11
12
1b
1c
96
98
12a
12c
13[c]
14[c]
13a
14a
13c
14c
56 (93)
60 (95)
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One-pot synthesis of unsymmetrical terti-
ary N-methylamines directly from primary
amines, aldehydes, and CO2 with H2 as
reductant
Table 2. (Continued)
Entry Substrate
Product
Yield [%][b,c]
14 (67)
15[c]
15a
16a
15c
With good reactivity established for the N-
methylation of isolated primary amines to
symmetrical tertiary amines, we explored
the possibility of a one-pot conversion of
primary amines, aldehydes, and CO2 to un-
symmetrical tertiary amines with H2 as the
reductant. Various types of aldehydes, which
include aliphatic (Table 3, entry 1) and aro-
matic aldehydes (Table 3, entries 2 and 3),
were reacted with benzylamine in the pres-
ence of CO2 and H2 with the Au/Al2O3-VS
catalyst to give the corresponding unsym-
metrical tertiary amines in high yields. Benz-
aldehyde, which features both electron-do-
nating and electron-withdrawing groups, re-
acted especially smoothly (Table 3, entries 2
and 3). To demonstrate the general applica-
bility of our procedure, we also studied the
reactivity for the one-pot conversion of hex-
ylamine and other types of aldehydes to
their corresponding unsymmetrical tertiary
amines. We were pleased to obtain the un-
symmetrical tertiary amines in excellent
yields from reactions that involve hexyla-
mine and aromatic or aliphatic aldehydes
under standard reaction conditions (Table 3,
entries 4–7). Besides aliphatic amines, we
also investigated the possibility of the direct
three-component coupling of the aryl
amine, aldehyde, and CO2 with H2 as the re-
ductant. The yield of the target product (un-
symmetrical tertiary amine) was 85% if 1a
was used (Table 3, entry 8). Recently, Klan-
kermayer and co-workers showed that a Ru-
based molecular catalyst [Ru(triphos)(tmm)]
in combination with HNTf2 additives can se-
lectively convert primary amines, aldehydes,
and CO2 to unsymmetrical tertiary amines.[16]
However, the use of aliphatic imines did not
result in the formation of the reductively
methylated product using this
16[c]
16c
17c
21 (78)
99
17
18
17a
18a
18c >99
19c >99
19
20
19a
20a
20c >99
21
22
21a
22a
21c
22c
99
99
23
23a
23c
95
[a] Reaction conditions: amine (1 mmol), CO2 (2 MPa), H2 (6 MPa), Au (0.5 mol%), hexane (10 mL),
1408C, 7 h. [b] Yields were determined by GC with n-octane as the internal standard. [c] Yields
obtained at a higher reaction temperature (1708C) are given in parentheses.
Ru-based molecular catalyst. In
contrast, our Au/Al2O3-VS cata-
lyst has the clear advantage of
enabling the construction of un-
symmetrical tertiary amines from
all types of aliphatic amines and
aldehydes.
Scheme 1. Proposed reaction pathway for the Au-catalyzed methylation of 1a with CO2 and H2.
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Table 3. Au-catalyzed one-pot synthesis of unsymmetrical tertiary N-methylamines directly from primary amines, aldehydes, and CO2 with H2 as the reduc-
tant.[a]
Entry
1
Amine
Aldehyde
Product
Yield[b]
[%]
92
94
2
3
4
5
98
97
99
6
7
97
91
8[c]
85
[a] Reaction conditions: amine (1 mmol), aldehyde (1 mmol), hexane (10 mL), CO2 (2 MPa), H2 (6 MPa), Au (0.5 mol%), 1708C, 7 h. [b] Yields were deter-
mined by GC with n-octane as the internal standard. [c] Reaction temperature=1408C.
Conclusions
tion of amines with CO2 and H2. The present findings open the
possibility to develop new sustainable processes for the con-
version of CO2 to produce high-value-added chemicals.
We have demonstrated that a highly active heterogeneous cat-
alyst based on Au deposited on alumina can be used in the N-
methylation of both aromatic and aliphatic amines to their cor-
responding tertiary amines in excellent yields using CO2 as the
C1 source and H2 directly as the reducing agent. Furthermore,
through a one-pot process, it is possible to convert primary
amines, aldehydes, and CO2 to unsymmetrical tertiary amines
with H2 as the reductant. To the best of our knowledge, this
Au-catalyzed approach is one of the most simple, efficient, and
robust catalytic systems developed to date for the N-methyla-
Experimental Section
Preparation of Al2O3 support
Al2O3 (specific surface area: 309 m2 gÀ1, gamma phase) powders
were prepared by a conventional precipitation method. Briefly,
Al(NO3)3·9H2O (45 g) was dissolved in deionized water (500 mL) at
RT, and the pH was adjusted to 9.0 by the dropwise addition of
NH4OH (2.5m). The resultant hydrogel was washed with deionized
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water until free of NO3Àions. The precipitate was then dried at
110 8C overnight followed by calcination at 4008C in air for 2 h to
obtain the final support.
three uses, the Au/Al2O3-VS catalyst remained highly active
(Table 1, entry 2).
One-pot synthesis of unsymmetrical tertiary N-methyla-
mines directly from primary amines, aldehydes, and CO2
with H2 as reductant
Preparation of Au/Al2O3-VS catalyst
The Au/Al2O3-VS catalyst was prepared by a deposition–precipita-
tion with urea (DPU). Typically, urea (1.16 g) was dissolved in
HAuCl4 solution (200 mL, 0.48 mmolLÀ1; urea/Au=200 molar ratio)
at RT. Al2O3 support (2 g) was added to this clear solution, and the
temperature of the resulting slurry was increased gradually to
808C. The temperature was maintained for 6 h, and the product
was collected by filtration and washed several times with distilled
water. The sample was dried under vacuum at 508C for 12 h and
reduced under a stream of 5 vol% H2/Ar at 3508C for 2 h. The re-
sulting sample, which contained 0.7 wt% Au as determined by in-
ductively coupled plasma atomic emission spectroscopy (ICP-AES),
was denoted as Au/Al2O3-VS and has a specific surface area of
A mixture of amine (1.0 mmol), aldehyde (1.0 mmol), hexane
(10 mL) and supported Au catalyst (Au 0.5 mol%) was charged into
a 50 mL Hastelloy-C high-pressure Parr reactor. The atmosphere
inside the reactor was exchanged with H2, and CO2 (2.0 MPa) and
H2 (6.0 MPa) were introduced. The reaction was performed at the
desired temperature for the given time under magnetic stirring.
Subsequently, the autoclave was cooled to RT, and n-octane
(1 mmol, internal standard) was added before quantitative analysis
by GC–FID (Agilent 7820 A).
ꢀ300 m2 gÀ1
.
Acknowledgements
This work was financially supported by the National Basic Re-
search Program of China (2013CB933104), the Ministry of Science
and Technology (2014DFG60230), and the National Natural Sci-
ence Foundation of China (No. 21303246, 11275258, 91127001).
XAFS research described in this paper was performed at the
HXMA beamline of the CLS, which is supported by the CFI,
NSERC, NRC, CIHR, the University of Saskatchewan, the Govern-
ment of Saskatchewan, and Western Economic Diversification
Canada.
XAFS spectroscopy
The XAFS data at the Au L3-edge of Au2O3, Au foil, and Au/Al2O3-VS
were obtained in transmission mode using three ion chambers by
using the Hard X-ray Micro-Analysis (HXMA) beamline at Canadian
Light Source (CLS) 06ID-1. The synchrotron radiation was mono-
chromatized with a Si(111) liquid-nitrogen-cooled double crystal
monochromator. Data processing was performed using the soft-
ware package of Ifeffit.[17] An S0 value of 0.81 was obtained from
the fitting of the data from the Au foil. The range of EXAFS data
used for Fourier transformation was 3–14 ŠÀ1. The range of the r-
space used for the curve fitting of EXAFS data was 1.2–3.8 Š.
2
Keywords: amines
·
gold
·
heterogeneous catalysis
·
hydrogen · supported catalysts
Methylation of 1a with CO2 and H2
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ChemSusChem 2015, 8, 3489 – 3496
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Received: April 7, 2015
Published online on September 14, 2015
ChemSusChem 2015, 8, 3489 – 3496
www.chemsuschem.org
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ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim