N-alkylation of ammonia and amines with alcohols catalyzed by Ni-loaded CaSiO3

Article abstract of DOI:10.1016/j.cattod.2013.09.002

Nickel nanoparticles loaded onto calcium silicate (Ni/CaSiO₃) have been prepared by ion-exchange method followed by in situ H ₂-reduction of the calcined precursor. Ni/CaSiO₃ was found to be effective for the catalytic direct synthesis of primary amines from alcohols and NH₃ under relatively mild conditions. Various aliphatic alcohols are tolerated, and the turnover number (TON) was higher than those of Ru-based homogeneous catalysts. The catalyst was recoverable and was reused. Effects of the surface oxidation states and particle size of Ni on the catalytic activity were studied by infrared (IR) investigation of the states of adsorbed CO and transmission electron microscopy (TEM). It is clarified that the surface Ni⁰ sites on small (3 nm) sized Ni nanoparticles are the catalytically active species. Ni/CaSiO₃ was also effective for the alkylation of anilines and aliphatic amines with various alcohols (benzyl and aliphatic alcohols) under additive free conditions; primary amines were converted into secondary amines and secondary amines into tertiary amines.

Full text of DOI:10.1016/j.cattod.2013.09.002

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N-alkylation of ammonia and amines with alcohols catalyzed by
Ni-loaded CaSiO3
Ken-ichi Shimizua,b,∗, Shota Kannoa, Kenichi Kona, S.M.A. Hakim Siddikib,
Hideyuki Tanakac, Yoshihisa Sakatac
a Catalysis Research Center, Hokkaido University, N-21, W-10, Sapporo 001-0021, Japan
b Elements Strategy Initiative for Catalysts and Batteries, Kyoto University, Katsura, Kyoto 615-8520, Japan
c Graduate School of Science and Engineering, Yamaguchi University, 2-16-1 Tokiwadai, Ube 755-8611, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 July 2013
Received in revised form 20 August 2013
Accepted 2 September 2013
Available online xxx
Nickel nanoparticles loaded onto calcium silicate (Ni/CaSiO3) have been prepared by ion-exchange
method followed by in situ H2-reduction of the calcined precursor. Ni/CaSiO3 was found to be effec-
tive for the catalytic direct synthesis of primary amines from alcohols and NH3 under relatively mild
conditions. Various aliphatic alcohols are tolerated, and the turnover number (TON) was higher than
those of Ru-based homogeneous catalysts. The catalyst was recoverable and was reused. Effects of the
surface oxidation states and particle size of Ni on the catalytic activity were studied by infrared (IR)
investigation of the states of adsorbed CO and transmission electron microscopy (TEM). It is clarified that
the surface Ni0 sites on small (3 nm) sized Ni nanoparticles are the catalytically active species. Ni/CaSiO3
was also effective for the alkylation of anilines and aliphatic amines with various alcohols (benzyl and
aliphatic alcohols) under additive free conditions; primary amines were converted into secondary amines
and secondary amines into tertiary amines.
Keywords:
Alcohols
Alkylation
Amines
Ammonia
Calcium silicate
Nickel
© 2013 Elsevier B.V. All rights reserved.
1. Introduction
of the selective synthesis of primary amines from primary alco-
hols and NH3 using Ru PNP pincer complex, but the system was
Amines are of significant importance for the bulk- and fine-
chemical industry as building blocks for polymers, surfactants,
dyes, pharmaceuticals and agrochemicals. Among the amines, the
terminal primary amines are the most useful intermediates for
further derivatization reactions [1]. Aliphatic primary amines can
be synthesized by the reductive amination of the corresponding
carbonyl compounds [2,3], but their selective synthesis is challeng-
ing due to their high reactivity. Although heterogeneous catalysts
are used for reductive aminations of simple alcohols under H2
[2–5], they suffer from drawbacks such as limited substrate scope,
low selectivity for primary amines and needs of high temperature
(>200 ◦C), high H2 pressure, and high NH3 pressure. Heterogeneous
Ru [6] and Cu [7] catalysts reported by Mizuno and co-workers
and homogeneous Ir catalysts reported by Fujita and co-workers
[8] were effective and reusable catalysts for the direct synthesis of
secondary and tertiary amines from alcohols and aqueous ammo-
nia (or urea), but selective formation of primary amines were not
reported. Milstein and co-worker [9] reported the first example
ineffective for the amination of secondary alcohols. Recently, Vogt
and co-worker [10] and Beller and co-worker [11] independently
discovered the selective amination of secondary alcohols with
NH3 to give primary amines. Although these systems, driven by
a borrowing-hydrogen [12] (or hydrogen-autotransfer [2]) mech-
anism (Scheme 1), provided successful examples catalytic primary
amines syntheses, the homogeneous Ru catalysts had problems
such as necessity of expensive noble metals and difficulties in
recovery and reuse of catalysts.
The N-alkylation of amines with alcohols to give higher order
amines has been also attracted considerable attention as an
environmentally friendly synthetic method of alkyl amines [1,2].
Recently, homogeneous Ru [13] and Ir [14] catalysts were shown to
be highly effective for this one-pot reaction, but these systems have
problems such as difficulty in the recovery and reuse of expensive
catalysts and the use of co-catalysts such as base and stabilizing
ligand. Recyclable heterogeneous noble metal catalysts (Pd [15],
Ru [6,16], Au [17], Pt [18] and Ag [19,20]) have been also reported,
but some of them suffer from low TON, low selectivity to mono-
alkylation, and necessity of co-catalysts. From the environmental
and economic viewpoints, it is desired to accomplish this reaction
by an inexpensive catalyst. However, most of the heterogeneous
base metal catalysts reported so far (Ni [21], Fe [22] and Cu [7]
∗
Corresponding author at: Catalysis Research Center, Hokkaido University, N-21,
W-10, Sapporo 001-0021, Japan. Fax: +81 11 706 9163.
E-mail address: kshimizu@cat.hokudai.ac.jp (K.-i. Shimizu).
0920-5861/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.cattod.2013.09.002
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was put in the tube, followed by inserting the tube inside stainless
OH
NH2
autoclave with a dead space of 33 cm3. Soon after being sealed,
the reactor was flushed with NH3 from a high pressure gas cylinder
and charged with 0.4 MPa NH3 at room temperature. The amount of
NH3 present in the reactor before heating was 6.7 mmol (2.2 equiv.
with respect to the alcohol). Then, the reactor was heated typically
at 160 ◦C under stirring (150 rpm).
M
R1
R1
R2
R2
R1
R2
NH
R2
O
M-H
For the reaction of alcohols with amines, the mixture of alcohol
(1.0 mmol) and amine (1.2 mmol) in o-xylene (1 g) was injected to
the pre-reduced catalyst inside a reactor (cylindrical glass tube)
through a septum inlet, followed by filling with N2. Then, the
resulting mixture was stirred under reflux; bath temperature was
155 ◦C and reaction temperature was ca. 144 ◦C. For both reactions,
conversion and yields of products were determined by GC using n-
dodecane as an internal standard. The products were identified by
GC–MS equipped with the same column as GC and by comparison
with commercially pure products.
R1
NH3
H2O
Scheme 1. Borrowing-hydrogen mechanism of transition metal-catalyzed amina-
tion of alcohols.
catalysts) generally suffer from low TON, limited scope and neces-
sities of high temperatures or basic co-catalyst. For example, Ni/Cu
co-loaded Al2O3 catalyst recently reported by Sun et al. exhibited
TON of 1.9 for N-alkylation of aniline with benzylalcohol in the
presence of 25 mol% NaOH and 12.5 mol% CaCl2 [21].
As shown above, the development of non-noble-metal-based
heterogeneous catalyst for the direct amination reactions is an
important research target. We report herein that calcium sili-
cate (CaSiO3)-supported nickel metal nanoparticle catalyst readily
prepared from inexpensive commercial materials [23] acts as a ver-
satile heterogeneous catalyst for the selective synthesis of primary
amines from alcohols and ammonia N-alkylation of amines with
alcohols to give higher order amines under relatively mild con-
ditions without any additives. In order to clarify the controlling
factors of the catalytic system, the effects of the particle size and
surface oxidation states of Ni on the activity is discussed based on
the results of catalyst characterization.
TEM measurements were carried out by using a JEOL JEM-2100F
TEM operated at 200 kV. Ni K-edge extended X-ray absorption
fine structure (EXAFS) was measured in transmission mode at the
BL01B1 in the SPring-8 (Proposal No. 2011B1137). The storage ring
was operated at 8 GeV. A Si(1 1 1) single crystal was used to obtain
a monochromatic X-ray beam. The EXAFS analysis was performed
using the REX version 2.5 program (RIGAKU). The Fourier transfor-
mation of the k3-weighted EXAFS oscillation from k space to R space
was performed over the range 3.0–16.0 A−1 to obtain a radial distri-
˚
bution function. The inversely Fourier filtered data were analyzed
−1
˚
with a usual curve fitting method in the k range of 3.0–16.0 A
.
The parameters for the Ni O and Ni Ni shells were provided by
the FEFF6.
The surface characterization of the Ni/CaSiO3 was carried out
by the infrared (IR) spectroscopic investigation of adsorbed CO
over the catalyst. The Ni/CaSiO3 catalyst (40 mg) was pressed into
self-supporting pellet of 20 mm in diameter, and was placed in
an infrared cell, which was connected to a closed gas circulation
system equipped with vacuum line. The Ni/CaSiO3 catalyst pre-
reduced at 600 ◦C was placed in the IR cell and reduced again by H2
at 500 ◦C for 10 h, followed by evacuation at the same temperature
for 1 h before use. Adsorption of CO was carried out at 25 ◦C. Infrared
spectra were recorded by an FT-IR (Jasco. FT/IR 7300) equipped
with an MCT detector. The spectra were obtained by 100 scans
at 4 cm−1 resolution. The spectra of adsorbed CO were obtained
from rationing the background spectra of the catalyst to those of
adsorbed CO.
2. Experimental
Commercially available organic and inorganic compounds (from
Tokyo Chemical Industry, Wako Pure Chemical Industries, or Kanto
Chemical) were used without further purification. The GC (Shi-
madzu GC-14B) and GCMS (Shimadzu GCMS-QP2010) analyses
were carried out with Ultra ALLOY capillary column UA+-5 (Fron-
tier Laboratories Ltd.) capillary column (Shimadzu) using nitrogen
as the carrier gas.
CaSiO3 was kindly supplied from Konoshima Chemical. Ni2+
-
exchanged CaSiO3 was prepared by treating the support with
aqueous solution of Ni nitrate for 12 h at room temperature,
followed by centrifuging and washing with deionized water
(three times), and by drying at 90 ◦C for 12 h. NiO-loaded CaSiO3
(NiO/CaSiO3) was prepared by calcining Ni2+-exchanged CaSiO3
in air for 4 h at 350 ◦C. Ni-loaded CaSiO3 (Ni/CaSiO3) was pre-
pared by in situ pre-reduction of NiO/CaSiO3 under H2 flow (20
cm3 min−1) at 600 ◦C for 0.5 h. ICP analysis showed that Ni con-
tent in the sample was 10 wt%. SiO2 (Q-10) was supplied from Fuji
Silysia Chemical Ltd. CaO was prepared by calcination of Ca(OH)2
at 500 ◦C for 3 h. CaO or SiO2-supported Ni (10 wt%) were prepared
by the impregnation method, followed by drying at 90 ◦C for 12 h,
and by in situ pre-reduction of the precursor under H2 at 600 ◦C.
Raney Ni (B113 W, Ni >90%) was supplied from Evonik Industries.
Ni/CaSiO3 pre-reduced at 600 ◦C was used as a standard catalyst.
For the reaction of alcohols with NH3, the pre-reduced catalyst in
the closed glass tube sealed with a septum inlet was cooled to room
temperature under H2 atmosphere. The mixture of o-xylene (4.0 g),
alcohol (3.0 mmol), and n-dodecane (0.5 mmol) was injected to the
pre-reduced catalyst inside the glass tube through the septum inlet.
Then, the septum was removed under air, and a magnetic stirrer
3. Results and discussion
The XRD spectrum of Ni/CaSiO3 (recorded under ambient con-
ditions) showed broad lines due to metallic Ni. Fig. 1 shows the
EXAFS spectrum of Ni/CaSiO3. The catalyst pre-reduced in a flow
of H2 for 0.5 h at 600 ◦C was cooled to room temperature in the
flow of H2 and was sealed in a cell made of polyethylene under
N2, and then the EXAFS spectrum was taken at room temperature.
Table 1 shows the results of curve-fitting analyses of the EXAFS. The
˚
EXAFS of Ni/CaSiO3 consists of a Ni-Ni shell (at 2.48 A with coordi-
nation number of 4.3) and a Ni O shell (at 2.00 A and coordination
˚
number of 2.6). By comparison with the crystallographic data of Ni
metal, the Ni Ni shell was assigned to metallic Ni. The weak con-
tribution of the Ni O shell indicates the presence of NiO or Ni2+
species as minor Ni species. Fig. 2 shows Ni particle size distribu-
tions of Ni/CaSiO3 pre-reduced at different temperatures (600 ◦C
and 700 ◦C). The average particle sizes of the catalysts reduced
at 600 ◦C and 700 ◦C were 3.0 0.8 nm and 12.6 2.9 nm, respec-
tively. The average size of Ni crystallites in Ni/CaSiO3 (reduced
at 600 ◦C) estimated by XRD (Fig. 1) using Scherrer equation is
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3
2030, 2084 cm-1
linear CO on Ni0
NiO x 0.3
1904, 1970 cm-1
bridged CO on Ni0
0.05
Ni/CaSiO3
Ni/CaSiO3-air
1600
Ni foil x 0.3
Ni/CaSiO3
5
2200
2000
1800
Wavenumber /cm-1
Fig. 3. IR spectra of CO adsorbed on in situ reduced Ni/CaSiO3 and air-exposed
catalyst, Ni/CaSiO3–air.
reduced at 700 ◦C. Combined with the TEM result that the average
Ni particle size of the former catalyst (3.0 nm) was smaller than
the latter catalyst (12.6 nm), it is suggested that smaller Ni metal
particles is the catalytically important species. The catalyst named
Ni/CaSiO3–air was prepared by exposing the as-reduced Ni/CaSiO3
to the ambient conditions for 0.5 h. Ni/CaSiO3–air as well as the
un-reduced precursor (NiO/CaSiO3) showed no activity, suggest-
ing that the metallic Ni0 species on the surface of Ni nanoparticles
are the active species and re-oxidation of them by O2 under ambi-
ent conditions results in the catalyst deactivation. This hypothesis
is confirmed by the following results. The oxidation states of sur-
face Ni species were studied by the examination of the states of
adsorbed CO by IR spectroscopy at 25 ◦C. IR spectra of adsorbed
CO species are shown in Fig. 3. The spectrum for the as-reduced
Ni/CaSiO3 showed four main bands centered at 2084, 2030, 1970,
and 1904 cm−1. According to the literature, the bands at 1970 and
1904 cm−1 are assignable to ␯(CO) of bridged CO on two Ni0 atoms.
A weak band at 2135 cm−1 is assignable to the CO adsorbed on Ni+
species (CO Ni+). Bands at 2084 and 2030 cm−1 are assignable to
␯(CO) of the linear CO on a Ni0 site [23,24]. Upon exposure to air at
25 ◦C, the bands attributable to CO adsorbed on the Ni0 sites com-
pletely disappeared. Combined with the result of catalytic test, the
result indicates that the surface metallic Ni0 sites are the catalyti-
cally active species. Under ambient conditions, the surface metallic
Ni0 species are completely converted to the inactive Ni2+ species.
From these results, it is concluded that the metallic Ni0 species on
the surface of small Ni metal particles are the active species.
The above results show that 10 wt% Ni/CaSiO3 catalyst reduced
at 600 ◦C is the optimal catalysts. Using this catalyst, we examined
the catalytic properties of Ni/CaSiO3 under the conditions shown
in Table 3 (1 mol%, 20 h). The amination of 2-octanol by Ni/CaSiO3
resulted in 86% yield of the primary amine, and the yields of sec-
ondary and tertiary amines were below the detection limits of GC
analyses. The reaction was completely terminated by a removal
of the catalyst from the reaction mixture after 23% conversion of
2-octanol (t = 1 h); further heating of the filtrate for 19 h under
NH3 (0.4 MPa) at 160 ◦C did not increase the yield. This confirms
that the reaction is attributed to the heterogeneous catalysis of
Ni/CaSiO3. After amination of 2-octanol by Ni/CaSiO3 for 20 h, the
catalyst was separated from the reaction mixture by a centrifu-
gation. Then, the catalyst was washed with acetone, followed by
drying in air at 90 ◦C for 12 h, and by reducing in H2 at 600 ◦C for
0.5 h. The recovered catalyst showed 26% yield of the product. This
indicates that Ni/CaSiO3 is not a reusable catalyst for this reaction.
The amination of 2-octanol at lower temperature (120 ◦C) resulted
in lower yield of the primary amine (15%) than the standard condi-
tion (86% yield at 160 ◦C). Ni/CaSiO3-catalyzed amination reactions
of various alcohols are also shown in Table 3. Various alcohols,
including aliphatic and aromatic alcohols were selectively con-
verted to the corresponding primary amines with good to high yield
(70–88%), while the yields of the secondary amines were below 6%.
0
1
2
3
4
5
6
R / Å
Fig. 1. Ni K-edge EXAFS Fourier transforms of Ni/CaSiO3 (TH = 600 ◦C) and refer-
2
ence compounds.
Table 1
Curve-fitting analysis of Ni K-edge EXAFS of Ni/CaSiO3.
Sample
Shell
Na
R/Åb
ꢀ/Åc
Rf/%d
O
Ni
2.6
4.3
2.00
2.48
0.088
0.065
0.9
Ni/CaSiO3
NiOe
O
Ni
Ni
6
12
12
2.02
2.94
2.49
–
–
–
–
–
–
Ni foile
a
Coordination numbers.
Bond distance.
Debye–Waller factor.
Residual factor.
b
c
d
e
Crystallographic data of Ni oxide and Ni metal.
TH2 = 600 oC
TH2 = 700 oC
20
10
0
20
10
0
D =3.0 0.8 (nm)
D = 12.6 2.9 (nm)
0
10
20
0
10
20
Particle size/ nm
Particle size/ nm
Fig. 2. Particle size distribution of Ni/CaSiO3 catalysts (TEM analyses).
2.5 nm, which is nearly consistent with the size from TEM anal-
ysis.
Table 2 summarizes the catalytic results of various catalysts
for the amination of 2-octanol (3 mmol) with NH3 (P = 0.4 MPa,
6.7 mmol) to the corresponding primary amine, 2-octylamine,
under the same conditions (Ni = 1 mol% with respect to alcohol,
T = 160 ◦C, t = 20 h). Ni/CaSiO3 reduced at 600 ◦C showed 86% yield of
the corresponding primary amine, while Ni/CaO, Ni/SiO2 and a con-
ventional Ni catalyst (as received Raney Ni) were nearly inactive for
the synthesis of the primary amine. Ni/CaSiO3 with various Ni load-
ings (1, 3, 10, 20 wt%) were also tested, and the catalyst with 10 wt%
Ni was found to be optimal (result not shown). Ni/CaSiO3 cata-
lysts pre-reduced at different temperatures (TH2 ) were also tested,
and the catalyst reduced at 600 ◦C showed higher yield than that
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Table 2
Amination of 2-octanol with NH3.a
n-C6H11
3 mmol
OH
cat. (1.0mol%)
o-xylene (4g)
160oC, 20 h
n-C6H11
NH2
+ NH3
.
0.4 MPa
Catalyst
TH2 /◦C
Conv. (%)
Yield (%)
NiO/CaSiO3
Ni/CaSiO3
–
600
600
700
600
600
–
0
95
0
75
45
1
0
86
0
Ni/CaSiO3–airb
c
Ni/CaSiO3
3
Ni/CaOd
Ni/SiO2
<1
<1
<1
Raney Ni
12
a
Conversion and yield were determined by GC based on alcohol.
Pre-reduced Ni/CaSiO3 was exposed to air at room temperature for 0.5 h.
2-Octanone (6%) and self-coupling products of 2-octanol (11%) were the byproducts.
2-Octanone (0.1%) was the byproduct.
b
c
d
Table 3
Amination of various alcohols with NH3.a
H
N
Ni/CaSiO3 (1 mol%)
R1 OH
R2
R1 NH2
R1
R1 R1
O
+
NH3
o-xylene
20 h
R2
2
R2 R2
3
R2
4
.
3.0 mmol
0.4 MPa
1
Entry
Alcohol
T (◦C)
Yield [%]
2
3
0
4
0
n-C6H11
OH
1
2
160
170
86
OH
OH
70
88
0
0
12
0
3
170
OH
4
170
140
74
71
0
0
21
18
OH
5b
OH
6b
140
160
74
70
6
0
0
0
OH
7b
a
Conversion and yields were determined by GC based on alcohol.
catalyst = 5 mol%.
b
The amination of 2-adamantanol resulted in 88% yield of the cor-
responding amine, corresponding to turnover number (TON) of 88.
This value is larger than those of the state-of-the-art homogeneous
Ru catalyst for the amination of secondary alcohols (TON of 46) [11]
and comparable to that of Ni/Al2O3 (TON of 96) recently reported
by our group [25]. Note that our heterogeneous system requires an
order of magnitude lower amount of ammonia (2.23 equiv.) with
respect to alcohols than the Ru catalysts (35–59 equiv.) [10,11].
Ni/CaSiO3 was also effective for the N-alkylation of amines
N-alkylated amine products were selectively produced. Aniline was
converted into mono N-alkylated anilines (entries 1–4) and sec-
ondary amines were converted to tertiary amines (entries 5, 6)
with good to excellent yields (72–96%). Both aromatic (entries 3,
4) and aliphatic alcohols (entries 1, 2, 5, 6) were tolerated. After
the reaction of aniline and 1-octanol (entry 1), the catalyst was
separated from the reaction mixture by a centrifugation. Then,
the catalyst was washed with acetone, followed by drying in air
at 90 ◦C for 12 h, and by reducing in H2 at 600 ◦C for 0.5 h. The
recovered catalyst showed 95% yield of the product. These catalytic
results show that Ni/CaSiO3 catalyst is an effective heterogeneous
catalyst for the direst alkylation of ammonia and amines with alco-
hols.
with various primary alcohols. Table
4 shows the scope of
the N-alkylation reactions of various amines with various alco-
hols using 2 mol% of as-reduced Ni/CaSiO3 catalyst in N2 under
reflux conditions in o-xylene solvent. For all the reactions, mono
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Table 4
N-alkylation of various amines with alcohols.a
OH
R3
R1
N
H
Ni/CaSiO3 (2 mol%)
N
+
R4
R2
R1
R4
R2
.
o-xylene(1 g)
R3
144 oC, N2
1.2 mmol
1 mmol
Entry
1
Amine
Alcohol
t (h)
T (◦C)
Conv. (%)
99 (98)b
Yield (%)
96 (95)b
OH
NH2
20
155
3
OH
NH2
NH2
NH2
2
3
4
12
6
155
140
155
100
100
100
91
93
78
4
MeO
OH
17
OH
H
N
OH
5
36
15
155
155
100
100
72
77
3
OH
H
6
N
3
a
Conversion and yield were determined by GC based on alcohol.
Reuse of Ni/CaSiO3.
b
4. Conclusions
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The same catalyst was effective for the N-alkylation of anilines
and aliphatic amines with alcohols; primary amines are converted
into secondary amines and secondary amines into tertiary amines.
Structure-activity relationship showed that surface metallic Ni0
species on smaller Ni nanoparticles are responsible for the high
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Please cite this article in press as: K.-i. Shimizu, et al., N-alkylation of ammonia and amines with alcohols catalyzed by Ni-loaded CaSiO3, Catal.
Today (2013), http://dx.doi.org/10.1016/j.cattod.2013.09.002