Production of Primary Amines by Reductive Amination of Biomass-Derived Aldehydes/Ketones

Article abstract of DOI:10.1002/anie.201610964

Transformation of biomass into valuable nitrogen-containing compounds is highly desired, yet limited success has been achieved. Here we report an efficient catalyst system, partially reduced Ru/ZrO₂, which could catalyze the reductive amination of a variety of biomass-derived aldehydes/ketones in aqueous ammonia. With this approach, a spectrum of renewable primary amines was produced in good to excellent yields. Moreover, we have demonstrated a two-step approach for production of ethanolamine, a large-market nitrogen-containing chemical, from lignocellulose in an overall yield of 10 %. Extensive characterizations showed that Ru/ZrO₂-containing multivalence Ru association species worked as a bifunctional catalyst, with RuO₂ as acidic promoter to facilitate the activation of carbonyl groups and Ru as active sites for the subsequent imine hydrogenation.

Full text of DOI:10.1002/anie.201610964

Angewandte
Communications
Chemie
International Edition: DOI: 10.1002/anie.201610964
German Edition: DOI: 10.1002/ange.201610964
Heterogeneous Catalysis Hot Paper
Production of Primary Amines by Reductive Amination of Biomass-
Derived Aldehydes/Ketones
Guanfeng Liang, Aiqin Wang,* Lin Li, Gang Xu, Ning Yan, and Tao Zhang*
Abstract: Transformation of biomass into valuable nitrogen-
containing compounds is highly desired, yet limited success has
been achieved. Here we report an efficient catalyst system,
nomic point of view, there is a strong incentive to develop
a biomass-based ETA production route.
Direct amination of aldehydes or ketones to primary
amines using ammonia as nitrogen source has been recently
partially reduced Ru/ZrO , which could catalyze the reductive
2
[6]
amination of a variety of biomass-derived aldehydes/ketones in
aqueous ammonia. With this approach, a spectrum of renew-
able primary amines was produced in good to excellent yields.
Moreover, we have demonstrated a two-step approach for
production of ethanolamine, a large-market nitrogen-contain-
ing chemical, from lignocellulose in an overall yield of 10%.
explored in the field of organic chemistry. Nevertheless, the
shortage of aldehyde/ketone feedstocks from petrochemical
industry significantly hinders the application of this amination
protocol. On the other hand, benefiting from the develop-
ment of biorefinery processes, renewable aldehydes and
ketones, such as glycolaldehyde, hydroxyacetone, glyceralde-
hyde, and aromatic aldehydes/ketones are now available even
at large scales, which provides new opportunities for produc-
Extensive characterizations showed that Ru/ZrO -containing
2
multivalence Ru association species worked as a bifunctional
catalyst, with RuO2 as acidic promoter to facilitate the
activation of carbonyl groups and Ru as active sites for the
subsequent imine hydrogenation.
[
7]
tion of biomass-based nitrogen-containing compounds. For
example, pyrrolidones and furfurylamine could be obtained in
good yields with biomass-derived levulinic acid and furfural
as feedstocks, respectively, through the reductive amination
[8]
T
he production of liquid fuels and chemicals from renewable
and non-food lignocellulosic biomass has been regarded as
approach. In spite of the encouraging progress, effective
heterogeneous catalyst systems that enable the amination
reaction to proceed under milder conditions (e.g., T< 1008C,
P < 5 MPa, aqueous phase, without any additive) and tolerate
various biomass-derived substrates are still lacking. In
particular, the production of important and large-market
ETA from lignocellulose has not been reported so far.
Herein, we report the development of a highly efficient
a promising strategy to mitigate CO emissions from fossil
2
[1]
resources. Great research efforts have been devoted to the
production of oxygenates from lignocellulose, such as etha-
nol, diols, hexitols, furfurals, aldehydes/ketones and organic
acids, thanks to the high O/C ratio (close to 1/1) in
[
2]
lignocellulosic feedstocks. In contrast, transformation of
biomass into valuable nitrogen-containing chemicals is still
very limited owing to the lack of efficient amination methods
and robust catalyst, Ru/ZrO containing multivalence Ru
2
association species, for the reductive amination of a variety of
biomass-derived aldehydes/ketones (Scheme 1). Good to
excellent yields of primary amines are achieved under mild
reaction conditions. More importantly, we for the first time
demonstrate the feasibility of directly converting cellulose
into ETA by a two-step approach, that is, cellulose conversion
[3]
for biomass-derived molecules.
Nitrogen-containing compounds, in particular primary
amines, are widely used for the synthesis of polymers, dyes,
[
4]
surfactants, pharmaceuticals, and agrochemicals. Among
them, ethanolamine (ETA) as an absorbent for CO and SO2
2
sequestration in power plants shares the largest market with
[
5]
an annual demand of two million tons. Currently, the
production of ETA is heavily dependent on ethylene epoxide,
an intermediate from ethylene oxidation and difficult to
handle and transport. From both environmental and eco-
[*] Dr. G. Liang, Prof. A. Wang, Dr. L. Li, Dr. G. Xu, Prof. T. Zhang
State Key Laboratory of Catalysis,iChEM
Collaborative Innovation Center of Chemistry for Energy Materials
Dalian Institute of Chemical Physics, Chinese Academy of Sciences
Dalian, 116023 (China)
E-mail: aqwang@dicp.ac.cn
taozhang@dicp.ac.cn
Prof. N. Yan
Department of Chemical and Biomolecular Engineering
National University of Singapore
4
Engineering Drive 4, Singapore 117585 (Singapore)
Supporting information for this article can be found under:
http://dx.doi.org/10.1002/anie.201610964.
Scheme 1. Production of primary amines from biomass-derived alde-
hydes and ketones.
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to glycolaldehyde followed by amination, in a total yield of
0%. In situ characterization techniques showed that co-
(entry 14), and almost the same ETA yield (94%) was
achieved, demonstrating the utility of the synthesis protocol.
Since glycolaldehyde could be produced from cellulose by
1
existence of Ru and RuO on Ru/ZrO played a crucial role
2
2
[
2c,7d]
on the selectivity of primary amines.
hydrolysis and retro-aldol condensation,
we directly used
Our study began with the reductive amination of glyco-
laldehyde with aqueous ammonia on Ru catalysts with
different supports. Direct hydrogenation of glycolaldehyde
was greatly suppressed on Ru catalysts, while ETA was
obtained as the major product with a small amount of
ethylenediamine. The activity of Ru catalysts depended
greatly on the supports (entries 1–7, Table 1), and Ru/ZrO2
cellulose as feedstock for the production of ETA (for details
see Sections 1.3 and 1.4 in the Supporting Information). In
a first step, cellulose was converted in hot water (1 wt%
cellulose in 10 mL water) using tungstic acid (5 mg H WO ),
2
4
affording glycolaldehyde in a yield of 20.6%. The collected
À1
solution (six runs) was concentrated to 1.2 mL (105 mgmL )
and then submitted to amination with ammonia over the best
catalyst Ru/ZrO -150, producing ETA in 52% yield. Thus, by
2
this two-step approach we produced ETA from cellulose in an
overall yield of about 10% (Scheme 2). To the best of our
knowledge, it is the first example demonstrating the produc-
tion of ETA from lignocellulose. Although the ETA yield is
far from a satisfactory level at present, we believe it will be
greatly enhanced by optimizing the catalyst formulations and
reaction conditions in both steps.
[
a]
Table 1: Catalyst screening for reductive amination of glycolaldehyde.
Entry
Catalyst
Yield [%]
ethylenediamine
ethanolamine
1
2
3
4
5
6
7
Blank
Ru/ZrO -250
Ru/AC
Ru/Al O3
Ru/SiO
Ru/HZSM-5
Ru/Nb O5
Ru/ZrO -250
Ru/ZrO -250
Ru/ZrO -250
Ru/ZrO -350
Ru/ZrO -150
Ru/ZrO -unred
Ru/ZrO -150
n.d.
5
4
7
3
2
n.d.
4
3
3
n.d.
56
16
27
23
26
n.d.
74
46
83
57
93
21
94
2
2
2
2
[
b]
c]
[
8
9
1
1
1
1
1
2
[
Scheme 2. Direct conversion of cellulose to ETA.
2
d]
d]
d]
d]
e]
0
1
2
3
4
2
[
[
[
[
4
2
6
1
2
2
The Ru/ZrO -150 was effective not only for reductive
2
2
amination of glycolaldehyde, but also for a broad range of
biomass-derived aldehydes and ketones, such as hydroxyal-
dehyde, hydroxyacetone, aliphatic and aromatic aldehydes
and ketones (Table 2). For example, glyceraldehyde, which
2
[
a] Reaction conditions: 2 mmol glycolaldehyde, 2.0 mL 25 wt% aque-
ous ammonia, 0.1 g catalyst (metal loading=5 wt%), 858C, 12 h,
.0 MPa H . For Ru/ZrO -x, x is the reduction temperature (8C). Ru/ZrO -
2
2
2
2
[7a]
could be obtained directly from cellulose degradation, or
unred is the unreduced catalyst. n.d.=Not detected. [b] 758C. [c] 758C,
[7e]
from glycerol oxidation,
was aminated smoothly under
1
2
5 h. [d] 758C,12 h, H 3.0 MPa. [e] 10 mmol glycolaldehyde, 10.0 mL
5 wt% aqueous ammonia, 0.5 g catalyst.
2
quite mild conditions (658C, 2.0 MPa H and 12 h) to give 3-
2
amino-1,2-propandiol in 82% yield (Table 2, entry 2). It has
been well known that 3-amino-1,2-propandiol is a primary
intermediate for producing iohexol, a contrast agent widely
stood out giving a promising yield of ETA (56%, entry 2). We
also tested other metals (Pt, Pd, and Ir) supported on ZrO2,
but all of them exhibited much lower activity than Ru/ZrO2
[9]
used as in computed tomography and magnetic resonance.
Clearly, the present approach is more environmentally
benign. In addition to hydroxylaldehydes, aliphatic aldehydes
such as butyraldehyde and pentanal were also readily
aminated to the corresponding primary amines in yields
larger than 70% (entries 3 and 4). The aldehydes containing
a furan ring and aromatic ring such as 5-methylfurfural and
benzaldehyde were also tolerated, producing 5-methylfurfur-
ylamine and benzylamine in yields of 61% and 90.2%,
respectively (Table 2, entries 5 and 6).
(
Table S1). These results indicate that co-existence of Ru
species and ZrO in close proximity is essential for a high yield
2
of ETA. The reaction parameters, such as temperature,
reaction time, hydrogen pressure, and substrate/ammonia
ratio, were also investigated over the Ru/ZrO catalyst (see
2
Figures S1–S4 in the Supporting Information). Under opti-
mized reaction conditions (758C, 3.0 MPa H , 12 h) the ETA
2
yield could reach 83% (Table 1, entry 10).
Our further investigations showed that pre-reduction
In comparison with aldehydes, the amination of ketones is
[
6b,c]
treatment of Ru/ZrO imposed a significant effect on the
more challenging because of their lower reactivity.
How-
2
ETA yield (entries 10–13, Table 1). Without pre-reduction
ever, our Ru/ZrO -150 catalyst was still able to afford
2
treatment, the Ru/ZrO catalyst was poorly active, and the
satisfactory yields for several important biomass-derived
ketones such as methyl isobutyl ketone, isophorone, cyclo-
pentanone and cyclohexanone (entries 7–10). Notably, the
selectivities to the primary amines were rather high (> 90%)
even at elevated temperatures (Table S2, entries 8–10). The
amination of aliphatic ketones such as 2-heptanone and 2-
pentanone was more efficient, producing a yield of amines
larger than 90% (entries 11–12). In contrast, hydroxypropa-
none is more difficult to amination, producing 2-amino-1-
2
ETA yield was only 21%. In contrast, Ru/ZrO reduced at
2
1
508C (denoted as Ru/ZrO -150) gave rise to an ETA yield as
2
high as 93% (entry 12). Further elevating the pre-reduction
temperature resulted in a decline of the ETA yield. These
results suggest that amination of glycolaldehyde is sensitive to
the microstructure and chemical environment of the Ru
species which were formed during the reduction pretreat-
ment. The reaction was also performed on a larger scale
2
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Table 2: Production of primary amines from biomass-derived aldehydes
TPR profile of calcined Ru/ZrO2 presented two peaks:
a shoulder peak at 1308C and a major peak at 1458C
and ketones by reductive amination in aqueous ammonia over Ru/ZrO
2
[
a]
catalyst.
6+
(Figure S6), which were ascribed to the reduction of Ru and
Entry
Substrate
Products
Yield [%]
RuO2, respectively (H -TPR = temperature-programmed
2
reduction of H ). Based on the difference between the
2
1
2
93
82
actual and theoretical consumption of H , the reduction
2
degree of the Ru species was calculated to be 91.9%
(
Table S4), suggesting the existence of unreducible Ru
3
4
76
71
species. Pseudo in situ XPS results further confirmed this
point. Prior to reduction, the Ru/ZrO sample contained both
Ru and RuO with a molar ratio of RuO /Ru being 3.29
2
6
+
6+
2
2
5
61
(Figure S7 and Table S5). This is in good agreement with the
H -TPR result. After H reduction at 1508C for 1 h, Ru oxides
2
2
6
7
90
73
were partially reduced to metallic Ru with a molar ratio of
Ru/RuO being 0.89, demonstrating the co-existence of Ru
2
and RuO on the Ru/ZrO -150 catalyst. Further elevating the
2
2
reduction temperature led to a significant increase of Ru/
RuO (12.9 at 2508C and 12.4 at 3508C). The reduction
degree of Ru species calculated from XPS was 92.8% at
2
8
9
96
99
2
508C and 92.5% at 3508C, respectively, which is in good
agreement with the values from the H -TPR. Therefore,
2
both the H -TPR and XPS results point to a nearly 8% RuO
2
2
species left on the catalyst surface even after reduction
at 3508C, implying a strong metal–support interaction
1
1
0
1
93
91
(SMSI).
High-resolution TEM images of the catalysts clearly show
the SMSI between Ru and ZrO . Figure 1 showed that
2
hemispherical particles of Ru, with an average size of 3.1 nm
1
1
2
3
93
26
(
Figure S8), were uniformly dispersed on the Ru/ZrO -150
2
10
1
1
4
5
88
[
b]
(75)
[a] The detailed reaction conditions are summarized in Table S2 in the
Supporting Information. [b] The isolated yield.
Figure 1. HRTEM images of 5 wt% a) Ru/ZrO -150 and b) Ru/ZrO -
2
2
propanol and 1,2-propanediamine, in 26 and 10% yields,
respectively (entry 13). To our delight, aromatic ketones
including acetophenone and valerophenone (entries 14–15)
were selectively transformed into the corresponding aromatic
primary amines with fairly good yields (> 75%) in spite of
growing steric hindrance.
350.
surface, suggesting a good ability of ZrO to wet and disperse
2
Ru species. When the catalyst was reduced at a higher
temperature, for example, 3508C, Ru particles became bigger
Furthermore, the Ru/ZrO -150 catalyst was rather stable
(5.1 nm). Clearly, the declined activity of the Ru/ZrO with an
2
2
under reaction conditions, and it could be recycled several
times without loss of activity (Figure S5). In comparison with
state-of-the-art catalysts reported in literature (Table S3), the
increase of the reduction temperature could be ascribed to the
sintering of Ru particles. Moreover, a thin layer of ZrO is
2
clearly seen to cover Ru nanoparticles, which is a sound
[
10]
Ru/ZrO -150 catalyst performed best in terms of activity,
indicator of SMSI. Even after reuse for six times, the Ru
2
selectivity and stability.
particles on the Ru/ZrO -150 catalyst (Figure S8) and the
2
In view of the remarkable effect of the pre-reduction
temperature on the catalysts performance, we subsequently
conducted extensive characterizations on the series of Ru/
RuO species (Figure S9) remained almost unchanged, which
is in line with the good stability in recycling tests.
Figure 2 displays in situ CO-DRIFT spectra of catalysts
reduced at different temperatures (DRIFT= diffuse reflec-
tance Fourier transform infrared). Three bands were
2
ZrO catalysts reduced at different temperatures to establish
2
the correlation between structure and performance. The H2-
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Figure 2. In situ DRIFT spectra of CO adsorbed on 5% Ru/ZrO2
reduced at different temperatures.
Figure 4. ATR-IR spectra of glycolaldehyde absorbed on a) 5% Ru/
ZrO , b) followed by introduction of 25 wt% aqueous ammonia, and
2
À1
subsequently by the introduction of 6 wt% NaBH solution (c, d, and
4
e) at 508C.
observed at 2142, 2084, and 2016 cm for the Ru/ZrO -150
2
catalyst; the former one were due to CO adsorbed on RuO2,
while the latter two were due to CO adsorbed on low-valence
Ru (0 < d < 1) and Ru nanoparticles, respectively. With
an increase in the reduction temperature, the bands at 2142
and 2084 cm attenuated, which was in accordance with the
d+
[11]
The reaction mechanism for the reductive amination was
probed by in situ attenuated total reflection FTIR (ATR-
À1
À1
FTIR). The bands at 1741 and 1728 cm in Figure 4a were
increase of Ru/RuO ratio in the XPS result (Table S5).
attributed to glycolaldehyde adsorbed on Lewis acid sites of
2
By correlating the above characterizations with the
catalytic activity, we propose that RuO on the Ru/ZrO -150
work as acidic promoter. To confirm this hypothesis, we
Ru/ZrO . Introduction of aqueous ammonia resulted in
appearance of a new band at 1621 cm , which was attributed
2
À1
2
2
[12]
to the formation of imine ad-species. Upon diluted NaBH4
solution was introduced as a hydrogen source, a new band at
performed NH -TPD experiments to measure the acidity of
3
À1
Ru/ZrO2 samples reduced at different temperatures
1597 cm was produced, which was due to the formation of
(
Figure 3). NH -TPD profile of the pristine ZrO displayed
ETA as a consequence of imine hydrogenation. This result
3
2
suggests that the RuO species promote the imine formation
2
by the activating C=O group of the aldehydes/ketones, while
metallic Ru is responsible for the hydrogenation of imine to
amine. The role of RuO in promoting the formation of imine
2
could also be confirmed in the reaction of benzaldehyde and
aniline over unreduced Ru/ZrO2 and Ru/ZrO -150 (Fig-
2
ure S10).
In summary, we have demonstrated that Ru/ZrO -con-
2
taining multivalence Ru association species functioned as
a highly efficient catalyst for the reductive amination of
a variety of biomass-based aliphatic and aromatic aldehydes/
ketones in aqueous ammonia under mild reaction conditions.
The co-existence of Ru and RuO on the surface of Ru/ZrO -
Figure 3. NH -TPD profile (left) and acidic sites density (right) of
3
2
2
a) ZrO and 5 wt% Ru/ZrO catalysts reduced at b) 3508C, c) 2508C,
2
2
1
50 furnishes it both strong Lewis acid sites and metallic
and d) 1508C.
hydrogenation sites. RuO2 works as acidic promoter to
facilitate the activation of carbonyl groups, while metallic
Ru works as active sites for imine hydrogenation. The
cooperation between two types of active sites leads to
excellent performance for the production of primary
amines. We also demonstrated that cellulose could be
converted into ethanolamine by a two-step approach, with
an overall yield of 10%. Thus, our present work opens a new
avenue for producing renewable primary amines including
large-market ethanolamine from lignocellulosic biomass.
two weak peaks at 124 and 3268C, which reflected the weak
acidity of the ZrO2 support. In contrast, Ru/ZrO -150
2
presented four desorption peaks of NH at 130, 229, 294,
3
and 4358C, indicating that the introduction of Ru species
created new and strong acid sites. Moreover, the peak at
4
358C decreased in intensity with an increase in the reduction
temperature, suggesting the strong acid sites are associated
with RuO2 species. Integration of the desorption peaks
showed the surface acidic sites density followed the order of
Ru/ZrO -150 > Ru/ZrO -250 > Ru/ZrO -350 > ZrO . More
2
2
2
2
importantly, some of the acidic sites (mainly Lewis acid Acknowledgements
sites) could survive even in excess ammonia (Figures S10 and
S11), which was responsible for the good stability of the
catalyst.
We are grateful to the supports from the National Natural
Science Foundation of China (grant numbers 21373206,
4
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Manuscript received: November 9, 2016
Revised: December 27, 2016
Final Article published: && &&, &&&&
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Communications
Heterogeneous Catalysis
Amines from biomass: Ru/ZrO works as
2
a highly efficient, bifunctional catalyst for
the reductive amination of a variety of
biomass-based aliphatic and aromatic
aldehydes/ketones in aqueous ammonia
for the production of primary amines
under mild reaction conditions. A broad
spectrum of renewable primary amines is
produced in good to excellent yields.
G. Liang, A. Wang,* L. Li, G. Xu, N. Yan,
T. Zhang*
&&&& — &&&&
Production of Primary Amines by
Reductive Amination of Biomass-Derived
Aldehydes/Ketones
6
www.angewandte.org
ꢀ 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2017, 56, 1 – 6
These are not the final page numbers!