Amine formylation via carbon dioxide recycling catalyzed by a simple and efficient heterogeneous palladium catalyst

Article abstract of DOI:10.1039/c3cc46427j

A simple and efficient Pd/Al₂O₃-NR-RD catalyst was prepared by depositing palladium on a shape controllable Al₂O ₃-NR support through a two-step process that involves hydrothermal synthesis of Al₂O₃-NRs followed by reductive-deposition of palladium. This catalyst showed high activity in the catalytic formylation of amines by CO₂-H₂ under mild conditions with up to 96% yield.

Full text of DOI:10.1039/c3cc46427j

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Amine formylation via carbon dioxide recycling
catalyzed by a simple and efficient heterogeneous
palladium catalyst†
Cite this: Chem. Commun., 2014,
50, 189
Received 22nd August 2013,
Accepted 25th October 2013
Xinjiang Cui, Yan Zhang, Youquan Deng and Feng Shi*
DOI: 10.1039/c3cc46427j
www.rsc.org/chemcomm
A simple and efficient Pd/Al2O3-NR-RD catalyst was prepared by investigated the role of lattice strain and defects in Cu–ZnO–Al2O3
depositing palladium on a shape controllable Al2O3-NR support catalyzed methanol synthesis.3c These results inspired us to develop
through a two-step process that involves hydrothermal synthesis of active heterogeneous catalysts for amine formylation with CO2–H2 by
Al2O3-NRs followed by reductive-deposition of palladium. This tuning the nano-structure of the catalyst support. In this work, we
catalyst showed high activity in the catalytic formylation of amines describe the preparation of a Al2O3 nano-rod (Al2O3-NR) supported
by CO2–H2 under mild conditions with up to 96% yield.
nano-palladium catalyst for the formylation of amines by CO2–H2.
The Al2O3-NR was prepared by a modified hydrothermal method
using AlCl3 as a precursor, 1-butyl-3-methyl imidazolium chloride
(BMImCl) as a template and (NH4)2CO3 as a precipitant.9 After
washing, drying and calcining, the Al2O3-NR was obtained and used
as a support. The Pd/Al2O3-NR-RD catalyst was prepared by the
reductive deposition (RD) of nano-Pd particles on Al2O3-NRs, Fig. 1.
Furthermore, the Pd/Al2O3-NR-RD catalyst was characterized in
detail. SEM and TEM images showed that the diameter of the
Al2O3-NR was in the range of 60–100 nm and most of the Pd NPs
were in the range of 2.5–3.5 nm, and the Pd NPs are well dispersed
on the surface of Al2O3-NR (Fig. 2a–c). Moreover, only the crystal
lattice of the Pd(110) plane is observable by HR-TEM (Fig. 2d). The
Pd content was 0.53 wt%, suggested by ICP-AES. According to the
XRD characterization (Fig. S1, ESI†), there are no observable diffrac-
tion patterns of Pd species, which also suggested that the Pd species
were highly dispersed. BET analysis showed that its BET surface area
was 177.9 m2 gÀ1. Other catalysts were characterized by BET, XPS,
Carbon dioxide (CO2) chemistry is the subject of increased attention in
both academic and industrial fields.1,2 In order to reduce the emission
of CO2 and utilize the carbon source, various technologies have been
explored. The catalytic hydrogenation of CO2 to high value-added
chemical fuels,3 such as alcohols, gasoline, and related higher hydro-
carbons, is one of the attractive approaches. Another direction is
the synthesis of carbonyl containing chemicals, such as carbonate,
formamide, carboxylic acid, ester or lactone, urea or carbamate,
polymer etc.,4 through a catalytic carbonylation reaction, among which
the production of formamide has attracted much attention because it
plays an important role in industry.5 Commonly, formamides are
synthesized using CO as the carbonyl source under rigorous reaction
conditions. The catalytic formylation of amines using CO2 is inviting yet
challenging because of the thermodynamic and kinetic stability of CO2.
Recently, conversion of amines to the corresponding formamides
through the reduction of CO2 using polymethylhydrosiloxane as the
hydrogen source has come into notice with homogeneous catalysts.2b,6
Besides, the catalytic transformation of amines to formamides using
CO2 and H2 as feedstock is another known process.2b,7 However, the
reported systems often require rigorous reaction conditions with
limited generality especially over heterogeneous catalysts.8
Nano-materials are regarded as either efficient catalysts themselves
or as a structure-directing support to gain specific activity. For example,
Tsang and co-workers reported the significant shape effect of plate-like
ZnO on the catalytic activity of Cu nanoparticles in the synthesis of
methanol by CO2 hydrogenation.3b Trunschke and co-workers
State Key Laboratory for Oxo Synthesis and Selective Oxidation, Centre for Green
Chemistry and Catalysis Lanzhou Institute of Chemical Physics, Chinese Academy
of Sciences No.18, Tianshui Middle Road, Lanzhou, 730000, China.
E-mail: fshi@licp.cas.cn; Fax: +86-931-8277088
Fig. 1 An illustration for the preparation of Pd/Al2O3-NR-RD.
Chem. Commun., 2014, 50, 189--191 | 189
† Electronic supplementary information (ESI) available: See DOI: 10.1039/c3cc46427j
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a
Table 1 Results of the formylation of amines using CO2–H2
Entry Substrates
Products
Yieldsb (%)
89 (83%c)
1
2
3
4
93
84
92
5
6
7
86
71
96
Fig. 2 SEM (a), TEM (b and c) and HR-TEM (d) images of Pd/Al2O3-NR-RD.
XRD, ICP-AES, SEM and TEM as well and the palladium loadings
were in the range of 0.47–0.85 wt% with BET surface areas of
154–281 m2 gÀ1 (Tables S1 and S2, Fig. S1, S3–S8, ESI†).
The redox properties of the catalysts were investigated by
Temperature-Programmed-Reduction (TPR) and the results are given
in Fig. S2, ESI.† The TPR profiles of Pd/g-Al2O3 and Pd/Al2O3-NR-RD
8
79
showed well defined positive peaks centered at 45 1C (H2 consump-
9
85
83
À1
tion: 9.5 mmol gcatÀ1) and 47 1C (H2 consumption: 13 mmol gcat
)
respectively, which were attributed to the reduction of supported
PdO. It indicated that more active Pd species existed and was highly
dispersed on Pd/Al2O3-NR-RD. The consumption peak shifted to
higher temperature and appeared at 70 1C (H2 consumption:
15 mmol gcatÀ1) in Pd/a-Al2O3, which indicates the strong interaction
between Pd and the support. In comparison with Pd/Al2O3-NR-RD,
the TPR profile of Pd/Al2O3-NR-DP, which was prepared by the
deposition precipitation (DP) method, showed an increase in H2
consumption (15 mmol gcatÀ1) and the reduction temperature started
at 44 1C but centered at 65 1C. Moreover, a broader peak of H2
consumption (45 mmol gcatÀ1) was observed for Pd/Al2O3-NR-IP
prepared by an impregnation method. The peak of PdO reduction
was in the range of 53–173 1C and centered at 112 1C, indicating the
formation of different reducible Pd species. These results were
consistent with the catalytic performance shown below.
10
11
12
86
84
13
14
15
79
86
83
16
17
37
0d
Subsequently, the formylation of 1-methylpiperazine was chosen
as the model reaction to optimize the reaction conditions, Table S3,
ESI.† Clearly, no reaction occurred under catalyst free conditions or
in the presence of Al2O3-NRs (entries 1 and 2). Exhilaratingly,
remarkably high conversion of morpholine and good selectivity to
the desired product were obtained when Pd/Al2O3-NR-RD was
employed but Pd/Al2O3-NR-IP, Pd/Al2O3-NR-DP, Pt, Ru or Rh/
Al2O3-NR-RD, Pd/a-Al2O3-RD and Pd/g-Al2O3-RD exhibited poor
activity (entries 3–10). Then, the pressure ratio of CO2 to H2, solvents
and reaction temperatures were screened (entries 11–22). Finally,
under the optimized reaction conditions, i.e. PCO :PH = 1:2 Mpa,
18
19
10d
18d
a
Reaction conditions: 1 mmol (100 mg) amine, 50 mg catalyst, 3 mL octane,
1 MPa CO2, 2 MPa H2, 130 1C, 24 h. b Isolated yields. c The catalyst was reused
in the 3rd run. d Determined by GC-FID using biphenyl as the standard
material.
2
2
50 mg Pd/Al2O3-NR-RD, 3 mL octane, 130 1C and 24 h, 96% yield of was removed by filtration after heating the reaction mixture for 2 h
4-methylpiperazine-1-carbaldehyde was obtained. Next, if the catalyst under the reaction conditions, the reaction did not proceed any
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further even if it was reacted for another 22 h, and ICP-AES reductive-deposition of palladium. This catalyst showed high
measurements showed that the Pd concentration was out of detec- activity in the catalytic formylation of amines by CO2–H2 under
tion limit. These results excluded the possible contribution of the mild conditions. The influence of the Al2O3 structure and the
leached palladium species. Moreover, the catalyst can be easily preparation method of catalysts on the catalytic performance
separated by centrifugation and can be reused three times without was also studied.
deactivation, and 83% yield was maintained (entry 23 and Table 1,
entry 1).
We thank the NSFC (21073208, 21203219 and 21173204) and
the CAS for financial support.
Furthermore, the gaseous phase was checked by GC-TCD after
the reaction of 1-methylpiperazine with CO2–H2 and the CO
concentration was out of the TCD test limit. So the formation
of CO should be negligible and the selectivity based on CO2
conversion should be >99%. If the formylation reaction was
performed with CO, the yield of the desired product was only
15%, suggesting that CO should not be the reaction intermediate.
Also we checked the catalytic performance of homogeneous
PdCl2 (2 mol%)/1,2-bis(diphenylphosphino) ethane (5 mol%)
but only o1% desired product was formed as determined by
GC-MS. So the catalytic behavior of Pd/Al2O3-NR-RD is unique.
Having a highly efficient catalyst in hand, we further explored
the formylation of various amines to examine the scope and
limitations of the current catalyst system, Table 1. By using
1-methylpiperazine and 1-ethylpiperazine as substrates, the reaction
proceeded successfully and furnished the desired products with
89–93% yields (entries 1 and 2). In addition, other cyclic secondary
amines, such as pyrrolidine, piperidine and 4-methylpiperidine,
were also converted into the formamides with 84–92% yields
under the optimized conditions (entries 3–5). Moreover, the steric
hindrance might decrease the reactivity of amine and the desired
product was obtained in 71% yield for the formylation of
2,6-dimethylpiperidine (entry 6). It should be mentioned that
morpholine, which has an oxygen on its ring, was also used and
96% yield was obtained (entry 7). Interestingly, the increase of
reaction sites on the ring did not reduce the reactivity of amine,
and piperazine was formylated with 79% yield (entry 8). Thus, it was
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In conclusion, we have prepared a simple and efficient
Pd/Al2O3-NR-RD catalyst by depositing palladium on a shape
controllable Al2O3-NR support through a two-step process that
involves hydrothermal synthesis of Al2O3-NR followed by
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