Article
Figure 2. (a) Kinetic curves for hydrogenation of quinoline with Co@NHF-900 (reaction conditions: with 5 mg of catalyst and 0.2 mmol substrate
dispersed in 15 mL of solution at 60 °C). (b) Reusability tests of the optimal catalyst.
resolution transmission electron microscopy (HRTEM),
Brunauer−Emmett−Teller (BET) techniques, and X-ray photo-
electron spectroscopy (XPS). The XRD patterns show that
Co@NHF-900 exhibits cobalt phase with the PDF card no. 15-
prove the practicability of the optimal catalyst, its stability and
recyclability have been tested. As shown in Figure 2b, due to the
N-doping carbon shell, the metal core as the active site can be
protected from etching and aggregating, leading to Co@NHF-
900 having good recyclability, which can be reused at least seven
times without any loss in the conversion. More interestingly, the
catalyst can be separated easily from the reaction medium by the
magnetism of the nature of the catalyst, which solves the
problem that catalysts are hard to separate during the catalysis
process in the practical industry.
0
806; however, in the case of Co @NHF-900, XRD patterns
ac
and CoO, Figure S2) which may cause the decrease in the
activity. Therefore the high activity may be attributed to Co
2
larger BET surface areas of 730 m /g (Figure S4, Co@NHF-700
2
and Co@NHF-800 show 414 and 467 m /g, respectively),
CONCLUSIONS
which causes concentration enrichment of the substrate to
enhance the catalysis process. More importantly, the large pore
size of the catalyst also exposes more active site to facilitate the
catalysis process.
There is a large cave of the carbon framework as a result of the
pyrolysis of ZIF-8, as shown in Figure 1a−c, and there are no
obviously big particles on the surface of the polyhedral
framework. Furthermore, the HRTEM analysis of the catalyst
reveals that the particle size of Co@NHF-900 is in the range of
ac. 8−10 nm; most of the particles were encapsulated in N-
doped carbon to form a core−shell structure (Figure 1d,e), and
all elements are scattered well (Figure 1f−i). Moreover, XPS
analysis was performed to confirm the nature of Co species of
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In summary, a hollow N-doping carbon framework supported
core−shell catalyst of Co@NHF-900 has been designed and
constructed by template synthesis of the Co−dopamine coating
on the ZIF-8 and subsequent pyrolysis. It was evidenced that the
catalyst shows excellent performance for hydrogenation of
quinolines due to the large surface areas of the carbon
framework, which facilitates substrate enrichment and transfer,
and the well-distributed Co particles, which provide uniform
active sites. Meanwhile, the Co-based catalyst can be separated
easily by magnetism and reused at least seven times due to the
carbon shell that well protects the nanoparticles from leaching in
the solvent. This work paves a new path to design hollow
structures with uniformly distributed nanoparticles and
promotes the performance of heterogeneous catalytic reactions.
the active catalyst (Figure 1j−l). Peaks observed at 778.48,
0
7
80.85, and 796.39 eV corresponded to Co and Co−N species,
which illustrates that the metal particles were anchored on the
inner surface of the shell through coordinated bonds.
32,33
ASSOCIATED CONTENT
sı Supporting Information
In
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addition, a series of peaks appear at 398.47, 400.40, and 401.57
eV, indicating the presence of pyridinic N and graphitic N in the
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N-doping graphitic carbon framework.
Considering the successful catalysis for hydrogenation of
quinoline, the catalyst was used for the derivatives of quinoline
with different functional groups, which are listed in Table 2. It is
noteworthy that the derivatives with both electron-withdrawing
and electron-donating groups are hydrogenated to obtain the
corresponding products with a high conversion of up to 99% and
without alkyl group removal and dehalogenation (entries 1−9).
Interestingly, although there are competitive unsaturated
groups, the catalyst still shows outstanding activity and excellent
selectivity (entries 10 and 12). The extreme results highlight the
activity and its eminent virtues compared with those of noble
metal catalysts in the process of hydrogenation of quinolines.
A time-dependent experiment of reduction of quinoline with
an optimal catalyst and using ammonia borane as the hydrogen
resource was used to conduct the reaction kinetic investigation
Experimental section; characterization (Figures S1−S5);
and gas chromatography graph (Table S1) (PDF)
Corresponding Authors
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Ruirui Yun − The Key Laboratory of Functional Molecular
Solids, Ministry of Education, College of Chemistry and
Tian Sheng − The Key Laboratory of Functional Molecular
Solids, Ministry of Education, College of Chemistry and
(
Figure 2a). The kinetic curve indicates that the conversion is
Baishu Zheng − Key Laboratory of Theoretical Chemistry and
Molecular Simulation of Ministry of Education, School of
fast within the first hour and without any byproducts. To further
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Inorg. Chem. 2021, 60, 9757−9761
Yun, Ruirui
