Paper
Catalysis Science & Technology
that the cleavage of the Pd–C bond in the phenoxycarbonyl
intermediate is the rate-determining step,14 the presence of
the benzene group might accelerate the cleavage rate by
steric repulsion.
as catalyst, the yield of DPC was 14.3% with a selectivity of
66.5%. Takagi et al.51 researched the Pd–Pb–NMe4Br catalyst,
the reported yield was 9.55%, and DPC selectivity was 78.8%.
CSAC tends to be harder, more resistant to abrasion, and 4. Conclusions
lower in ash than similar grades of coal or wood-based
Bidentate nitrogen ligands were successfully grafted onto the
carbons. Therefore, the CSAC granules can be directly used
as catalyst carriers for application in a packed-bed continu-
ous process. The ethylenediamine and benzyl malononitrile
complexed Pd2+ catalysts were also evaluated in a packed-bed
reactor. In the reaction, the liquid flow rate was 5 mL min−1
and the gas flow rate was 200 mL min−1. After 10 h of
running, the reaction liquid was analyzed. For the ethylene-
diamine complexed Pd2+, the conversion rate of phenol and
the DPC selectivity were 12.03% and 93.05%, respectively.
Meanwhile, the benzyl malononitrile complexed Pd2+ had a
phenol conversion rate of 9.36% and a DPC selectivity of
90.82%. Their phenol conversion and DPC selectivity were
comparative to those achieved in a high pressure reaction
vessel. TOF was 10.6 mol DPC/(mol Pd h−1) for the ethylene-
diamine complexed catalyst, and 11.9 mol DPC/(mol Pd h−1)
for the benzyl malononitrile complexed one. Generally
speaking, a catalyst would display a higher TOF in a batch
reaction. When batch reactions were carried out in CH2Cl2
under a pressure of 5 MPa at 100 °C, TOF values were 34.5
and 55.0 mol DPC/(mol Pd h−1) for the ethylenediamine and
benzyl malononitrile complexed catalysts, respectively.
The catalysts displayed relatively good catalytic stabilities
in the packed-bed reactor. After 75 h of running, the conver-
sion rates of phenol were 11.5% and 8.9% for the ethylene-
diamine and benzyl malononitrile complexed Pd2+ catalysts,
respectively. The DPC selectivities nearly remained unchanged.
Relatively stable catalytic performance is mainly due to the
strong interaction of metal ion and organic complex. Bidentate
ligand nitrogen complexes generally display stronger
chelation with metal ions than monodentate ligand
complexes. Furthermore, most of the active components are
located inside the pores of the supports. The leaching of
active species is very small after 75 h of catalytic reaction in
packed bed reactor, as seen in Table 2. It cannot be ruled out
that catalytic performance in a packed bed may reduce the
leaching of active species compared to that in a slurry reactor.
In Fig S7,† the presence of the bands ascribed to stretching
vibrations of Pd–N and Cu–N indicated the stability of the cat-
alysts in a packed bed reactor.
CSAC by silanization of the oxidized AC. Among three
bidentate ligand complexed Pd2+ catalysts, the ethylene-
diamine ligand has a relatively stronger electron-donating
ability and complexes more metal ions. The ethylenediamine
grafted AC has a bigger BET surface area and larger average
pore size. Therefore, it exhibited a higher catalytic efficiency.
In addition to the reaction temperature and pressure, the
polarity of solvent has an influence on the oxidative carbonyl-
ation of phenol. More polar solvent may accelerate phenol
conversion. The CSAC granules immobilized metal complexes
can be directly applied in a packed bed reactor and exhibited
good catalytic performance, which is an obvious advantage
over mesoporous molecular sieves. These results imply the
CSAC granules can be extended to immobilize other organic
group containing catalysts, such as enzymes, ionic liquids,
etc., for application in a packed bed reactor.
Acknowledgements
The authors would like to acknowledge the National Natural
Science Foundation of China (grant no. 21063006), Preferred
Project of Chinese Ministry of Personnel for the Returned
Overseas Chinese Scholars (excellent class), and the national
science and technology support program (grant no.
2012BAC18B02 and 2013BAE03B02-01) for financing this work.
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For comparison, catalytic tests of other supported catalysts
found in references were carried out in a high pressure reac-
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1062 | Catal. Sci. Technol., 2014, 4, 1055–1063
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