Na Huo et al. / Chinese Journal of Catalysis 38 (2017) 1148–1154
1153
°C in N2. Investigation of various supports (MgO, activated car‐
bon, NaX, NaY, and CaO) showed the choice of support greatly
affected the catalytic activity and selectivity toward the target
ester product. The Co‐N‐C/MgO catalyst exhibited excellent
performance for the oxidative esterification of furfural to
methylfuroate (93.0% conversion and 98.5% selectivity)
without the requirement for a basic additive under 0.5 MPa O2
at 100 °C for 12 h. However, use of Co‐N‐C(HCl) as the catalyst
produced mainly an acetal as a condensation product. Chloride
ions had a negative effect on the oxidative esterification. The
inclusion of MgO as a support increases the catalytic efficiency
of the cobalt‐nitrogen‐doped carbon species, and as additive
greatly reduces the negative effect of Cl. Additionally, the oxy‐
gen pressure (0.3–1.0 MPa) has a negligible effect on the oxida‐
tive esterification of furfural with Co‐N‐C/MgO. This knowledge
could be used to develop non‐precious metal catalysts for the
oxidative esterification of biomass‐derived compounds.
CH3OH, O2
OCH3 (A) Oxidative esterification
OCH3
OH
O
O
Co-N-C/MgO
O
CH3OH
CH3OH
OCH3
OH
OCH3 (B) Condensation
O
CHO
O
O
Co-N-C(HCl)
OCH3
Scheme 1. Oxidative esterification and condensation of furfural with
methanol.
methylfuroate. These results show that the Co‐N‐C/MgO
catalyst is stable and can be reused in the oxidation of furfural
to methylfuroate.
The oxidative esterification of furfural involves oxidative
esterification and condensation of –CHO with –OH (Scheme 1).
In methanol, furfural is converted into the intermediate
hemiacetal, and subsequently undergoes dehydrogenation to
form the target product methylfuroate. A competitive reaction
of hemiacetal condensation with methanol can occur to
generate the side product acetal in the presence of specific
catalytic sites or in the blank reaction (without any catalyst or
additive). In our case, with Co‐N‐C/MgO as the catalyst, the
main product was methylfuroate. This suggests that the
dehydrogenation of hemiacetal to methylfuroate is dominant.
By contrast, with Co‐N‐C(HCl) as the catalyst, the main reaction
was the condensation of –CHO with –OH generating the acetal
as the main product. To exclude the possibility of producing
methylfuroate via esterification of the hydroxyl and carboxyl
groups, an oxidative esterification experiment using
furancarboxylic acid as the starting substrate was performed in
the presence of Co‐N‐C/MgO under the same conditions. No
methylfuroate was detected in the GC chromatogram (data not
shown). This clearly proved that the oxidative esterification did
not proceed along the esterification pathway. The details for
the mechanism of the Co‐N‐C/MgO catalyst are being clarified
in further investigations.
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Graphical Abstract
Chin. J. Catal., 2017, 38: 1148–1154 doi: 10.1016/S1872‐2067(17)62841‐9
High‐efficiency oxidative esterification of furfural to methylfuroate
with a non‐precious metal Co‐N‐C/MgO catalyst
Na Huo, Hong Ma, Xinhong Wang, Tianlong Wang, Gang Wang, Ting Wang,
Leilei Hou, Jin Gao *, Jie Xu *
Dalian Polytechnic University;
Co-N-C/MgO
Methylfuroate
Conv. 93.0% Select. 98.5%
Dalian Institute of Chemical Physics, Chinese Academy of Sciences
Furfural
The non‐precious metal catalyst Co‐N‐C/MgO showed high efficiency in the
oxidative esterification of furfural to methylfuroate (93.0% conversion and
98.5% selectivity). The reaction with the catalyst Co‐N‐C(HCl) proceeded
via a condensation pathway with acetal as the dominant product.
Co-N-C(HCl)
Acetal