Selective Hydrogenation of 2-Ethylanthraquinone Over An Environmentally Benign Ni-B/SBA-15 Catalyst Prepared by A Novel Reductant-Impregnation Method
Selective Hydrogenation of 2-Ethylanthraquinone Over An Environmentally Benign Ni-B/SBA-15 Catalyst Prepared by A Novel Reductant-Impregnation Method
Selective Hydrogenation of 2-Ethylanthraquinone Over An Environmentally Benign Ni-B/SBA-15 Catalyst Prepared by A Novel Reductant-Impregnation Method
cn
Research Note
Abstract
An environmentally benign SBA-15-supported amorphous nickel boride alloy catalyst, prepared by a novel reductantimpregnation
method, exhibits superior activity, selectivity, and stability in the selective hydrogenation of 2-ethylanthraquinone (eAQ) to 2-ethylanthrahydroquinone (H2 eAQ), which is the dominating process for the production of hydrogen peroxide in industrial scale. The unique characters
of the amorphous alloy as well as the pore structure of the mesoporous SBA-15 molecular sieve are crucial for the excellent catalytic behavior
of the title catalyst.
2003 Elsevier Inc. All rights reserved.
Keywords: NiB; Mesoporous molecular sieve; SBA-15; eAQ; Hydrogenation; H2 O2
1. Introduction
The hydrogenation of 2-ethylanthraquinone (eAQ) into 2ethylanthrahydroquinone (H2 eAQ) is one of the key steps
in the industrial manufacturing of H2 O2 , which is a nonpolluting oxidizing agent [13]. In industry, Raney Ni and
palladium are the most frequently used catalysts for this
reaction. However, even on the most selective palladium
catalyst some degradation products [3] are easily formed,
which leads to the loss of fed hydrogen and the expensive eAQ. Moreover, the palladium catalyst is expensive.
Thus, it is highly desirable to develop nonnoble catalysts
with exclusive selectivity in carbonyl group hydrogenation,
at the same time preventing hydrogenation of the aromatic
ring.
In previous work, our group reported on two kinds of
catalysts which exhibit higher selectivity than the conventional Raney Ni catalyst, one is the rapid-quenched skeletal
Ni catalyst (RQ-Ni) and the other is a nanosized amorphous NiCrB catalyst [4,5]. However, a detailed chromatographic analysis reveals that over the RQ-Ni catalyst
* Corresponding authors.
18% of eAQ was converted to 2-ethyltetrahydroanthrahydroquinone (H4 eAQH2 ) and 3% of eAQ was deteriorated [4].
It is noted that the oxidation rate of H4 eAQH2 is sharply
slowed down compared to that of eAQH2 , leading to lower
efficiency in H2 O2 production [5]. Besides, H4 eAQH2 can
be further hydrogenated to 2-ethyloctahydroanthrahydroquinone (H8 eAQH2 ) which does not produce H2 O2 [3].
Although the nanosized NiCrB catalyst shows 100% selectivity in eAQ hydrogenation to H2 eAQ [5], its low thermal stability and difficulty in separation from the reaction
products impede its practical application. Moreover, the
Cr additive in the NiCrB catalyst is enviromentally hazardous.
Here we report on a mesoporous molecular sieve SBA15-supported amorphous nickel boride alloy catalyst (denoted as NiB/SBA-15) prepared by a novel reductant
impregnation method. This NiB/SBA-15 catalyst exhibits
higher activity and stability than the nanosized amorphous
NiCrB catalyst and can efficiently block the hydrogenation of the aromatic rings in eAQ. Even after a reaction
time of 240 min, the amount of eAQ only dropped by 6%,
while no degradation products were detected. Along with
its enviromentally benign nature, this novel NiB/SBA-15
catalyst shows an attractive perspective for industrial application.
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The activity test was carried out in a 220-ml stainlesssteel autoclave with a magnetic stirrer. A mixture of trioctylphosphate and trimethylbenzene (volume ratio 3/7)
was used as the solvent and the concentration of eAQ in the
working solution was 50 g l1 . The reaction conditions were
as follows: 70 ml of working solution, 1.0 g of catalyst, reaction temperature of 323 K, H2 pressure of 0.3 MPa, and a
stirring rate of 1000 rpm to exclude diffusion effects. The reaction process was monitored by sampling the reaction mixture at intervals for O2 oxidation. The H2 O2 produced was
extracted by distilled water and then titrated with KMnO4 .
The percentage yield of H2 O2 (X) is expressed as the ratio of the molar number of H2 O2 to the initial molar number
of eAQ in the reactor, i.e., X = ntH2 O2 /n0eAQ 100%, which
also represents the selectivity to H2 eAQ and H4 eAQH2 . The
organic layer was further analyzed by HPLC (HP 1100)
with an ultraviolet detector and the Zorbax column (ODS,
4.6 mm 15 cm) to quantify eAQ and H4 eAQ.
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256
Fig. 1. TEM images of (a) NiB/SBA-15 (inset showing its SAED pattern)
and (b) NiB/MCM-41 catalysts.
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and hydrogenation of the carbonyl groups, therefore promoting the selectivity in eAQ hydrogenation. Third, the unique
pore structure of SBA-15 [6,13] may also contribute greatly
to the superior performance of the NiB/SBA-15 catalyst.
The large pore size of the SBA-15 mesoporous molecular
sieve ( 6.5 nm) makes it possible for the amorphous NiB
alloys to be formed inside the SBA-15 channels as verified
by the TEM image. Thus the aggregation of the nanosized
particles can be readily impeded by the isolation of the channel walls. At the same time, the mesopores of SBA-15 are
large enough for the diffusion and reaction of eAQ inside
the SBA-15 channels. The pore size of MCM-41 or HMS
(< 3 nm) may be too small to incorporate the amorphous
NiB particles, thus leading to inferior stability and less active sites accessible by the reactants.
4. Conclusions
257
Acknowledgments
This work was supported by the State Key Basic Research Development Program (G2000048009) and the National Science Foundation of China (20005310, 20073008,
20203004).
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