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Chemistry Letters Vol.38, No.3 (2009)
Direct Conversion of Ethane to Ethylene Oxide over Ni–Ag–O Catalyst
Ying Wu,ꢀ1 Binfu Wu,1 Yiming He,2 and Tinghua Wuꢀ1
1Institute of Physical Chemistry, Zhejiang Key Laboratory for Reactive Chemistry on Solid Surfaces,
Zhejiang Normal University, Jinhua 321004, P. R. China
2College of Mathematics, Physics and Information Engineering, Zhejiang Normal University, Jinhua 321004, P. R. China
(Received November 25, 2008; CL-081109; E-mail: ying-wu@zjnu.cn, thwu@zjnu.cn)
Ethylene oxide was directly synthesized by oxidation of
ethane over Ni–Ag–O catalyst with ethane conversion of 10%
and ethylene oxide yield of 1.2% at 310 ꢁC. NiOx and Ag in
the catalyst favor ethane activation and the formation of ethylene
oxide, respectively.
Since ethylene oxide (EO) is a raw material for glycol, poly-
mer, and many chemical products,1,2 the epoxidation of ethylene
to EO is industrially important.3,4 The industrial process is car-
ried out exclusively using silver catalysts supported on inert
alumina from feed ethylene.5,6 On the other hand, ethylene is
mainly produced by the thermal pyrolysis of ethane or naphtha,
a process that operates under severe conditions, which is highly
energy consuming.7,8 Thus it would be desirable to have a meth-
od by which ethylene oxide could be directly synthesized via a
one-step reaction from ethane under mild reaction conditions.
Although the oxidative dehydrogenation of ethane to ethyl-
ene in the presence of a suitable catalytic material constitutes the
most attractive alternative to steam cracking, the reaction tem-
perature is generally not lower than 400 ꢁC.9–12 For the epoxida-
tion of ethylene to ethylene oxide, however, such a high reaction
temperature easily causes further oxidation of product to COx.
It obstructs the probability of combining the two reactions,
namely, oxidation dehydrogenation of ethane to ethylene and
epoxidation of the intermediate ethylene to ethylene oxide.
In our previous work, nanosized NiO exhibited considerable
low-temperature catalytic performance for oxidative dehydro-
genation of ethane to ethylene below 300 ꢁC.13 The adsorptive
electrophilic oxygen species was considered to be the active spe-
cies involved in the reaction, which differs from the reduction of
transition-metal oxide over other bulk catalysts.14
Figure 1. H2-TPR profiles of the catalysts: (a) NiO, (b) Ag–Ni–
O, (c) Ag.
BET result, respectively. XRD patterns of the fresh and used
Ni–Ag–O catalysts only show the presence of large Ag particles,
but no peaks related to NiO was observed, owing to low content
or high dispersion.
Figure 1 shows H2-TPR profiles of the catalysts. The profile
of pure NiO catalyst shows two main reduction peaks at 245 and
418 ꢁC, attributed to reduction of Ni2O3 to NiO and NiO to Ni,
respectively. A shoulder peak at 527 ꢁC might be ascribed to the
reduction of NiO of different size. For Ni–Ag–O catalyst, only a
small reduction peak at about 363 ꢁC is observed, which corre-
sponds to the reduction of NiOx which interacts with Ag. This
result indicates that the addition of Ag decreased the reduction
of NiOx. There is no detection of any XRD peaks that could
be related to phases of solid solution of Ag and NiOx. This is
probably a result of the very low extent of metal ion infiltration.
Nevertheless, it can be speculated that NiOx has interaction with
Ag by hydrothermal method from TPR results.
The catalytic test was carried out in a fix-bed quartz tubular
reactor, using 0.1 g of the catalyst. A gas mixture of 12.5%
ethane, 12.5% oxygen, and 75% nitrogen passed through the
catalyst bed, with a flow rate of 40 mLꢂminꢃ1. The reactants
and products were analyzed using an on-line gas chromatograph
equipped with a TCD detector attached with a porapak Q and a
Herein we report on a one-step reaction that ethylene oxide
is directly synthesized by oxidation of ethane over NiO-doped
Ag catalyst (Ni–Ag–O).
Ni–Ag–O catalyst was prepared by a hydrothermal method
.
.
using Ni(NO3)2 6H2O and Ag(NO3)4 5H2O. The selected mo-
lar ratio of Ni to Ag was 1/19 by the investigation of the depend-
ence of catalytic behavior on Ni content. Stoichiometric urea
solution was added to the mixture solution of nickel and silver
nitrate. The mixture was transferred into a Teflon-lined stainless
steel autoclave and aged at 100 ꢁC for 20 h. The resulting solid
was filtered and washed with deionized water and absolute etha-
nol. Then it was dried at 110 ꢁC for 10 h, followed by calcination
at 400 ꢁC for 4 h in air. For comparison purposes, pure NiO and
Ag were prepared by the same method.
˚
5 A molecular sieve column.
Table 1 lists the catalytic activities of the catalysts at 290 ꢁC.
It is found that the pure Ag catalyst was ethane inactive from the
reaction. At the reaction temperature over Ag catalyst C2H4
could be epoxidized to ethylene oxide. It is known that catalysts
based on Ag are effective for ethene to ethylene oxide. The ad-
sorption electrophilic oxygen species on the catalyst was thought
to be the epoxidative species of the C=C double bond. Neverthe-
less, the species cannot activate the C–H bond of ethane. The
oxygen species on the surface of NiO catalyst is more active
The XRD patterns of these samples (not shown) indicate that
broader diffraction peaks corresponding to NiO are observed on
the pure NiO sample, suggesting small particle size and large
surface area, which is consistent with SEM observation and
Copyright Ó 2009 The Chemical Society of Japan
Wu, Ying
