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ambient pressure) with high activity and selectivity, are
environmentally benign owing to H2O as the only by-
product [12–14]. Therefore, TS-1 and H2O2 seem to con-
struct optimum partners for the epoxidation of small
alkenes. In 2000, TS-1/H2O2 system was applied to the
liquid-phase epoxidation of BD. VO turnover number
(TON, determined as the molar VO obtained per molar Ti
atom) was 193 and VO concentration was 0.15 mol/L at
optimal conditions, away from the theoretic equilibrium
value (0.60 mol/L) [15].
of the active center towards the BD epoxidation reaction
was investigated. The introduced Ni effectively improved
VO yield and H2O2 utilization. The catalyst kept high
activity during five runs of reusability test. In all, Ni
modifying TS-1 catalysts provided an environmentally
benign and effective method for BD epoxidation.
2 Experimental
Water soluble compounds of transition metals (e.g.
sodium tungstate, molybdate and vanadate or potassium
chromate and dichromate) have been used as homogeneous
catalysts earlier in the epoxidation of olefinic compounds
[16, 17]. Nevertheless, the process was inapplicable due to
difficulties in the homogeneous catalysts separation/recy-
cling. The simple, inexpensive metal oxides, such as NiO,
CoO or MoO3, were employed as heterogeneous catalysts
for the epoxidation of styrene using tertiary butylhydro-
peroxide as an oxidant [18]; among these transition metal
oxides, NiO showed the best performance (styrene con-
version was 52 %, and styrene oxide selectivity reached
86 %). Although the problem of catalysts separation/
recycling has been solved, the activity of simple transition
metal oxide for alkenes epoxidation still requires
promotion.
2.1 Materials
Hydrogen peroxide (H2O2,5 0 wt%; local vender) concen-
trations were determined by iodometric titration prior to
use. Titanium Silicalite 1 (TS-1, SiO2/TiO2 = 40) with
specific surface area 463.1 m2/g was from Shanghai Novel
Chemical Technology Co. Ltd. Nickel nitrate hexahydrate
(Ni(NO3)2ꢀ6H2O, Shanghai NO. 2 Reagent Factory, China)
and methanol (CH3OH, local vendor) employed were all
A.R. grade. All chemicals were used without further
purification.
2.2 Preparation of xNi–TS-1
The TS-1 catalysts with different Ni contents (denoted as
xNi–TS-1, where x stands for NiO mass percent contents:
x = mNiO/(mNiO ? mTS-1) 9 100, x range of 0–10) were
prepared via supersonic impregnation method. This method
facilitated Ni into TS-1 structure and potentiated the
interaction between embedded Ni and Ti active site.
The typical synthesis process was as follows: 1.00 g of
TS-1 was dissolved in 3 mL distilled water, and then
5 mL distilled water containing designed amount of
Ni(NO3)2ꢀ6H2O was added into the above solution with
vigorous stirring. The mixture was treated under ultrasonic
wave, and then put into infrared drying oven with vigorous
stirring until it changed to dry powder, finally further dried
up overnight at 120 °C. The final powder in light green was
calcined at 550 °C for 360 min. Chemical analysis of
prepared catalysts was done by atomic absorption spec-
troscopy (ICP-AES) on an ARL 3520 spectrometer.
The local environment of Ti studied in depth confirmed
that titanium was in a tetrahedral environment in TS-1, and
the type of species presenting as tetrapodal [Ti(OSi)4] and
tripodal [Ti(OSi)3(OH)] were observed [19]. Consequently,
a certain kind of acidity was introduced into the TS-1
catalyst. Although TS-1 exhibited remarkable selectivity,
byproducts formed in the solvolysis of epoxides, which is
catalyzed by the acid site on TS-1, are quite serious
problems. Nowadays, alkali and alkaline-earth metals
modified TS-1 catalysts were well studied to promote the
selectivity of epoxides [20, 21]. However, the introduction
of alkali and alkaline-earth metals suppresses the conver-
sion of H2O2. Furthermore, the content of modified metal is
difficult to control.
Based on the fact above, TS-1 exhibits attractive pros-
pect for BD epoxidation due to its advantages in environ-
mental benign and mild reaction condition. In recent years,
the epoxidation of BD in liquid phase was studied rarely
whatever using H2O2 or other oxidants. Herein, being
inspired by the catalytic activity of simple transition metal
oxide for alkenes epoxidation, we choose inexpensive
transition metal Ni to modify TS-1, aiming to influence the
electron environment of Ti active site and improve the
electrophilicity of active oxygen in the five-member-ring
intermediate. TS-1 catalysts modified with Ni were facilely
prepared through supersonic impregnation method. The
specific Ni role to Ti-site and the variation in the property
For comparation, the pure NiO particles were obtained
by calcinating Ni(NO3)2ꢀ6H2O at 450 °C for 3 h.
2.3 Physicochemical Characterization
2.3.1 Powder X-ray Diffraction (XRD)
XRD measurements were performed using an X’Pert Pro
multipurpose diffractometer (PANalytical, Inc.) with Ni-
filtered Cu Ka radiation (0.15046 nm) from 10.0° to 80.0°.
Measurements were conducted using a voltage of 40 kV,
current setting of 40 mA, step size of 0.02°, and count time
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