Titanosilicate beads as versatile catalysts for the conversion of trioses to lactates and for the epoxidation of alkenes

Article abstract of DOI:10.1016/j.cattod.2011.03.055

Titanosilicate beads with hierarchical porosity (TiSil-HPB-60) were prepared from an anion-exchange resin and proved to be a versatile heterogeneous catalyst displaying activity both in the conversion of trioses to ethyl lactate and in the epoxidation of alkenes. In the former reaction, TiSil-HPB-60 showed higher catalytic activity compared to two well-known titanosilicate catalysts: the crystalline microporous TS-1 and the ordered mesoporous Ti-MCM-41. Notably, TiSil-HPB-60 displayed significantly high selectivity towards ethyl lactate due to the absence of strong Br?nsted acid sites. In the epoxidation of alkenes with aqueous H₂O₂, TiSil-HPB-60 displayed improved epoxide yield compared to TS-1 and Ti-MCM-41 when the bulky cyclohexene was used as substrate, while TS-1 was the most active catalyst with the linear 1-octene. In both reactions, the separation of TiSil-HPB-60 from the reaction mixture is very straightforward, thanks to its bead format, and the catalyst can be reused in successive catalytic cycles without significant loss of activity.

Full text of DOI:10.1016/j.cattod.2011.03.055

Catalysis Today 173 (2011) 89–94
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Titanosilicate beads as versatile catalysts for the conversion of trioses to lactates
and for the epoxidation of alkenes
Kaifeng Lina,b,c,∗, Li Lia, Bert F. Selsa, Pierre A. Jacobsa, Paolo P. Pescarmonaa,∗∗
a Centre for Surface Chemistry and Catalysis, University of Leuven (K.U. Leuven), Kasteelpark Arenberg 23-bus 2461, 3001 Heverlee, Belgium
b State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, 150090 Harbin, China
c Natural Science Research Center, Academy of Fundamental and Interdisciplinary Science, Harbin Institute of Technology, Mailbox-3026, 150080 Harbin, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Titanosilicate beads with hierarchical porosity (TiSil-HPB-60) were prepared from an anion-exchange
resin and proved to be a versatile heterogeneous catalyst displaying activity both in the conversion of
trioses to ethyl lactate and in the epoxidation of alkenes. In the former reaction, TiSil-HPB-60 showed
higher catalytic activity compared to two well-known titanosilicate catalysts: the crystalline microp-
orous TS-1 and the ordered mesoporous Ti-MCM-41. Notably, TiSil-HPB-60 displayed significantly high
selectivity towards ethyl lactate due to the absence of strong Brønsted acid sites. In the epoxidation of
alkenes with aqueous H2O2, TiSil-HPB-60 displayed improved epoxide yield compared to TS-1 and Ti-
MCM-41 when the bulky cyclohexene was used as substrate, while TS-1 was the most active catalyst
with the linear 1-octene. In both reactions, the separation of TiSil-HPB-60 from the reaction mixture is
very straightforward, thanks to its bead format, and the catalyst can be reused in successive catalytic
cycles without significant loss of activity.
Received 10 January 2011
Received in revised form 11 March 2011
Accepted 28 March 2011
Available online 6 May 2011
Keywords:
Hierarchical porosity
Titanosilicate beads
Triose
Lactates
Epoxidation
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
HPB-60, by employing this material as heterogeneous catalyst both
for epoxidation reactions and for the conversion of dihydroxyace-
Porous titanosilicates (e.g. TS-1 and Ti-MCM-41) have long been
known to possess remarkable activity in the selective oxidation of
organic molecules at mild conditions using H2O2 as oxidant [1–14].
On the other hand, some studies opened up to their novel applica-
tion in the reactions of transesterification, aldol condensation and
aminolysis of epoxides, indicating that porous titanosilicates can be
employed as Lewis-acid catalysts [15,16]. Recently, we synthesized
titanosilicate beads with hierarchical porosity (TiSil-HPB-60) from
a preformed titanosilicate solution using a porous anion-exchange
resin as hard template [17]. TiSil-HPB-60 was used as a catalyst for
the epoxidation of a wide range of bulky alkenes with tert-butyl
hydroperoxide and aqueous H2O2 and showed improved catalytic
performances compared to Ti-MCM-41 and TS-1. It is worth not-
ing that the separation of TiSil-HPB-60 from the reaction solutions
is very straightforward, which is relevant in the perspective of an
industrial application. Here, we demonstrate the versatility of TiSil-
tone to ethyl lactate. Lactic acid and alkyl lactates can be used as
environmentally friendly solvents and play an important role in
the production of biodegradable polymers such as polylactic acid
(PLA) [18,19]. The conventional process to synthesize lactic acid is
based on the microbial fermentation of glucose and sucrose [20].
However, such process is limited by low productivities and needs
expensive and energy-inefficient separation and purification steps.
An alternative and sustainable route to produce lactic acid or alkyl
lactate is provided by the catalytic conversion of triose sugars, i.e.
dihydroxyacetone (DHA) and glyceraldehyde (GLA). Considering
that DHA and GLA can be obtained by the oxidation of glycerol,
which is the main by-product of the production of biodiesel via
transesterification, the catalytic conversion of trioses to lactates
represents an important reaction in the field of renewable biomass
conversion and green chemistry. Recently, various solid acid mate-
rials have been reported as heterogeneous catalysts for the con-
version of trioses to lactic acid or alkyl lactate [21–25]. Systematic
studies with zeolites with different types and number of acid sites
showed that a combination of Lewis acidity and mild Brønsted acid-
ity catalyzes the selective conversion of trioses to the desired lactate
product. On the other hand, strong Brønsted acid sites catalyze the
formation of the dialkyl acetal of pyruvic aldehyde side-product
[23]. TiSil-HPB-60 is expected to have a suitable population of acid
sites for catalyzing the selective synthesis of lactates from trioses.
∗
Corresponding author at: Natural Science Research Center, Academy of Funda-
mental and Interdisciplinary Science, Harbin Institute of Technology, Mailbox-3026,
150080 Harbin, China. Tel.: +86 451 86402559; fax: +86 451 86402528.
∗∗
Corresponding author. Tel.: +32 16 321592; fax: +32 16 321998.
E-mail addresses: linkaifeng@hit.edu.cn (K. Lin),
paolo.pescarmona@biw.kuleuven.be (P.P. Pescarmona).
0920-5861/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.cattod.2011.03.055

90
K. Lin et al. / Catalysis Today 173 (2011) 89–94
Fig. 1. SEM (A and B) and TEM (C and D) images of TiSil-HPB-60.
2. Experimental
XL30 FEG: each sample was measured 5 times in five randomly
selected areas and the average of the results was calculated.
Transmission electron microscopy (TEM) investigation was made
on special prepared plan-view sample, using a Philips CM20
electron transmission microscope operating at 200 kV [17]. NH3
temperature-programmed desorption (NH3-TPD) measurements
were carried out to characterize the acidity of the samples. After
pretreatment of the samples (70.1 mg) in He with a flow rate of
20 ml/min at 500 ◦C for 1 h, the samples were exposed to 5% ammo-
nia in N2 at 100 ◦C for 15 min and were then purged with He for
30 min. NH3-TPD profiles were obtained between 100 and 750 ◦C
with a heating ramp at 10 ◦C/min by monitoring the desorbed
ammonia with a Pfeiffer Omnistar quadrupole mass spectrometer.
2.1. Materials
The preparation of titanosilicate beads with hierarchical poros-
ity (TiSil-HPB-60) was performed according to our recently
reported procedure [17]. Briefly, Amberlite® IRA-900 resin was
used as the hard template and a preformed titanosilicate solution
(with Si/Ti = 31.8) was used as the inorganic source. TiSil-HPB-60
with Si/Ti = 36 was obtained after hydrothermal treatment at 60 ◦C
for 24 h followed by calcination at 550 ◦C for 6 h. Titanosilicate
beads with lower Ti content (Si/Ti = 54 and 76) were prepared via
similar procedures, using a molar ratio of Si to Ti of 47.7 and 95.5
in the preformed titanosilicate solution.
Ti-MCM-41 (Si/Ti = 59) and TS-1 zeolite (Si/Ti = 35) with crys-
tal size of ca. 190 20 nm were synthesized according to literature
methods [2,26]. Si-MCM-41 was prepared via similar procedure as
that for Ti-MCM-41, except for no addition of Ti source. TiO2 used
in this work was purchased from Aldrich.
2.3. Catalytic tests
Conversion of dihydroxyacetone to ethyl lactate. All the catalysts
were treated at 120 ◦C overnight prior to use. Typically, 5 ml of 0.4 M
dihydroxyacetone in ethanol and decane (GC internal standard)
were added to 0.2 g of catalysts. The reaction was performed in
closed glass vials at the selected temperature for 6 h under magnetic
stirring. The product yields were determined using an Interscience
Trace GC Ultra equipped with a RTX-5 fused silica column (5 m,
0.1 mm). TiSil-HPB-60 deposited spontaneously at the bottom of
the reaction vial a few seconds after the stirring was stopped. Before
the recycling tests, the reaction solution was removed with a glass
pipette. Next, ethanol was added and the sample was stirred for
few minutes. After the stirring was stopped and the beads had
deposited, the ethanol solution was removed with a pipette. The
procedure was repeated for a total of four times, after which the
beads were dried at 120 ◦C and reused.
2.2. Characterization
X-ray diffraction (XRD) patterns were measured on a STOE
STADI P instrument using Cu K␣ radiation. The isotherms of
nitrogen adsorption/desorption were measured at liquid nitro-
gen temperature using a Coulter Omnisorp and a Micromeritics
TriStar 3000. The pore-size distribution was calculated using
Horvath–Kawazoe (HK) and Barrett–Joyner–Halenda (BJH) mod-
els [27,28]. UV–visible spectra were measured with a Varian
Cary 5 spectrophotometer in the 200–800 nm region. The sam-
ples were not treated before measurement and the UV–visible
spectra were recorded in air. Scanning electron microscopy (SEM)
images were taken on a Philips XL30 FEG apparatus. Si/Ti molar
ratios were determined by means of EDX analysis on a Philips
Epoxidation of alkenes with aqueous H2O2. The epoxidation reac-
tions were carried out in a glass vial under vigorous stirring. In
a typical run, the alkene, the solvent (methanol or acetonitrile),

K. Lin et al. / Catalysis Today 173 (2011) 89–94
91
2.5
2.0
1.5
1.0
0.5
0.0
C
E
D
C
B
A
B
A
100
200
300
400
500
600
700
Temperature (ºC)
200
300
400
500
600
700
800
Wavelength (nm)
Fig. 3. Temperature programmed desorption of NH3 (NH3-TPD) profiles of TS-1 (A),
Ti-MCM-41 (B), and TiSil-HPB-60 (Si/Ti = 36) (C).
Fig. 2. UV–Vis spectra of TS-1 (A), Ti-MCM-41 (B), TiSil-HPB-60 (Si/Ti = 76) (C), TiSil-
HPB-60 (Si/Ti = 54) (D) and TiSil-HPB-60 (Si/Ti = 36) (E). For the sake of clarity, spectra
B-E are offset along the vertical axis.
acid sites (Fig. 3). The different intensity of this peak indicates
that the number of acid sites (per gram of material) increases in
the order: TS-1 < Ti-MCM-41 < TiSil-HPB-60. Although it has been
reported that Lewis acid sites in titanosilicates are the predomi-
nant species [15,16], it is likely that the observed NH3-TPD peak
also contains a contribution from mild Brønsted acid sites. Particu-
larly, the presence of a large population of surface silanol groups in
TiSil-HPB-60, which can act as weak Brønsted acid sites, was proved
by 29Si NMR results in our previous work [17].
aqueous H2O2 and the catalyst were mixed in the vial and heated
to 60 ◦C. After reaction for 5 h, the products were analyzed on the
same GC Ultra used for monitoring the synthesis of lactates.
3. Results and discussion
3.1. Characterization of the materials
3.2. Catalytic performances
TS-1 and Ti-MCM-41 were characterized by X-ray diffraction:
the patterns correspond to the expected MFI-type zeolitic struc-
ture for TS-1 and to the typical hexagonal (P6mm) arrangement of
mesoporous channels for Ti-MCM-41. TiSil-HPB-60 has been char-
acterized in detail in previous work [17]: it can be described as
amorphous titanosilicate beads (0.5–1.5 mm) with a hierarchical
porosity including micropores (0.5 nm) and large mesopores with
a diameter of ca. 40–50 nm (Fig. 1). The BET surface area of TS-1,
Ti-MCM-41 and TiSil-HPB-60 (Si/Ti = 36) is 425, 916 and 618 m2/g,
respectively. The BJH pore-size distribution (from adsorption) of
Ti-MCM-41 presents a maximum at 2.4 nm and the cumulative
pore volume is 0.54 cm3/g. It is worth mentioning that TiSil-HPB-
60 contains TS-1 zeolite building units [17], which is an important
difference compared to other conventional mesoporous titanosili-
cates such as Ti-MCM-41.
The coordination environment of Ti in TS-1, Ti-MCM-41 and
TiSil-HPB-60 was investigated by UV–Vis spectroscopy. A main
band centered at 210, 220 and 220–230 nm (Fig. 2A–E), respec-
tively, indicates that most of the Ti species are located in the
framework in tetrahedral coordination. The variety in band cen-
ter position of the three titanosilicates is ascribed to the presence
of different types of tetrahedral Ti-sites, such as Ti(OSi)4 and
Ti(OH)(OSi)3. The latter would generate a broad band centered at
230 nm [29,30]. Moreover, a small amount of higher-coordinated
Ti species coexist with the tetrahedral Ti sites both in Ti-MCM-
41 and TiSil-HPB-60 materials, as indicated by the broad signal
extending up to 290 nm. These higher-coordinated Ti species are
assigned to species originating from the reversible interaction of
tetrahedral Ti with moisture, and/or to polymerized octahedral
species. The absence of the band characteristic of octahedral extra-
framework titanium at about 330 nm indicates that no separated
titania (anatase) phase was formed during the synthesis of any of
the titanosilicates.
TiSil-HPB-60 was studied as heterogeneous catalyst in two reac-
tions for the sustainable production of valuable chemicals: the
conversion of the triose sugar dihydroxyacetone to ethyl lactate
and the epoxidation of alkenes with aqueous hydrogen peroxide.
The catalytic performance of TiSil-HPB-60 in these reactions was
compared to that of two well-known titanosilicate materials: TS-1
and Ti-MCM-41.
TiSil-HPB-60 displayed much higher epoxide yield than both Ti-
MCM-41 and TS-1 in the epoxidation of cyclohexene with aqueous
H2O2 (Table 1) [17]. The improved catalytic behavior of TiSil-HPB-
60 is mainly ascribed to its large mesopores, which can promote
higher activity than with TS-1 by improving the accessibility of
active titanium sites to cyclohexene molecules, and higher selectiv-
ity than with Ti-MCM-41 thanks to a higher rate of diffusion of the
products out of the larger pores of TiSil-HPB-60 [17]. The combined
selectivity towards cyclohexene epoxide plus 1,2-cyclohexanediol
(formed from the hydrolysis of the epoxide) on TiSil-HPB-60 is ca.
95%, indicating that the radical mechanism leading to allylic oxi-
dation products does not take place in a significant amount [17].
Furthermore, TiSil-HPB-60 proved to be active in the epoxidation of
Table 1
Catalytic performances in the epoxidation of alkenes.a
Catalyst
Si/Tib
XCH (%)c
YCHE (%)d
X1O (%)e
YEO (%)f
TiSil-HPB-60
Ti-MCM-41
TS-1
36
59
35
20.2
28.8
8.7
8.2
2.6
3.7
12.6
4.9
29.4
1.1
0.4
18.8
a
Epoxidation of cyclohexene: 4.5 mmol of cyclohexene, 4.5 ml of acetonitrile,
2.25 mmol of aqueous H2O2 (50 wt.%), 60 mg of catalyst, 5 h at 60 ◦C. Epoxidation
of 1-octene: 5 mmol of 1-octene, 7.6 ml of methanol, 2.5 mmol of aqueous H2O2
(35 wt.%), 30 mg of catalyst, 5 h at 60 ◦C.
b
Molar ratios measured by EDX.
XCH = conversion of cyclohexene.
YCHE = yield of cyclohexene epoxide.
X1O = conversion of 1-octene.
c
To determine the population of acid sites, an NH3-TPD study
was performed on the titanosilicates: all the materials show a main
desorption peak between 216 and 224 ◦C, corresponding to mild
d
e
f
YEO = yield of 1,2-epoxyoctane.

92
K. Lin et al. / Catalysis Today 173 (2011) 89–94
Table 2
100
Catalytic performances in the conversion of DHA to ethyl lactate.a
90
80
70
60
50
40
30
20
10
0
Catalyst
Si/Tib
YEL (%)c
YAc (%)d
YHe (%)e
SEL (%)f
TONg
TiSil-HPB-60
Si-MCM-41
Ti-MCM-41
TS-1
36
–
59
35
–
29.6
0
11.7
13.1
0.1
0.6
0
0.9
0
0
0
1.4
0.3
0
97.9
–
83.7
97.6
100
6.6
–
4.2
2.9
<0.1
TiO2
0
a
5 ml of ethanol solution containing dihydroxyacetone (0.4 M) and 200 mg of
catalyst, 90 ◦C, 6 h.
b
Molar ratios measured by EDX.
YEL = yield of ethyl lactate.
YAc = yield of diethyl acetal of pyruvic aldehyde.
YHe = yield of ethyl hemiacetal of pyruvic aldehyde.
SEL = selectivity towards ethyl lactate.
Turnover number (TON) expressed as moles of ethyl lactate obtained per mole
c
d
e
f
g
of Ti in the catalyst.
0
5
10
15
20
25
Reaction time (h)
other bulky substrates, such as cyclooctene, cyclodecene, cyclodo-
decene and cyclododecatriene [17]. However, TiSil-HPB-60 gave
only poor epoxide yield in the epoxidation of the linear 1-octene
with aqueous H2O2. With this substrate, TS-1 gave much higher
epoxide yield, while Ti-MCM-41 was even less active than TiSil-
HPB-60 (Table 1). The major side-products in the epoxidation of
1-octene are 1,2-octanediol and the corresponding methyl ether,
generated from the epoxide by reaction with water and methanol,
respectively. The lower activity in the epoxidation of 1-octene with
TiSil-HPB-60 compared to TS-1 is ascribed to the higher surface
hydrophobicity of TS-1 (see Refs. [17,31]), which favors the diffu-
sion of the apolar, linear 1-octene through the pores of the catalyst,
and to the higher ratio of active Ti centres in framework tetrahe-
dral sites in TS-1 (see Section 3.1). These results demonstrate that
TiSil-HPB-60 is the most favorable catalyst in the epoxidation of
bulky substrates, while for linear alkenes TS-1 remains the catalyst
of choice.
For the conversion of dihydroxyacetone to lactate in ethanol, the
catalytic performance of TiSil-HPB-60 was compared to that of the
other titanosilicates, TS-1 and Ti-MCM-41, and to that of all-silica
MCM-41 (Si-MCM-41) and of titanium dioxide. All three titanosili-
cates were active in the conversion of dihydroxyacetone (Table 2).
Three products were observed: ethyl lactate, the diethyl acetal of
pyruvic aldehyde, and a small amount of the reaction intermedi-
ate ethyl hemiacetal of pyruvic aldehyde [32]. It has been proposed
that the reaction starts with the formation of pyruvic aldehyde,
from which it can proceed towards the lactate by rearrangement
via a hydride-shift mechanism with incorporation of an ethanol
molecule on Lewis acid sites, or towards the acetal by the reversible
addition of ethanol on strong Brønsted acid sites [23,32]. While all
tested titanosilicates were active in the reaction, negligible DHA
conversion and ethyl lactate formation were observed when Si-
MCM-41 and TiO2 were used as catalysts (Table 2), indicating that
Ti sites incorporated in the framework of silica, which act as Lewis
acid sites, are playing an essential role as catalytic active sites. All
active catalysts gave very high selectivity towards ethyl lactate, in
agreement with the expected lack of strong Brønsted acid sites in
these materials. Compared with TS-1 and Ti-MCM-41, TiSil-HPB-60
displayed much higher yield of ethyl lactate and TON based on ethyl
lactate (Table 2): these results are ascribed to the larger number of
acid sites in TiSil-HPB-60 (see Section 3.1) and to the presence of
larger mesopores in these titanosilicate beads, which is helpful for
faster diffusion of reactants and products.
Fig. 4. Conversion of DHA (as sum of the yields of all reaction products) (ꢀ) and
selectivity towards ethyl lactate (᭹) on TiSil-HPB-60 as a function of reaction time.
In order to evaluate whether all the Ti atoms in the titanosil-
icate beads contribute to the conversion of the triose to lactate,
we synthesized and tested titanosilicate beads with different Ti
content. Characterization of the titanosilicate beads by UV–Vis
spectroscopy shows that all three TiSil-HPB-60 materials exhibit
analogous absorption bands, indicating that the coordination envi-
ronments of the titanium sites are similar among these materials
(Fig. 2C–E). The titanosilicate beads displayed a linear increase in
the activity in the conversion of DHA with increasing Ti content
(Fig. 5), suggesting that most, if not all, of the Ti sites equally con-
tribute to the catalytic activity of the material. This result also
indicates that most of the Ti species in the titanosilicate beads are
accessible for the reactants, implying that TiSil-HPB-60 with hier-
archical porosity does not suffer from diffusion limitations in this
reaction.
The effect of the catalyst amount on the activity was studied
as well for TiSil-HPB-60 (Fig. 6): the linear increase in the activ-
ity observed with increasing amount of the catalyst employed (at
least up to 0.4 g) is in agreement with the absence of mass diffu-
sion limitations. When 0.1 g of catalyst were used in the reaction,
the selectivity towards ethyl lactate was lower than that with a
35
30
25
R2=0.9874
20
15
10
5
0
Fig. 4 shows the dependence of catalytic activity and selectiv-
ity towards ethyl lactate on reaction time with TiSil-HPB-60. The
activity gradually increased with reaction time and tended to reach
a plateau after 5 h up to 24 h. Notably, the selectivity towards ethyl
lactate remained higher than 90% and no significant change was
observed as the reaction proceeds.
0.000
0.005
0.010
0.015
0.020
0.025
0.030
Ti/(Ti+Si)
Fig. 5. Conversion of DHA (as sum of the yields of all reaction products) as a function
of Ti content in TiSil-HPB-60 (as determined by EDX analysis). The conversions were
measured after reaction for 6 h at 90 ◦C.

K. Lin et al. / Catalysis Today 173 (2011) 89–94
93
100
90
80
70
60
50
40
30
20
10
0
In view of a possible industrial application, it is important to
evaluate the reusability of TiSil-HPB-60: for this purpose, the beads
were tested in several catalytic cycles. The recycling procedure for
TiSil-HPB-60 only implied four washings in ethanol at room tem-
perature without any calcination. It is worth noting that the bead
shape of TiSil-HPB-60 was unaffected by stirring during the cat-
alytic tests. The beads deposited automatically on the bottom of
the vial in a few seconds after stopping the stirring and, therefore,
could be easily separated from the reaction solution without cen-
trifugation or filtration, as observed in the epoxidations [17]. No
significant loss of catalytic activity was observed and the selectiv-
ity towards ethyl lactate remained approximately constant when
reusing TiSil-HPB-60 in three successive catalytic runs (Fig. 7),
proving the stability of this material under the employed reaction
and recycling conditions. This result also reveals that no deactiva-
tion due to adsorbed reaction residues occurs, probably thanks to
the large non-ordered mesopores that favor a rapid mass transport
of reaction residues away from the active titanium sites.
R2=0.9953
0.0
0.1
0.2
0.3
0.4
0.5
Amount of catalyst (g)
Fig. 6. Conversion of DHA (as sum of the yields of all reaction products) (ꢀ) and
selectivity towards ethyl lactate (᭹) as a function of the amount of TiSil-HPB-60
employed in the reaction. The conversions and selectivities were measured after
reaction for 6 h at 90 ◦C.
4. Conclusions
Titanosilicate beads with hierarchical porosity (TiSil-HPB-60)
are active and highly selective catalysts for the formation of ethyl
lactate from the triose sugar dihydroxyacetone. TiSil-HPB-60 is
more active than TS-1 and Ti-MCM-41 and more selective than het-
erogeneous catalysts containing Brønsted acid sites under the same
reaction conditions. The good activity and high selectivity towards
ethyl lactate and the ease of reuse demonstrate the potential of
TiSil-HPB-60 titanosilicate beads as catalyst in the conversion of
these renewable compounds to desirable chemicals. This versatile
catalyst is also superior to the other studied titanosilicates in the
epoxidation of cycloalkenes, while it displays lower activity than
TS-1 in the conversion of the linear 1-octene.
Table 3
Catalytic performances in the conversion of DHA with TiSil-HPB-60 at different
temperatures (of the reaction block).a
T (◦C)
YEL (%)
YAc (%)
YHe (%)
SEL (%)
75
90
105
15.5
29.6
47.5
1.0
0.6
1.2
3.1
0
0.3
79.1
97.9
97.0
a
For the reaction conditions, see Table 2.
higher amount of catalyst (0.2 and 0.4 g) and a higher amount of
ethyl hemiacetal of pyruvic aldehyde (1% yield) was observed, in
line with the role of hemiacetal as reaction intermediate and with
the lower selectivity at lower conversion previously observed with
other heterogeneous catalysts [23,32].
TiSil-HPB-60 showed higher lactate yield and selectivity at
higher reaction temperature (Table 3), in accordance with previous
results and with the hypothesis for which the lactate is the most
thermodynamically favorable product of the conversion of trioses
[23].
Acknowledgements
The authors acknowledge sponsoring in the frame of the fol-
lowing research programs: START1, CREA, Methusalem and CECAT
(K.U. Leuven, Flemish Government), SBO-BIPOM (IWT), IAP-PAI
(BELSPO, Federal Government), NoE IDECAT (EU) and GOA (Flem-
ish Government). We thank Walter Vermandel for assistance in
the measurements of NH3-TPD and for a helpful discussion on the
acid strength and Dr. Oleg I. Lebedev and Prof. Gustaaf Van Tende-
loo (University of Antwerpen) for the TEM analyses. KL is grateful
for National Natural Science Foundation of China (21003031) and
Open Project of State Key Laboratory of Urban Water Resource and
Environment, Harbin Institute of Technology (No. QA201021).
100
80
60
40
20
0
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and selectivities were measured after reaction for 6 h at 90 ◦C.

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