Sustainable production of acrolein: Effects of reaction variables, modifiers doping and ZrO2 origin on the performance of WO 3/ZrO2 catalyst for the gas-phase dehydration of glycerol

Article abstract of DOI:10.1039/c3ra46511j

Zirconia-supported tungsten oxide (WO₃/ZrO₂ or WZ) is known as an efficient catalyst for selective acrolein (AC) production from gas-phase dehydration of glycerol (GL). Two catalysts (WZ-CP and WZ-AN) were prepared herein using, respectively, a ZrO(OH)₂ hydrogel (ZrO(OH)₂-CP) and its derived alcogel (ZrO(OH)₂-AN) for a precursor of ZrO₂. To optimize the reaction variables and improve the catalyst performance, the WZ-CP catalyst was employed to show the effects of (A) reaction variables (temperature, partial pressures of GL and H₂O, and co-feeding H₂ or O₂); (B) catalyst modification with alkali and alkali earth metal ions (Na⁺, K⁺ and Mg ²⁺), or transition metals (Pt, Pd, Rh and Ni). The reaction at 315 °C always produced the highest AC selectivity, and this temperature was then used to investigate the effects of the other variables and catalyst modifications. Increasing the molar GL/H₂O ratio led to lower AC selectivity and accelerated the catalyst deactivation. Introducing 4-8 kPa O₂ to the reaction feed significantly reduced the catalyst deactivation rate but the AC selectivity was only slightly lowered. However, an addition of 4 kPa H₂ produced almost no effect on the reaction. The modified catalysts performed no better during the reaction unless the modifier was Pt or Pd, whose catalytic stabilities in the O₂-containing (4 kPa) feed were significantly higher and their selectivity for AC production slightly lowered. Working under the conditions optimized with WZ-CP, the WZ-AN catalyst offered a high AC yield (62-68%) for longer than 30 h, during which the GL conversion remained higher than 93%.

Full text of DOI:10.1039/c3ra46511j

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Sustainable production of acrolein: effects of
reaction variables, modifiers doping and ZrO2
origin on the performance of WO3/ZrO2 catalyst for
the gas-phase dehydration of glycerol
Cite this: RSC Adv., 2014, 4, 4619
*
Song-Hai Chai, Li-Zhi Tao, Bo Yan, Jacques C. Vedrine and Bo-Qing Xu
Zirconia-supported tungsten oxide (WO3/ZrO2 or WZ) is known as an efficient catalyst for selective
acrolein (AC) production from gas-phase dehydration of glycerol (GL). Two catalysts (WZ-CP and
WZ-AN) were prepared herein using, respectively, a ZrO(OH)2 hydrogel (ZrO(OH)2-CP) and its derived
alcogel (ZrO(OH)2-AN) for a precursor of ZrO2. To optimize the reaction variables and improve the
catalyst performance, the WZ-CP catalyst was employed to show the effects of (A) reaction variables
(temperature, partial pressures of GL and H2O, and co-feeding H2 or O2); (B) catalyst modification with
alkali and alkali earth metal ions (Na+, K+ and Mg2+), or transition metals (Pt, Pd, Rh and Ni). The
reaction at 315 ꢀC always produced the highest AC selectivity, and this temperature was then used to
investigate the effects of the other variables and catalyst modifications. Increasing the molar GL/H2O
ratio led to lower AC selectivity and accelerated the catalyst deactivation. Introducing 4–8 kPa O2 to
the reaction feed significantly reduced the catalyst deactivation rate but the AC selectivity was only
slightly lowered. However, an addition of 4 kPa H2 produced almost no effect on the reaction. The
modified catalysts performed no better during the reaction unless the modifier was Pt or Pd, whose
catalytic stabilities in the O2-containing (4 kPa) feed were significantly higher and their selectivity for AC
production slightly lowered. Working under the conditions optimized with WZ-CP, the WZ-AN catalyst
offered a high AC yield (62–68%) for longer than 30 h, during which the GL conversion remained
higher than 93%.
Received 30th August 2013
Accepted 2nd December 2013
DOI: 10.1039/c3ra46511j
www.rsc.org/advances
Ta2O5$yH2O32), mixed oxides,30 supported phosphoric acid,12,16
tungstated zirconia (WO3/ZrO2)16,25 and various hetero-
polyacids,15,16,18,19,21,23 have been investigated for the gas-phase
1. Introduction
Renewable resources like biomass have become increasingly
important in energy-related catalysis, as the depletion of non-
renewable fossil resources could happen in a few decades.1–3
Glycerol (GL), a co-product of the so-called biodiesel in natural
triglyceride methanolysis, is becoming an attractive feedstock
and viable building block for the synthesis of many other
chemicals due to its increasing production and declining
price.4–6 Acrolein (AC), an intermediate for acrylic acid, ber
treatment, medicine and other chemical products, can be
obtained from a catalytic selective double dehydration of GL,
providing a sustainable alternative to the present AC production
technology relied on petroleum-derived propylene.7–11 Much
research has consequently been conducted to investigate this
route of AC production from GL using either liquid or solid acid
catalysts.12–32 Various solid acid catalysts, including hydrated
niobium and tantalum oxides (Nb2O5$xH2O17 and
dehydration of aqueous GL but their catalytic performance were
not satisfactory. Some of these catalysts were reported to
produce an AC selectivity up to 60–80% but the reaction vari-
ables (like the space velocity of GL, concentration of GL in water
(or GL/H2O ratio), temperature, carrier or added gas, etc.) and
also the reaction time-on-stream (TOS) and even mass balance
were usually not calibrated or not in their optimized conditions,
making it difficult to comprehend the catalytic results reported
from different laboratories. For instance, WO3/ZrO2 was iden-
tied as a good catalyst for selective AC production from
aqueous GL.16,25 In our earlier work16 using an aqueous feed
containing a high concentration of GL (36.2 wt% or 10 mol%)
the AC selectivity was 60–71 mol% at 315 ꢀC and TOS ¼ 3–10 h
when the gas hourly space velocity of GL (GHSVGL) was 400 hꢁ1
25
¨
but in the work of Holderich et al. the AC selectivity was
ꢀ
64–72% at 280 C (TOS undened) using a 20 wt% (4.6 mol%)
aqueous GL as the reactant feed (GHSVGL ¼ 250 hꢁ1).
Innovative Catalysis Program, Key Lab of Organic Optoelectronics & Molecular
Engineering, Department of Chemistry, Tsinghua University, Beijing 100084, China.
E-mail: bqxu@mail.tsinghua.edu.cn; Fax: +86-10-62771149
In the present work, a WO3/ZrO2 catalyst (denoted as WZ-CP)
prepared by impregnation of
a conventionally prepared
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 4619–4630 | 4619

View Article Online
RSC Advances
Paper
ZrO(OH)2 hydrogel33,34 with aqueous (NH4)6H2W12O40 was
employed to optimize the reaction variables for the selective
production of AC by gas-phase dehydration of GL. The reaction
variables include temperature, partial pressures of GL and H2O,
and co-feeding gases (N2, H2 and O2). Modication of this
WZ-CP catalyst by doping with alkali or alkali earth ions (Na+, K+
or Mg2+), or transition metals (Pt, Pd, Rh or Ni) was also con-
ducted, attempting to improve catalyst performance. Another
WO3/ZrO2 catalyst (denoted as WZ-AN) was also prepared using
a ZrO(OH)2 alcogel (instead of the ZrO(OH)2 hydrogel)33,34 as the
precursor of ZrO2 for the reaction, considering that this WZ-AN
catalyst would have a narrower particle size distribution and
higher surface area in comparison to its counterpart WZ-CP.23
Our earlier uses of ZrO2-AN derived from the ZrO(OH)2 alcogel
as a support material have also led to superior H3PW12O40/ZrO2
catalyst for this GL dehydration reaction,22 Ni/ZrO2 for methane
reforming,33–37 WO3/ZrO2 for n-heptane isomerization38 and Au/
ZrO2 for CO oxidation.39
Table 1 Texture properties of the catalyst samples
BET surface area Pore volumeb Pore diameterc
Catalyst
(m2 gꢁ1
)
(cm3 gꢁ1
)
(nm)
WZ-CPa
WZ-ANa
78
115
0.09
0.30
0.08
—
0.09
0.09
0.09
0.09
0.08
—
4.2
9.2
4.5
—
4.7
4.6
4.7
4.7
4.6
—
0.05 wt% Na+/WZ-CP 75
0.1 wt% K+/WZ-CP
0.3 wt% K+/WZ-CP
0.1 wt% Mg+/WZ-CP
0.2 wt% Ni/WZ-CP
0.1 wt% Pt/WZ-CP
0.1 wt% Pd/WZ-CP
0.1 wt% Rh/WZ-CP
—
74
79
78
77
79
—
a
The loading of WO3 was 15 wt%, as determined by XRF analysis. b Pore
c
volume measured at P/P0 ¼ 0.995. Average pore diameter measured
from the desorption branch according to the BJH method.
Before the measurements, the samples were dehydrated under
vacuum at 200 ꢀC for 5 h. The results for each sample are
compared in Table 1.
2. Experimental
2.1 Catalyst preparation
The WZ-CP (WO3 loading: 15 wt%) catalyst with a BET
surface area of 78 m2 gꢁ1 and a pore volume of 0.09 cm3 gꢁ1
was prepared by impregnation of a ZrO(OH)2-CP hydrogel
with an aqueous solution of (NH4)6H2W12O40 (Shanghai
Chemical Reagent, AR), as in our previous study. Aer
removal of water in a rotary evaporator at 50–60 ꢀC, the
2.3 Catalytic reaction
The catalytic gas-phase dehydration reaction of GL was carried
out under atmospheric pressure in a vertical down-ow xed-
bed tubular quartz reactor (i.d. 9 mm, length 50 cm), which was
placed in the center of a tubular furnace in a height of 40 cm for
heating and temperature control.16,18,23 A constant volume
(0.63 cm3) of the catalyst bed was sandwiched in the middle of
the reactor with quartz wool. A layer of quartz sand (2 cm in
high, ca. 2 cm3) was placed above the catalyst to enable
complete evaporating the liquid feed. Prior to the reaction, the
catalyst was pretreated at 315 ꢀC for 1.5 h in owing dry
nitrogen (30 cm3 minꢁ1). The reaction feed, an aqueous solu-
tion of GL (36.2 wt% or 10 mol% GL unless otherwise specied
for investigating the GL partial pressure effect), was fed into the
reactor by a micro-pump, the gas hourly space velocity of GL was
GHSVGL ¼ 400 hꢁ1. The reaction was done rst in the temper-
ature range of 250–350 ꢀC to show the reaction temperature
effect and identify the temperature offering the maximum AC
selectivity. The temperature (315 ꢀC) identied as such was then
used for investigating effects of the other variables and perfor-
mance evaluation of the modied catalysts.
ꢀ
remaining powders were dried at 110 C overnight and then
calcined in owing air (50 cm3 minꢁ1) at 650 C for 4 h. The
ꢀ
WZ-AN sample (BET surface area: 115 m2 gꢁ1, pore volume:
0.30 cm3 gꢁ1) was prepared similarly by using a ZrO(OH)2
alcogel (ZrO(OH)2-AN) as an alternative of ZrO(OH)2-CP; the
WO3 loading was again 15 wt%, as in our earlier work.16 The
alcogel ZrO(OH)2-AN was prepared by extensive washing of
the hydrogel ZrO(OH)2-CP with anhydrous ethanol, as
detailed earlier.33,34
The Na+-, K+- and Mg2+-doped WO3/ZrO2 samples were
prepared by impregnation of WZ-CP with aqueous NaNO3,
KNO3 or Mg(NO3)2, respectively. The Pt-, Pd-, Rh- and Ni-
modied WO3/ZrO2 samples were prepared also by impregna-
tion of WZ-CP with aqueous H2PtCl6, PdCl2, RhCl3 or Ni(NO3)2,
respectively. Aer removal of the excess water, the remaining
powders were dried at 110 ꢀC overꢀnight and then calcined in
owing air (50 cm3 minꢁ1) at 500 C for 4 h. The loadings of
dopant or metal ions were 0.05 wt% for Na+, 0.1 and 0.3 wt% for
K+, 0.1 wt% for Mg2+, 0.1 wt% for Pt, Pd and Rh, and 0.2 wt% for
Ni, respectively. The calcined catalyst powders were pressed,
crushed, and sieved to 20–40 mesh (ca. 0.43–0.85 mm) before
they were charged to the reactor.
Each run of the reaction was conducted at least for 10 h,
during which the reaction products were condensed with an ice-
ꢀ
water trap (0 C) and collected hourly for off-line analysis on a
HP6890 GC equipped with a HiCap CBP20-S25-050 (Shimadzu)
capillary column (i.d. 0.32 mm
detector.16–18,32 The mass balance of the reaction was always
found higher than 95%, which was determined by comparing
the absolute weight of the hourly collected condensate from the
ꢂ
25 m) and a FID
2.2 Textural properties of the catalyst samples
Nitrogen adsorption and desorption isotherms were measured reactor with the weight of the reaction feed introduced hourly to
at ꢁ195 ꢀC on a Micromeritics ASAP 2010C instrument to the reactor, except during the initial 30 minutes of reaction.
determine the textural properties (BET surface areas, pore
The GL conversion and product selectivity data were calcu-
volumes and average pore diameters) of the catalyst samples. lated according to the following equations:16–18,32
4620 | RSC Adv., 2014, 4, 4619–4630
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
moles of glycerol reacted
glycerol conversion ð%Þ ¼
ꢂ 100
ꢂ 100
moles of glycerol in the feed
product selectivity ðmol%Þ ¼
moles of carbon in a product defined
moles of carbon in glycerol reacted
3. Results and discussion
3.1 Effects of reaction variables on the catalytic performance
of WZ-CP
3.1.1 Reaction temperature. Fig. 1 shows the effect of
reaction temperature on the catalytic performance of WZ-CP for
the GL dehydration reaction in the temperature range of
250–350 ꢀC. The data featured a decrease in the GL conversion
with TOS and an induction period (ca. 2–4 h) to develop the
selectivity for AC formation. Increasing the reaction tempera-
ture improved the initial GL conversion (TOS ¼ 0–1 h: 89% at
250 ꢀC, 94% at 270 ꢀC, 98% at 315 ꢀC and 99% at 350 ꢀC) but led
to unfortunately faster catalyst deactivation, as shown by the
much lower GL conversion levels at TOS ¼ 9–10 h. This could be
due to more severe carbon deposition over catalyst surface as
the reaction temperature increased.
It is also seen that the highest AC selectivityꢀwas always
obtained when the reaction temperature was 315 C (Fig. 1B).
ꢀ
Increasing the reaction temperature from 250 C to 315 ꢀC led
to an AC selectivity increase from 57 mol% to 62 mol% at TOS
Fig. 1 Effect of reaction temperature on the catalytic performance of
WZ-CP catalyst by the time courses of (A) GL conversion and (B) AC
selectivity. Rxn temp: , 250 ꢀC; , 270 ꢀC; , 315 ꢀC; , 350 ꢀC. (Other
conditions: 10 kPa GL, 90 kPa H2O, GHSVGL ¼ 400 hꢁ1).
¼ 0–1 h and 61 mol% to 64 mol% at TOS ¼ 9–10 h. However,
ꢀ
further increasing the reaction temperature to 350 C signi-
cantly lowered the AC selectivity (to below 60 mol%), probably
due to that the secondary reactions of AC, including the
decomposition, oligomerization, condensation with GL and
other products,17,20 occur more easier at higher temperatures.
The product distribution data shown in Table 2 indeed showed
that the selectivity for acetaldehyde and allyl alcohol
(secondary products) increased when the reaction temperature
the GL partial pressure between 6 and 37 kPa under the reaction
conditions; the balance carrier gas was solely H2O. As shown in
Fig. 2, increasing the GL partial pressure resulted in lowering
the GL conversion as well the AC selectivity but the catalyst
deactivation rate hardly changed. The highest AC selectivity was
72 mol%, which was obtained at TOS ¼ 2–4 h when the GL
partial pressure was 6 kPa; the lowest AC selectivity was 50 mol
%, which was obtained at TOS ¼ 9–10 h when the GL partial
pressure was 37 kPa (Fig. 2B).
ꢀ
25
¨
was raised from 315 to 350 C. Holderich et al. also reported
that the un-trapped products including CO and CO2 increased
with increasing the reaction temperature. It should be
ꢀ
mentioned, however, that 280 C was identied in the work of
Holderich et al. as the optimum temperature offering the
25
¨
The H2O partial pressure effect was investigated employing
pure GL (100%), 36.2 wt% and 25.4 wt% aqueous GL as the
reaction feeds and N2 as a balance gas. The variation in the GL
concentration changed the H2O partial pressure between 0 and
94 kPa under the reaction conditions. Increasing the H2O
partial pressure generally resulted in increasing the GL
conversion (Fig. 3A). The AC selectivity was improved signi-
cantly when the H2O partial pressure was increased to 54 kPa
(about a half of the total pressure) but became unchanged when
the H2O partial pressure increased further (Fig. 3B).
highest AC selectivity (68–72 mol%) over a 19 wt% WO3/ZrO2
catalyst, probably due to their using different catalyst prepa-
rations and other conditions for the reaction (GHSVGL: 162 hꢁ1
,
GL concentration: 20 wt% (4.7 mol%), TOS: undened, in
presence of 0.48 kPa O2).
We then decided to use the temperature of 315 ꢀC as a
standard reaction temperature in the other parts of this study
because this temperature produced the highest selectivity for
AC formation, regardless of the reaction time.
3.1.2 GL and H2O partial pressures. Aqueous GL with
different GL concentrations (25.4 wt%, 36.2 wt% and 75.0 wt%)
were employed as the reaction feeds for investigating the GL
pressure effect. The variation in the GL concentration changed
The similar time course behavior of the reaction, as judged
by comparing the variations of the GL conversion and AC
selectivity in Figs. 1–3, was generally not affected by the GL and
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 4619–4630 | 4621

View Article Online
RSC Advances
Paper
Table 2 Product distribution of catalytic dehydration of aqueous GL over WZ-CP catalyst at different temperaturesa
Product selectivity (mol%)
Rxn temp. (ꢀC)
TOS (h)
GL conv. (%)
Acrolein
Acetal-dehyde
Allyl alcohol
1-Hydroxy-acetone
Othersb
250
270
315
350
1–2
9–10
1–2
9–10
1–2
9–10
1–2
82
34
85
20
77
15
75
10
64.0
61.0
68.0
63.0
71.0
64.0
60.0
54.0
0.5
0.3
1.0
0.3
3.0
3.0
4.0
6.0
0.6
0.4
0.6
0.5
1.0
2.0
1.0
2.0
P
6.0
9.1
9.0
10.0
10.0
17.0
9.0
28.9
29.2
21.4
26.2
15.0
14.0
26.0
23.0
9–10
15.0
Catalyst load: 0.63 ml (0.80 g); GHSVGL: 400 hꢁ1
.
Selectivity for the others (mol%) ¼ 100 ꢁ (selectivity for each listed products).
a
b
involving AC, such as condensation and oligomerization that
would lead to formation of carbonaceous deposits on the
catalyst surface. Other possible reasons for the requirement of
sufficient water for more selective production of AC could be
associated with a modication of the catalyst acidity by water.
The presence of enough amount of water would compete with
precursors of carbonaceous deposits (including the reacting GL
Fig. 2 Effect of GL partial pressure on the catalytic performance of
WZ-CP catalyst at 315 ꢀC by the time courses of (A) GL conversion and
(B) AC selectivity. GL partial pressure: , 6 kPa; , 10 kPa; , 37 kPa.
Other conditions: H2O (steam) balance, GHSVGL ¼ 400 hꢁ1
.
H2O partial pressures, not to mention no change in the induc-
tion period (2–4 h) for developing the AC selectivity.
However, both sets of data in Figs. 2 and 3 apparently
demonstrate that the existence of a sufficient amount of water
(steam) was essential to improve the selectivity for AC forma-
tion. The presence of a sufficient high H2O partial pressure
Fig. 3 Effect of H2O partial pressure on the catalytic performance of
WZ-CP catalyst at 315 ꢀC by the time courses of (A) GL conversion and
(B) AC selectivity. H2O partial pressure: , 94 kPa; , 54 kPa; , none.
could inhibit undesirable secondary bimolecular reactions Other conditions: 6 kPa GL, N2 balance, GHSVGL ¼ 400 hꢁ1
.
4622 | RSC Adv., 2014, 4, 4619–4630
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
molecules) for adsorption on those very strong acidic sites (e.g.,
with Hammett acidity function of H0 # ꢁ8.2) on the WZ cata-
lyst,40,41 weakening their acidity to favor GL activation for
selective dehydration to form AC. On the one hand, water
interaction with Lewis acidic sites40,42 could result in trans-
formation of a signicant part of the latter into Brønsted acidic
sites, which were required for the selective catalysis towards
the formation of AC.16,17,41 Water (steam) inhibition on forma-
tion of surface carbonaceous deposits has also been well
known in many other acid-catalyzed alcohol conversions such
as methanol to olen/gasoline and bioethanol to ethene/
gasoline.42–44
As high GL pressure and low H2O pressure would lead to
lower AC selectivity and more rapid catalyst deactivation, the GL
and H2O partial pressures were kept constant at 6 kPa and
54 kPa, respectively, in our hereaer investigation of the effects
of co-feeding gases and catalyst modications unless specied
otherwise.
3.1.3 Co-feeding gases: H2 and O2. Fig. 4 shows the effects
of co-feeding H2 and O2 on the GL conversion and AC selectivity
at 315 ꢀC over the WZ-CP catalyst. The partial pressure of the co-
feeding gas was kept at 4 kPa; the other components in the
reaction feed were 6 kPa GL and 54 kPa H2O (N2 balance). The
co-feeding of H2 had almost no effect on the catalyst perfor-
mance; both the GL conversion and AC selectivity were not
changed during the reaction up to TOS ¼ 10 h. As shown in
Table 3, the co-feeding of H2 had also no inuence on the
selectivity data of by-products such as 1-hydroxyacetone, acet-
aldehyde and allyl alcohol.
Barton et al.45 observed that a co-feeding of H2 had a positive
effect on the isomerization of o-xylene over a WOx-ZrO2 cata-
lyst, due to that H2 activation by dissociative adsorption on
Lewis acidic WOx clusters on the catalyst surface could
generate Brønsted acidic sites stemming from electron delo-
calization at the activated H atoms. This seems therefore
contradictory to the present observation that the co-feeding of
Fig. 4 Effects of co-feeding H2 and O2 on the catalytic performance
of WZ-CP catalyst at 315 ꢀC by the time courses of (A) GL conversion
and (B) AC selectivity. Co-feeding gas: , none; , 4 kPa H2; , 4 kPa
O2. Other conditions:
6 kPa GL, 54 kPa H2O, N2 balance,
GHSVGL ¼ 400 hꢁ1
.
H2 did not improve the selectivity for AC formation because However, no attempt was made to optimize the O2 partial pres-
Brønsted acidic sites would be advantageous over Lewis acidic sure for AC production in these earlier documentations.
ones in catalyzing the selective synthesis of AC from GL
To understand if there would be an optimized O2 partial
dehydration.17,46 A reasonable explanation for this contradic- pressure for AC production from the aqueous GL over WZ-CP
tion would be that the co-presence of a much higher H2O catalyst, we further investigated the effect of O2 partial pressure
pressure (54 kPa) during the present reaction could be more change (from 4 to 24 kPa) on the catalyst performance. As
effective in inducing the transformation of Lewis acidic sites to shown in Fig. 5, the catalyst performance appeared not
Brønsted acid ones.
changed essentially when the O2 partial pressure was increased
Unlike the case of co-feeding H2, a co-feeding of O2 signi- from 4 to 8 kPa; the feature was that the presence of these
cantly improved the catalyst stability with only a little loss in the amounts of O2 signicantly reduced the catalyst deactivation
AC selectivity (from 70 mol% to 67 mol%); the GL conversion rate without sacricing the selectivity for AC production,
remained at 100% for up to TOS ¼ 5 h and was kept as high as actually the AC selectivity data at TOS $ 7 h being equal or even
56% at TOS ¼ 10 h. To the contrary, a co-feeding of 2.78 kPa O2 higher than that in the case without presence of O2. The AC
into an aqueous GL (20 wt%) feed in ref. 25 declined the GL selectivity was, however, dramatically declined (to 25 mol%) on
conversion but improved the AC selectivity. Wang et al.26,29 increasing the O2 partial pressure from 8 to 12 kPa though the
observed, however, that both the GL conversion and AC selec- GL conversion was always kept at 100% during the reaction up
tivity were increased when the GL dehydration reaction over a to TOS ¼ 10 h. And, a further increasing of the O2 partial
vanadium phosphate oxide (VPO) catalyst was carried out in the pressure to 24 kPa still declined the AC selectivity to no more
presence of 1.7–18.3 kPa O2, due to that the presence of O2 would than 8 mol%.
help to keep the vanadium in its oxidized state that was required
As shown in Table 3, however, the dramatic loss of AC
to maintain the catalyst acidity for selective AC production. selectivity on increasing the O2 partial pressure to higher than 8
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 4619–4630 | 4623

View Article Online
RSC Advances
Paper
Table 3 Effects of co-feeding gases on the product distribution of catalytic dehydration of aqueous GL over WZ-CP catalysta
Product selectivity (mol%)
TOS
(h)
GL conv.
(%)
Carbon depositsc
Co-feeding gas
Acrolein
Acetal-dehyde
Allyl alcohol
1-Hydroxy-acetone
Othersb
(mg gꢁ1 catꢁ1
)
40 kPa N2
1–2
9–10
1–2
9–10
1–2
9–10
1–2
9–10
1–2
9–10
1–2
89
13
90
12
100
56
100
58
100
100
100
100
70.0
63.0
68.0
64.0
67.0
66.0
63.0
63.0
24.0
25.0
3.0
5.0
3.0
4.0
3.0
6.0
3.0
10.0
5.0
9.0
10.0
5.0
7.0
1.0
2.0
1.0
1.0
0
1.0
0
1.0
0
7.0
15.0
10.0
13.0
5.0
6.0
1.0
3.0
0
17.0
17.0
17.0
19.0
22.0
24.0
26.0
28.0
67.0
65.0
92.0
86.0
P
90
88
89
86
52
29
4 kPa H2 + 36 kPa N2
4 kPa O2 + 36 kPa N2
8 kPa O2 + 32 kPa N2
12 kPa O2 + 28 kPa N2
24 kPa O2 + 16 kPa N2
0
0
0
0
0
0
9–10
7.0
a
b
Catalyst load: 0.63 ml (0.80 g); rxn temp.: 315 ꢀC; GHSVGL: 400 hꢁ1
.
Selectivity for the others (mol%) ¼ 100 ꢁ (selectivity for each listed
products). c Carbon deposits accumulated aer reaction for 10 h.
On the other hand, the amounts of carbon deposits on the
surface of the catalysts that had served the reaction for 10 h, as
determined by temperature-programmed oxidation (TPO)
measurements, were 90, 88, 86, 52 and 29 mg g catꢁ1 when the
O2 partial pressure was 0, 4, 8, 12 and 24 kPa, respectively
(Table 3). These data feature a clear function of O2 in sup-
pressing formation of the carbon deposits and/or their precur-
sors. The signicantly lowered formation of the carbon deposits
would be responsible for the improved catalyst stability for the
GL conversion when O2 partial pressure was higher than 8 kPa
(Fig. 5). On randomly checking the gas composition at the exit
of the ice-water trap, we noticed that the amount of un-
condensed or un-trapped gas products (mainly CO2 and CO)
increased with increasing the O2 partial pressure, especially
when the O2 partial pressure was higher than 8 kPa. It is
therefore that the steady and dramatic declines of the product
selectivity with increasing the O2 partial pressure (Table 3)
should be due to that the GL dehydration reaction under these
high O2 partial pressures was heavily coupled with oxygen-
involving combustion reactions of the surface intermediates
and products from GL dehydration, including AC and its
surface precursor.
The above investigation of the O2 partial pressure effect on
AC production from the GL dehydration reaction discloses that
the optimum O2 partial pressure would be between 4 and 8 kPa,
under which deactivation of the WZ-CP catalyst can be
inhibited greatly without losing the long-term selectivity for AC
production (Fig. 5). We then made a re-investigation of the
temperature effect on the GL dehydration reaction using the
feed composition of 6 kPa GL, 54 kPa H2O, 4 kPa O2 and 36 kPa
Fig. 5 Effect of O2 partial pressure on the catalytic performance of
WZ-CP catalyst at 315 ꢀC by the time courses of (A) GL conversion and
N2 (balance), the space velocity of GL was again GHSVGL
¼
(B) AC selectivity. O2 partial pressure: , none; , 4 kPa O2; , 8 kPa;
,
400 hꢁ1. The catalytic data (Fig. 6) again featured an induction
period of 2–4 h for developing the selectivity for AC production
and gradual decrease with TOS of the GL conversion unless the
reaction temperature was 350 or 365 ꢀC, at which the GL
12 kPa; , 24 kPa. Other conditions: 6 kPa GL, 54 kPa H2O, N2 balance,
GHSVGL ¼ 400 hꢁ1
.
kPa was also accompanied by loss of ally alcohol and 1- conversion remained at 100% up to TOS ¼ 10 h. As it would be
hydroxyacetone; they became even lower than the detection expected, increasing the reaction temperature from 300 to
ꢀ
limit of the GC analysis under the higher O2 partial pressures. 365 C resulted in continued increment in the GL conversion
4624 | RSC Adv., 2014, 4, 4619–4630
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
levels at longer TOS though the initial conversion levels were
complete at every temperature. However, the highest AC
selectivity was again obtained when the reaction was con-
ꢀ
ducted at 315 C. This observation is similar to the preceding
results presented in Fig. 1, where the reaction was conducted
with aqueous GL (10 kPa GL and 90 kPa H2O) without addition
of any other component, and gives a piece of further evidence
ꢀ
to support the use of 315 C as our standard reaction temper-
ature for the study of GL dehydration reaction for AC
production.
3.2 GL dehydration over the modied WZ-CP catalysts
3.2.1 Modication by Na+, K+ and Mg2+ ions. Fig. 7
compares the catalytic performance of WZ-CP and its modied
counterparts involving 0.05 wt% Na+, 0.1 wt% and 0.3 wt% K+
and 0.1 wt% Mg2+, using the reaction variables optimized in the
preceding section as the standard reaction conditions, i.e., at
315 ꢀC with a feed composition of 6 kPa GL, 54 kPa H2O, 4 kPa
O2 and 36 kPa N2 (balance). The main features of the GL
dehydration reaction over these modied catalysts were similar
to those of their un-modied catalyst (WZ-CP). Specically, the
GL conversion over these catalysts varied in the following order
Fig. 7 Performance under the presence of 4 kPa O2 at 315 ꢀC of WZ-
CP catalysts doped with alkali and alkali earth ions by the time courses
of (A) GL conversion and (B) AC selectivity. Dopant: , none; , 0.05 wt
% Na+; , 0.1 wt% K+; , 0.3 wt% K+; , 0.1 wt% Mg2+. Other conditions:
6 kPa GL, 54 kPa H2O, N2 balance, GHSVGL ¼ 400 hꢁ1
.
according to the nature and content of the dopant: unmodied
> 0.1 wt% K+ > 0.05 wt% Na+ > 0.1 wt% Mg2+ > 0.3 wt% K+,
showing that the doping with alkali and alkali earth ions even
made the catalyst deactivate faster. For the production of AC,
however, the modied catalysts appeared at least no more
selective than the unmodied WZ-CP catalyst; over the sample
with a relatively high loading of K+ (0.3 wt%), the AC selectivity
was reduced to ca. 60 mol% from that over the unmodied WZ-
CP (ca. 68 wt%). The modication with alkali and alkali earth
ions slightly improved the production of acetaldehyde at the
early stage (TOS # 2 h) and of 1-hydroxyacetone at later stage of
the reaction (TOS ¼ 9–10 h); the amount of “others” also
increased signicantly when loading of K+ was increased to 0.3
wt% (Table 4). Therefore, the modication with alkali and alkali
earth ions of the WZ-CP catalyst did not result in improvements
in the catalytic performance.
3.2.2 Modication by transition metals (Pt, Pd, Rh and Ni).
Fig. 8 compares the catalytic performance of WZ-CP and its
modied counterparts involving different transition metals
(0.2 wt% Ni, 0.1 wt% Pt, 0.1 wt% Pd and 0.1 wt% Rh) under the
standard reaction conditions. The modication with Pt and
Pd improved the catalyst stability according to the time course
Fig. 6 Effect of reaction temperature on the catalytic performance of
WZ-CP catalyst under the presence of 4 kPa O2 by the time courses of
(A) GL conversion and (B) AC selectivity. Rxn temp: , 300 ꢀC; , 315 ꢀC;
, 330 ꢀC; , 340 ꢀC; , 350 ꢀC; , 365 ꢀC. Other conditions: 6 kPa GL,
54 kPa H2O, N2 balance, GHSVGL ¼ 400 hꢁ1
.
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 4619–4630 | 4625

View Article Online
RSC Advances
Paper
of the GL conversion but the AC selectivity was reduced by ca. selectivity are compared in Fig. 9. Apparently, the modication
6–8%, from 68 mol% over un-modied catalyst to 62 mol% with the transition metals produced no positive effect on both
and 64 mol% over the ones modied with Pd and Pt, respec- the catalytic stability or on the AC selectivity. On the other
tively. However, the Ni-modied sample showed essentially hand, H2 substitution of O2 in the standard reaction condi-
the same time courses for both the GL conversion and AC tions resulted in formation of much more 1-hydroxyacetone
selectivity. On the other hand, modication with Rh reduced and lesser acetaldehyde over these transition metals modied
the catalyst stability and also the selectivity for AC production catalysts (Table 4). Consequently, the production of the
during the reaction; the GL conversion declined to ca. 44% “others” became signicantly lowered.47 It should be
and the AC selectivity 52 mol% at TOS ¼ 9–10 h. To make a mentioned that the amount of carbon deposits formed over
ranking, the GL conversion over these transition metals the used catalysts (reacted for 10 h) appeared not affected by
modied WZ-CP catalysts under the standard reaction the presence of any modier; the amount was between 79 and
conditions (at 315 ꢀC in feed composition of 6 kPa GL, 54 kPa 93 mg g catꢁ1 for all catalysts including the unmodied
H2O, 4 kPa O2 and 36 kPa N2) was in the order of: 0.1 wt% Pt > WZ-CP.
0.1 wt% Pd > no-modication z0.2 wt% Ni > 0.1 wt% Rh
A referee of this paper questioned if a higher concentration
while the ranking of the AC selectivity was no-modication of Pt or Pd (>0.1 wt%) would result in a higher selectivity of
z0.2 wt% Ni > 0.1 wt% Pt > 0.1 wt% Pd > 0.1 wt% Rh. As seen acrolein. The answer was negative as an increase of Pt loading
in Table 4, the modication with these transition metals from 0.1 wt% to 0.5 wt% in the Pt-modied WZ-AC catalyst not
resulted in the formation of lesser 1-hydroxyacetone but more only led to slightly decreased AC selectivity but also caused
acetaldehyde and “others”.
more signicant catalyst deactivation, regardless of the addi-
In order to investigate if the modication with the transi- tion of 4 kPa O2 or 4 kPa H2 (data not shown).
tion metals of the WZ-CP catalyst would improve the catalytic
In summary, the modication with alkali and alkali earth
performance in presence of H2, the modꢀied catalysts were metal ions or transition metals of the WZ-CP catalyst generally
pretreated with a ow of 5% H2/Ar at 315 C for 2 h and then did not result in consistent improvements in the catalyst
evaluated by conducting the GL dehydration reaction under stability and selectivity for AC production. However, the cata-
the conditions where the 4 kPa O2 gas in the standard reaction lysts modied with Pt or Pd signicantly inhibited under the
conditions was substituted with 4 kPa H2; the time courses of standard reaction conditions the catalyst deactivation, at the
the catalytic reaction for both the GL conversion and AC expense of a minor lowering of the AC selectivity.
Table 4 Product distribution of catalytic dehydration of aqueous GL over modified WZ-CP catalystsa
Product selectivity (mol%)
TOS
(h)
GL conv.
(%)
Carbon depositsc
Catalyst modier
0.1 wt% K+
Acrolein
Acetal-dehyde
Allyl alcohol
1-Hydroxy-acetone
Othersb
(mg gꢁ1 catꢁ1
)
1–2
9–10
1–2
9–10
1–2
9–10
1–2
9–10
1–2
9–10
1–2
9–10
1–2
9–10
1–2
9–10
1–2
9–10
1–2
9–10
1–2
9–10
1–2
100
50
100
47
100
44
99
40
100
52
100
89
100
79
99
44
86
10
82
9
65.0
62.0
65.0
62.0
67.0
62.0
60.0
55.0
67.0
65.0
64.0
64.0
62.0
62.0
58.0
52.0
69.0
64.0
60.0
63.0
68.0
64.0
69.0
63.0
7.0
3.0
10.0
5.0
10.0
4.0
8.0
2.0
10.0
5.0
13.0
7.0
11.0
6.0
8.0
8.0
4.0
4.0
4.0
3.0
4.0
3.0
6.0
3.0
0.1
0.2
0.1
1.0
0.1
1.0
0.3
1.0
0
1.0
0
1.0
0
1.0
0.2
1.0
1.0
3.0
1.0
3.0
2.0
3.0
2.0
3.0
0.4
7.0
0.3
10.0
0.6
9.0
2.2
9.0
0
3.0
0
1.0
1.0
2.0
2.0
2.0
10.0
24.0
10.0
17.0
11.0
20.0
11.0
20.0
27.5
27.8
24.6
22
91
93
88
86
88
83
79
91
90
93
93
93
0.05 wt% Na+
0.1 wt% Mg2+
0.3 wt% K+
22.3
24.0
29.5
33.0
23.0
26.0
23.0
27.0
26.0
29.0
31.8
37.0
16.0
5.0
25.0
14.0
15.0
10.0
12.0
11.0
0.2 wt% Ni
0.1 wt% Pt
0.1 wt% Pd
0.1 wt% Rh
0.2 wt% Nid
0.1 wt% Ptd
0.1 wt% Pdd
0.1 wt% Rhd
79
9
78
9
9–10
a
Catalyst load: 0.63 ml (0.80 g); rxn temp: 315 ꢀC; pressures: 6 kPa GL + 54 kPa H2O + 4 kPa O2 + 36 kPa N2. b Selectivity for the others (mol%) ¼ 100
P
ꢁ
(selectivity for each listed products). c Carbon deposits accumulated aer reaction for 10 h. d Pressures: 6 kPa GL + 54 kPa H2O + 4 kPa H2 +
36 kPa N2.
4626 | RSC Adv., 2014, 4, 4619–4630
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
Fig. 9 Performance under the presence of 4 kPa H2 at 315 ꢀC of
WZ-CP catalysts modified by transition metals by the time courses of
(A) GL conversion and (B) AC selectivity. Modifier: , none; , 0.2 wt%
Ni; , 0.1 wt% Pt; , 0.1 wt% Pd; , 0.1 wt% Rh. Other conditions: 6 kPa
Fig. 8 Performance under the presence of 4 kPa O2 at 315 ꢀC of
WZ-CP catalysts modified by transition metals by the time courses of
(A) GL conversion and (B) AC selectivity. Modifier: , none; , 0.2 wt%
Ni; , 0.1 wt% Pt; , 0.1 wt% Pd; , 0.1 wt% Rh. Other conditions: 6 kPa
GL, 54 kPa H2O, N2 balance, GHSVGL ¼ 400 hꢁ1
.
GL, 54 kPa H2O, N2 balance, GHSVGL ¼ 400 hꢁ1
.
would be lies in the dispersed monotungstate (isolated WOx)
and polytungstate [(WOx)y] species when the surface density of
WO3 is below its monolayer threshold (<4.5 W nmꢁ2), form
nanoparticles (or nano-WO3) when the density is beyond this
3.3 Effect of support (ZrO2) origin on the performance of WZ
catalyst
The WZ-AN sample prepared by using the alcogel ZrO(OH)2- threshold but below 9.0 W nmꢁ2, and evolve to bulk-like WO3
AN as the precursor of ZrO2 was not involved in the above polycrystals when the density become still higher (>9 W
investigations. We now show in Fig. 10 a comparison of the nmꢁ2).48,49 We assume that those well dispersed mono-
catalytic performance between this WZ-AN and the un-modi- tungstate (isolated WOx) and polytungstate [(WOx)y] species
ed WZ-CP. The reaction was conducted at 315 ꢀC with the are responsible for the superior catalytic stability of the WZ-
aqueous GL (36.2 wt% or 10 mol% GL) as the feed without AN catalyst, which is in line with the literature observations of
addition of any gas. The catalyst WZ-AN clearly appeared similar catalysts, WO3/ZrO2, WO3/TiO2 and WO3/Nb2O5, in
superior to WZ-CP by featuring a much higher catalytic catalyzing the dehydration of methanol for dimethyl ether
stability during the reaction though no signicant difference production.49 Also, we demonstrated earlier that ZrO2-sup-
in the AC selectivity was observed over both catalysts. This ported 12-tungstophosphoric acid (H3PW12O40) catalyst would
superiority of the WZ-AN catalyst could be due to its signi- show the best catalytic performance for AC production from
cantly higher surface area (115 m2 gꢁ1) and pore volume aqueous GL under conditions similar to this present study
(0.30 cm3 gꢁ1), compared to those (78 m2 gꢁ1 and 0.09 cm3 when the surface density of Keggin-anion (PW12O403ꢁ) was in
gꢁ1) for WZ-CP (Table 1). Thus, WO3 entities in the WZ-AN the range of 0.20–0.45 per square nanometer,23 which corre-
sample would show a higher dispersion; for reference, the sponding to 2.4–5.4 W nmꢁ2
calculated surface density of W atom was 3.4 per square We further investigated the effect of reaction temperature on
.
nanometer in WZ-AN while it was 5.0 per square nanometer in the GL dehydration over this superior WZ-AN catalyst, also
WZ-CP. It has been known that WO3 entities on ZrO2 support using the aqueous GL (36.2 wt% or 10 mol% GL) as the feed
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 4619–4630 | 4627

View Article Online
RSC Advances
Paper
Fig. 10 Performance at 315 ꢀC of ( ) WZ-CP and ( ) WZ-AN catalysts
by the time courses of (A) GL conversion and (B) AC selectivity. Other Fig. 11 Effect of reaction temperature on the catalytic performance of
conditions: 10 kPa GL, 90 kPa H2O, GHSVGL ¼ 400 hꢁ1
.
WZ-AN catalyst by the time courses of (A) GL conversion and (B) AC
selectivity. Rxn temp: , 280 ꢀC; , 300 ꢀC; , 315 ꢀC; , 350 ꢀC. Other
conditions: 10 kPa GL, 90 kPa H2O, GHSVGL ¼ 400 hꢁ1
.
without addition of any gas; the results are given in Fig. 11.
Clearly, the effect of reaction temperature on the AC selectivity
over this WZ-AN was qualitatively similar to that of WZ-CP
(Fig. 1), conrming that the reaction was most selective for AC
production at 315 ꢀC; quantitatively, the highest AC selectivity at
TOS ¼ 9–10 h increased to 72 mol% over this WZ-AN from
64 mol% over its counterpart WZ-CP catalyst. However, this
WZ-AN catalyst also exhibited at 315 ꢀC the best catalytic
stability, which was in contrast to performance of the WZ-CP
catalyst whose deactivation rate increased in Fig. 1 with
increasing the reaction temperature in the investigated
further conrm that WZ-AN was a more superior catalyst to
WZ-CP for the gas-phase dehydration of GL for the selective
production of AC.
ꢀ
temperature range (270–350 C).
The WZ-AN catalyst was nally evaluated using the standard
reaction conditions (at 315 ꢀC in the feed composition of 6 kPa
GL, 54 kPa H2O, 4 kPa O2 and 36 kPa N2); the results are
compared in Fig. 12 with those of WZ-CP. Although both cata-
lysts showed similar selectivity for production of the desired AC
(66–68 mol%), the GL conversion could remain at 100% for
longer than 20 h over the WZ-AN catalyst, which demonstrates a
distinctly higher catalytic stability than its WZ-CP counterpart.
The GL conversion and AC selectivity remained at 93% and
67 mol%, respectively, even when the reaction was extended to
longer than 30 h, marking a record for making the AC yield
Fig. 12 Performance of ( and ) WZ-CP and ( and ) WZ-AN cata-
lysts by the time courses of (open symbol) GL conversion and (solid
symbol) AC selectivity, under the standard reaction conditions: 315 ꢀC,
higher than 62% for more than 30 h. These data therefore 6 kPa GL, 54 kPa H2O, 4 kPa O2, N2 balance, GHSVGL ¼ 400 hꢁ1
.
4628 | RSC Adv., 2014, 4, 4619–4630
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
´
´
´
Aer being reacted for 30 h, the WZ-AN catalyst was switꢀched
4 I. Dıaz, C. Marquez-Alvarez, F. Mohino, J. Perez-Pariente and
to a ow of dry air (30 ml minꢁ1) and then heated to 550 C to
“oxidize” the used catalyst for 5 h. This air-treatment appeared
to be long enough to completely regenerate the reacted WZ-AN
to its fresh state because a reuse of the air-treated catalyst for
the dehydration of GL under the standard reaction conditions
for another 30 h produced essentially the same results as of the
fresh WZ-AN. These results would have important implication
in application.
E. Sastre, J. Catal., 2000, 193, 295.
5 T. Miyazawa, Y. Kusunoki, K. Kunimori and K. Tomishige,
J. Catal., 2006, 240, 213.
6 J. M. Clacens, Y. Pouilloux and J. Barrault, Appl. Catal., A,
2002, 227, 181.
7 E. Schwenk, M. Gehrke and F. Aichner, US Pat., 1,916,743, to
A.-G. Scheering-Kahlbaum, 1933.
8 H. Adkins and W. H. Hartung, Organic Syntheses Coll., 1941,
1, 15.
9 S. Ramayya, A. Brittain, C. DeAlmeida, W. Mok and
M. J. Antal Jr, Fuel, 1987, 66, 1364.
4. Conclusions
10 M. J. Antal Jr, W. S. L. Mok and G. N. Richards, Carbohydr.
Res., 1990, 199, 111.
11 T. Hass, A. Neher and D. Arntz, US. Pat., 5,426,249, 1995.
12 A. Neher, T. Haas, D. Arntz, H. Klenk and W. Girke, US. Pat.,
5,387,720, 1995.
13 L. Ott, M. Bicker and H. Vogel, Green Chem., 2006, 8, 214.
14 M. Watanabe, T. Iida, Y. Aizawa, T. M. Aida and H. Inomata,
Bioresour. Technol., 2007, 98, 1285.
15 E. Tsukuda, S. Sato, R. Takahashi and T. Sodesawa, Catal.
Commun., 2007, 8, 1349.
16 S.-H. Chai, H.-P. Wang, Y. Liang and B.-Q. Xu, Green Chem.,
2007, 9, 1130.
17 S.-H. Chai, H.-P. Wang, Y. Liang and B.-Q. Xu, J. Catal., 2007,
250, 342.
18 S.-H. Chai, H.-P. Wang, Y. Liang and B.-Q. Xu, Green Chem.,
2008, 10, 1087.
19 H. Atia, U. Armbruster and A. Martin, J. Catal., 2008, 258, 71.
20 A. Corma, G. W. Huber, L. Sauvanaud and P. O'Connor,
J. Catal., 2008, 257, 163.
This work provides a comprehensive investigation on effects of
the reaction variables on the performance of WO3/ZrO2 catalyst
for the selective production of AC from the gas-phase dehy-
dration of aqueous GL under atmospheric pressure. When the
GL feeding rate (space velocity) was invariant (e.g., GHSVGL
¼
400 hꢁ1), the temperature, molar GL/H2O ratio and concentra-
tion of O2 in the feed were shown as the important variables for
the reaction. The most favorable reaction temperature was
ꢀ
identied as 315 C as the reaction at this temperature always
offered the highest AC selectivity. A higher partial pressure of
H2O was also favorable for producing a higher selectivity for AC
formation as H2O (steam) in the reaction system could serve to
inhibit undesirable secondary bimolecular reactions involving
AC. However, a molar GL/H2O ratio of 1/9 was found sufficient
low for this purpose because a further lowing of the ratio to GL/
H2O < 1/15 only led to a little further increase in the AC selec-
tivity. The presence of a small amount of O2 (4–8 kPa) in the
reaction feed would signicantly inhibit the catalyst deactiva-
tion with a little reduction of the AC selectivity.
The modication with alkali and alkali earth metal ions, and
transition metals of WO3/ZrO2 catalyst did not result in
improvements in the catalyst stability and selectivity for AC
production unless Pt or Pd was used as the modier, whose
modication resulted in signicantly improved catalytic
stability in the O2-containing (4 kPa) feed. Moreover, precursor
of the ZrO2 support was also found to be a key to the catalytic
performance of WO3/ZrO2. The catalyst prepared by using a
ZrO(OH)2 alcogel as the precursor showed much superior
catalytic performance to that prepared employing a conven-
tional ZrO(OH)2 hydrogel as the precursor of ZrO2, making it
possible to produce the desired AC with a yield higher than 62%
for longer than 30 h.
21 L. Ning, Y. Ding, W. Chen, L. Gong, R. Lin, Y. Lu and Q. Xin,
Chin. J. Catal., 2008, 29, 212.
22 Y. Wei and S. Galen, Ind. Eng. Chem. Res., 2009, 48, 3279.
23 S.-H. Chai, H.-P. Wang, Y. Liang and B.-Q. Xu, Appl. Catal., A,
2009, 353, 213.
24 Q.-B. Liu, Z. Zhang, Y. Du, J. Li and X.-G. Yang, Catal. Lett.,
2009, 127, 419.
¨
25 A. Ulgen and W. Holderich, Catal. Lett., 2009, 131, 122.
26 F. Wang, J.-L. Dubois and W. Ueda, J. Catal., 2009, 268, 260.
¨
27 C.-J. Jia, Y. Liu, W. Schmidt, A.-H. Lu and F. Schuth, J. Catal.,
2010, 269, 71.
28 Y.-T. Kim, K.-D. Jung and E.-D. Park, Microporous Mesoporous
Mater., 2010, 131, 28.
29 F. Wang, J.-L. Dubois and W. Ueda, Appl. Catal., A, 2010, 376,
25.
30 L.-Z. Tao, S.-H. Chai, Y. Zuo, W.-T. Zheng, Y. Liang and
B.-Q. Xu, Catal. Today, 2010, 158, 310.
31 A. Alhanash, E. F. Kozhevnikova and I. V. Kozhevnikov, Appl.
Catal., A, 2010, 378, 11.
Acknowledgements
This work is partly supported by NSF of China (grant: 2103304).
32 L.-Z. Tao, B. Yan, Y. Liang and B.-Q. Xu, Green Chem., 2013,
15, 696.
References and note
33 B.-Q. Xu, J.-M. Wei, Y.-T. Yu, J.-L. Li and Q.-M. Zhu, Top.
Catal., 2003, 22, 77.
1 D. L. Klass, Biomass for Renewable Energy, Fuels and
Chemicals, Academic Press, San Diego, 1998.
34 B.-Q. Xu, J.-M. Wei, Y.-T. Yu, Y. Li, J.-L. Li and Q.-M. Zhu,
J. Phys. Chem. B, 2003, 107, 5203.
2 H. Van Bekkum and P. Gallezot, Top. Catal., 2004, 27, 1.
3 G. W. Huber and J. A. Dumesic, Catal. Today, 2006, 111, 119.
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 4619–4630 | 4629

View Article Online
RSC Advances
Paper
35 Q.-H. Zhang, Y. Li and B.-Q. Xu, Catal. Today, 2004, 98, 44 C. B. Phillips and R. Datta, Ind. Eng. Chem. Res., 1997, 36,
601. 4466.
36 Y. Li, Q. Ye, J.-M. Wei and B.-Q. Xu, Chin. J. Catal., 2004, 25, 45 D. G. Barton, S. L Soled and E. Iglesia, Top. Catal., 1998, 6,
326. 87.
37 H.-M. Liu, Q. Ye and B.-Q. Xu, Stud. Surf. Sci. Catal., 2007, 46 B. Katryniok, S. Paul, V. Belliere-Baca, P. Ray and
172, 473. F. Dumeignil, Green Chem., 2010, 12, 2079.
38 J. Song, H. Wang and B.-Q. Xu, Chin. J. Catal., 2004, 25, 599. 47 H2 substitution of O2 for the reaction under the standard
`
39 X. Zhang, H. Wang and B.-Q. Xu, J. Phys. Chem. B, 2005, 109,
9678.
40 H. Hattori, S. Miyashita and K. Tanabe, Bull. Chem. Soc. Jpn.,
1971, 44, 893.
conditions led to signicantly reduced formation of
heavier products in the “others” but induced instead a
formation of considerable amount of lower hydrocarbons
(methane, ethane and propane), probably due to co-
occurrence of undesired hydrogenolysis reactions. These
hydrocarbons were also counted as components of the
“others” in these cases.
41 M. Craus, in Handbook of Heterogeneous Catalysis, ed. G. Ertl,
}
H. Knozinger and J. Weitkamp, VCH, Weinheim, 1997, vol.
5, p. 2370.
´
42 A. G. Gayubo, A. T. Aguayo, A. L. Moran, M. Olazar and 48 I. E. Wachs, T. Kim and E. I. Ross, Catal. Today, 2006, 116,
J. Bilbao, AIChE J., 2002, 48, 1561. 162.
43 A. G. Gayubo, A. T. Aguayo, A. Atutxa, M. Olazar and J. Bilbao, 49 T. Kim, A. Burrows, C. J. Kiely and I. E. Wachs, J. Catal., 2007,
Ind. Eng. Chem. Res., 2004, 43, 2610. 246, 370.
4630 | RSC Adv., 2014, 4, 4619–4630
This journal is © The Royal Society of Chemistry 2014