ZrMn Oxides for Aqueous-Phase Ketonization of Acetic Acid: Effect of Crystal and Porosity

Article abstract of DOI:10.1002/asia.201800114

Aqueous-phase ketonization of bio-based acetic acid is important to improve the conversion efficiency of biomass resources. In this study, ZrMn mixed oxides (ZrMnO_x) with high aqueous-phase ketonization activity are synthetized through a carbonization/oxidation method (COM) and solvothermal method (STM). The results show that ZrMnO_x prepared by COM possesses tetragonal ZrO₂, and hausmannite Mn₃O₄ is observed only at a high oxidation temperature of 750 °C. Low-temperature and long oxidation results in decreased crystallinity and crystallite size, which is related to highly dispersed Mnⁿ⁺ species. The catalysts with improved acid sites possess high ketonization activity. Surface areas and pore size of ZrMnO_x synthetized by STM are controlled by the solvents for thermal treatment. Compared with water as solvent, ethanol increases the surface area and pore size, resulting in high ketonization activity.

Full text of DOI:10.1002/asia.201800114

CHEMISTRY
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Accepted Article
Title: ZrMn oxides for aqueous-phase ketonization of acetic acid: effect
of crystal and porosity
Authors: Kejing Wu, Mingde Yang, Husheng Hu, Junmei Liang, and
Yulong Wu
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Chemistry - An Asian Journal
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ZrMn oxides for aqueous-phase ketonization of acetic acid: effect
of crystal and porosity
Kejing Wu,[a], [b] Mingde Yang,* Husheng Hu, Junmei Liang, Yulong Wu,*
[a]
[a]
[a]
[a], [c]
Abstract: Aqueous-phase ketonization of bio-based acetic acid is
ketonization is the crucial step for conversion of bio-based acetic
acid in aqueous phase. Previous work[1c,
1d]
showed that
important to improve conversion efficiency of biomass resources. In
this study, ZrMn mixed oxides (ZrMnO
x
) with high aqueous-phase
hydrothermal liquefaction (HTL) at 300 – 400 °C efficiently
converted algae to bio-oil. Aqueous-phase ketonization is
feasible through applying similar reactors with HTL, and
drawbacks of high temperature for efficient ketonization reaction
may be resolved.
ketonization activity are synthetized through carbonization/oxidation
method (COM) and solvothermal method (STM). The results show
that ZrMnO
x
prepared via COM possesses tetragonal ZrO
2
, and
hausmannite Mn
3 4
O
is observed only at high oxidation temperature
of 750 °C. Low-temperature and long-time oxidation results in
decreased crystallinity and crystallite size, which is related to highly
Generally, ketonization of acetic acid (with typical reaction
Cat.
equation of 2CH COOH   CH COCH +CO +H O ) is carried
3
3
3
2
2
n+
[7]
dispersed Mn species. The catalysts with improved acid sites
out in gas phase. However, gas-phase ketonization of acetic
acid in aqueous phase requires large amount of energy for
vaporization, which leads to low efficiency of overall energy
recovery. Recently, ketonization in condensed toluene phase is
achieved at 150 − 300 °C with high ketone yield.[8] Because of
the difficult extraction of aqueous-phase acetic acid and
environmental concerns on organic solvents, organic-phase
ketonization is also of low efficiency. Therefore, aqueous-phase
possess high ketonization activity. Surface areas and pore size of
x
ZrMnO synthetized via STM are controlled by the solvents for
thermal treatment. Compared with water as solvent, ethanol benefits
the increase in surface areas and pore size, resulting in high
ketonization activity.
ketonization is very important for the conversion of bio-based
acetic acid.[4b, 5a, 7a]
Introduction
Recently, literatures on aqueous-phase ketonization of acetic
Biomass resources, especially algae,[1] possess promising
potential to resolve energy and environmental concerns, such as
depletion of fossil fuel reserves and greenhouse gas
emissions.[ During hydrothermal conversion of biomass, large
amount of acetic acid, one of major bio-based chemicals, exists
in the aqueous-phase product.[3] Pyrolysis of biomass also
produces an aqueous fraction rich in acetic acid.[4] Therefore,
utilization of bio-based acids, especially acetic acid, is very
important to improve conversion efficiency of biomass
resources.[ An aqueous process can be used to convert acetic
acid to liquid alkanes through ketonization, followed by aldol
condensation and hydrogenation. The obtained hydrophobic
liquid alkanes can directly be separated from water, avoiding
separation costs of intermediate products during aqueous-phase
conversion.[5a] Huber et al.[6] exhibited that aldol condensation of
acetone and furfural, and subsequent hydrogenation could be
efficiently achieved through aqueous catalysis. Thus,
[4b, 9]
acid over TiO
2
and ZrO
2
catalysts are available.
Pham et
al.[4b] introduced a highly selective Ru/TiO
2
/C catalyst and acid
conversion was limited to 54.2 % after 5 h reaction because of
irreversible deactivation. Faria et al. suggests that rutile TiO
2]
2
decorated with Ru nanoparticles possesses high activity and
stability.[9a] However, noble metal Ru significantly increases
synthesis cost of catalysts. Thus, it is necessary to develop non-
noble catalysts for efficient aqueous-phase ketonization, and
2
ZrO is a promising candidate. Our previous work shows that
5]
carbon materials could efficiently promote aqueous-phase
[9c]
2
ketonization of acetic acid over ZrO catalysts. High acetone
yield of 88.27% was achieved over non-noble ZrMn mixed
oxides, and Mn leaching and crystal phase transformation were
the main reasons of deactivation.[9b] Because different synthesis
methods result in varied crystal phase, pore properties and acid
sites,[8b] synthesis effect on ZrMn oxides should be investigated
to understand relationship between aqueous-phase ketonization
and catalyst properties.
Typically, two different methods are used to synthetize ZrMn
[
a]
Dr. K.J. Wu, Dr. M.D. Yang, Master H.S. Hu, Dr. J.M. Liang, Dr. Y.L.
Wu
Institute of Nuclear and New Energy Technology
Tsinghua University
Beijing 100084, China
E-mail: wylong@tsinghua.edu.cn; yangmd@tsinghua.edu.cn
Dr. K.J. Wu
Institute of New Energy Low-Carbon Technology
Sichuan University
Chengdu 610065, China
Dr. Y.L. Wu
Beijing Key laboratory of fine ceramics
Beijing 100084, China
[
7e, 10]
oxides, namely citric acid method
and co-precipitation
method.[ Herein, carbonization process is applied for citric acid
11]
method to produce graphite carbon in catalysts.[9c] Subsequently,
different oxidation processes are used to remove carbon and
control crystalline size and Mn dispersion. It is reported that
hydrothermal treatment was efficient to synthetize mesoporous
zirconium phosphate catalysts.[12] Thus, solvothermal treatment
[
b]
c]
is applied to controllably synthetize porous ZrMn oxides with
higher surface areas and pore volumes/size than single co-
precipitation method.[
[
11]
In this article, ZrMn oxide catalysts are controllably synthetized
with different crystal phase, pore properties and acid sites for
Supporting information for this article is given via a link at the end of
the document.
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aqueous-phase ketonization of acetic acid. X-ray diffraction
Compared with ZrMn-COM-350-4 with the same oxidation
(
XRD), N
desorption (NH
TPR) and scanning electron microscopy (SEM) with energy
2
absorption−desorption, NH
3
temperature-programmed
process, ZrMn-STM catalysts possess only t-ZrO
higher crystal peaks (Figure 1b). This result indicates co-
precipitation and solvothermal treatment enhances
crystallization of ZrO phase. Meanwhile, the peak height
decreases when using ethanol to replace water as solvent.
Lattice distance of (011) facet increases in the order of W,
W+Eth, Eth, while crystallite size decreases follow this order, as
2
phase with
3
-TPD), temperature-programmed reduction
(
dispersive X-ray (EDX) are applied for better understanding of
relationship between catalyst characterization and activity.
2
shown in Table 1. Thus, ethanol solvents will decrease ZrO
crystallization during solvothermal treatment.
2
Results and Discussion
Catalyst Characterization
Table 1. Crystal parameters of ZrMn-COM and ZrMn-STM catalysts.
XRD patterns of ZrMn-COM catalysts show typical tetragonal
Catalysts
2theta[a]
º)
d[a] of (011)
(Å)
Crystallite size[b]
(nm)
ZrO
as shown in Figure 1a. When oxidized at 350 and 550 °C, poorly
crystalized t-ZrO is similar with ZrMn-COM catalyst without
oxidation. Sharp peaks are observed for ZrMn-COM-750-4, and
a new phase of hausmannite Mn (ICDD PDF No. 24-0734)
occurs. When oxidized at 750 °C for 24h, t-ZrO peaks tend to
2 2
(t-ZrO ) (ICDD PDF No. 50-1089) with different crystallinity,
(
ZrMn-COM-None
ZrMn-COM-350-4
ZrMn-COM-350-24
ZrMn-COM-550-4
ZrMn-COM-550-24
ZrMn-COM-750-4
ZrMn-COM-750-24
ZrMn-STM-W
30.55
30.47
30.55
30.56
30.51
30.55
30.39
30.69
30.61
30.48
2.924
2.932
2.924
2.923
2.928
2.924
2.939
2.911
2.918
2.930
3.5
3.7
3.5
4.0
3.6
22.8
13.2
8.9
8.3
7.0
2
3
O
4
2
be flatter. According to XRD data, peak parameters for the
strongest (011) peak and related crystal parameters are
calculated in Table 1. Peak positions of different catalysts have
no significant differences with each other, but are larger than
that of Zr-COM-350-4 (Figure S1 and Table S1). As no
crystalized Mn species are observed for ZrMn-COM-350-4, Mnn+
should exist in t-ZrO
discussions will be done in TPR results. Compared with Zr-
COM-350-4, no monoclinic ZrO is observed in ZrMn-COM
catalysts, indicating that Mn species promote stabilization of t-
ZrO
.[10] It is interesting that crystallite sizes of ZrMn-COM
2
crystal or be highly dispersed, and more
2
ZrMn-STM-W+Eth
ZrMn-STM- Eth
2
catalysts increase with temperature when oxidized for the same
time, but decrease with oxidation time at the same temperature,
as shown in Table 1.
[
a] 2theta and d (lattice distance) is the peak position of t-ZrO
2
(011) facet. [b]
Crystallite size is calculated according to data of t-ZrO (011) facet.
2
As shown in Figure 2, TPR curve of ZrMn-COM-None is broad
without typical peaks, which may results from the existence of
carbon species (Figure S2), while TPR curves of oxidized ZrMn-
COM catalysts possess identified peaks. Wide peaks from 175
to 400 °C are observed for ZrMn-COM-350(550), which are
[
10, 11c, 13]
attributed to reduction of highly dispersed MnO
according to XRD results in Figure 1. Furthermore, two sub-
peaks with different height near T = 223 °C and T = 303 °C can
be observed through peak fitting. Considering the existence of
x
0
1
4
+
3+ [9b]
Mn and Mn , sub-peak near T
0
is attributed to the reduction
of Mn4 species close to ZrO
solution, and sub-peak near T
dimensional species of highly dispersed MnO
TPR curve of ZrMn-COM-750-4 is broad without clear sub-peaks
+
phase, namely in ZrMn solid
1
is related to aggregated 3-
2
.[13] Differently, the
x
near T
0 1
and T . The combined peaks near 350 and 440 °C is
Figure 1. Figure 1. XRD patterns of ZrMn-COM catalysts oxidized at different
temperature and time (a) and ZrMn-STM catalysts with different solvent (b).
, respectively.[10, 13]
attributed to reduction of MnO
x
and Mn O
3 4
The peak higher than 500 °C is related to ZrO
Complex reduction of MnO and ZrO species results in the
broad peak for ZrMn-COM-750-4. This result confirms that Mn
3 4
species escape from highly crystalized ZrO to form Mn O
reduction.[10]
2
(●) refers to tetragonal ZrO
2 3 4
, (◊) refers to hausmannite Mn O . Only the strong
and obvious peaks are noted and signal range is the same for (a) and (b).
x
2
2
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according to XRD results (Figure 1). However, TPR curve of
ZrMn-COM-750-24 is similar with that oxidized at 350 and
into ZrO
2
crystal, according to ZrMn-COM-750 oxidized for
different time. Thus, highly dispersed MnO
benefits the stability of t-ZrO crystal and small crystal size.
2
N absorption/desorption curves and average pore size
x 2
in ZrO solid solution
5
50 °C, and a new peak is also observed near T
Because Mn exists in ZrMn-COM-750-24 (Figure 1) and
reduction of Mn is more difficult than MnO and Mn
,[13]
should be attributed to the reduction of Mn
2
= 406 °C.
2
3
O
4
3
O
4
2
2
O
3
distribution are shown in Figure 3. All isothermals of ZrMn-COM
and ZrMn-STM catalysts can be classified as type ІV with
hysteresis loops at relative pressures (P/P0 > 0.8), indicating the
mesoporous structure caused by interparticle absorption.[ The
pore size of different catalysts allocates mainly in two
distributions of 2~3 nm and 10~20 nm. Pore size of ZrMn-STM
increases gradually when using ethanol to replace water as
thermal treatment solvent. ZrMn-COM-350-4 possesses much
smaller pore size than ZrMn-STM catalysts, which is directly
observed in Table 3. Surface areas and pore volumes of ZrMn-
COM-350-4 (Table 3) are significantly larger than results in
literature [ , which confirms benefit of carbonization process.
Without Mn species, Zr-COM-350-4 possesses much lower
surface areas and pore volumes (Table S1), indicating
significant enhancement of Mn species on surface properties.
sub-peak near T
to MnO.[11c]
2
3 4
O
14]
10]
Figure 2. TPR curves of ZrMn-COM catalysts oxidized at different
temperature and time, where None means no oxidation process.
Table 2. The normalized peak area of Mn species for ZrMn-COM catalysts
according to TPR.
Catalysts
Sub-peak[a] area percentage (%)
T
0
T
1
T
2
ZrMn-COM-350-4
ZrMn-COM-350-24
ZrMn-COM-550-4
ZrMn-COM-550-24
ZrMn-COM-750-24
37.8
40.2
33.1
36.1
11.6
62.2
59.8
66.9
63.9
55.8
0
0
0
0
2
Figure 3. N absorption and desorption curves of different catalysts. The off-
sets of ZrMn-STM-W, ZrMn-STM-W+Eth, and ZrMn-STM-Eth are 100, 200,
3
and 300 cm /g, respectively. The open and filled symbols represent absorption
3
and desorption data, respectively. The volume axis refers to 100 cm /g, and
the inserted figure are related average pore size distribution.
32.6
As for different ZrMn-STM catalysts, morphology of irregular bulk
particles is much similar, and surface Mn/Zr atom ratios are also
similar with synthetized value of 0.4, as shown in Figure S3. The
differences in surface areas of ZrMn-STM catalysts mainly result
from thermal treatment solvents (Table 3). Thermal treatment
with ethanol solvents can significantly improve surface areas
and pore volumes over water solvent. During the thermal
treatment, the organic solvents serve as temples for
crystallization of ZrMn oxides, resulting in more mesoporous
structure than water solvent. Higher surface areas and larger
pore volumes/size would offer more surface active sites for
ketonization reaction.
[
0 1 2
a] Sub-peak of T , T and T are 223, 303 and 406 °C, respectively.
The normalized sub-peak areas are listed in Table 2. Higher
area percentage of indicates higher amount of highly
dispersed MnO in solid solution. Obviously, higher oxidation
temperature leads to lower MnO in solid solution, but longer
T
0
x
x
oxidation time improves content of MnO
x
species in solid
n+
solution. Because Mn in ZrO
2
crystal has negative effect on
crystallization,[
9b]
high amount MnO in solid solution is
x
accompanied by small crystallite size (Table 1). Meanwhile,
escaped Mnn+ has potential to diffuse from individual Mn species
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desorption peaks exist for ZrMn-STM catalysts (Figure 4b). The
ethanol is a better solvent than water to increase total acid and
Lewis acid sites (Table 4). High surface areas mainly devote to
more surface Zr and Mn atoms and benefit increase in acid sites.
However, SBET of ZrMn-COM-350-4 catalyst is slightly higher
than ZrMn-STM-Eth, but acid sites of the former is only half of
the latter. The result is mainly attributed to the larger pore
volumes and pore size of ZrMn-STM-Eth.
Table 3. Surface and pore properties of different catalysts.
BET (m2 g )
[
a]
-1
V
[b]
(cm3 g-1)
D
[c]
p
(nm)
Catalysts
S
p
ZrMn-COM-350-4
ZrMn-STM-W
158
84
0.309
0.285
0.376
0.719
7.83
13.3
13.7
16.2
ZrMn-STM-W+Eth
ZrMn-STM- Eth
106
147
Table 4. Total and Lewis acid sites of ZrMn-COM and ZrMn-STM catalysts.
Lewis acid sites[
(mmol g )
a]
Catalysts
Total acid sites
[
a] BET surface areas. [b] Pore volumes. [c] Average pore size.
-1
-1
(mmol g )
ZrMn-COM-None
ZrMn-COM-350-4
ZrMn-COM-350-24
ZrMn-COM-550-4
ZrMn-COM-550-24
ZrMn-COM-750-4
ZrMn-COM-750-24
ZrMn-STM-W
0.035
0.373
0.450
0.360
0.458
0.009
0.066
0.342
0.360
0.732
0.017
0.141
0.165
0.114
0.160
0
0.007
0.089
0.117
0.228
ZrMn-STM-W+Eth
ZrMn-STM- Eth
[
a] Lewis acid sites are calculated from the desorption areas at temperature
range higher than middle position of 218 °C.
3
Figure 4. NH -TPD curves of ZrMn-COM catalysts (a) and ZrMn-STM (b). The
intensity range is the same for (a) and (b).
Ketonization Activity
The acetone yields of ZrMn-COM catalysts are shown in Figure
. Maximum yield of 72.95% is observed for ZrMn-COM-350-24,
which is significantly higher than that for noble Ru/TiO /C
catalysts in aqueous phase.[4b] Oxidation process at 350 and
50 °C significantly improve the acetone yield. When oxidation
time increases from 4 to 24 h, crystallite size decreases and acid
sites increase significantly for ZrMn-COM oxidized at both 350
and 550 °C, resulting in similar enhancement in acetone yield.
However, activity becomes much low when oxidized at 750 °C
for 4h. An obvious improvement of oxidation time on activity is
observed, especially that acetone yield for ZrMn-COM-750-24 is
three times of that for ZrMn-COM-750-4. Similarly prepared Mn-
COM-350-4 and Zr-COM-350-4 both possess lower activity than
ZrMn-COM-350-4 (Table S1), and acetone yield of Mn-COM-
3
The acid properties are analyzed via NH -TPD, as shown in
5
Figure 4. No significant NH
ZrMn-COM-None catalyst, and oxidation processes at 350 and
50 °C enhance acid properties (Figure 4a). Two peaks are
3
desorption peak is observed for
2
5
5
significantly observed near 180 and 265 °C, representing
different acid sites of the formation of NH4+ on Brønsted acid
sites and coordinated absorption on Lewis acid sites,
respectively.[10] However, peaks almost disappear for ZrMn-
COM-750-4, and longer oxidation time results in weak NH
3
desorption peaks for ZrMn-COM-750-24. The total and Lewis
acid sites are calculated as shown in Table 4. Oxidation at low
temperature and long time benefits increase in acid sites. High
total acid and Lewis acid sites are significantly accompanied by
small crystallite size and highly dispersed MnO
Table 1 and 2). Meanwhile, ZrMn-COM-750-24 with high
aggregated 3-dimensional MnO content (T in Table 2)
possesses relatively less acid sites. Thus, aggregated 3-
dimensional MnO is not related to main acid sites. Therefore,
poorly crystalized t-ZrO incorporated with highly dispersed
MnO , namely Zr-O-Mn, is the main acid site. Similarly, two
x 2
in ZrO phase
3
50-4 is only 4.7%. Our previous work showed that Mn leaching
(
in aqueous acid solution was the deactivation process.[ High
Mn content in solid solution of ZrMn-COM-350-24 and ZrMn-
COM-550-24 results in low Mn leaching at active sites (Table
S2). Thus, high aqueous-phase ketonization of ZrMn-COM
9b]
2
1
2
2
x
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catalysts is mainly resulted from interaction between Zr and Mn
species, as shown in characterization results.
Despite the larger crystallite size than ZrMn-COM catalysts,
activity of ZrMn-STM catalysts is still high (Table 5). Acetone
yield increases when using ethanol to replace water as thermal
treatment solvent, due to increase in surface areas and acid
sites. According to literature,[7a] Lewis acid sites, rather than
Brønsted acid sites, are crucial important for ketonization.
Acetone production per total acid sites is listed in Table 5. The
results show that acetone production per total acid sites of
ZrMn-STM-W+Eth is higher than that of ZrMn-STM-W, which is
resulted from higher Lewis acid sites (Table 4). Considering the
similar total acid sites, the higher performance of ZrMn-STM-
W+Eth can be explained that Lewis acid sites can absorb O
atoms of acid molecule to promote acid ketonization on catalyst
surface. The significantly low acetone production per total acid
sites of ZrMn-STM-Eth might result from limitation of reactant
concentration and accesability to acid sites in aqueous phase.
As for acetone yield, the results confirm that high surface areas
and large pore volumes/size, accompanied with high acid sites,
benefit the catalyst performance.
Highly dispersed Mn4+ in ZrO
crystal (T reduction peak in
2 0
Figure 2) contributes to more Zr-O-Mn sites than other Mn
species. Meanwhile, two nearby acid molecules absorbed on Zr-
O-Mn sites can easily form β-ketoacid, which is key intermediate
for surface ketonization reaction [9b]. However, acid molecules
efficiently absorbed on highly dispersed aggregated 3-
2 1
dimensional MnO (T reduction peak in Figure 2) are difficult to
react without nearby Zr sites, as confirmed by low ketonization
activity of Mn-COM-350-4. Besides, more Zr-O-Mn sites are
accompanied with smaller crystal size and higher acid sites.
2
Small ZrO crystal possesses higher surface atoms, resulting in
more active sites exposed on catalyst surface. Absorption of O
atoms in acid molecules onto Lewis acid sites is crucial
important for ketonization,[4b] and high Lewis acid sites
significantly improve aqueous-phase ketonization.[7a] Therefore,
Zr-O-Mn sites are recommended as main active centers, and
suitable oxidation process can controllably increase content of
4
+
Mn highly dispersed in ZrO
2
crystal to improve the activity.
Acid conversion of ZrMn-STM-Eth at 340 °C for different
reaction time is shown in Figure 6. The rate equation,
n−1
n
dX/dt=k·C
0
·(1−X) , is applied to fit the experiment data, where
is the initial acid
X is acid conversion, t is reaction time, C
0
concentration, n is reaction order, and k is rate constant. The
result indicates that acid conversion satisfies first-order reaction
-1
(
n = 1) with k = 0.117 h , rather than stoichiometric second-
[
9b]
order reaction, which is in accordance with previous study. Mn
cations near Zr4 at Zr-O-Mn sites can easily absorb acetic acid,
and thus, bimolecular surface reaction of absorbed carboxylates
is promoted.[15] The fast formation of carboxylates between
acetic acid and Mn species results in limited bimolecular
reaction due to one molecule of acid absorbed on Zr cations.
Thus, it is reasonable to observe a first-order ketonization of
acetic acid in aqueous phase.
+
Figure 5. Acetone yield of ZrMn-COM oxidized at different temperature for 4
and 24 h. None refers to no oxidation.
Table 5. Acetone yields of ZrMn-STM catalysts thermally treated in
different solvents.
Solvents
Acetone yield (%)
Acetone produced per total acid sites[a]
W
51.5
61.9
63.5
100
114
57.9
W+Eth
Eth
Figure 6. Acetone yield (dot) of ZrMn-STM-Eth at 340 °C for different reaction
time. Three lines represent calculation value according to rate equation
n−1
·(1−X)n with different reaction order n (0.5, 1 and 1.5) and
dX/dt=k·C
0
-
1
optimized reaction constant k (0.117 h ).
[
a] Mole of acetone produced (mmol) is divided by the Lewis acid sites
(mmol) of the added catalyst (1.5 g).
Conclusions
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In this study, COM and STM are used to synthetize ZrMn mixed
oxides catalyst for aqueous-phase ketonization. Crystal phase of
ZrMn-COM catalysts can be controlled by oxidation process at
different temperatures and times. Solvothermal treatment
significantly affects surface areas and pore properties of ZrMn-
STM catalysts. The results indicate that highly dispersed Mn
2
Surface area and pore volume were measured via N absorption
isotherms carried out on Tristar II 3020 (MICROMERITICS, United
States) at 77K. Samples were pre-treated in vacuum at 300 °C. The
specific surface areas were determined from Brunauer−Emmett−Teller
(
BET) equation, and pore volumes and average pore size were
calculated using the Barrett−Joyner−Halenda (BJH) formula.
NH -TPD tests were carried out with a TP-5076 multifunctional automatic
3
species in t-ZrO
2
crystal phase promote the ketonization activity
absorption instrument (Xianquan Industry and Trade Development Co.,
Tianjin, China). 100 mg sample was pre-treated at 350 °C for 1 h in He
stream (30 mL/min) before ammonia absorption. After saturated
absorption in the stream of pure NH for 30 min, the sample was purged
3
by He at 100 °C for 2 h to remove physisorbed ammonia. Then the TPD
measurement was carried out from 100 to 350 °C with heating rate of
of ZrMn-COM catalysts. Small crystallite size benefits exposure
of active Zr-O-Mn sites on catalyst surface, resulting in improved
acid sites. Thermal treatment with ethanol solvent results in high
surface areas and pore volumes/size, which benefit increase in
acid site and ketonization activity. Controllable crystal and
porous properties benefit the catalytic activity of ZrMn oxides
synthetized via COM and STM for aqueous-phase ketonization
of acetic acid.
5
°C /min in He flow of 30 ml/min. The thermal conductivity detector was
used for continuously monitoring the desorbed ammonia. The acid sites
were measured via external standard of pure NH
3
.
TPR experiments were similar with NH -TPD. Typically, 100 mg sample
3
was pretreated at 350 °C for 1 h in He stream (30 mL/min), and after
2 2 2
being cooled down to room temperature, a mixed H /N gas (5% H ) was
used for TPR with a heating rate of 3 °C /min to 900 °C. A thermal
conductivity detector was applied for H signal detection.
2
Experimental Section
Catalyst preparation
As for carbonization/oxidation method (COM), 40 mmol Zr(NO
Catalytic Activity Measurement
3 4 2
) ·5H O
and 16 mmol Mn(NO were dissolved in 200 mL deionized water, and
then, citric acid was added into the solution, mole of which equalled to
four times of Zr4+ plus twice of Mn2+. The solution was vaporized at 90 ºC
under vigorous stirring to remove water, and yellow and viscous sol-gel
was obtained. The sol-gel was dried at 105 °C for 24h to form a porous
and foam-like solid, similarly with citric acid method. Subsequently,
3 2
)
Measurements of aqueous-phase ketonization activity were similar with
previous work [9b]. Briefly, 100 mL aqueous solution of 2 mol/L acetic acid
and 1.5g catalyst were added in 500 mL steel batch reactor (Parr). The
2
reactor was purged with 1 MPa N for three times to remove existing air
and finally pressured at 5 MPa N . The reactor was heated to 340 °C at a
2
heating rate of 5 °C/min and kept for 12h under 300 rpm stirring. The
pressure at 340 °C was about 19 MPa, which was higher than vapor-
liquid pressure of water (14.5MPa) to maintain liquid phase reaction. The
liquid product was collected after cooling down to room temperature, and
acetone product and the remained acetic acid was quantified via GC
analysis. Acetone was the mainly product in the aqueous phase, and
acetone yields were calculated to measure catalyst activity.
2
carbonization process was applied at 600 °C for 4h under 100 mL/min N .
The dark solid was ground and sieved to 200 mesh. Finally, oxidation
process was carried out under 100 mL/min air for 4 or 24h at different
temperature (350, 550 and 750 °C). Here, different catalysts are marked
as ZrMn-COM-Temperature-Time, for example, ZrMn-COM-350-4 means
oxidized at 350 °C for 4h under 100 mL/min air, and ZrMn-COM-None
refers to catalyst without oxidation treatment.
As for solvothermal method (STM), 24 mmol Zr(NO
3 4 2
) ·5H O and 9.6
mmol Mn(NO were dissolved to obtain an aqueous solution of 0.2
3 2
)
mol/L Zr4+, and the solution was transferred into a 500 mL beaker under
vigorous stirring. Then, ammonia solution (25%) was dropped in the
solution for completely precipitation, keeping a pH value of 10. After
completely precipitation, the brown solid was aged for 24h, then filtered
and washed with water until neutral pH. Subsequently, the filtered
precipitation was dispersed in 100 mL solvent under ultrasonic, sealed in
a 180 mL Teflon lining and thermal treated at 180 °C for 24h. Here, three
kinds of solvents, water (W), water and ethanol mixture with volume ratio
Acknowledgements
This study was supported financially by National Natural Science
Foundation of China (No. 21776159, No. 21576155 and No.
21376140), Research Project of Guangdong Provincial
Department of Science and Technology Department (No.
2015B020215004) and Program for Changjiang Scholars and
=
1:1 (W+Eth), and ethanol (Eth), were applied for thermal treatment.
The obtained solid was filtered, dried, and calcined at 600 °C for 4h in
00 mL/min N to totally remove solvent. Finally, ZrMn-STM catalysts
Innovative Research Team in University (No.IRT13026).
1
2
were oxidized at 350 °C under 100 mL/min air for 4h. The catalysts are
marked as ZrMn-STM-Solvent, according to the solvents used for
thermal treatment.
Keywords: Acetic acid • Aqueous-phase ketonization • ZrMn
oxides • Oxidation • Solvothermal treatment
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Entry for the Table of Contents (Please choose one layout)
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ZrMnO
x
is synthetized through
Author(s), Corresponding Author(s)*
carbonization/oxidation method with
controlled crystal, and though
solvothermal method with modified
porosity. Crystal and porosity
properties have significant effluence
on ketonization of acetic acid in
aqueous phase.
Page No. – Page No.
Title
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