Direct conversion of bio-ethanol to propylene in high yield over the composite of In2O3 and zeolite beta

Article abstract of DOI:10.1039/c7gc02400b

A series of In₂O₃-beta composites with different contents of zeolite beta were prepared by the deposition-precipitation method, followed by calcination at 700 °C, and their catalytic performance in the conversion of ethanol to propylene (ETP) was investigated. The physicochemical properties of the as-synthesized materials were characterized by XRD, N₂ adsorption, SEM, NH₃-TPD, CO₂-TPD and a probe reaction. The combination of In₂O₃ and zeolite beta improves the propylene yield significantly. The optimal result was observed for the composite with a beta content of 20-50%, which gave ca. 50% yield of propylene. The role of beta in the In₂O₃-beta composite catalyst is to promote the conversion of the intermediate of acetone to propylene via an additional reaction pathway, which accounts for the superior propylene yield of the In₂O₃-beta composite in comparison with In₂O₃ (ca. 32%). The proximity of these two components (In₂O₃ and zeolite beta) plays a crucial role in achieving a high yield of propylene for the ETP reaction.

Full text of DOI:10.1039/c7gc02400b

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PAPER
Direct conversion of bio-ethanol to propylene with high yield over
the composite of In2O3 and zeolite Beta
Fangqi Xue,a Changxi Miao,*b Yinghong Yue,a Weiming Hua*a and Zi Gaoa
Received 7th August 2017,
Accepted 00th September 2017
A series of In2O3-Beta composites with different content of zeolite Beta were prepared by deposition-precipitation
method, followed by calcination at 700 oC, and their catalytic performance in conversion of ethanol to propylene (ETP) was
investigated. The physicochemical properties of the as-synthesized materials were characterized by XRD, N2 adsorption,
SEM, NH3-TPD, CO2-TPD and a probe reaction. The combination of In2O3 and zeolite Beta improves the propylene yield
significantly. The optimal result was observed for the composite with Beta content of 20-50%, which gave ca. 50% yield of
propylene. The role of Beta in In2O3-Beta composite catalyst is to promote the conversion of the intermediate of acetone
to propylene via an additional reaction pathway, which accounts for the superior propylene yield of In2O3-Beta composite
in comparison with In2O3 (ca. 32%). The proximity of these two components (In2O3 and zeolite Beta) plays a crucial role in
DOI: 10.1039/x0xx00000x
www.rsc.org/
achieving
a
high
yield
of
propylene
for
the
ETP
reaction.
modified with alkaline and phosphorous, and found
significantly better stability than for traditional HZSM-5.17,18
More recently, much attention has been transferred to
Introduction
Fossil fuels are main energy sources to support human life and
social development. The excessive exploitation of fossil fuels
leads to the deterioration of environment and irreversible
exhaustion of these resources. So there is an urgent need to
accelerate the development and utilization of renewable
energies. The use of biomass, as a sustainable energy, can
alleviate the energy shortage problem. Bio-ethanol is usually
produced from the fermentation of plants, and it is widely
used as a platform molecule to produce many value-added
23
metal oxide catalysts for the ETP reaction.19
Iwamoto’s
−
group reported a propylene yield of 34% on Sc/In2O3 for the
ETP reaction in N2 atmosphere at 500 oC.19 They also found
that on Y/CeO2, the yield of propylene was constant at 30% for
the ETP reaction in the presence of water during continuous
experiment at 430 oC for 56 h.21 Xia et al. prepared Y/ZrO2
catalyst and achieved a yield for propylene of 44% for the ETP
o
reaction at 450 C and 1.11 MPa.23 However, the exploration
1
3
of a catalyst with both higher propylene yield and longer
lifetime is still a tremendous challenge.
−
chemicals such as ethylene, propylene, isobutene and so on.
The reaction of ethanol to propylene (ETP) has been widely
studied in recent years, as propylene is one of the most
important raw materials to produce industrial commodities
such as polypropylene, polyacrylonitrile, acrolein and acrylic
acid. Zeolites (mainly MFI-type) and modified zeolites are
In the present study, we report for the first time the use of
In2O3-Beta composite as a new efficient catalyst in the ETP
reaction. Our results have shown that the combination of In2O3
and zeolite Beta can improve the yield of propylene
14 substantially. Moreover, the In2O3-Beta composite catalyst
exhibits good stability in terms of propylene yield. The reasons
for the remarkable propylene yield of In2O3-Beta composite
were elucidated.
generally employed for this reaction in previous studies.4
−
Ethanol firstly dehydrates to ethylene, then ethylene goes
through oligomerization-cracking way to get propylene.8,15,16
Because of the randomness of oligomerization, the yield of
propylene is just 20−30%, and the main by-products are
Results and discussion
Structural and textural properties
ethylene, butenes and aromatic hydrocarbons. Moreover,
coke is more prone to be produced on strong acid sites,
leading to the fast deactivation of catalysts.4,9 Mao’s group
prepared fluorinated nano-HZSM-5 and HZSM-5 zeolite co-
Fig. 1 shows the XRD patterns of In2O3-Beta composites with
different zeolite Beta content. The intensities of In2O3
diffraction peaks (PDF#06-0416) gradually decrease and the
peak width becomes broader with the decrease of In2O3
content, indicating the smaller crystallite size of In2O3 (Table
1). When the content of Beta is up to 20%, its characteristic
peak at 2θ = 22.6o can be discernible (Fig. 1c). When the
content of Beta is up to 50%, its another characteristic peak at
2θ = 7.8o appears (Fig. 1f). The intensities of these two peaks
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(PDF#06-0416) increase gradually with increasing the Beta
content.
Fig. 1 XRD patterns of In2O3-Beta composites with different
Beta content. (a) In2O3, (b) In2O3-10%Beta, (c) In2O3-20%Beta,
(d) In2O3-30%Beta, (e) In2O3-40%Beta, (f) In2O3-50%Beta; (g)
In2O3-60%Beta, (h) In2O3-70%Beta, (i) Beta.
The textural properties of the samples are listed in Table 1.
Fig. 2 displays the SEM images of different samples. The
In2O3 particles are approximately sphere-shaped with
diameters in the range of 30-70 nm (Fig. 2a). The Beta particles
are approximately sphere-shaped with diameters in the range
of 200-500 nm (Fig. 2e), much larger than In2O3 particles. For
the In2O3-20%Beta composite, only a few Beta particles can be
observed (Fig. 2b), indicating that most of zeolite Beta were
buried by In2O3 nanoparticles when the Beta content is low.
With the increase of Beta content up to 50%, most of the
observed particles are zeolite Beta covered by In2O3
nanoparticles (Fig. 2c). It is noteworthy to point out that the
density of Beta is much less than that of In2O3 so that the
volume of Beta is much larger than that of In2O3, although
Beta and In2O3 have the same weight in the In2O3-50%Beta
composite. For the In2O3-70%Beta composite, almost all the
observed particles are zeolite Beta with the presence of tiny
In2O3 particles on the surface of Beta (Fig. 2d). The sizes of
In2O3 particles in In2O3-20%Beta, In2O3-50%Beta and In2O3-
70%Beta composites are 34.3, 16.4 and 14.3 nm, respectively,
which are smaller than pure In2O3 (55.2 nm). This observation
is consistent with the XRD result (Table 1).
Fig. 2 SEM images of (a) In2O3, (b) In2O3-20%Beta, (c) In2O3-
50%Beta, (d) In2O3-70%Beta and (e) Beta.
Table 1 Textural properties of In2O3-Beta composites with
different Beta content
a
b
SBET
Vmicro
Vmeso
Vtotal
Crystallite
sizec (nm)
1
1
1
1
Sample
In2O3
(m2 g− ) (cm3 g− ) (cm3 g− ) (cm3 g− )
22
0
0.186
0.165
0.169
0.197
0.235
0.243
0.270
0.279
0.316
0.186
0.180
0.189
0.243
0.295
0.318
0.372
0.393
0.499
56.8
33.2
32.4
26.7
19.9
16.7
15.9
15.8
−
In2O3-10%Beta 84
In2O3-20%Beta 117
In2O3-30%Beta 167
In2O3-40%Beta 228
In2O3-50%Beta 268
In2O3-60%Beta 327
In2O3-70%Beta 371
0.015
0.020
0.046
0.060
0.075
0.102
0.114
0.183
546
Beta
a Calculated by t-plot method. b Total pore volume adsorbed at P/P0 =
0.99. c The crystallite size of In2O3 determined using Scherrer equation.
2 | Green Chem., 2017, 19, 1-3
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Amount of acidic sites (mmol g−1)
In2O3
In2O3-10%Beta
0.065
0.135
0.223
0.254
0
0.065
0.189
0.295
0.352
0
4.1
0.051
0.083
0.078
0.079
0.082
0.054
0.072
0.098
0.129
0.158(0.085)c
0.184
0.192
0.364
In2O3-20%Beta
In2O3-30%Beta
In2O3-40%Beta
In2O3-50%Beta
In2O3-60%Beta
In2O3-70%Beta
Beta
16.3
25.5
30.7
38.4(4.7)c
48.9
55.3
78.2
0.314
0.443
0.359(0.233)c
0.389
0.517(0.318)c
0.573
0.068(0.062)c
0.066
0.397
0.515
0.589
0.879
0.073
0.063
a NH3 desorbing between 80 and 250oC. b NH3 desorbing between 250 and 500oC.
c The values inside the bracket are the data measured after the stability test.
1
In2O3 shows a small BET surface area (22 m2 g− ) and no peaks. The low temperature peak at 150 oC and the high
micropores, which means In2O3 is
1
a
dense phase. The temperature peak at 311 oC correspond to the weak and
mesopore volume of 0.186 cm3 g− is contributed from voids strong acid sites of Beta. The NH3-TPD profiles of In2O3-Beta
between the In2O3 particles. Different from In2O3, zeolite Beta composites display the feature with combination of Beta and
1
has a very large surface area (546 m2 g− ) and co-existence of In2O3. With the increase of Beta content, the amount of acid
micropores and mesopores with pore volume of 0.183 and sites (weak, strong and total, respectively) becomes larger
1
0.316 cm3 g− , respectively. With the increase of Beta content, (Table 2). Cumene cracking is a typical Brønsted acid-catalyzed
the surface area and pore volume of In2O3-Beta composites reaction.24,25 In2O3 is inactive for cumene cracking, indicating
become larger. It can be concluded from Table 1 that the that there are no Brønsted acid sites on In2O3, i.e. In2O3 is a
surface areas of In2O3-Beta composites mainly result from Lewis acid catalyst. When zeolite Beta was composited with
zeolite Beta, and the micropore volumes of In2O3-Beta In2O3, the conversion of cumene over In2O3-Beta composites
composites arise from zeolite Beta.
increases with increasing the Beta content, which is a
consequence of enhanced Brønsted acidity. In addition, the
surface basicity of In2O3-Beta composites was measured by
CO2-TPD, and the results are given in Fig. S2 and Table 2. One
broad CO2 desorption peak was observed for all samples. The
amount of basic sites on In2O3-Beta composites does not differ
Acid and base properties
The surface acidity of In2O3-Beta composites was measured by
NH3-TPD, and the results are given in Fig. S1 and Table 2. As
shown in Fig. S1, In2O3 exhibits only one broad small peak
desorbing from 80 to 250 oC, suggesting that In2O3 has no
strong acid sites. Zeolite Beta possesses two large desorption
1
significantly, ranging from 0.066 to 0.083 mmol g− (Table 2).
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The data in Table 2 shows that there is a much greater number (Scheme 1). The conversion of acetone to propylene or
of acidic sites than of basic sites on In2O3-Beta composites.
isobutene is a slow step.19,26,32 Therefore, the products of C3H6
and i-C4H8 are generated though the same intermediate of
acetone, i.e., the conversion of acetone to C3H6 and i-C4H8 are
two parallel procedures. The production of C3H6 and i-C4H8
competes with each other. Correlation of C3H6 yield (Fig. 3)
with surface acidity and basicity (Table 2) suggests that
different acidity of the catalysts is responsible for different
C3H6 yield achieved on the catalysts since these catalysts have
similar amount of basic sites. As the amount of acidic sites
increases from 0.065 to 0.295 mmol g−1, the yield of C3H6 is
obviously increased. When the amount of acidic sites is
between 0.295 and 0.517 mmol g−1, the C3H6 yield is similar. A
Catalytic performance
Effect of zeolite Beta content
All catalysts give 100% ethanol conversion under the reaction
conditions studied in this work. Nevertheless, the product
distribution is significantly dependent on the catalyst
composition. Fig. 3 shows the product distribution on In2O3-
o
Beta composites at 460 C after 3 h of the reaction. The In2O3
catalyst gives a 32.1% yield of propylene. Besides that, there
are 25.6% yield of C4H8 (almost entirely isobutene) and 30.1%
yield of COx (ca. 95% CO2 and 5% CO). CO2 is concurrently
produced along with propylene and isobutene during the
conversion of ethanol.19,26 Minor by-products are acetone,
C2H4, CH4 and C2-C4 paraffins. However, the catalytic results on
zeolite Beta are different from those on In2O3. Ethylene
accounts for 59.7% of products, which is stemmed from
ethanol dehydration. And 16.0% yield of BTX (benzene,
toluene and xylenes) is generated via successive steps of
ethylene oligomerization, cracking and/or cyclization and
1
further increase of acidity from 0.517 to 0.879 mmol g− leads
to an evident decline in C3H6 yield, which is due to the fact that
too many acidic sites (i.e. higher content of zeolite Beta in the
composites) favors the formation of BTX and C2H4.
hydrogen transfer reactions over Brønsted acid sites of zeolite
Beta.27 Moreover, there are 13.8% yield of C2-C4 paraffins
29
−
formed by olefins hydrogenation and/or hydrogen transfer
reactions.27
29
−
Only a small amount of propylene (5.2%) is
produced. It is expected that the formation of C3H6 on zeolite
Beta follows the same reaction pathway as that on other acidic
zeolites such as SAPO-34 and ZSM-5, i.e. trimerization of C2H4
followed by β-scission.15,16,30 Zeolite Beta gives a yield of C4H8
as low as 2.6%. No acetone and very small amount of COx
(1.8%) were observed. When In2O3 is composited with zeolite
Beta, the yield of C3H6 is enhanced significantly. The C3H6 yield
on In2O3-10%Beta is 39.0%. When the Beta content in In2O3-
Beta composites is between 20% and 50%, the yield of C3H6 is
similar, reaching as high as ca. 50%. But a further increase in
zeolite Beta content brings about a decrease in C3H6 yield. The
C3H6 yield on the In2O3-70%Beta catalyst with 70% Beta is
decreased to 38.2%. It should be mentioned that butenes
(C4H8) formed over In2O3-Beta composites are primarily
isobutene (> 80%).
Scheme 1 Reaction pathways for ethanol conversion to
propylene and isobutene over In2O3-based oxides.
The results in Fig. 3 reveals that the combination of
appropriate amount of zeolite Beta (20-50%) with In2O3 can
improve the C3H6 yield markedly for the conversion of ethanol
to propylene, but obviously diminish the yield of butenes
(mainly isobutene). According to the reaction pathways shown
in Scheme 1, the reason could be attributed to enhanced
dehydration of isopropanol to propylene caused by higher
amount of acid sites, thus promoting the conversion of
acetone to propylene. The possibility of conversion of acetone
to isobutene is declined accordingly. To verify our hypothesis,
The reaction pathways for the catalytic conversion of
ethanol to propylene over In2O3-based oxides have been
proposed by Iwamoto and co-workers,19,22,31 as shown in
Scheme 1. Ethanol dehydrogenation to acetaldehyde is
catalyzed by both acidic and basic sites through a concerted
mechanism, followed by formation of acetone from
acetaldehyde through ketonization catalyzed by basic sites. At
last, acetone is hydrogenated to isopropanol and then
isopropanol is converted to propylene through dehydration
process. The dehydration of isopropanol to propylene is
catalyzed by acidic sites. It should be mentioned that hydrogen
is produced during the process of ethanol to acetaldehyde
(CH3CH2OH = CH3CHO + H2) and acetaldehyde to acetone
(2CH3CHO + H2O = CH3COCH3 + CO2 + 2H2). On the other hand,
the intermediate of acetone can be also converted to
isobutene via aldolization and cracking catalyzed by Lewis acid-
base pairs on In2O3-based oxides, as suggested by Sun et al.32
we employed γ-Al2O3, which is a good catalyst for isopropanol
dehydration to propylene,33 35 as a substitution of zeolite Beta
to prepare In2O3-50%Al2O3 composite. This catalyst possesses
−
1
0.365 mmol g− of acid sites, which is slightly higher than that
of In2O3-30%Beta. Unexpectedly, the yields of C3H6 and C4H8
over the In2O3-50%Al2O3 composite are similar to those over
In2O3 (Fig. S3), suggesting that this hypothesis is not true.
Dolejšek et al.36 found that acetone can be converted to
propylene through the intermediate of allene (C3H4) catalyzed
by Brønsted acid sites on HZSM-5. According to the
literature,36 it could be inferred that the role of zeolite Beta in
In2O3-Beta composites is to provide an additional reaction
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pathway to convert the intermediate of acetone to propylene,
thus enhancing the formation of propylene from ethanol. To
verify this, we chose acetone as reactant to compare the
catalytic performance of In2O3, In2O3-50%Beta and In2O3-
50%Al2O3. As mentioned above, H2 is produced during the
process of ethanol to acetone. Therefore, we added some H2
in the feed. The conversion of acetone for these catalysts is ca.
98%. The product distribution on three catalysts at 460 oC after
3 h of the reaction is shown in Fig. 4. It is clear that the yield of
C3H6 over In2O3-50%Beta composite is substantially higher
than that over In2O3, whereas the yield of C4H8 (mainly
isobutene) is markedly lower than that over In2O3. This result
strongly suggests that zeolite Beta in In2O3-50%Beta composite
can promote the conversion of acetone to propylene
significantly. Accordingly, the possibility of conversion of
acetone to isobutene is diminished. The yields of C3H6 and
C4H8 over both In2O3 and In2O3-50%Al2O3 composite do not
The effect of the proximity of these two components (In2O3
and zeolite Beta) on the catalytic performance was also
investigated. We prepared three In2O3-50%Beta catalysts with
different distance between In2O3 and zeolite Beta using
different preparation methods. The product distribution on
o
three catalysts at 460 C after 3 h of the reaction is shown in
Fig. 5. As the proximity of two components increases (Fig. 5a
to Fig. 5c), the yield of C3H6 rises substantially. Meanwhile, the
yields of C2H4 and BTX dramatically decrease. The results in Fig.
5 suggest that the proximity of two components (In2O3 and
zeolite Beta) plays a crucial role in giving a high yield of C3H6
for the ETP reaction. Propylene can be produced via two
pathways from ethanol over In2O3-Beta composites.
Conversion of ethanol on the surface of In2O3 forms acetone.
Then a part of acetone molecules are converted to C3H6 on
In2O3. Another part of acetone molecules move to the surface
of zeolite Beta to produce C3H6 catalyzed by Brønsted acid
sites. The nearer distance between In2O3 and Beta will
facilitate the fast diffusion of acetone molecules from In2O3 to
zeolite Beta, thus enhancing the conversion of acetone to
propylene on the surface of zeolite Beta. That is to say, the
second reaction pathway to produce propylene from ethanol is
promoted. Consequently, the C3H6 yield is higher for the ETP
reaction.
differ significantly. This result indicates that γ-Al2O3 in In2O3-
50%Al2O3 composite can not enhance the conversion of
acetone to propylene due to the lack of Brønsted acid sites on
o
-Al2O3 is inactive for cumene cracking at 300 C
γ
-Al2O3, since
γ
(not shown here). When the Beta content in In2O3-Beta
composites is low (In2O3-10%Beta), the promoting effect of
zeolite Beta on the conversion of acetone to propylene is
relatively small due to lower amount of Brønsted acid sites.
Thus, the propylene yield over In2O3-10%Beta for the ETP
reaction is also relatively low. However, when the Beta
content in In2O3-Beta composites is high (In2O3-60%Beta and
In2O3-70%Beta), the propylene yield for the ETP reaction is also
relatively low. The reason is that too many Brønsted acid sites
favors the formation of BTX and C2H4. As a result, the optimum
yield of propylene is achieved on In2O3-Beta composites with
20-50% Beta.
Fig. 5 Influence of the proximity of In2O3 and zeolite Beta on
catalytic behaviors of the In2O3-Beta (1:1 mass ratio)
composite catalysts for ethanol conversion. (a) Stacking of 40-
60 mesh In2O3 and 40-60 mesh Beta. (b) In2O3 and Beta
powders were fully mixed in an agate mortar and then sieved
to 40-60 mesh. (c) Prepared by deposition-precipitation
method (see Experimental section), sieved to 40-60 mesh.
Fig. 4 Product distribution over In2O3, In2O3-50%Beta and
In2O3-50%Al2O3 catalysts for acetone conversion. Reaction
conditions: reaction temperature, 460 oC; acetone:H2O:H2:N2 =
1
5:11:8:76, molar ratio; WHSV of acetone, 0.12 h− ; time-on-
stream, 3 h.
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Reaction conditions: reaction temperature, 460 oC; WHSV of Fig. 7 Influence of WHSV on product distribution over In2O3-
ethanol, 0.2 h−1; time-on-stream, 3 h.
50%Beta composite for
ethanol conversion. Reaction
conditions: reaction temperature, 460 oC; time-on-stream, 3 h.
Effect of reaction conditions
We further investigated the effect of space velocity
(WHSV) on the product distribution over In2O3-50%Beta
We chose In2O3-50%Beta composite as
a representative
catalyst to investigate the effect of reaction temperature on
the product distribution for the ETP reaction, and the results
are shown in Fig. 6. The C3H6 yield increases from 43.9% to
50.0% with an increase in reaction temperature from 440 oC to
o
composite for the ETP reaction at 460 C, and the results are
shown in Fig. 7. In these experiments, WHSV was adjusted by
varying the weight of the In2O3-50%Beta composite catalyst,
while other reaction conditions were kept unchanged. Higher
WHSV value implies shorter residence time. As discussed
above, acetone is the intermediate for the conversion of
ethanol to propylene, and its conversion to propylene is a slow
step. Hence, higher propylene yield will be expected at longer
o
460 C, which is mainly due to the decrease in yields of C2H4,
C4H8, COx, C2-C4 paraffins and BTX. A further increase in
reaction temperature leads to the decrease in C3H6 yield,
which is mainly due to the increase in yields of COx, CH4 and
C2-C4 paraffins. The C3H6 yield at 500 oC is similar to that at 480
oC. Thus the highest yield of C3H6 is obtained at 460 oC. In
addition, with increasing the reaction temperature from 440 oC
1
residence time. When the WHSV value drops from 0.8 h− to
0.2 h−1, the C3H6 yield increases from 45.2% to 50.0%, but the
acetone yield drops obviously from 9.8% to 1.7%. The yield of
C4H8 (mainly isobutene) declines slightly, whereas that of BTX
increases slightly.
o
to 500 C, the CH4 yield also increases slightly (from 0.8% to
2.6%), but the BTX yield drops slightly (from 4.6% from 1.9%).
Catalyst stability
The stability of the In2O3-50%Beta composite in terms of
propylene yield was also evaluated, and the results are shown
in Fig. 8. The ethanol conversion keeps 100% during 105 h of
time-on-stream operation at 460 oC. The yield of C3H6 remains
stable at around 50% during the initial 43 h. After that, the
yield of C3H6 diminishes slowly and that of acetone increases
concurrently, which is due to the loss of active sites for
acetone-to-propylene conversion. The C3H6 yield is still above
40% after 81 h of the reaction and it drops to around 34% after
105 h of the reaction. Accordingly, the acetone yield increases
from around 4% after 43 h time-on-stream to 25% after 105 h
time-on-stream. The yield of BTX decreases slightly from
around 4% at the initial 1 h to 0.5%, and that of C2-C4 paraffins
decreases slightly from around 6% to 4%. Meanwhile, the
yields of other products remain almost constant.
Fig.
distribution over In2O3-50%Beta composite for ethanol
6
Influence of reaction temperature on product
1
conversion. Reaction conditions: WHSV of ethanol, 0.2 h−
time-on-stream, 3 h.
;
Fig. 8 Stability test for the ETP reaction over In2O3-50%Beta
composite. Reaction conditions: reaction temperature, 460 oC;
1
WHSV of ethanol, 0.2 h−
.
The In2O3-50%Beta composite collected before and after the
stability test were characterized by XRD. As shown in Fig. 9, no
differences in the diffraction patterns were seen for fresh and
spent catalysts, demonstrating the maintenance of phase
6 | Green Chem., 2017, 19, 1-3
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structure after the stability test. 27Al MAS NMR was used to
characterize the In2O3-50%Beta composite collected before
and after the stability test, and the results are shown in Fig. 10.
For both fresh and spent catalysts, only an intense signal at 54
ppm, which is assigned to tetrahedral coordinated framework
Al,37,38 was seen. The absence of the signal at 0 ppm attributed
to extra-framework Al in octahedral coordination37,38 for both
fresh and spent catalysts suggests that no dealumination
occurred during the long-term experiment. The 27Al NMR
signal of spent catalyst is obviously broader than that of fresh
one. This can be attributed to coke species interacting with the
AlO4 groups of the zeolite framework.39,40
Coking is generally responsible for the catalyst deactivation
in acid-catalyzed conversion of ethanol.4,9,26 The TG analysis
shows that 4.7 wt% coke was detected on the In2O3-50%Beta
composite after 105 h time-on-stream. Raman spectroscopy
was used to investigate the nature of deposited carbon, and
the result is shown in Fig. S4. The G-band and D-band were
observed at 1609 and 1374 cm−1, respectively, for spent In2O3-
50%Beta composite. This observation is indicative of graphitic
and amorphous carbon deposition.41,42 As presented in Table
2, the amount of acid sites on In2O3-50%Beta obviously
decreases from 0.517 to 0.318 mmol g−1 after the stability test,
whereas the amount of basic sites remains almost unchanged.
Coke deposition is responsible for the decrease in acidity. In
contrast, the conversion of In2O3-50%Beta for cumene cracking
decreases more significantly from 38.4% to 4.7% after the
stability test, suggesting that coke is more readily to deposit on
Brønsted acid sites.43,44 Due to the decrease in acidity, the
intermediate of acetone can not be converted in time. Thus,
the yield of acetone increases and that of propylene
decreases.
Fig. 10 27Al MAS NMR spectra of In2O3-50%Beta composite
before and after the stability test.
Conclusions
We report for the first time the excellent catalytic
performance of In2O3-Beta composite in the reaction of
ethanol to propylene (ETP). The propylene yield is strongly
dependent on the composite composition, i.e. acidity of the
catalyst. The optimal result is achieved on the catalyst with 20-
50% Beta, which can afford around 50% propylene yield. The
superior propylene yield of In2O3-Beta composite compared to
In2O3 (around 32%) is due to the fact that zeolite Beta in In2O3-
Beta composite catalyst enhances the conversion of the
intermediate of acetone to propylene via an additional
reaction pathway. The proximity of these two components
(In2O3 and zeolite Beta) plays a crucial role in giving a high yield
of propylene for the ETP reaction. The yield of propylene over
the In2O3-50%Beta composite remains stable at around 50%
o
for 43 h at 460 C and a space velocity of 0.2 h−1. This work
affords a new strategy for the design of a high-performance
catalyst by combining In2O3 and zeolite for the ETP reaction.
Experimental
Catalyst preparation
A series of In2O3-x%Beta composite catalysts (x% = 10%, 20%,
30%, 40%, 50%, 60%, 70%) were prepared via deposition-
precipitation method, where x% represents the weight
percentage of H-Beta in the catalysts. 1.5 g H-Beta zeolite
(Si/Al molar ratio = 14, Nankai University Catalyst Co., Ltd.) was
dispersed in 250 mL deionized water and the pH value was
adjusted to 9 with aqueous ammonia (3 mol L−1). Then
aqueous ammonia (3 mol L−1) and a calculated amount of
aqueous In(NO3)3 (0.2 mol L−1) were simultaneously added
dropwise into the above Beta suspension under vigorous
stirring. During the whole precipitation process, the pH value
was kept constant at 9 until the In(NO3)3 solution was used up.
Fig. 9 XRD patterns of In2O3-50%Beta composite before and
after the stability test.
The obtained suspension was aged for 24 h at room
temperature, washed with deionized water and dried at 100 oC
overnight. Finally, the product was calcined at 700 oC in air
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flow for 6 h. For comparison, In2O3 was prepared in the same evaporators filled with ethanol and H2O, respectively., then
way without use of H-Beta zeolite. In2O3-50%Al2O3 with 50 were mixed and passed through the catalyst. Unless otherwise
o
stated, the reaction temperature was 460 C, the catalyst load
was 0.8 g (40–60 mesh), and the weight hourly space velocity
(WHSV) of ethanol was 0.2 h−1. Prior to the reaction, the
catalyst was pretreated in N2 flow at 500 oC for 1 h. The
hydrocarbon reaction products including hydrocarbon
oxygenates were analyzed periodically on-line with a gas
chromatograph (GC) equipped with a FID and a PoraPLOT Q
capillary column (50 m × 0.32 mm × 10 µm). CH4 and COx (CO
and CO2) were analyzed on-line by another GC equipped with a
wt% γ-Al2O3 in the catalyst was prepared in the same way
1
using γ
-Al2O3 (268 m2 g− , Alfa Aesar) as a substitution of H-
Beta zeolite.
Catalyst characterization
X-ray diffraction (XRD) patterns were recorded on a Bruker D8
Advance X-ray diffractometer using nickel-filtered Cu Kα
radiation at 40 kV and 40 mA. The BET surface areas and pore
volumes of the samples were analyzed by N2 sorption at
oC using a Quantachrome Autosorb iQ2 instrument. Before
analysis, all samples were degassed in vacuum at 300 oC for 10 by TCD, the products were passed through a cold trap at
h. Field-emission scanning electron microscopy (FE-SEM) to remove the majority of water. The yield and selectivity were
−196
TCD and a 3 m long TDX
−
01 packed column. Before analyzing
3 oC
−
images were recorded on a Nova NanoSEM 450 instrument.
27Al magic-angle spinning nuclear magnetic resonance (27Al
MAS NMR) characterization was performed on an AVANCE III
400WB instrument at a resonance frequency of 104.3 MHz.
The samples were hydrated in a desiccator over a saturated
calculated on the carbon basis.
Acknowledgements
This work was supported by National Key R&D Program of
China (2017YFB0602200), the Science and Technology
Commission of Shanghai Municipality (13DZ2275200) and
NaCl solution for
3 days prior to the measurements.
Thermogravimetric (TG) analysis was performed in air flow on
a TA SDT Q600 apparatus to determine the amount of coke Shanghai Research Institute of Petrochemical Technology
SINOPEC.
deposited on the catalyst after the stability test. The nature of
deposited carbon was investigated by Raman spectra recorded
on a HORIBA Jobin Yvon XploRA spectrometer with an exciting
wavelength of 532 nm.
Notes and references
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A table of contents entry
The superior propylene yield of In2O3-Beta composite (ca. 50%) for conversion
of ethanol to propylene compared to In2O3 (ca. 32%) is due to the fact that zeolite
Beta in the composite enhances the conversion of the intermediate of acetone to
propylene via an additional reaction pathway.