Direct synthesis of ethanol from dimethyl ether and syngas over combined H-Mordenite and Cu/ZnO catalysts

Article abstract of DOI:10.1002/cssc.201000109

Ethanol was directly synthesized from dimethyl ether (DME) and syngas with the combined H-Mordenite and Cu/ZnO catalysts that were separately loaded in a dual-catalyst bed reactor. Methyl acetate (MA) was formed by DME carbonylation over the H-Mordenite catalyst. Thereafter, ethanol and methanol were produced by MA hydrogenation over the Cu/ZnO catalyst. With the reactant gas containing 1.0 % DME, the optimized temperature for the reaction was at 493 K to reach 100 % conversion. In the products, the yield of methanol and ethanol could reach 46.3 % and 42.2 %, respectively, with a small amount of MA, ethyl acetate, and CO₂. This process is environmentally friendly as the main byproduct methanol can be recycled to DME by a dehydration reaction. In contrast, for the physically mixed catalysts, the low conversion of DME and high selectivity of methanol were observed.Do or dual not: A dual-catalyst bed reactor loaded separately with the Cu/ZnO and H-Mordenite catalyst is employed to directly synthesize ethanol from dimethyl ether (DME) and syngas. The yield of ethanol and the main byproduct methanol are 42.2 % and 46.3 %, respectively. The latter can be further recycled to DME realizing an environmentally friendly process.

Full text of DOI:10.1002/cssc.201000109

DOI: 10.1002/cssc.201000109
Direct Synthesis of Ethanol from Dimethyl Ether and
Syngas over Combined H-Mordenite and Cu/ZnO Catalysts
Xingang Li,*[a] Xiaoguang San,[c] Yi Zhang,*[b] Takashi Ichii,[c] Ming Meng,[a] Yisheng Tan,[d] and
Noritatsu Tsubaki*[c]
Ethanol was directly synthesized from dimethyl ether (DME)
and syngas with the combined H-Mordenite and Cu/ZnO cata-
lysts that were separately loaded in a dual-catalyst bed reactor.
Methyl acetate (MA) was formed by DME carbonylation over
the H-Mordenite catalyst. Thereafter, ethanol and methanol
were produced by MA hydrogenation over the Cu/ZnO cata-
lyst. With the reactant gas containing 1.0% DME, the opti-
mized temperature for the reaction was at 493 K to reach
100% conversion. In the products, the yield of methanol and
ethanol could reach 46.3% and 42.2%, respectively, with a
small amount of MA, ethyl acetate, and CO2. This process is en-
vironmentally friendly as the main byproduct methanol can be
recycled to DME by a dehydration reaction. In contrast, for the
physically mixed catalysts, the low conversion of DME and
high selectivity of methanol were observed.
Introduction
Industrially, ethanol is mainly synthesized by catalytic hydration
of ethylene, which mainly comes from petroleum with a high
price. To reduce the greenhouse effect and to improve the
energy efficiency, bioethanol is regarded as one of the most
promising alternative fuels, and it is mainly produced by the
traditional fermentation with corn or other foods. However,
the rapidly growing demand causes high food prices and even
worldwide food shortage, and the EtOH production from non-
edible biomass or other cheaper fossil resources becomes a
new challenge.
of the precious Rh metal as the carbonylation catalyst increas-
es the economic cost, and the used promoter, such as aryl and
halogen, can corrode the reactor, easily poison the catalyst,
and induce environmental pollution. Based on this method,
the selective hydrogenolysis of methyl and ethyl acetate to
EtOH in the gas phase has been studied,[6] but it is hardly com-
mercialized due to the expensive price of acetic ester.
Recently, it was found that the solid zeolites or the solid
acids, which are much cheaper than noble metals and environ-
mentally friendly, can be utilized for MeOH or dimethyl ether
(DME) carbonylation.[7] Among these catalysts, H-Mordenite (H-
MOR) is one of the most promising catalysts, and its potential
application in catalytic conversion of DME or MeOH to acetate
Presently, syngas (CO+H2) can be efficiently produced from
biomass and coal. Therefore, direct synthesis of EtOH from
syngas is considered as one of the most interesting routes[1]
with shortcomings of severe reaction conditions and quite low
purity of EtOH. Pan et al. reported a spatially confined Rh sup-
ported catalyst on the interior of the carbon nanotubes, which
could greatly enhance EtOH productivity.[2] Unfortunately, the
usage of the expensive Rh catalyst prevented it from commer-
cialization. Synthesis of EtOH from syngas and methanol
(MeOH) over copper catalysts is also regarded as an attractive
process. However, this reaction is strongly inhibited by CO2
produced in the course of the reaction, and the obtained se-
lectivity of EtOH is rather low.[3] Moreover, direct EtOH synthe-
sis from MeOH by the homologation method was also stud-
ied,[4] using the expensive Ru catalyst and corrosive alkyl
iodide, but a large amount of the higher alcohols and complex
products was produced as the byproducts.
[a] Prof. X. Li, Prof. M. Meng
Tianjin Key Laboratory of Applied Catalysis Science and Technology
School of Chemical Engineering and Technology Institution
Tianjin University, Tianjin 300072 (PR China)
Fax: (+86)22-27892275
E-mail: xingang_li@tju.edu.cn
[b] Y. Zhang
Research Center of the Ministry of Education
for High Gravity Engineering and Technology
Beijing University of Chemical Technology
Beijing 100029m (PR China)
E-mail: yizhang@mail.buct.edu.cn
[c] Dr. X. San, T. Ichii, Prof. N. Tsubaki
Department of Applied Chemistry
School of Engineering, University of Toyama
Gofuku 3190, Toyama 930-8555 (Japan)
Fax: (+81)76-445-6846
Another interesting method is MeOH carbonylation to form
acetic acid. The latter is then converted to acetate ester by
esterification, followed by hydrogenolysis of the formed ace-
tate ester to produce EtOH.[5] This route includes the carbony-
lation, esterification, and hydrogenation processes with MeOH
and syngas acting as the raw materials. These complicated
techniques limited its application. In particular, the utilization
E-mail: tsubaki@eng.u-toyama.ac.jp
[d] Prof. Y. Tan
State Key Laboratory of Coal Conversion
Institute of Coal Chemistry, Chinese Academy of Science
Taiyuan 030001 (PR China)
Supporting Information for this article is available on the WWW under
http://dx.doi.org/10.1002/cssc.201000109.
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Direct Synthesis of Ethanol over H-Mordenite and Cu/ZnO
ester[8–10] or acetic acid,[11,12] respectively, has attracted much at-
tention. Iglesia and co-workers reported that H-MOR was very
active and selective for DME carbonylation to methyl acetate
(MA) at the low temperature from 423 to 463 K,[8,9] and the
active sites for carbonylation located in the 8-member-ring (8-
MR) channel.[10] The carbonylation process included the surface
reaction between DME and the hydroxyl groups to form the
surface methoxy, and then the insert of CO on the methoxy.
The latter was the rate-determining step to form acetyls.
Thereafter, the obtained acetyls reacted with another DME
molecule to produce MA and to regenerate the surface me-
thoxy.[11–13] If MeOH is substituted for DME here, a lot of water
would be produced through MeOH dehydration. The carbony-
lation reaction would be seriously hindered because of the
competitive adsorption between water and MeOH on the
acidic sites of the zeolite catalyst.[11,14] Therefore, DME is the
more suitable feedstock for the carbonylation reaction than
MeOH over the H-MOR zeolite. Furthermore, DME carbonyla-
tion seems more favorable than MeOH from the economic
viewpoint because it can directly be produced from syngas
with enhanced efficiency.[15]
Results and Discussion
Physicochemical properties of the catalysts
For the H-MOR catalyst, the BET surface area could reach
383 m2 gꢀ1 and the pore volume was 0.14 cm3 gꢀ1. The proper-
ty of the Cu/ZnO catalyst was characterized by H2-TPR
(Figure 1). Only one broad peak was observed from 400 to
Presently, DME production from syngas is an effective and
mature technology.[15,16] Considering that the reactions of DME
carbonylation to MA and ester hydrogenation to alcohol oc-
curred at a similar temperature, we first proposed a novel two-
step route for EtOH synthesis directly from DME and syngas
using a dual-catalyst bed reactor. This work has been shortly
introduced in our previous publication.[17] Briefly, DME was ini-
tially converted to MA through carbonylation over a series of
zeolite catalysts, such as the H-MOR, H-ZSM5, and H-b, and the
produced MA was then hydrogenated to EtOH over a Cu/ZnO
catalyst. Very interestingly, the two processes as mentioned
above could be synergistically enhanced.[17] This new route is a
potential way to meet the industrial request for EtOH synthe-
sis, because only two processes occur in one reactor and the
utilized catalysts are cheap. The complete reaction of the two
combined processes [Equations (1)+(2)] can be described as
follows:
Figure 1. TPR profile of the Cu/ZnO catalyst.
550 K. To ensure the sufficient reduction of Cu/ZnO, the cata-
lyst was reduced at 573 K before it was used in the activity
test. The detailed physicochemical properties of the Cu/ZnO
catalyst are listed in Table 1. The BET surface area of the Cu/
ZnO catalyst was 64.3 m2 gꢀ1 and the Cu surface area measured
by titrating of Cu surface atoms with N2O was 23.2 m2Cu gcꢀa1t.
Table 1. The physicochemical properties of the Cu/ZnO catalyst.
Sample
BETsurface
area[a] [m2 gꢀ1
Exposed Cu surface
area[b] [m2 Cug
Average crystallite
size[c] [nm]
ꢀ1
]
]
cat
CO þ CH3OCH3 Ð CH3COOCH3
ð1Þ
ð2Þ
ð3Þ
dCu
dZnO
Cu/ZnO
64.3
23.2
7.7
6.3
CH3COOCH3 þ 2H2 Ð CH3CH2OH þ CH3OH
CO þ 2H2 þ CH3OCH3 Ð CH3CH2OH þ CH3OH
[a] The surface area was determined by N2 physisorption. [b] N2O pulse ti-
tration was employed to measure the exposed metallic copper surface
area. [c] Crystal sizes were calculated with the Scherrer equation at 43.28
and 36.38 for the metallic copper and zinc oxide, respectively.
In this work, EtOH was directly synthesized from DME and
syngas using a dual-catalyst bed reactor. The H-MOR zeolite
was loaded on the first catalyst bed for DME carbonylation,
and the Cu/ZnO catalyst was loaded on the second one for
MA hydrogenation. The structures of the catalysts were charac-
terized by the BET surface area, X-ray diffraction (XRD), temper-
ature-programmed reduction (TPR), and Cu surface area mea-
surement. The catalytic performance of EtOH synthesis was
evaluated in detail to find the optimized reaction conditions,
and was also compared with the physically mixed catalysts.
Moreover, the different behavior of the catalytic activity under
various reaction conditions was also discussed.
The XRD pattern of the Cu/ZnO catalyst after reduction is
shown in Figure 2. Only two phases, that is, the metallic Cu
and ZnO, were clearly observed. It indicates that the H2-TPR
peak in Figure 1 was correlated to the reduction of copper
oxide. The Scherrer equation was used to determine the mean
size of the crystallites of the Cu/ZnO catalyst at their strongest
diffraction peaks, 43.28(Cu) and 36.38(ZnO). The average crys-
tallite size of the Cu and ZnO was about 7.7 and 6.3 nm, re-
spectively.
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X. Li, N. Tsubaki et al.
was obtained at above 513 K. However, the productivity of MA
presented a volcano-type variation, and its maximum value,
1020.4 mmolkgꢀ1 hꢀ1, was achieved at 493 K. Here, the conver-
sion of DME was 82.4%. Figure 3b clearly shows that the prod-
ucts of the carbonylation reaction included MA, ethyl acetate
(EA), CO2, and CH4. With the increase of reaction temperature
from 423 to 493 K, the selectivity of MA dropped slightly from
100 to 91.6%. Whereas, when the reaction temperature was
above 493 K, it decreased significantly, indicating that the side
reactions were preferred at a high temperature. At 493 K, the
optimized catalytic performance for DME carbonylation was
achieved with a maximum yield of 75.0% of MA, which is simi-
lar to the results of the productivity of MA in Figure 3a.
As proposed by Cheung et al.,[9] DME carbonylation to MA
on the H-MOR zeolite includes the following processes [Equa-
tions (4)–(22)]:
Figure 2. XRD pattern of the Cu/ZnO catalyst.
CH3OCH3 þ ½SiOðHÞAlꢁ Ð CH3OCH3ꢀ½SiOðHÞAlꢁ
CH3OCH3ꢀ½SiOðHÞAlꢁ Ð ½SiOðCH3ÞAlꢁ þ CH3OH
CH3OH þ ½SiOðHÞAlꢁ Ð ½SiOðCH3ÞAlꢁ þ H2O
ð4Þ
ð5Þ
ð6Þ
ð7Þ
ð8Þ
ð9Þ
DME carbonylation over the H-MOR catalyst
Figure 3 shows the influence of the reaction temperature for
DME carbonylation over the H-MOR catalyst. As in Figure 3a,
the conversion of DME increased dramatically following the in-
crease of the reaction temperature, and 100% DME conversion
*
*
H2O þ Ð H2O
*
*
CO þ Ð CO
*
*
½SiOðCH3ÞAlꢁ þ CO ! ½SiOðCOCH3ÞAlꢁ þ
½SiOðCOCH3ÞAlꢁ þ CH3OCH3 ! ½SiOðCH3ÞAlꢁ þ CH3COOCH3
½SiOðCOCH3ÞAlꢁ þ CH3OH ! ½SiOðHÞAlꢁ þ CH3COOCH3
ð10Þ
ð11Þ
Here, a small amount of CO2 was detected in the products
from 453 to 493 K, and its selectivity increased greatly with
CH4 appearing simultaneously among the products at above
513 K. At the temperature below 513 K, CO2 was mainly attrib-
uted to water–gas shift (WGS) reaction, which has been con-
firmed by our results of the WGS reaction in the Supporting In-
formation. Table S1 clearly shows the results of the WGS reac-
tion at 493 K. The trace amount of CO2 could be produced
even without water injection. At above 513 K, the formed MA
might be decarbonized to hydrocarbons[18] such as CH4. In ad-
dition, it was reported that DME could be decomposed to CO,
[19]
H2, and CH4 on the acidic sites at high temperature.
Moreover, a trace amount of EA was also observed in Fig-
ure 3b, which might be produced by the reaction between
MA and methyl formed in Equations (5) and (6). At the high
temperature, hydrocarbons and coke were formed due to the
oligomerization reactions.
The thermal analysis experiments were carried out to charac-
terize the coke formation on the catalyst after the reaction.
The thermal gravimetry (TG) spectra for the fresh H-MOR cata-
lyst and the used H-MOR catalysts after the reaction at 493
and 533 K for 2 h are presented in Figure 4. For the used cata-
lyst at 493 K, its weight loss percentage and variation tendency
were very similar to those of the fresh catalyst. Nevertheless,
the weight of the used catalyst at 533 K lost about 11%, more
than that of the fresh one. Simultaneously, a strong exothermic
Figure 3. Effect of the reaction temperature for DME carbonylation over the
^
H-MOR catalyst on a) the conversion of DME ( ) and the productivity of MA
("), and b) the selectivity of MA (&), EA (*), CO2 (~), CH4 (!), and the
yield of MA (N). Reaction conditions: WeightH-MOR =0.5 g; reactant gas DME/
CO/Ar/He (1.0:47.4:1.6:50.0); pressure=1.5 MPa; total flow rate=40
mLminꢀ1
.
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Direct Synthesis of Ethanol over H-Mordenite and Cu/ZnO
MA hydrogenation over the Cu/ZnO catalyst
MA hydrogenation over the Cu/ZnO catalyst was investigated
under the atmosphere pressure because MA is easily liquefied
due to its high boiling point (i.e., 330 K). H2 acted as the carrier
gas to bring the saturated vapor of MA into the reactor. The
results of the reaction at 493 K are listed in Table 3. The con-
Table 3. MA hydrogenation over the Cu/ZnO catalyst.[a]
Conversion [%]
MA
Selectivity [%]
MeOH
EtOH
42.7
EA
24.1
50.8
6.5
Figure 4. Thermal analysis of the fresh H-MOR catalyst (solid lines) and the
used H-MOR catalysts after the reaction at 493 K (dot lines) and 533 K (dash
lines).
[a] Reaction conditions: temperature=493 K; weightCu/ZnO =0.5 g; reac-
tant gas MA/CO/Ar/H2 (1.1:25.0:1.5:72.4); pressure=0.1 MPa; total flow
rate=80 mLminꢀ1
.
peak was observed from the differential thermal analysis (DTA)
profile. Moreover, we observed that the white color of the
fresh H-MOR zeolite changed to a brown color after the reac-
tion at the high reaction temperature, which demonstrated
that a lot of coke was formed on the catalyst after the catalytic
test at 533 K. This formation may be a result of the oligomeri-
zation of hydrocarbons formed by DME and MA decomposi-
tion at the high reaction temperature.
version of MA was only 24.1%, which might be due to the low
reaction pressure. As presented in Equation (2), one MA and
two H2 molecules produce one EtOH and one MeOH molecule.
Thus, the high pressure is favorable to the proceeding of MA
hydrogenation. Here, the selectivity of MeOH and EtOH in the
products was 50.8% and 42.7%, respectively. EA with 6.5% se-
lectivity was formed by transesterification of MA with EtOH.
Accounting the proportion of EtOH consumed by transesterifi-
cation, the molar ratio of MeOH and EtOH in the products was
almost 1:1.
Here, H2 was substituted for helium in the feeding gas mix-
ture to investigate the influence of H2 for DME carbonylation.
As listed in Table 2, the conversion of DME, the selectivity of
From the results of Figure 3 and Table 3, it is very clear that
DME carbonylation over the H-MOR catalyst or MA hydrogena-
tion over the Cu/ZnO catalyst is practical. Most importantly,
the two reactions could be conducted at a similar temperature.
Therefore, the two reactions were combined to produce EtOH
directly with the separately loaded catalysts in the dual-catalyst
bed reactor or the physically mixed catalysts for comparison.
Table 2. DME carbonylation over the H-MOR catalyst in the presence of
H2.[a]
Conversion [%]
Selectivity [%]
Productivity [mmolkgꢀ1 hꢀ1
MA
]
DME
CO
MA
EA
CO2
5.4
83.1
1.7
92.2
2.4
1076.1
[a] Reaction conditions: temperature=493 K; weightH-MOR =0.5 g; reactant
gas DME/CO/Ar/H2 (1.0:47.4:1.6:50.0); pressure=1.5 MPa; Total flow
EtOH synthesis over the physically mixed H-MOR and Cu/
ZnO catalysts: A comparative study
rate=40 mLminꢀ1
.
Here, the EtOH synthesis process was evaluated with the feed-
ing stream of DME and syngas over the physically mixed H-
MOR and Cu/ZnO catalysts. The weight ratio of the H-
MOR/(Cu/ZnO) catalysts was 0.5, 1, and 2. The conversion of
the reactants and the selectivity of the products are listed in
Table 4. The conversion of DME was very low for all of the
physically mixed catalysts, and the selectivity of MeOH in the
products was more than 94%.
MA, and the productivity of MA were 83.1%, 92.2%, and
1076.1 mmolkgꢀ1 hꢀ1, respectively, at 493 K. These results were
very similar to those of DME carbonylation without H2 in the
feeding gas (Figure 3), indicating that the addition of H2 had
little influence on the reaction of DME carbonylation over the
H-MOR catalyst.
Based on the above results, the optimized catalytic perfor-
mance for DME carbonylation could be realized at 493 K over
the H-MOR catalyst. The methoxy production and the followed
carbonylation with CO occurred selectively within the 8-MR
channels of the H-MOR zeolite,[10] whereas the acidic sites pre-
sented in the 12-MR channels were responsible for the forma-
tion of hydrocarbons at the higher temperature.[12]
In our previous work, it was found that MeOH could be syn-
thesized from CO hydrogenation over the Cu/ZnO catalyst at
the temperature range from 423 to 443 K.[20] In the present
conditions, a high proportion of CO and H2 (DME/CO/Ar/H2 =
1.0:47.4:1.6:50.0) existed in the reactants, and a small amount
of CO could be hydrogenated to form MeOH. Because the con-
centration of CO and H2 was much higher than that of DME,
MeOH became the main product even if the conversion of CO
was quite low. Moreover, it was reported that a hybrid catalyst
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X. Li, N. Tsubaki et al.
MOR catalyst to form MA, which finally resulted in the fairly
low EtOH selectivity in the products.
Table 4. Effect of the different weight ratio of the physically mixed H-
MOR and Cu/ZnO catalysts.[a]
H-MOR to Cu/ZnO
(weight ratio)
Conversion [%]
Selectivity [%]
EtOH synthesis with the dual-catalyst bed reactor containing
the H-MOR and Cu/ZnO catalysts
DME
CO
MeOH
EtOH
CO2
2:1
1:1
1:2
7.1
6.7
6.0
1.3
1.8
2.4
94.1
95.1
95.4
3.3
2.5
1.5
2.6
2.4
3.1
With the dual-catalyst bed reactor, the H-MOR catalyst for DME
carbonylation and the Cu/ZnO catalyst for MA hydrogenation
were separately loaded in the reactor as shown in Scheme S1
(see the Supporting Information). Figure 5 summarizes these
reaction results obtained at 493 K with the various feeding gas
compositions. For comparison, one of the experiments with
the dual-catalyst bed reactor was carried out with the same re-
actant gas composition (DME/CO/Ar/H2 =1.0:47.4:1.6:50.0) as
the physically mixed catalysts. Apparently, the conversion of
DME increased continuously following the decrease of DME
partial pressure. When the composition of the feeding gas was
DME/CO/Ar/H2 =1.0:47.4:1.6:50.0, 100% DME conversion was
achieved. Meanwhile, the selectivity of MeOH and EtOH was
almost constant and maintained at about 46% and 41%, re-
spectively. Here, the selectivity of MA in the products was
much lower than that of DME carbonylation alone over the H-
MOR catalyst (Figure 3b), which suggests that the produced
[a] Reaction conditions: temperature=493 K; weightH-MOR,Cu/ZnOmixedcat.
1.0 g; reactant gas DME/CO/Ar/H2 (1.0:47.4:1.6:50.0); pressure=1.5 MPa;
total flow rate=40 mLminꢀ1
=
.
containing H-MOR and Cu/ZnO/Al2O3 catalysts could be uti-
lized to directly synthesize DME from syngas.[21] This mainly
contains two steps, that is, CO hydrogenation to MeOH over
the Cu/ZnO/Al2O3 catalyst, and MeOH dehydration to DME
over the H-MOR catalyst. Therefore, there are several possible
processes involved in this reaction:
* DME was carbonylated over the H-MOR catalyst to pro-
duce MA.
* MA was hydrogenated to EtOH and MeOH over the
neighboring Cu/ZnO catalyst.
* Abundant MeOH was produced from CO hydrogenation
over the Cu/ZnO catalyst.
* MeOH adsorbed competitively over the acidic sites of
the H-MOR catalyst with DME.
* MeOH was dehydrated to DME over the acidic sites of
the H-MOR catalyst.
Under such a condition, CO hydrogenation to MeOH with
low conversion over the Cu/ZnO catalyst occurred.[20] The com-
petitive adsorption between DME and MeOH in the 8-MR
channel on the H-MOR catalyst, which was regarded as the
active centers for DME carbonylation, also hindered the pro-
ceeding of DME carbonylation. If the raw material DME was
substituted by MeOH, the proton at the acidic sites would be
regenerated as shown in Equation (11). Thereafter, a lot of
water could be produced in Equation (6). Moreover, MeOH
could also be dehydrated to water and DME on the acidic sites
of the H-MOR catalyst,[21,22] in which the newly-formed DME
could not be identified with the original DME in the raw mate-
rials. Consequently, a rather low apparent DME conversion was
observed. As reported by Cheung et al.[8,9] and Bhan et al.,[10]
water severely inhibited DME carbonylation. Accordingly, the
MA formation was greatly suppressed as well as the EtOH pro-
duction.
All of these findings indicate that the reaction over the phys-
ically mixed catalysts was very complex. The Cu/ZnO catalyst
acted here mainly as the MeOH synthesis catalyst rather than
the competitive ester hydrogenation catalyst. MeOH became
the major product by CO hydrogenation over the Cu/ZnO cata-
lyst. Particularly, the formed MeOH could also be dehydrated
to DME on the acidic sites of the H-MOR catalyst, significantly
lowering the apparent DME conversion. Due to the unfavora-
ble influence of H2O formed through MeOH dehydration, only
a small amount of DME reacted with CO over the acidic H-
Figure 5. Effect of the concentration of DME and CO in the DME/CO/Ar/H2
feeding gas with the dual-catalyst bed reactor on a) the conversion of CO
^
(&) and DME ( ) and the selectivity of products MeOH (!), EtOH (~), MA
^
(N), EA( ), CO2 (*), and b) the productivity of MeOH (3), EtOH ("), MA
(I) and the yield of MeOH (&), EtOH (*). Reaction conditions: Temperatur-
e=493 K; weightH-MOR =0.5 g; weightCu/ZnO =0.5 g; pressure=1.5 MPa (con-
taining 50.0% H2); total flow rate=40 mLminꢀ1
.
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Direct Synthesis of Ethanol over H-Mordenite and Cu/ZnO
MA by DME carbonylation over the H-MOR catalyst was mainly
in situ hydrogenated to EtOH and MeOH over the Cu/ZnO cat-
alyst. Moreover, the conversion of DME increased from 82.4%
over the single H-MOR catalyst (Figure 3a) to 100% with the
dual-catalyst bed reactor (Figure 5a), which was due to the
synergistic effect of the two reactions as we reported before.[17]
MA hydrogenation in the second Cu/ZnO catalyst layer pro-
moted the proceeding of DME carbonylation in the first H-
MOR catalyst layer.[17]
which saved a lot of DME in the feeding gas, and the unreact-
ed CO and H2 gas could be recycled as the raw material for
the reaction.
Figure 6 presents the effect of the reaction pressure on the
EtOH synthesis with the feeding gas of DME/CO/Ar/H2
(1.0:47.4:1.6:50.0) with a flow rate of 160 mLminꢀ1. As the re-
Here, the reaction routes were the initial DME carbonylation
to MA occurring in the H-MOR catalyst layer, followed by MA
hydrogenation in the Cu/ZnO catalyst layer:
In this process, the main byproduct MeOH was the potential
raw material for EtOH synthesis. It could be easily separated by
distillation to leave EtOH as the main product, and then dehy-
drated to produce DME. Other tiny byproducts, such as EA and
MA, could also be recycled and hydrogenated to EtOH and
MeOH. Accordingly, DME can be completely consumed to pro-
duce EtOH without any loss in theory to realize a green and
economical process.
Figure 6. Effect of the reaction pressure with the dual-catalyst bed reactor
on the conversion of CO (*) and DME (~), and the selectivity of MeOH
^
^
(&), EtOH ( ), MA (N), EA( ), and CO2 ("). Reaction conditions: Tempera-
ture=493 K; weightH-MOR =0.5 g; weightCu/ZnO =0.5 g; reactant gas DME 1.0/
CO/Ar/H2 (1.0:47.4:1.6:50.0); total flow rate=160 mLminꢀ1
.
With the reactant gas composition of DME/CO/Ar/H2 =
1.0:47.4:1.6:50.0, the productivity of EtOH and MeOH was
944.4 and 1154.2 mmolkgꢀ1 hꢀ1, respectively, which was similar
to that of MA obtained at 493 K in Figure 3a, (i.e.,
1020.4 mmolkgꢀ1 hꢀ1). This catalytic performance was signifi-
cantly better than that of the physically mixed catalysts. It was
also observed that the selectivity of MeOH in the final products
was slightly higher than that of EtOH. Even taking into account
the one EA molecule in the products that could produce two
additional EtOH molecules, the selectivity of MeOH was still
higher than that of EtOH. As discussed for the results of the
physically mixed catalysts (Table 4), this selectivity is mainly
due to CO hydrogenation over the Cu/ZnO catalyst to a slight
extent, as we reported before.[20]
action pressure increased from 1.5 to 5.0 MPa, the conversion
of DME increased from 31.7 to 54.6%. It coincided with the re-
sults of Bhan et al.[10] that the rate of MA synthesis did not rely
on the DME pressure, but increased linearly with the CO pres-
sure. Concerning the product distribution, more than 90% of
the products were MeOH and EtOH. The selectivity of EtOH in-
creased slightly from 42.6 to 45.0% following the reaction
pressure enhancement indicating that the increase of the reac-
tion pressure would improve the production of MA. Here, the
slight decrease of the selectivity of MA from 3.4 to 0.7% was
observed in Figure 6 following the increase of the reaction
pressure from 1.5 to 5.0 MPa. This result demonstrates that the
high partial pressure of H2 in the feeding gas accelerated MA
hydrogenation.
In Figure 5a, when the CO/DME ratio in the feeding gas
stream increased from 11:1 to 47:1, the conversion of DME in-
creased dramatically from 42.5 to 100% and the conversion of
CO dropped from 6.8 to 2.3%. It is very interesting that the
productivity of EtOH was almost constant as shown in Fig-
ure 5b, and did not depend on the concentration of DME. This
suggests that the active sites were saturated with the DME-de-
rived intermediates,[8] and the subsequent hydrogenation of
MA to MeOH and EtOH did not rely on the CO/DME ratio in
the feeding gas. Because the CO adsorption and methoxy spe-
cies carbonylation are very slow (acting as the rate-determin-
ing steps), the adsorbed CO surface concentration is lowered
with the low CO/DME ratio, especially considering the fact that
there is no metallic site on the H-MOR zeolite to accelerate CO
adsorption. If the CO/DME ratio is lower than 10, the DME con-
version is sharply reduced, whereas the CO conversion is
slightly enhanced. Here, the reactants containing 47.44% CO
and 1.02% DME (CO/DME=46.5) is the best composition,
Conclusions
For the direct EtOH synthesis from DME and syngas, a dual-cat-
alyst bed reactor containing the combined H-MOR and Cu/
ZnO catalysts was proposed and studied. The optimized reac-
tion temperature was found to be 493 K for DME carbonylation
over the H-MOR catalyst. Under such a condition, the produc-
tivity of MA could approach the maximum at
1020.4 mmolkgꢀ1 hꢀ1. The conversion of DME could reach
82.4%, and the selectivity of MA production was 91.6%. It was
also confirmed that MA hydrogenation could occur at this tem-
perature. For direct EtOH synthesis, 100% DME conversion and
42.2% EtOH selectivity were achieved using the dual-catalyst
ChemSusChem 2010, 3, 1192 – 1199
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X. Li, N. Tsubaki et al.
formed water during the reduction before entering the TCD. Ther-
mal analysis was carried out with the fresh and the used catalysts
on a DTG-60 (Shimadzu) to investigate the possible coke formed
on the catalyst. It was implemented in the air flow with
50 mLminꢀ1. The temperature increased from 300 to 1000 K at a
bed reactor, whereas the conversion of DME was quite low
and more than 94% in the products was MeOH for the physi-
cally mixed catalysts. Moreover, the increase of the reactant
pressure could promote DME carbonylation, and also further
enhance slightly the selectivity of EtOH.
rate of 5 Kminꢀ1
.
In conclusion, EtOH can be efficiently synthesized via combi-
nation of DME carbonylation over the H-MOR catalyst and MA
hydrogenation over the Cu/ZnO catalyst with the dual-catalyst
bed reactor. This novel EtOH synthesis method is environmen-
tally friendly, starting from DME and syngas, without using any
agriculture feed stocks and with the only byproduct of water,
as the other formed byproducts, such as MeOH, MA, and EA,
can be recycled as the raw material.
Catalytic test
All of the catalytic reactions were conducted with a packed-bed
stainless steel reactor (9.5 mm OD). To optimize the reaction tem-
perature for DME carbonylation, H-MOR (0.5 g , 0.2–0.4 mm) was
loaded into the reactor as mentioned above and was then heated
from room temperature to 773 K (8 Kminꢀ1) under flowing dry air
(80 mLminꢀ1) and maintained at that temperature for 2 h to
remove the adsorbed water and the organic impurities. After
being cooled to the reaction temperature, the reactant gas DME/
CO/Ar/He (1.0:47.4:1.6:50.0; 40 mLminꢀ1 with 1.5 MPa) was intro-
duced. To investigate the influence of H2 in the feeding gas to
Experimental Section
Catalyst preparation
The commercial H-MOR zeolite (SiO2/Al2O3 =15.8, SBET =383 m2 gꢀ1
)
DME
carbonylation,
the
reactant
gas
DME/CO/Ar/H2
(1.0:47.4:1.6:50.0; 40 mLminꢀ1 with 1.5 MPa) was also used to
compare the above experiment. MA hydrogenation was also stud-
ied using the same packed-bed stainless steel reactor loaded with
the Cu/ZnO catalyst (0.5 g). The catalyst was reduced by a flow of
hydrogen online for 2 h at 573 K, and then the saturation steam of
MA and superfluous hydrogen were introduced into the reactor.
The reaction pressure was 0.1 MPa.
for DME carbonylation was provided by Tosoh Corporation (Japan).
The Cu/ZnO catalyst (Cu/Zn=1:1, molar ratio) for MA hydrogena-
tion was prepared by a conventional co-precipitation method. Cu-
(NO3)2·3H2O (7.5 g; Kanto Chemical Co.) and Zn(NO3)2·6H2O (9.3 g;
Kanto Chemical Co.) were dissolved into diluted water (300 mL),
and then the obtained mixture solution and aqueous Na2CO3 solu-
tion (300 mL, 0.4 molLꢀ1; Kanto Chemical Co.) were added drop-
wise synchronously to keep a constant pH value of 8.5 at 333 K
with continuous stirring to form a blue-colored slurry. The slurry
was then aged overnight. The precipitate was filtrated and washed
with deionized water four times. The obtained solid was dried at
393 K for 12 h and was then calcined at 623 K for 1 h in air, fol-
lowed by being pelletized and screened to the size of 0.4 to
0.9 mm. Thereafter, the obtained precursor was reduced by a flow
of pure hydrogen (150 mLminꢀ1) at 573 K for 10 h, and then was
passivated by 1% oxygen diluted with nitrogen (30 mLminꢀ1) at
room temperature for 1 h.
For comparison, the H-MOR zeolite for DME carbonylation and the
Cu/ZnO catalyst for MA hydrogenation were also physically mixed
with various ratios. The physically mixed powder was pressed into
a pellet and was then screened to the size of 0.4 to 0.9 mm. The
obtained catalysts were also reduced by a flow of pure hydrogen
at 573 K for 10 h and passivated by 1% oxygen diluted with nitro-
gen at room temperature for 1 h.
For EtOH synthesis, a dual-catalyst bed reactor was used. H-MOR
(0.5 g) for DME carbonylation was put into the reactor at the
upper layer, and Cu/ZnO (0.5 g) for MA hydrogenation was loaded
at the lower layer. Before the reaction, the catalysts were reduced
by a flow of pure hydrogen at 573 K for 2 h. After being cooled to
493 K,
the
reactant
gas
containing
DME/CO/Ar/H2
(3.8:43.8:2.4:50.0), DME/CO/Ar/H2 (2.4:45.2:2.4:50.0), DME/CO/Ar/H2
(1.5:46.1:2.4:50.0, DME/CO/Ar/H2 (1.2:46.3:2.5:50.0), or DME/CO/Ar/
H2 (1.0:47.4:1.6:50.0) was introduced and the reaction pressure was
maintained at 1.5 MPa with the flow rate of 40 mLminꢀ1. For com-
parison, the physically mixed catalysts (1.0 g) with H-MOR/(Cu/
ZnO)=2:1, 1:1, or 1:2 in weight ratio was also evaluated for EtOH
synthesis. The detailed schematic drawing of the reactor is shown
in the Supporting Information (Scheme S1).
Effluent in gas phase from the reactor was analyzed by a gas chro-
matograph equipped with TCD (Porpak Q column for DME, CO,
CO2 and Ar). Ar in the feeding gas acted as an internal standard for
TCD–GC analysis. The liquid products were collected with an ice–
water trap with 1-butanol acting as the solvent, and were analyzed
by a flame-ionization detector (FID) with a connected dual column
packed by Gaskuropack 54 and Porapak N packing materials. 1-
propanol was employed as the internal standard. All liquid prod-
ucts were confirmed by GC–MS (Shimadzu GCMS 1600). All of the
selectivity values in the figures and the tables were calculated in
molecular selectivity, instead of carbon molar base. The productivi-
ty of EtOH was calculated by the collection of the liquid products
after 2 h.
Catalyst characterization
The BET surface area was determined by N2 physisorption method
using an automatic gas adsorption system (Quantachrome, Auto-
sorb-1, Yuasa Co.). The powder XRD patterns of the passivated
samples were collected using a Rigaku RINT 2400 X-ray diffractom-
eter with Cu-Ka radiation (l=0.154 nm). The X-ray tube was oper-
ated at 40 kV and at 40 mA. The mean crystallite sizes (d) of Cu
and ZnO were determined from the line half broadening of the dif-
fraction lines with the Scherrer equation. The Cu surface areas
were measured by pulse titrating of Cu surface atoms in the pre-
reduced samples with N2O.[23] The detailed experimental procedure
is described in the Supporting information. The reduction behavior
of the Cu catalysts was studied by TPR using a thermal conductivi-
ty detector (TCD). The temperature of the sample reactor increased
from 303 to 700 K at a rate of 5 Kminꢀ1. 5% H2/N2 mixture gas was
introduced into the reactor with the flow rate of 50 mLminꢀ1. The
5 ꢁ molecular sieve at the outlet of the reactor absorbed the
Acknowledgements
This work was financially supported by the “863 Program” of the
Ministry of Science & Technology of China (No. 2008AA06Z323),
the National Natural Science Foundationof China (No. 20806056),
the Doctoral Fund of Ministry of Education of China (No.
200800561002), the Foundation of State Key Laboratory of Coal
1198
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ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemSusChem 2010, 3, 1192 – 1199

Direct Synthesis of Ethanol over H-Mordenite and Cu/ZnO
[9] P. Cheung, A. Bhan, G. J. Sunley, D. J. Lawb, E. Iglesia, J. Catal. 2007, 245,
110–123.
[10] A. Bhan, A. D. Allian, G. J. Sunley, D. J. Law, E. Iglesia, J. Am. Chem. Soc.
2007, 129, 4919–4924.
conversion (No. 10–11–902), the Program for Introducing Talents
of Discipline to Universities of China (No. B06006), and the NSF
of Tianjin (No. 09ZCGHHZ00400).
[11] T. Blasco, M. Boronat, P. Concepciꢄn, A. Corma, D. Law, J. Alejandro
Vidal-Moya. Angew. Chem. 2007, 119, 4012–4015; Angew. Chem. Int. Ed.
2007, 46, 3938–3941; Angew. Chem. Int. Ed. 2007, 46, 3938–3941.
[12] M. Boronat, C. Martꢅnez-Sꢃnchez, D. Law, A. Corma, J. Am. Chem. Soc.
2008, 130, 16316–16323.
Keywords: alcohols · carbonylation · ethers · heterogeneous
catalysis · hydrogenation
[1] a) R. Burch, M. I. Petch, Appl. Catal. A 1992, 88, 39–60; b) C. Mazzocchia,
P. Gronchi, A. Kaddouri, E. Tempesti, L. Zanderighi, A. Kiennemann, J.
Mol. Catal. A 2001, 165, 219–230; c) M. Ojeda, M. L. Granados, S. Rojas,
P. Terreros, F. J. Garcia-Garcia, J. L. G. Fierro, Appl. Catal. A 2004, 261, 47–
55; d) M. A. Haider, M. R. Gogate, R. J. Davis, J. Catal. 2009, 261, 9–16.
[2] X. Pan, Z. Fan, W. Chen, Y. Ding, H. Luo, X. Bao, Nat. Mater. 2007, 6,
507–511.
[3] a) D. J. Elliott, F. J. Pennella, J. Catal. 1988, 114, 90–99; b) J. G. Nunan,
C. E. Bogdan, K. Klier, K. J. Smith, C. W. Young, R. G. Herman, J. Catal.
1988, 113, 410–433; c) E. M. Calverley, K. J. Smith, Stud. Surf. Sci. Catal.
1992, 73, 111–118; d) M. Xu, E. Iglesia, Catal. Lett. 1998, 51, 47–52;
e) M. Xu, E. Iglesia, J. Catal. 1999, 188, 125–131.
[13] a) Y. Jiang, M. Hunger, W. Wang, J. Am. Chem. Soc. 2006, 128, 11679–
11692; b) S. Walspurger, Y. Sun, A. S. S. Sido, J. Sommer, J. Phys. Chem. B
2006, 110, 18368–18373.
[14] W. J. Smith, Eur. Pat. Appl. EP0596632, 1993.
[15] T. Shikada, Y. Ohno, T. Ogawa, M. Ono, M. Mizuguchi, K. Tomura , K. Fuji-
moto, Stud. Surf. Sci. Catal. 1998, 119, 515–520.
[16] a) G. H. Graaf, P. J. J. M. Sijtsema, E. J. Stamhuis, G. E. H. Joosten, Chem.
Eng. Sci. 1986, 41, 2883–2890; b) N. Tsubaki, J. Zeng, Y. Yoneyama, K.
Fujimoto, Catal. Commun. 2001, 2, 213–217.
[17] X. San, Y. Zhang, W. Shen, N. Tsubaki, Energy Fuels 2009, 23, 2843–2844.
[18] P. Mꢆki-Arvela, I. Kubickova, M. Snare, K. Eranen, D. Y. Murzin, Energy
Fuels 2007, 21, 30–41.
[4] a) G. Jenner, P. Andrianary, J. Catal. 1984, 88, 535–537; b) J. R. Fox, F. A.
Pesa, B. S. Curatolo, J. Catal. 1984, 90, 127–138; c) G. Jenner, J. Mol.
Catal. A 1995, 96, 215–222.
[5] a) M. W. Bradley, N. Harris, K. Turner, WO 83/03409, 1983; b) K. J. Wilson,
R. Colin, UK GB2162172 A, 1986.
[6] a) A. K. Agarwal, N. W. Cant, M. S. Wainwright, D. L. Trimm, J. Mol. Catal.
1987, 43, 79–92; b) P. Claus, M. Lucas, B. Lꢂcke, Appl. Catal. A 1991, 79,
1–18; c) M. A. Natal-Santiago, M. A. Sꢃnchez-Castillo, R. D. Cortright,
J. A. Dumesic, J. Catal. 2000, 193, 16–28.
[19] a) K. Faungnawakij, Y. Tanaka, N. Shimoda, T. Fukunaga, S. Kawashima,
R. Kikuchi, K. Eguchi, Appl. Catal. A 2006, 304, 40–48; b) T. A. Semels-
berger, K. C. Ott, R. L. Borup, H. L. Greene, Appl. Catal. B 2005, 61, 281–
287.
[20] a) N. Tsubaki, M. Ito, K. Fujimoto, J. Catal. 2001, 197, 224–227; b) Y.
Zhang, R. Q. Yang, N. Tsubaki, Catal. Today 2008, 132, 93–100.
[21] a) N. Khandan, M. Kazemeini, M. Aghaziarati, Catal. Lett. 2009, 129, 111–
118; b) G. R. Moradi, M. Nazari, F. Yaripour, Fuel Process. Technol. 2008,
89, 1287–1296.
[7] a) B. Ellis, M. J. Howard, R. W. Joyner, K. N. Reddy, M. B. Padley, W. J.
Smith, Stud. Surf. Sci. Catal. 1996, 101, 771–779; b) A. G. Stepanov, M. V.
Luzgin, V. N. Romannikov, V. N. Sidelnikov, K. I. Zamaraevy, J. Catal.
1996, 164, 411–421; c) Q. Xu, S. Inoue, N. Tsumori, H. Mori, M. Kameda,
M. Tanaka, M. Fujiwara, Y. Souma, J. Mol. Catal. A 2001, 170, 147–153;
d) K. Fujimoto, T. Shikada, K. Omata, H. Tominaga, Chem. Lett. 1984, 13,
2047–2050.
[22] J. Zheng, J. Ma, Y. Wang, Y. Bai, X. Zhang, R. Li, Catal. Lett. 2009, 130,
672–678.
[23] J. W. Evans, M. S. Wainwright, A. J. Bridgewater, D. J. Young, Appl. Catal.
1983, 7, 75–83.
Received: April 12, 2010
Revised: June 11, 2010
[8] P. Cheung, A. Bhan, G. J. Sunley, E. Iglesia, Angew. Chem. 2006, 118,
1647–1650; Angew. Chem. Int. Ed. 2006, 45, 1617–1620.
Published online on August 16, 2010
ChemSusChem 2010, 3, 1192 – 1199
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemsuschem.org
1199