Promotional Influence of Hydroxyl Complexing Agent on Ethanol Synthesis from Syngas Over CuZnAl Catalysts Without Other Metal Promoters

Article abstract of DOI:10.1007/s10562-018-2545-7

Ternary CuZnAl catalysts promoted with three kinds of hydroxyl complexing agents were prepared by a complete liquid-phase method and tested for ethanol synthesis from syngas in a slurry bed reactor. The catalysts were characterized by XRD, H₂-TPR, NH₃-TPD, N₂ adsorption, XPS and TEM techniques. Activity results showed that ethanol selectivity enhanced significantly after the addition of hydroxyl complexing agents. Overall, the catalyst promoted by ethanolamine exhibited the best catalytic performance, with the concentration of ethanol and higher alcohols in the total alcohols reached up to 56.5% and 75.1%, respectively. The addition of hydroxyl complexing agents caused the reduction temperature of Cu⁺ shifted to be higher and the amount of weak acid sites to be decreased. It also favored the formation of AlOOH and Cu particles with larger particle size. These factors together contributed to the remarkable selectivity of ethanol and higher alcohols. Graphical Abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s10562-018-2545-7

Catalysis Letters
https://doi.org/10.1007/s10562-018-2545-7
Promotional Influence of Hydroxyl Complexing Agent on Ethanol
Synthesis from Syngas Over CuZnAl Catalysts Without Other Metal
Promoters
1
1
1
1
2
Yong‑Jun Liu · Lei Jia · Xuan Deng · Wei Huang · Vladimir A. Vinokurov
Received: 4 June 2018 / Accepted: 2 September 2018
©
Springer Science+Business Media, LLC, part of Springer Nature 2018
Abstract
Ternary CuZnAl catalysts promoted with three kinds of hydroxyl complexing agents were prepared by a complete liquid-
phase method and tested for ethanol synthesis from syngas in a slurry bed reactor. The catalysts were characterized by XRD,
H -TPR, NH -TPD, N adsorption, XPS and TEM techniques. Activity results showed that ethanol selectivity enhanced
2
3
2
significantly after the addition of hydroxyl complexing agents. Overall, the catalyst promoted by ethanolamine exhibited the
best catalytic performance, with the concentration of ethanol and higher alcohols in the total alcohols reached up to 56.5%
+
and 75.1%, respectively. The addition of hydroxyl complexing agents caused the reduction temperature of Cu shifted to
be higher and the amount of weak acid sites to be decreased. It also favored the formation of AlOOH and Cu particles with
larger particle size. These factors together contributed to the remarkable selectivity of ethanol and higher alcohols.
Graphical Abstract
80
70
60
50
40
30
20
10
0
CO+H2
Ethanol
Ethanol
C OH
2
+
After hydroxyl
complexing
agents added
CuZnAl catalyst
CAT-Al
CAT-Gl CAT-MEA CAT-GB
Keywords Ethanol · Syngas · Complete liquid-phase method · CuZnAl · Hydroxyl complexing agents
1
Introduction
*
Wei Huang
Gasification of coal to syngas and its subsequent conver-
sion to hydrocarbons and alcohols via the Fischer–Tropsch
reaction has been identified as a promising process for the
production of “green” [1]. Ethanol obtained from this pro-
cess has attracted researcher’s close attention due to its
potential application as a promising route for the produc-
tion of fuel blends and value-added chemicals in fine chemi-
cal synthesis [2, 3]. Typically, catalysts investigated for CO
huangwei@tyut.edu.cn
1
Key Laboratory of Coal Science and Technology of Ministry
of Education and Shanxi Province, Taiyuan University
of Technology, Taiyuan 030024, Shanxi, China
2
Department of Physical and Colloid Chemistry, Gubkin
Russian State University of Oil and Gas (National
Research University), Leninskiy prospect 65/1, Moscow,
Russia 119991
Vol.:(0
1
123456789)
3

Y.-J. Liu et al.
hydrogenation to ethanol mainly includes noble metal Rh-
based catalysts [4], Mo-based catalysts [5], alkalis modified
Cu-based methanol synthesis catalysts [6], and Cu-modified
Fischer–Tropsch (F–T) synthesis catalysts [7]. Among them,
Cu-based catalysts with low cost have become the optimal
option.
the catalysts are characterized by X-ray diffraction (XRD),
H temperature-programmed reduction (H -TPR), tempera-
2
2
ture-programmed desorption of ammonia (NH -TPD-MS),
3
N adsorption, X-ray photoelectron spectrometry (XPS) and
2
transmission electron microscopy (TEM).
Ternary CuZnAl catalysts have been widely employed
in the industrial low-temperature methanol synthesis since
the early 1960s [8]. The catalytic conversion of syngas to
obtain relatively higher selectivity of ethanol over CuZnAl
catalysts without alkalis or F–T elements (Fe, Co and Ni)
is rarely reported except our group. And some researchers
also surprised that the syngas could be directly catalyzed to
ethanol and C OH with relatively higher selectivity over
2 Experiment
2.1 Catalyst Preparation
The CuZnAl catalysts with various hydroxyl complexing
agents were prepared by a complete liquid-phase method
which was invented by our group [9]. The atomic ratio of
Cu/Zn/Al in the starting solution was kept at 2/1/0.8, and
the amount of hydroxyl complexing agent was equal to that
of 1/4 copper molar content. Typically, 6.4 g of citric acid
was dissolved in 90 mL of distilled water, then 19.8 g of
aluminum isopropane[(C H O) Al] was added to the above
2
+
ternary CuZnAl catalysts without promoters according to
our previous results [9, 10]. However, the carbon number
distributions of alcohols and hydrocarbons always meet the
Anderson–Schulz–Flory (ASF) distribution, causing the
concentration of ethanol in the total alcohols is not high,
which is similar with CuFe or CuCo catalysts [11–13]. Thus,
research and development of catalysts with higher selectivity
and efficiency for the short-chain alcohols (such as ethanol)
is highly desirable.
3
7
3
solution and the mixture was hydrolyzed at 50 °C for 3 h.
After a solution of Cu(II) and Zn(II) nitrates was mixed
with the hydroxyl complexing agent in 100 mL ethylene
glycol solution, the mixture was slowly added dropwise to
the above Al solution and stirred constantly until a sol was
formed. After aging for 10 days to obtain the sel, then it
was dispersed in 300 mL liquid paraffin and heated under
In order to narrow the distribution of alcohols and then
improve the ethanol selectivity, a suitable promoter is neces-
sary. Feng et al. [14] found that the addition of pyrogallol
in preparing the Cu–Co catalyst favored the distribution of
Cu, Co species as well as their interaction, as a result, the
selectivity of ethanol increased from 33.1 to 43.5%. Yu et al.
N atmosphere from 60 to 300 °C with a heating rate of
2
−
1
5 °C min and maintained for 8 h at 300 °C. After that,
a slurry catalyst was consequently obtained. For conveni-
ence, the catalysts promoted with glucose, ethanolamine and
glycerol were denoted as CAT-GB, CAT-MEA and CAT-
GL, respectively, and the catalyst without the addition of
hydroxyl complexing agent was named as CAT-Al.
[
15] reported that a certain amount of complexing agents
enhanced the basicity on catalyst surface and the ethanol
selectivity reached up to 24.5% in CO hydrogenation reac-
tion. Gao et al. [16] prepared ZnCr catalysts at different pH
value by ammonia solution, results showed that the catalysts
prepared at pH=2 had more hydroxyl groups and a relative
small size particle of ZnO and ZnCr O , exhibiting the opti-
2.2 Catalyst Characterization
2
4
mal catalytic performance both on CO conversion (20.9%)
Prior to characterization, all liquid-phase slurry catalysts
were centrifuged, extracted with petroleum ether for 48 h
and then dried at room temperature for 24 h to obtain powder
samples.
and isobutanol selectivity (24.2 wt%).
In our previous study, several kinds of metal promot-
ers (include La, Zr etc) also were added and investigated,
unfortunately, these catalysts still produced a wide distribu-
tion of C –C linear alcohols and methanol remained the
Powder X-ray diffraction (XRD) patterns were collected
using Rigaku D/MAX-2500 Diffractometer with Cu Kα radi-
ation. The instrument was operated at 40 kV accelerating
voltage and 40 mA current in a scanning angle (2θ) range
1
5
major product among the alcohols formed [17]. In addi-
+
tion, it was found that Cu might have positive effect on the
−
1
CO hydrogenation to ethanol, while ethanolamine, glucose
and glycerol was a kind of reducing agent and complex-
ing agent. Meanwhile, compared with glucose and glycerol,
ethanolamine itself was an alkaline substance which could
adjust the acidity on the catalyst surface. Thus, in this manu-
script, three kinds of hydroxyl complexing agents including
ethanolamine, glucose and glycerol are added during the
process of the catalysts preparation. The influence of these
promoters on the catalytic performance is investigated and
of 5°–85° at a speed of 2° min .
H temperature-programmed reduction (H -TPR) tests
2
2
were carried out in a quartz reactor at atmospheric pres-
sure to investigate the reducibility of the samples using a
chemisorption instrument (TP-5080). For each TPR test,
the sample (100 mg) was pre-treated at 150 °C under a
−
1
flow of He (40 mL min ) for 30 min to remove physically
adsorbed water and other impurities. It was then reduced in
a flow of 5 vol% H /N gaseous mixture at a heating rate of
2
2
1
3

Promotional Influence of Hydroxyl Complexing Agent on Ethanol Synthesis from Syngas Over CuZnAl…
−
1
1
0 °C min . A thermal conductivity detector (TCD) was
3 Results and Discussion
used to record the consumption of H .
2
Temperature programmed desorption of NH (NH -TPD)
3.1 XRD Characterization
3
3
experiments were conducted on the TP5080 instrument
equipped with a mass spectrum detector. Prior to tests,
the samples were first pre-treated in He flow at 150 °C to
remove the adsorbed species for 1 h. After coolling down to
The XRD patterns of all catalysts with different hydroxyl
complexing agents before reaction were presented in Fig. 1.
As seen in Fig. 1, the diffraction peaks at 2θ angles of 43.3°,
50.4° and 74.1° were corresponded to the (111), (200) and
5
0 °C, the samples were saturated with pure NH for 30 min
3
0
and then purged with He to remove the physisorbed mol-
ecules at 50 °C for 30 min. Subsequently, The TPD data
were collected from 100 to 800 °C by an AMETEK mass
spectrometer.
(220) reflections of Cu crystalline phase. One could not see
+
2+
the diffraction lines of Cu and Cu which might below
the detection limit of XRD since the following TPR char-
acterization showed two reduction peaks. This was due to
the partly decomposition of liquid paraffin which resultantly
generated the free carbon and then caused the reduction of
N adsorption–desorption measurement was performed
2
by a Micromeritics Quantachrome instrument at − 196 °C.
Prior to analysis, the samples were degassed at 200 °C in
high vacuum for 5 h. The Brunauer–Emmett–Teller (BET)
equation was used to calculate the specific surface areas, the
pore size analysis were evaluated by Barret–Joyner–Halenda
0
most oxidized copper to Cu [18]. In addition, no obvious
diffraction peaks of Zn and Al species were observed in the
range of diffraction angle. Therefore, it was hypothesized
that the two species were homogeneously dispersed in the
catalysts. Nonetheless, in our previous studies, it had been
convinced that Zn existed in the form of ZnO, and Al was
in the form of AlOOH when the catalyst preparing by the
complete liquid phase method [19, 20].
(
BJH) method using the desorption branch.
X-ray photoelectron spectroscopy (XPS) experiments
were performed on an ESCALAB 250 spectrometer
equipped with monochromatic Al Kα to obtain the infor-
mation of oxidation state. The binding energies were cali-
brated internally by adventitious carbon deposit C(1s) with
3.2 H ‑TPR Characterization
2
E = 284.60 eV.
b
Transmission electron microscopy (TEM) experiments
were carried on G2F-20 FEITECNAI apparatus with an
accelerating voltage of 300 kV. Prior to each measurement,
the samples were dispersed in ethanol, ultrasonicated,
and deposited on carbon-film-covered copper grids for
measurement.
To provide an insight into the reduction behavior of cata-
lysts, H -TPR measurement was performed and the results
2
were displayed in Fig. 2. As seen in Fig. 2, all of them
showed two reduction peaks in the temperature range of
150–350 °C, which indicated that two different types of
Cu species existed in the catalysts. Zhu et al. [21] reported
that the peak at about 250 °C was ascribed to the reduction
2
+
2.3 Catalytic Activity Measurements
of Cu species, and the reduction peak at relatively higher
The CO hydrogenation to ethanol reaction was carried out
in a 0.5 L slurry bed reactor with a mechanical agitator. The
syngas (CO/H =1/2) was introduced into the reactor under
0
2
Cu
the reaction conditions of 280 °C and 4.5 MPa with a feed
free carbon
−
1
flow rate of 150 mL min without reduction process. After
passing through a cold trap (0–5 °C), the tail gas was ana-
lyzed online by GC which equipped with a thermal conduc-
tivity detectors (TDX-01 column) to analyze H , CO, CH
2
4
CAT-GB
and CO , and a flame ionization detector (PLOT/Q) to ana-
2
lyze C –C hydrocarbons, respectively. The alcohols prod-
CAT-MEA
1
5
ucts were collected from the cold trap daily and analyzed
off-line using the flame ionization detector. CO conversion
and selectivity of products were calculated according to the
following equations:
CAT-Gl
CAT-Al
ꢀ
ꢁꢂ
10
20
30
40
50
60
70
80
Conversion for CO (%) = CO − CO
in
CO × 100%
in
out
2
θ(°)
Selectivity for M (%) = Quantity of M∕
total quantity of products × 100%.
Fig. 1 XRD patterns of fresh catalysts with different hydroxyl com-
plexing agents
1
3

Y.-J. Liu et al.
146
2
81
2
41
CAT-GB
1
47
2
91
2
70
150
CAT-GB
150
CAT-MEA
CAT-Gl
CAT-MEA
CAT-Gl
2
45
304
257
46
2
CAT-Al
CAT-Al
1
00
200
300
400
500
600
700
1
50
200
250
300
350
Temperature(°C)
Temperature(°C)
Fig. 3 NH -TPD-MS profiles of fresh catalysts with different
3
Fig. 2 H -TPR profiles of fresh catalysts with different hydroxyl com-
hydroxyl complexing agents
2
plexing agents
Table 1 The desorbed amount
+
Catalyst
Acidity
temperature was attributed to the reduction of Cu . Gao
of NH over different catalysts
mmol g−1)
3
(
et al. [22] found that an excess of Zr would cause strong
+
interaction of some Cu species and t-ZrO /mZrO , which
CAT-GB
CAT-MEA
CAT-Gl
7.76
6.37
7.73
8.36
2
2
led to higher reduction temperature. In light of this, for this
manuscript, it was speculated that the peak at the lower-
2
+
temperature side was ascribed to the reduction of Cu
,
CAT-Al
and the higher-temperature profiles could be assigned to
+
the reduction of Cu . Meanwhile, it could be found clearly
that the second reduction profiles of CAT-GB, CAT-MEA
and CAT-Gl shifted to higher temperature compared with
possessed weak acid sites which was assigned to the des-
orption of NH3 that occurred between the OH groups of
the oxides and NH3 [28], indicating that the addition of
hydroxyl complexing agents had little effect on the strength
of the surface acid sites. However, it could be found that the
density of peak decreased after hydroxyl complexing agent
added, corresponding to the decrease of weak acid (see
Table 1). Interestingly, combined with the following cata-
lytic activity results, it was noticed that there was inverse
correlation between the amount of surface weak acid and
the ethanol/C2+OH concentration in total alcohols. This
inverse correlation between selectivity and acidity was in
accordance with the general notion that ethanol formation
required basic sites for the aldol-type condensation from
lower alcohols to higher alcohols, which was also consist-
ent with E. Heracleous et al. results [6, 29]. The addition
of hydroxyl complexing agents in CuZnAl catalyst reduced
acidity and thus promoted the production of ethanol. There-
fore, it was concluded that a certain number of weak acid
was beneficial to the synthesis of ethanol over our novel
catalytic system.
+
CAT-Al, which indicated that Cu could be reduced more
0
difficultly to Cu after the addition of these promoters. It
was generally thought that the synergistic effect between
0
+
Cu and Cu species are responsible for the activity of the
catalyst with high yield of ethanol [23, 24]. Such as latest
work by Heracleous et al. [25] reported that the incorpora-
tion of Mn into Cu-based catalysts increased the percentage
+
of Cu species which adsorbed CO more strongly, and thus
favored the formation of C OH. In our previous work, it
2
+
+
was also revealed that the strong interactions between Cu
and zinc or aluminum oxide would increase the ethanol
selectivity [26], which was also proved by molecular-level
theoretical study [27]. The following activity results also
+
confirmed it, which further suggested that Cu was indis-
pensable for CO hydrogenation to ethanol over Cu-based
catalysts.
3
.3 NH ‑TPD‑MS Characterization
3
Figure 3 presented the NH -TPD-MS profiles of the fresh
3
catalysts and the acidity of all catalysts (expressed as mmol
3.4 N2 Adsorption Characterization
of desorbed NH /g) was compared in Table 1. It could be
3
found from Fig. 3 that all catalysts only had a desorption
The N2 adsorption isotherms of the four catalysts prepared
with different hydroxyl complexing agent before and after
peak at around 150 °C, suggesting that all catalysts only
1
3

Promotional Influence of Hydroxyl Complexing Agent on Ethanol Synthesis from Syngas Over CuZnAl…
5
00
400
00
200
600
400
200
CAT-GB
before reaction
after reaction
CAT-GB
CAT-MEA
CAT-Gl
3
1
5
4
3
00
00
00
00
0
00
6
4
2
CAT-MEA
00
00
200
00
500
00
1
0
00
6
4
2
4
00
00
0
CAT-Gl
CAT-Al
300
200
100
0
4
00
00
400
200
0
CAT-Al
2
0
0
.00
0.25
0.50
0.75
1.00
0.00
0.25
0.50
0.75
1.00
P/P0
P/P0
CAT-GB
CAT-MEA
CAT-Gl
CAT-Al
5
CAT-GB
CAT-MEA
CAT-Gl
CAT-Al
5
before reaction
0.2
0
.02
.01
.00
after reaction
0
0.1
0
0.0
0.015
0.010
0.005
0.10
0.08
0.06
0.04
0.02
0.00
0
0
.000
.020
-
0.02
0.2
0.015
0.010
0.005
0.000
0.1
0.0
-
0.0 20 05
0.20
0
.015
.010
.005
.000
0.15
0.10
0.05
0.00
0
0
0
-
0.005
-0.05
0
10
15
20
25
30
35
0
10
15
20
25
30
35
Pore diameter (nm)
Pore diameter (nm)
Fig. 4 Nitrogen adsorption–desorption isotherms and pore size distributions of different catalysts
1
3

Y.-J. Liu et al.
δ+
0
reaction were presented in Fig. 4. As seen in Fig. 4, the
2
been reduced to Cu (δ<2) with lower valences (e.g., Cu
+
N adsorption isotherms of all catalysts were belonged to
and Cu ), which was consistent with XRD results. How-
+
type IV isotherms with H3 hysteresis loops in the IUPAC
classification. This type of hysteresis loop indicated sig-
nificant presence of mesoporous material with a relatively
uniform size. After reaction, the hysteresis loop of the four
catalysts was assigned to type H4, which suggested also the
presence of micropores [30]. The Barrett–Joyner–Halenda
ever, it was difficult to differentiate the Cu species from
0
Cu species since the peaks of all catalysts were widely
dispersed from the XAES spectra, thus, the concentra-
tion of copper species on the catalyst surface was too low
to detect (Fig. 5b). This was also ascribed to the special
catalyst preparation method, which would cause a certain
amount of carbon membrane on catalysts surface and thus
the signal of Cu was very weak [31]. Nonetheless, it could
be found that Cu 2p peaks slightly shifted toward higher
(
BJH) model was presented to calculate the pore size dis-
tributions of the catalysts. As observed, these catalysts
showed less uniform mesopores with size larger than 5 nm
before reaction, indicating that no regular and well-defined
channel structures were exist. Interesting, these catalysts
had a similar pore size distribution with a pronounced
peak at around 3.5 nm after reaction. Table 2 displayed
the detailed textural properties of the four catalysts before
and after reaction. One could see that no obvious changes
for the textural properties were observed before reaction
after these promoters added, which suggested that these
hydroxyl complexing agents had little effect on the textural
properties. However, it was clearly seen that the specific
surface areas of all catalysts significantly increased after
reaction, which illustrated that the reaction process was the
main reason for the increase of BET surface area. It was
speculated due to the slurry bed reactor with continuous
mechanical agitator during the reaction, which resulted in
the change of bigger pores into smaller pores, and even
some micropores. However, any correlation between the
BET surface area and the catalytic performance was not
shown.
3
/2
binding energy values for CAT-MEA catalyst, suggesting
+
0
that the proportion of Cu /Cu increased over the catalyst
surfaces after the addition of ethanolamine. The Zn Auger
peak (Zn LMM) was used to obtain the state of Zn species.
As seen in Fig. 5c, the auger peak of Zn species was located
at around 987 eV, which could be assigned to ZnO accord-
ing to the standard data [32]. Similarly, the Al 2p peak was
located at about 73.5 eV for CAT-Al catalyst, and a slightly
shift toward higher binding energy value was observed after
these hydroxyl complexing agents added. Ebina et al. [33]
reported that the binding energy values of tetrahedral and
octahedral Al sites were about 73.7 and 74.5 eV, respec-
tively. Meanwhile, several groups reported that these tetra-
hedral and octahedral Al sites were associated with Al O
2
3
and AlOOH, respectively [34, 35]. Therefore, it was spec-
ulated that the catalysts contained more octahedral AlO
6
sites of AlOOH after the addition of hydroxyl complexing
agents, especially for CAT-MEA. The octahedral AlO site
6
of AlOOH was believed to play an important role in etha-
nol and higher alcohols synthesis according to our previous
study of density functional theory [36].
3.5 XPS Characterization
The chemical states of CuZnAl catalysts with different
hydroxyl complexing agents were analyzed by XPS, and the
binding energies (B.E) of Cu2p , Al2p, Zn LMM and the
3.6 TEM Characterization
TEM analysis was conducted to confirm the copper dis-
persion and the particle size in CuZnAl samples, the
obtained figures were shown in Fig. 6. As shown, the
component of dark-field for all catalysts was copper nano-
particles, while the white domain contained both elemen-
tal Zn and Al. The Cu particle of CAT-Al catalyst were
3
/2
X-ray excited Auger electron spectroscopy (XAES) spectra
were presented in Fig. 5. For all fresh catalysts, XPS peaks
of Cu2p were found at around 931.5–932.5 eV (BE) and
3
/2
no shake-up satellite peaks were observed in the range of
9
40–945 eV (Fig. 5a), indicating that copper species had
Table 2 The textural property
of catalysts with different
hydroxyl complexing agents
Catalyst
Before reaction
After reaction
Surface area Pore volume
Pore diam-
eter (nm)
Surface area Pore volume
Pore
2
−1
3
−1
2
−1
3
−1
(
m g
)
(cm g
)
(m g
)
(cm g
)
diameter
(
nm)
CAT-GB
CAT-MEA
CAT-Gl
68.2
41.3
46.7
48.7
0.6
0.5
0.5
0.5
12.4
17.5
6.5
216.6
185.6
234.7
187.9
0.4
0.4
0.4
0.3
17.6
3.1
3.1
3.1
CAT-Al
17.5
1
3

Promotional Influence of Hydroxyl Complexing Agent on Ethanol Synthesis from Syngas Over CuZnAl…
Cu2p3/2
(a)
(b)
931.7
CAT-GB
932.3
CAT-GB
CAT-MEA
CAT-Gl
CAT-MEA
9
31.6
CAT-Gl
CAT-Al
931.5
CAT-Al
930
935
940
945
950
955
960
910 912 914 916 918 920 922 924 926
Binding Energy (eV)
Kinetic energy (eV)
9
86.9
86.9
87.4
(c)
(d)
7
3.9
9
CAT-GB
74.1
CAT-GB
9
CAT-MEA
7
3.7
CAT-MEA
CAT-Gl
CAT-Gl
CAT-Al
987.2
73.5
CAT-Al
982
984
986
988
990
992
994
68
70
72
74
76
78
80
Kinetic Energy (eV)
Fig. 5 Cu 2p (a), Cu XAES (b), Zn LMM (c) and Al 2p (d) spectra of fresh catalysts
Fig. 6 TEM images of fresh
catalysts with different hydroxyl
complexing agents
1
3

Y.-J. Liu et al.
Table 3 CO hydrogenation
performance on different
catalysts
Catalyst
CO conversion Selectivity (C-mol%)
C
OH/
2
+
(
%)
ROH
DME
ROH
CnHm
CO2
(
wt%)
CAT-GB
CAT-MEA
CAT-Gl
4.6
4.5
5.1
13.1
0.3
21.1
31.9
36.4
28.3
13.9
38.5
9.8
28.8
11.6
2.8
40.7
42.6
53.4
26.9
59.8
75.1
62.4
39.6
CAT-Al
14.0
grouped together separate from the support and their size
was about 20–40 nm. After the addition of hydroxyl com-
plexing agent, the black region became larger, which indi-
cated that the Cu species aggregated to larger particles
and intimately bound up with Zn and Al oxide, especially
for CAT-GB and CAT-MEA catalysts. It was speculated
that these enhanced metal-support interactions, together
with the formation of Cu particles with larger size favored
the ethanol synthesis according to Zhu et al. results [37].
synthesis of ethanol often accompanied by the produc-
tion of water, which would promote the water gas shift
reaction (CO + H O → CO + H ). Interestingly, forma-
2
2
2
tion of the undesirable by-product dimethyl ether (DME)
appeared to be suppressed over the CAT-MEA catalyst,
on which the DME selectivity was the lowest, which sug-
gested that the synthesis of ethanol and DME might be
controlled by the opposite active center. Moreover, for
all promoted catalysts, the ethanol concentration nearly
increased to 40% and the C OH concentration nearly
2
+
3.7 Catalytic Performance
increased to ~ 60%, which were considerably higher than
that of our previously results [9, 10].
The catalytic performance of the CAT-Al catalyst towards
CO hydrogenation to ethanol was tested and compared
with that of CAT-Gl, CAT-MEA and CAT-GB under
the reaction conditions: 4.5 MPa, 553 K, flow rate of
4 Conclusions
−
1
1
50 mL min , n(H )/n(CO) = 2.0. The data were pre-
2
sented in Tables 3 and 4. It could be seen that the CAT-
Al catalyst exhibited a relatively higher CO conversion
To summarize, we have demonstrated that ternary CuZ-
nAl catalysts prepared by the complete liquid-phase
method could directly catalyze syngas to a rather higher
(
14.0%) and lower concentration of ethanol (14.5%) and
C
OH (39.6%) in the total alcohols. After the addition
selectivity of ethanol (56.5%) and C OH (75.1%) with a
2
+
2+
of these hydroxyl complexing agents, the CO conversion
narrow range distribution during CO hydrogenation in a
slurry bed reactor. It was concluded from the characteri-
zations that the addition of hydroxyl complexing agents
decreased, while the concentration of ethanol and C OH
2
+
in the total alcohols increased significantly. Among these
+
catalysts, the highest concentration of ethanol (reaching
caused the reduction temperature of Cu shifted to be
5
6.5%) and C OH (reaching 75.1%) with a narrow range
higher and the amount of weak acid sites to be decreased.
It also favored the formation of AlOOH and enhanced
metal-support interactions as well as the formation of Cu
particles with larger size. These factors together contrib-
uted to the remarkable selectivity of ethanol and higher
alcohols.
2
+
distribution was obtained for CAT-MEA catalyst. These
results indicated that alcohols did not obtain the ASF
distribution and ethanol showed a positive deviation from
the ASF behavior. In addition, compared with CAT-Al
catalyst, the CO selectivity also increased for these pro-
2
moted catalysts overall, this might probably be due to the
Table 4 Product distributions of
Catalyst
ROH distribution (wt%)
HC distribution (wt%)
catalysts with different hydroxyl
complexing agents
C1
C2
C3
C4
C5
C1
C2
C3
C4
C5
CAT-GB
CAT-MEA
CAT-Gl
40.2
24.9
37.6
60.4
37.9
56.5
40.0
14.5
8.9
9.4
8.7
7.8
12.5
9.0
13.1
16.8
0.5
0.2
0.6
0.5
10.8
18.8
10.2
12.7
38.7
25.1
36.8
33.3
24.6
29.6
22.4
21.6
15.5
13.9
17.9
22.7
10.3
12.6
12.7
9.6
CAT-Al
1
3

Promotional Influence of Hydroxyl Complexing Agent on Ethanol Synthesis from Syngas Over CuZnAl…
Acknowledgements The authors gratefully acknowledge financial
16. Gao XF, Wu YQ, Yang GH, Zhang T, Li XL, Xie HJ, Pan JX, Tan
support from the Key Project of Natural Science Foundation of China
YS (2017) Appl Catal A Gen 547:1–11
(
Grant No. 21336006), the Natural Science Foundation of China (Grant
17. Deng X, Liu YJ, Huang W (2018) J Energy Chem 27:319–325
18. Liu YJ, Deng X, Han PD, Huang W (2017) Fuel 208:423–429
19. Liu L, Huang W, Gao ZH, Yin LH (2012) J Ind Eng Chem
No. 21176167) and the National Key Technology R&D Program (Grant
No. 2013BAC14B04).
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Compliance with Ethical Standards
2
Conflict of interest The authors declare that they have no conflict of
(
2015) Appl Catal B: Environ 166–167:551–559
interest.
2. Gao P, Li F, Zhan HJ, Zhao N, Xiao FK, Wei W, Zhong LS, Wang
H, Sun YH (2013) J Catal 298:51–60
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