Surfactant-assisted preparation of Cu/ZnO/Al2O3 catalyst for methanol synthesis from syngas

Article abstract of DOI:10.1016/j.molcata.2012.09.007

Cu/ZnO/Al₂O₃ (CZA) catalysts were prepared by two-step precipitation method with the assistance of the surfactant, tetraethylammonium hydroxide (TEAH) or polyethylene glycol (PEG), and evaluated in methanol synthesis from syngas. Effects of input amount of the surfactant and accelerated thermally induced deactivation (ATD) on the activity of the catalyst were investigated under the reaction conditions of 230 °C, 5 MPa, gas hourly space velocity (GHSV) of 10,000 h^-1 and the syngas composition of CO/CO₂/H₂/N₂ (volume ratio) = 15:5:70:10. Among the catalysts investigated, 2T-CZA catalyst, prepared with addition of 2 wt.% TEAH in the course of the coprecipitation of Cu²⁺ and Zn²⁺, exhibited better catalytic performance due to its smaller crystallite size of Cu and higher Cu surface area, over which methanol space-time yield (STY) was 1.26 times as heavy as that over blank CZA catalyst, prepared without any surfactant's assistance, and 1.25 times as that over commercially famous CX catalyst for methanol synthesis from syngas in China. Meanwhile, 2T-CZA catalyst showed satisfactory thermal stability, in which methanol STY decreased by only 5.2% because of growing up of crystallite size of Cu and decrease in the number of surface Cu atoms after the ATD test to be conducted in situ at 350°C for 20 h in syngas.

Full text of DOI:10.1016/j.molcata.2012.09.007

Journal of Molecular Catalysis A: Chemical 366 (2013) 48–53
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Surfactant-assisted preparation of Cu/ZnO/Al2O3 catalyst for methanol synthesis
from syngas
Zheng Chua,b, Haibo Chenb, Yang Yub, Qiong Wangb, Dingye Fanga,∗
a State Key Laboratory of Chemical Engineering, Engineering Research Center of Large Scale Reactor Engineering and Technology, East China University of Science and Technology,
Shanghai 200237, China
b Research Institute of Nanjing Chemical Industry Group, Nanjing 210048, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 19 March 2012
Received in revised form 5 September 2012
Accepted 6 September 2012
Available online 14 September 2012
Cu/ZnO/Al2O3 (CZA) catalysts were prepared by two-step precipitation method with the assistance of
the surfactant, tetraethylammonium hydroxide (TEAH) or polyethylene glycol (PEG), and evaluated in
methanol synthesis from syngas. Effects of input amount of the surfactant and accelerated thermally
induced deactivation (ATD) on the activity of the catalyst were investigated under the reaction condi-
tions of 230 ◦C, 5 MPa, gas hourly space velocity (GHSV) of 10,000 h−1 and the syngas composition of
CO/CO2/H2/N2 (volume ratio) = 15:5:70:10. Among the catalysts investigated, 2T-CZA catalyst, prepared
with addition of 2 wt.% TEAH in the course of the coprecipitation of Cu2+ and Zn2+, exhibited better cat-
alytic performance due to its smaller crystallite size of Cu and higher Cu surface area, over which methanol
space-time yield (STY) was 1.26 times as heavy as that over blank CZA catalyst, prepared without any
surfactant’s assistance, and 1.25 times as that over commercially famous CX catalyst for methanol syn-
thesis from syngas in China. Meanwhile, 2T-CZA catalyst showed satisfactory thermal stability, in which
methanol STY decreased by only 5.2% because of growing up of crystallite size of Cu and decrease in the
number of surface Cu atoms after the ATD test to be conducted in situ at 350 ◦C for 20 h in syngas.
© 2012 Elsevier B.V. All rights reserved.
Keywords:
Methanol synthesis
Cu/ZnO/Al2O3 catalyst
Surfactant-assisted preparation
Thermal stability
1. Introduction
on the properties of CZA catalyst in methanol synthesis from syn-
gas and proposed that Mn and Zr promoted catalysts have high
With the rapid development of modern industry, the energy
and environmental issues have become two major concerns.
Methanol is a kind of important chemical feedstock, transporta-
tion fuel and clean energy carrier for fuel cells [1]. Therefore,
methanol synthesis from syngas has been attracting evergrowing
attention.
The catalyst was considered unanimously as a key factor in
the production of methanol. Methanol synthesis catalyst mainly
included Cu-based [2–5] and noble metal catalysts [6–8], in which
the former with inexpensive price and high activity has some
advantages over the latter. Cu/ZnO/Al2O3 (CZA) catalyst was the
methanol synthesis catalyst to be studied extensively and applied
largely in industrial production. It was corroborated that the syner-
gism of Cu and ZnO resulted in good activity in methanol synthesis
[9,10], and Al2O3 as a promoter not only can prevent agglomeration
of active phase but also accelerate the adsorption and activation of
CO because of its disorder and defect surface domain [11]. Bah-
mani et al. [12,13] investigated the effect of metal oxide additives
performance. Phan et al. [14] prepared the CZA monoliths and
obtained higher activity of monolith in methanol synthesis in terms
of fixed bed reactor, which was attributed to the thermal proper-
ties of the steel monolith. More efforts were put into improving the
preparation method of CZA catalyst. Jensen et al. [15] studied the
flame combustion synthesis of CZA catalyst, in which the optimal
composition was obtained and the role of individual catalyst com-
ponents was also discussed. Hu et al. [16,17] prepared nanosize CZA
methanol synthesis catalyst by the metal surfactant phase trans-
fer technique and investigated effects of additives, chain length
of surfactant and preparation conditions. Liu et al. [1] reported
that polyoxyethylene octylphenol, as a surfactant, had promoting
effect on Cu/ZnO catalyst for low-temperature methanol synthe-
sis by lowering particle size and increasing Cu specific surface
areas.
In this work, the assistant effects of two typical surfactants
on preparing CZA methanol synthesis catalyst were investigated,
respectively, and the activity loss of the catalyst after the ATD test
was also studied. The physicochemical properties of catalysts were
characterized by XRD, H2-TPR, N2 sorption, N2O chemisorption,
HR-TEM, XPS and TG-DTG.
∗
Corresponding author. Tel.: +86 21 64251002; fax: +86 21 64251002.
E-mail address: dyfang@ecust.edu.cn (D. Fang).
1381-1169/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2012.09.007

Z. Chu et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 48–53
49
Table 1
The composition and physicochemical properties of the catalysts.
Catalysts
Addingamountofsurfactants(wt.%)a
SBET (m2 g−1
)
SCu (m2 g−1
)
Crystallite size of Cu (nm)
TEAH
PEG
CX
0
0
0
0
0
2
5
10
0
0
2
5
10
0
81.9
79.5
90.4
96.5
83.0
121.5
92.2
88.9
22.3
17.9
23.4
30.8
24.1
41.6
26.7
31.9
18.1
19.0
16.5
17.2
16.8
15.3
16.3
16.1
Blank CZA
2P-CZA
5P-CZA
10P-CZA
2T-CZA
5T-CZA
10T-CZA
0
0
a
The mass percentage = (adding amount of surfactant/Cu content in the catalyst) × 100.
2. Experimental
obtained online by using Infrared Gas Analyzer with precision of
0.1% of F.S. made in China, and the crude alcohols were collected by
ice-bath and analyzed by using Agilent 7890A gas chromatography
equipped with FID detector and a HP-Innowax capillary column
(60 m × 0.32 mm × 0.05 ␮m).
2.1. Preparation of CZA catalysts
CZA
catalysts,
with
the
mass
ratio
of
Cu/Zn/Al = 70.0%:23.6%:6.4%, were prepared by the two-step
precipitation method. The binary matrix containing Cu2+ and
Zn2+ was first obtained by adding the mixed nitrates of Cu and
Zn dropwise to the given volume of 1 mol L−1 NaHCO3 aqueous
solution with or without the surfactant, tetraethylammonium
hydroxide (TEAH) or polyethylene glycol (PEG), at 75 ◦C until
pH was 7.0–7.2. The binary matrix was aged and then washed
using deionized water at 75 ◦C until meeting the requirement
of diphenylamine sulfate test, indicative of a negligible content
of residual Na+ in the binary matrix. The Al2O3 support slurry
was prepared by dropwise adding 10 wt.% ammonia to Al(NO3)3
aqueous solution at room temperature until pH was about 7.0 and
then was poured into the binary matrix under vigorous stirring
at 75 ◦C to obtain the precursor of CZA catalyst. The precursor
obtained was washed, filtered, dried overnight at 120 ◦C, calcined
at 350 ◦C for 2 h, pressed and crushed into 16–40 mesh. The CZA
catalysts prepared with no surfactant, 2 wt.% of TEAH and 2 wt.% of
PEG were marked as blank CZA, 2T-CZA and 2P-CZA, respectively,
and other CZA catalysts were marked similarly. A commercially
famous methanol synthesis catalyst CX in China, with the same
composition as the catalyst prepared in this work, was selected
as a reference catalyst. The symbols and main physicochemical
properties of the catalysts are listed in Table 1.
2.3. Characterization of the catalysts
The powder X-ray diffraction (XRD) patterns were recorded on
a Bruker AXS D8 Focus diffractometer operated at 40 kV, 40 mA
(Cu K␣ radiation, ꢀ = 0.15406 nm), and the diffraction patterns were
taken in the range of 10◦ < 2ꢁ < 80◦.
H2-temperature programmed reduction (H2-TPR) characteriza-
tion was performed in a U type tubular quarts reactor filled with
50 mg catalyst by using a gas mixture 5 vol.% H2/N2 as a carrier
gas at a flow rate of 40 mL min−1. The heating rate was controlled
at 10 ◦C min−1. The hydrogen uptake was continuously monitored
using a gas chromatography equipped with TCD detector during
the reaction.
The specific surface area was measured by N2 sorption at
−196 ◦C with BET method on a NOVA 4200e surface area and pore
size analyzer.
The Cu specific surface area of the reduced CZA catalysts
was measured by N2O chemisorption at 60 ◦C assuming a molar
stoichiometry of Cu:N2O = 2 and a surface atomic density of
1.46 × 1019 Cu atoms m−2 [19].
X-ray photoelectron spectroscopies (XPS) of samples were
recorded on a Thermo ESCALAB 250 spectrometer (Perkin Elmer,
USA) using Al K␣ radiation (1486.6 eV). The binding energies were
calculated with respect to C 1s peak at 285 eV with a precision of
0.2 eV.
2.2. Activity test of the catalysts
High-resolution transmission electron microscopy (HR-TEM)
was used to observe the size change of metal Cu after the ATD test
on a JEM-2100 with an acceleration voltage of 200 kV.
Thermal gravity analysis (TGA) and differential thermal gravity
(DTG) characterizations were carried out on a PerkinElmer Pyris
Diamond TG-DTA analyzers, in which the catalyst was heated pro-
grammedly from 50 ◦C to 800 ◦C at the rate of 10 ◦C min−1 in the
Methanol synthesis from syngas over the CZA catalyst was
carried out in a continuous flow stainless steel tubular fixed-
bed reactor (inside diameter = 6 mm). 1 mL catalyst was loaded in
the constant temperature zone of the reactor, and some quartz
sand was packed in two ends of the catalyst. The catalyst was
first reduced in situ by 1500 mL min−1 5 vol.% H2/N2 at pro-
grammed temperature which varied from room temperature to
210 ◦C and was kept at this temperature for 20 h. Then the tem-
perature was increased to 230 ◦C and reached stable, the syngas
of 10,000 h−1, with the composition of CO/CO2/H2/N2 (volume
ratio) = 15:5:70:10, was fed into the reactor at 5 MPa. To investigate
the thermal stability of the catalysts in shorter time, the accel-
erated thermally induced deactivation (ATD) test was universally
applied [18,13]. In this work, the ATD test was conducted in the
middle of the catalytic performance evaluation at 350 ◦C for 20 h
under the atmosphere of syngas, after which the reaction condi-
tions of 230 ◦C and 5 MPa were recovered again. Not only before
the ATD treatment but also after that, the products were analyzed
after the reaction for 5 h. The products were sampled for 3 times
at intervals of 2.5 h, and CO conversion and methanol space-time
yield (STY) were the averages of 3 results. The CO conversion was
atmosphere of air of 100 mL min−1
.
3. Results and discussion
3.1. Assay results of the catalysts
In Fig. 1, the activities of the different CZA catalysts are compared
in terms of CO conversion in methanol synthesis from syngas. It can
be seen that, before the ATD test, the CO conversion (60.7%) over
blank CZA catalyst was quite lower than that (65.9%) over CX cat-
alyst. However, as the introduction of the surfactant in preparing
the binary matrix, the CO conversion over resultant CZA catalysts
increased significantly and was higher than that over CX catalyst, in
which CO conversion reached 71.1% over both 5P-CZA and 10T-CZA

50
Z. Chu et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 48–53
Fig. 3. XRD patterns of four representative calcined CZA catalysts.
Fig. 1. Catalytic performance over different CZA catalysts before and after the ATD
test under the reaction conditions of 230 ◦C, 5 MPa, GHSV of 10,000 h−1, 1 mL catalyst
and syngas composition of CO/CO2/H2/N2 (volume ratio) = 15:5:70:10.
PDF# 35-0502), the peaks at 2ꢁ = 27.5◦, 33.0◦, 36.6◦, 39.5◦, 46.5◦ and
47.0◦ to (Cu,Zn)5(CO3)2(OH)6 (aurichalcite phase, PDF# 17-0743)
and the peaks at 2ꢁ = 31.9◦, 36.0◦, 41.3◦, 56.4◦ to (Cu)2CO3(OH)2
(malachite, PDF# 02-0806). It is noticed that rosasite is dominant
crystal phase in CZA catalyst precursor prepared with the assistance
of the surfactants. Many authors reported [10,20–22] that rosasite
can be thermally decomposed into CuxZn1−xO solid solution which
is the main active phase in methanol synthesis. Wang et al. [10]
considered that the catalyst precursor with higher diffraction peak
intensity at 2ꢁ = 17.3◦ contained more rosasite phases. In Fig. 2, the
peak intensity of 2T-CZA catalyst precursor at 2ꢁ = 17.3◦ is the high-
est in three representative ones, so it can be concluded that more
rosasite phases were generated with addition of 2 wt.% TEAH in
the course of preparing the binary matrix, which can also account
for better catalytic performance over 2T-CZA catalyst in methanol
synthesis from syngas.
Fig. 3 displays XRD patterns of four representative calcined CZA
catalysts. The two main characteristic diffraction peaks of CuO
(PDF# 65-3411) and three weak but visible characteristic diffrac-
tion peaks of ZnO (PDF# 65-2309) can be identified, in which
they locate at 2ꢁ = 35.7◦, 38.9◦ and 2ꢁ = 31.8◦, 66.4◦, 67.9◦, respec-
tively. The characteristic diffraction peak of graphite C (2ꢁ = 26.4◦,
PDF# 01-0646) resulted from the addition of 1.5 wt.% additive dur-
ing catalyst tableting process. Fig. 4 shows XRD patterns of the
four reduced CZA catalysts. The characteristic diffraction peaks of
catalysts. After the ATD test, CO conversion over all CZA catalysts
dropped in different extents, in which the CO conversion over 2T-
CZA catalyst was the highest to be 67.7% that was even higher
than that over CX catalyst before the ATD test. The methanol STYs,
during the stability phase of the reaction, over different CZA cat-
alysts before and after ATD test are presented also in Fig. 1. It
is clear that the methanol STYs over the CZA catalysts prepared
with the assistance of two surfactants are all higher than not only
that over blank CZA catalyst (1.066 g gcat−1 h−1 before the ATD test
and 0.944 g gcat−1 h−1 after the test), but also that over CX cata-
lyst (1.072 g gcat−1 h−1 before the ATD test and 0.991 g gcat−1 h−1
after the test). Among all CZA catalysts investigated, 2T-CZA cata-
lyst showed highest catalytic performance with the methanol STYs
of 1.342 g gcat−1 h−1 before the ATD test and 1.272 g gcat−1 h−1 after
the test.
3.2. Characterization of the catalysts
3.2.1. XRD
Fig. 2 shows XRD patterns of three representative CZA catalyst
precursors (before calcination). As shown in Fig. 2, three crystal
phases can be identified in each XRD pattern, in which the char-
acteristic diffraction peaks located at 2ꢁ = 11.9◦, 14.6◦, 17.3◦, 18.9◦,
24.6◦ and 29.6◦ are assigned to (Cu,Zn)2CO3(OH)2 (rosasite phase,
Fig. 2. XRD patterns of the precursors of three representative CZA catalysts.
Fig. 4. XRD patterns of four representative reduced CZA catalysts.

Z. Chu et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 48–53
51
Fig. 5. TPR profiles of four representative calcined CZA catalysts.
Fig. 6. XPS spectra of Cu(2p) core level region of the four representative reduced
CZA catalysts.
ZnO remain, and the characteristic diffraction peaks of CuO dis-
appear however, and the characteristic diffraction peaks of Cu
(PDF# 65-9026) appeared at 2ꢁ = 43.3◦, 50.5◦ and 74.2◦, corre-
sponding to the crystal planes of Cu (1 1 1), (2 0 0) and (2 2 0),
respectively. It indicates that CuO was reduced completely by
5 vol.% H2/N2 to Cu0 and the state of ZnO did not change, in
which Cu0 is the main active site in methanol synthesis from syn-
gas [23–25]. The characteristic diffraction peaks of Al2O3 are not
observed in Figs. 3 and 4, which means that Al2O3 existed as the
amorphous phase or high dispersion in the catalysts.
The crystallite sizes of Cu in the reduced CZA catalysts are
determined by Scherrer formula with the full peak width at half
maximum height of the characteristic diffraction peak of Cu (1 1 1)
and listed in Table 1. As shown in Table 1, the crystallite size of Cu in
the reduced blank CZA catalyst is higher than that in the reduced CX
catalyst. However, with the introduction of the surfactant TEAH or
PEG in the course of preparing the binary matrix, the crystallite size
of Cu decreased and became smaller than that in the reduced CX
catalyst, of which the reduced 2T-CZA catalyst exhibited the small-
est crystallite size of Cu. As for CZA methanol synthesis catalyst,
smaller crystallite size of Cu is favorable to increase its catalytic
performance.
promote the catalytic performance of the catalyst in methanol syn-
thesis from syngas, which is in agreement with some observations
reported [26,27].
3.2.4. XPS
In order to ascertain further the active site of the CZA catalyst in
methanol synthesis from syngas, XPS characterization was carried
out, and Cu(2p) XPS spectra of the four representative reduced CZA
catalysts are presented in Fig. 6. In Fig. 6, two main peaks in each XPS
spectrum, which locate at binding energy (BE) = 932–933 eV and
BE = 952–953 eV, should be ascribed to the XPS characteristic peaks
of Cu2p3/2 and Cu2p1/2, respectively. In addition, no characteristic
satellite peak of Cu2+ at BE of about 945 eV appears in each XPS
spectrum, which reveals that the Cu2+ was completely reduced to
Cu0 or Cu+ under the reduction conditions in this work. Since the
BE of Cu0 (932.7 eV) and Cu+ (932.4 eV) in Cu2p3/2 band are almost
the same, they can be assigned according to the different kinetic
energy (KE) of Auger Cu-KLL line position in Cu0 (918.6 eV) and Cu+
(916.8 eV) [28]. Fig. 7 shows Cu-KLL Auger spectrum of the reduced
2T-CZA catalyst. The Auger line position is located at KE = 918.2 eV,
which demonstrates further that the element of Cu exists mainly
as Cu0. Accordingly, the active site is speculated mainly to be Cu0
over CZA catalysts in methanol synthesis from syngas. It can be seen
that, with the introduction of surfactant in catalyst preparation, the
3.2.2. H2-TPR
The reducibility of the copper species in the four representa-
tive CZA catalysts was characterized by H2-TPR technique. As can
be shown in Fig. 5, each of TPR profiles shows single reduction
peak and the reduction temperature at peak maximum varies at
232–257 ◦C from blank CZA to 2T-CZA catalyst. H2-TPR character-
ization indicates that with the introduction of the surfactant in
the course of preparing the binary matrix, the reduction temper-
ature at peak maximum of resultant CZA catalyst shifts to higher
temperature. It was reported [10,26] that the shift of the reduc-
tion temperature related to the interaction between CuO and ZnO
lattices in CZA catalyst, in which the shift to higher reduction tem-
perature in H2-TPR profile implied a stronger interaction between
the two lattices. In Fig. 5, the reduction temperature at peak max-
imum of 2T-CZA catalyst is the highest to be 257 ◦C, meaning that
the stronger interaction between CuO and ZnO occurred.
3.2.3. N2 sorption and N2O chemisorption
The BET specific surface area (SBET) and the Cu specific surface
area (SCu) over all the CZA catalysts are shown in Table 1. As shown
in Table 1, SCu increases with introduction of the surfactant, and
the higher SBET is favorable to increase SCu. Combining Table 1 with
Fig. 2, it is concluded that the higher SCu over CZA catalyst can
Fig. 7. Cu-KLL Auger spectrum of the reduced 2T-CZA catalyst.

52
Z. Chu et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 48–53
Fig. 10. TGA and DTG profiles of 2T-CZA(B) and 2T-CZA(A) catalysts.
Fig. 8. XRD profiles of 2T-CZA(B) and 2T-CZA(A) catalysts.
according to Scherrer formula, it can be inferred that the crystallite
size of Cu increased.
BE of Cu2p3/2 over the reduced CZA catalysts shifts to high value
to different extents, of which the reduced 2T-CZA catalyst shows
the highest BE of Cu2p3/2, being equal to 933.4 eV. The high BE of
Cu2p3/2 over the reduced CZA catalyst is beneficial to the adsorption
of electron-rich CO over active site of Cu0 [11], and adsorption of
the reactants over the catalyst is a precondition for a heterogeneous
catalytic reaction.
Further information was acquired by using HR-TEM technique.
The images of 2T-CZA(B) and 2T-CZS(A) catalysts are shown in
Fig. 9(a) and (b), respectively. It can be observed that the metal Cu
with smaller particle, marked by black areas in Fig. 9, is separately
dispersed in 2T-CZA(B), but by contrast the interparticle aggrega-
tion occurs in 2T-CZA(A), which is indicative of growing up of metal
Cu particle after the ATD test and thereby is in good agreement with
the inference obtained by XRD analysis.
3.3. Thermal stability of the 2T-CZA catalyst
More useful information was obtained by TGA and DTG tech-
niques. As shown in Fig. 10, an unusual phenomenon is found that
weight loss curves of two used 2T-CZA catalysts both rise after a
slight drop, which is attributed to removing of adsorbed water,
between 50 and 150 ◦C. The increase in mass can be explained as
the incorporation of oxygen into the catalyst by the oxidation of Cu0
in air. Additionally, it indicates also that carbon deposition over 2T-
CZA catalyst is considerably little during the reaction. DTG curves
of 2T-CZA(B) and 2T-CZA(A) catalysts are displayed also in Fig. 10.
There exist mainly two peaks, in which the peak at lower temper-
ature should be assigned to the oxidation of surface Cu0, and the
other one at higher temperature be assigned to the oxidation of
bulk Cu0 in the used 2T-CZA catalyst. The atomic ratio of surface
Cu0 to bulk Cu0 is evaluated to be 1.93 in 2T-CZA(B) and 1.15 in
2T-CZA(A), respectively, by calculating the ratio of the correspond-
ing peak area using computer program. The results imply that the
quantity of surface Cu0 decreased after the ATD test, which can be
explained as the growing up of Cu0 crystal. Thus, it can be concluded
that the slight decrease in activity of 2T-CZA catalyst after the ATD
test resulted from the decrease in the number of surface Cu atoms
which related to growing up of Cu crystal.
Thermal stability of Cu-based catalyst is a fatal criterion to evalu-
ate its catalytic performance due to the lower Hütting temperature
(about 0.3 Tm), at which surface atoms become significantly mobile,
and lower Tamman temperature (about 0.5 Tm) of metal Cu, at
which lattices begin to be appreciably mobile, where Tm, refer to
melting point of metal Cu, is about 1356 K. As mentioned in Section
2.2, the ATD test can considerably shorten the investigation time
of thermal stability. 2T-CZA catalyst shows better catalytic per-
formance and satisfactory thermal stability in methanol synthesis
from syngas, but after the ATD test, the CO conversion and methanol
STY all showed still a slight drop. The similar phenomenon was
also observed over the CZA catalyst prepared by Wang et al. [10].
To detect the causes of the activity loss, XRD, HR-TEM, TGA and
DTG characterizations were implemented. The reduced 2T-CZA cat-
alyst that was used for 10 h in methanol synthesis before the ATD
test is designated as 2T-CZA(B) and used for 10 h after the test as
2T-CZA(A) catalyst.
Fig. 8 shows XRD profiles of the 2T-CZA catalyst before and after
the ATD test. It is evident that the two characteristic diffraction
peaks of Cu in the pattern of 2T-CZA(A) become narrower than
the corresponding peaks in the pattern of 2T-CZA(B), by which
Fig. 9. HR-TEM photographs of 2T-CZA(B) (a) and 2T-CZA(A) (b) catalysts.

Z. Chu et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 48–53
53
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Effects of input amount of two kinds of surfactants, TEAH and
PEG, and accelerated thermally induced deactivation on the activ-
ity of CZA catalysts, prepared by two-step precipitation method,
were investigated in methanol synthesis from syngas. The results
show that the addition of the surfactant in the course of preparing
the binary matrix of the CZA catalyst can improve catalytic activ-
ity significantly, in which 2T-CZA catalyst displayed better catalytic
activity and satisfactory thermal stability. Characterizations show
that Cu0 is the main active site over CZA catalysts, and smaller crys-
tallite size of Cu and higher Cu specific surface area are favorable
to promote its catalytic activity. The precursors of the surfactant-
assisted prepared CZA catalysts contained more rosasite phases
which can be decomposed to CuxZn1−xO solid solution. A strong
electronic interaction between Cu and ZnO was induced after the
CZA catalyst containing more CuxZn1−xO solid solution was reduced
by 5 vol.% H2/N2, which decreased BE of Cu2p3/2 and therefore made
the adsorption of electron-rich CO over CZA catalyst easier. The
slight drop of activity over 2T-CZA catalyst after the ATD test should
be ascribed to growing up of Cu crystal and decrease in the number
of surface Cu atoms.
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