A study on the precipitating and aging processes of CuO/ZnO/Al2O3 catalysts synthesized in micro-impinging stream reactors

Article abstract of DOI:10.1039/c6ra02512a

CuO/ZnO/Al₂O₃ catalyst precursors were precipitated in a novel micro-impinging stream reactor (MISR) and a traditional stirred tank reactor (STR), respectively, followed by a period time of aging in the mother liquid. Being different from the simultaneous precipitating and aging of catalyst precursors within the same STR reactor, these two processes occurred in two separate containers in the MISR route, hence providing a more uniform and steady environment for both the precipitating and aging processes on top of the higher micromixing efficiency and better process control of the MISR. Therefore, substantial changes in the phase compositions and microstructures of the catalyst precursors were obtained with MISR, which resulted in smaller and more homogeneous catalyst particles with a larger BET surface area and specific copper surface area, better Cu/Zn dispersion as well as higher catalytic activity when compared to those prepared in the STR. The aging process also played an important role in catalyst preparation and it could be controlled more easily and precisely in the MISR route to form a more desirable phase structure, morphology and eventually more superior catalytic performance in methanol synthesis for the final catalysts.

Full text of DOI:10.1039/c6ra02512a

View Article Online
View Journal
RSC Advances
This article can be cited before page numbers have been issued, to do this please use: Q. Zhang, K.
Cheng, L. Wen, K. Guo and J. Chen, RSC Adv., 2016, DOI: 10.1039/C6RA02512A.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. This Accepted Manuscript will be replaced by the edited,
formatted and paginated article as soon as this is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/advances

Page 1 of 37
RSC Advances
View Article Online
DOI: 10.1039/C6RA02512A
Study on the Precipitating and Aging Processes of
CuO/ZnO/Al O Catalysts Synthesized in Micro-
2
3
impinging Stream Reactors
a
a
a,b,
Qing-Cheng Zhang , Kun-Peng Cheng , Li-Xiong Wen *,
b
a,b
Kai Guo , Jian-Feng Chen
aState Key Laboratory of Organic-Inorganic Composites, Beijing University of
Chemical Technology, Beijing 100029, China.
bResearch Center of the Ministry of Education for High Gravity Engineering and
Technology, Beijing University of Chemical Technology, Beijing 100029, China.
*Corresponding author. Tel.: +86-10-64443614; Fax: +86-10-64434784.
E-mail: wenlx@mail.buct.edu.cn

RSC Advances
Page 2 of 37
View Article Online
DOI: 10.1039/C6RA02512A
Abstract
CuO/ZnO/Al
2
O catalyst precursors were precipitated in a novel micro-impinging
3
stream reactor (MISR) and a traditional stirred tank reactor (STR), respectively,
followed by a period time of aging in the mother liquid. Being different from the
simultaneous precipitating and aging of catalyst precursors within the same STR reactor,
these two processes occurred in two separate containers in the MISR route, hence
providing a more uniform and steady environment for both precipitating and aging
processes on top of the higher micromixing efficiency and better process control of
MISR. Therefore, substantial changes in the phase compositions and microstructures of
the catalyst precursors were obtained with MISR, which resulted in smaller and more
homogeneous catalyst particles with larger BET surface area and specific copper
surface area, better Cu/Zn dispersion as well as higher catalytic activity when compared
to those prepared in STR. The aging process also played an important role for the
catalyst preparation and it could be controlled more easily and precisely in MISR route
to form more desirable phase structure, morphology and eventually more superior
catalytic performance in methanol synthesis for the final catalysts.
Keywords: Micro-impinging stream reactor; CuO/ZnO/Al
2
3
O catalysts; Precursors;
Aging; Methanol synthesis

Page 3 of 37
RSC Advances
View Article Online
DOI: 10.1039/C6RA02512A
1
. Introduction
Methanol is an important solvent and feedstock for the production of many
chemicals such as formaldehyde, dimethyl ether, acetic acid, and a wide variety of other
1
2
products. It can also be used as a fuel additive and a clean burning fuel. Industrial
production of methanol from synthesis gas (a mixture of CO/CO
2
/H
2
) is mainly carried
o
3,4
out over CuO/ZnO/Al
2
O
3
catalysts at 200-300 C and 5-10 MPa. It is generally
suggested that the particle size, specific surface area and Cu/Zn dispersion of
CuO/ZnO/Al catalysts are the most important factors influencing the catalytic
process.5-7 Commercially, CuO/ZnO/Al
catalysts are prepared by co-precipitation
2
O
3
2
O
3
method in stirred tank reactors using aqueous solutions of metal nitrates and sodium
carbonate to generate mixed Cu/Zn/Al hydrocarbonate precursors, followed by
calcination and reduction processes to form the active Cu/ZnO/Al
2
O
catalysts.8
3
Constant pH condition is required in the catalyst synthesis to avoid independent or
2+
2+
sequential precipitation of Cu and Zn , which prevents homogeneous distribution of
both species in the precipitate.9,10 Additionally, other conditions like temperature,11,12
1
3
14
reactant concentration and stirring speed will also play significant roles on the
physicochemical properties of the precursors and, in turn, the catalytic activity of the
final catalysts. However, it is hard to precisely control this big set of parameters for one
specific precipitation process in traditional stirred reactors. Even under the so-called
“constant” precipitating conditions in drop-adding stirred reactors, the chemical
potential of the reactants vary spatially and temporally when a droplet of the
precipitating agent is added into the reactor, in which precipitates and dissolved ions

RSC Advances
Page 4 of 37
View Article Online
1
5
DOI: 10.1039/C6RA02512A
already coexist. In addition, it was also found high levels of supersaturation, which
are the thermodynamic driving force of phase transition, are necessary in the
precipitation of crystal particles because of the highly nonlinear dependency of the
1
6
nucleation rate on supersaturation. During the conventional precipitation in stirred
tank reactor (STR), local supersaturation is created when a droplet of precipitating agent
is added into the other solution, and then vanishes through intensive stirring. A rapid
micromixing is hence essential for the formation of uniform supersaturation level and
consequently the product quality; however, it is difficult to achieve a rapid micromixing
in traditional stirred reactors due to their poor mixing and mass transfer performance.17
When the precipitating agent is added into the reactor quickly, a distinct feed rich zone
will be formed near the feed pipe and result in an uneven concentration distribution,
thus fast reactions may have already occurred or completed before the reactants
18
accomplish homogeneous mixing. On the other hand, a slow addition of fresh feed
will lead to a wide residence time distribution and backmixing (the addition rates during
the CuO/ZnO/Al
2
3
O catalyst synthesis are usually kept at 5-10 mL/min or even
smaller).12,13,19,20 As a consequence, the initial precipitates formed in stirred batch
reactors may differ significantly, which can further lead to different microstructures and
properties of CuO/ZnO/Al
2
3
O catalysts.
The precipitation of CuO/ZnO/Al
2
3
O catalyst precursors is often followed by an
aging step. During the aging process, the precipitate remains in contact with its mother
liquid and several reactions may take place at the same time, which can strongly affect
the properties and consequently the catalytic performance of the final catalyst.8,21,22

Page 5 of 37
RSC Advances
View Article Online
DOI: 10.1039/C6RA02512A
Firstly, the initially formed precipitates will slowly transform by partial dissolution/re-
precipitation reactions, and a recrystallization will occur at the same time
accompanying with a change in color from blue to bluish green and, as expected, a
change in chemical composition, particle size and morphology.23,24 Secondly, a mixture
of intermixed hydrocarbonates such as rosasite (Cu,Zn)
2
(OH)
2
CO
3
and aurichalcite
(
Cu,Zn) (OH) (CO will be formed through exchange reactions between the
5
6
3 2
)
preformed phases.10,25 Here, the efficient incorporation of Zn into malachite forming
rosasite (zincian malachite) is regarded as the key to CuO/ZnO catalysts preparation,
since a significant amount of atomically distributed Zn in rosasite will lead to an
effective stabilization of the Cu phase and thus highly active CuO/ZnO catalysts will
be obtained after thermal decomposition.10,26 Therefore, the aging of fresh precipitates
is also a crucial step for the synthesis of homogeneous CuO/ZnO/Al
2
3
O catalysts, and
hence a uniform and steady environment will play a key role for the aging process as
well as the quality of the final products. However, the aging environment in STR-
operation mode is barely uniform or stable not only because of the simultaneous
precipitating and aging processes but also the poor micromixing performance in STR.
All precipitated particles get accumulated in STR for the whole precipitation process
(
it usually lasts ~20 min or even longer in the drop-adding method),13,19,20,27 and the
aging of precursors has already started before the precipitation is completed, which can
lead to an inhomogeneous product distribution, as the initially formed precursors may
differ significantly from the phase formed at the end of the precipitation.
A micro-impinging stream reactor (MISR) was built and applied to prepare

RSC Advances
Page 6 of 37
View Article Online
catalysts for methanol synthesis in our previous studies.2
D8 O, 2 I9: 10.1039/C6RA02512A
The
CuO/ZnO/Al
2
O
3
MISR is constructed with two steel capillaries connected to a commercial T-junction,
but no tube is connected to the T-junction outlet, which provides a big-sized channel to
lead the reacted precipitates into sample collectors for the next step. The two streams
impinge on each other directly inside the T-junction to create a quick and constant
supersaturation level and therefore a more homogeneous nucleation environment for
the quick precipitating process, which may have been completed within the T-junction
chamber. Therefore, the following aging process will have a uniform and steady
environment. MISR also offers a better process control on reactant concentration, pH,
volumetric flow rates and etc., and the residence time distribution for both of
precipitating and aging processes is sharp, hence a better product quality of
CuO/ZnO/Al
2
3
O catalysts will be achieved. In addition, unlike most of micro-structured
3
0
31
32
devices such as microchannel reactor, microfluidic reactor and micromixer, which
are difficult to be fabricated due to their complicated configuration or easy to have
severe blocking problems during the precipitation process due to the tiny channels
inside the reactors, MISR can be easily constructed and has negligible blocking problem
because of its bigger geometric dimensions and faster stream flows as compared to
conventional microreactors.
In previous work, CuO/ZnO/Al
2
3
O catalysts have been prepared in MISR with
better microstructures and properties as well as higher catalytic activity in methanol
2
9
synthesis than those prepared in STR, as a result of the intensified micromixing within
the MISR reactor for the precipitating process as well as a more uniform and steady

Page 7 of 37
RSC Advances
View Article Online
DOI: 10.1039/C6RA02512A
environment for the subsequent aging process. In this work, we combined fast
precipitation and freeze-drying to investigate the phase transitions during the first
seconds of the precipitation, and then provided a detailed study on the effects of post-
precipitation processes on the properties and activity of CuO/ZnO/Al
their precursors produced in MISR and traditional STR, respectively.
2
3
O catalysts and
2
2
. Experimental
.1. Materials
Copper nitrate trihydrate Cu(NO
3
)
23H
2
O was purchased from Sinopharm
O,
O and sodium carbonate anhydrous
were provided by Beijing Reagent Factory, China. All reagents were of
analytical grade and used without further purification.
.2. Catalysts preparation
Ternary CuO/ZnO/Al
Chemical Reagent Co. Ltd., China. Zinc nitrate hexahydrate Zn(NO
aluminum nitrate nonahydrate Al(NO
Na CO
3
)
26H
2
3
)
39H
2
2
3
2
2
3
O catalyst precursors were prepared in MISR, which was
2
9
the same as reported previously by co-precipitation as follows: A solution of metal
nitrates (C=0.8 mol/L, with a molar ratio of Cu/Zn/Al = 4.5/4.5/1) and aqueous sodium
carbonate (C=1.15 mol/L) were injected into MISR simultaneously at a constant
volumetric flow rate of 80 mL/min and impinged into each other by using two constant-
flux pumps. The precipitation was conducted at room temperature and exactly
controlled pH of 7.0 measured in the effluent of MISR. After impinging and
precipitation within MISR, the precipitates were collected into a stirred and heated glass
beaker filled with a small amount of deionized water. The suspension was then further

RSC Advances
Page 8 of 37
View Article Online
o
DOI: 10.1039/C6RA02512A
aged at 80 C for a certain length of time (0, 10, 30, 60, 120 min) under vigorously
stirring. After aging, the precursors were filtered and washed with deionized water for
o
several times, and then dried overnight at 110 C. Finally, the dried precursors were
o
calcined at 350 C for 4 h to obtain the CuO/ZnO/Al
2
3
O catalysts, which were then
pelletized under a pressure of 10 MPa and crushed to 20-40 meshes for methanol
synthesis.
The co-precipitation was also performed through a traditional route by
simultaneously dropping two aqueous solutions containing metal nitrates and sodium
carbonate, respectively, into a glass beaker filled with a small amount of deionized
o
water under vigorous stirring at 80 C. The metal nitrates solution was added at a rate
of 5 mL/min, while the adding rate of the Na
2
CO solution was controlled to maintain
3
the desired pH (7.0) in the mother liquid. After complete addition of the solutions, the
o
suspension was further aged under continuous stirring at 80 C for 0, 10, 30, 60 and 120
min, respectively. The post-processes were as same as those in the MISR route.
In addition, in order to investigate the phase transitions occurred during the first
seconds of the precipitation, a part of non-aged precipitates were filtrated immediately
after complete precipitation and no washing procedure was applied so that to minimize
possible effects on the solids. The precipitates were then dried overnight in the freeze-
dryer for subsequent analyses.
2
.3. Characterization
Powder X-ray diffraction (XRD) analysis was carried out on a Bruker D8 Advance
X-ray diffractometer using Cu-Kα radiation (λ≈1.54 Å) and scanning 2θ range from 10-

Page 9 of 37
RSC Advances
View Article Online
DOI: 10.1039/C6RA02512A
8
4
0°.
Fourier transform infrared spectra (FT-IR) were measured in the range of 4000-
-1
00 cm using the KBr disc technique on a PE2000 FT-IR spectrometer.
The particle morphologies were observed with a JEOL 3010 transmission electron
microscopy (TEM) operated at 300 KV. The samples were ultrasonically dispersed in
high purity ethanol and then deposited onto ultrathin carbon-coated nickel grids.
The temperature-programmed reduction (TPR) experiments were performed with
an Autochem II 2920 multifunctional adsorption instrument. The samples (50 mg) were
firstly purged with Ar for 0.5 h to remove physically absorbed water and then reduced
o
in 10 vol.% H
2
/Ar mixture gas (30 mL/min) at a heating rate of 10 C /min up to 600
oC. The consumption of H
was analyzed by gas chromatograph (SP-2100A, China)
2
equipped with a thermal conductivity detector (TCD).
X-ray photoelectron spectra (XPS) were conducted with an ESCALAB 250
spectrometer using Al-Kα radiation. The binding energies were calculated with respect
to C 1s peak at 284.8 eV.
The specific surface area (SBET) of the calcined catalysts was calculated by the
BET method from nitrogen adsorption-desorption isotherms obtained with an ASAP
2
010 surface area analyzer (Micromeritics Instrument Corporation, USA). All samples
o
were pretreated under vacuum at 200 C for 2 h.
The exposed copper surface area (SCu) was determined by N O reactive frontal
2
chromatography (N
2
O-RFC) and carried out with a Micromeritics AutoChem 2920
instrument through the method proposed by Gao et al.33 The catalysts (0.1 g) were

RSC Advances
Page 10 of 37
View Article Online
o
DOI: 10.1039/C6RA02512A
first reduced with 10 vol.% H
2
/Ar mixture (30 mL/min) at 350 C for 2 h, followed by
o
purging with Ar for 30 min and cooling to 65 C. The reduced catalysts were then
exposed to N
that the samples were flushed with Ar to remove the N
temperature. Finally, the Cu O at the surface was reduced back to metallic Cu at 350
oC in the H
/Ar flow (30 mL/min). The SCu was calculated from the amount of
consumed H during the reduction steps, assuming a molar stoichiometry of N O/Cu
2 and a value of 1.4×10 Cu atoms/m as the copper atoms density.
.4. Catalytic activity test
The catalytic performance of CO hydrogenation was carried out in a stainless steel
2
O (30 mL/min) for 1 h to oxidize surface copper atoms to Cu
2
O. After
2
O and cooled to room
2
2
2
2
s
1
9
2
34
=
2
tubular fixed-bed reactor (internal diameter = 1 cm), which was heated in a tube furnace
o
controlled to ±0.1 C by a programmable temperature controller. 1.0 g CuO/ZnO/Al
2
O
3
catalyst diluted with 2.0 g inert quartz sand was placed in the constant temperature zone
of the reactor. The sample was firstly reduced in situ with 10 vol.% H
2
/N at
2
o
programmed temperature, which was raised from room temperature to 250 C and then
o
maintained at 250 C for 6 h under atmospheric pressure. After reduction, the syngas of
3
3 vol.% CO and 67 vol.% H
2
was switched as feed gas with the space velocity of 4000
o
mL/(gcat·h) and the catalytic test was performed under 5.0 MPa and 250 C to synthesize
methanol. The outlet gas from the reactor was quantitatively analyzed every 30 min
with a computer-interfaced online gas chromatograph (Shanghai Linghua Electronics
Institute, GC-9890B), which was equipped with a Porapak T column (3 mm × 2 m)
connected to a TCD detector using H as carrier gas. The effluents from the reactor
2

Page 11 of 37
RSC Advances
View Article Online
o
DOI: 10.1039/C6RA02512A
were kept at 200 C before entering GC to avoid product condensation. The catalytic
activity was evaluated at the steady state of reacting system.
The conversion of CO is defined as:

mol carbon monoxide converted to all products
mol carbon monoxide in the feed gas

(1)


The selectivity to methanol is defined as:

mol produced methanol

(2)

mol carbon monoxide converted to all products

3
. Results and discussion
Since the precipitating and aging processes are separated in the MISR route for the
preparation of CuO/ZnO/Al catalysts, it can provide a uniform and steady
2
O
3
environment for both processes and, therefore, offers the possibility to investigate the
phase transitions of the initial precipitates right after the precipitation by a freeze-drying
technology, as well as the aging behaviors for different length of time and their effects
on the structures and properties of the precursors and final catalysts, which is not
possible with the traditional stirred tank reactor (STR) route due to the simultaneous
precipitating and aging processes.
3
.1 Phase structure analysis of the initial precipitates prepared in different routes
The XRD patterns of fresh precipitates, which were quenched immediately in
freeze-dryer, are shown in Fig. 1. In addition to the intensive diffraction peaks of the
byproduct NaNO , which existed because no washing procedure was applied,
crystalline sodium zinc carbonate Na Zn (CO (JCPDS No. 86-0607) was identified
3
2
3
)
3 4

RSC Advances
Page 12 of 37
View Article Online
DOI: 10.1039/C6RA02512A
as the kinetically metastable product in MISR. The typical peak for Cu precursor was
not observed because the solid formation started with the initial precipitation of
amorphous copper-containing species.21,35 However, the initial precipitate formed in
STR was mostly X-ray amorphous, except for the diffraction peak at 2θ = 34.0° ascribed
to hydrozincite Zn
5
(OH)
6
(CO
3
2
) (JCPDS No. 72-1100) or aurichalcite (JCPDS No. 82-
1
253) along with NaNO
3
diffraction peaks. Such phase structure differences of the
initial precipitates prepared in these two different routes was mainly due to the different
micromixing performances and co-precipitation modes in MISR and STR, respectively.
Previous studies indicated that Na
2
Zn
3
(CO
3
4
) was quite unstable in the mother liquid
and would easily transform into the more thermodynamically stable zinc-enriched
hydrocarbonates (hydrozincite or aurichalcite).36-39 In the STR-operation mode, all
precipitated particles remained in the same reaction vessel for the whole precipitation
process, a chemical phase transition of Na
2
Zn
3
(CO
3
4
) induced by water or thermal
treatment would have already taken place for a long residence time before the
precipitation was completed (the co-precipitation process in this study took ~15 min),
3
8
and this phase transition would be accelerated by vigorous stirring. Therefore, the
initial precipitates formed at different precipitating time and the different places of STR
might differ significantly in chemical compositions and phase structures. By contrast,
the whole precipitation in MISR was very fast (the residence time was ~ 1 s and the
whole process took only ~1 min), and the characteristic micromixing time of MISR was
2
8
in the range of 1~10 ms, thus more homogeneous precipitates would be obtained in
MISR.

Page 13 of 37
RSC Advances
View Article Online
DOI: 10.1039/C6RA02512A
3
.2 Characterization of precursors aged for different length of time
Residual sodium in precursors is known to poison the catalysts and to enhance the
sintering of metallic particles in methanol synthesis, thus the washing treatment is of
4
0
crucial importance for the preparation of highly active CuO/ZnO/Al
2
O catalysts. For
3
this reason, the precursors in the subsequent sections were analyzed after repeated
washing treatment with deionized water and then dried in oven overnight.
Fig. 2a shows the XRD patterns of precursors prepared in MISR and aged for
different length of time. It was found that, after washing and oven-drying processes, the
diffraction peaks belonging to Na
2
Zn
3
(CO
3
4
) were mostly disappeared and the complete
removal of crystalline NaNO was achieved as the diffraction peak at 2θ = 29.0° was
3
not observed anymore, which was very strong for the samples without washing as
shown in Fig. 1. Therefore, a structural rearrangement of the system took place when
the fresh precipitate was exposed to water and it was unlikely that any Na
2
Zn
3
3 4
(CO )
would have remained in the sample after being vigorously stirred and washed in STR-
route, followed by drying at 110 C overnight.36-39 When the precipitates were
intensively stirred in the mother liquid for a certain aging time (10, 30, 60 or 120 min),
o
Na
2
Zn
3
(CO
3
)
4
was completely converted into zinc-enriched hydrocarbonate phases.
(OH) CO and rosasite from amorphous
Meanwhile, the crystallization of malachite Cu
2
2
3
copper-containing species would start as well, accompanying with a color change from
blue to bluish green. It was found that the characteristic peaks of malachite (JCPDS No.
4
1-1390) and rosasite (JCPDS No. 18-1095) at 2θ = 14.8°, 17.6°, 24.2° and 31.9°
appeared after 30 min aging and increased in intensities with time, which is in good

RSC Advances
Page 14 of 37
View Article Online
1
3
DOI: 10.1039/C6RA02512A
accordance with the studies of Farahani et al. who proposed that further increase in
aging time after the appearance of color change would cause a progressive crystalline
growth as a result of Ostwald ripening. In addition, the Zn-Al hydrotalcite
Zn
6
Al
2
(OH)16CO
3
·4H
2
O (JCPDS No. 38-0486) represented by the diffraction peaks at
2
θ = 11.5° and 23.3° was observed for precursors aged for 120 min. Therefore, aging
of the freshly precipitated solids would eventually result in a mixture of hydrocarbonate
phases, which could strongly affect the microstructures and consequently the catalytic
performance of the final catalyst.
The XRD patterns of precursors prepared in STR aged for different length of time
are shown in Fig. 2b. No noticeable variation was found in the XRD patterns of the
hydrocarbonate phases through the washing treatment except for the removal of
crystalline NaNO , and then STR samples followed the same transitional tracks in aging
3
process as those prepared in MISR. In addition, a slight shift of the malachite diffraction
̅
peak near 2θ = 32° (201 peak) to higher angles was observed when the aging time was
increased from 30 min to 60 min (Fig. 2c), which was correlated with the substitution
chemistry of malachite as Zn2+ is incorporated into malachite structure forming
rosasite.10,41 Therefore, the exchange reactions between the preformed phases took
place during the aging of precursors, which would enhance the Cu/Zn dispersion of
̅
final catalysts. However, the 201 peak shifted back to lower angles when the precursor
was aged for 120 min, which was due to the formation of Zn-Al hydrotalcite as shown
in the XRD patterns.
Compared to the MISR-route, all precursors prepared in STR exhibited much

Page 15 of 37
RSC Advances
View Article Online
DOI: 10.1039/C6RA02512A
sharper copper-enriched hydrocarbonates (malachite and rosasite) diffraction peaks
indicating larger crystallites according to Scherrer equation. In addition, a considerable
̅
shift of 201 peak towards higher angles (2θ = 32.1°) was observed for the precursor
prepared in MISR as compared to STR samples, which suggested a highest degree of
Cu-substitution by Zn in rosasite phase should be achieved in MISR-route after 60 min
aging of precursor, and thus CuO/ZnO/Al
2
3
O catalyst of fine dispersion was obtained.
Such differences in the compositions and microstructures of precursors were traced
back to the different pathways of solid formation for two precipitation routes. As
discussed earlier, in the drop-adding stirred reactor, particle growth takes place when a
droplet of precipitating agent is added into the reactor in which precipitates have already
42
existed. On the other hand, the intense impinging in MISR creates a fast and uniform
micromixing as well as a high supersaturation level, which favors nucleation rather than
crystal growth, thus results in smaller and more uniform particles in the
precipitation.43,44 In addition, the aging mechanism has shown that no binary
9
precipitates can be directly obtained, however, MISR can be used to form a pseudo-
homogeneous precipitate with the best possible distribution of Cu- and Zn-
intermediates due to its homogeneous nucleation environment, which will further
accelerate the exchange reactions between the preformed phases and, in turn, favor the
Cu/Zn dispersion of final catalysts.
A comparison of the FT-IR spectra for precursors prepared at different conditions
(different routes and aging times) is shown in Fig. 3. All samples displayed a weak
-1
absorption band around 1630 cm ascribed to the bending vibration of water. For the

RSC Advances
Page 16 of 37
View Article Online
-1
DOI: 10.1039/C6RA02512A
MISR-prepared samples (Fig. 3a), there was a small peak at 1385 cm representing the
asymmetric N-O vibration in the non-aged precursor, which was due to the existence
of a small amount of gerhardtite Cu
2
(OH)
3
NO
3
generated by the reaction between
Cu(OH) and NO
2
3
-. However, an unambiguous discrimination of poorly crystallized
samples on the basis of XRD patterns is difficult due to their high similarity in crystal
structures, thus gerhardtite was not detected in XRD analysis in Fig. 2. Gerhardtite was
believed to exert adverse effect for production of active catalyst by forming larger
11
copper particles (i.e. sintering effect). Fortunately, gerhardtite would then slowly react
upon aging with hydroxide and carbonate to form amorphous georgeite Cu(OH) CO
the chemical formula of georgeite was the same as that of malachite),21 thus the
2
3
(
asymmetric N-O vibration disappeared when the precipitate was aged for 10 min. The
strong absorption bands of the amorphous precursors (0, 10 min aging) around 1480
-1
20,27
and 837 cm were quite similar to those of georgeite reported by Shen et al.
In
-1
addition, the characteristic bands in the region of 1520-1390 cm were attributed to
-1
asymmetric C-O stretching vibration, whereas the bands around 835 cm were ascribed
4
1
to out-of-plane OCO bending mode. Increasing the aging time from 10 min to 30 min
-1
-1
forced the asymmetric C-O stretching vibration around 1480 cm shift to 1499 cm ,
which was mainly ascribed to the recrystallization of amorphous georgeite, either
directly crystallized to malachite or transformed into rosasite.20,27,35 All crystallized
samples displayed the spectra with only small differences in position and intensity,
hence the characterization of a phase mixture would be complicated for the carbonate
bands originating from the malachite, rosasite and aurichalcite that overlapped

Page 17 of 37
RSC Advances
View Article Online
DOI: 10.1039/C6RA02512A
significantly. However, previous studies45,46 have suggested that the incorporation of
2
+
Zn into the malachite lattice forming rosasite would result in a shift of the asymmetric
-1
C-O stretching vibration (around 1500 cm ) to higher wavenumber. Compared to other
-1
precursors, the precursor aged for 60 min showed the higher wavenumber (1506 cm )
of the asymmetric C-O stretching vibration; therefore, a more homogeneous
microstructure of the CuO/ZnO/Al
min aging of precursor.
2
3
O catalyst might be obtained in the MISR with 60-
For the samples prepared in STR (Fig. 3b), it was found that the non-aged
-
1
precursor displayed a very small peak at 1385 cm representing the asymmetric N-O
vibration; however, its intensity was much lower than the MISR-prepared sample (Fig.
3
a), which was due to the gradual transformation of gerhardtite to georgeite during the
precipitation process in STR as already discussed. Therefore, it confirmed that several
reactions took place in the long residence time before the complete precipitation in STR.
The small differences of IR spectra in positions and intensities (Fig. 3a and 3b)
indicated that the two precipitation routes generated precipitates and precursors with
different chemical compositions and phase structures, which was mainly due to the
different micromixing performances, nucleation environments and residence time
distributions of the STR and MISR, respectively.
3
.3 Characterization of calcined catalysts after aging for different length of time
The XRD patterns of the calcined catalysts prepared at different conditions are
shown in Fig. 4. It showed that the phase structures of the catalyst samples were mainly
composed of CuO (JCPDS No. 48-1548) and ZnO (JCPDS No. 36-1451). The overlap

RSC Advances
Page 18 of 37
View Article Online
DOI: 10.1039/C6RA02512A
of diffraction peaks for CuO at 2θ = 35.4° and ZnO at 2θ = 36.2° indicated the formation
of CuO-ZnO solid solution. Besides, the typical peaks for Al
not observed, suggesting that Al
2
O
3
(2θ = 19°, 45°) were
5
2
O
3
might exist in an amorphous state. For the MISR-
prepared catalysts (Fig. 4a), it was found that the non-aged catalyst exhibited sharp
diffraction peaks indicating large crystallite sizes, which was mainly due to the
existence of Na
2
Zn
3
(CO
3
4
) and gerhardtite in the precursor as already discussed in the
11
XRD analysis (Fig. 2a) and IR spectra (Fig. 3a) on the precursors. However, only
weak peaks ascribed to ZnO could be found in the catalyst obtained from the 10-min
aged precursor and the absence of CuO diffraction peaks in XRD pattern indicated that
CuO was poorly crystallized. When the aging time was prolonged, the diffraction peaks
ascribed to CuO increased in intensities, which were correlated to the remarkable
crystalline growth of copper-enriched hydrocarbonate phases in the corresponding
precursors (Fig. 2a). On the other hand, a very weak CuO diffraction peak at 2θ = 38.8°
was observed for the non-aged catalyst prepared in STR (Fig. 4b), which was due to
the gradual transformation of Na
2
Zn
3
(CO
3
4
) and gerhardtite during the precipitation
process into zinc-enriched hydrocarbonates and amorphous georgeite, respectively.
However, it should be concerned that these important phase transitions would also take
place when the precipitate was vigorously stirred after complete precipitation in MISR
(
~1 min). The separated precipitating and aging processes in the MISR-route provided
a uniform and steady environment for both processes and, therefore, a better product
quality of CuO/ZnO/Al catalysts might be achieved. In addition, for the catalysts
aged for the same length of time (10, 30, 60, 120 min) after the complete precipitation,
2
O
3

Page 19 of 37
RSC Advances
View Article Online
DOI: 10.1039/C6RA02512A
sharper diffraction peaks were observed for the catalysts prepared in STR as compared
to MISR-route, which suggested larger CuO and ZnO crystallites were obtained in STR.
Therefore, both precipitating and aging of precursors played important roles in
determining the phase structures of the precursors and final catalysts.
TPR profiles were given in Fig. 5 to investigate the reduction patterns of copper
species for the CuO/ZnO/Al
2
3
O catalysts prepared at different conditions. Samples
prepared in both routes exhibited a broad peak without any shoulders in the range of
o
2
00-300 C, which was obtained from the reduction of CuO. Under the experimental
4
7
conditions in this work, ZnO and Al
2
O
3
would not be reduced. For the MISR-prepared
o
catalysts (Fig. 5a), the non-aged catalyst showed a reduction peak at 265 C, and a
o
shift of reduction temperature towards 238 C was observed when the aging time was
increased to 10 min, which was correlated to smaller CuO crystallites in the prepared
catalyst as demonstrated by the weak CuO diffraction peaks in XRD patterns (Fig. 4a).
In addition to the particle size effect, the shift of reduction peak to lower temperature
might also be caused by the better copper dispersion of the mixed oxides.48,49 Therefore,
the shift of reduction peak to lower temperature might be mainly owing to the higher
zinc content into the malachite structure forming rosasite when aging time was
prolonged (from 10 min to 60 min) as already discussed in XRD patterns (Fig. 2a) and
IR analysis (Fig. 3a), thus favoring the copper dispersion and finally improving the
reducibility of CuO/ZnO/Al
reduction peaks for the CuO/ZnO/Al
profiles of the catalysts prepared in STR (Fig. 5b) were broader and shifted to higher
2
O
3
catalysts. In addition, compared with the narrow
2
O
3
catalysts obtained from MISR route, the TPR

RSC Advances
Page 20 of 37
View Article Online
DOI: 10.1039/C6RA02512A
reduction temperature, suggesting much larger CuO particles with a much wider size
distribution were obtained in STR. Previous studies concerning the reducibility of
copper-based catalysts for methanol synthesis and methanol steam reforming have
revealed that a high catalytic activity is associated with good reducibility of
catalysts;50,51 therefore, higher catalytic performance would be expected for the MISR-
prepared catalysts.
Fig. 6 illustrates the typical XPS spectra of Cu 2p3/2 levels of the CuO/ZnO/Al
2
O
3
catalysts prepared at different conditions. The binding energy (BE) range for the main
Cu 2p3/2 peak was around 933.5 eV, generally with characteristic satellite peaks between
5
2
53-55
9
40 and 945 eV due to the electron shake-up process. Various studies
have shown
that the positions of these peaks depend on the chemical composition and crystalline
2
+
structure of the catalyst, and particularly on the near environment of Cu . The binding
energy of Cu 2p3/2 for pure CuO was 934.0 eV, which was higher than those of ternary
CuO/ZnO/Al
2
O
3
catalysts, indicating that CuO and other metal oxides were not simply
catalysts but an interaction between them was
physically mixed in the CuO/ZnO/Al
2
O
3
present. This is because that the electronegativity of Cu (1.90) is stronger than that of
Zn (1.65), which induced the migration of electron cloud to Cu and finally resulted in
5
3
a shift of Cu 2p3/2 to lower BE. In addition, it was found that the MISR-prepared
catalyst that was aged for 60 min displayed lower BE compared to other catalysts,
which was mainly attributed to the enhanced interaction between CuO and ZnO because
of their fine particle size and better Cu/Zn dispersion.
TEM images of the CuO/ZnO/Al
2
3
O catalysts prepared at different conditions and

Page 21 of 37
RSC Advances
View Article Online
DOI: 10.1039/C6RA02512A
after methanol synthesis are shown in Fig. 7. The samples showed very similar
morphology and comprised agglomerates of round and oval particles. TEM analysis of
MISR-prepared catalysts as a function of aging time revealed a decrease of primary
particle size from ~10 nm (non-aged) to ~6 nm (10 min aging) (Fig. 7a,b), which was
well consistent with the XRD analysis in Fig. 4a. It was also found that, after aging for
6
0 min, the catalyst produced in MISR contained mostly round particles with a mean
size of 8-10 nm (Fig. 7c), whereas slightly larger and more irregular particles were
obtained in STR route (Fig. 7d). This observation agreed well with the XRD analysis
(Fig. 4) and TPR results (Fig. 5), which indicated that larger and ununiformed catalyst
particles were obtained in STR due to its poor mixing and mass transfer performance.17
In addition, the TEM images showed that significant aggregation of catalyst particles
took place after methanol synthesis reaction for both MISR- and STR-prepared
catalysts (Fig. 7e, 7f), but with a more severe aggregation for the STR-prepared catalyst.
Such aggregation might be caused by the highly exothermic effect of the methanol
synthesis reaction and would result in less active sites and a decrease of catalytic
activity during the synthesis process.56-58
3
.4 Catalytic activities of the calcined catalysts after aging for different length of
time
The physicochemical properties of the CuO/ZnO/Al
2
3
O catalysts prepared at
different conditions are summarized in Table 1. It was found that the non-aged catalyst
2
prepared in MISR displayed the lowest SBET (54.1 m /g) and SBET increased remarkably
2
when the catalysts were aged for a period of time. The maximum SBET of 141.6 m /g

RSC Advances
Page 22 of 37
View Article Online
DOI: 10.1039/C6RA02512A
was obtained when the aging t = 10 min, and a reduction of SBET was observed with
further increasing aging time due to the slight increase in particle size as already
described in XRD analysis (Fig. 4a) and TEM images (Fig. 7). The exposed copper
surface area (SCu) is a more important parameter for Cu-based catalysts since metallic
copper is generally regarded as the main active component. Table 1 showed that the
2
non-aged catalyst had the lowest SCu of 7.5 m /g. However, SCu for the MISR-prepared
2
catalysts did not follow the same trend as that of SBET. The maximum SCu of 22.4 m /g
was observed for the MISR-prepared catalyst aged for 60 min, which can provide more
catalytically active sites due to its better Cu/Zn dispersion. Further increase in aging
time to 120 min caused the remarkable growth of crystallite size and decreased the
catalyst SCu. In addition, the sample prepared in STR, which has poor micromixing and
mass transfer performance, displayed much lower SBET and SCu than MISR-prepared
catalyst (both aged for 60 min) due to its larger particle size and poor Cu/Zn dispersion
as already discussed in previous sections.
The catalytic performances in methanol synthesis via CO hydrogenation for the
CuO/ZnO/Al
2
3
O catalysts prepared at different conditions are also shown in Table 1. It
demonstrated that the catalytic activity (CO conversion, XCO) would be enhanced
greatly with increasing SCu for the MISR-prepared samples, which was mostly
enhanced with increasing aging time until it reached a proper length of time (60 min).
But the positive influence of SCu on the CH OH selectivity (SMeOH) was much slighter.
3
Therefore, the non-aged MISR-prepared catalyst had the lowest XCO and SMeOH, while
the highest XCO and SMeOH were achieved by the MISR-prepared catalyst with 60 min

Page 23 of 37
RSC Advances
View Article Online
DOI: 10.1039/C6RA02512A
aging-treatment. Such results agreed well with the previous observations that the aging
process with proper time would lead to more homogeneous microstructure of the
precursors and final CuO/ZnO/Al
2
3
O catalyst, and the well dispersed CuO could
enhance the synergy reaction with ZnO crystallites and hence improve the catalytic
activity of the catalyst. Table 1 also showed that the MISR-prepared catalyst with 60
min aging-treatment had significantly higher SBET, SCu and XCO than those of the STR-
prepared catalyst with 60 min aging-treatment, which agreed well with its larger particle
size and poorer Cu/Zn dispersion for the STR products and clearly demonstrated the
advantages of the MISR-route over the STR-route for catalyst preparation.
It is widely accepted that the methanol synthesis via CO hydrogenation is a
structure-sensitive catalytic reaction. The different catalytic performances of these
catalysts were associated with the combining effects of their different phase structures,
crystallite sizes, Cu/Zn dispersion, exposed copper surface area and specific surface
area as already discussed in previous sections. In addition, defects on the surface and/or
in the bulk structure, such as microstrain, impurities, and structural disorder were also
suggested to be responsible for the catalytic performances of the copper-based catalysts,
which needs further investigation.59-62 Therefore, both precipitating and aging
processes will play key roles for the catalytic performance of the final CuO/ZnO/Al
catalysts.
2
O
3
4
. Conclusions
This study examined the specific effects of washing and aging treatments on the

RSC Advances
Page 24 of 37
View Article Online
DOI: 10.1039/C6RA02512A
structures and properties of the precipitated precursors and the final CuO/ZnO/Al
catalysts with two different co-precipitation routes: via micro-impinging stream reactor
MISR) or traditional stirred tank reactor (STR). The MISR route conducted the
2
O
3
(
precipitating and aging processes in two separated steps, thus providing a uniform and
steady environment for both of them. In addition, significantly intensified micromixing
performance could be achieved with MISR. Therefore, catalysts with smaller crystallite
size, better Cu/Zn dispersion, higher BET surface area and specific Cu surface area, and
superior catalytic activity in methanol synthesis were obtained with MISR as compared
to the STR route. It was also found that the washing and aging treatments affected the
microstructure and consequently the catalytic performance of CuO/ZnO/Al
2
O
3
catalysts remarkably. A mixture of sodium zinc carbonate and amorphous copper-
containing species were formed in the initial stage of precipitation. Aging of fresh
precipitates induced a structural rearrangement of sodium zinc carbonate to the more
thermodynamically stable hydrozincite or aurichalcite, while amorphous copper-
containing species were gradually transformed into crystal malachite and rosasite
accompanied with a color change from blue to bluish green. In addition, increasing the
aging time of precursors (from 0 to 60 min) resulted in more uniform microstructures
of the CuO/ZnO/Al
2
3
O catalysts, which exhibited higher specific Cu surface area and
more superior catalytic performance in methanol synthesis. However, further increase
in aging time (120 min) of precursor caused remarkable growth of crystallite size and
lowered the catalytic activity of the final catalysts.

Page 25 of 37
RSC Advances
View Article Online
DOI: 10.1039/C6RA02512A
Acknowledgments
The authors gratefully acknowledge the financial support provided by National
Natural Science Foundation of China (Nos. 21376015, 21576012 and 91334206).
References
1
2
3
4
E. E. Ortelli, J. Wambach and A. Wokaun, Appl. Catal., A, 2001, 216, 227-241.
G. A. Olah, Angew. Chem., Int. Ed., 2005, 44, 2636-2639.
Y. L. Zhang, Q. Sun, J. F. Deng, D. Wu and S. Y. Chen, Appl. Catal., A, 1997, 158, 105-120.
P. Mierczynski, T. P. Maniecki, K. Chalupka, W. Maniukiewicz and W. K. Jozwiak, Catal. Today,
2
011, 176, 21-27.
P. Gao, F. Li, F. K. Xiao, N. Zhao, W. Wei, L. S. Zhong and Y. H. Sun, Catal. Today, 2012, 194, 9-
5.
G. J. Millar, I. H. Holm, P. J. R. Uwins and J. Drennan, J. Chem. Soc., Fataday Trans., 1998, 94,
93-600.
5
6
7
1
5
M. Kurtz, N. Bauer, C. Büscher, H. Wilmer, O. Hinrichsen, R. Becker, S. Rabe, K. Merz, M.
Driess, R. Fischer and M. Muhler, Catal. Lett., 2004, 92, 49-52.
8
9
M. Behrens and R. Schlögl, Z. Anorg. Allg. Chem., 2013, 639, 2683-2695.
M. Behrens, D. Brennecke, F. Girgsdies, S. Kißner, A. Trunschke, N. Nasrudin, S. Zakaria, N. F.
Idris, S. B. A. Hamid, B. Kniep, R. Fischer, W. Busser, M. Muhler and R. Schlögl, Appl. Catal., A,
2
011, 392, 93-102.
1
0
S. Zander, B. Seidlhofer and M. Behrens, Dalton Trans., 2012, 41, 13413-13422.
J. L. Li and T. Inui, Appl.Catal., A, 1996, 137, 105-117.
11
1
2
C. Baltes, S. Vukojević and F. Schüth, J. Catal., 2008, 258, 334-344.
B. V. Farahani, F. H. Rajabi, M. Bahmani, M. Ghelichkhani and S. Sahebdelfar, Appl. Catal., A,
13
2
014, 482, 237-244.
1
4
G. Simson, E. Prasetyo, S. Reiner and O. Hinrichsen, Appl.Catal., A, 2013, 450, 1-12.
X. H. Liu, Y. Y. Bao, Z. P. Li and Z. M. Gao, Chin. J. Chem. Eng., 2010, 18, 588-599.
H.-C. Schwarzer and W. Peukert, AIChE J., 2004, 50, 3234-3247.
15
16
1
7
J. Bałdyga, J. R. Bourne and S. J. Hearn, Chem. Eng. Sci., 1997, 52, 457-466.
S. Bhattacharya and S. M. Kresta, Chem. Eng. Res. Des., 2004, 82, 1153-1160.
G. C. Shen, S. I. Fujita and N. Takezawa, J. Catal., 1992, 138, 754-758.
18
19
20
G. C. Shen, S. I. Fujita, S. Matsumoto and N. Takezawa, J. Mol. Catal. A: Chem., 1997, 124, 123-
1
36.
B. Bems, M. Schur, A. Dassenoy, H. Junkes, D. Herein and R. Schlögl, Chem. - Eur. J., 2003, 9,
039-2052.
21
2
22
E. N. Muhamad, R. Irmawati, Y. H. Taufiq-Yap, A. H. Abdullah, B. L. Kniep, F. Girgsdies and T.
Ressler, Catal. Today, 2008, 131, 118-124.
23
S. Klokishner, M. Behrens, O. Reu, G. Tzolova-Müller, F. Girgsdies, A. Trunschke and R.
Schlögl, J. Phys. Chem. A, 2011, 115, 9954-9968.

RSC Advances
Page 26 of 37
View Article Online
DOI: 10.1039/C6RA02512A
24
D. M. Whittle, A. A. Mirzaei, J. S. J. Hargreaves, R. W. Joyner, C. J. Kiely, S. H. Taylor and G. J.
Hutchings, Phys. Chem. Chem. Phys., 2002, 4, 5915-5920.
B. L. Kniep, F. Girgsdies and T. Ressler, J. Catal., 2005, 236, 34-44.
M. Behrens, J. Catal., 2009, 267, 24-29.
2
5
26
27
S. I. Fujita, A. Satriyo, G. Shen and N. Takezawa, Catal. Lett., 1995, 34, 85-92.
2
8
Z. W. Liu, L. Guo, T. H. Huang, L. X. Wen and J. F. Chen, Chem. Eng. Sci., 2014, 119, 124-133.
Q. C. Zhang, Z. W. Liu, X. H. Zhu, L. X. Wen, Q. F. Zhu, K. Guo and J. F. Chen, Ind. Eng. Chem.
Res., 2015, 54, 8874-8882.
29
3
0
N. Kockmann, J. Kastner and P. Woias, Chem. Eng. J., 2008, 135, Supplement 1, S110-S116.
H. Wang, X. Li, M. Uehara, Y. Yamaguchi, H. Nakamura, M. Miyazaki, H. Shimizu and H.
Maeda, Chem. Comm., 2004, 48-49.
31
32
M. Schur, B. Bems, A. Dassenoy, I. Kassatkine, J. Urban, H. Wilmes, O. Hinrichsen, M. Muhler
and R. Schlögl, Angew. Chem., Int. Ed., 2003, 42, 3815-3817.
33
P. Gao, F. Li, N. Zhao, F. K. Xiao, W. Wei, L. S. Zhong and Y. H. Sun, Appl. Catal., A, 2013, 468,
4
42-452.
34
Z. L. Yuan, L. N. Wang, J. H. Wang, S. X. Xia, P. Chen, Z. Y. Hou and X. M. Zheng, Appl. Catal.,
B, 2011, 101, 431-440.
35
A. M. Pollard, M. S. Spencer, R. G. Thomas, P. A. Williams, J. Holt and J. R. Jennings, Appl.
Catal., A, 1992, 85, 1-11.
36
S. Kaluza, M. Behrens, N. Schiefenhövel, B. Kniep, R. Fischer, R. Schlögl and M. Muhler,
ChemCatChem, 2011, 3, 189-199.
37
S. Kaluza, M. K. Schröter, R. Naumann d'Alnoncourt, T. Reinecke and M. Muhler, Adv. Funct.
Mater., 2008, 18, 3670-3677.
38
S. Kaluza and M. Muhler, Catal. Lett., 2009, 129, 287-292.
3
9
S. Kaluza and M. Muhler, J. Mater. Chem., 2009, 19, 3914-3922.
K. W. Jun, W. J. Shen, K. S. Rama Rao and K. W. Lee, Appl. Catal., A, 1998, 174, 231-238.
M. Behrens, F. Girgsdies, A. Trunschke and R. Schlögl, Eur. J. Inorg. Chem., 2009, 2009, 1347-
40
41
1
357.
4
2
L. Wantha and A. E. Flood, J. Cryst. Growth, 2011, 318, 117-121.
J. Nvlt, Cryst. Res. Technol., 1995, 30, 737-745.
43
44
D. V. Alexandrov, Chem. Eng. Sci., 2014, 117, 156-160.
45
D. Stoilova, V. Koleva and V. Vassileva, Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy, 2002, 58, 2051-2059.
46
Z. Li, S. W. Yan and H. Fan, Fuel, 2013, 106, 178-186.
47
S. Velu, K. Suzuki, M. Okazaki, M. P. Kapoor, T. Osaki and F. Ohashi, J. Catal., 2000, 194, 373-
3
84.
48
P. Gao, F. Li, F. K. Xiao, N. Zhao, N. N. Sun, W. Wei, L. S. Zhong and Y. H. Sun, Catal. Sci.
Technol., 2012, 2, 1447-1454.
4
9
F. Meshkini, M. Taghizadeh and M. Bahmani, Fuel, 2010, 89, 170-175.
X. M. Guo, D. S. Mao, G. Z. Lu, S. Wang and G. S. Wu, Catal. Commun., 2011, 12, 1095-1098.
P. Kurr, I. Kasatkin, F. Girgsdies, A. Trunschke, R. Schlögl and T. Ressler, Appl. Catal., A, 2008,
50
51
3
48, 153-164.
J. W. Bae, S.-H. Kang, Y.-J. Lee and K.-W. Jun, J. Ind. Eng. Chem., 2009, 15, 566-572.
R. T. Figueiredo, A. Martınez-Arias, M. L. Granados and J. L. G. Fierro, J. Catal., 1998, 178,
52
53
́

Page 27 of 37
RSC Advances
View Article Online
DOI: 10.1039/C6RA02512A
1
46-152.
5
4
L. H. Zhang, C. Zheng, F. Li, D. G. Evans and X. Duan, J. Mater. Sci., 2008, 43, 237-243.
F. Garbassi and G. Petrini, J. Catal., 1984, 90, 106-112.
55
5
6
J. T. Sun, I. S. Metcalfe and M. Sahibzada, Ind. Eng. Chem. Res., 1999, 38, 3868-3872.
G. Prieto, J. D. Meeldijk, K. P. de Jong and P. E. de Jongh, J. Catal., 2013, 303, 31-40.
X. Zhai, J. Shamoto, H. Xie, Y. Tan, Y. Han and N. Tsubaki, Fuel, 2008, 87, 430-434.
T. Ressler, B. L. Kniep, I. Kasatkin and R. Schlögl, Angew. Chem., Int. Ed., 2005, 44, 4704-4707.
I. Kasatkin, P. Kurr, B. Kniep, A. Trunschke and R. Schlögl, Angew. Chem., Int. Ed., 2007, 46,
57
58
59
60
7
324-7327.
61
S. Natesakhawat, J. W. Lekse, J. P. Baltrus, P. R. Ohodnicki, B. H. Howard, X. Deng and C.
Matranga, ACS Catal., 2012, 2, 1667-1676.
62
M. Behrens, S. Zander, P. Kurr, N. Jacobsen, J. Senker, G. Koch, T. Ressler, R. W. Fischer and R.
Schlögl, J. Am. Chem. Soc., 2013, 135, 6061-6068.

RSC Advances
Page 28 of 37
View Article Online
DOI: 10.1039/C6RA02512A
Table 1. Physicochemical properties and catalytic activity of the catalysts prepared
at different conditions.
Reactor
Aging time
S
BET
2
S
Cu
2
X
CO
S
MeOH (C-
mol %)
97.7
97.9
98.9
99.3
98.6
98.8
Y
MeoH
(min)
(m /g)
54.1
141.6
103.3
103.4
77.0
(m /g)
(mol %)
12.8
25.9
30.6
33.7
(mol %)
12.4
25.3
30.2
33.5
MISR
MISR
MISR
MISR
MISR
STR
0
10
30
60
120
60
7.5
16.9
18.5
22.4
16.1
13.4
28.4
27.2
28.0
26.8
64.7
o
Reaction conditions: T = 250 C, V(CO):V(H
2
) = 33:67, P = 5 MPa, GHSV = 4000
mL/(gcath).

Page 29 of 37
RSC Advances
View Article Online
DOI: 10.1039/C6RA02512A
NaNO3
*
Na Zn (CO )
3 4
2
3
Aurichalcite
Hydrozincite
*
*
*
*
*
*
*
MISR
STR
10
20
30
40
50
60
70
2
Theta (degree)
Fig. 1. XRD patterns of the initial precipitates formed in different reactors.