Catalyst synthesis by continuous coprecipitation under micro-fluidic conditions: Application to the preparation of catalysts for methanol synthesis from CO2/H2

Article abstract of DOI:10.1016/j.cattod.2015.09.028

A new method of synthesis based on micro-fluidic continuous coprecipitation has been used to prepare CuO-ZnO-ZrO₂ catalyst. The catalytic behavior was then investigated for CO₂ hydrogenation into methanol and compared with a CuO-ZnO-ZrO₂ catalyst prepared by classical coprecipitation and with the same amount of Cu⁰ (30%). The novel synthesis method allows a better repeatability and homogeneity of the catalyst which leads to the best methanol productivity of 486 g_MeOH kg_cata^-1 h^-1 at 280 °C under 50 bar and a GHSV of 10,000 h^-1.

Full text of DOI:10.1016/j.cattod.2015.09.028

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Contents lists available at ScienceDirect
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journal homepage: www.elsevier.com/locate/cattod
Catalyst synthesis by continuous coprecipitation under micro-fluidic
conditions: Application to the preparation of catalysts for methanol
synthesis from CO /H
2
2
a
b
b
c
Laetitia Angelo , Maria Girleanu , Ovidiu Ersen , Christophe Serra ,
a
a,∗
Ksenia Parkhomenko , Anne-Cécile Roger
ICPEES, Équipe “Énergie et Carburants pour un Environnement Durable” UMR CNRS 7515, ECPM, Université de Strasbourg (UdS),
5 rue Becquerel, 67087 Strasbourg Cedex 2, France
a
2
b
Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), UMR 7504 CNRS-Université de Strasbourg (UdS), 23,
rue du Loess, 67037 Strasbourg Cedex 2, France
c
Université de Strasbourg (UdS), Ecole de Chimie Polymères et Matériaux (ECPM), Charles Sadron Institute (ICS) – UPR 22 CNRS,
Precision Macromolecular Chemistry Group (CMP), 23 rue du Loess, BP84047, 67034 Strasbourg Cedex 2, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 June 2015
Received in revised form 28 August 2015
Accepted 28 September 2015
Available online xxx
A new method of synthesis based on micro-fluidic continuous coprecipitation has been used to prepare
CuO-ZnO-ZrO2 catalyst. The catalytic behavior was then investigated for CO2 hydrogenation into
methanol and compared with a CuO-ZnO-ZrO2 catalyst prepared by classical coprecipitation and with the
same amount of Cu0 (30%). The novel synthesis method allows a better repeatability and homogeneity
−
1
−1
◦
of the catalyst which leads to the best methanol productivity of 486 gMeOH kgcata
h
at 280 C under
−1
5
0 bar and a GHSV of 10,000 h
.
Keywords:
©
2015 Elsevier B.V. All rights reserved.
CO2 hydrogenation
Methanol synthesis
CuO-ZnO-ZrO2
Synthesis effect
Continuous coprecipitation
1
. Introduction
molecules [6], for the synthesis of olefins [7,8] such as propylene
and ethylene (biopolymer precursors). Methanol is also known as
fuel [7,9–11] either for fuel cells [12,13] or mixed with gasoline,
or indirectly as a raw material for the synthesis of diesel, gasoline,
dimethylether, hydrocarbons. . .. Thus the synthesis of methanol
allows getting stable and easily stored carbon energy, as an alter-
native to fossil fuels.
Numerous measures to reduce anthropogenic greenhouse gas
emissions, especially CO , already exist such as its capture and stor-
age. Another solution is to develop a method for converting CO into
2
2
valuable chemical compounds such as methanol, methane, formic
acid or dimethylether [1–4]. The context of this work is to trans-
form CO2 emitted by industries into methanol by reduction with
hydrogen produced by water electrolysis, using excess of electricity
provided by decarbonized energies such as nuclear and renewable
energies (Power to Liquid process). Beyond the valorization of CO2,
this process also allows to provide a management function for the
electric grid. In fact, the production of hydrogen is correlated with
the quantity of surplus electricity from the network.
At first methanol was mostly produced by catalytic hydrogena-
tion of CO [14] with a feed gas of CO/H2 or CO/CO /H . In the 90s
2
2
some studies comparing the reactivity of CO/H2 and CO /H2 have
2
shown that hydrogenation of CO2 is faster than that of CO [15–17].
The same studies show that even starting from CO/CO /H2 mix-
2
tures, methanol is mainly produced from hydrogenation of CO2.
Thereafter, in the early 2000s the number of publications about
CO2 hydrogenation increased.
Methanol is produced over 50 million tons per year [5] and is
present in many industrial sectors. It is used as a raw material for
the synthesis of formaldehyde, one of the most important organic
The conventional methanol synthesis catalysts were designed
for CO/CO /H2 and must be optimized and modified for the hydro-
2
genation of CO2 without CO addition. The literature review clearly
shows that copper is the favored metal and highlights the impor-
tance of the presence of ZnO along with a good interface between
Cu and ZnO [18,19] for this reaction which increases respectively
∗ Corresponding author. Tel.: +33 (0)3 68 85 27 69; fax: +33 (0)3 68 85 27 68.
E-mail address: annececile.roger@unistra.fr (A.-C. Roger).
http://dx.doi.org/10.1016/j.cattod.2015.09.028
0
920-5861/© 2015 Elsevier B.V. All rights reserved.
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2
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the copper dispersion and the adsorption of CO . The beneficial
The micro-fluidic continuous coprecipitation was realized in a
micro-fluidic system (Scheme 1) [36] by a continuous formation
of little droplets, of diameter around 1 mm, made by the solution
of nitrates (1 M) and the precipitating agent (1.6 M Na CO ) in a
2
effect of the support was also discussed for Cu/ZnO based catalysts.
The addition of ZrO2 leads to an increase of the copper dispersion
and ZrO2 is involved in the adsorption of CO2 [20,21]. This higher
metal dispersion is due to a large interfacial area of CuO and ZrO2
favored by the formation of surface oxygen vacancies on the ZrO2
support [22]. This high interfacial area was as well discussed to play
a role in the improvement of the methanol formation due to micro-
crystalline copper particles which are stabilized by interaction with
an amorphous zirconia support [23]. This is why it is important to
have a right control of the synthesis parameters such as pH and
temperature. These CuO-ZnO-ZrO2 catalysts were synthesized by
coprecipitation [24], a classical synthesis in discontinuous mode
2
3
−
1
constant flux (0.9 mL min ) of silicon oil. The aqueous solutions
−
1
are delivered to a constant total flow of 40 ␮L min with a 1.13
molar ratio of carbonate/metal cations. The precipitate was aged
for one night in the mother liquor, and then the aqueous phase
is separated, filtered, washed with water and dried for 2 days at
◦
100 C.
◦
The resulting powders were then calcined in air at 400 C for 4 h
with a heating ramp of 2 C min to give fresh catalysts.
◦
−1
(
batch) using a buffer solution of controlled pH [25] where nitrates
are added in continuous and where the precipitating agent is used
to regulate the pH throughout the reaction [26,27].
2.2. Catalyst characterization
In this work we present the study of a new method of synthe-
sis based on continuous coprecipitation to overcome the problems
of repeatability and homogeneity of solutions and conditions dur-
ing the conventional coprecipitation. It was inspired by the use
of the micromixer [28,29] or microemulsion [30]. This continuous
method is based on the formation of droplets formed by reagents
brought about an immiscible fluid carrier [31]. These droplets are
more precisely formed by the merger of two droplets, each contain-
ing one of the starting aqueous solutions [32,33]. Upon the merger
of these solutions, coprecipitation occurs, allowing the same envi-
ronment and the same conditions (pH and temperature) for each
droplet during the coprecipitation, leading to better repeatability
and homogeneity.
The catalyst apparent density was determined using a cylin-
drical glass tube of internal diameter of 1.5 cm, on fresh catalyst
initially sieved to particle size fraction between 100 and 125 ␮m.
Specific surface areas measurements were performed by
◦
nitrogen adsorption–desorption at −196 C using the Brunauer-
Emmet-Teller (BET) method on
apparatus. Samples were previously outgassed at 250 C for 3 h to
remove the adsorbed moisture.
a
Micromeritics ASAP 2420
◦
The crystalline structure of the catalysts was determined by
X-ray diffraction (XRD) with a Bruker D8 Advance diffractometer
equipped with a LYNXEYE detector and a Ni filter for Cu K␣ radia-
◦
◦
tions over a 2ꢀ range of 10–95 and a step of 0.016 every 0.5 s. The
crystallite size was calculated using the Debye-Scherrer equation
[37].
Here are presented the effects of the catalyst synthesis condi-
tions on the characterization and the catalytic behavior of efficient
CuO-ZnO-ZrO2 catalysts in CO2 hydrogenation into methanol.
Reducibility studies were performed by temperature pro-
grammed reduction (TPR) on a Micromeritics AutoChem II 2920
with 400 mg of fresh catalyst and a total gas flow rate of
−
1
◦
−1
5
0 mL min
of 10% H2 in Ar with a heating ramp of 1 C min
◦
2
. Experimental
until 300 C.
Metal surface area was determined by N O reactive frontal
2
2
.1. Catalyst preparation
chromatography [38,39] on a Micromeritics AutoChem II 2920 in
−
0 mL min of 2% N O in Ar. Approximately 400 mg of fresh cata-
2
1
5
◦
−1
Two CuO-ZnO-ZrO2 catalysts were synthesized by two differ-
lyst were first reduced at 300 C for 12 h under a flow of 50 mL min
of 10% H in Ar and then cooled to 50 C after a Ar purge. The copper
◦
ent coprecipitation methods: a coprecipitation at constant pH and
a continuous coprecipitation. These catalysts contain 37.5% by
weight of CuO (corresponding to 30% Cu ), 41 wt% of ZnO and
2
surface area was calculated by quantifying the amount of consumed
0
19
N O and assuming 1.46 × 10 copper atoms per square meter [40].
2
2
1.5 wt% of ZrO . The notation is exemplified as follows: 30CuZn-
The morphology after calcination was studied using conven-
tional transmission electron microscopy (TEM) as well as scanning
transmission electron microscopy (STEM) or electron tomography.
All the investigations were performed on a JEOL 2100F TEM/STEM
microscope, operating at 200 kV and equipped with a probe cor-
rector and a GIF Tridiem energy filter. For S/STEM analyses, after
sonication of the catalysts powder in ethanol, a droplet of the solu-
tion was dropped on a holy carbon silver TEM grid.
2
0
ZX refers to a catalyst containing 30 wt% of Cu completed by zinc
oxide and zirconia where X corresponds to the synthesis method
(
pH = coprecipitation at constant pH and M = micro-fluidic contin-
uous coprecipitation).
The constant pH coprecipitation [34,35] was realized in a buffer
◦
solution at pH 6–6.5 heated at 60–65 C. A solution (1 M) of Cu
nitrate, Zn nitrate and ZrO nitrate was added drop by drop in
parallel with a solution of Na CO3 (1.6 M), used as precipitating
agent and pH control leading to a 1.13 molar ratio of carbon-
ate/metal cations. The precipitate was aged for 3.5 h in the mother
For the electron tomography analysis, a high tilt sample holder
from GATAN Company was used in order to acquire the tilt image
series. The angles range from +65 to −65 degrees, with projections
2
◦
liquor, and then filtered, washed with water and dried for 5 days at
taken every 2 according to Saxton scheme. 84 TEM images were
◦
1
00 C.
recorded per tilt series with a cooled GATAN ULTRASCAN 1000 CCD
Scheme 1. Schematization of micro-fluidic continuous coprecipitation.
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detector (2048 × 2048 pixels with a pixel size of 0.2 nm). The images
were first roughly aligned using a cross-correlation algorithm. A
refinement of this initial alignment and a precise determination
of the tilt axis direction were then obtained using the IMOD soft-
ware where the centers 5 nm Au NPs were used as fiducial markers
[
41]. The volume reconstructions have been computed using an
iterative approach consisting of a simultaneous algebraic recon-
struction technique implemented using the TOMO3D software. [42]
The number of iterations did not exceed 30. Visualization of the final
volumes was carried out using ImageJ software.
For the high angle annular dark field STEM (HAADF-STEM)
analyses the camera focal length used in HAADF was 10 cm, cor-
responding to inner and outer diameters of the annular detector
of 60 mrad and 160 mrad, respectively. Furthermore, the limit res-
olution in HAADF-STEM mode was about 0.11 nm. Moreover, EDX
analyses in HAADF-STEM mode were performed on various frag-
ments of 30CuZn-Z samples. The exposure time and the spectra
were been performed using the DigiScan routine for Digital Micro-
graph software.
Fig. 1. XRD of the fresh 30CuZn-ZpH and 30CuZn-ZM catalysts.
2.3. Catalytic activity
The carbon dioxide hydrogenation into methanol was per-
formed in a stainless steel fixed bed reactor with an internal
diameter of 1 cm. The powdered catalyst was initially sieved to
particle size fraction between 100 and 125 ␮m to obtain a bed
3
volume of 0.24 cm . The reaction temperature was controlled by
a thermocouple located in the furnace and contacting the external
metallic walls of the reactor at the level of the catalytic bed. The gas
flows were regulated by mass flow controllers in order to deliver a
−
1
constant total flow rate of 40 mL min of H /CO /N .
2
2
2
The catalyst was first reduced under H (6.18 mL min−1) at
00 C and 50 bar for 12 h with a ramp of 1 C min . After
cooling the catalyst to 100 C, the gas flows were adjusted to
deliver the reaction flow of 35 mL min of H :CO2 (3.89:1) and
mL min of N2 (as internal standard). After the purge, the tem-
perature is first increased to 150 C to analyze the compounds
of the gas phase before the reaction. The CO2 hydrogenation
Fig. 2. TPR profiles of the fresh 30CuZn-ZpH and 30CuZn-ZM catalysts.
2
◦
◦
−1
3
◦
−
1
and the liquid phase. The methanol productivity was calculated in
the same way by two methods: one giving productivity per catalyst
2
−
1
5
−
1
−1
h ) and the other one giving productivity per
◦
mass (gMeOH kgcata
−
2
−1
h ).
copper surface area (mgMeOH
m
Cu
was then carried out at different temperatures between 240 and
◦
3
1
20 C under 50 bar and a Gas Hourly Space Velocity (GHSV) of
3. Results and discussion
−
1
0,000 h
.
The analysis of the reaction products was performed in two
3.1. Characterization
steps. First the outgas was analyzed online every 30 min using a
gas microchromatograph (Inficon 3000 Micro GC) equipped with a
The main characteristics of the fresh CuO-ZnO-ZrO catalysts are
2
TCD detector and two columns: a PoraPlot Q column to separate N2,
CO, CH , CO , CH OH and a molecular sieve 5 A˚ column to separate
given in Table 1. The apparent density of the catalyst prepared by
coprecipitation at constant pH is higher than that of catalyst synthe-
4
2
3
−
3
N , H , CH , CO. Secondly, the liquid phase collected in the trap dur-
sized by continuous coprecipitation, 0.51 compared to 0.35 g cm
respectively.
,
2
2
4
ing the reaction was recovered at the end of the reaction and then
analyzed offline using a gas chromatograph (Agilent Technologies
2
−1
2
−1
The specific surface areas changes from 79 m g to 40 m g
6
890N Network GC Systems) with ZB-WAX Plus (Zebron) column
to quantify methanol.
The conversions (XCO2 and XH ) and selectivities (S
for 30CuZn-ZpH and 30CuZn-ZM, respectively. The highest BET sur-
face is then observed for the catalyst prepared by coprecipitation at
constant pH. However no correlation was found between BET sur-
faces and pore characteristics. The mean pore volume diameter of
and SCO
CH3OH
)
2
were then determined by the total carbon balance of the gas phase
Table 1
Characterizations of the fresh 30CuZn-ZpH and 30CuZn-ZM catalysts.
Apparent density (g cm 3
−
)
BET
XRD-Crystallite
size (nm)
Cu surface area
(m gcata
d
Catalyst
2
−1
)
SBETa (m2
g
−1
)
Dporeb (nm)
Vporec (cm3
g
−1
)
CuO
ZnO
3
3
0CuZn-ZpH
0CuZn-ZM
0.51
0.35
79
40
17
20
0.38
0.37
10.0
9.7
10.4
8.8
10.5
14.5
a
b
c
Specific surface area.
Pore diameter.
Pore volume.
d
Determined by N2O chemisorption.
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Fig. 3. Bright field TEM images of 30CuZn-ZpH catalyst: (a) representative fragment highlighting the two types of morphologies, (b) zone A (large particles) and (c) zone B
small particles).
(
Fig. 4. EDX analysis of the 30CuZn-ZpH catalyst corresponding to (a) zone A (large particles) and (b) zone B (small particles).
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these catalysts is around 20 nm independently of the preparation
method, and in spite of different specific surface areas, same pore
3
−1
volumes were calculated (around 0.38 cm g ).
The crystalline structures of the catalysts after calcination are
presented in Fig. 1. Diffraction peaks corresponding to copper
oxide and zinc oxide are observed for both catalysts. The zirco-
nium oxide diffraction peaks are not observed suggesting that this
phase is in an amorphous or a micro-crystallite state [43]. The
◦
◦
wide peak located between a 2␪ of 15 and 30 is due to the sam-
ple holder glass. By comparing both methods of synthesis, same
diffractograms are obtained and also similar CuO and ZnO crys-
tallite sizes, around 10 nm (Table 1), supposing that the choice
of the synthesis does not lead to deep modifications in catalyst
structure.
The reducibility of copper species was determined by TPR exper-
iments and the results are presented in Fig. 2. For 30CuZn-ZpH, TPR
◦
profile shows one reduction peak at 152 C with a shouldered peak
◦
at 164 C suggesting two reduction steps, probably because of dif-
ferent insertions or interactions between copper and the support
[
38]. This profile can be explained by distinct copper oxide reduc-
tion steps, the first one related to the reduction of small crystalline
CuO clusters, and the second one attributed to a strong interaction
between copper ions and the support [38]. The use of micro-
fluidic continuous coprecipitation to prepare 30CuZn-ZM catalyst
modifies the reduction profile leading to two reduction peaks but
Fig. 5. Section in the reconstructed volume of a representative fragment of the
30CuZn-ZpH catalyst.
a different distribution of copper oxide depending on the region
nature.
Similar study has been performed on 30CuZn-ZM catalyst
and the results are presented in Figs. 6–9. This catalyst does
not present two regions contrary to 30CuZn-ZpH and seems to
be more homogeneous (Fig. 6 compared to Fig. 3). In fact, the
◦
◦
which are spread over a wide zone (between 140 C and 210 C)
◦
and are switched to higher temperatures (peaks at 167 C and
1
◦
85 C).This suggests that the micro-fluidic preparation method
leads to a modification of CuO-support interactions. The theoreti-
−
1
cal hydrogen consumption (4.72 mmolH2
g
) was compared to the
three oxides (CuO, ZnO and ZrO ) location is clearly less obvi-
values obtained for 30CuZn-Z catalysts and the reduction percent-
2
0
ous to distinguish than for 30CuZn-ZpH. Furthermore, the EDX
analysis of the zone 1 of Fig. 6a detailed in Fig. 7 and Fig. 8,
shows the presence of copper, zinc and zirconium regardless to
the area studied. The presence of silver on the EDX analysis is
due to the use of a silver grid. These results attest for a better
homogeneity of the catalyst 30CuZn-ZM prepared by continuous
coprecipitation. The electron tomography analysis (Fig. 9) high-
lights the presence of two CuO particles sizes: around 5.3 nm
age of CuO to Cu were determined assuming the only reduction
of CuO and a copper oxide content of 30% (respectively 98%
and 105% for 30CuZn-ZpH and 30CuZn-ZM). The catalysts present
finally similar reducibility closed to 100% confirming a total copper
reduction.
The copper surface areas calculated by N O reactive frontal
2
chromatography are given in Table 1. The highest copper sur-
2
−1
face area is observed for 30CuZn-ZM (14.5 m gcata ) which
presented the lowest BET surface area and not for 30CuZn-ZpH
(pink circle) and 2 nm (red arrow), corresponding respectively to
2
−
1
2
−
1
the previously observed sizes for the two zones, one rich in zinc
and the second rich in zirconium, for 30CuZn-ZpH. Consequently,
there seems to be the presence of two different morphologies
but which are not obvious to distinguish. It is thus difficult to
conclude if the zinc oxide and the zirconia are mixed or if a
ZnO layer covers a zirconia layer. However the assumed better
homogeneity for 30CuZn-ZM explains the highest copper surface
area.
These results obtained by TEM analysis were also used to
highlight the zirconium oxide state that could not be previously
determined by XRD. Since no crystalline lattice has been observed
on the particles attributed to zirconia, ZrO2 is considered amor-
phous in the studied samples.
(
10.5 m gcata ) whose BET surface area was of 79 m gcata , sug-
gesting that a high copper surface area is not directly correlated
with a high BET surface.
The catalyst morphology after calcination observed by TEM is
shown in Fig. 3 for 30CuZn-ZpH. This catalyst presents two different
morphologies: a first region (zone A) composed of large particles
and a second region (zone B) composed of small particles. This
highlights an inhomogeneous morphology of the sample. To bet-
ter understand this inhomogeneity, STEM-EDX analyses (Fig. 4)
in these two regions were conducted. It shows that the zone A
is rich in zinc with a high level of copper but only a few traces
of zirconium, while for the zone B a high level of both zirco-
nium and copper is observed. The same observations were made
by analyzing different areas of the sample. The copper oxide is
then present in both regions. In order to have a better understand-
ing of the copper oxide dispersion in these two regions, electron
tomography approach was used. It provides a three dimensional
representation of the studied object and the location of different
phases within the material. The reconstruction volume of a repre-
sentative fragment of 30CuZn-ZpH catalyst is presented in Fig. 5.
The zone A, rich in zinc oxide, shows that copper covers part of
the surface of large ZnO particles, evidenced by red arrows in
Fig. 5. In contrary, in the zone B, rich in zirconium oxide, copper
oxide is under the form of nanoparticles (green arrows) dispersed
3.2. Catalytic activity
The results obtained for 30CuZn-Z catalysts in CO2 hydrogena-
◦
tion reaction at 240, 260, 280, 300 and 320 C at 50 bar and with a
−
1
GHSV of 10,000 h are presented in Table 2.
Firstly the influence of reaction temperature on catalytic activ-
ity was studied. The catalytic results indicate that the conversions
of H2 and CO2 increase gradually with the reaction temper-
◦
ature until 280 C when the H2 conversions stabilize around
9% whereas the CO2 conversions keep increasing from 22% at
◦
◦
on ZrO . The CuO particle sizes were different depending on the
280 C to 26% to 320 C. These results are directly correlated
2
◦
zone: zone A ≈ 5.5 nm and zone B ≈ 2.4 nm. These results evidence
to a progressive decrease in methanol selectivity (at 240 C,
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Fig. 6. Bright field TEM images of two areas of the catalyst 30CuZn-ZM (a) area 1 and (b) area 2.
Fig. 7. (a) EDX analysis of the area 1 of the 30CuZn-ZM catalyst in region 1 (b).
◦
SCH
≈ 50% and at 320 C, S
≈ 14%) in favor of carbon
(corresponding to the methanol synthesis produced by CO hydro-
3OH
CH3OH
2
◦
◦
monoxide selectivity (at 240 C, S ≈ 50% and at 320 C, S ≈ 86%).
genation), then with the temperature increase, this is the Reverse
Water Gas Shift reaction with a H /CO stoichiometry of 1 which is
CO
CO
The stabilization of H conversion is directly related to these selec-
2
2
2
tivity changes due to different H /CO stoichiometry depending of
favored. No noticeable catalyst deactivation was observed over the
tests.
2
2
these two competitive reactions. First the H /CO stoichiometry is 3
2
2
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Fig. 8. (a) EDX analysis of the area 1 of the 30CuZn-ZM catalyst in the region 2 (b).
◦
productivity is obtained for 30CuZn-ZM at 280 C with
Secondly the influence of synthesis method on catalytic activity
was investigated by comparing the results of both catalyst for
CO2 hydrogenation. The conversions of 30CuZn-ZM at 260 C show
−
1
−1
486 gMeOH kgcata
h .
◦
In the literature similar catalysts were also studied. With
a Cu-ZnO-ZrO2 catalyst containing similar amount of metal-
lic copper, Arena et al. [44] have obtained a CO2 conversion
of 16.4%, a methanol selectivity of 38% and a methanol pro-
◦
identical values to those of 30CuZn-ZpH at 240 C: HH ≈ 7% and
2
XCO2 ≈ 14%. In this way, the 30CuZn-ZM conversions correspond,
at low temperature, to those of 30CuZn-ZpH but for temperatures
◦
−2
−1
cata h
◦
of 20 C higher. However, this gap is not observed for selectivities
which are similar at iso temperature, for example at 280 C the
ductivity of 1 mg
m
at 240 C, 30 bar, GHSV of
MeOH
−1
◦
−1
8800 NL h kgcata and H /CO = 3. In another publication [45] by
2
2
methanol selectivity is of 34% for both catalysts. The 30CuZn-ZM
catalyst presents similar methanol productivities at low temper-
ature and better methanol productivities at high temperature in
comparison with 30CuZn-ZpH catalyst. In order to have a better
understanding of these results, the methanol productivities are
presented at iso conversions of H2 and CO2 (Fig. 10). The 30CuZn-
ZM catalyst shows the best productivities per catalyst mass and
similar productivities per copper surface area. These results can
increasing the copper content from 30 to 60 wt%, better CO2 con-
versions (18%) and methanol selectivity (51%) were obtained. The
−
1
−1
methanol productivity was also improved to 305 g
at 240 C, 30 bar, GHSV of 10,000 NL h kgcata
kgcata
h
MeOH
−1
◦
−1
and H /CO = 3.
2 2
By modifying some parameters like increasing the GHSV at
−
1
−1
80,000 NL h kgcata , a clearly higher methanol productivity
−
1
−1
of 1200 gMeOH kgcata
h was obtained. Saito et al. [46] have
also published results from 50Cu-ZnO-ZrO catalyst leading to
2
0
−1 −1
◦
be explained by a lower apparent density (0.35) and a higher Cu
665 gMeOH kgcata
h
of methanol productivity at 250 C, 50 bar,
GHSV of 10,000 L h and H /CO = 3. Compared to these results,
2
Cu
−1
−1
surface (14.5 m
◦
gcata ) for this catalyst prepared by a micro-
2
2
fluidic continuous coprecipitation. These two catalysts present
finally similar intrinsic activity. However, the best methanol
our catalyst appears very promising even if it still needs to be
optimized.
Please cite this article in press as: L. Angelo, et al., Catalyst synthesis by continuous coprecipitation under micro-
fluidic conditions: Application to the preparation of catalysts for methanol synthesis from CO /H , Catal. Today (2015),
2
2
http://dx.doi.org/10.1016/j.cattod.2015.09.028

G Model
CATTOD-9820; No. of Pages9
ARTICLE IN PRESS
L. Angelo et al. / Catalysis Today xxx (2015) xxx–xxx
8
Fig. 9. Sections in the reconstructed volume of a representative fragment of 30CuZn-ZM catalyst showing CuO particles sizes (a) 5.3 nm (pink circle) and (b) 2 nm (red arrow).
(
For interpretation of the references to colour in this figure legend, the reader is referred to the web version of the article.)
Fig. 10. Productivity of 30CuZn-ZpH and 30CuZn-ZM catalysts in CO2 hydrogenation reaction at 50 bar and a GHSV of 10,000 h−1.
Table 2
Catalytic results of 30CuZn-ZpH and 30CuZn-ZM catalysts in CO2 hydrogenation reaction at 50 bar and a GHSV of 10,000 h−1.
Catalyst
Catalyst
mass (mg)
Reaction
temperature ( C)
Conversion (%)
H2
Selectivity (%)
MeOH
MeOH productivity
◦
−1 −1
)
(gMeOH kgcata
h
CO2
CO
3
0CuZn-ZpH
0CuZn-ZM
125
84
240
7.2
9.4
10.0
9.6
13.7
19.6
22.2
24.0
25.7
50
50
34
22
14
50
50
66
78
86
314
453
346
248
165
260
280
300
320
9.1
3
240
4.5
7.1
9.2
9.0
9.4
9.3
15.1
21.0
23.9
26.8
47
42
34
22
14
53
58
66
78
86
298
429
486
366
262
260
280
300
320
4
. Conclusions
The effect of the synthesis method on the optimization
carbon dioxide into methanol. The best methanol productivity
−
1
−1
was obtained for 30CuZn-ZM catalyst with 486 g
kgcata
h
MeOH
−1
◦
at 280 C under 50 bar and a GHSV of 10,000 h , compared to
−
1
−1
of CuO-ZnO-ZrO2 catalysts have been investigated and it was
found that the continuous micro-fluidic coprecipitation provides
a much more homogeneous and repeatable catalyst leading
to better metallic copper surface area directly correlated to
a better reactivity observed for the catalytic hydrogenation of
346 gMeOH kgcata
h in the same conditions for the catalyst of
identical composition prepared by batch coprecipitation.
This new synthesis method will therefore allow to control and
vary different synthesis parameters (pH, temperature, molar ratio
of carbonate/metal cations, speed flow, droplet size) in order to
Please cite this article in press as: L. Angelo, et al., Catalyst synthesis by continuous coprecipitation under micro-
fluidic conditions: Application to the preparation of catalysts for methanol synthesis from CO /H , Catal. Today (2015),
2
2
http://dx.doi.org/10.1016/j.cattod.2015.09.028

G Model
CATTOD-9820; No. of Pages9
ARTICLE IN PRESS
L. Angelo et al. / Catalysis Today xxx (2015) xxx–xxx
9
obtain better copper surface areas and Cu/ZnO/ZrO2 interfaces to
improve the Cu-ZnO-ZrO2 systems reactivity.
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Please cite this article in press as: L. Angelo, et al., Catalyst synthesis by continuous coprecipitation under micro-
fluidic conditions: Application to the preparation of catalysts for methanol synthesis from CO /H , Catal. Today (2015),
2
2
http://dx.doi.org/10.1016/j.cattod.2015.09.028