Catalytic Activity of Nanosized CuO-ZnO Supported on Titanium Chips in Hydrogenation of Carbon Dioxide to Methyl Alcohol

Article abstract of DOI:10.1166/jnn.2016.12009

In this study, titanium chips (TC) generated from industrial facilities was utilized as TiO₂ support for hydrogenation of carbon dioxide (CO₂) to methyl alcohol (CH₃OH) over Cu-based catalysts. Nanosized CuO and ZnO catalysts were deposited on TiO₂ support using a co-precipitation (CP) method (CuO-ZnO/TiO₂), where the thermal treatment of TC and the particle size of TiO₂ are optimized on CO₂ conversion under different reaction temperature and contact time. Direct hydrogenation of CO₂ to CH₃OH over CuO-ZnO/TiO₂ catalysts was achieved and the maximum selectivity (22%) and yield (18.2%) of CH₃OH were obtained in the range of reaction temperature 210～240 °C under the 30 bar. The selectivity was readily increased by increasing the flow rate, which does not affect much to the CO₂ conversion and CH₃OH yield.

Full text of DOI:10.1166/jnn.2016.12009

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Catalytic Activity of Nanosized CuO–ZnO Supported on
Titanium Chips in Hydrogenation of Carbon
Dioxide to Methyl Alcohol
Ho-Geun Ahn1ꢀ∗, Hwan-Gyu Lee1, Min-Chul Chung1, Kwon-Pil Park1, Ki-Joong Kim2,
Byeong-Mo Kang3, Woon-Jo Jeong3, Sang-Chul Jung4, and Do-Jin Lee5
1Deparment of Chemical Engineering, Sunchon National University, Suncheon, Jeonnam 540-742, South Korea
2School of Chemical, Biological and Environmental Engineering, Oregon State University, Corvallis, Oregon 97331, United States
3OT&T, Inc., Gwangju 500-470, South Korea
4Deparment of Environmental Engineering, Sunchon National University, Suncheon, Jeonnam 540-742, South Korea
5Deparment of Agricultural Education, Sunchon National University, Suncheon, Jeonnam 540-742, South Korea
In this study, titanium chips (TC) generated from industrial facilities was utilized as TiO2 support for
hydrogenation of carbon dioxide (CO2) to methyl alcohol (CH3OH) over Cu-based catalysts. Nano-
sized CuO and ZnO catalysts were deposited on TiO2 support using a co-precipitation (CP) method
(CuO–ZnO/TiO2), where the thermal treatment of TC and the particle size of TiO2 are optimized
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on CO2 conversion under different reaction temperature and contact time. Direct hydrogenation of
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CO2 to CH3OH over CuO–ZnO/TiO2 catalysts was achieved and the maximum selectiviꢀty (22%)
Copyright: American Scientific Publishers
and yield (18.2%) of CH3OH were obtained in the range of reaction temperature 210∼240 C under
the 30 bar. The selectivity was readily increased by increasing the flow rate, which does not affect
much to the CO2 conversion and CH3OH yield.
Keywords: Titanium Chip, CuO, ZnO, Carbon Dioxide, Hydrogenation, Methyl Alcohol.
1. INTRODUCTION
such as CO, hydrocarbons, and higher alcohols. Therefore,
a highly selective catalyst is in need for CH3OH synthe-
sis. High activity for CH3OH synthesis from CO2 and H2
was obtained on CuO–ZnO catalyst supported on TiO2,
regarding as a promoter.8ꢀ9
The increased concentration of carbon dioxide (CO2) in
the atmosphere causes a green house effect, which has
recently become an important global issue.1 In order to
control the concentration of CO2 in the air, various kinds
of technologies that transform CO2 into useful products via
chemical reactions have been studied intensively. Catalytic
hydrogenation of carbon dioxide (CO2) has been used to
diminish the CO2 because large amounts of CO2 can be
converted to reusable chemical resources such as methanol
(CH3OH) and other oxygenates compounds.2ꢀ3 Among
various catalysts, the most extensive work were per-
formed on CuO–ZnO-based catalysts because they showed
a highly active and selective for CH3OH synthesis from
CO2 and H2.4–7
In a previous study, simple thermal treatment of titanium
chip (TC) has proven to be an efficient means of form-
ing TC into useful TiO2 support for the supported CuO–
ZnO/TiO2 catalyst.10 The effects of preparation method
and reaction pressure on the catalytic actꢀivity were tested.
It was shown that the activity at 250 C under 30 bar
of CuO–ZnO/TiO2 catalyst prepared by co-precipitation
(CP) method was higher than that of catalyst prepared by
impregnation method. However, the effects of other param-
eters (such as particle size of catalyst, reaction tempera-
ture, and flow rate) were also needed to gain information
on the relationships between physicochemical properties
and the catalytic activity of CO2 hydrogenation on CuO–
ZnO/TiO2 catalysts. In this work, CuO–ZnO/TiO2 catalysts
with different particle size were prepared by CP method
Until now oxide-based supports such as SiO2, Al2O3 and
MgO utilized for the catalyst support. However, un-desired
products are formed during the hydrogenation of CO2,
∗Author to whom correspondence should be addressed.
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J. Nanosci. Nanotechnol. 2016, Vol. 16, No. 2
1533-4880/2016/16/2024/004
doi:10.1166/jnn.2016.12009

Ahn et al.
Catalytic Activity of Nanosized CuO–ZnO Supported on TC in Hydrogenation of CO2 to CH3OH
Table I. Preparation conditions and physical parameters of CuO–
ZnO/TiO2 catalysts prepared by CP method.
and the reaction properties for catalytic hydrogenation of
CO2 to CH3OH were investigated.
Catalyst
aTCalꢂ (ꢀC) bDTC (mesh) cSBET (m2 g−1
ꢁ
2. EXPERIMENTAL DETAILS
2.1. Catalysts Preparation
CuO–ZnO/TiO2 (900-4)
CuO–ZnO/TiO2 (900-2)
CuO–ZnO/TiO2 (900-4)
CuO–ZnO/TiO2 (900-6)
CuO–ZnO/TiO2 (1100-4)
900
1000
1000
1000
1100
40–60
20–30
40–60
60–80
40–60
7ꢂ8
23ꢂ6
16ꢂ8
14ꢂ3
12ꢂ4
Thermal treatment of TC to form TiO2 was performed at
900, 1000, 1100 ꢀC under air atmosphere. CP method was
used to prepare CuO–ZnO/TiO2 catalyst containing weight
ratio copper, zinc and TC (40.6:50.3:9.1 wt%). Aqueous
solution of Cu(NO3ꢁ2 ·3H2O, Zn(NO3ꢁ2 ·6H2O, and TiO2
powder were mixed, and the mixture was add to the deion-
ized water with vigorous stirring as well as the aqueous
solution of Na2CO3 as a precipitant and pH of the sus-
pension liquid was kept constant at the value of 8.0. After
filtration and washing, the catalyst was dried at 100 ꢀC for
Notes: aTemperature of thermal treatment. bParticle size of catalysts. cBET specific
surface area.
ꢀ
is readily decreased above 1100 C. The sieved different
particles had similar values in the range of 14∼23 m2 g−1
.
SEM images of as-prepared CuO–ZnO on different size
of treated TC are shown in Figures 1(A)–(C). It can be
seen that well dispersed nanosized CuO and ZnO parti-
cles are formed on treated TC surface and the particles
contained Cu, Zn, and Ti species (Fig. 1(D)). TEM image
(Fig. 1(E)) shows that the well-dispersed small particles
are CuO–ZnO species, indicating that strong adhesion of
CuO–ZnO nanoparticles on thermally treated TC could be
obtained by improving superficial roughness, which could
enhance the both catalytic activity and selectivity toward
CH3OH synthesis.
ꢀ
ꢀ
24 hrs, calcined at 200 C for 1 hr and then at 300 C
for 3 hrs.
The prepared CuO–ZnO/TiO2 catalysts were character-
ized by using N2 gas adsorption analyzer (ASAP-2010,
Micromeritics), scanning electron microscopy (SEM,
S-3500N, Hotachi) and transmission electron microscopy
(TEM, JEM-2100F, Jeol). The chemical composition of
representative surface particles was analyzed by energy
dispersive spectroscopy (EDS).
Activity results for CH3OH synthesis from CO2 hydro-
genation over the CuO–ZnO/TiO2 catalysts prepared
from treated TC at different temperature are shown in
2.2. Catalytic Activity
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Figure 2(A). Maximum treatment temperature of TC
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Catalytic activities were tested for CH3OH synthesis using
a fixed-bed down stream flow reactor. Catalyst was loaded
in the reactor and the reduced in a stream of a gas H2 at
300 ꢀC for 3 hrs. The temperature of pre-heater and reactor
were controlled by PID controller, and total reaction pres-
sure was regulated with a back pressure regulator. After
cooling the catalyst bed to the reaction temperature 250 ꢀC,
the reaction gas, which consisted of CO2 (27 mol%) and
H2 (73 mol%), was fed at 40 mL min−1 using a mass flow
controller. The exit line from the reactor to the gas sampler
was heated to prevent condensation of any volatile prod-
ucts. Reactant and product gas mixtures were analyzed by
using the gas chromatograph (GC-2014, Shimadzu) with a
thermal conductivity detector, in which two parallel con-
nected columns, Porapak-Q and MS-5A, were used to sep-
arate reaction products. Gas chromatograph was equipped
with a two 6-way valves for on-line sampling.
was performed at 1100 ꢀC because TC became to be
so brittle when it was treated at above 1100 ꢀC. The
CuO–ZnO/TiO2 (1100-4) catalyst shows over 20% CO2
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(A)
(C)
(E)
(B)
(D)
3. RESULTS AND DISCUSSION
Table I shows the BET specific surface area of all samples
tested in this study. Untreated TC used as a raw material
exhibited very low surface area with near zero and it was
increased when it was treated by thermal oxidation (data
not shown), which would expect to improved adhesive
ability of metal oxide active species to treated TC surface.
BET surface area of CuO–ZnO/TiO2 catalyst is increased
Figure 1. SEM imagꢀes of CuO–ZnO/TꢀiO2 catalysts using TC treated at
(A) 900 ꢀC, (B) 1000 C, and (C) 1100 C. (D) EDS spectrum of dotted
square in (C). (E) TEM image of CuO–ZnO nanoparticles prepared by
CP method (Insert of EDS spectrum).
ꢀ
with increasing the treated temperature up to 1000 C and
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Catalytic Activity of Nanosized CuO–ZnO Supported on TC in Hydrogenation of CO2 to CH3OH
Ahn et al.
(A)
Figure 3. Effect of reaction temperature on catalytic activity
over CuO–ZnO/TiO2 (900-6) catalyst. (Pressure = 30 bar, W/F =
4ꢂ67 gcatꢂhr mol−1).
(B)
the synthesis of CH3OH.11 The formation of CH3OH and
CO is almost independent of the partial pressure of CO2.
Therefore, further optimization should lead to increases in
selectivity and yield of CH3OH. The maximum selectivity
to CH3OH from CO2 hydrogenation over CuO–ZnO/TiO2
(900-6) catalyst was obtained in the range of reaction tem-
perature 210∼240 ꢀC.
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The effect of contact time on catalytic activity in
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CO2 hydrogenation over CuO–ZnO/TiO2 catalyst is shown
Copyright: American Scientific Publishers
in Figure 4. Flow rates of reactant were varied from
20 mL min−1 (9.33 gcatꢂhr mol−1) to 100 mL min−1
(1.17 gcatꢂhr mol−1ꢁ. Conversion of CO2 and yield of
CH3OH show similar values in varied flow rates, while the
selectivity was readily increased with increasing the flow
rate. It is well known that the rate-determining step is CO
Figure 2. (A) Effect of treatment temperature of TC with the size of
40∼60 mesh and (B) effect of size of treated TC at 1100 ꢀC on CO2 con-
version over CuO–ZnO/TiO2 catalysts. (Reaction temperature = 250 ꢀC,
pressure = 30 bar, W/F = 4ꢂ67 gcatꢂhr mol−1).
conversion. Figure 2(B) shows effect of size of treated TC
ꢀ
at 1100 C on CO2 conversion. Highest conversion was
obtained over the CuO–ZnO/TiO2 (900-6) catalyst haviꢀng
smaller particle size. Therefore, TC treated at 1100 C
with smaller particle size (CuO–ZnO/TiO2 (900-6)) was
considered to further investigations.
Figure 3 shows the effect of reaction temperature on
CO2 conversion, CH3OH selectivity, and CH3OH yield
over CuO–ZnO/TiO2 (900-6) catalyst. X, S and Y on
x-axis in Figures 3 and 4 denote CO2 conversion, CH3OH
selectivity, and CH3OH yield, respectively. With increasing
reaction temperature, the CO2 conversion was increased,
while CH3OH selectivity and yield were decreased, which
is due to increased CO formation instead of CH3OH
according to reverse water gas shift reaction (CO2 +H2 →
2CO + H2O, ꢃH298K = 41ꢂ2 kJ mol−1). From the ther-
modynamic point of view (CO2 +3H2 → CH3OH+H2O,
ꢃH298K = −49ꢂ5 kJ mol−1), a decrease in reaction tem-
perature or an increase in reaction pressure could favor
Figure 4. Effect of contact time ꢄW/F ꢁ on catalytic activity over
CuO–ZnO/TiO2 (900-6) catalyst. W/F is defined as weigh of used cat-
alyst per flow rate of reactant in the reaction. (Reaction temperature =
250 ꢀC, pressure = 30 bar).
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Ahn et al.
Catalytic Activity of Nanosized CuO–ZnO Supported on TC in Hydrogenation of CO2 to CH3OH
hydrogenation to produce formate (HCO) intermediates,
which is then react with chemisorbed H2, subsequently
CH3OH for the overall reaction. However, no formation
of the CO was observed in all tested reactions over the
CuO–ZnO/TiO2 catalyst. More systematic study is needed
to understand the mechanism on this system.
Acknowledgment: This research was financially sup-
ported by the Ministry of Education, Science Technol-
ogy (MEST) and National Research Foundation of Korea
(NRF) through the Human Resource Training Project for
Regional Innovation.
References and Notes
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4. CONCLUSION
We have investigated the hydrogenation of CO2 to CH3OH
synthesis over CuO–ZnO/TiO2 catalysts, where the effect
of thermal treatment and the particle size of TC are opti-
mized on CO2 conversion under different reaction temper-
ature and contact time. Nanosized CuO and ZnO particles
were well supported on thermally treated TC using the
CP method. High CO2 conversion was obtained at a
higher reaction temperature, while selectivity and yield of
CH3OH were decreased. Maximum selectivity (22%) and
yield (18.2%) of CH3OH wereꢀobtained in the range of
reaction temperature 210∼240 C under the 30 bar. The
selectivity was readily increased by increasing the flow
rate; however, it does not much affect to the CO2 conver-
sion and the CH3OH yield.
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Received: 17 April 2015. Accepted: 20 April 2015.
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