CO2 hydrogenation to methanol over Rh/In2O3 catalyst

Article abstract of DOI:10.1016/j.cattod.2020.05.020

CO₂ hydrogenation to methanol is of great significance for the emission control and utilization of CO₂. In this work, the Rh/In₂O₃ catalyst with high Rh dispersion was prepared by deposition-precipitation method. The catalyst characterization demonstrates that the highly dispersed Rh species promotes the dissociative adsorption and spillover of hydrogen, which further enhances not only the formation of surface oxygen vacancy of In₂O₃ but also CO₂ adsorption and activation. Enhanced activity was thereby achieved for selective hydrogenation of CO₂ to methanol. A CO₂ conversion of 17.1 % with methanol selectivity of 56.1 %, corresponding to a methanol space time yield (STY) up to 0.5448 g_MeOH h^?1 g_cat^?1, has been obtained under 300 °C, 5 MPa, 76/19/5 of H₂/CO₂/N₂ (molar ratio) and 21,000 cm³ h^?1 g^?1 of gas hourly space velocity. Under the same reaction condition, the CO₂ conversion is only 9.4 % with a methanol STY of 0.3402 g_MeOH h^?1 g_cat^?1 over In₂O₃. The methanol selectivity can be even higher than 70 % at the reaction temperatures below 275 °C for Rh/In₂O₃ catalyst.

Full text of DOI:10.1016/j.cattod.2020.05.020

CatalysisTodayxxx(xxxx)xxx–xxx
Contents lists available at ScienceDirect
Catalysis Today
journal homepage: www.elsevier.com/locate/cattod
CO2 hydrogenation to methanol over Rh/In2O3 catalyst
Jing Wang, Kaihang Sun, Xinyu Jia, Chang-jun Liu*
School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
A R T I C L E I N F O
A B S T R A C T
Keywords:
Rh
In2O3
CO2 hydrogenation to methanol is of great significance for the emission control and utilization of CO2. In this
work, the Rh/In2O3 catalyst with high Rh dispersion was prepared by deposition-precipitation method. The
catalyst characterization demonstrates that the highly dispersed Rh species promotes the dissociative adsorption
and spillover of hydrogen, which further enhances not only the formation of surface oxygen vacancy of In2O3 but
also CO2 adsorption and activation. Enhanced activity was thereby achieved for selective hydrogenation of CO2
CO2
Hydrogenation
Methanol
Oxygen vacancy
to methanol. A CO2 conversion of 17.1 % with methanol selectivity of 56.1 %, corresponding to a methanol space
time yield (STY) up to 0.5448 gMeOH
h
g
−1, has been obtained under 300 °C, 5 MPa, 76/19/5 of H2/CO2/N2
cat
−1
(molar ratio) and 21,000 cm3
h
−1 g−1 of gas hourly space velocity. Under the same reaction condition, the CO2
conversion is only 9.4 % with a methanol STY of 0.3402 gMeOH
−1
h
g
−1 over In2O3. The methanol selectivity
cat
can be even higher than 70 % at the reaction temperatures below 275 °C for Rh/In2O3 catalyst.
1. Introduction
On the other hand, CO2 hydrogenation to methanol (Eq. (1)) has
attracted great attentions for CO2 utilization because methanol is an
CO2 is one of the major greenhouse gases. With the increasing
worldwide concern on CO2 issue, a great progress has been made in CO2
capture. The captured CO2 has been considered as potential feedstock
for the synthesis of chemicals and fuels. However, two big challenges
remain for how to utilize the captured CO2 [1]. One is the CO2-free
energy for the conversion of CO2. The other is the catalyst needed to
activate the inert CO2 molecule and also to convert the activated CO2
selectively to the desired chemical. For the energy issue, a rapid de-
velopment of renewable energy has been observed in the recent years.
This has made the CO2 utilization feasible. For the other catalyst
challenge, intense research efforts are being made. Many new catalysts
have been reported with significantly increasing publications and pa-
tents. Some recent reviews have well summarized these publications
and patents [2–7].
Among various catalysts being investigated, rhodium (Rh) catalysts
have drawn remarkable interests with its extensive applications as
homogeneous catalysts for CO2 conversion. Increasing publications can
be found in the literature with the use of heterogeneous Rh catalysts for
CO2 utilization [6,7]. These heterogeneous Rh catalysts have shown
high activity for CO2 reforming [8–11]. They have also shown high
activity towards hydrogenation of CO2 to CO [12–15] and methane
[16–22]. Although there were some reported works on the supported
Rh catalysts for CO2 hydrogenation to methanol [7,23–26], the me-
thanol selectivity was not sufficiently high.
important intermediate for chemical syntheses. Methanol can be used
directly as fuel with easy transportation. The catalyst applied for this
reaction normally prefers sufficiently high reaction temperature in
order to overcome the kinetic limitation and to achieve high CO2
conversion. However, CO2 hydrogenation to methanol has to compete
with the endothermic reverse water-gas shift (RWGS) reaction (Eq. (2))
at elevated temperatures. The development of novel catalysts with
improved methanol selectivity is immediately needed.
CO2 + 3H2 → CH3 OH+ H2O Δ H= −49.7kJ mol−1
(1)
CO2 + H2 → CO+ H2O Δ H= 41.2kJ mol−1
(2)
In 2013, In2O3 with surface oxygen vacancy was predicted via
density functional theoretical (DFT) study by our group to be excellent
catalyst for activation and hydrogenation of CO2 selectively to me-
thanol [27]. It was experimentally confirmed later in 2015 [28]. Fur-
ther studies confirmed that the combination of In2O3 with other oxides
(like Ga2O3 [29] and ZrO2 [30–33]) and the addition of metals, like
palladium [34,35], nickel [36] and cobalt [37], to In2O3 lead to a sig-
nificantly improved activity. It has been suggested that an intense
metal-In2O3 interaction exists with the loading of the metal, which
causes a big change in the electronic structure of the catalyst and favors
the methanol formation. For example, the supported nickel catalyst is
normally a highly active catalyst for CO2 hydrogenation to methane
[5–7,38]. However, the methane selectivity is ignorable over the In2O3
⁎ Corresponding author.
E-mail address: coronacj@tju.edu.cn (C.-j. Liu).
https://doi.org/10.1016/j.cattod.2020.05.020
Received 6 February 2020; Received in revised form 19 April 2020; Accepted 5 May 2020
0920-5861/©2020ElsevierB.V.Allrightsreserved.
Pleasecitethisarticleas:JingWang,etal.,CatalysisToday,https://doi.org/10.1016/j.cattod.2020.05.020

J. Wang, et al.
CatalysisTodayxxx(xxxx)xxx–xxx
supported Ni catalyst [36]. The methanol selectivity is more than 64 %
at temperatures below 275 °C and is even more than 54 % at tem-
perature up to 300 °C over Ni/In2O3 [36].
In this work, Rh/In2O3 catalyst was prepared and tested for CO2
hydrogenation to methanol. High methanol selectivity has been
achieved. The formation of methane is ignorable. The mechanism for
the improved methanol yield of Rh/In2O3 has been discussed as well.
sample (about 100 mg) was pretreated under flowing argon for 1 h at
300 °C to remove moisture and absorbed water. Then the sample was
reduced by 10 % H2/Ar at 300 °C for 1 h. After that, the sample was
cooled down to 50 °C under the same gas stream, followed by CO2
adsorption at 50 °C for 1 h. After purged with flowing argon to remove
physically adsorbed CO2 at the same temperature, the sample was he-
ated to 700 °C at a rate of 10 °C/min. The products were analyzed using
a TCD.
2. Experimental
In-situ and ex-situ X-ray photoelectron spectroscopy (XPS) analyses
were performed on a ThermoFischer ESCALAB 250Xi spectrometer
using Al Kα (hν = 1486.6 eV) radiation. The sample was heated to 300
°C and reduced by H2 (H2/N2 = 1/9, mole ratio) for 1 h. The C1 s
(284.8 eV) was used as reference for the calibration of binding energies.
2.1. Catalyst preparation
In2O3 was prepared by precipitation method. 5.025 g of indium
nitrate In(NO3)3•4H2O (HWRK Chem, 99.99 %) and 7 g Na2CO3•10H2O
(Tianjin Kemiou Chemical Reagent, 99 %) were firstly dissolved in 100
mL and 120 mL, respectively. Then the aqueous solution of Na2CO3
(0.15 mol/L) was added to the In(NO)3 solution (0.2 mol/L) until pH
reaches 7.0 at 80 °C. The mixture was stirred for 3 h at 80 °C. The
precipitate was then washed by deionized water several times. Prior to
calcination in static air at 450 °C for 3 h, the obtained sample was dried
at 80 °C overnight.
RhOx/In2O3 catalyst was prepared by deposition-precipitation
method. To make the RhOx/In2O3 catalyst with 1 wt% of Rh loading,
0.0162 g Rh(NO3)3·2H2O (Energy Chemical, 98 %) was firstly dissolved
in 50 mL deionized water. 0.495 g as-prepared In2O3 was subsequently
added into the solution. The resulting slurry was stirred for 1 h at room
temperature. Urea (0.3 g) was then added into the slurry. The mixture
was subsequently stirred for another 3 h at 80 °C. The precipitate was
then washed by deionized water. After that, the obtained sample was
freezing dried overnight.
2.3. Activity test
The activity tests for CO2 hydrogenation were conducted in a ver-
tical fixed bed reactor. 0.2 g of the catalyst diluted with 1.0 g of SiC,
was loaded in the reactor. Prior to the activity test, the catalyst was
purged by N2 for 0.5 h at room temperature. The catalyst was then pre-
reduced by H2 (H2/N2 = 1/9, mole ratio) at 300 °C for 1 h under at-
mospheric pressure. The feed of reactants (H2/CO2/N2 = 76/19/5,
mole ratio) was then introduced to the reactor at a gaseous hourly space
velocity (GHSV) of 21,000 cm3 h−1 gcat
under 5 MPa. The effluent
−1
was analyzed by an online gas chromatograph (Agilent 7890D)
equipped with a two-column system connected to a flame ionized de-
tector (FID) and a thermal conductivity detector (TCD). All the post-
reactor lines and valves were heated to 140 °C to prevent the con-
densation of methanol.
The CO2 conversion (XCO ), the selectivity of product i (Si) and the
2
space time yield of product i (STYi) were calculated according to the
2.2. Catalyst characterization
following equations:
FCO ,in − FCO ,out
2
2
The catalyst composition was analyzed by using a PerkinElmer
Optima 8300 inductively coupled plasma optical emission spectrometer
XCO
=
× 100 %
2
FCO ,in
2
(ICP-OES) equipped with
a Teflon sample introduction system.
F
i,out
Si =
× 100 %
According to the ICP-OES analysis, the Rh loading is 1.07 wt% in RhOx/
In2O3, suggesting that Rh was successfully loaded onto In2O3 during the
catalyst preparation.
FCO ,in − FCO ,out
2
2
FCO ,in × XCO × Si
2
2
STY =
× Mi
i
The structural properties, including Brunauer-Emmett-Teller (BET)
surface area (SBET), total pore volume (V) and average pore diameter
(D), were determined by N2 adsorption/desorption isotherms at 77 K,
obtained with an AUTOSORB-1-C instrument (Quantachrome).
The powder X-ray diffraction (PXRD) patterns were recorded on a
Rigaku D/MAX-2500 V/PC diffractometer equipped with a Ni-filtered
Cu Kα radiation source (40 kV, 200 mA) at a scanning speed of 4°/min
over the 2θ range of 10°−90°. The phase identification was made by
comparison with the X-ray spectrum cards from the Joint Committee on
Powder Diffraction Standards (JCPDSs).
Transmission electron microscopy (TEM) measurements were per-
formed on a JEOL JEM-2100 F system equipped with an energy-dis-
persive X-ray spectrometer (EDX) operated at 200 kV. To do so, the
catalyst sample was suspended in ethanol and then dispersed ultra-
sonically for 30 min. A drop of the suspension was deposited on a
copper grid coated with carbon. The suspension was then dried under
air.
Hydrogen temperature programed reduction (H2-TPR) was con-
ducted on a TPDRO 1100 apparatus (Thermo Finnigan, LLC) equipped
with a thermal conductivity detector (TCD). The catalyst sample (about
50 mg) was pretreated under flowing argon for 1 h at 200 °C to remove
moisture and absorbed water. The sample was then cooled down to
room temperature under the flowing Ar. Finally, the sample was heated
from room temperature to 700 °C (10 °C/min) under a flow of 10 % H2/
Ar. The consumption of H2 was measured by the TCD.
W
where F is the molar flow rates of CO2 or products, Mi is the molar mass
of product i, and W is the weight of the catalyst sample.
3. Results and discussion
3.1. Catalyst activity
Fig. 1 shows the profiles of CO2 conversion, selectivity and STY of
methanol and CO with the reaction temperature over In2O3 and Rh/
In2O3 catalysts. Rh/In2O3 catalyst shows much higher CO2 conversion
than In2O3 in the whole range of temperatures tested. Both catalysts
show almost the same methanol selectivity at the reaction temperatures
below 275 °C. 100 % methanol selectivity has been obtained at tem-
peratures below 225 °C. The selectivity of methanol is more than 70 %
between 225 and 275 °C. When the reaction temperature further in-
creases, the methanol selectivity on Rh/In2O3 catalyst is a little lower
than In2O3. However, at 300 °C, the methanol selectivity is still suffi-
ciently high (56.1 %) with CO2 conversion of 17.1 % and STYMeOH of
−1
0.5448 gMeOH h−1 gcat
over Rh/In2O3 catalyst. This represents a
higher methanol selectivity characteristic, compared to the reported Rh
catalysts, as shown in Table 1. Carbon monoxide is the main by-product
produced from the competitive RWGS reaction (2), which is an en-
dothermic reaction. The higher reaction temperature favors the RWGS
reaction. Methane cannot be detected below 275 °C. When the tem-
perature rises to 300 °C, trace methane can be observed. However, the
Temperature programmed desorption of CO2 (CO2-TPD) was carried
out to investigate the surface oxygen vacancy of the catalyst. The
2

J. Wang, et al.
CatalysisTodayxxx(xxxx)xxx–xxx
Fig. 1. Catalytic performance of In2O3 and Rh/In2O3 catalysts: (a) CO2 conversion, (b) methanol and CO selectivity, (c) methanol STY, (d) CO STY.
peak assigned to methane is too small to be quantitatively measured.
The methane formation is therefore ignorable.
3.2. Catalyst characterization
Based on N2 physisorption measurements at 77 K, the specific BET
surface area of In2O3 is 72.9 m2/g, whereas the BET surface area of
RhOx/In2O3 is 84.6 m2/g, which can be attributed to the high Rh dis-
persion.
The XRD patterns of In2O3 and Rh/In2O3 catalysts are presented in
Fig. 2. Rh/In2O3 refers the catalyst after H2 reduction (H2/N2 = 1/9,
mole ratio) at 300 °C for 1 h, while In2O3-AR and Rh/In2O3-AR re-
present the catalysts after the reaction. Only the peaks of the body-
centered cubic In2O3 crystalline lattice can be identified for all the
catalysts tested. The diffraction peaks at 21.5°, 30.6°, 35.5°, 45.7°, 51.0°
and 60.7° belong to the cubic structure of (211), (222), (400), (431),
(440) and (622), respectively, according to PDF#06-0416. For the Rh/
In2O3 catalyst, no characteristic diffraction peaks of rhodium species
Fig. 2. XRD patterns of In2O3 and Rh/In2O3 catalysts. (H2 reduction conditions:
300 °C, H2/N2 = 1/9, molar ratio).
Table 1
Comparison of Rh catalysts for CO2 hydrogenation to methanol.
T (oC)
P (MPa)
GHSV (cm3 gcat
h−1
)
XCO2 (%)
SMeOH (%)
STYMeOH (gMeOH gcat
h−1
)
Ref.
−1
−1
Catalyst
Rh/SiO2
RhY
Li/RhY
Rh-Fe/TiO2
Rh/TiO2
Rh-Co/SiO2
Rh-Li/SiO2
Rh-Fe/SiO2
Rh-Co/SiO2
Rh-Sn/SiO2
Rh/In2O3
Rh/In2O3
Rh/In2O3
200
150
250
270
270
260
240
240
240
240
250
275
300
5.0
3.0
3.0
2.0
2.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
6000
6000
6000
8000
8000
6000
6000
6000
6000
6000
21,000
21,000
21,000
0.5
2.8
13.1
9.2
7.9
15.9
7.0
10.4
3.7
2.8
4.0
6.8
1.9
2.3
1.3
0.8
19.9
5.2
16.0
27.4
43.1
82.0
72.6
56.1
0.0008
0.0011
0.0065
0.0066
0.0036
0.0678
0.0078
0.0357
0.0217
0.0259
0.1882
0.3853
0.5448
[12]
[16]
[23]
[24]
[24]
[25]
[26]
[26]
[26]
[26]
This work
This work
This work
9.3
17.1
3

J. Wang, et al.
CatalysisTodayxxx(xxxx)xxx–xxx
Fig. 3. TEM images: (a) and (b) of fresh In2O3; (c) and (d) of In2O3-AR.
can be observed. This means ultra-high rhodium dispersion with too
small particle size to be measured by XRD analyses. No metallic indium
is observed either after the reaction according to the XRD patterns of
In2O3-AR and Rh/In2O3-AR. This suggests In2O3 remains the stable
crystal structure during the reaction.
Fig. 3 shows the TEM image of In2O3 and In2O3-AR. Particles of
around 10−15 nm are observed in fresh In2O3. The lattice fringes with
interplanar distance of 0.259 nm and 0.292 nm correspond to the (400)
and (222) planes. The (211) plane with interplanar distance of 0.413
nm is also observed. These results are consistent well with the peaks of
the cubic In2O3 obtained from the XRD analyses. Fig. 4 shows the TEM
image of RhOx/In2O3 and Rh/In2O3-AR. Rhodium particles cannot be
observed in the high resolution TEM analyses. This suggests rhodium is
highly dispersed with too small particle size to be identified [39], as
discussed in the XRD analyses.
The reducibility of In2O3 and RhOx/In2O3 was studied using H2-
TPR, as shown in Fig. 5. For In2O3, the broad peaks centered at 150 °C
and 300 °C are assigned to the surface reduction of In2O3, corre-
sponding to the formation of surface oxygen vacancy. Higher tem-
perature peaks can be attributed to the reduction of bulk In2O3 [31,34].
For RhOx/In2O3, H2-TPR gives an additional peak centered at about 66
°C, which can be assigned to the reduction of RhOx [40,41]. The pre-
sence of supported rhodium nanoparticles makes the peak for the In2O3
surface reduction shift to lower temperature at around 125 °C. It also
makes the intensity of this peak increase significantly compared with
that of pure In2O3. This stronger reduction peak at lower temperature
indicates more hydrogen is consumed. This means that rhodium can
enhance the surface reduction of In2O3 and generate more surface
oxygen vacancy [34,35].
The CO2 adsorption and activation were further characterized using
CO2-TPD, as shown in Fig. 6. In addition, it is well known that the
surface oxygen vacancy of In2O3 can promote CO2 adsorption and ac-
tivation so that CO2 can be also considered as a probe molecular to
investigate the properties of surface oxygen vacancy. A single peak at
approximate 90 °C for both samples is associated with the physically
adsorbed CO2 [31,34]. The peaks at higher temperature are assigned to
the desorption of chemically adsorbed CO2. For In2O3, the peak located
at 220 °C is attributed to CO2 adsorption in the surface oxygen vacancy
induced by hydrogen reduction. The peak at about 442 °C is assigned to
CO2 adsorption in the thermally induced oxygen vacancy sites [42]. The
presence of Rh species makes the peaks shift to much higher tempera-
ture at 263 °C and 542 °C, respectively. It is worth noting that the peaks
are also rather stronger, indicating significantly increased surface
oxygen vacancy density and enhanced basicity with the load of Rh on
In2O3. The lower reduction temperature and stronger reduction peak in
H2-TPR curves suggest that rhodium species can enhance the dis-
sociative adsorption and spillover of hydrogen [43,44], which promotes
the surface reduction of In2O3 and the generation of surface oxygen
vacancy, as indicated in CO2-TPD curves [34,35]. Oxygen vacancy on
the In2O3 surface then improves the adsorption and activation of CO2.
Consequently, significantly enhanced catalytic activity of CO2 hydro-
genation to methanol is achieved.
XPS analyses were employed to characterize the chemical environ-
ment of In, O, and Rh species of the catalysts, as shown in Fig. 7. In 3d
core level spectra in Fig. 7(a) presents two peaks at 444.2 and 451.8 eV,
which can be attributed to the characteristic spin-orbit split 3d5/2 and
4

J. Wang, et al.
CatalysisTodayxxx(xxxx)xxx–xxx
Fig. 4. TEM images: (a) and (b) of fresh RhOx/In2O3; (c) and (d) of Rh/In2O3-AR.
Fig. 6. CO2-TPD profile of In2O3 and Rh/In2O3 catalysts.
Fig. 5. H2-TPR profile of In2O3 and RhOx/In2O3 catalysts.
To characterize the chemical environment of Rh under hydrogen
reduction, in-situ XPS spectra were recorded for both fresh and in-situ
treated catalyst under H2 (H2/N2 = 1/9, mole ratio) at 300 °C for 1 h.
The Rh 3d5/2 peak at 307.3 eV is assigned to Rho, while the peak at
309.5 eV is for Rh3+ [39,48,49]. In addition, the peaks at higher
binding energies are attributed to Rh 3d3/2. The position of the Rh 3d5/2
peak for the fresh catalysts is 309.5 eV, confirming that the rhodium
valence is mainly +3. After the H2 treatment, most of rhodium is de-
tected as the form of Rho, which is confirmed by the binding energy of
307.3 eV. Herein, Rho serves as the active site for dissociative adsorp-
tion of H2, providing sufficient active H atoms for the formation of
3d3/2, respectively. This indicates the indium valence is mainly +3 for
both In2O3 and Rh/In2O3 catalysts [45].
The O 1s core level spectra are shown in Fig. 7(b). Indeed, the O 1s
peak can be deconvoluted into two distinct peaks. The peak at about
529.8 eV corresponds to oxygen in In-O-In (Olattice), and the peak at
531.0 eV is commonly attributed to the presence of surface oxygen
vacancy (Ovacancy) [45–47]. CO-vacancy was used to estimate the relative
molar fraction of surface oxygen vacancy (CO-vacancy = AO-vacancy/(AO-
vacancy + AO-lattice)). CO-vacancy is 20 % for In2O3 and 30 % for Rh/In2O3
catalyst. The extra surface oxygen vacancy on Rh/In2O3 catalyst is
believed to contribute to the superior performance of the catalyst.
5

J. Wang, et al.
CatalysisTodayxxx(xxxx)xxx–xxx
Fig. 7. In-situ and ex-situ XPS spectra of In2O3 and RhOx/In2O3 catalysts: (a) In 3d spectra of ex-situ XPS; (b) O 1s spectra of ex-situ XPS; (c) Rh 3d spectra of in-situ
XPS.
surface oxygen vacancy and CO2 hydrogenation.
40 (2019) 1421–1437.
[5] X. Jiang, X. Nie, X. Guo, C. Song, J.G. Chen, Chem. Rev. (2020), https://doi.org/10.
1021/acs.chemrev.9b00723.
[6] S. Kattel, P. Liu, J.G. Chen, J. Am. Chem. Soc. 139 (2017) 9739–9754.
[7] A. Erdőhelyi, Catalysts 10 (2020) 155.
4. Conclusions
[8] Z.-J. Wang, Y. Zhao, L. Cui, H. Du, P. Yao, C.-J. Liu, Green Chem. 9 (2007) 554–559.
[9] I.V. Yentekakis, G. Goula, M. Hatzisymeon, I. Betsi–Argyropoulou, G. Botzolaki,
K. Kousi, D.I. Kondarides, M.J. Taylor, C.M.A. Parlett, A. Osatiashtiani, G. Kyriakou,
J.P. Holgado, R.M. Lambert, Appl. Catal. B: Environ. 243 (2019) 490–501.
[10] C. Dang, S. Wu, G. Yang, Y. Cao, H. Wang, F. Peng, H. Yu, J. Energy Chem. 43
(2020) 90–97.
[11] S. Praserthdam, P.B. Balbuena, Catal. Today 312 (2018) 23–34.
[12] H. Kusama, K.K. Bando, K. Okabe, H. Arakawa, Appl. Catal. A: Gen. 205 (2001)
285–294.
[13] R. Büchel, A. Baiker, S.E. Pratsinis, Appl. Catal. A: Gen. 477 (2014) 93–101.
[14] D. Heyl, U. Rodemerck, U. Bentrup, ACS Catal. 6 (2016) 6275–6284.
[15] J.C. Matsubu, V.N. Yang, P. Christopher, J. Am. Chem. Soc. 137 (2015) 3076–3084.
[16] K.K. Bando, K. Soga, K. Kunimori, N. Ichikuni, K. Okabe, H. Kusama, K. Sayama,
H. Arakawa, Appl. Catal. A: Gen. 173 (1998) 47–60.
In this work, Rh/In2O3 catalyst with high Rh dispersion was pre-
pared by deposition-precipitation method. The obtained catalyst was
confirmed to be highly active for CO2 hydrogenation with high me-
thanol selectivity, which is 100 % at the reaction temperatures below
225 °C, more than 70 % at temperatures below 275 °C and up to 56 % at
300 °C. The achieved methanol selectivity is higher than the reported
Rh catalysts, supported by other oxides. CO is the main by-product
produced from the competitive RWGS reaction. The formation of me-
thane is ignorable. The catalyst characterization demonstrates that the
highly dispersed Rh species enhance the hydrogen dissociative ad-
sorption and hydrogen spillover, which further promotes the formation
of surface oxygen vacancy of In2O3. The increased surface oxygen va-
cancy enhances the adsorption and activation of CO2 and stabilizes
intermediates for synthesis of methanol.
[17] A. Beuls, C. Swalus, M. Jacquemin, G. Heyen, A. Karelovic, P. Ruiz, Appl. Catal. B:
Environ. 113–114 (2012) 2–10.
[18] C. De Leitenburg, A. Trovarelli, J. Catal. 156 (1995) 171–174.
[19] F. Solymosi, A. Erdöhelyi, Stud. Surf. Sci. Catal. 7 (1981) 1448–1449.
[20] P. Reyes, I. Concha, G. Pecchi, J.L.G. Fierro, J. Mol. Catal. A: Chem. 129 (1998)
269–278.
Author statement
[21] N.M. Martin, F. Hemmingsson, A. Schaefer, M. Ek, L.R. Merte, U. Hejral,
J. Gustafson, M. Skoglundh, A.C. Dippel, O. Gutowski, M. Bauer, P.A. Carlsson,
Catal. Sci. Technol. 9 (2019) 1644–1653.
[22] J.B. Branco, P.E. Brito, A.C. Ferreira, Chem. Eng. J. 380 (2020) 122465.
[23] K.K. Bando, K. Soga, K. Kunimori, H. Arakawa, Appl. Catal. A: Gen. 175 (1998)
67–81.
[24] M.R. Gogate, R.J. Davis, Catal. Commun. 11 (2010) 901–906.
[25] H. Kusama, K. Okabe, K. Sayama, H. Arakawa, Appl. Organomet. Chem. 14 (2000)
836–840.
[26] H. Kusama, K. Okabe, K. Sayama, H. Arakawa, Catal. Today 28 (1996) 261–266.
[27] J. Ye, C. Liu, D. Mei, Q. Ge, ACS Catal. 3 (2013) 1296–1306.
[28] K. Sun, Z. Fan, J. Ye, J. Yan, Q. Ge, Y. Li, W. He, W. Yang, C.-J. Liu, J. CO2 Util. 12
(2015) 1–6.
Jing Wang and Chang-jun Liu conceived and designed the experi-
ments. Jing Wang prepared the catalysts. Jing Wang, Kaihang Sun and
Xinyu Jia carried out the experiments of CO2 hydrogenation and cata-
lyst characterization. Jing Wang, Kaihang Sun, Xinyu Jia and Chang-jun
Liu co-wrote the manuscript. Chang-jun Liu supervised the project. All
authors discussed the results and commented on the manuscript.
Declaration of Competing Interest
[29] N. Akkharaphatthawon, N. Chanlek, C.K. Cheng, M. Chareonpanich, J. Limtrakul,
T. Witoon, Appl. Surf. Sci. 489 (2019) 278–286.
[30] T. Chen, C. Cao, T. Chen, X. Ding, H. Huang, L. Shen, X. Cao, M. Zhu, J. Xu, J. Gao,
Y. Han, ACS Catal. 9 (2019) 8785–8797.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
[31] O. Martin, A.J. Martín, C. Mondelli, S. Mitchell, T.F. Segawa, R. Hauert, C. Drouilly,
D. Curulla–Ferré, J. Pérez–Ramírez, Angew. Chem. Int. Ed. 55 (2016) 6261–6265.
[32] M. Zhang, M. Dou, Y. Yu, Appl. Surf. Sci. 433 (2018) 780–789.
[33] M. Dou, M. Zhang, Y. Chen, Y. Yu, Surf. Sci. 672–673 (2018) 7–12.
[34] N. Rui, Z. Wang, K. Sun, J. Ye, Q. Ge, C.-J. Liu, Appl. Catal. B: Environ. 218 (2017)
488–497.
[35] M.S. Frei, C. Mondelli, R. García–Muelas, K.S. Kley, B. Puértolas, N. López,
O.V. Safonova, J.A. Stewart, D.C. Ferré, J. Pérez–Ramírez, Nat. Commun. 10 (2019)
3377.
Acknowledgment
This work was supported by the National Natural Science
Foundation of China (21536008 and 21621004).
[36] X. Jia, K. Sun, J. Wang, C. Shen, C. Liu, J. Energy Chem. 50 (2020) 409–415.
[37] A. Bavykina, I. Yarulina, A.J. Al Abdulghani, L. Gevers, M.N. Hedhili, X. Miao,
A.R. Galilea, A. Pustovarenko, A. Dikhtiarenko, A. Cadiau, A. Aguilar–Tapia,
J.L. Hazemann, S.M. Kozlov, S. Oud–Chikh, L. Cavallo, J. Gascon, ACS Catal. 9
(2019) 6910–6918.
[38] X. Jia, X. Zhang, N. Rui, X. Hu, C.-J. Liu, Appl. Catal. B: Environ. 244 (2019)
159–169.
[39] A. Bueno–López, I. Such–Basáñez, C. Salinas–Martínez de Lecea, J. Catal. 244
References
[1] C.-J. Liu, Greenh. Gases Sci. Technol. 2 (2012) 75–76.
[2] X. Su, X. Yang, Y. Huang, B. Liu, T. Zhang, Acc. Chem. Res. 52 (2019) 656–664.
[3] S. Liu, H. Yang, X. Su, J. Ding, Q. Mao, Y. Huang, T. Zhang, B. Liu, J. Energy Chem.
36 (2019) 95–105.
[4] T. Zhao, G. Feng, W. Chen, Y. Song, X. Dong, G. Li, H. Zhang, W. Wei, Chin. J. Catal
6

J. Wang, et al.
CatalysisTodayxxx(xxxx)xxx–xxx
R. Uecker, K. Irmscher, R. Fornari, M. Michling, D. Schmeißer, J.R. Weber,
J.B. Varley, C.G. Van De Walle, New J. Phys. 13 (2011) 85014.
[46] W.C. Chang, C.H. Kuo, C.C. Juan, P.J. Lee, Y.L. Chueh, S.J. Lin, Nanoscale Res. Lett.
7 (2012) 684.
(2006) 102–112.
[40] G. Wang, R. Luo, C. Yang, J. Song, C. Xiong, H. Tian, Z.J. Zhao, R. Mu, J. Gong, Sci.
China Chem. 62 (2019) 1710–1719.
[41] Q. Zhang, C. Xu, H. Yin, S. Zhou, ACS Omega 4 (2019) 20829–20837.
[42] L. Wang, J. Cai, Y. Xie, J. Guo, L. Xu, S. Yu, X. Zheng, J. Ye, J. Zhu, L. Zhang,
S. Liang, L. Wang, IScience 16 (2019) 390–398.
[47] L.B. Hoch, L. He, Q. Qiao, K. Liao, L.M. Reyes, Y. Zhu, G.A. Ozin, Chem. Mater. 28
(2016) 4160–4168.
[43] R.E. Ambrusi, M.E. Pronsato, Appl. Surf. Sci. 464 (2019) 243–254.
[44] V.K. Markova, G.N. Vayssilov, N. Rösch, J. Phys. Chem. C 119 (2015) 1121–1129.
[45] C. Janowitz, V. Scherer, M. Mohamed, A. Krapf, H. Dwelk, R. Manzke, Z. Galazka,
[48] J. Soria, A. Martinez–Arias, J.L.G. Fierro, J.C. Conesa, Vacuum 46 (1995)
1201–1204.
[49] C.P. Hwang, C.T. Yeh, Q. Zhu, Catal. Today 51 (1999) 93–101.
7