Heterogeneous Pt and MoOx Co-Loaded TiO2 Catalysts for Lowerature CO2 Hydrogenation to Form CH3OH

Article abstract of DOI:10.1021/acscatal.9b01225

Efficient conversion of CO₂ into useful chemicals, exemplified by the development of methods for lowerature hydrogenation of CO₂ to form methanol (CH₃OH), is a highly attractive research target. Herein, we report that Pt nanoparticles, loaded on MoO_x/TiO₂ as a support (Pt(3)/MoO_x(30)/TiO₂; Pt 3 wt %, MoO₃ 30 wt %), promote selective hydrogenation of CO₂ to produce CH₃OH in 73% yield under mild conditions (T = 150 °C; t = 48 h; p_CO2 = 1 MPa; p_H2 = 5 MPa). It is significant that the observed yield is almost the equilibrium yield of CH₃OH expected under the current reaction conditions. In terms of both the yield and selectivity for CH₃OH production, the performance of Pt(3)/MoO_x(30)/TiO₂ is better than that of other metal catalysts supported on MoO_x(30)/TiO₂ and of Pt catalysts on other supports. Moreover, the results of an investigation of the reaction mechanism using in situ X-ray absorption fine structure (XAFS) suggest that reduced MoO_x species are responsible for the progress of this efficient reaction.

Full text of DOI:10.1021/acscatal.9b01225

Subscriber access provided by GUILFORD COLLEGE
Article
x
2
Heterogeneous Pt and MoO Co-Loaded TiO Catalysts
2
3
for Low-Temperature CO Hydrogenation to Form CHOH
Takashi Toyao, Shingo Kayamori, Zen Maeno, S. M. A. Hakim Siddiki, and Ken-Ichi Shimizu
ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.9b01225 • Publication Date (Web): 25 Jul 2019
Downloaded from pubs.acs.org on July 26, 2019
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a service to the research community to expedite the dissemination
of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in
full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully
peer reviewed, but should not be considered the official version of record. They are citable by the
Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore,
the “Just Accepted” Web site may not include all articles that will be published in the journal. After
a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web
site and published as an ASAP article. Note that technical editing may introduce minor changes
to the manuscript text and/or graphics which could affect content, and all legal disclaimers and
ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or
consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W.,
Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 29
ACS Catalysis
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
Heterogeneous Pt and MoOx Co-Loaded TiO2 Catalysts for
Low-Temperature CO2 Hydrogenation to Form CH3OH
Takashi Toyao,*†,‡ Shingo Kayamori,† Zen Maeno,† S. M. A. Hakim Siddiki,†
Ken-ichi Shimizu*†,‡
† Institute for Catalysis, Hokkaido University, N-21, W-10, Sapporo 001-0021, Japan
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
‡ Elements Strategy Initiative for Catalysts and Batteries, Kyoto University, Katsura, Kyoto 615-
8520, Japan
ACS Paragon Plus Environment
1

ACS Catalysis
Page 2 of 29
1
2
3
4
ABSTRACT
5
6
7
8
9
Efficient conversion of CO2 into useful chemicals, exemplified by the development of methods
for low-temperature hydrogenation of CO2 to form methanol (CH3OH), is a highly attractive
research target. Herein, we report that Pt nanoparticles, loaded on MoOx/TiO2 as a support
(Pt(3)/MoOx(30)/TiO2; Pt = 3 wt%, MoO3 = 30 wt%), promote selective hydrogenation of CO2 to
produce CH3OH in a 73% yield under mild conditions (T = 150 ˚C; t = 48 h; pCO2 = 1 MPa; pH2 =
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
5 MPa). It is significant that the observed yield is almost the equilibrium yield of CH3OH expected
under the current reaction condition. In terms of both the yield and selectivity for CH3OH
production, the performance of Pt(3)/MoOx(30)/TiO2 is better than that of other metal catalysts
supported on MoOx(30)/TiO2 and Pt catalysts on other supports. Moreover, the results of an
investigation of the reaction mechanism using in situ X-ray absorption fine structure (XAFS)
suggest that reduced MoOx species are responsible for progress of this efficient reaction.
KEYWORDS: Hydrogenation of CO2, CH3OH synthesis, platinum, MoOx, TiO2, in situ
spectroscopy
ACS Paragon Plus Environment
2

Page 3 of 29
ACS Catalysis
1
2
3
1. INTRODUCTION
4
5
6
7
8
Energy generation and chemical production from renewable carbon sources has
gathered much attention recently because of the increasing concern about the fossil fuels
depletion and climate change.1,2 Carbon dioxide (CO2), which is one of the major
components of green-house gases, is a promising substance for potential use as an
abundant and inexpensive carbon source in the production of useful chemicals.3,4,13,5–12
Among various chemicals that can be synthesized from CO2, preparation of methanol
(CH3OH) by CO2 hydrogenation reactions has been of great interest in the industrial and
scientific communities.14–20 The reason for this interest lies in the fact that CH3OH can be
a precursor for various chemicals.21 In addition, CH3OH can be utilized as a fuel and a
liquid energy carrier.22,23
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
In the 1920’s, it was observed that CH3OH can be produced from syngas (CO/H2
mixtures) by using a ZnO catalyst.24 However, this process is highly inefficient, and it
requires extremely high pressures and temperatures (p = 20 MPa; T = 400 ˚C). Although
addition of Al2O3 or Cr2O3 improved the stability of the catalyst and its activity, it had only
a minor impact on the requirement for harsh reaction conditions. Also, addition of Cu was
found to significantly improve the activity, but the catalytic activity of Cu/ZnO/Al2O3 was
short lived due to poisoning or sintering. In the 1960’s, workers at Imperial Chemical
Industries (ICI) discovered a new co-precipitation method for the preparation of a highly
active and stable Cu/ZnO/Al2O3 catalyst for CH3OH synthesis. Since then, much effort
has been devoted to this problem and, consequently, CH3OH is mainly manufactured
from fossil-derived synthesis gas, which is composed of H2 and CO in addition to a little
amounts of CO2, by using the Cu-based catalysts operated under harsh reaction
conditions (p = 5-10 MPa; T > 200 ˚C).25 Recently, direct production of CH3OH through
CO2 hydrogenation has been realized industrially by employing similar Cu catalysts.26,27
Although seminal and impactful, this method suffers from a low equilibrium conversion of
CO2. Because the hydrogenation process is an exothermic reaction,28,29 use of a lower
reaction temperature would be preferred for CH3OH formation.
Low-temperature hydrogenation reaction of CO2 (T ≤ 150 ˚C) to afford CH3OH
using homogeneous catalysts has been investigated recently.30–42 The homogeneous
catalysts generally exhibit good catalytic performance and operate under mild conditions.
ACS Paragon Plus Environment
3

ACS Catalysis
Page 4 of 29
1
2
3
4
5
6
7
8
9
However, these processes normally require additives in order to accomplish high catalytic
activity and they suffer from problems associated with product separation. Methods
employing solid catalysts have also been examined but most of the catalytic systems
developed to date suffer from low catalytic activity.43–48 Yet some systems based on solid
catalysts for low-temperature CO2 hydrogenation display high catalytic performance.49–53
These catalytic systems include Pt3Co octapods,49 Rh75W25 nanosheets,50 Pt/MoS2,51
carbon-supported Pt4Co nanowires,52 and RhCo catalysts.53 Although being important
progress for realizing the low-temperature synthesis of CH3OH, the methods utilize
catalyst systems that require complicated synthetic pathways and performance of the
catalysts still needs to be improved. Hence, the design and development of easily
prepared heterogeneous catalysts that operate to selectively and efficiently form CH3OH
under mild conditions typically temperature below 150 ˚C is highly important. In addition,
the previous reports describing these catalysts do not discuss the by-products formation
such as CH4 and CO, which is problematic with CO2 hydrogenation as we normally
observe these by-products even when employing homogeneous catalytic systems.54
In this study described below, we employed Pt nanoparticles loaded on a
MoOx/TiO2 support (Pt(3)/MoOx(30)/TiO2; Pt = 3 wt%, MoO3 = 30 wt%) as a catalyst for
CO2 hydrogenation to form CH3OH at low reaction temperature (150 ˚C). We observed
that the catalyst is highly active, selective for CH3OH production, and can be readily
prepared and handled. A comparison of the performance of several catalysts, including
the Cu-based CH3OH synthesis catalyst (Cu/Zn/Al2O3) which is industrially used,
revealed that the performance of Pt(3)/MoOx(30)/TiO2 surpasses those of all others
tested in terms of both the yield and selectivity for production of CH3OH. Finally, the
results of this effort demonstrate that a combination of Pt and Mo is crucial to achieve the
observed high activities.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ACS Paragon Plus Environment
4

Page 5 of 29
ACS Catalysis
1
2
3
2. EXPERIMENTAL
4
5
6
7
Chemicals and Preparation of the Catalysts
8
9
Chemicals and materials were purchased from commercial suppliers and used without further
purification. TiO2 (P25) was obtained from Degussa. The carbon support and MoO3 were
commercially obtained from Kishida Chemical. Al2O3 was prepared by calcination of boehmite
(Catapal B, Sasol) for 3 h at T = 900 °C. ZrO2 (JRC-ZRO-2) was supplied by the Catalysis
Society of Japan. HZSM-5 with SiO2/AI2O3 ratio = 22:1 was purchased from TOSOH Co., Ltd.
SiO2 (CariACT Q-10) was purchased from Fuji Silysia Chemical Company Ltd. Nb2O5 was
prepared by calcination of niobic acid (Nb2O5∙nH2O, HY-340) supplied from CBMM (Companhia
Brasileira de Metalurgia e Mineração), at 500 °C for 3 h. CeO2 was prepared by calcination (600
°C, 3 h, in air) of CeO2 (Type A) obtained from Daiichi Kigenso Kagaku Kogyo Co., Ltd. An
industrial Cu/Zn/Al2O3 catalyst (MDC-7; Cu = 34 wt%) was obtained from Clariant.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Pt(3)/MoOx(30)/TiO2 (3 wt% Pt, 30 wt% MoO3) was prepared by using the sequential
impregnation method. First, MoO3-loaded TiO2 (MoO3(30)/TiO2) was prepared by using
impregnation of TiO2. In the process, a mixture of 1.4 g of TiO2 and 0.74 g of (NH4)6Mo7O24‧
4H2O in a 500 mL glass vessel containing 100 mL of deionized water was stirred for 15 min with
200 rpm agitation at room temperature. The mixture was evaporated to dryness at 50 °C, dried
at 110 °C for 12 h and calcinated in air at 500 °C for 3 h to give MoO3(30)/TiO2. The formed
MoO3(30)/TiO2 was then added to an aqueous HNO3 solution containing Pt(NH3)2(NO3)2. The
mixture was evaporated to dryness at 50 °C and further dried in air at 110 °C for 12 h to give
PtO2(3)/MoO3(30)/TiO2 (Unreduced sample). The catalyst used in the hydrogenation process
was prepared by reduction of Pt(3)/MoO3(30)/TiO2 in a quartz tube under a flow of H2 (20 cm3
min-1) at 300 °C for 0.5 h to give Pt(3)/MoOx(30)/TiO2. The Pt/MoOx/TiO2 catalysts having
different Pt and MoO3 contents were prepared in the same manner using different amounts of
MoO3(30)/TiO2 and Pt(NH3)2(NO3)2.
Other supported catalysts were prepared in the manner described above by using
MoO3(30)/TiO2 and other metal sources including aqueous solutions of NH4ReO4, RuCl3,
IrCl3·nH2O, AgNO3, Cu(NO3)2‧3H2O, Ni(NO3)2‧6H2O, and Co(NO3)2‧6H2O and aqueous HNO3
solutions of Rh(NO3)3 and Pd(NH3)2(NO3)2. For the preparation of Pt(3)/MOx(30)/TiO2 (M = V
and W), NH4VO3 and (NH4)10W12O41‧5H2O were independently used as respective precursors,
ACS Paragon Plus Environment
5

ACS Catalysis
Page 6 of 29
1
2
3
4
5
6
and the procedure is the same manner as described above. TiO2-supported Re catalysts
(Re/TiO2) were prepared with TiO2 (ST-01; Ishihara Sangyo Co., Ltd.) and NH4ReO4
(SigmaAldrich) as precursors according to the literature.55
7
8
9
Catalysts Characterization
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
X-ray diffraction (XRD) measurements were carried out using Miniflex (Rigaku) with CuK
radiation. Scanning transmission electron microscopy (STEM) observations were performed
using a JEM-ARM200F microscope equipped with a JED-2300 EDX spectrometer (JEOL).
Samples were prepared by dropping an ethanol solution containing the catalyst on carbon-
supported Cu grids. Temperature programmed reduction with H2 (H2-TPR) was performed by
using BELCAT II (MicrotracBEL) with a cryo apparatus. A sample was mounted in a cell and
then heated at a ramping rate of 10 °C min-1 under a flow of 5% H2/Ar (20 cm3 min-1). The effluent
gas was passed through a trap system that contains MS4A to remove the produced water and
then through a thermal conductivity detector (TCD) to determine the consumed amount of H2 in
the process. Due to the experimental setup, separate experiments were carried out using
temperature range of -100-50 °C and 100-900 °C.
Pt L3-edge and Mo K-edge X-ray absorption fine structure (XAFS) spectra were collected
at the BL01B1 of SPring-8 at the Japan Synchrotron Radiation Research Institute (JASRI)
(proposal 2018B1126). A Si(311) double crystal monochromator was used for the
measurements. For pseudo in situ analysis, Pt(3)/MoOx(30)/TiO2, pre-reduced under a flow of
H2 (20 cm3 min-1) for 0.5 h at 300 °C, was cooled down to room temperature under the H2 flow
and sealed in a cell made of polyethylene under N2 atmosphere. The XAFS spectrum was then
recorded at room temperature. Fourier transformation of the k3-weighted extended XAFS
(EXAFS) was conducted over a k range 3.0-12.0 Å-1. Curve-fitting EXAFS analysis was
performed using the REX ver. 2.5 program provided by RIGAKU and parameters for the Pt–Pt
and Pt–O shells simulated with FEFF6. For in situ analysis, samples in pellet forms (φ10 mm)
were introduced into a cell equipped with Kapton film windows and gas lines. Pretreatment of
the samples involved heating under a flow of 5% H2/He (100 cm3 min-1) at 300 °C. Spectra were
recorded on samples under a flow of 5% H2/He (100 cm3 min-1) and under subsequent exposure
to 10% CO2/He (100 cm3 min-1) at 150 ˚C.
ACS Paragon Plus Environment
6

Page 7 of 29
ACS Catalysis
1
2
3
4
5
6
7
IR measurements were carried out using JASCO FT/IR-4200 equipped with a MCT
detector. Self-supporting pellets were prepared using 40 mg samples ( = 2 cm), and placed in
a quartz cell having CaF2 windows. Prior to measurements, the pellets were subjected to
pretreatment (300 °C, 0.5 h) using 30% H2/He flow (70 cm3 min-1). This was followed by lowering
temperature to 150 °C under He (100 cm3 min-1). Subsequently, the mixed gas that contains
CO2 (10 cm3 min-1), H2 (30 cm3 min-1), and He (50 cm3 min-1) was fed into the in situ IR cell, and
the IR observations were performed. A spectrum for a reference collected at 150 °C under the
30% H2/He flow was subtracted from each measured spectrum.
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Catalytic CO2 Hydrogenation Reactions
The following representative procedure was used for the CO2 hydrogenation reactions. After
being reduced with H2 at 300 °C (cf. preparation of the catalyst), the catalyst (300 mg) and 1,4-
dioxane (1 mL) were added to an autoclave (10 mL). The reaction mixture was magnetically
stirred at 150 °C under a pressurized condition (pCO2 = 1 MPa and pH2 = 5 MPa). CH3OH was
analyzed employing a GC-FID (Shimadzu GC-2014 equipped with a capillary column PoraBond
Q; Agilent Technologies) using n-decane (0.3 mmol) as an internal standard while other products
analysis was accomplished by employing a GC-FID (Shimadzu GC-2014 having a Porapak Q
column) equipped with a Shimadzu MTN-1 methanizer.
ACS Paragon Plus Environment
7

ACS Catalysis
Page 8 of 29
1
2
3
4
3. RESULTS AND DISCUSSION
5
6
7
Characterization of the Pt(3)/MoOx(30)/TiO2 Catalyst
8
9
Pt(3)/MoOx(30)/TiO2 was prepared employing a sequential impregnation method using
Pt(NH3)2(NO3)2, (NH4)6Mo7O24‧4H2O and TiO2 followed by H2 reduction (T = 300 °C). XRD was
used to characterize the prepared materials (Figure 1). The XRD pattern of pristine TiO2 (P25)
contains peaks associated with both the anatase and rutile phase. Analysis of the peaks formed
after loading the Mo species shows that the introduced Mo species in MoO3(30)/TiO2 exist as
MoO3. These MoO3 peaks were also seen in the pattern of PtO2(3)/MoO3(30)/TiO2 (Unreduced
sample). After H2 reduction at 300 °C, peaks corresponding to MoO3 were minimal and only
those corresponding to TiO2 are present, indicating the absence of the crystalline Mo oxides
which can be detectable by XRD. It should be noted that peaks assignable to Pt species are not
present in the XRD patterns.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
In order to investigate the morphologies and particle sizes of the introduced Mo and Pt
species, high-angle annular dark-field STEM observations were made. Figure 2 displays
HAADF-STEM images of pristine TiO2 (P25), MoO3(30)/TiO2 and Pt(3)/MoOx(30)/TiO2 (see also
Fig. S1-3 in Supporting Information). Analysis of the image of MoO3(30)/TiO2 shows that the Mo
oxide species is highly dispersed over the TiO2 surface. In addition, Pt nanoparticles, which can
be seen in the image of Pt(3)/MoOx(30)/TiO2, were found to be highly dispersed. The average
Pt particle diameter was determined to be 2.7 nm. In addition, energy dispersive x-ray
spectroscopy (EDX) mapping of Pt(3)/MoOx(30)/TiO2 was also performed (Figure 3). The results
of EDX analysis show that Mo species are present and highly dispersed over the TiO2 particles,
and that the bright nanoparticles are Pt.
ACS Paragon Plus Environment
8

Page 9 of 29
ACS Catalysis
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
Figure 1. XRD patterns of pristine TiO2, MoO3(30)/TiO2, PtO2(3)/MoO3(30)/TiO2, and
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Pt(3)/MoOx(30)/TiO2.
ACS Paragon Plus Environment
9

ACS Catalysis
Page 10 of 29
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 2. HAADF-STEM images for pristine TiO2 (P25), MoO3(30)/TiO2, and
Pt(3)/MoOx(30)/TiO2 together with the particle size distribution of Pt.
ACS Paragon Plus Environment
10

Page 11 of 29
ACS Catalysis
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 3. A HAADF-STEM image and EDX mapping for Pt(3)/MoOx(30)/TiO2. The Pt, Mo, Ti,
and O signals are related to the catalyst composition. The C and Cu signals arise from the grid
used for the measurement.
XAFS measurements were performed in order to determine the states in which Pt and
Mo species exist in the catalyst. Figure 4(A,B) show the results of the Pt L3-edge X-ray
absorption near-edge structure (XANES) and EXAFS measurements for unreduced
PtO2(3)/MoO3(30)/TiO2, reduced Pt(3)/MoOx(30)/TiO2, and the reference compounds (PtO2 and
Pt foil). The atomic distances and coordination numbers (CNs) for the Pt–O and Pt–Pt shells
were obtained by a curve-fitting analysis of the EXAFS, as given in Table 1. The XANES
spectrum of PtO2(3)/MoO3(30)/TiO2 contains a prominent white-line peak which is similar to that
in the spectrum of PtO2. The EXAFS of PtO2(3)/MoO3(30)/TiO2 is composed of only a Pt–O
contribution at 1.99 Å with a CN of 5.4. These results show that the Pt species in
PtO2(3)/MoO3(30)/TiO2 are PtO2. The XANES spectrum of the reduced Pt(3)/MoOx(30)/TiO2 is
identical to that of Pt foil used as a reference. The EXAFS analysis of Pt(3)/MoOx(30)/TiO2 shows
the presence of Pt–Pt bonds with CN of 3.5 at 2.77 Å. The observed distance is slightly longer
ACS Paragon Plus Environment
11

ACS Catalysis
Page 12 of 29
1
2
3
4
5
6
7
8
9
than the distance of Pt–Pt seen in bulk Pt metal (2.76 Å) although it is known that the distance
becomes shorter if nanoparticles are formed,56 as we observed to exist by using STEM
measurements. The elongation of the Pt–Pt bond in reduced Pt(3)/MoOx(30)/TiO2 might be a
result of formation of Pt–Mo bimetals for some Pt species.57
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The results of Mo K-edge XAFS measurements are shown in Fig. 4(C). The XANES
spectra demonstrate that the edge position and shape of PtO2(3)/MoO3(30)/TiO2 are almost the
same as those observed for MoO3 as a reference. This result is in agreement with observations
made using XRD measurements. On the other hand, the absorption edge of reduced
Pt(3)/MoOx(30)/TiO2 is shifted to lower energy, indicating that the Mo oxide species is reduced
in the H2 pretreatment. These results were confirmed by performing H2-TPR using a cryo
apparatus (Fig. 4(D)). A peak corresponding to the reduction of Pt species appeared below
temperature of 0 °C. The fact that XANES spectrum of PtO2(3)/MoO3(30)/TiO2 after H2 reduction
at room temperature is essentially the same as that of Pt foil confirms this conclusion (Figure
S4). Also, a small peak can be found at around 250 °C. Considering the fact that the reduced
Mo species was identified by XAFS analysis for Pt(3)/MoOx(30)/TiO2 which is reduced at 300 °C,
this small peak is assignable to the reduction of Mo oxide species. A broad peak around 500 °C
and another peak at around 850 °C were also observed. On the other hand, MoO3(30)/TiO2
exhibits only two peaks at around 500 °C and 850 °C. These observations indicate that Pt
promotes reduction of Mo oxide species.
ACS Paragon Plus Environment
12

Page 13 of 29
ACS Catalysis
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 4. Pt L3-edge (A) XANES, (B) EXAFS Fourier transforms, and (C) Mo K-edge XANES of
PtO2(3)/MoO3(30)/TiO2, Pt(3)/MoOx(30)/TiO2, and the reference compounds. The spectra were
recorded at room temperature. The spectra of Pt(3)/MoOx(30)/TiO2 were recorded on samples
that were not exposed to air after the reduction pretreatment and contained in sealed vessels
under N2. (D) H2-TPR profile of MoO3(30)/TiO2, and Pt(3)/MoOx(30)/TiO2. The sample was
heated using a temperature ramp-rate of 10 °C min-1 in a flow of 5% H2/Ar (20 cm3 min-1).
Table 1. Curve-fitting analysis of the Pt L3-edge EXAFS of the PtO2(3)/MoO3(30)/TiO2 and
Pt(3)/MoOx(30)/TiO2 catalysts.
Sample
Shell
CN a
5.4
R (Å) b
1.99
2.77
σ (Å) c
0.055
0.050
Rf (%) d
3.6
2.9
PtO2(3)/MoO3(30)/TiO2 Pt–O
Pt(3)/MoOx(30)/TiO2
Pt–Pt
3.5
a Coordination number. b Bond distance. Debye-Waller factor. d Residual factor.
c
ACS Paragon Plus Environment
13

ACS Catalysis
Page 14 of 29
1
2
3
4
Low-Temperature (T = 150 ˚C) Hydrogenation of CO2
5
6
7
8
9
CO2 hydrogenation reactions were carried out to assess the catalytic properties of catalysts.
Reactions were performed employing a catalyst (300 mg) that is pretreated with H2 at 300 °C in
a stainless autoclave (V = 10 mL; T = 150 ˚C; pCO2 = 1 MPa; pH2 = 5 MPa; t = 24 h). Analysis of
the results displayed in Table 2 shows that a process catalyzed by Pt(3)/MoOx(30)/TiO2
generates CH3OH in 66% yield (entry 1) and that CH4 is produced as a minor by-product. In
contrast, reactions promoted by other metal catalysts supported on MoOx(30)/TiO2 do not form
significant amounts of CH3OH (entries 2-10) and no reaction occurs when MoO3(30)/TiO2 is
used (entry 11). In reactions promoted by the other supported Pt catalysts (entries 12-20),
formation of CH3OH was not observed. Finally, using Pt(3)/MoO3 leads to formation of a small
amount of CH3OH along with by-products such as CO and CH4. This observation indicates that
catalysts comprised of bulk MoO3 as a support are ineffective in this reaction.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
It is well known that combining more than two active components is highly effective in
creating catalysts for various hydrogenation reactions. Also, it is known that catalysts which
combine group 5–7 metals with group 8–10 metals efficiently promote these processes.58–64
Therefore, we explored the use of a combination of Pt and other metals such as W and V (entries
21-22). However, these catalyst combinations were found to be ineffective. We also explored
other supports that utilize a combination of Pt and Mo species (entries 23-26). The results show
that these catalysts promote generation of CH3OH relatively efficiently, indicating the importance
of combination of Pt and Mo as active components. However, the yields of these processes are
still lower than that using Pt(3)/MoOx(30)/TiO2, suggesting that TiO2 as a catalyst support plays
roles for efficient progression of the reaction. Furthermore, the industrially-used Cu-based
catalyst Cu/Zn/Al2O3 (MDC-7; Cu = 34 wt%) was employed and found to be ineffective under
our low-temperature reactions conditions (entry 27). We have also tried Re/TiO2 which were
reported to be active for the low-temperature hydrogenation of CO2 to form CH3OH (entries 28-
29).55 While a catalyst with Re loading amount of 1 wt% (Re(1)/TiO2) showed the best catalytic
performance based on CH3OH formation rate per Re in the previous study, we also employed a
catalyst with Re loading amount of 3 wt% (Re(3)/TiO2) that has the same loading amount of the
supported metal for Pt(3)/MoOx(30)/TiO2. The result shows that Pt(3)/MoOx(30)/TiO2 exhibits
better CH3OH yield. Thus, Pt(3)/MoOx(30)/TiO2 is the best catalyst for low-temperature CO2
hydrogenation to form CH3OH.
ACS Paragon Plus Environment
14

Page 15 of 29
ACS Catalysis
1
2
3
4
5
6
7
8
9
Table 2. Hydrogenation of CO2 promoted by various catalysts.a
Yield / %
Entry
Catalyst
CH3OH
66
6
<1
3
14
<1
<1
<1
<1
<1
<1
<1
<1
CO
<1
<1
<1
1
CH4
4
1
4
19
5
1
2
3
4
5
6
7
8
Pt(3)/MoOx(30)/TiO2
Re(3)/MoOx(30)/TiO2
Ru(3)/MoOx(30)/TiO2
Ir(3)/MoOx(30)/TiO2
Rh(3)/MoOx(30)/TiO2
Pd(3)/MoOx(30)/TiO2
Ag(3)/MoOx(30)/TiO2
Cu(3)/MoOx(30)/TiO2
Ni(3)/MoOx(30)/TiO2
Co(3)/MoOx(30)/TiO2
MoOx(30)/TiO2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
<1
<1
<1
<1
<1
<1
<1
1
4
<1
<1
4
<1
<1
<1
<1
<1
<1
<1
<1
<1
1
2
3
<1
5
1
8
9
10
11
12
13
Pt(3)/Carbon
Pt(3)/Al2O3
14
15
Pt(3)/ZrO2
Pt(3)/HZSM-5(22)
<1
<1
2
<1
16
17
18
Pt(3)/SiO2
Pt(3)/Nb2O5
Pt(3)/CeO2
<1
<1
<1
1
3
2
19
20
21
Pt(3)/TiO2
Pt(3)/MoO3
Pt(3)/WOx(30)/TiO2
<1
5
9
6
4
3
22
23
24
25
26
27
28c
29c
Pt(3)/VOx(30)/TiO2
<1
33
4
7
1
4
2
<1
2
1
Pt(3)/MoOx(30)/Al2O3
Pt(3)/MoOx(30)/SiO2
Pt(3)/MoOx(30)/Carbon
Pt(3)/MoOx(30)/ZrO2
8
42
20
5
5
b
Cu/Zn/Al2O3
<1
<1
4
Re(1)/TiO2
Re(3)/TiO2
19
1
aPretreatment: H2 (20 cm3 min-1), 300 ˚C, 0.5 h; catalytic reaction conditions: Catalyst (300 mg),
CO2 (1 MPa), H2 (5 MPa), 1,4-dioxane (1 mL), 150 ˚C, 24 h. b 34 wt% of Cu. c H2 reduction as a
pretreatment was performed at 300 ˚C.
To further optimize the Pt/MoOx/TiO2 catalysts, the effects varying loading amount of Pt
and Mo were investigated (Figure 5). The highest yield and selectivity for CH3OH formation was
achieved using Pt(3)/MoOx(30)/TiO2 with a Pt loading of 3 wt% and a MoO3 loading of 30 wt%.
Although the CH3OH yield increases with increasing Pt loading, the selectivity for formation of
CH3OH decreases and a large amount of CH4 is produced when a catalyst containing 10 wt%
Pt is employed. This finding suggests that larger Pt nanoparticles favor the production of CH4,
ACS Paragon Plus Environment
15

ACS Catalysis
Page 16 of 29
1
2
3
4
5
6
7
8
9
which is in good agreement with previous reports on CO2 hydrogenation over Rh/TiO2 and
Re/TiO2.55,65 Moreover, the results show that addition of Mo has a huge impact on the efficiency
of CH3OH generation and that a 30 wt% loading is optimal for the process. As a consequence,
we conclude that among the catalysts explored in this study Pt(3)/MoOx(30)/TiO2 is the best for
low-temperature (150 ˚C) CO2 hydrogenation of to form CH3OH.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Using this optimized catalyst, the time course of the CO2 hydrogenation reaction was
observed. Inspection of the time-course plot shown in Fig. 6 demonstrates that the
concentrations of CH3OH and CH4 increase with increasing reaction time. It is significant that
the CH3OH yield after a reaction time of 48 h is 73%, which is almost the equilibrium yield
expected under the reaction conditions used. Note that other possible by-products such as
formaldehyde (HCOH) and formic acid (HCOOH) are not formed in this process. In addition,
recycling tests of Pt(3)/MoOx(30)/TiO2 were carried out to investigate the recyclability of our
heterogeneous catalyst system, as shown in Fig. S5. Following the reaction,
Pt(3)/MoOx(30)/TiO2 was separated from the reaction solution, washed with 1,4-dioxane, dried
in an oven (110 °C) under air atmosphere, and subsequently reused for an ensuing reaction.
Note that the recycling reaction was carried out with and without H2 reduction at T = 300 °C as
a pretreatment for every catalytic run. The obtained results show that the catalyst can be reused
but the CH3OH yield and selectivity gradually decreased for both recycling tests. It was also
found that the activity loss was more significant when the H2 reduction was performed for each
recycling run. This finding indicates that the catalyst does not need to be reduced for recycling.
The total turnover number on the basis of CO adsorption amount performed at 30 °C for the
fresh sample was determined to be 3588 (Fig. S5(A)). In order to assess reasons of the catalyst
deactivations, HAADF-STEM observations were made for samples after the 4th recycling
experiments (Figs. S6 and S7). Both spent catalysts show larger average Pt particle diameters
than that of the fresh Pt(3)/MoOx(30)/TiO2 catalyst. The average Pt particle diameter for the used
catalyst recycled with the H2 reduction pretreatment for each recycling run (3.7 nm) was larger
than that for the one that a pretreatment was only performed before the first run (3.2 nm). These
results suggest that aggregation of Pt particles would be a reason for the observed activity loss.
It should also be noted that formation of Pt–Mo bimetals can also be a possible reason for the
deactivation.57
ACS Paragon Plus Environment
16

Page 17 of 29
ACS Catalysis
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 5. Effect of the (A) Pt and (B) MoO3 loading amount on the hydrogenation reaction of
CO2 over Pt/MoOx/TiO2. Pretreatment: H2 (20 cm3 min-1), 300 ˚C, 0.5 h; catalytic reaction
conditions: Catalyst (300 mg), CO2 (1 MPa), H2 (5 MPa), 1,4-dioxane (1 mL), 150 ˚C, 24 h. 30
wt% of MoO3 loading was employed for investigation on the effect of Pt loading while 3 wt% of
Pt loading was employed for investigation on the effect of MoO3 loading.
Figure 6. Time course for the hydrogenation reaction of CO2 over Pt(3)/MoOx(30)/TiO2.
Pretreatment: H2 (20 cm3 min-1), 300 ˚C, 0.5 h; catalytic reaction conditions: Catalyst (300 mg),
CO2 (1 MPa), H2 (5 MPa), 1,4-dioxane (1 mL), 150 ˚C, 24 h.
ACS Paragon Plus Environment
17

ACS Catalysis
Page 18 of 29
1
2
3
4
Mechanistic Study
5
6
7
8
Catalytic hydrogenation reactions using HCOOH or CO as a starting material were performed in
order to obtain additional insights into the catalytic reaction promoted by Pt(3)/MoOx(30)/TiO2
(Scheme 1). Hydrogenation of CO, employing the same pressure used in the CO2 reduction
reaction catalyzed by Pt(3)/MoOx(30)/TiO2 (1 MPa), proceeds to form CH3OH. However,
hydrogenation of CO2 forms CH3OH at the higher rate of 0.16 mmol h-1. Also, a larger amount
of CH4 is generated as a by-product when CO is employed as starting material. This result
suggests that it is possible that CO is an intermediate in the formation of CH3OH but direct
hydrogenation of CO2 to form CH3OH would be a preferable process. It is worth mentioning here
that CO2 can be formed through the water-gas shift reaction between CO and the produced H2O
to give CO2 and H2. In contrast, reaction of HCOOH generates CH3OH at a higher rate than that
for the reaction of CO2, implying that derivatives of HCOOH such as HCOO- adsorbed on the
surface of the catalyst can be intermediates for the CH3OH formation. Note that the
decomposition of HCOOH to form CO and CO2 may occur faster although they can be recycled
for the CH3OH forming process.66 Decomposition of the CH3OH produced in this process is also
an important issue. As a result, we explored the decomposition reaction of 5 mmol of CH3OH
under N2 atmosphere (0.5 MPa). Note that the amount of CH3OH used is almost the same as
that of CO2 used in the hydrogenation process (1 MPa). The result shows that although CH3OH
does decompose in the presence of the Pt(3)/MoOx(30)/TiO2 catalyst, the decomposition rate is
not as high as that for CH3OH formation in the direct hydrogenation of CO2.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The hypothesis suggested by observations made in the experiments described above
was confirmed by using in situ IR analysis (Fig. 7A). For this purpose, generation of surface
species was investigated for a reaction carried out using Pt(3)/MoOx(30)/TiO2 at ambient
pressure and 150 °C under a gas flow containing CO2 (10 cm3 min-1), H2 (30 cm3 min-1) and He
(50 cm3 min-1). The samples were subjected to a pretreatment under H2 flow for 30 min at 300
°C prior to each measurement. Several features in the range of 1300-1600 cm-1 associated with
carbonate and formate species were found to be present in the IR spectrum. For example, the
bands at 1340 and 1555 cm-1 indicate the formation of formate species.67 In addition, a band
occuring at 1430 cm-1 can be assigned to asymmetric stretching vibration of monodentate
carbonates (νas(COO)).68 In contrast, these bands are not prominent in the reaction promoted
by MoOx(30)/TiO2, demonstrating the importance of Pt as a supported metal. Finally, in situ Mo
ACS Paragon Plus Environment
18

Page 19 of 29
ACS Catalysis
1
2
3
4
5
6
7
8
9
K-edge XANES analysis was carried out on Pt(3)/MoOx(30)/TiO2 using CO2 (Fig. 7B). Prior to
the XANES measurement, the sample was pretreated by heating at 300 °C under 5% H2/He flow
(100 cm3 min-1). The spectrum was then recorded under 5% H2/He flow (100 cm3 min-1) and
under subsequent exposure to 10% CO2/He flow (100 cm3 min-1) at 150 ˚C. XANES analysis
shows that the edge position in the spectrum of Pt(3)/MoOx(30)/TiO2 is positively shifted by
introducing CO2, demonstrating that CO2 acts as an oxidant. In other words, the Mo species is
oxidized by CO2. This result suggests that redox reaction of the Mo species takes place in order
to promote the CO2 hydrogenation reaction, consistent with an oxygen-vacancy driven
mechanism (or reverse Mars−van Krevelen mechanism69) wherein oxygenates are activated at
undercoordinated Mo sites as reported for hydrodeoxygenation reactions.70 Namely, the surface
defect sites, formed during pretreatment by H2, play important roles in the hydrogenation of CO2.
Note that only CO was detected by a thermal conductivity detector GC (490 Micro GC, Agilent
Technologies Inc.) upon the introduction of CO2. This is probably because the in situ Mo K-edge
XAFS experiment was performed ambient pressure unlike the catalytic CH3OH forming process
performed at pCO2 = 1 MPa; pH2 = 5 MPa.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Scheme 1. Hydrogenation and decomposition of model reaction substrates over
Pt(3)/MoOx(30)/TiO2. (a) CO2, (b) CO, (c,d) HCOOH, (e) CH3OH. Pretreatment: H2 (20 cm3 min-
1), 300 ˚C, 0.5 h; catalytic reaction conditions: Catalyst (300 mg), 1,4-dioxane (1 mL).
ACS Paragon Plus Environment
19

ACS Catalysis
Page 20 of 29
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 7. (A) In situ IR spectra measured at 150 °C under a gas flow containing CO2 (10 cm3
min-1), H2 (30 cm3 min-1), and He (50 cm3 min-1). Pretreatment: H2 (20 cm3 min-1), He (50 cm3
min-1), 300 °C, 0.5 h. (B) In situ Mo K-edge XANES spectra of Pt(3)/MoOx(30)/TiO2 collected at
150 °C just after the H2 reduction at 300 °C (orange line) and after subsequent introduction of
10% CO2/He (100 cm3 min-1) (blue line).
ACS Paragon Plus Environment
20

Page 21 of 29
ACS Catalysis
1
2
3
CONCLUSIONS
4
5
6
7
8
The catalytic hydrogenation reaction of CO2 was performed under mild conditions (pCO2
= 1 MPa; pH2 = 5 MPa; T = 150 ˚C) employing a Pt(3)/MoOx(30)/TiO2 catalyst and various
catalysts including MoOx(30)/TiO2-supported catalysts, and oxide-supported as well as
the industrially-used Cu-based catalyst. Pt(3)/MoOx(30)/TiO2 exhibited the best CH3OH
yield among the catalysts tested and the CH3OH yield after the reaction time of 48 h
reached 73%. The obtained findings indicate that the combination of Pt and Mo is highly
important to achieve the high activities for CH3OH production. More specifically, the
reduced MoOx species would be a key to success realizing the low-temperature
hydrogenation of CO2. Given the importance of the low-temperature hydrogenation of
CO2 for both academic research and the industrial manufacture of methanol, the
presented system would be a highly active and versatile hydrogenation catalyst.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
AUTHOR INFORMATION
Corresponding author: Ken-ichi Shimizu, Takashi Toyao
E-mail: kshimizu@cat.hokudai.ac.jp, toyao@cat.hokudai.ac.jp
ASSOCIATED CONTENT
Supporting Information
STEM, XAFS, and recycling tests.
ACKNOWLEDGEMENT
This study was supported financially by NEDO (New Energy and Industrial Technology
Development Organization), KAKENHI grants 18K14057, 18K14051, and 17H01341 from JSPS,
by MEXT within the projects Elements Strategy Initiative to Form Core Research Center and the
JST-CREST project JPMJCR17J3, as well as by IRCCS. The authors appreciate the technical
staffs of Institute for Catalysis of Hokkaido University (HU) for preparing experimental setup and
thank staffs of the Open Facility of HU for their help with STEM analysis. XAFS measurements
were performed at BL-01B1 of SPring-8 (proposal: 2018B1126).
ACS Paragon Plus Environment
21

ACS Catalysis
Page 22 of 29
1
2
3
4
REFERENCES
5
6
7
8
9
(1)
(2)
(3)
(4)
(5)
(6)
Kondratenko, E. V.; Mul, G.; Baltrusaitis, J.; Larrazábal, G. O.; Pérez-Ramírez, J. Status and
Perspectives of CO2 Conversion into Fuels and Chemicals by Catalytic, Photocatalytic and
Electrocatalytic Processes. Energy Environ. Sci. 2013, 6, 3112–3135.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Artz, J.; Müller, T. E.; Thenert, K.; Kleinekorte, J.; Meys, R.; Sternberg, A.; Bardow, A.; Leitner,
W. Sustainable Conversion of Carbon Dioxide: An Integrated Review of Catalysis and Life Cycle
Assessment. Chem. Rev. 2018, 118, 434–504.
Wang, W. H.; Himeda, Y.; Muckerman, J. T.; Manbeck, G. F.; Fujita, E. CO2 Hydrogenation to
Formate and Methanol as an Alternative to Photo- and Electrochemical CO2 Reduction. Chem.
Rev. 2015, 115, 12936–12973.
Motokura, K.; Naijo, M.; Yamaguchi, S.; Miyaji, A.; Baba, T. Silicone Wastes as Reducing Agents
for Carbon Dioxide Transformation: Fluoride-Catalyzed Formic Acid Synthesis from CO2, H2O,
and Disilanes. Chem. Lett. 2015, 44, 1464–1466.
Mitsudome, T.; Urayama, T.; Fujita, S.; Maeno, Z.; Mizugaki, T.; Jitsukawa, K.; Kaneda, K. A
Titanium Dioxide Supported Gold Nanoparticle Catalyst for the Selective N-Formylation of
Functionalized Amines with Carbon Dioxide and Hydrogen. ChemCatChem 2017, 9, 3632–3636.
Toyao, T.; Siddiki, S. M. A. H.; Morita, Y.; Kamachi, T.; Touchy, A. S.; Onodera, W.; Kon, K.;
Furukawa, S.; Ariga, H.; Asakura, K.; Yoshizawa, K.; Shimizu, K. Rhenium-Loaded TiO2: A
Highly Versatile and Chemoselective Catalyst for the Hydrogenation of Carboxylic Acid
Derivatives and the N-Methylation of Amines Using H2 and CO2. Chem. - A Eur. J. 2017, 23,
14848–14859.
(7)
(8)
Bao, J.; Tsubaki, N. Design and Synthesis of Powerful Capsule Catalysts Aimed at Applications
in C1 Chemistry and Biomass Conversion. Chem. Rec. 2018, 18, 4–19.
Liu, L.; Puga, A. V.; Cored, J.; Concepción, P.; Pérez-Dieste, V.; García, H.; Corma, A. Sunlight-
Assisted Hydrogenation of CO2 into Ethanol and C2+ Hydrocarbons by Sodium-Promoted
Co@C Nanocomposites. Appl. Catal. B Environ. 2018, 235, 186–196.
(9)
Ramirez, A.; Gevers, L.; Bavykina, A.; Ould-Chikh, S.; Gascon, J. Metal Organic Framework-
Derived Iron Catalysts for the Direct Hydrogenation of CO2 to Short Chain Olefins. ACS Catal.
2018, 8, 9174–9182.
(10) Mori, K.; Sano, T.; Kobayashi, H.; Yamashita, H. Surface Engineering of a Supported PdAg
Catalyst for Hydrogenation of CO2 to Formic Acid: Elucidating the Active Pd Atoms in Alloy
Nanoparticles. J. Am. Chem. Soc. 2018, 140, 8902–8909.
ACS Paragon Plus Environment
22

Page 23 of 29
ACS Catalysis
1
2
3
4
5
6
7
(11) Wang, Y.; Tan, L.; Tan, M.; Zhang, P.; Fang, Y.; Yoneyama, Y.; Yang, G.; Tsubaki, N. Rationally
Designing Bifunctional Catalysts as an Efficient Strategy to Boost CO2 Hydrogenation Producing
Value-Added Aromatics. ACS Catal. 2018, 9, 895−901.
8
9
(12) Dabral, S.; Schaub, T. The Use of Carbon Dioxide (CO2) as a Building Block in Organic
Synthesis from an Industrial Perspective. Adv. Synth. Catal. 2018, 361, 223–246.
(13) AlSabban, B.; Falivene, L.; Kozlov, S. M.; Aguilar-Tapia, A.; Ould-Chikh, S.; Hazemann, J. L.;
Cavallo, L.; Basset, J. M.; Takanabe, K. In-Operando Elucidation of Bimetallic CoNi
Nanoparticles during High-Temperature CH4/CO2 Reaction. Appl. Catal. B Environ. 2017, 213,
177–189.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(14) Rodriguez, J. A.; Liu, P.; Stacchiola, D. J.; Senanayake, S. D.; White, M. G.; Chen, J. G.
Hydrogenation of CO2 to Methanol: Importance of Metal-Oxide and Metal-Carbide Interfaces in
the Activation of CO2. ACS Catal. 2015, 5, 6696–6706.
(15) Bahruji, H.; Bowker, M.; Hutchings, G.; Dimitratos, N.; Wells, P.; Gibson, E.; Jones, W.; Brookes,
C.; Morgan, D.; Lalev, G. Pd/ZnO Catalysts for Direct CO2 Hydrogenation to Methanol. J. Catal.
2016, 343, 133–146.
(16) Martin, O.; Martín, A. J.; Mondelli, C.; Mitchell, S.; Segawa, T. F.; Hauert, R.; Drouilly, C.;
Curulla-Ferré, D.; Pérez-Ramírez, J. Indium Oxide as a Superior Catalyst for Methanol Synthesis
by CO2 Hydrogenation. Angew. Chemie Int. Ed. 2016, 55, 6261–6265.
(17) Wang, J.; Li, G.; Li, Z.; Tang, C.; Feng, Z.; An, H.; Liu, H.; Liu, T.; Li, C. A Highly Selective and
Stable ZnO-ZrO2 Solid Solution Catalyst for CO2 Hydrogenation to Methanol. Sci. Adv. 2017, 3,
e1701290.
(18) Álvarez, A.; Bansode, A.; Urakawa, A.; Bavykina, A. V.; Wezendonk, T. A.; Makkee, M.; Gascon,
J.; Kapteijn, F. Challenges in the Greener Production of Formates/Formic Acid, Methanol, and
DME by Heterogeneously Catalyzed CO2 Hydrogenation Processes. Chem. Rev. 2017, 117,
9804–9838.
(19) Larmier, K.; Liao, W. C.; Tada, S.; Lam, E.; Verel, R.; Bansode, A.; Urakawa, A.; Comas-Vives,
A.; Copéret, C. CO2-to-Methanol Hydrogenation on Zirconia-Supported Copper Nanoparticles:
Reaction Intermediates and the Role of the Metal–Support Interface. Angew. Chemie - Int. Ed.
2017, 56, 2318–2323.
(20) Jiang, X.; Nie, X.; Wang, X.; Wang, H.; Koizumi, N.; Chen, Y.; Guo, X.; Song, C. Origin of Pd-Cu
Bimetallic Effect for Synergetic Promotion of Methanol Formation from CO2 Hydrogenation. J.
Catal. 2019, 369, 21–32.
(21) Kattel, S.; Liu, P.; Chen, J. G. Tuning Selectivity of CO2 Hydrogenation Reactions at the
Metal/Oxide Interface. J. Am. Chem. Soc. 2017, 139, 9739–9754.
ACS Paragon Plus Environment
23

ACS Catalysis
Page 24 of 29
1
2
3
4
5
6
(22) Song, C. Global Challenges and Strategies for Control, Conversion and Utilization of CO2 for
Sustainable Development Involving Energy, Catalysis, Adsorption and Chemical Processing.
Catal. Today 2006, 107, 2−32.
7
8
9
(23) Palo, D. R.; Dagle, R. A.; Holladay, J. D. Methanol Steam Reforming for Hydrogen Production.
Chem. Rev. 2007, 107, 3992−4021.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(24) Waugh, K. C. Methanol Synthesis. Catal. Letters 2012, 142, 1153–1166.
(25) Olah, G. A.; Goeppert, A.; Prakash, G. K. S. Chemical Recycling of Carbon Dioxide to Methanol
and Dimethyl Ether: From Greenhouse Gas to Renewable, Environmentally Carbon Neutral
Fuels and Synthetic Hydrocarbons. J. Org. Chem. 2009, 74, 487–498.
(26) Saito, M.; Murata, K. Development of High Performance Cu/ZnO-Based Catalysts for Methanol
Synthesis and the Water-Gas Shift Reaction. Catal. Surv. from Asia 2004, 8, 285–294.
(27) Olah, G. A. Towards Oil Independence through Renewable Methanol Chemistry. Angew.
Chemie - Int. Ed. 2013, 52, 104–107.
(28) Gaikwad, R.; Bansode, A.; Urakawa, A. High-Pressure Advantages in Stoichiometric
Hydrogenation of Carbon Dioxide to Methanol. J. Catal. 2016, 343, 127–132.
(29) Porosoff, M. D.; Yan, B.; Chen, J. G. Catalytic Reduction of CO2 by H2 for Synthesis of CO,
Methanol and Hydrocarbons: Challenges and Opportunities. Energy Environ. Sci. 2016, 9, 62–
73.
(30) Huff, C. A.; Sanford, M. S. Cascade Catalysis for the Homogeneous Hydrogenation of CO2 to
Methanol. J. Am. Chem. Soc. 2011, 133, 18122–18125.
(31) Wesselbaum, S.; Vom Stein, T.; Klankermayer, J.; Leitner, W. Hydrogenation of Carbon Dioxide
to Methanol by Using a Homogeneous Ruthenium-Phosphine Catalyst. Angew. Chemie - Int. Ed.
2012, 51, 7499–7502.
(32) Rezayee, N. M.; Huff, C. A.; Sanford, M. S. Tandem Amine and Ruthenium-Catalyzed
Hydrogenation of CO2 into Methanol. J. Am. Chem. Soc. 2015, 137, 1028−1031.
(33) Wesselbaum, S.; Moha, V.; Meuresch, M.; Brosinski, S.; Thenert, K. M.; Kothe, J.; Stein, T. vom;
Englert, U.; Hölscher, M.; Klankermayer, J.; Leitner, L. Hydrogenation of Carbon Dioxide to
Methanol Using a Homogeneous Ruthenium–Triphos Catalyst: From Mechanistic Investigations
to Multiphase Catalysis. Chem. Sci. 2015, 6, 693–704.
(34) Kothandaraman, J.; Goeppert, A.; Czaun, M.; Olah, G. A.; Prakash, G. K. S. Conversion of CO2
from Air into Methanol Using a Polyamine and a Homogeneous Ruthenium Catalyst. J. Am.
Chem. Soc. 2016, 133, 778–781.
ACS Paragon Plus Environment
24

Page 25 of 29
ACS Catalysis
1
2
3
4
5
6
7
(35) Schneidewind, J.; Adam, R.; Baumann, W.; Jackstell, R.; Beller, M. Low-Temperature
Hydrogenation of Carbon Dioxide to Methanol with a Homogeneous Cobalt Catalyst. Angew.
Chemie - Int. Ed. 2017, 56, 1890 –1893.
8
9
(36) Kar, S.; Goeppert, A.; Kothandaraman, J.; Prakash, G. K. S. Manganese-Catalyzed Sequential
Hydrogenation of CO2 to Methanol via Formamide. ACS Catal. 2017, 7, 6347−6351.
(37) Ribeiro, A. P. C.; Martins, L. M. D. R. S.; Pombeiro, A. J. L. Carbon Dioxide-to-Methanol Single-
Pot Conversion Using a C-Scorpionate Iron(II) Catalyst. Green Chem. 2017, 19, 4811–4815.
(38) Everett, M.; Wass, D. F. Highly Productive CO2 Hydrogenation to Methanol - a Tandem Catalytic
Approach: Via Amide Intermediates. Chem. Commun. 2017, 53, 9502–9504.
(39) Zhang, F. H.; Liu, C.; Li, W.; Tian, G. L.; Xie, J. H.; Zhou, Q. L. An Efficient Ruthenium Catalyst
Bearing Tetradentate Ligand for Hydrogenations of Carbon Dioxide. Chinese J. Chem. 2018, 36,
1000－1002.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(40) Kar, S.; Sen, R.; Goeppert, A.; Prakash, G. K. S. Integrative CO2 Capture and Hydrogenation to
Methanol with Reusable Catalyst and Amine: Toward a Carbon Neutral Methanol Economy. J.
Am. Chem. Soc. 2018, 140, 1580–1583.
(41) Scharnagl, F.; Hertrich, M.; Neitzel, G.; Jackstell, R.; Beller, M. Homogeneous Catalytic
Hydrogenation of CO2 to Methanol – Improvements with Tailored Ligands. Adv. Synth. Catal.
2019, 361, 374 –379.
(42) Sordakis, K.; Tsurusaki, A.; Iguchi, M.; Kawanami, H.; Himeda, Y.; Laurenczy, G. Carbon Dioxide
to Methanol: The Aqueous Catalytic Way at Room Temperature. Chem. - A Eur. J. 2016, 22,
15605–15608.
(43) Zeng, J.; Fujimoto, K.; Tsubaki, N. A New Low-Temperature Synthesis Route of Methanol:
Catalytic Effect of the Alcoholic Solvent. Energy and Fuels 2002, 16, 83–86.
(44) Reller, C.; Pöge, M.; Lißner, A.; Mertens, F. O. R. L. Methanol from CO2 by Organo-Cocatalysis:
CO2 Capture and Hydrogenation in One Process Step. Environ. Sci. Technol. 2014, 48,
14799−14804.
(45) Chen, Y.; Choi, S.; Thompson, L. T. Low-Temperature CO2 Hydrogenation to Liquid Products via
a Heterogeneous Cascade Catalytic System. ACS Catal. 2015, 5, 1717−1725.
(46) Chen, Y.; Choi, S.; Thompson, L. T. Low Temperature CO2 Hydrogenation to Alcohols and
Hydrocarbons over Mo2C Supported Metal Catalysts. J. Catal. 2016, 343, 147–156.
(47) He, Z.; Qian, Q.; Ma, J.; Meng, Q.; Zhou, H.; Song, J.; Liu, Z.; Han, B. Water-Enhanced
Synthesis of Higher Alcohols from CO2 Hydrogenation over a Pt/Co3O4 Catalyst under Milder
Conditions. Angew. Chemie - Int. Ed. 2016, 55, 737–741.
ACS Paragon Plus Environment
25

ACS Catalysis
Page 26 of 29
1
2
3
4
5
6
(48) Kothandaraman, J.; Dagle, R. A.; Dagle, V. L.; Davidson, S. D.; Walter, E. D.; Burton, S. D.;
Hoyt, D. W.; Heldebrant, D. J. Condensed-Phase Low Temperature Heterogeneous
Hydrogenation of CO2 to Methanol. Catal. Sci. Technol. 2018, 8, 5098–5103.
7
8
9
(49) Khan, M. U.; Wang, L.; Liu, Z.; Gao, Z.; Wang, S.; Li, H.; Zhang, W.; Wang, M.; Wang, Z.; Ma,
C.; Zeng, J. Pt3Co Octapods as Superior Catalysts of CO2 Hydrogenation. Angew. Chemie - Int.
Ed. 2016, 55, 9548 –9552.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(50) Zhang, W.; Wang, L.; Liu, H.; Hao, Y.; Li, H.; Khan, M. U.; Zeng, J. Integration of Quantum
Confinement and Alloy Effect to Modulate Electronic Properties of RhW Nanocrystals for
Improved Catalytic Performance toward CO2 Hydrogenation. Nano Lett. 2017, 17, 788−793.
(51) Li, H.; Wang, L.; Dai, Y.; Pu, Z.; Lao, Z.; Chen, Y.; Wang, M.; Zheng, X.; Zhu, J.; Zhang, W.; Ma,
C.; Zeng, J. Synergetic Interaction between Neighbouring Platinum Monomers in CO2
Hydrogenation. Nat. Nanotechnol. 2018, 13, 411–417.
(52) Bai, S.; Shao, Q.; Feng, Y.; Bu, L.; Huang, X. Highly Efficient Carbon Dioxide Hydrogenation to
Methanol Catalyzed by Zigzag Platinum–Cobalt Nanowires. Small 2017, 13, 1604311.
(53) Zheng, X.; Lin, Y.; Pan, H.; Wu, L.; Zhang, W.; Cao, L.; Zhang, J.; Zheng, L.; Yao, T. Grain
Boundaries Modulating Active Sites in RhCo Porous Nanospheres for Efficient CO2
Hydrogenation. Nano Res. 2018, 11, 2357–2365.
(54) Tominaga, K.; Sasaki, Y.; Kawai, M.; Watanabe, T.; Saito, M. Ruthenium Complex Catalysed
Hydrogenation of Carbon Dioxide to Carbon Monoxide, Methanol and Methane. J. Chem. Soc.
Chem. Commun. 1993, 629–631.
(55) Ting, K. W.; Toyao, T.; Siddiki, S. M. A. H.; Shimizu, K. Low-Temperature Hydrogenation of CO2
to Methanol over Heterogeneous TiO2-Supported Re Catalysts. ACS Catal. 2019, 9, 3685–3693.
(56) Kang, J. H.; Menard, L. D.; Nuzzo, R. G.; Frenkel, A. I. Unusual Non-Bulk Properties in
Nanoscale Materials: Thermal Metal-Metal Bond Contraction of γ-Alumina-Supported Pt
Catalysts. J. Am. Chem. Soc. 2006, 128, 12068–12069.
(57) Dietrich, P. J.; Lobo-Lapidus, R. J.; Wu, T.; Sumer, A.; Akatay, M. C.; Fingland, B. R.; Guo, N.;
Dumesic, J. A.; Marshall, C. L.; Stach, E.; Jellinek, J.; Delgass, W. N.; Ribeiro, F. H. Aqueous
Phase Glycerol Reforming by PtMo Bimetallic Nano-Particle Catalyst: Product Selectivity and
Structural Characterization. Top. Catal. 2012, 55, 53–69.
(58) He, D. H.; Wakasa, N.; Fuchikami, T. Hydrogenation of Carboxylic Acids Using Bimetallic
Catalysts Consisting of Group 8 to 10, and Group 6 or 7 Metals. Tetrahedron Lett. 1995, 36,
1059–1062.
(59) Chia, M.; Pagán-Torres, Y. J.; Hibbitts, D.; Tan, Q.; Pham, H. N.; Datye, A. K.; Neurock, M.;
Davis, R. J.; Dumesic, J. A. Selective Hydrogenolysis of Polyols and Cyclic Ethers over
ACS Paragon Plus Environment
26

Page 27 of 29
ACS Catalysis
1
2
3
4
5
6
7
8
9
Bifunctional Surface Sites on Rhodium-Rhenium Catalysts. J. Am. Chem. Soc. 2011, 133,
12675–12689.
(60) Koso, S.; Furikado, I.; Shimao, A.; Miyazawa, T.; Kunimori, K.; Tomishige, K. Chemoselective
Hydrogenolysis of Tetrahydrofurfuryl Alcohol to 1,5-Pentanediol. Chem. Commun. 2009, 2035–
2037.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(61) Beamson, G.; Papworth, A. J.; Philipps, C.; Smith, A. M.; Whyman, R. Selective Hydrogenation
of Amides Using Rh/Mo Catalysts. J. Catal. 2010, 269, 93–102.
(62) Mizugaki, T.; Nagatsu, Y.; Togo, K.; Maeno, Z.; Mitsudome, T.; Jitsukawa, K.; Kaneda, K.
Selective Hydrogenation of Levulinic Acid to 1,4-Pentanediol in Water Using a Hydroxyapatite-
Supported Pt-Mo Bimetallic Catalyst. Green Chem. 2015, 17, 5136–5139.
(63) Mitsudome, T.; Miyagawa, K.; Maeno, Z.; Mizugaki, T.; Jitsukawa, K.; Yamasaki, J.; Kitagawa,
Y.; Kaneda, K. Mild Hydrogenation of Amides to Amines over Platinum-Vanadium Bimetallic
Catalyst. Angew. Chemie Int. Ed. 2017, 8531, 9381–9385.
(64) Toyao, T.; Hakim Siddiki, S. M. A.; Kon, K.; Shimizu, K. The Catalytic Reduction of Carboxylic
Acid Derivatives and CO2 by Metal Nanoparticles on Lewis-Acidic Supports. Chem. Rec. 2018,
18, 1374–1393.
(65) Matsubu, J. C.; Yang, V. N.; Christopher, P. Isolated Metal Active Site Concentration and
Stability Control Catalytic CO2 Reduction Selectivity. J. Am. Chem. Soc. 2015, 137, 3076–3084.
(66) Kecskés, T.; Raskó, J.; Kiss, J. FTIR and Mass Spectrometric Study of HCOOH Interaction with
TiO2 Supported Rh and Au Catalysts. Appl. Catal. A Gen. 2004, 268, 9–16.
(67) Bobadilla, L. F.; Santos, J. L.; Ivanova, S.; Odriozola, J. A.; Urakawa, A. Unravelling the Role of
Oxygen Vacancies in the Mechanism of the Reverse Water-Gas Shift Reaction by Operando
DRIFTS and Ultraviolet-Visible Spectroscopy. ACS Catal. 2018, 8, 7455−7467.
(68) Gaur, S.; Wu, H.; Stanley, G. G.; More, K.; Kumar, C. S. S. R.; Spivey, J. J. CO Oxidation
Studies over Cluster-Derived Au/TiO2 and AUROliteTM Au/TiO2 Catalysts Using DRIFTS. Catal.
Today 2013, 208, 72–81.
(69) Mironenko, A. V.; Vlachos, D. G. Conjugation-Driven “Reverse Mars-van Krevelen”-Type Radical
Mechanism for Low-Temperature C–O Bond Activation. J. Am. Chem. Soc. 2016, 138, 8104–
8113.
(70) Murugappan, K.; Anderson, E. M.; Teschner, D.; Jones, T. E.; Skorupska, K.; Román-Leshkov,
Y. Operando NAP-XPS Unveils Differences in MoO3 and Mo2C during Hydrodeoxygenation. Nat.
Catal. 2018, 1, 960–967.
ACS Paragon Plus Environment
27

ACS Catalysis
Page 28 of 29
1
2
3
4
TOC
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(8.5 cm × 4.4 cm)
ACS Paragon Plus Environment
28

Page 29 of 29
ACS Catalysis
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
TOC
1083x571mm (96 x 96 DPI)
ACS Paragon Plus Environment