CO2 hydrogenation to formic acid over heterogenized ruthenium catalysts using a fixed bed reactor with separation units

Article abstract of DOI:10.1039/c9gc03685g

Along with the mitigation of CO₂ emission, recently, the CO₂-derived formic acid process has drawn attention as a promising platform for the renewable-energy-derived hydrogen storage cycle by using formic acid as a liquid organic hydrogen carrier (LOHC). Here, a heterogenized Ru molecular catalyst on a bpyTN-30-CTF support is prepared and successfully implemented in an integrated trickle-bed reactor system for continuous CO₂ hydrogenation to produce formic acid. The bpyTN-30-CTF support with an alternative structure of the bpy and TN motif increases the porosity and metal anchoring sites. The Ru/bpyTN-30-CTF catalyst prepared using the bpyTN-30-CTF support displays sufficient catalytic activity for commercialization. Under the continuous process, the catalyst exhibits substantial catalytic performance with the highest productivity of 669.0 g_form. g_cat^-1 d^-1 with CO₂ conversion of 44.8% for a superficial gas velocity of 72 cm s^-1. Furthermore, the catalyst shows excellent stability in the continuous hydrogenation process with a trickle-bed reactor over 30 days of operation, reaching a total turnover number of 524?000 without any significant deactivation. Based on kinetic data, a new process to produce formic acid by CO₂ hydrogenation has thus been proposed here.

Full text of DOI:10.1039/c9gc03685g

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DOI: 10.1039/C9GC03685G
ARTICLE
CO hydrogenation to formic acid over heterogenized ruthenium
2
catalysts using a fixed bed reactor with separation units
Received 00th January 20xx,
Accepted 00th January 20xx
a
b
c
c
Kwangho Park,† Gunniya Hariyanandam Gunasekar,† Seong-Hoon Kim, Hongjin Park, Samhwan
d
d
,b
,c
Kim, Kiyoung Park, Kwang-Deog Jung, * and Sungho Yoon*
DOI: 10.1039/x0xx00000x
2 2
Along with the mitigation of CO emission, recently, the CO -derived formic acid process has drawn attention as a
promising platform for the renewable-energy-derived hydrogen storage cycle by using formic acid as a liquid organic
hydrogen carrier (LOHC). Here, a heterogenized Ru molecular catalyst on a bpyTN-30-CTF support is prepared and
2
successfully implemented in an integrated trickle-bed reactor system for continuous CO hydrogenation to produce formic
acid. The bpyTN-30-CTF support with the alternative structure of bpy and TN motif enhances the porosity and metal
anchoring sites. The Ru/bpyTN-30-CTF catalyst prepared using the bpyTN-30-CTF support displays sufficient catalytic
activity for commercialization. Under the continuous process, the catalyst exhibits substantial catalytic performance with
–1
the highest productivity of 669.0 gform.
Furthermore, the catalyst shows excellent stability in the continuous hydrogenation process with a trickle-bed reactor over
0 days of operation reaching the total turnover number of 524,000 without any significant deactivation. Based on kinetic
data, a new process to produce formic acid by CO hydrogenation has thus been proposed here.
g
2
cat d–1 with CO conversion of 44.8% for a superficial gas velocity of 72 cm s–1.
3
2
and low toxicity. In addition, the milder energy requisition for
Introduction
the conversion than that of other CO -based LOHCs renders
2
1
2,13
formic acid highly attractive for large-scale processes
.
However, industrial implementation of the formic acid
hydrogen storage cycle through hydrogenation and
dehydrogenation remains sluggish due to the hurdles suffered
by the efficiency. Therefore, the reversible hydrogen charge
and discharge processes need to be conducted using
appropriate catalytic systems to overcome the kinetic and
thermodynamic barriers.
Chemical storage of renewable energy in a secondary energy
carrier like hydrogen by water splitting has garnered great
1
,2
interest , because hydrogen has a high gravimetric energy
density of 33.3 kWh kg–1 and produces only water as a
byproduct during combustion. However, its low volumetric
–1
energy density of 2.5 W h L poses a hurdle in its use as an
3
energy carrier . Therefore, liquid organic hydrogen carriers
(LOHCs) have been intensively investigated because of their
facile handling for transportation and the scope of hydrogen
4
,5
release by dehydrogenation depending on the purpose .
Utilization of CO as a platform molecule to produce LOHCs
has been considered a promising strategy for efficient
2
hydrogen storage systems and an alternative method for CO
2
2
Scheme 1. CO -based reversible hydrogen storage cycle using formate as a LOHC
6
–11
storage at the same time . Particularly, CO
2
-derived formic
acid is a relevant candidate for hydrogen storage because it For decades, remarkable progress has been made in the
can provide 4.4 wt% of hydrogen with perfect atom efficiency development of efficient catalytic systems to close the formic
1
4–16
acid-based hydrogen storage cycle
. As a state of the art in
dehydrogenation, practical application of formic acid as a
hydrogen carrier has been boosted by a smart attempt made
by Gabor Laurenczy and coworkers in the École Polytechnique
Fédérale de Lausanne and GRT groups. They could generate
nominal power of 850 W with electrical efficiency of 45% from
a. Department of Applied Chemistry, Kookmin University, 77 Jeongneung-ro,
Seongbuk-gu, Seoul, Republic of Korea.
Clean Energy Research Centre, Korea Institute of Science and Technology, P.O.
b.
Box 131, Cheongryang, Seoul, Republic of Korea
Department of Chemistry, Chung Ang University, 84 Heukseok-ro, Dongjak-gu,
c.
1
7
Seoul, Republic of Korea
Department of Chemistry, KAIST, 291 Daehak-ro, Yuseong-gu, Daejeon, Republic
formic acid using a Ru-based catalyst . In addition, Pidko and
co-workers have recently devised Ru- catalyzed integrated 25-
kW formic acid-to-power systems, and successfully
demonstrated that this compact electricity generator could be
d.
of Korea.
†These authors contributed equally to this work.
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
1
8
applied to the scale of a city bus . However, in terms of
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DOI: 10.1039/C9GC03685G
2
Figure. 1 Structural representation of Ru/bpyTN-CTFs synthesis and a schematic of structured CO hydrogenation in trickle-bed reactor
2
sustainability, formic acid availability from CO hydrogenation induced by a rationally designed catalyst support such as
on a large scale and its affordable price are crucial enhanced porosity and the presence of various heteroatom
prerequisites for the widespread utilization of the technique ligand sites enable diversification of heterogenized catalytic
commercially. Meanwhile, the hydrogenation process systems. Previously, we reported a Ru molecular catalyst
significantly lags behind the dehydrogenation owing to the low heterogenized on a bipyridine functionalized covalent triazine
efficiency. Therefore, the development of a novel system for framework (CTF), which exhibited high efficiency with
the production of formic acid by CO
remained challenging for decades in attempts to close the reactor
2
hydrogenation has exceptional stability during successive runs in a batch
4
0-42
. The consequent robustness and outstanding
hydrogen cycle and has shown fruitful results.
In the last decades, homogeneous catalytic systems for CO
catalytic activity of the CTF-based molecular Ru catalyst
encouraged us to investigate the continuous production of
2
2
hydrogenation to formic acid have been intensively formate via CO hydrogenation. Very recently, Urakawa’s
investigated to demonstrate superior catalytic activity and group reported that Ir molecular catalyst heterogenized on
selectivity16,19–24. Meanwhile, continuous processes with CTF was successfully demonstrated to be active under high-
homogeneous systems have been conducted at the laboratory pressure condition for continuous CO
2
hydrogenation to
scale and patented by chemical companies25–33. However, formic acid. Further, they elucidated that the rich nitrogen
homogeneous catalysts should be completely separated from content on the pore surface of CTF support is to assist for the
the reaction mixture to be reused; the incomplete recovery of carbon dioxide in close proximity to the active site of the
homogeneous catalyst makes formic acid decomposed during catalyst. However, it is still required to attain high productivity
4
3
the separation process. Toward the realization of formic acid for commercial feasibility . In this paper, we present a Ru
production, heterogeneous systems for catalytic CO molecular catalyst heterogenized on a bipyridine (bpy)-
2
hydrogenation are very attractive because they make catalyst terephthalonitrile (TN) mixed-CTF (Ru/bpyTN-30-CTF) system
separation easy2
1,34–37
2
. Fachinetti and coworkers have for the continuous hydrogenation of CO to formate in a
attempted the formation of a total of 1.326 kg of formate trickle-bed reactor, which is a conventional fixed-bed reactor
4
4
using a reactor with supported gold catalyst that could be (Figure 1) . The heterogenized catalyst produced formate at
3
8
–1 –1
cat 2
with a CO conversion of 44.8 % for a
reused for 37 days without fastidious separation . Walter 669.0 gform.
Leitner’s group has used immobilized catalysis systems with superficial gas velocity of 72 cm s , also exhibiting excellent
supercritical CO flow for the continuous process of CO stability with the total turnover number of 524,000 for 30 days
g
d
–1
2
2
9
3
hydrogenation, and successfully produced pure formic acid . without deactivation. This may be attributed to the enhanced
However, the slurry reactor requires catalyst separation and surface area induced by the TN-based skeletal framework that
the disintegration of catalyst particles results in significant helps the reactive metal centers to be more efficiently
catalyst loss and further commercial implementations is dispersed on the support pore surface, which plays a key role
hindered by the low efficiency of heterogeneous systems.
in ensuring improved interaction of reagents with the catalytic
For the preparation of heterogenized catalysts, immobilization active sites, as well as the stable binding environment arising
of a homogeneous catalyst on catalytic supports via the from the bidentate coordination of the RuCl
3
-bpy motif.
formation of covalent bonds has garnered much interest in the
2
context of CO hydrogenation to formic acid, as the method
Experimental
Materials and instrumentation
combines the advantages of homogeneous and heterogeneous
systems3 . In particular, various advantageous properties
4–37
2
| J. Name., 2012, 00, 1-3
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ARTICLE
All chemicals were purchased from commercial suppliers and (MicroActive Autopore 9600, Micromeritics Inst Inc, USA) in the
View Article Online
DOI: 10.1039/C9GC03685G
used without further purifications. 2-bromo-5-cyanopyridine pressure range of 0.2~61,000 psi.
(
>99%) and terephthalonitrile (>98%) were purchased from
T.C.I. chemicals. Ruthenium(III) chloride hydrate, zinc(II)
chloride (ZnCl ) (>98%), nickel chloride hexahydrate, lithium
chloride, triethylamine (Et N), zinc dust, iodine, anhydrous DCBPY and TN were mixed in varied molar ratios and ground in
Synthesis of bpyTN-mixed CTFs
2
3
methylene chloride, and anhydrous dimethylformamide were a mortar thoroughly to afford homogenously mixed powders
purchased from Sigma Aldrich. 5,5’-dicyano-2,2’-bipyridine (Table S1). The reagents were transferred to 50 mL glass
4
5
(
DCBPY) was synthesized according to a previous report . CO
2
ampoules and dried under vacuum overnight. Then, ZnCl
2
(5
and N were obtained from Sinyang Gas Industries.
2
eq for each ampoule) was charged into the ampoules in a
Fourier transform infrared (FT-IR) analysis was performed on a glove box, which were then taken out outside and sealed by a
Nicolet iS 10 with MCT detector (Thermo Fisher Scientific) by flame. The ampoules were heated in a furnace following the
the KBr pellet technique. Scanning electron microscopy (SEM) preset temperature program (Table S1). After the reaction, the
and energy dispersive spectrometry (EDS) measurements were furnace was cooled to room temperature. The crude product
performed on a JEOL LTD (JAPAN) JEM-7610F operated at an was ground well and stirred with 200 mL of a 1 M HCl aqueous
accelerating voltage of 20.0 kV. N
measurements were conducted at 77 K using a BELSORP mini II with 40 mL of water and this process was repeated. The
JAPAN). The samples were degassed for 1 day at 150 °C sample was then refluxed with 200 mL of the 1 M HCl aqueous
2
adsorption–desorption solution for 2 h. The black powder was filtered and washed
(
before the measurements. Powder X-ray diffraction (PXRD) solution overnight. After this, the afforded powder was filtered
was performed on a RIGAKU D/Max 2500 V using Cu (40 kV, 30 and washed with a 1 M HCl aqueous solution, water,
mA) radiation. Elemental analysis (EA) was performed with an methanol, acetone (3 × 200 mL for each solvent). The black
elemental analyzer (Vario Micro cube, Germany). solid was dried under vacuum at 150 °C overnight.
Thermogravimetric analysis (TGA) and differential thermal
Synthesis of Ru/bpyTN-30-CTF
analysis (DTA) were performed on a Q600 analyzer (TA
Instrument, US). The experiments were carried out at a bpyTN-30-CTF (9.38 g) was charged into a solution of RuCl
3
heating rate of 10 °C per minute up to 700 °C under a nitrogen (0.623 g) and anhydrous methanol (300 mL) in a 500 mL
atmosphere. The ruthenium content was determined by round-bottomed flask with a condenser and stirred for 30 min
inductively coupled plasma optical emission spectrometry under a nitrogen atmosphere and refluxed for 48 h. After the
(ICP-OES) (iCAP-6000, Thermo fisher scientific) using a reaction, the mixture was cooled to room temperature and the
microwave-assisted acid digestion system (MARS6, black colored powder was filtered (filtrates were kept for ICP-
CEM/U.S.A.). X-ray photoelectron spectroscopy (XPS) analysis OES measurements) and washed with an excess of methanol
was performed on an ESCA 2000 (VG Microtech) at a pressure (3 × 500 mL), acetone (3 × 100 mL), and methylene chloride (3
of ~3 × 10-9 mbar using Al Ka as the excitation source (hγ = × 100 mL). The filtered powder was dried under vacuum at 100
1
486.6 eV) with a concentric hemispherical analyzer. High- °C overnight.
angle annular dark-field imaging transmission electron
microscopy (HAADF-TEM) analyses were performed on a Jeol
Hydrogenation procedure in trickle-bed reactor
JEM-2100F HRTEM operated at 200 kV. The samples were Continuous hydrogenation was carried out in homemade
prepared by dispersing in ethanol and placed on a carbon film stainless-steel tubular reactor with an internal diameter of 7
grid by dropping and analyzed after drying under vacuum at 60 mm and length of 460 mm. In a typical run, the 1.5 g of
°
C overnight. The concentration of formate was determined by Ru/bpyTN-30-CTF powder (particle size = 50-200 μ m) was
high-performance liquid chromatography (HPLC) on an Aminex charged in the middle of the vertically positioned reactor with
HPX-87H column with a RI detector using 5 mM of H SO as an the catalyst height of 65 mm and covered by glass wools. To
eluent. X-ray absorption fine structure (XAFS) measurements prevent back flow of catalyst, the remaining empty space was
were conducted by the 7D beamline of Pohang Light Source filled with 2.5 mm glass beads. After flushing with H and CO
PLS-II, 3.0 GeV, South Korea). The incident X-ray beam was the reactor was pressurized to the desired pressure (60–140
monochromatized using Si(111) double crystal bar) under varied feed gas (CO :H =1:1) flows and heated to
monochromator. The spectra for K-edges for Ru (E = 22,117 60–140 °C before the reaction. The pressure was maintained
eV) were obtained in the fluorescence mode in ambient at the desired temperature using a back-pressure regulator
atmosphere. Gas chromatography was analysed by YL-6500 and the H gas flow rate was controlled by the mass flow
Younglin, Rep. of Korea) equipped with a Flame ionization and controller. Liquid CO supply from the siphon cylinder was
thermal conductivity detectors, and Mol Sieve 13X and controlled using a high-pressure liquid pump and gasified by
porapak N columns using N as a carrier gas (20 mL/min). the heating line before addition to the reactor. The distilled
Calibrations were determined with a gas mixture containing water and Et N were respectively supplied to the reactor using
C , H a high-pressure liquid pump. All the gaseous and liquid feeds
2
4
2
2
,
(
a
2
2
0
2
(
2
2
3
1
3
1
4
known amounts (100, 1000, 5000 ppm) of CO and CH .
NMR spectra were recorded on a Bruker Ascend 400 MHz. were thoroughly homogenized and equilibrated in
Mecury porosimetery was obtained using Mecury porosimeter temperature through the tubular preheating zone (7 mm x 460
mm), which was entirely filled with 2.5 mm glass beads, before
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Journal Name
entering into the reactor. The liquid product was collected and
analyzed using high-performance liquid chromatography and
nuclear magnetic resonance to determine acid to amine ratio
View Article Online
DOI: 10.1039/C9GC03685G
(AAR) and the concentration of formate. The gaseous product
was collected using gas sampling bag and analyzed by gas
chromatography. The production rates of formate, superficial
gas and liquid velocities (u and u ), formate productivity, CO
g l 2
conversion, and total turnover number were then calculated
using eqn. (1-6):
Molar production rate of HCOO–
molform./h
( )
Figure 2. FT-IR spectra of bpy-CTF-250 (gray), bpyTN-1-CTF-250 (black), bpyTN-5-CTF-
=
3
3
Et N flow rate molEt N/h × AAR
( )
2
50 (blue), bpyTN-10-CTF-250 (orange), and bpyTN-30-CTF-250 (red).
(
1)
Production rate of HCOO–
molar production rate of HCOO– × M.W of HCOO–
molform./h
( )
gform./h
( )
CTF support, bpy, is expensive. Accordingly, the mixed-linker
strategy was introduced to prepare the function-enhanced and
cost-effective CTF support to reduce the catalyst preparation
=
(2)
5
2–54
volumetric feed flow rate (ml/s)
cross sectional area of the reactor (cm2)
cost through the use of commercially affordable linkers
.
Superficial velocity (cm/s) =
For this purpose, the mixed CTF supports were designed to
comprise TN as building blocks for the skeletal structure and
bpy as the ligand moiety to stabilize the active metal
component. The bpyTN-mixed CTFs were prepared with
different ratios of bpy to TN under ionothermal conditions
(3)
HCOO–
)
productivity
Formate
(
production rate of HCOO–
charged catalyst mass
gform./h
)
(
2
with ZnCl at 250 °C for 72 h to monitor the intact chemical
=
× 24 (h/d)
(
gcat.
)
structure preserving from thermal graphitization. FT-IR
spectroscopy was used to analyze the functional groups on the
architecture of the mixed CTFs (Figure 2). The results revealed
vibrations corresponding to the bpy-based motif at 1560 and
(
4)
molar production rate of HCOO–
molform./h
( )
CO2 conversion =
× 100
–1
–1
1
595 cm , the TN-based motif at 1580 cm , implying C=N and
CO2 Feed rate (molCO /h)
2
C=C stretching of triazine and pyridine, which indicated the
(
5) successful formation of a cooperative structure consisting of
bpy and TN in the supports. As the ratio of TN to bpy
increased, the vibration frequency of TN increased; on the
other hand, that of bpy decreased but remained as a shoulder
Total turnover number
molar production rate of HCOO–
molform./h
( )
=
× operation time (h)
charged molar content of Ru (molRu )
peak, indicating the unchanged presence of bpy. The isotherm
revealed that N sorption for bpyTN-mixed CTFs synthesized at
50 °C was almost negligible (Figure S1), which was due to the
2
(6)
2
limited accessibility of the adsorbent into the narrow pores.
To enhance the porosity of the bpyTN-mixed CTFs, the
preparation temperature was increased to 400 °C, which is
advisable for facile incorporation of metal complexes. Through
Results and Discussion
Synthesis and characterization of heterogeneous Ru/bpyTN-
0-CTF catalyst
3
the N
of bpyTN-mixed CTFs was confirmed. The adsorption of N
the mixed-CTFs synthesized at 400 °C increased significantly
Figure S2). The sorption followed the typical shape of a type I
2
adsorption–desorption isotherm analysis, the porosity
in
For an industrially viable catalytic process, several requisites
need to be fulfilled by the catalyst, such as long-term stability
as well as high performance, and feasibility of affordable large-
scale synthesis. In this respect, a CTF-based material is a
relevant catalytic support for our purpose as it offers
advantages such as high robustness and thermochemical
2
(
isotherm, suggesting the presence of abundant micropores. In
particular, as the TN ratio compared to bpy increased, the BET
surface area of bpyTN-mixed CTF also increased (Table S2),
indicating that the TN-based skeletal structure in the
framework drove the high surface area on the CTF supports.
Further, elemental analysis was performed to track the outline
of the structural change for bpyTN-CTF supports, in
comparison to that of bpy-CTF and CTF-1 (Table 1). CTF-1 was
4
6
stability . Accordingly, it has been extensively reported that
CTF-based heterogenized catalysts show excellent activity and
stability in various applications, particularly CO
2
hydrogenation4
0-42, 46–51
. However, given the continuous flow
conditions of gas/liquid reagents in the process, the catalyst is
required to possess an enhanced surface area for high
dispersion of metal centers. Furthermore, additional
considerations are required for an economically reasonable
synthesis of CTF on a large scale, because the source of the
4
6
prepared using TN only . In the evaluation, C/N ratio of bpy-
CTF was found to be 2.59, which was very similar to the
calculated value of 2.57. However, as the proportion of TN
increased in the support composition, the difference between
4
| J. Name., 2012, 00, 1-3
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Table 1. Elemental analysis of bpyTN-CTFs
ARTICLE
View Article Online
DOI: 10.1039/C9GC03685G
a
b
c
Sample
C
N
H
C/N
C/N
Differ.
0.02
0.52
1.19
1.34
2.41
2.36
bpy-CTF
bpyTN-1-CTF
bpyTN-5-CTF
bpyTN-10-CTF
bpyTN-30-CTF
CTF-1
59.72
63.88
71.71
71.14
73.12
73.79
23.05
18.90
16.42
15.37
12.65
12.74
3.13
3.26
2.62
2.58
2.45
2.47
2.59
3.38
4.37
4.63
5.78
5.79
2.57
2.86
3.18
3.29
3.37
3.43
a
Experimentally obtained C/N ratio. bTheoretically calculated C/N ratio.
c
Difference between the experimentally obtained and theoretically calculated
C/N ratio.
the calculated and experimental C/N ratios gradually increased
from 0.52 for bpyTN-1-CTF to 2.41 for, bpyTN-30-CTF
indicating the gradually increasing N loss from the support
structure. This result implied that the bpy-based structure
Figure 3. Atomic dispersion of Ru by EDS mapping (top left), HAADF-STEM image (top
showed relatively high thermal stability than the TN-based right), deconvoluted C 1s and Ru 3d XPS spectrum (bottom left), and the normalized
3
structure and the thermal graphitization phenomenon was XANES spectra at the Ru K-edge (bottom right, a) the k -weighted EXAFS data in R space
for the Ru/bpyTN-30-CTF (bottom right, b)
predominant with the TN-based structure at high synthetic
temperatures. Therefore, it is concluded that the higher
EDS mapping analyzed the homogeneous distribution of Ru
degree of thermal graphitization on TN-based structure
atoms throughout the support, but no distinct Ru particles
induced the high surface area to the CTF-based support, which
were found in the HAADF-TEM measurements, suggesting that
5
5
is consistent with the previous result .
In the FT-IR
Ru cations were tightly bounded to the binding sites provided
by the support (Figure 3, top left and right, and Figure S5). XPS
was measured to determine the more accurate coordination
state of Ru atoms on the bpyTN-30-CTF. The observed binding
energy of Ru 3d5/2 was 282.01 eV, which was fitted to Ru3+
measurements, vibrations were observed in the range of
450–1600 cm–1 (C=N or C=C) and 1000–1400 cm–1 (C-N or C-
1
C), which were broadened due to the thermal graphitization of
CTF structure5 ; however, this may still indicate the
presence of the bipyridine and triazine site on the CTF support
5–57
5
8
oxidation state (Figure 3, bottom left) . It also showed a
(Figure 2).
5
9
3 2
somewhat reduced binding energy than RuCl xH O , which
We examined the catalytic activity of the prepared four bpyTN
was ascribed to the increased electron density of Ru due to the
strong interaction with N-based coordination sites of the
support. Ru/bpyTN-30-CTF was also assessed with XAFS
analysis (Figure 3, bottom right). Consequently, the normalized
shape and edge position in the Ru K-edge X-ray absorption
near edge structure (XANES) spectrum were found to be
o
-
CTFs as preliminary tests under 80 MPa and 120 C for 2h
2 2
(CO :H =1:1) in a batch reactor. The 3 wt% of Ru was
metalated to bpyTN-CTFs. Among them, the bpyTN-30-CTF
based catalyst showed the highest activity (Table S3), which
may be attributed to higher dispersion of Ru cation on the
pore surface of bpyTN-30-CTF support than other bpyTN-
mixed CTFs. Therefore, bpyTN-30-CTF was chosen as a catalytic
support for further studies. The catalyst was also characterized
through the nitrogen sorption isotherm analysis, and it was
2
2126.7 eV, which suggested the presence of Ru in the +3
oxidation state; this result corresponds to the XPS analysis and
a previous study. In the extended X-ray absorption fine
structure (EXAFS) for Ru/bpyTN-30-CTF, a broad band from
2
confirmed that the N uptake and BET surface area decreased,
1
.5~2.5 Å was observed and this may be assigned to the Ru-Cl
2
–1
when Ru was metalated to bpyTN-30-CTF, i.e.,1010 m g for
the Ru/bpyTN-30-CTF compared to the bpyTN-30-CTF support,
peak on ~1.9 Å and to the Ru-N peak on ~1.7 Å,
6
0,61
respectively
. Therefore, it was concluded that the isolated
2
–1
i.e., 1251 m g , suggesting the partial occupation of pores by
immobilized RuCl units (Table S2 and Figure S3). To examine
Ru complex motif was successfully immobilized onto N sites
originating from the surface of the bpyTN-30-CTF support.
3
the thermal stability of the catalyst, TGA was performed. The
result revealed that the weight loss of 4.0 % for Ru/bpyTN-30-
Catalytic performance tests of Ru/bpyTN-30-CTF with trickle-bed
o
CTF was observed up to 400 C except for the 3.3 % weight loss
reactor system for continuous CO
2
hydrogenation to formate
by adsorbed water. This suggested that the catalyst possessed
Hydrogenation of CO with TBR was driven by a plug-flow type
2
high thermal stability for high reaction temperature in CO
2
reaction in which gas and liquid reactants were continuously
introduced into a fixed-bed catalyst. Because of the short
residence time of reactant feed in TBR the diffusion limitation
was important for the reaction. Although this type of reactor
generally shows a rather lower activity than the stirred batch
hydrogenation. ICP-OES measurements were carried out for
both the catalyst and the filtrate to grasp the accurate Ru
loading amount. The result showed that the Ru content in the
catalyst was 3.03 wt% and was negligible for the filtrate, which
indicates almost complete metalation to the support (Table
S4).
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DOI: 10.1039/C9GC03685G
Figure 4. Catalytic CO
2
hydrogenation activities screening in the trickle-bed reactor with the influence of reaction temperature (top left), pressure (top right), concentration of Et
3
N
(
bottom left), and superficial gas velocity (bottom right): (solid line) CO conversion, (dashed line) formate productivity.
2
reactor, the simple design and operation have advantages over increase in the solubility of gas reactants in the liquid flow
the stirred tank reactor. Additionally, no requirement of the increasing the reaction pressure.
recovery of catalysts during the reaction makes this type of For the investigation of the effect of the Et
3
N concentration,
N feed concentration was adjusted by varying the
amount of water in the liquid feed flow by fixing the Et N flow
reactor feasible for commercialization.
the Et
3
Under the TBR process, the catalyst selectively converted CO
2
3
-
1
to formate with side products generation only in ppm scale rate for the superficial gas velocity of 24 cm s , 120 °C, and 12
such as CO (300-600 ppm), CH (<5 ppm), and CH OH MPa (Figure 4, bottom left and Table S9, entry 10-14). At a
negligible to detect) (Figure S8-10), representing less than 1 % feed concentration of 1 M aqueous Et N, the formate
with 0.40 of AAR and CO
4
3
(
3
–1
–1
of carbon loss in carbon balance. Therefore, the CO
conversion (eqn. 5) was determined based on generated conversion of 40.8% at the superficial gas velocity of 24 cm s .
formate amount relative to the input CO . The temperature When the Et N concentration was increased, the catalyst
effect on the catalytic activity through the trickle bed was showed improved catalytic activity, reaching 326.8 gform
investigated under the conditions of 100 bar and an aqueous 2 d with 0.61 of AAR and CO
M Et
2
productivity was 204.9 gform
g
cat
d
2
-1
2
3
–1
g
cat
–1
2
conversion of 65.1% at superficial
N solution for a superficial gas velocity of 24 cm s and gas velocity of 24 cm s for 3 M of Et N. However, at the Et
-1
-1
3
3
3
N
the temperatures of 60, 80, 100, and 120 °C (Figure 4, top left concentration of 5 M, an abrupt decrease in the productivity of
and Table S9, entry 1-5) in terms of formate productivity and the formate was confirmed. Clear phase separation was
CO
2
conversion. The catalyst showed a formate productivity of observed in the product solution for the 5 M Et
3
N feed. The
–1
–1
2
5.9 gform
g
cat
d
with 0.05 of acid to amine ratio (AAR) in the reaction did not occur in neat conditions without water. This
conversion of 5.2% at 60 °C, and both the result supports that water is required for the formation of
product and CO
2
productivity and CO
the reaction temperature. Here, AAR means a molar ratio of aqueous phase. Et
formic acid to Et N in reaction products. Finally, the However, in the feed system of Et
performance of the catalyst showed a productivity of a 355.1 switchable polarity solvents (SPSs) during CO
2
conversion increased with an increase in bicarbonate and for the stabilization of formate adduct in the
N is immiscible with water (Figure S12).
N, H O and CO constitutes
hydrogenation
3
3
3
2
2
2
–1
–1
g
1
form
g
cat
d
with 0.67 of AAR and CO
2
conversion of 71.3% at process, the aqueous Et
3
N solution became miscible through
+
-
40 °C. The effect of reaction pressure on the catalytic activity formation of Et
3
NH :HCO
3
in the presence of CO
2
at the Et
3
N
6
2
was also examined at the temperature of 120 °C and the concentration lower than 3.2 M (eqn. 7) .
superficial gas velocity of 24 cm s (Figure 4, top right and
-1
Table S9, entry 6-9). The productivity of formate tended to Et
3
N + CO
2
+ H
2
O ⇄ Et
3
NH + :HCO
3
–
(7)
increase proportionally with pressure. This is attributed to the
6
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Therefore, the maximum productivity at ca 3.0 M can be
closely related to the miscibility of Et N and water through
bicarbonate formation in the presence of CO . Further, it was
found that the product miscibility is very much dependent on
the concentration of formic acid and feed Et N concentration
View Article Online
DOI: 10.1039/C9GC03685G
3
2
3
by the obtained ternary phase diagram at 28 °C (Figure S12). If
the concentration of formic acid is low, the product solution
can become immiscible depending on the concentration of
water and Et
in the feed of approx. 3.0 M Et
3
N. As a result, a further reaction was performed
N, since an AAR above 0.64 is
3
obtained and the solution is miscible.
In terms of energy, the higher water content in feed requires
higher energy consumption in the purification step to
concentrate the formic acid. Therefore, the molar ratio of Et
3
N
2
Figure 5. Long-term stability test of the Ru/bpyTN-30-CTF for CO hydrogenation
to CO was adjusted to 1.00, 0.75, and 0.50 in order to check
2
in trickle-bed reactor
the probability to decrease the amount of water and amine
solvent while the productivity was not affected so much.
To examine this phenomenon closely, the reaction was carried
out under the optimal conditions of 120 °C, 12 MPa, and 3M
and CO
2 3
conversion decreased as the feed molar ratio of Et N
to CO decreased; however, the AAR increased.
2
In order to test the stability of the catalyst in the continuous
process, the hydrogenation was carried out under the optimal
conditions of 120 °C, 12 MPa, and 3M Et
with a superficial gas velocity of 24 cm s- (Figure 5, bottom
right and Table S9, entry 26-54). The reaction products were
collected once every 24 hours. As a result, the catalyst
3
Et N feed concentration for varied feed flow rates in order to
confirm the dependence of catalytic performance on the
superficial gas velocity (Figure 4, bottom right and Table S9,
entry 15-25). During the reaction, although the use of a
3
N feed concentration
1
-1
-1
powdery catalyst (0.50 g ml of bulk density, 1.09 g ml and
3.8 % of porosity, Figure S3), no pressure drop was observed.
5
exhibited excellent stability for continuous CO
process reaching the total turnover number of 524,000 during
0-day operation with only less than 5 % decrease of catalytic
2
hydrogenation
This may contribute to small scale of the reaction size (only 1.5
g of catalyst amount was used) and the particle size was
enough for the reaction feed to pass thorough under the
conducted hydrogenation conditions. Meanwhile, since the
3
performance; a slight drop in catalytic performance was
observed on 13 -day stability test, because the reactant feed
supply might not stable for a short time. In order to
understand the leaching of Ru metal, the liquid phase products
collected for 24 h were measured by ICP-OES, showing that the
amount of Ru in the products was less than the detection limit
th
2 2
molar ratio of H to CO in the gas feed was maintained at 1:1
(stoichiometric molar ratio), there was no enrichment in the
feed gas by the recycling of the unreacted gas stream and little
purge is to enhance the process yield.
Under the optimal conditions with Et N/CO molar ratio of 1.0,
3 2
the formate productivity increased as the superficial gas
velocity decreased, reaching the highest productivity of a 699.
(<0.5 ppm). Meanwhile, 2.67 wt% of Ru content in the spent
catalyst after the 30-day process was confirmed, which is
equal to 0.0005 wt%/h of Ru leaching from the catalyst. This is
attributed to the stable coordination of the Ru atoms with the
stable binding provided by the abundant N-based sites on the
catalyst support derived from bipyridine or triazine groups.
After the reaction, additional measurements were carried out
to precisely understand the state of the spent catalyst. STEM
and EDS analysis found that no metal particles were present in
the spent catalyst after the 30-day reaction and the active
metal components were still uniformly distributed throughout
the support (Figure 6, top left and middle). Through further
EDS analysis, the amount of Cl was confirmed to have
decreased due to possible substitution by water and hydride
during the reaction, as it is known that Cl does not play a
substantial role in hydrogenation (Figure S11).
–
1
–1
g
form
g
cat
2
d with 0.42 of AAR and CO conversion of 44.8% at
-1
the superficial gas velocity of 72 cm s . As the molar ratio of
Et N to CO in feed flow decreased to 0.75, AAR in product
increased to 0.7 at the superficial gas velocity of 24 cm s ,
3
2
-1
–1
–1
reaching a productivity of 283.5 gform
g
cat
d
with CO
2
conversion of 56.9%. This means that the high proportion of
gas-phase reactants in the reaction caused itself to be
dissolved more in the reaction media, thereby improving the
mass transfer of the reagents by increasing the CO
2
solubility.
As the flow rate increased, the productivity of formate
–1
–1
increased as well, and reached 650.8 gform
g
cat
d
with an
AAR of 0.54 and CO conversion of 43.6% at the superficial gas
2
-
1
velocity of 72 cm s . Furthermore, as the amine ratio to CO
decreased to 0.5, the AAR increased to the maximum of 0.83,
2
Then, FT-IR and N
2
isotherm adsorption analysis was
6
3
attaining chemical equilibrium at the superficial gas velocity
of 24 cm s , affording 239.0 gform
conducted to observe the changes in the physical and chemical
catalyst structure (Figure 6, top right and bottom left). The
catalyst showed almost the same trend of IR spectrum ranges
and porosity as the fresh catalyst, suggesting that the catalytic
support structure was not decomposed or degraded by the
-1
–1 –1
cat 2
d with CO conversion
g
of 48.0%. With subsequent increase in the flow rate, the
–1
–1
productivity reached a 549.4 gform
g
cat
d with an AAR of 0.68
and CO conversion of 36.8% at the superficial gas velocity of
2
-1
7
2 cm s . Based on the results, the formate productivity
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DOI: 10.1039/C9GC03685G
Figure 6. Characterization of the spent Ru/bpyTN-30-CTF. Atomic dispersion of Ru by EDS mapping (top left), HAADF-STEM image (top middle), FT-IR spectra (top right, blue line for
3
fresh catalyst and red line for spent catalyst), N
EXAFS data in R space (bottom right)
2
sorption isotherm analysis (bottom left), the normalized XANES spectra at the Ru K-edge (bottom middle), and the k -weighted
+
–
harsh conditions of the CO
peaks emerged at 1948 and 2056 cm , indicating carbonyl and reboiler (eqn. 8), while all the Et
hydride, respectively, which were generated during the of the amine exchange column. The nBIMH :HCOO is
2
hydrogenation. In particular, new column, the nBIMH :HCOO with 1.0 AAR is produced from the
–1
3
N is produced in the overhead
+
–
6
4
hydrogenation process . The consequence of the oxidation introduced into formic acid separation column to produce
state change of Ru and the ligand exchange effects were pure formic acid (eqn. 9). A more details are described as
analyzed by XPS measurements (Figure 6, bottom middle). The follows.
binding energy of Ru in the spent catalyst was 281.92 eV,
which indicates that Ru still retained the 3+ oxidation state. Et
NH + HCOO + 푛BIM→푛BIMH + HCOO ― + Et
–
N
3
3
(8)
(9)
Further, this Ru binding energy decreased by 0.09 eV from 푛BIMH + HCOO ― →HCOOH + 푛BIM
82.01 eV for the fresh catalyst, which means that the
substituted ligands had a greater electron donation effect than From CO
the electronegative chloride. Consistent with this XPS analysis, produced in molar ratios of 0.8 with a CO
the Ru K-edge of the spent catalyst was slightly lower in energy at 120 °C, 12 MPa, feed Et N concentration of 3.0 M, feed
than that of the fresh catalyst due to the ligand exchange molar ratio of Et N to CO of 0.5, and superficial gas velocity of
under the hydrogenation (Figure 6, bottom right). In the EXAFS 24 cm s . Formic acid can be associated to Et N with a
N is 10.8.
2
+
–
2
hydrogenation, the Et
3
NH :HCOO adduct is
conversion of 48%
2
3
3
2
-1
3
6
5
spectrum, the Ru-Cl peak on 1.9 Å diminished while peaks maximum AAR molar ratio of 2.5 . The pKa of Et
3
+
from Ru-N on ~1.7 Å remained, indicating the substitution of Cl Due to the strong binding of Et
3
N and H in the cation of
+
into the other ligands and intact coordination of Ru and N sites Et
from the support; this result was consistent with XPS data. Et
3
NH , direct separation of formic acid from the adduct of
NH :HCOO is not achievable. Therefore, the separation
+
–
3
process was conducted with reference to a patent claimed by
Validation of formic acid process by CO
the trickle-bed reactor
2
hydrogenation through
+
–
BP chemicals to produce formic acid from the Et
3
NH :HCOO :
(
1) enrichment of formic acid by removing water and Et N
3
Here, we propose the feasible process scheme to produce from the reaction product, (2) amine exchange from
+
–
+
–
formic acid from CO
2
hydrogenation here. Fresh feed of CO
2
3
Et NH :HCOO to nBIM using nBIMH :HCOO . Then, (3) formic
+
–
and hydrogen is introduced into the formic acid formation acid can be produced from the nBIMH :HCOO by a
6
6
reactor with the recycled gases and the recycled water and distillation . The enrichment of formic acid from 0.8 of AAR to
Et N. The liquid product from the reactor is feeding to the 2.3 of AAR could be achieved by evaporation using a silver-
evaporator to concentrate Et
3
+
–
3
NH :HCOO from ~0.83 AAR to coated packed glass column (column I.D.: 1 inch, column
+
–
~2.3 AAR. Then, the concentrated Et
3
NH :HCOO adduct with length: 120 cm, packing material: 1 cm
~
2.3 AAR is combined with n-butyl imidazole (nBIM) and
+
–
formate adduct (nBIMH :HCOO ), (0.18 AAR) which is
introduced into amine exchange column. In amine exchange
8
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View Article Online
DOI: 10.1039/C9GC03685G
2
Figure 7. Schematic representation of an integrated TRB reactor system for continuous CO hydrogenation to produce pure formic acid
rash ring) without the recycling of the top product. The was 160 cm and the metal random packing was used. The feed
operating pressure was 150 mmHg. The feed flow rate (Et N: flow rate (formic acid: 1.08 g/min, nBIM: 2.92 g/min) was 4.0
.29 g/min, H O: 4.38 g/min, formic acid: 0.83 g/min) was 7.5 g/min, which was introduced through the preheater (100 °C).
3
2
2
g/min, which was introduced into the evaporating column The pressure was maintained at 50 mmHg and the
through a preheater (100 °C). Due to the low condensing temperatures of the overhead condenser and the cold trap
capacity of a lab-scale overhead glass, the overhead were maintained at 5 °C and –10 °C, respectively. The reboiler
temperature was subcooled to 5 °C and a cold trap (–15 °C) temperature was maintained at 145 °C at the steady state. 96
was placed before the vacuum pump. No decomposition mol% formic acid (1 g/min) was obtained from the overhead
products were observed by NMR analysis. The reboiler product and the molar ratio of formic acid to nBIM in the
temperature was 140 °C at the steady state and the bottom bottom product was 0.17 (15 mol formic acid %). To clarify
product flow rate was 1.5–1.6 g/min (AAR was approx. 2.3). whether pure formic acid could be separated or not, VLE of
An immiscible mixture of water and Et
overhead of the evaporator. The experimental results of Et
formic acid were corresponding to earlier reported vapor– apparatus. Based on the VLE data, pure formic acid can be
3
N was obtained in the nBIM and formic acid is necessary. The vapor–liquid
3
N- equilibrium was obtained (Figure S13) using iFisher VLE
6
5
liquid equilibrium (VLE) . The azeotropic concentration was produced from the distillation and it was observed that there
reported at the AAR of approx. 2.7. The experimental AAR was was an azeotropic point at approx. 15 mol% formic acid. The
less than the azeotropic composition of Et
3
N and formic acid. simulation of Pro-II for the VLE data gives 21 of theoretical
+
–
The Et
3
NH :HCOO adduct with the AAR of approx. 2.3 needed numbers of plates for 99.99% formic acid using NTRL and
+
–
to be converted to nBIMH :HCOO . The pKa of nBIM (6.9) and HOCV model.
the high boiling point of nBIM (244.8 °C) can make the amine Based on the above experiments, it can be concluded that the
+
–
exchange possible. For the distillation, the same column with separation scheme to produce formic acid from Et
random metal packing (5 mm) was used. The feed flow rate adduct is valid. Based on the experimental results, the process
Et N: 0.89 g/min, formic acid : 0.94 g/min, nBIM: 2.66 g/min) to produce formic acid by CO hydrogenation is proposed here
was 4.5 g/min, which was introduced through the preheater as shown in Figure 7.
100 °C). The pressure was maintained at 100 mmHg and the
3
NH :HCOO
(
3
2
(
overhead condenser temperature and cold trap were
maintained at 5 °C and –10 °C, respectively. The reboiler
temperature was maintained at 155 °C at the steady state.
Conclusions
In summary, heterogenization of a Ru molecular catalyst on a
bpyTN-30-CTF support synthesized by the mixed-linker
strategy was successfully conducted. The improved porosity
and the presence of well-defined binding sites for the metal
centers derived from the cooperative network structure of bpy
and TN led to both efficient dispersion of active metal sites on
+
–
3
Only Et N was obtained in the overhead and nBIMH :HCOO
adduct was obtained. There were no nBIM and formic acid in
the overhead product. Therefore, it can be concluded that the
amine exchange of the second step is valid.
Finally, formic acid could be separated from the
+
–
nBIMH :HCOO adduct. For the distillation, the column length
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Journal Name
1
1
1
0 M. Aresta, A. Dibenedetto and A. Angelini, ChemVie.wRAervti.c,le2O0n1lin3e,
14, 1709-1742.
1 Q. Liu, L. Wu, R. Jackstell and M. Beller, Nat. Commun., 2015,
, 5933.
the pore surface and increased electron donation ability to the
1
DOI: 10.1039/C9GC03685G
metal center, resulting in improved catalytic CO
2
hydrogenation activity. Moreover, the heterogeneous
character of the Ru/bpyTN-30-CTF allowed it to be suitably
exploited in the trickle-bed reactor system, which is a
representative fixed-bed reactor for multiphase reactions. In
6
2 A. Boddien, C. Federsel, P. Sponholz, D. Mellmann, R.
Jackstell, H. Junge, G. Laurenczy and M. Beller, Energy
Environ. Sci., 2012, 5, 8907-8911.
1
1
3 T. C. Johnson, D. J. Morris and M. Wills, Chem. Soc. Rev.,
the continuous CO
2
hydrogenation process, the Ru/bpyTN-30-
2
010, 39, 81-88.
CTF catalyst displayed significant catalytic performance with a
4 D. Mellmann, P. Sponholz, H. Junge and M. Beller, Chem. Soc.
Rev., 2016, 45, 3954-3988.
–1
–1
2
highest productivity of 669.0 gform. gcat h and CO conversion
-1
of 44.4 % for a superficial gas velocity of 72 cm s . Moreover, 15 B. Loges, A. Boddien, F. Gärtner, H. Junge and M. Beller, Top.
Catal., 2010, 53, 902-914.
superior long-term stability of the Ru/bpyTN-30-CTF catalyst
for 30 days reaching the total turnover number of 524,000
without noticeable deactivation demonstrated high feasibility
for industrial operation. Based on the results, a new process
1
1
6 K. Sordakis, C. Tang, L. K. Vogt, H. Junge, P. J. Dyson, M.
Beller and G. Laurenczy, Chem. Rev., 2017, 118, 372-433.
7 GRT group (2019), Hyform-PEMFC; https://grtgroup.swiss/
(accessed 19 july 2019).
has been proposed to produce formic acid by CO
2
18 R. van Putten, T. Wissink, T. Swinkels and E. A. Pidko, Int. J.
Hydrogen Energy, 2019. doi:10.1016/j.ijhydene.2019.01.153
hydrogenation with an integrated pilot-scale system for the
production of pure formic acid with a separation units for the
formate adduct, which could lead to a platform for an
19 W. Leitner, Angew. Chem. Int. Ed. Engl., 1995, 34, 2207-
221.
20 P. G. Jessop, T. Ikariya and R. Noyori, Chem. Rev., 1995, 95,
59-272.
21 W. Wang, S. Wang, X. Ma and J. Gong, Chem. Soc. Rev., 2011,
0, 3703-3727.
22 A. Behr and K. Nowakowski, in Adv. Inorg. Chem., Elsevier,
014, vol. 66, pp. 223-258.
2
2
industrially viable CO hydrogenation process.
2
4
Conflicts of interest
There are no conflicts to declare.
2
2
2
2
2
3 L. Wu, Q. Liu, R. Jackstell and M. Beller, in Carbon Dioxide
and Organometallics, Springer, 2015, pp. 279-304.
4 W.-H. Wang, Y. Himeda, J. T. Muckerman, G. F. Manbeck and
E. Fujita, Chem. Rev., 2015, 115, 12936-12973.
Acknowledgements
This work was financially supported by the Korea CCS R&D Center
5 T. Schaub and R. A. Paciello, Angew. Chem. Int. Ed., 2011, 50,
7
278-7282.
6 T. Schaub, R. A. Paciello, K. D. Mohl, D. Schneider, M. Schäfer
and S. Rittinger, WO2010149507A2, 2010.
of the Ministry of Science, ICT
&
Future Planning
(
2014M1A8A1049300) and the Korea Institute of Science and 27 T. Schaub, O. Bey, A. Meier, D. Fries and R. Hugo,
WO2013050367A2, 2013.
Technology (KIST). We thanks for professor Jung-Ho Cho in
Kongju National University for the discussion on VLE of n-butyl
imidazole and formic acid.
2
8 We take care of equipment systems amp space to let you
focus on whats important converting carbon dioxide.
http://www.carboncenter.org/ (accessed 19 july, 2017).
9 Pilot & Test Center|ReactWell. http://www.reactwell.com/
case-studies/test-center/ (accessed 19 july, 2017).
2
3
3
3
0 W. Leitner, U. Hintermair, S. Wesselbaum, WO Patent
2
,012,095,345, 2012.
Footnotes
1 M. Scott, B. Blas Molinos, C. Westhues, G. Franciò and W.
Leitner, ChemSusChem, 2017, 10, 1085-1093.
Electronic supplementary information (ESI) available. See DOI:
2 C. M. Jens, M. Scott, B. Liebergesell, C. G. Westhues, P.
Schäfer, G. Franciò, K. Leonhard, W. Leitner and A. Bardow,
Adv. Synth. Catal., 2019, 361, 307-316.
References
3
3 J. Artz, T. E. Müller, K. Thenert, J. Kleinekorte, R. Meys, A.
Sternberg, A. Bardow and W. Leitner, Chem. Rev., 2017, 118,
1
2
3
4
5
6
7
S. E. Hosseini and M. A. Wahid, Renew. Sustain. Energy Rev.,
016, 57, 850-866.
M. R. Shaner, H. A. Atwater, N. S. Lewis and E. W. McFarland,
Energy Environ. Sci., 2016, 9, 2354-2371.
4
34-504.
2
3
3
4 G. H. Gunasekar, K. Park, K.-D. Jung and S. Yoon, Inorg.
Chem. Front., 2016, 3, 882-895.
5 A. Álvarez, A. Bansode, A. Urakawa, A. V. Bavykina, T. A.
Wezendonk, M. Makkee, J. Gascon and F. Kapteijn, Chem.
Rev., 2017, 117, 9804-9838.
6 D. A. Bulushev and J. R. Ross, Catal. Rev., 2018, 60, 566-593.
7 W.-H. Wang, X. Feng and M. Bao, in Transformation of
Carbon Dioxide to Formic Acid and Methanol, Springer, 2018,
pp. 43-52.
8 D. Preti, C. Resta, S. Squarcialupi and G. Fachinetti, Angew.
Chem. Int. Ed., 2011, 50, 12551-12554.
9 S. Wesselbaum, U. Hintermair and W. Leitner, Angew. Chem.
Int. Ed., 2012, 51, 8585-8588.
P. Häussinger, R. Lohmüller and A. M. Watson, Ullmann's
Encyclopedia of Industrial Chemistry, 2011.
P. Preuster, C. Papp and P. Wasserscheid, Acc. Chem. Res.,
3
3
2
016, 50, 74-85.
D. Teichmann, W. Arlt, P. Wasserscheid and R. Freymann,
Energy Environ. Sci., 2011, 4, 2767-2773.
S. Enthaler, J. von Langermann and T. Schmidt, Energy
Environ. Sci., 2010, 3, 1207-1217.
3
3
4
M. Grasemann and G. Laurenczy, Energy Environ. Sci., 2012,
5
, 8171-8181.
8
9
Y. Yang and J.-W. Lee, Chem. Sci., 2019, 10, 3905-3926.
M. Peters, B. Koehler, W. Kuckshinrichs, W. Leitner, P.
Markewitz and T. E. Müller, ChemSusChem, 2011, 4, 1216-
0 K. Park, G. H. Gunasekar, N. Prakash, K. D. Jung and S. Yoon,
ChemSusChem, 2015, 8, 3410-3413.
1
240.
1
0 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 11 of 12
Please Gd roe en no tC ha ed mj u iss tt r my argins
Journal Name
ARTICLE
4
4
4
4
1 G. H. Gunasekar, J. Shin, K.-D. Jung, K. Park and S. Yoon, ACS 53 S. Dey, A. Bhunia, I. Boldog and C. Janiak, ViMewicArrtoicpleoOrnoliunes
Catalysis, 2018, 8, 4346-4353. Mesoporous Mater., 2017, 241, 303-315.
2 G. H. Gunasekar, K.-D. Jung and S. Yoon, Inorg. Chem., 2019, 54 A. Bhunia, I. Boldog, A. Möller and C. Janiak, J. Mater. Chem.
8, 3717-3723 A, 2013, 1, 14990-14999.
3 J. J. Corral-Pérez, A. Billings, D. Stoian and A. Urakawa, 55 S. Hug, M. B. Mesch, H. Oh, N. Popp, M. Hirscher, J. Senker
ChemCatChem, 2019, 11, 4725-4730 and B. V. Lotsch, J. Mater. Chem. A, 2014, 2, 5928-5936.
DOI: 10.1039/C9GC03685G
5
4 V. V. Ranade, R. Chaudhari and P. R. Gunjal, Trickle bed 56 K. Park, K. Lee, H. Kim, V. Ganesan, K. Cho, S. K. Jeong and S.
reactors: Reactor engineering and applications, Elsevier,
011.
5 L.-Y. Liao, X.-R. Kong and X.-F. Duan, J. Org. Chem., 2014, 79,
77-782.
6 P. Kuhn, M. Antonietti and A. Thomas, Angew. Chem. Int. Ed.,
008, 47, 3450-3453.
Yoon, J. Mater. Chem. A, 2017, 5, 8576-8582.
57 S. Hug, L. Stegbauer, H. Oh, M. Hirscher and B. V. Lotsch,
Chem. Mater., 2015, 27, 8001-8010.
58 F. Wang, Q. Xu, Z. a. Tan, L. Li, S. Li, X. Hou, G. Sun, X. Tu, J.
Hou and Y. Li, J. Mater. Chem. A, 2014, 2, 1318-1324.
59 D. J. Morgan, Surf. Interface Anal., 2015, 47, 1072-1079.
2
4
4
4
7
2
7 M. Liu, L. Guo, S. Jin and B. Tan, J. Mater. Chem. A, 2019, 7, 60 K. Mori, T. Taga and H. Yamashita, ACS Catalysis, 2017, 7,
5
153-5172.
3147-3151.
4
4
8 J. Artz, ChemCatChem, 2018, 10, 1753-1771.
61 S. Yamaguchi, K. Kamiya, K. Hashimoto and S. Nakanishi,
Chem. Commun., 2017, 53, 10437-10440.
9 G. H. Gunasekar, K. Park, V. Ganesan, K. Lee, N.-K. Kim, K.-D.
Jung and S. Yoon, Chem. Mater., 2017, 29, 6740-6748.
0 G. Gunasekar, K. Park, H. Jeong, K.-D. Jung, K. Park and S.
Yoon, Catalysts, 2018, 8, 295.
62 P. G. Jessop, S. M. Mercer and D. J. Heldebrant, Energy
Environ. Sci., 2012, 5, 7240-7253.
5
5
63 Y. Himeda, Eur. J. Inorg. Chem., 2007, 2007, 3927-3941.
1 A. V. Bavykina, E. Rozhko, M. G. Goesten, T. Wezendonk, B. 64 A. Kann, H. Hartmann, A. Besmehn, P. J. Hausoul and R.
Seoane, F. Kapteijn, M. Makkee and J. Gascon,
ChemCatChem, 2016, 8, 2217-2221.
Palkovits, ChemSusChem, 2018, 11, 1857-1865.
65 K. Narita and M. Sekiya, Chem. Pharm. Bull., 1977, 25, 135-
140.
5
2 S. Dey, A. Bhunia, H. Breitzke, P. B. Groszewicz, G.
Buntkowsky and C. Janiak, J. Mater. Chem. A, 2017, 5, 3609- 66 J. J. Anderson, D. J. Drury, J. E. Hamlin and A. G. Kent (BP),
3
620.
US4855496A , 1989.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 11
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