Molecular H2O promoted catalytic bicarbonate reduction with methanol into formate over Pd0.5Cu0.5/C under mild hydrothermal conditions

Article abstract of DOI:10.1039/d0gc02785e

Direct reduction of bicarbonate, a typical product of CO2 captured in alkaline solution, into value-added organics is one promising way to achieve a simplified and green CO2 capture and utilization process. In this work, a new strategy of bicarbonate reduction coupled with methanol oxidation into a dual formation of formate under mild hydrothermal conditions is reported. A 68% formate production efficiency based on the reductant methanol and nearly 100% selectivity of formate were obtained via a Pd0.5Cu0.5/C catalyst at 180 °C. An operando hydrothermal ATR-FTIR study proved that the bicarbonate was reduced by the in situ generated hydrogen from methanol, which was stepwise oxidized to formaldehyde and formic acid. Notably, DFT calculations and a qNMR study of the 13C and 2H (D) isotopic labelling revealed that H2O molecules not only supplied the hydrogen for bicarbonate reduction but also acted as an indispensable promoter to enhance the catalytic performance of Pd0.5Cu0.5/C for methanol activation.

Full text of DOI:10.1039/d0gc02785e

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DOI: 10.1039/D0GC02785E
Journal Name
PAPER
Molecular H O promoted catalytic bicarbonate reduction with
2
methanol into formate over Pd Cu /C under mild hydrothermal
0
.5
0.5
conditions
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
,a,b,c
Tianfu Wang,a,c Jiong Cheng, and Fangming
a
Xiaoguang Wang, Yang Yang, Heng Zhong,*
,
a,b,c
DOI: 10.1039/x0xx00000x
Jin*
www.rsc.org/
Direct reduction of bicarbonate, a typical product of CO
organics is one promising way to achieve a simplified and green CO
2
captured in alkaline solution, into value-added
capture and utilization process. In this
2
work, a new strategy of bicarbonate reduction coupled with methanol oxidation to a dual formation of formate
at mild hydrothermal conditions is reported. A 68% formate production efficiency based on the reductant
methanol and nearly 100% selectivity of formate were obtained via a Pd0.5Cu0.5/C catalyst at 180 °C. An
operando hydrothermal ATR-FTIR study proved that the bicarbonate was reduced by the in situ generated
hydrogen from methanol, which was stepwise oxidized to formaldehyde and formic acid. Notably, DFT
1
3
2
2
calculation and qNMR study of C and H (D) isotopic labelling revealed that H O molecules not only supplied
the hydrogen for bicarbonate reduction but also acted as an indispensable promoter to enhance the catalytic
performance of Pd0.5Cu0.5/C for methanol activation.
8
H
2
CO
3
, HCO
3
–, CO
3
2–) in a CO
2
saturated alkaline solution. If the
1
. Introduction
–
captured CO
2
could be converted directly in the form of HCO
not only much energy will be saved but also the process of CO
capture and utilization will be greatly simplified. Therefore, the
3
,
Reduction of CO
has shown considerable environmental and economic benefits
since the fixation of CO would significantly alleviate the
associated environmental risks and the stress of fossil fuel
depletion. Although the direct conversion of CO
industrial flue gas have been reported, CO
2
, a typical greenhouse gas, to useful chemicals
2
–
2
direct reduction of HCO
greener strategy for CO
could be considered as a promising
capture and utilization.
3
2
2
– from
is generally needed
1
2
to be captured from either atmosphere or point sources by
commonly using alkaline absorbents before further utilization.
–
2–
This process transforms the CO
2
into HCO
3
and/or CO
3
(the
2
, 3
final products are pH-dependent). However, as shown in Fig.
1
2
, the current technologies for CO conversion are mainly
limited in gaseous CO
CO
2
transformation.4-6 Thus, the captured
(in the form of HCO –
and/or CO
2–
) needs to be
2
3
3
regenerated and released at a relatively high dissociation
temperature of ca. 200 – 1000 °C and re-compressed to high-
pressure CO
2
gas before being applied with these methods,
which is not only complicated but also consumes huge
7
–
energies. On the other hand, HCO
(
3
is the dominant substance
(aq),
nearly 100%) among all the dissolved carbon species (CO
2
a. School of Environmental Science and Engineering, State Key Lab of Metal Matrix
Composites, Shanghai Jiao Tong University, Shanghai 200240, China
Center of Hydrogen Science, Shanghai Jiao Tong University, Shanghai, 200240,
2
Fig. 1 Scheme of CO capture and utilization – a comparison of
previous methods and this study.
b.
China
c.
Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092,
Among the organics derived from CO
2
/HCO
3
–, formic acid is
P.R. China
*
Fangming Jin: fmjin@sjtu.edu.cn; Heng Zhong: zhong.h@sjtu.edu.cn.
one of the most important products due to its versatile
application in modern chemical industry. More importantly,
†
Electronic supplementary information (ESI) available. See DOI: 10.1039/
x0xx00000x
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Journal Name
formic acid with a 4.4 wt.% hydrogen content has been recently effectively bind and activate the alcohol molecules.26,
27
View Article Online
DOI: 10.1039/D0GC02785E
regarded as a promising hydrogen carrier because of its Therefore, combining metallic Pd catalyst with Cu would
–
stability, low toxicity, biodegradability, and convenience in probably be a logical strategy to catalyse the HCO
storage and transportation.
3
reduction
9
, 10
Current methods of formic acid with methanol effectively.
In general, heterogeneous catalysts are the primary target for
production generally require fossil-based CO and extensive
alkali, suffering from environmental threat and heavy reliance development due to their prominent role in catalysing the
–
on fossil feedstock. Thus, replacing CO with HCO
3
for the formic reaction. However, since the catalysis occurs at interfacial sites,
acid production, especially when driven by renewable energy, substances in liquid or gaseous phases can also affect the
2
8
could be an ideal green and clean strategy for formic acid catalytic properties. In a typical hydrothermal reaction, water
generation.
For the CO
is generally considered to be an environmentally benign
gas is usually medium due to its unique inherent properties of high ion
/HCO –
reduction, high-pressure H
2
3
2
an indispensable element, which is currently mainly derived product (K
w
)
and low dielectric constant under high
1
1, 12
29
from non-renewable natural gas and petroleum,
resulting temperature and high pressure. However, beyond the well-
in energy consumption and environmental problems. In known function as solvent, there is evidence that the water was
addition, the use of high-pressure H gas involves energy indispensable for the hydrothermal conversion of biomass and
consumption, storage, and transportation issues. On the other HCO
hand, biomass or their derivatives rich in reducing functional unknown.
groups show great potential to offer renewable alternatives for Here, we propose a new route of HCO
molecular H
the pathway known as aqueous reforming with the assistance hydrothermal conditions. Methanol was oxidized into formate
2
–
30, 31
3
based on previous works,
but the mechanism is still
–
3
reduction into
2
, which can act as active hydrogen donors through formate with methanol as the reductant under mild
1
3, 14
of hydrothermal reactions.
Meanwhile, hydrothermal simultaneously, which led to a dual formation of formate.
–
–
environment has been verified to show robustness for HCO
reduction according to our previous works.
3
Results showed that HCO
3
could be reduced efficiently at 180
O was found
1
5, 16
Thus, with the °C on a Pd0.5Cu0.5/C catalyst. More importantly, H
2
in situ generated hydrogen from biomass hydrothermal to not only serve as an environmental-benign solvent but also
–
reforming, HCO
3
reduction is expected to be achieved in a H
2
-
act as a bridge for methanol activation and oxidation to produce
1
7, 18
–
free pathway under hydrothermal conditions.
Methanol (CH
H
2
and thereby achieve the HCO
3
reduction. Also, loads of
O with
3
OH) has a wide application in chemical effort are paid in this research on exploring the role of H
2
1
3
2
reaction, and can be easily produced from renewable sources the aid of C- and H-qNMR and DFT study. The presented study
such as biomass.19 It has been reported that over 300,000 proposed a new and green method of direct reduction of
metric tons of methanol was annually produced from bicarbonate with alcohols as renewable hydrogen sources to
renewable resource in the United States. Given to the achieve a dual formation of formic acid/formate in one-step.
functional group of -OH stored in methanol, it can be served as These results could provide new insights in developing a
2
0
one clean, efficient and renewable hydrogen source, which simplified and greener process for CO
2
capture and utilization.
–
makes it a highly potential hydrogen source for HCO
reduction. More importantly, as shown in eqn (1), HCO
reduction with methanol can achieve a dual formation of formic
acid/formate simultaneously, indicating good energy efficiency
and high atomic economy can be obtained.
3
–
3
2
. Experimental
2
.1 Materials
Methanol (CH
and copper nitrate trihydrate (Cu(NO
purchased from Shanghai Macklin Biochemical Technology Co.,
Ltd. Sodium bicarbonate (NaHCO , 99.9%) was purchased from
Sinopharm Chemical Reagent Co., Ltd and was selected as the
CO source for considerations that NaHCO is the main product
of trapping CO from waste streams by alkaline solutions. Cabot
Vulcan XC-72 carbon was used as the catalyst support. D
3
OH, 99.9%), palladium chloride (PdCl
2
, 99.99%)
3 2
)
·3H O, 99.99%) were
2
OH + 2HCO –
→ HCOOH + 2HCOO + H
–
(1)
CH
3
ϴ
3
2
O
ϴ
Δ
Δ
r
H (298 K) = -74.7 kJ/mol; Δ
r
G (298 K) = -32.1 kJ/mol
G (453 K) = -15.8 kJ/mol
3
ϴ
ϴ
r
H (453 K) = -49.7 kJ/mol; Δ
r
2
3
While the overall reduction of HCO –
with methanol into
3
2
formate is thermodynamically favourable, a reasonable catalyst
is expected to drive the reaction more efficient. Pd-based
materials are well-known hydrogenation catalysts due to their
2
O
13
(99.9%, Sinopharm Chemical Reagent Co.), NaH CO
3
(99%,
Cambridge Isotope
3
COOH (≥95%, J Cambridge Isotope
13
Sigma-Aldrich), H COOH (≥95%,
J
2
1, 22
excellent hydrogen absorption capacity,
however, the high
13
Laboratories Ltd.) and CH
cost and limited reserve impeded its wide application. Diluting
Pd with earth-abundant materials is a feasible and facile
strategy to decrease the cost of Pd-based catalysts and to
Laboratories Ltd.) were used for determination of formate
source. All reagents were used without further purification.
Deionized water was used throughout the study.
2
3, 24
further increase its catalytic performance and stability.
Cu
is one of the most extensively studied metal catalysts for CO
2
2.2 Catalyst Preparation
hydrogenation.25 Also, Cu has been reported to be efficient in
activating alcohols due to the enrichment of atomic oxygen
species at copper surface and sub-/near-surface region to form
a copper suboxide phase during the reaction, which can
Pd0.5Cu0.5/C catalyst with a 7.5 wt.% total loading was prepared
by an impregnation method. First, a certain amount of PdCl
was dissolved into 1 mol/L HCl to obtain a 0.2 mol/L H PdCl
2
2
4
2
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solution. Then, 1.05 mL of 0.2 mol/L H
2 4
PdCl and 5 mL 11.4 g/L showed that nanoparticles (NPs) of ca. 100 nm wVeirewe AortbicsleeOrvnleinde
Cu(NO ·3H
)
3 2
2
O solution were slowly added into a 100 mL flask for the Pd0.5Cu0.5/C catalyst, which shoulDdObI:e10a.s1s0o39c/iDat0eGdC0to27t8h5eE
and mixed with 0.4625 g carbon powder under vigorously carbon support since similar morphologies were also observed
stirring. The pH of the mixture was increased to 10 by adding for Pd/C and carbon black particle samples (Fig. S2 and S3 †).
0
.5 mol/L NaOH solution. After stirring for 24 hours, 10 mL of 2 TEM image of the Pd0.5Cu0.5/C catalyst showed that metal
mol/L NaBH was added dropwise into the mixture. After nanoparticles with an average diameter of 3.4±0.3 nm was
4
continuous stirring for another 12 hours, the black suspension successfully dispersed on the carbon support (Fig. 2a).
was filtered, washed with deionized water thoroughly and dried Composition of the NPs was verified by an energy-dispersive X-
in a vacuum dryer to obtain the final Pd0.5Cu0.5/C catalyst. By ray spectroscopy (EDS) analysis, which clearly demonstrates
keeping the total loading of metals (Pd and Cu) at 7.5 wt.%, Pd- that Cu and Pd atoms are randomly and homogeneously
Cu catalysts with different molar ratios (Pd0.75Cu0.25/C, distributed in each NPs (Fig. 2b-e), suggesting PdCu alloy was
Pd0.66Cu0.33/C, Pd0.33Cu0.66/C and Pd0.25Cu0.75/C) as well as Pd/C successfully formed. In a high-resolution TEM (HRTEM) image of
and Cu/C were also prepared by using similar method, and the a typical NP from Pd0.5Cu0.5/C (Fig. 2f), the measured lattice
ICP-OES results of each catalysts were summarized in Table S1 distance was 2.28 Å, which can be attributed to the 1/3(422)
3
3-35
†
.
fringes of PdCu alloy face-centred cubic structure.
In
addition, the Pd nanoparticles had an average diameter of 2.6
nm from the TEM image of Pd/C (Fig. S4 † ). From the XRD
patterns (Fig. 2g), both Pd/C and Pd0.5Cu0.5/C showed a broad
2
.3 Experimental procedures
In this study, all experiments were conducted in a stainless-steel
SUS 316) tubular reactor (3/8 inch o.d., 1-mm wall thickness)
with an inner volume of 5.7 mL. The schematic drawing of the
(
3
2
reacting system can be found in our previous research.
typical reaction procedure was as follow: 0.1 mol/L methanol, 1
mol/L NaHCO and 50 mg catalyst were loaded into the reactor.
A
3
Then, the reactor was sealed and put into a salt bath which was
preheated to a desired temperature. After a certain reaction
time, the reactor was removed out of the salt bath and quickly
submerged into a cold-water bath to quench the reaction. The
liquid and solid samples were separated through a 0.22 μm
syringe filter and collected for further analysis. Gas sample was
collected by a water-gas replacement method in a measuring
cylinder immersed in a saturated NaCl aqueous solution tank.
In this study, the amount of formate obtained from the HCO
by one hydroxyl is used to evaluate the efficiency of NaHCO
–
3
3
Fig. 2 TEM image (a), TEM-
EDS elemental mapping
reduction with methanol (abbreviated as ‘formate production
efficiency’). The detailed definition can be found in ESI†.
(b-e), HRTEM image (f),
and XRD patterns (g) of the
as-synthesized Pd0.5Cu0.5/C
catalyst.
2
.4 Analytical methods
Liquid samples were analysed by high-performance liquid
chromatography (HPLC), gas chromatography-mass
spectrometry (GC-MS), gas chromatography-flame ionization
1
3
2
detector (GC-FID) and C/ H-quantitative nuclear magnetic
1
3
2
resonance ( C/ H-qNMR). Gas samples were characterized by
GC-MS and quantified by gas chromatography-thermal
conductivity detector (GC-TCD). Solid samples were analysed by
X-ray diffractometer (XRD), X-ray photoelectron spectroscopy
peak located at around 25°, which was attributed to the (002)
plane of carbon with hexagonal structure. The diffraction
pattern of Pd/C showed a weak peak located at around 40°,
which is attributed to the (111) plane of the Pd face-centred
cubic (fcc) structure (ICDD 46-1043). On the other hand, Pd
alloying with Cu caused the diffraction peaks of Pd in the
Pd0.5Cu0.5/C catalyst to shift slightly to higher 2θ values. ICP-OES
analysis of the Pd0.5Cu0.5/C revealed that the weight percentage
of Pd and Cu were 4.46% and 2.68%, respectively, which were
close the designed values (Pd 4.5 wt.% and Cu 3.0 wt.%). In
brief, a carbon-supported PdCu alloy NP catalyst was
successfully synthesized.
(XPS) and transmission electron microscope (TEM). Operando
hydrothermal ATR-FTIR was emloyed to monitor the reaction
process (Fig. S1 † ). The detailed analytical conditions can be
found in ESI†.
3
. Results and discussion
3
.1 Characterization of catalysts
First, the Pd0.5Cu0.5/C catalyst was prepared and characterized.
For comparison, a Pd/C catalyst was also synthesized by the
similar procedure without adding the Cu precursor. SEM image
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.2 HCO –
Possibility of HCO –
Journal Name
3
3
reduction with methanol over Pd0.5Cu0.5/C catalyst
3.3 Reaction characteristics and catalyst stabilityView Article Online
DOI: 10.1039/D0GC02785E
3
reduction with methanol as the reductant To enhance the production of formate from the NaHCO
3
and Pd0.5Cu0.5/C as the catalyst was investigated. Results reduction with methanol, effects of different reaction
showed that formate were successfully produced after the parameters such as reaction temperature, time (Fig. S7†) and
reaction as predicted, and the total formate concentration was catalyst amount (Fig. S8†) were investigated. The temperature
1
21.9 mmol/L. For comparison, formic acid production from profile shows that only a trace amount of formate was formed
methanol alone was investigated in the absence of NaHCO at 150 °C. Increasing the temperature significantly promoted
Table 1). However, only negligible trace amount of formic acid the formation of formate, especially when the temperature
3
(
3
was produced when CH OH reacted alone. Furthermore, even 1 exceeded 160 °C. On the other hand, when temperature
mol/L NaOH was added to adjust the reaction pH, only 21.1 reached 180 °C, the formate production efficiency increased
mol/L formate was produced without the addition of NaHCO continuously with the extension of time. However, the reaction
which was much lower than that (121.9 mmol/L) obtained with tended to slow down when the reaction time exceeded 16 h. At
NaHCO . These results indicated the participation of NaHCO in 200 °C, a high efficiency of 75% from NaHCO was obtained. The
3
,
3
3
3
the formation of formate. It should be noted that the formate effect of catalyst amount results showed that increasing the
and formic acid displayed a single peak in the HPLC analysis (Fig. catalyst amount lead to an obvious promotion in the production
S5†). Since both formic acid and formate were produced from of formate. However, when the catalyst amount reached 50 mg,
–
13
the reaction of methanol with HCO
measurement was performed to distinguish and quantify the the reaction efficiency. Stability of the Pd0.5Cu0.5/C catalyst was
NaHCO -sourced formate and CH OH-sourced formic acid. In a further examined. Although a slight decrease in the formate
labelling experiment using NaH CO
3
(eqn (1)), C-qNMR further increase in catalyst amount had no significant effect on
3
3
1
3
3
(Fig. S6†), a strong signal production efficiency was observed in the 2nd cycle, further
associated with H COO was observed at 171.2 ppm. The decline was not observed in the following 5 cycles (Fig. S9†). The
1
3
–
1
3
concentration of NaH CO
be 67.3 mmol/L by adding 50 mmol/L CH
standard. Based on the NaHCO -sourced formate concentration morphology and crystallinity of Pd0.5Cu0.5/C catalyst had no
determined by qNMR and the total formate concentration obvious change after the reaction. However, TEM analysis
determined by HPLC, a quantification of NaHCO -sourced revealed that the PdCu alloy slightly aggregated after the
formate and CH OH-sourced formic acid was summarized in reaction, and the NPs size increased to ca. 4.5 nm, which
Table 1. Results revealed that the NaHCO -sourced formate and probably caused the decrease in formate production efficiency
CH OH-sourced formic acid were 67.3 and 54.6 mmol/L, in the 2nd cycle. ICP analysis of the liquid sample after the
respectively, which indicates dual formation of reaction discovered no dissolved Pd or Cu species. These results
formate/formic acid from NaHCO and CH OH was achieved. In indicated that the Pd0.5Cu0.5/C catalyst was relatively stable.
addition, formaldehyde (HCHO) was also detected by GC-MS,
suggesting that CH
OH was stepwise oxidized into 3.4 Catalytic property and mechanism
3
-sourced formate was determined to Pd0.5Cu0.5/C catalyst after reaction was collected and analysed
1
3
3
COOH as an internal by SEM, TEM and XRD (Fig. S10 † ). Results showed that the
3
3
3
3
3
a
3
3
3
formaldehyde and formic acid. It is encouraging that the
selectivity of formate was nearly 100% although a trace amount
of HCHO was detected in liquid samples. GC-TCD analysis for
Based on the detected intermediates of HCHO and H
the overall process of CH OH reacting with NaHCO
divided into two parts: the hydrogen generation from methanol
2
(Table 1),
could be
3
3
gaseous samples was further applied and only H
2
was observed
oxidation, which contains two steps (eqn (2) and (3)), and the
(
Table 1). These results indicate that the coexistence of NaHCO
3
–
HCO
3
hydrogenation to formate (eqn (4)).
3
and CH OH is beneficial necessary to the formation of formate.
CH
HCHO + H
H + NaHCO → HCOONa + H O
2 3 2
3
OH → HCHO + H
2
(2)
(3)
(4)
Table 1 Product distribution of NaHCO
methanola
3
reduction with
O → HCOOH + H
2 2
Gaseous
products
Liquid products (mmol/L)
Formate
Then, the catalytic property of Pd0.5Cu0.5/C for these two parts
were studied separately to explore the catalytic mechanism.
First, H production from methanol oxidation was investigated
2
in the presence and absence of Pd0.5Cu0.5/C catalyst. For
comparison, results obtained from Pd/C, Cu/C catalyst were
also employed. As summarized in Table 2, only trace amount of
(mL)
NaHCO
3
CH
3
OH
HCHO
H
2
sourced
67.3
sourced
54.6
with NaHCO
3
Trace 10.1 ml
Trace
Trace 13.5 ml
w/o NaHCO
3
-
-
Trace
21.1
-
H
2
was produced in the absence of any catalyst and in the
presence of carbon black (Table 2, Entries 1 and 2). On the other
hand, H generation was clearly promoted when Pd/C,
b
w/o NaHCO
Reaction condition: 0.1 mol/L CH
3
a
3
OH, 1 mol/L NaHCO
3
, 50%
2
b
water filling, 50 mg Pd0.5Cu0.5/C, 180 °C, and 16 h. 1 mol/L
NaOH was added to simulate the alkalinity induced by
NaHCO .
3
Pd0.5Cu0.5/C and Cu/C were used, and the Pd0.5Cu0.5/C catalyst
exhibited the best performance (Table 2, Entries 3-5). The TON
for hydrogen generation obtained on Pd0.5Cu0.5/C was 1.4 and
3
.8 times higher than those obtained on Pd/C and Cu/C,
4
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respectively. These results indicate that Pd0.5Cu0.5/C could and Pd 3d3/2 peaks shifted to 335.3 and 340.6 eV,VrieewspAreticclteiOvenllinye.
effectively promote methanol hydrothermal reforming for This is probably attributed to a smaller elDecOtIr:o10n.1n0e39g/aDt0ivGitCy0o27f8C5uE
hydrogen generation. Subsequently, NaHCO
3
hydrogenation than that of Pd, which leads to an electron injection from Cu to
with ex situ gaseous H
2
on the Pd0.5Cu0.5/C, Pd/C, and Cu/C were Pd.36, 37 The XPS result of Cu can be found in Fig. S11†. These
studied. Results showed that no formate production was results indicated that the incorporation of Cu could change the
observed in the absence of any catalyst, and a significant electronic structure of Pd, further leading to a downward shift
3
8
formate increase appeared in the presence of Pd0.5Cu0.5/C of Pd d-band centre. The shift of d-band centre resulted in a
catalyst (Table S2 † ). The above results demonstrated that decrease in the binding energy of hydrogen on Pd surface,
Pd0.5Cu0.5/C catalyst played irreplaceable part in both H
generation from methanol and NaHCO hydrogenation.
2
which positively improved the catalytic performance of Pd for
3
9, 40
3
hydrogen generation.
On the other hand, when compared
In addition, the effect of different Pd/Cu ratio (molar ratio) on to the unalloyed state, the electronic structure of Pd modified
hydrogen generation and formate production were tested by Cu doping caused Pd d-band centre to be far away from its
3
8, 41
(Table 2, Entries 4, and 6-9). Pd0.5Cu0.5/C exhibited the highest Fermi level.
The farther d-band centre of transition metals
catalytic activities in formate production, indicating that a 1:1 to their Fermi level, the lower adsorption energy on transition
4
2, 43
Pd/Cu ratio was the optimum condition (Table 2, Entry 4). metal surface for C1 products.
Thus, the formate adsorption
Notably, it was less sensitive for formate production when the enthalpy on the PdCu alloy surface became lower than that on
molar ratio of Pd was higher than 50% (Table 2, Entries 6 and 7). the single Pd. As a result, when formate was formed on PdCu
On the other hand, increasing the proportion of Cu could alloy, it detached from the catalyst surface, leading to an
improve the efficiency of H
was unfavourable for the formate production. Therefore, Pd is HCO
2
generation, however, excessive Cu enhanced formate production and selectivity of formate from
–
3
reduction. In brief, Pd should be the core reaction site for
the core component in the PdCu alloy catalyst, and the both steps of hydrogen generation and formate production,
introduction of Cu not only effectively reduced the cost of while the introduction of Cu improved Pd performance by
precious metal, but also improved the hydrogen generation and altering the electronic structure of Pd.
further formate production.
Table 2 Hydrogen generation and formate production
efficiency obtained from different catalystsa
Pd 3d3/2
Pd(II)
Pd 3d5/2
Pd(II)
Pd(0)
Pd(0)
Formate
production
TON of hydrogen
Entry Catalyst
generationb
2
mol H per mol PdCu)
efficiency
(
c
(%)
Pd0.5Cu0.5/C
1
2
3
4
5
6
7
8
9
None
Trace
Trace
Trace
46.3
67.6
15.2
67.0
67.5
38.1
22.2
Trace
Pd(II)
carbon black Trace
Pd/C
Pd(0)
10.4
14.3
3.8
Pd(II)
Pd(0)
Pd0.5Cu0.5/C
Cu/C
Pd0.75Cu0.25/C 12.8
Pd0.66Cu0.33/C 13.1
Pd0.33Cu0.66/C 9.0
Pd0.25Cu0.75/C 7.6
Pd/C
3
50
345
340
B.E (eV)
335
330
1
0d
Pd0.5Cu0.5/C
Trace
a
H
2
generation and formate production are two independent
OH, 1 mol/L
NaOH, 50% water filling, 50 mg catalysts, 180 °C, and 16 h. c
experiments. b Reaction condition: 0.1 mol/L CH
3
Fig. 3 XPS spectra of Pd 3d in Pd0.5Cu0.5/C and Pd/C.
Reaction condition: 0.1 mol/L CH
3
OH, 1 mol/L NaHCO
3
, 50%
d
3.5 Role of H
As shown in eqn (3), one obvious role of H
HCHO to produce H , indicating that H O participated in the
reaction as a hydrogen source. However, H and HCHO was
hardly detected when methanol reacting with HCO
absence of H O (Table 2, Entry 10), indicating that H O was also
indispensable for the first step of methanol activation (eqn (2)).
To further verify the role of H O and its mechanism, DFT
calculations were performed on the process of hydrogen
generation from methanol with or without H O. The structures
of methanol molecule, transition state without H O, and the
2
O
water filling, 50 mg catalysts, 180 °C, and 16 h. Methanol was
used as a solvent instead of water, and other conditions are
the same as “b” and “c”.
2
O was to react with
2
2
2
The interaction between Pd and Cu should have an
indispensable role in hydrogen generation and NaHCO
–
3
in the
3
2
2
hydrogenation. To further verify the property of PdCu alloy, XPS
analysis was conducted. Fig. 3 illustrates the XPS results of
Pd0.5Cu0.5/C and Pd/C before reaction. Compared to Pd/C, the
Pd 3d peaks of PdCu alloy shifted to a lower binding energy. For
Pd/C, the Pd 3d5/2 and Pd 3d3/2 peaks centred at 335.9 and 341.3
eV, respectively, while for Pd0.5Cu0.5/C, the position of Pd 3d5/2
2
2
2
2
transition state with H O were determined, which are shown in
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Fig. 4a, b and c, respectively. The transition state structure understanding the mechanism, in which D
Journal Name
1
3
2
O and NaH CO
View Article Online
3
DOI: 10.1039/D0GC02785E
exhibited a narrow angle of 1C-5O-6H in the absence of H
2
O
were used instead of H
2
O and NaHCO
-sourced formate consisted of H COO and
compared with that of the equilibrium structure of the isolated D COO in the ratio of 1:1.
methanol (Fig. 4a). This result indicates that the H generation
from methanol without H O requires overcoming a huge CH
potential energy barrier. On the other hand, the 1C-5O-6H angle HCHO + D
DH + 2NaH CO
3
, respectively. This leads
1
3
13
–
(Fig. 4b), which was significantly bent (from 108.9 ° to 53.6 °) as to the NaH CO
3
1
3
–
2
2
3
OH + D
2
O→HCHO + DH + DHO
O→HCOOD + DH
(5)
(6)
(7)
2
1
3
13
13
2
3 2
→H COONa + D COONa + DHO + H O
To further confirm the DFT calculation results and above
assumption (eqn (5-7)), isotopic tracing reaction with D
2
O
1
3
substituting of H
was used instead of NaHCO
2
O was conducted. In the meantime, NaH CO
to trace the reaction path of
3
3
carbon. It should be noted first that we confirmed that the H of
–
-CH
3
in CH
3
OH, -CH in HCHO or HCOO would not undergo
hydrogen-deuterium exchange under hydrothermal conditions
in an independent run (Fig. S12†). As displayed in Fig. 5a, the
1
3
–
peak assigned to D COO was clearly observed in the D-qNMR
spectrum, and it consisted of 2 parallel peaks, while the
1
3
13
corresponding C-qNMR image showed that NaH CO
3
sourced
formate contained 3 parallel peaks, which was caused by the
1
3
resonance effect between C and D (Fig. 5a, b). The COSY
1
3
spectra of the liquid sample after NaH CO
methanol in D O was also shown in Fig. 5c. These results
confirmed that formate from NaHCO reduction carried D from
O. Furthermore, the concentration of D-labelled and 13C-
labelled formate were determined with dimethyl sulfoxide-D6
3
reacting with
2
3
D
2
1
3
44
and CH
3
COOH as the internal standards, respectively. The
results showed the final product of formate was comprised of
1
3
–
13
–
nearly identical amount of H COO and D COO (Table 3),
which was perfectly consistent with the DFT calculations and
further confirmed the promoting effect of H
activation.
2
O in methanol
Fig. 4 Transition states (a)-(c) and energy profiles (d) for
methanol dissociation into H with or without H O (a: methanol
molecule; b: the transition state without H O; c: the transition
state with H O; d: the profile with H O as the promoter is
2
2
2
2
2
2
depicted in orange while the profile without H O is depicted in
blue).
relaxed to 106.4 ° in the presence of H
nearly comparable to that of the isolated methanol. Moreover,
the added H O molecule (7O-8H-9H) behaves as a proton
acceptor and formed a deformed H O-cation-like conformation
2
O (Fig. 4c), which is
2
3
with the transition state atom 6H from methanol molecule,
which would drastically reduce the activation energy for the
ionic water dissociation. As a result of these effects, the energy
barrier of hydrogen generation from methanol with H
addition was significantly reduced (from 378 kJ/mol to 220
kJ/mol) compared to that in the absence of H O (Fig. 4d),
suggesting the critical role of H O as a promoter in this process.
Then, the corresponding reaction mechanism based on the
calculation results is proposed in Fig. 4d. One H O molecule acts
as a bridge for methanol breaking down to produce one H and
one HCHO. Thus, it is suggested that the H generated from
methanol in eqn (2) should consist of one atom from methanol
and one atom from H O. Based on these results, eqn (2-4) could
be re-written as isotope-labelled forms (eqn (5-7)) for a better
2
O
2
2
Fig. 5 D-qNMR (a), 13C-qNMR (b) and COSY spectra (c) of the
2
1
3
3 2
liquid sample after NaH CO reacting with methanol in D O
2
1
3
(reaction conditions: 0.1 mol/L CH
3
OH, 1 mol/L NaH CO
3
, 50%
2
D
2
O filling, 50 mg Pd0.5Cu0.5/C, 180 °C, and 16 h; dimethyl
1
3
sulfoxide-D6 and CH
standards to calculate D-labelled and C-labelled formate
concentration, respectively).
3
COOH were used as the internal
2
1
3
6
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Journal Name
Paper
belonging to the ω(C-H) of formaldehyde, was clearly observed
at 100 °C and its absorbance signal increased with the reaction
View Article Online
DOI: 10.1039/D0GC02785E
1
3
Table 3 Product distribution of NaH CO
3
reduction with
a
methanol in D
Formate
concentration H COO
2
O
temperature. Nevertheless, when temperature reached 180 °C,
the formaldehyde vibration disappeared with prolonged time,
this was probably attributed to rapid transformation of
formaldehyde to formate during the reaction, making it difficult
1
3
NaH CO
3
sourced
CH OH
3
Total
1
3
–
D13COOH–
32.1
Reaction conditions: 0.1 mol/L CH
0% D O filling, 50 mg Pd0.5Cu0.5/C, 180 °C, and 16 h.
sourced
(
mmol/L)
33.3
53.1
118.5
a
13
to capture. Furthermore, the peaks at 1110 and 1082 cm-1
,
3
OH, 1 mol/L NaH CO
3
,
5
2
which could be assigned to the C-O bond of methanol, was blue-
shifted along with the increase in reaction time. This was
In summary, the results of DFT and 13C/ H-qNMR clearly
2
probably attributed to the methanol oxidation into
demonstrated that H
2
O played as a promoter for methanol formaldehyde, that is the transforming from C-O bond to C=O
activation in eqn (2). Thus, the total three roles of H
2
O in the bond, causing the increase in bonding energy of C-O bond.
reduction with methanol can be summarized
–
process of HCO
3
as: (1) acting as an indispensable promoter by lowering the
reaction energy barrier of methanol activation into
formaldehyde; (2) reacting with formaldehyde to release
hydrogen; (3) serving as a green solvent.
It should be noted that according to eqn (1), the ratio of
–
–
3 3
CH OH-sourced HCOOH to the HCO -sourced HCOO should be
1
:2. However, our isotopic results showed that the actual ratio
–
–
of CH
1
3
OH-sourced HCOOH to the HCO
3
-sourced HCOO was ca.
–
:1.2. These results suggested that in the reduction of HCO
3
with CH
3
OH, the first part (eqn (2) and (3)) was easier to react
2
than the second part (eqn (4)). Thus, unreacted H product was
detected in the gaseous phase.
3
.6 Operando ATR-FTIR study
To obtain a full understanding of the reaction mechanism, an
operando hydrothermal ATR-FTIR was further carried out to
examine the transformation of reactants. All the operando ATR-
FTIR spectra were collected as subtraction spectrum with the
initial state (25 °C, before starting the heating reaction) as
background. First, the spectrum during the reaction with or
without catalyst were captured. As shown in Fig. 6a, the peaks
-
1
-1
at 1633 cm and 1400 cm are assigned to the asymmetrically
–
45, Fig. 6 Operando ATR-FTIR subtraction spectra recorded during
and symmetrically adsorbed HCO
3
(COO bond), respectively.
The 1012 cm peaks can be ascribed to the C-O bond of
adsorbed CH OH, and the vibration signals caused by metal-O
bond at 840 cm and 713 cm also confirmed the adsorption of
–
4
6
-1
HCO3 reduction with methanol (All the spectra subducted the
spectrum of the initial state as the background; initial state: 0.1
mol/L CH OH, 1 mol/L NaHCO , 100% water filling, 5 mg
3 3
Pd Cu /C, 25 °C; (a) ATR-FTIR spectra comparison with or
0.5 0.5
3
-1
-1
4
7
methanol on the catalyst surface. Furthermore, the vibration
peak due to the adsorption of reactants tended to weaken as
the reaction proceeds, indicating that the HCO
were consumed for further reaction on the Pd0.5Cu0.5/C surface.
Then, as shown in Fig. 6b, upon heating the mixture of CH OH
and NaHCO in aqueous solution, peaks located at 1585 cm
without catalyst; (b) temperature and time sequence spectra of
operando ATR-FTIR obtained with Pd Cu /C catalyst; test
–
and CH
3
OH
0.5
0.5
3
condition: 0.1 mol/L CH
filling, 5 mg Pd0.5Cu0.5/C).
3 3
OH, 1 mol/L NaHCO , 100% water
3
-1
3
-1
3.7 Reaction mechanism
and 1385 cm , which represented the OCO asymmetric and
symmetric stretches of HCOO , appeared and intensified
–
Based on the above research, a possible reaction mechanism of
gradually with increasing temperature, and the peak of C-H
–
HCO
proposed in Fig. 7. First, CH
the catalyst with a H generation through the promotion effect
of H O molecule. Then, the formed HCHO (iii) reacts with a
second H O molecule to produce another H and HCOOH (v).
Thus, one CH OH molecule produces two molecules of H with
one H O molecule as the promoter and another as the hydrogen
source. Subsequently, the formed in situ H
3
reaction with methanol in water on Pd0.5Cu0.5/C is
-1
–
bond stretching vibration at 2850 cm related to HCOO also
increased gradually. These results indicate that formate
production rate was promoted with temperature and time
increasing. The main formaldehyde bands are located at 2923,
3
OH (i) is oxidized into HCHO (iii) on
2
2
2
2
-
1
48
2
853, and 1354 cm based on the previous report, however,
3
2
-1
the peaks at 2923 and 2853 cm overlapped with formate ν(C-
2
H) bands in Fig. 6b, indicating that they were difficult to
–
2
3
and HCO are
-1
distinguish. On the other hand, the band at 1354 cm ,
activated by adsorbing on the Pd0.5Cu0.5/C surface ((vii) and
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Journal Name
(
viii)), and then the activated H nucleophilic attacks the C=O, reduction. Based on the above results, the alcohol-bicarbonate
View Article Online
DOI: 10.1039/D0GC02785E
–
leading to the formation of HCOO ((ix) and (x)) through the system can be expected to be applied to the synergistic
cleavage of C-OH bond. conversion of various hydroxyl-rich organics and CO sources.
2
Table 4 Reduction of various CO
alcoholsa
2
sources with different
Carbon
Formate production
Entry Alcohols
sourceb
efficiency (%)
Trace
Trace
48.6
87.3
70.5
83.4
67.6
68.9
72.3
1
2
3
4
5
6
7
8
9
methanol
methanol
methanol
methanol
methanol
methanol
methanol
ethanol
-
CO
CO
2
2
c
K
2
CO
KHCO
Na CO
3
3
2
3
NaHCO
NaHCO
NaHCO
NaHCO
3
3
3
3
1-propanol
1-butanol
1
a
0
73.4
–
Reaction condition: 0.1 mol/L alcohol, 1 mol/L HCO
3
or
2
–
CO
3
, 50% water filling, 50 mg Pd0.5Cu0.5/C, 180 °C, and 16 h.
b
c
CO
2
: 2.5 MPa, others: 1 mol/L. 1 mol/L NaOH was added.
Fig. 7 Reaction scheme of HCO –
methanol in water on Pd0.5Cu0.5/C catalyst.
reduction into formate with
3
4. Conclusions
–
In summary, we have developed an efficient strategy for HCO
3
3
.8 Universality research
reduction with methanol as hydrogen source on a Pd0.5Cu0.5/C
catalyst under mild hydrothermal conditions. A 68% formate
production efficiency and nearly 100% selectivity of formate
from bicarbonate were obtained via a Pd0.5Cu0.5/C catalyst at
Applicability of the hydrothermal reduction of various inorganic
carbon sources with different alcohols were examined. As
summarized in Table 4, when gaseous CO
starting material instead of bicarbonate, only trace amount of
formate was detected (Table 4, Entry 2), suggesting CO gas was
2
was used as the
1
80 °C. Notably, DFT calculations and qNMR studies confirmed
2
that the molecular H O not only supplied the hydrogen but also
2
hardly to be directly converted in this system. However, when 1
mol/L NaOH was added, a 48.6% formate production efficiency
acted as an indispensable promoter to enhance the catalytic
performance of Pd0.5Cu0.5/C for methanol activation.
Furthermore, the operando ATR-FTIR revealed that the
was successfully obtained (Table 4, Entry 3), which should be
–
attributed to the transformation of CO
2
to HCO
3
in NaOH
mechanism of methanol oxidation to generate hydrogen is
solution. This result further suggests that a one-step CO
2
–
CH
3
OH→HCHO→HCOOH, and the HCO
3
is reduced into
capture and conversion reaction can be achieved by using the
presented method. Furthermore, other carbonates and
formate with the in situ formed hydrogen. The present study
provided a potential way towards simple and green one-step
CO capture and utilization, which is of great interest in the
2
2
practical application of CO conversion.
bicarbonates such as K
tested, and the formate production efficiency reached 87.3%,
0.5% and 83.4%, respectively (Table 4, Entries 4-6). Notably,
2 3 3 2 3
CO , KHCO , and Na CO were also
7
the hydrogenation of carbonates is generally more difficult than
that of bicarbonates because the protonation of carbonate ions
Conflicts of interest
4
9, 50
was considered to be inferior in aqueous solutions.
To our
There are no conflicts to declare.
delight, the carbonates showed better performance than the
corresponding bicarbonates in the presented research. This is
probably due to the weak acidity of methanol was enhanced by
Acknowledgements
2
–
the hydrothermal reaction, which then attacked the inert CO
3
The authors thank the financial support of the National Key R&D
Program of China (2018YFC0309800 and 2017YFC0506004), the
–
and made it more reactive than the ex situ HCO
3
.
In addition, the activity of various alcohols using as reductant National Natural Science Foundation of China (No. 21978170),
–
for the hydrothermal reduction of HCO
3
was examined. Results the Natural Science Foundation of Shanghai (No.
revealed that ethanol, 1-propanol and 1-butanol exhibited 19ZR1424800), the National Postdoctoral Program for
–
similar activity to methanol in the reduction of HCO
3
to Innovative Talent (No. BX20200208), the Oceanic
formate, while themselves were converted to corresponding Interdisciplinary Program of Shanghai Jiao Tong University (No.
acids (Table 4, Entries 8-10, Fig. S13†). Notably, the reactivity of SL2020MS022), Start-up Fund for Youngman Research at SJTU,
alcohols slightly increased with the growth of the carbon chains and the Centre of Hydrogen Science, Shanghai Jiao Tong
–
and the 1-butanol exhibited the best activity for HCO
3
University, China.
8
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2
3
2
9. F. Jin and H. Enomoto, Energy Environ. Sci., 2011, 4, 382-397.
View Article Online
0. Y. Zhang, Z. Shen, X. Zhou, M. Zhang aDnOdI:F1.0J.1in0,39G/rDe0eGnCC0h27e8m5.E,
012, 14, 3285-3288.
Notes and references
1
. A. Barthel, Y. Saih, M. Gimenez, J. D. A. Pelletier, F. E. Kühn, V. 31. L. Lu, H. Zhong, T. Wang, J. Wu, F. Jin and T. Yoshioka, Green
D'Elia and J. M. Basset, Green Chem., 2016, 18, 3116-3123.
Chem., 2020, 22, 352-358.
. D. W. Keith, G. Holmes, D. S. Angelo and K. Heidel, Joule, 2018, 2, 32. F. M. Jin, A. Kishita, T. Moriya and H. Enomoto, J Supercrit Fluids,
573-1594.
2001, 19, 251-262.
. E. S. Sanz-Perez, C. R. Murdock, S. A. Didas and C. W. Jones, Chem. 33. N. Yang, Z. Zhang, B. Chen, Y. Huang, J. Chen, Z. Lai, Y. Chen, M.
Sindoro, A. L. Wang and H. Cheng, Adv. Mater., 2017, 29, 1700769.
. S. Das, J. Pérez-Ramírez, J. Gong, N. Dewangan, K. Hidajat, B. C. 34. X. Huang, S. Tang, X. Mu, Y. Dai, G. Chen, Z. Zhou, F. Ruan, Z. Yang
2
1
3
Rev., 2016, 116, 11840-11876.
4
Gates and S. Kawi, Chem. Soc. Rev., 2020, 49, 2937-3004.
and N. Zheng, Nat. Nanotechnol., 2011, 6, 28.
5
2
6
. M. Ding, R. W. Flaig, H.-L. Jiang and O. M. Yaghi, Chem. Soc. Rev., 35. W.-C. Cheong, C. Liu, M. Jiang, H. Duan, D. Wang, C. Chen and Y.
019, 48, 2783-2828.
. H. Zhong, K. Fujii and Y. Nakano, J. Electrochem. Soc., 2017, 164, 36. Z. Guo, X. Kang, X. Zheng, J. Huang and S. Chen, J Catal, 2019,
374, 101-109.
. S. H. Kim, K. H. Kim and S. H. Hong, Angew. Chem. Int. Ed., 2014, 37. F. Pang, Z. Wang, K. Zhang, J. He, W. Zhang, C. Guo and Y. Ding,
3, 771-774.
Nano Energy, 2019, 58, 834-841.
. H. Zhong, K. Fujii, Y. Nakano and F. Jin, J. Phys. Chem. C, 2015, 38. J. Fan, S. Yu, K. Qi, C. Liu, L. Zhang, H. Zhang, X. Cui and W. Zheng,
19, 55-61.
J. Mater. Chem. A, 2018, 6, 8531-8536.
. H. Zhong, M. Iguchi, M. Chatterjee, Y. Himeda, Q. Xu and H. 39. G. W. Huber, J. W. Shabaker, S. T. Evans and J. A. Dumesic, Appl.
Catal. B, 2006, 62, 226-235.
0. H. Zhong, M. Iguchi, M. Chatterjee, T. Ishizaka, M. Kitta, Q. Xu and 40. J. Greeley and M. Mavrikakis, Nat. Mater., 2004, 3, 810-815.
Li, Nano Res., 2016, 9, 2244-2250.
F923-F927.
7
5
8
1
9
Kawanami, Adv. Sustain. Syst., 2018, 2, 1700161.
1
H. Kawanami, ACS Catal., 2018, 8, 5355-5362.
41. X. Yu, X. Tian and S. Wang, Surf. Sci., 2014, 628, 141-147.
1
1. R. Navarro, M. Sanchez-Sanchez, M. Alvarez-Galvan, F. Del Valle 42. G. C. Wang, Y. H. Zhou and J. Nakamura, J Chem Phys., 2005, 122,
and J. Fierro, Energy Environ. Sci., 2009, 2, 35-54.
044707.
1
2
1
2
1
1
1
2. S. Choi, T. C. Davenport and S. M. Haile, Energy Environ. Sci., 43. H. Ma, G. Wang, Y. Morikawa and J. Nakamura, Sci. China. Ser. B,
019, 12, 206-215.
3. G. W. Huber, J. Shabaker and J. Dumesic, Science, 2003, 300, 44. Y. Yang, H. Zhong, R. He, X. Wang, J. Cheng, G. Yao and F. Jin,
075-2077.
Green Chem., 2019, 21, 1247-1252.
4. D. M. Alonso, J. Q. Bond and J. A. Dumesic, Green Chem., 2010, 45. A. Rodes, E. Pastor and T. Iwasita, J. Electroanal. Chem., 1994,
2, 1493-1513.
376, 109-118.
5. F. Jin, Y. Gao, Y. Jin, Y. Zhang, J. Cao, Z. Wei and R. L. Smith Jr, 46. L. F. Liao, C. F. Lien, D. L. Shieh, M. T. Chen and J. L. Lin, J. Phys.
Chem. B, 2002, 106, 11240-11245.
6. J. Duo, F. Jin, Y. Wang, H. Zhong, L. Lyu, G. Yao and Z. Huo, Chem 47. N. A. Anan, S. M. Hassan, E. M. Saad, I. S. Butler and S. I. Mostafa,
2009, 52, 1427-1433.
Energy Environ. Sci., 2011, 4, 881.
1
Comm, 2016, 52, 3316-3319.
Carbohydr. Res., 2011, 346, 775-793.
1
7. H. Zhong, L. Wang, Y. Yang, R. He, Z. Jing and F. Jin, ACS Appl. 48. J. De Souza, S. Queiroz, K. Bergamaski, E. R. Gonzalez and F. C.
Mater. Interfaces, 2019, 11, 42149-42155.
Nart, J. Phys. Chem. B, 2002, 106, 9825-9830.
1
2
1
9
2
8. H. Zhong, G. Yao, X. Cui, P. Yan, X. Wang and F. Jin, Chem. Eng. J., 49. T. Wang, D. Ren, Z. Huo, Z. Song, F. Jin, M. Chen and L. Chen,
019, 357, 421-427.
Green Chem., 2017, 19, 716-721.
9. M. Wang, M. Liu, J. Lu and F. Wang, Nat. Commun., 2020, 11, 1- 50. J. Su, M. Lu and H. Lin, Green Chem., 2015, 17, 2769-2773.
.
0. M. Liu, Y. Wang, X. Kong, R. T. Rashid, S. Chu, C.-C. Li, Z. Hearne,
H. Guo, Z. Mi and C. J. Li, Chem, 2019.
1. Z. Luo, Y. Ouyang, H. Zhang, M. Xiao, J. Ge, Z. Jiang, J. Wang, D.
Tang, X. Cao and C. Liu, Nat. Commun., 2018, 9, 1-8.
2. N. J. Johnson, B. Lam, B. P. MacLeod, R. S. Sherbo, M. Moreno-
Gonzalez, D. K. Fork and C. P. Berlinguette, Nat. Mater., 2019, 18,
2
2
4
2
2
54-458.
3. J. D. A. Pelletier and J. Basset, Acc. Chem. Res., 2016, 49, 664-677.
4. M. K. Samantaray, V. Delia, E. Pump, L. Falivene, M. Harb, S. O.
Chikh, L. Cavallo and J. Basset, Chem. Rev., 2020, 120, 734-813.
2
9
2
5. S. Kattel, P. Liu and J. G. Chen, J. Am. Chem. Soc., 2017, 139, 9739-
754.
6. T. Schedel-Niedrig, M. Hävecker, A. Knop-Gericke and R. Schlögl,
Phys. Chem. Chem. Phys., 2000, 2, 3473-3481.
7. H. Bluhm, M. Hävecker, A. Knop-Gericke, E. Kleimenov, R.
2
Schlögl, D. Teschner, V. I. Bukhtiyarov, D. F. Ogletree and M.
Salmeron, J. Phys. Chem. B, 2004, 108, 14340-14347.
2
8. H. Duan, J. C. Liu, M. Xu, Y. Zhao, X. L. Ma, J. Dong, X. Zheng, J.
Zheng, C. S. Allen, M. Danaie, Y. K. Peng, T. Issariyakul, D. Chen, A. I.
Kirkland, J. C. Buffet, J. Li, S. C. E. Tsang and D. O’Hare, Nat. Catal.,
2
019.
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