A nanoporous nickel catalyst for selective hydrogenation of carbonates into formic acid in water

Article abstract of DOI:10.1039/c6gc02866g

An efficient unsupported nanoporous nickel (NiNPore) material for the hydrogenation of carbonates to formic acid (FA) in water was investigated for the first time. NiNPore is an environmentally benign catalyst and it exhibited remarkable catalytic activity in the reduction of a wide range of carbonates to afford formic acid in excellent yields with high selectivity, and maximum values of 86.6% from NaHCO₃ and even up to 92.1% from KHCO₃ were obtained. The hydrogen pressure and pK_a of the carbonates had a significant influence on the formation of FA. The catalyst was easily recovered and could be recycled at least five times without leaching and loss of activity. The present study demonstrated a potential application for the synthesis of FA from CO₂ or carbonate compounds.

Full text of DOI:10.1039/c6gc02866g

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Nanoporous Nickel catalyst for selective hydrogenation of
carbonates into formic acid in water
Received 00th January 20xx,
Accepted 00th January 20xx
a,1
a,1
, a
a
, a, b
,b
Tian Wang, Dezhang Ren, Zhibao Huo, * Zhiyuan Song, Fangming Jin,*
Mingwei Chen *
DOI: 10.1039/x0xx00000x
www.rsc.org/
An efficient unsupported nanoporous nickel (NiNPore) material for the hydrogenation of carbonates to formic acid (FA) in
water was firstly investigated. NiNPore represented an environmentally benign catalyst and exhibited remarkable catalytic
activity in the reduction of a wide range of carbonates to afford formic acid in excellent yields with high selectivity, and the
3 3
maximum values of 86.6% from NaHCO and even up to 92.1% from KHCO were obtained, respectively. Hydrogen
pressure and pKa of carbonates showed significant influence on the formation of FA. The catalyst was easily recovered and
could be recycled at least five times without leaching and loss of activity. The present study provided a potential
application for the synthesis of FA from CO
2
or carbonate compounds.
2
catalysts for the hydrogenation of CO to FA have been
1
. Introduction
reported, such as homogeneous metal catalysts (M: Rh, Ir, Ru,
1
1-21
Co, Fe, etc.)
and heterogeneous supported metal catalysts
However, most of those reactions still have considerable
drawbacks. For example, due to the high kinetic and
thermodynamic stability of CO , the reaction requires high-
, thus inorganic or organic bases
are always added into the reaction in order to make the
As is known to all, CO
2
is the main greenhouse gas that
2
2-24
.
causes global warming which has a series of bad influence on
both environment and ecology, such as temperature growth,
forests degradation, glaciers melt, sea level rise, etc., which
2
2
5-29
1
energy starting materials
may destroy the natural balance . To reduce CO2 in the
atmosphere is one of the most important and difficult
2
2
3, 30
,
thermodynamics favourable
. The reactions using
challenges that requires scientific and technological methods
3
homogeneous catalysts were hardly applied in industries
because of two main obstacles: the cleavage of FA from
corresponding salts as bases that are required in the
hydrogenation; the recycling and separation of the bases and
.
CO is often considered as a renewable C1 source to be
2
converted into useful chemicals and fuels such as formic acid
3
, 4
(FA) due to its abundant, nontoxic and readily available
.
FA is a very important organic chemical feedstock because
2
3, 24, 31
the noble catalysts
. Therefore, to avoid that, the
of its numerous applications which has often been found as
acid and reductant and widely used as a precursor in the
5
leather and textile in chemical industries and agriculture .
development of an efficient and green reaction process with a
highly active and selective heterogeneous catalyst for
2
hydrogenation of CO to FA is highly desirable.
Besides, FA has the potential to power fuel cells for electricity
6
-9
Recently, unsupported nanoporous nickel (NiNPore)
material has attracted much attention because of their large
surface-to-volume ratios, distinguished electronic property,
nontoxic nature, high recyclability and simple recovery.
generation and automobiles . Moreover, from the aspect of
energy storage, FA is considered as a hydrogen storage media
or carrier while hydrogen is difficult to handle and transfer due
1
0
to its low density and easily explosive nature . The catalytic
hydrogenation of CO2 to FA is greener and safer as an
attractive route. Advantageous and desirable the way is, it
deserves exploration. The researches focused on different
NiNPore can be prepared by selective leaching of Mn from an
32, 33
alloy foil of Ni30Mn70 at electrochemical conditions
behoves us to think that NiNPore as
hydrogenation of CO to FA should be ideal from
. It
a
catalyst for
2
environmental and industrial viewpoints. Besides, there has
not been reported for the transformation using NiNPore
catalyst so far.
a.
School of Environmental Science and Engineering, Shanghai Jiao Tong University,
Shanghai 200240, China
State Key Laboratory of Metal Matrix Composites, School of Materials Science
and Engineering, Shanghai Jiao Tong University, Shanghai 200030, China
b.
Herein, we first report a safer and greener route for
1
These authors contributed equally to this work and should be considered co-first
authors
hydrogenation of carbonates (as CO
2
sources) to FA by
*
Corresponding Author: Zhibao Huo, E-mail: hzb410@sjtu.edu.cn
unsupported nanoporous nickel in aqueous phase, NiNPore
exhibits significant catalytic activity in the reduction of a wide
range of carbonates to afford formates in excellent yields with
high selectivity (Scheme 1).
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
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ARTICLE
Journal Name
Cat. NiNPore
carried out in a Parr reactor whose internal volume is 100 mL.
The procedure of hydrogenation of NaHCO was as follows.
Firstly, NaHCO (1 mmol, 0.084 g), 10 mL deionized water and
Carbonate
+
H
2
HCOOH
2-
-)
(
CO
3
or HCO
3
3
2
H O
Scheme 1. Hydrogenation of carbonates to FA over NiNPore in
water.
3
desired catalysts were loaded into the reactor. Then, desired
pressure of hydrogen at ambient temperature was introduced
into the reactor from hydrogen cylinder though the intake of
2
. Experimental
2
Parr after purified the reactor three times with 1 MPa H . And
then we began heating and kept stirring at 800 rpm. Once the
temperature inside Parr reactor was heated to the setting
temperature, we started to time. After reaction, we stopped
heating and cooled Parr by an electric fan. Finally, liquid and
gaseous samples were collected for analysis. Solutions were
filtered with 0.45 μm Syringe Filter and solid samples were
washed with deionized water several times and then saved in
ethanol.
2
.1 Experimental materials
NaHCO as the initial reactant was purchased from
Sinopharm Chemical Reagent Co., Ltd, as well were KHCO
NH HCO , Na CO , K CO , CaCO . Hydrogen (99.999%) was
obtained from Shanghai Wetry Standard Reference Gas
Analytical Technology Co., LTD. Ni power, NiO, Ni(NO ·6H O,
3
3
,
4
3
2
3
2
3
3
3
)
2
2
Al-Ni alloy were also purchased from Sinopharm Chemical
Reagent Co., Ltd. And Ru/C (5 wt.%, Aladdin) was as well used
in our experiments. Raney Ni was prepared by ourselves
2
.4 Products analysis
3
4
according to the previous literatures . Formic Acid (Sigma–
Aldrich, >98%) was used in the quantitative analysis of liquid
samples.
Liquid samples were analysed by GC-MS, HPLC and GC-FID
qualitatively and quantitatively. Products were confirmed by
GC-MS (Agilent7890A GC system, 5975C inert MSD with Triple-
AxisDetector) equipped with a HP Innowax polyethylene glycol
capillary column whose dimensions are 30 m × 250 μm × 0.5
μm. The quantitative calculation of FA and byproducts was
conducted by HPLC (Agilent1200 system, equipped with RI and
VW detectors) and GC-FID (Agilent7890A GC system, 5975C
inert MSD with Triple-Axis Detector) equipped with the same
2
.2 Preparation and characterization of catalyst
Ni nanoporous catalyst was prepared according to previous
3
2, 33
literatures
. First, pure Ni and Mn (purity >99.9%) were
melted using an Ar-protected arc melting furnace to form
Ni30Mn70 ingots. Then the ingots were cold-rolled to thin
sheets whose thickness was around 50 µm at room
temperature after annealing at 900 °C for 24 hours for
homogenizing microstructure and composition. Next, Ni
column as GC-MS. The solid samples were analysed by XRD
(
−1
Shimadzu, Lab-XRD-6100, scanning rate: 6◦min , 2θ ranges:
1
0–80◦). Gaseous samples were detected by TCD (thermal
conductivity detector, Agilent Technologies). And a TOC
Analyzer (Shimadzu TOC-V) was used to measure the total
4 2 4
nanoporous was prepared by dealloying in 1.0 M (NH ) SO
aqueous solution at 50 °C. Final, the already prepared samples organic carbon concentration.
were washed thoroughly with water and ethanol and dried in The yields of products (formic acid, acetic acid and methanol)
were calculated as the following equations:
vacuum. The prepared microstructure of dealloyed material
NiNPore by transmission electron microscopy (TEM) is shown
in Figure 1. The structure of NiNPore with bright nano-pores
nproduct after reaction, mmol
Yieldproduct (%) =
× 100%
3
3
nNaHCO in the initial time, mmol
and dark-contrast ligaments can be observed clearly (Figure
(a)) and the pore size is around 7 nm (Figure 1 (b)). The
3
1
2
specific surface area of NiNPore is around 62 m /g (calculated
by the Brunauer–Emmett–Teller (BET) method). The pore size 3. Results and discussion
distributions were also determined from the adsorption
A series of experiments were conducted systematically in
order to investigate the optimum reaction parameters for the
branch of the isotherms based on the density functional
theory (DFT), and calculative pore size is 7.1 nm (Figure SI-2),
which is in good agreement with the TEM observation.
3
hydrogenation of NaHCO to FA. The influences of different
catalysts, amounts of catalyst, temperatures, hydrogen
pressures and reaction times on FA yields were investigated.
Details are showed as follows.
2
.3 Experimental procedure
NaHCO was selected as a source of CO
of reaction conditions in all reactions. All the reactions were
3
2
for the optimization
3
.1 Catalyst screening
Table 1 showed that the effect of different catalysts on FA
(
a)
(b)
yield. To examine the feasibility of hydrogenation of NaHCO
to FA, we tried the reaction with 1 mmol NaHCO and 3 MPa
3
3
2 2
H in the presence of 10 mg (17 mol%) NiNPore catalyst in H O
o
at 200 C for 2 h. The results indicated that the main product
FA was obtained in 63.2% yield with trace amount of methanol
(MA) and acetic acid (AA) (entry 7). These products were
identified by GC-MS as shown in Figure SI-3. The absence of
catalyst only afforded trace amount of FA (entry 1). Among the
Figure 1. TEM images of NiNPore.
2
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a
3
Table 1. Effect of catalysts on the hydrogenation of NaHCO to FA.
Yield (%)
b
FA
Entry
Catalyst
Catalyst loading
b
b
MA
0
AA
1
2
3
4
5
6
7
8
9
none
Ni power
NiO
0
0.5
1.8
3.5
2.2
56.5
60.0
63.2
20.9
62.2
72.6
70.8
54.7
0
17 mol%
13 mol%
10 mg
trace
trace
trace
trace
trace
trace
trace
trace
trace
trace
trace
trace
0.1
trace
trace
0.1
trace
trace
0.3
0.3
0.4
Ni(NO
3
)
2
·6H
2
O
Al-Ni alloy
Raney Ni
NiNPore
Ru/C
NiNPore
NiNPore
NiNPore
NiNPore
10 mg
17 mol%
17 mol%
10 mg
15 mol%
22 mol%
25 mol%
22 mol%
10
11
12
c
0.3
a
c
o
b
Reaction conditions: 1 mmol NaHCO
Temperature was 150 C.
3
, 3 MPa H
2
, H
2
O 10 mL, 200 C, 2 h. FA: Formic acid; MA: Methanol; AA: Acetic acid.
o
3 2 2
various nickels investigated，nickel power, Ni(NO ) ·6H O and It can be seen obviously that the yield of FA increased
NiO catalysts were proved to be not effective for this significantly with the hydrogen pressure increasing from 2 MPa
transformation (entries 2-4). The use of Al-Ni alloy and Raney Ni to 6 MPa (entries 1-4), and the maximum value of 86.6% was
-1
gave good results, but yields were lower relative to NiNPore achieved (TOF of 1738 h , TON of 3476) as hydrogen pressure
catalyst (entries 5 and 6). This might be because big specific surface reached to 6 MPa. FA yield remained unchanged when
area of NiNPore contributed to the hydrogenation of NaHCO
see Table SI-1). The use of Ru/C afforded 20.9% yield (entry 8). The that high hydrogen pressure contributed to the hydrogenation
effect of NiNPore loadings on FA yield was investigated (also see of NaHCO to FA. To promote the hydrogenation of FA, some
Figure SI-4). Decreasing the NiNPore loading gave low yield (entry attempts by adding an alkaline additive (NEt ), decreasing
). When NiNPore loading was increased to 22 mol%, the yield of FA temperature and changing reaction time were also tested, but
increased from 63.2% to 72.6%, further up to 25 mol% gave a low the yields were not improved (entries 5-6 and 8-9, also see
0.8% yield (entries 10 and 11). Decreasing yield might be because Figure SI-7). To understand the effect of additive for the
increasing NiNPore loading could cause the formed FA to reaction, the experiments was conducted with 2 mmol NEt
decompose into CO and H more easily，which was a reversible under the standard conditions. Results showed that residual
reaction competing with hydrogenation process. To confirm this FA (68.7 mmol/L) with 2 mmol NEt was lower than the
3
to FA hydrogen pressure increased to 7 MPa (entry 7). It indicated
(
3
3
9
7
3
2
2
3
hypothesis, reactions were conducted with formed FA as starting without NEt
o
3
(78.7 mmol/L) (see Table SI-3). Moreover, CO
2
material at 3 MPa H
2
for 2 h at 200 C in water using different
a
NiNPore loadings. The results showed that the concentration of FA Table 2. Effect of hydrogen pressure on FA yield.
was decreased from 62.4 mmol/L to 57.3 mmol/L as catalyst
loading increasing from 15 mol% to 22 mol% (Table SI-2) and CO
H2 Pressure
(MPa)
Yield (%)
MA AA
Entry
Time (h)
2
FA
was also detected by GC-MS (Figure SI-5), which supported our
assumption. Besides, low temperature was completely ineffective
1
2
3
4
5
6
7
8
9
2
3
5
6
6
6
7
6
6
2
2
2
2
2
2
2
1
3.5
57.9
72.6
80.5
86.6
84.2
67.7
86.1
83.3
84.7
trace 0.3
trace 0.3
trace 0.3
trace 0.3
trace 0.3
trace 0.4
trace 0.3
for the hydrogenation of NaHCO
3
to FA (entry 12). However, due to
o
the safety factor of Teflon material inside Parr, more than 200
was not inspected.
C
b
c
0.4
0.5
0.3
0.3
3
.2 Effect of hydrogen pressure
Normally, hydrogen pressure has great influence on FA yield.
Further studies on the effect of hydrogen pressure were
a
3 2
Reaction conditions: 1 mmol NaHCO , 22 mol% NiNPore, H O
o
0 mL, 200 C. 2 mmol NEt
b
c
was used. Temperature was
1
1
3
conducted for hydrogenation of NaHCO
3
using NiNPore
o
50 C.
catalyst. The results are summarized in Table 2 and Figure SI-6.
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1
00
80
60
40
20
0
to 90.5% as the ratio of Ni increased, which is consistent with
our assumption. Besides, XRD patterns of fresh NiNPore in
Figure SI-9 indicated that fresh NiNPore was oxidized partly as
o
a broad peak associated with a Ni oxide (located between 60
.
o
and 65 ) can be observed
33
Next, we checked the possibility whether the dissolved
nickel species in water played a catalytic role in the
Fresh
1
2
3
4
5
Recycle times
3
hydrogenation of NaHCO to FA under the optimal conditions.
Figure 2. Recycling tests for the hydrogenation of NaHCO
NaHCO 1 mmol, H 6 MPa, Catalyst 22 mol%, H O 10 mL, 200
C, 2 h).
3
After 0.5 h, we stopped the reaction and filtered to remove
the NiNPore catalyst, and then continued the reaction without
NiNPore for 0.5 h, the result showed that FA yield almost kept
unchanged. Finally, NiNPore was put back to solution and
(
3
2
2
o
was also detected (see Figure SI-8). We thus concluded that
NEt can promote FA decomposition, which can explain the
decreasing yield of FA with NEt in the reaction.
hydrogenation of NaHCO
4.8% yield after 1 h. As an evidence, NiNPore was an efficient
catalyst for the hydrogenation of NaHCO , and no nickel
species was found in water by inductively coupled plasma
ICP).
3
reacted completely to give the FA in
3
8
3
3
3.3 Reusability test
(
Recycling tests of NiNPore catalyst were performed under
the optimal conditions. Results were shown in Figure 2. After 3.4 Catalytic hydrogenation of various carbonates
each recycle, the NiNPore catalyst was simply washed by
Further expanding the scope of the feedstock was carried
deionized water for several times to remove the surface
substances and then reused in the next run without further
purification. After five recycles, high FA yields were still
obtained, indicating that the activity of NiNPore was not lost.
Interestingly, the FA yield was further increased in the first
four recycles and then remained unchanged. It is supposed
that NiNPore catalyst had a little oxidation before the reaction,
and was reduced step by step by hydrogen during the reaction
leading to the increasing yield of FA. To confirm the
hypothesis, XPS measurements of fresh, 1st cycle and 5th cycle
catalysts were provided to investigate the change of nickel and 38
nickel oxide on the surface. The states of nickel on the surface
can be determined from the binding energies (BE). Previous
out with various bicarbonates and carbonates as CO
and the results were summarized in Table 3. As the results
showed, KHCO , K CO and Na CO were also good CO
2
sources,
3
2
3
2
3
2
sources and afforded 92.1%, 76.6% and 71.2% yields,
respectively (entries 2, 5 and 6). It is worth noting that
bicarbonates can give much better yields than corresponding
3
carbonates, and KHCO afforded higher FA yield of 92.1% than
NaHCO (entries 1 and 2). In aqueous solutions, hydrogenation
3
of carbonates is difficult than that of bicarbonates because the
37,
protonation of carbonate ions was considered to be inferior
,
thus bicarbonates can give much better yields compared to
the carbonates. Cations of bicarbonates can affect the
-
2-
3
5, 36
equilibrium between HCO
3
and CO
3
. The concentration of
literatures
54.9 eV and 860.9 eV to Ni 2p3/2 XPS spectra corresponding to
Ni, Ni(OH) and NiO, respectively. From Figure 3 and Table SI-4,
had supported information of BEs of 852.6 eV,
-
HCO3 in KHCO3 solution is higher than that in NaHCO3
solution: NaHCO (0.61M) < KHCO
explain the higher FA yield of KHCO . Bicarbonate with an
ammonium cation (NH ) is not effective and only gave 7.2%
4
yield (entry 3). That’s because HCOONH is more easily to
decompose into NH
HCOONa, The results were shown in Table SI-5. However, the
8
37, 38
3
3
(0.89M)
, which can
2
3
we can see that the ratio of Ni increased from 9.8% to 25.6%
while the ratio of NiO decreased from 24.3% to 17.7% and
Ni(OH) decreased from 65.9% to 56.7% as recycle-times
+
4
2
39
3
, CO
2
and H
2
compared to formed
increased. Results showed that FA yield increased from 86.6%
hydrogenation
of
(a)
(b)
(c)
Ni(OH)2
Ni(OH)2
Ni(OH)2
NiO
Ni
Ni
NiO
NiO
Ni
865
860
855
850
845
865
860
855
Binding energy (eV)
850
845
865
860
855
850
845
Binding energy (eV)
Binding energy (eV)
Figure 3. X-ray photoelectron spectra (XPS) of fresh, 1st cycle and 5th cycle catalyst. (a) fresh catalyst, (b) 1st cycle catalyst, (c)
5th cycle catalyst
4
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H
O
H
O
H
O
Formic Acid
(FA)
O
Methanol
(MA)
O
+
H
2
- H
2
O
H
+ H
2
+ H
2
H
H
H
H
O
O
H
H
O
MO
OH
-O
- H
2
O
a
(
M: Na, K, NH )
4
Table 3. Hydrogenation of various feedstocks as CO
2
source.
NiNPore
NiNPore
NiNPore
NiNPore
Yield (%)
Entry
Feedstock
FA
MA
0.4
AA
0.3
0.3
0
O
H
H
H
O
Acetic Acid
(AA)
1
2
3
4
5
6
7
NaHCO
KHCO
NH HCO
(NH HCO
CO
Na CO
CaCO
3
86.6
92.1
7.2
O
H
O
+ H
2
O
-
2
H O
3
trace
0
NiNPore
NiNPore
4
3
3-
Scheme 2. Plausible pathway for the hydrogenation of HCO
into FA over NiNPore.
4
)
2
3
6.5
0
0
K
2
3
76.6
71.2
0
trace
trace
trace
0
o
2
3
0
aqueous phase at 200 C for 2 h. Extending the scope of the
feedstock showed that the hydrogenation of a wide range of
carbonates can also be catalyzed to formic acid in excellent
yields over NiNPore without any additives. Recycling tests of
NiNPore catalyst indicated that no catalytic activity and
capability lost obviously after recycling five times. The present
study proposed a promising and green method of FA
3
3
0
1
b
8
NaH CO
Na CO
3
3
84.1
(1.2 : 1)
trace
0.2
+
2
a
2
Reaction conditions: 1 mmol Feedstock, 6 MPa H , 22 mol%
o
O 10 mL, 200 C, 2 h. 0.5 mM NaH CO
were used.
b
13
NiNPore, H
mM Na
2
3
and 0.5
2
CO
3
formation by the hydrogenation of carbonates or CO
Further research is underway and to develop efficient methods
2
in water.
2
calcium carbonate as CO source didn’t take place under
for the conversion of CO
2
to value-added chemicals.
optimal conditions due to poor solubility of calcium carbonate
in water (entry 7). In addition, the reactivity was investigated
1
3
simultaneously in hydrogenation of labelled NaH CO
Na CO
under the optimal conditions, and we found that the Acknowledgements
reactivity of NaH CO
3
and
2
3
1
3
3
2 3
was better than that of Na CO with the
ratio of 1.2 to 1 (entry 8). The observation indicated it is
consistent well with the results in entries 1 and 5.
Supported by the State Key Program of National Natural
Science Foundation of China (No. 21436007). Key Basic
Research Projects of Science and Technology Commission of
Shanghai (14JC1403100). The Program for Professor of Special
Appointment (Eastern Scholar) at Shanghai Institutions of
Higher Learning (ZXDF160002). We thank the all reviewers and
editors for reviewing the manuscript and providing valuable
comments.
4
. Mechanistic Studies
4
0, 41
Based on the present findings and previous literatures
,
a plausible mechanism for the hydrogenation of bicarbonates
to FA over NiNPore in water is proposed in Scheme 2. Firstly,
hydrogen is absorbed on the surface of NiNPore catalyst
though the formation of hydrogen bonds between NiNPore
and hydrogen. Additionally, bicarbonate is adsorbed on the
surface of NiNPore by the combination of NiNPore with
carbonylic C and O atoms. When the hydrogen reacts with
bicarbonate molecule, formate is obtained along with the 1.
Notes and references
M. Aresta, in Carbon Dioxide as Chemical Feedstock, ed.
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In summary, we developed an efficient and green process for
the hydrogenation of CO to FA over NiNPore catalyst in water.
2
With optimized conditions in hand, NiNPore exhibited high
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DOI: 10.1039/C6GC02866G
Nanoporous Nickel catalyst for selective hydrogenation of
carbonates into formic acid in water
a,1
a,1
, a
a
, a, b
Tian Wang, Dezhang Ren, Zhibao Huo, * Zhiyuan Song, Fangming Jin, *
,
b
Mingwei Chen *
Graphic abstract