Base-free hydrogen generation from formaldehyde and water catalyzed by copper nanoparticles embedded on carbon sheets

Article abstract of DOI:10.1039/c8cy02079e

Catalytic dehydrogenation from formaldehyde and water provides a promising pathway to produce renewable and clean energy hydrogen resources. Copper-based heterogeneous catalysts show promise to catalytically generate hydrogen from formaldehyde. However, t

Full text of DOI:10.1039/c8cy02079e

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ISSN 2044-4753
PAPER
Qingzhu Zhang et al.
Catalytic mechanism of C–F bond cleavage: insights from QM/MM
analysis of fluoroacetate dehalogenase
rsc.li/catalysis

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Base-free hydrogen generation from formaldehyde and water
catalyzed by copper nanoparticles embedded on carbon sheets
a
a
a
a
a
Xiao Chen, Huan Zhang, Zhaoming Xia, Sai Zhang * and Yuanyuan Ma *
Received 00th January 20xx,
Accepted 00th January 20xx
Catalytic dehydrogenation from formaldehyde and water provides a promising pathway to produce the renewable and clean
energy resource of hydrogen. Copper-based heterogeneous catalysts show promises to catalytically generate hydrogen
from formaldehyde. However, those catalysts incompletely dehydrogenate formaldehyde into formic acid and hydrogen in
the presence of base, leading to only partial utilization of carrier. Herein, we report a simple and facile synthesis of uniform
Cu nanoparticles embedded on carbon sheets (Cu@CS), which enable hydrogen generation through the complete
dehydrogenation between formaldehyde and water in the absence of any additives under mild reaction conditions. The
exceptional performance is linked to the unique embedded structure of catalysts by confining Cu nanoparticles within
carbon sheets as well as the strong interaction between Cu and supports.
DOI: 10.1039/x0xx00000x
www.rsc.org/
Advances have now been made in the developments of
various catalytic systems for the low-temperature hydrogen
1
. Introduction
1
9-36
generation from methanol or formaldehyde.
Compared
The decrease in fossil fuel supply and severe fossil fuel-related
environmental problems have stimulated the ever-growing and
intensive efforts to seek for the renewable and clean energy
resources. As a clean energy resource with a high energy density
of 142 MJ kg , hydrogen is a promising alternative of the fossil
fuels.1
Unfortunately, its gaseous and explosive
physicochemical properties make the transport and handling of
hydrogen difficult, which might restrict its wide utilizations.
Various solid or liquid chemicals have been investigated as
hydrogen storage materials for both mobile and stationary
applications.3 Currently, the most promising materials are the
hydrides with high hydrogen weight densities, such as ammonia
borane and it’s derivatives,
acid,1
with a high theoretical gravimetric hydrogen capacity of 19.4
wt%.5 However, the release of hydrogen from ammonia
borane entails the problem with accompany of large scale solid
wastes. Although formic acid as liquid hydrogen carrier can
release hydrogen at room temperature catalyzed by various
homogeneous or heterogeneous catalysts,
with the endothermic process for hydrogen generation from
methanol and water, the exothermic process from
formaldehyde and water should provide a stronger driving force
2
9
for H
2
production. Most of the successful systems are
-1
catalyzed by homogeneous noble metal complexes (e. g. Rh, Ru,
1
9,23,24,26,31
Ir).
Generally, the sophisticated ligands, strong base
and/or other additives are required to promote the efficient
hydrogen generation under mild conditions. Among them, the
complete dehydrogenation between water and formaldehyde
2
2 2
with the release of H and CO can further improve the effective
,4
hydrogen content from 6.7 wt% of formaldehyde to 8.4 wt% of
formaldehyde and water. Noble metal Ru and Ir complexes have
been reported to deliver high catalytic performance for
dehydrogenation between formaldehyde and water.2
5
-10
11
hydrous hydrazine, formic
Ammonia borane is a stable solid
2-18
19-26
and methanol.
7,28,30
Nevertheless, the separation and recycle of those expensive
catalysts from the homogeneous hydrogen generation system
are difficult and costly. Moreover, some of those homogeneous
noble metal catalysts might be sensitive to air and decompose
,7
6
1
9
under oxidative conditions. Also, their catalytic activities are
highly dependent on the basicity of reaction solution and/or
assisted by other additives, leading to the harsh reaction
environments and additional cost for the reactors with high
resistance to the basic corrosion. Therefore, the developments
of the heterogeneous catalysts based on earth-abundant
metals (e.g. Fe, Co, Ni, Cu) with copious supply are important to
realize sustainable hydrogen generation from formaldehyde
and water. Among various transition metals, heterogeneous
copper nanocatalysts delivered the capability for efficient
1
4-18
its relative low
hydrogen content (4.4 wt%) limits its practical applications.
Thus, small organic molecules with high hydrogen contents,
such as methanol with a hydrogen capacity of 12.5 wt% and
formaldehyde with a hydrogen capacity of 6.7 wt%, would be
better choices as liquid hydrogen carriers.
a. Center for Applied Chemical Research, Frontier Institute of Science and Technology
and School of Chemical Engineering and Technology, Xi’an Jiaotong University,
Xi’an, 710049, China.
2
5,37-43
*
Corresponding authors.
E-mail: zhangsai058@mail.xjtu.edu.cn and yyma@mail.xjtu.edu.cn
Footnotes relating to the title and/or authors should appear here.
catalytic dehydrogenation.
The Cu-based nanoparticles
anchored on supports have been reported to catalyze
formaldehyde into hydrogen and formic acid under room
†
Electronic Supplementary Information (ESI) available: See DOI: 10.1039/x0xx00000x
3
7-39
temperature with basic additives.
The incomplete
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dehydrogenation of formaldehyde leads to the significantly with 10 wt% metal loading were prepared thrVoieuwgAhrticlae Ownlienet
decreased hydrogen content of 4.2wt% compared with the impregnation method. Briefly, 200 mgDOofI: 1C0.1s0u3p9/pCo8rCtYs02w0e79reE
theoretical value of 8.4 wt%. Also, the formed formates might dispersed in a 15 mL of ethanol solution with 0.3125 mmol
3 2 2
corrode the metal catalysts, leading to their poor catalytic Cu(NO ) ·3H O. Then, the ethanol solution was evaporated at
3
7
stability. In addition, the Cannizzaro reaction of formaldehyde 40 °C after continuous stirring for several hours at room
could happen under the high concentration of base, lowering temperature, and the obtained solid catalysts were dried
3
8
the effective hydrogen storage content. In this case, it is of overnight at 60 °C. Finally, the catalysts were treated with 5
o
-1
2
great significance to realize the complete dehydrogenation vol% H /Ar at 300 °C for 2 h with a ramping rate of 1 C min .
from formaldehyde and water, which is catalyzed by non-noble Characterization. The structure and composition of the samples
metal heterogeneous catalysts in the absence of base and other were monitored by powder X-ray diffraction (XRD, Cu Kα
additives under the mild conditions.
radiation, Shimadzu XRD-6000), Transmission electron
Herein, we report a base-free hydrogen generation through microscopy (TEM, Hitachi HT-7700) with an accelerating voltage
the completed dehydrogenation from formaldehyde and water of 120 kV and high-resolution TEM (FEI Tecnai G2 F20 S-TWIN)
catalyzed by Cu nanoparticles embedded on carbon sheets with an accelerating voltage of 200 kV were performed to
(
Cu@CS). The Cu@CS catalysts were synthesized by a facile and analyze the microstructures of Cu@CS catalysts. The yield of
2
+
cost-effective pyrolysis of the solid mixture of Cu and chitosan hydrogen was analyzed by gas-chromatography (Techcomp GC
under argon (Ar) atmosphere. Experimental results showed that 7900). The X-ray photoelectron spectroscopy (XPS, Thermo
one molecule of formaldehyde and one molecule of water were Fisher Scientific ESCALAB Xi+) was measured with
2
completely transformed into two molecules of H and one monochromatic Al Kα line. The mass spectrum was obtained on
molecule of CO . The hydrogen generation rate reached 1.15 a Pfeiffer Vacuum instrument with model GSD 320 O2. The Cu
2
-1
-1
mol molCu h at 120 °C and remained catalytic activity for at content of Cu-based catalysts were identified by inductively
least 50 h. Control experiments, kinetic and X-ray photoelectron coupled plasma mass spectrometry (ICP-MS, PerkinElmer
spectroscopy (XPS) analysis exhibited that the unique NexION 350D ICP-MS). The Brunauer-Emmett-Teller (BET)
embedded structures of Cu@CS catalysts not only stabilized the specific surface areas of catalysts are measured from the
Cu nanoparticles during the hydrogen generation reaction but nitrogen adsorption-desorption isotherms at 77 K (Quadrasorb
also promoted their catalytic activity.
si-3).
.2. Catalytic activity test.
2
In general reaction conditions, 5 mg of Cu@CS catalysts were
added to 4.3 mL of solution with various concentration of
formaldehyde in a 30 mL sealed glass bottle. After bubbled with
argon for 30 min, the hydrogen generation between
formaldehyde and water were proceeded at certain
temperatures (100, 110, 120, and 130 °C) with reflux
condensation. For other catalysts, 20 mg of carbon sheets,
carbon particles (C) and Cu/C catalysts were used. For
quantifying the generated hydrogen, 100 μL of gases was taken
out from the vessel and tested by GC at intervals. The hydrogen
generation rates were normalized based on each exposed Cu
atoms to avoid the affection of morphology, specific surface
area and the size of Cu nanoparticles.
2
. Experimental
2
.1 Sample preparation and characterization
Materials: All chemicals were purchased from commercial
suppliers and used as provided: Cu(NO ·3H O (Energy
3
)
2
2
Chemical, 99%), Chitosan (TCI, 200-600mPa.s, 0.5% Acetic Acid
at 20 °C), Acetic acid (Sigma-Aldrich, 99.7%), Formaldehyde
(
Alfa Aesar, 37 wt% in aq. soln., ACS, 36.5-38.0%, stab. with 10-
5% methanol Liquid), D O (Energy Chemical, 99.9% D, for
NMR), sodium hydroxide (Sigma-Aldrich, ≥ 97%).
Synthesis of Cu@CS catalysts. Briefly, Cu(NO ·3H
1
2
3
)
2
2
O (473 mg)
and chitosan (500 mg) were dissolved in 80 mL of 1.25 wt%
acetic acid solution and adequately mixed under stirring to
obtain the blue Cu-chitosan solution at 80 °C. After dried at 100
°
C overnight, the obtained Cu-chitosan precursor was pyrolyzed
3
. Results and discussion
-1
at 600 °C for 2 h with heating rate of 1 °C min under Ar
atmosphere.
Synthetic schematic of the Cu@CS catalysts was illustrated in
·3H O and chitosan were dissolved
00 mg of chitosan dissolved in 80 mL of 1.25 wt% acetic acid in 1.25 wt% acetic acid aqueous solution and mixed under the
solution under stirring to obtain the transparent solution at 80 vigorous stirring to obtain the blue Cu-chitosan solution. After
C. After dried at 100 °C overnight, the obtained precursor was drying at 100 °C overnight, the obtained Cu-chitosan precursors
Synthesis of carbon particles (C). In the absence of copper salts, Figure 1a. Typically, Cu(NO
)
3 2
2
5
°
-1
pyrolyzed at 600 °C for 2 h with heating rate of 1 °C min under were pyrolyzed under Ar atmosphere. The powder X-ray
Ar atmosphere. diffraction (XRD) patterns of as-synthesized Cu@CS exhibited
Chemical etching of Cu nanoparticles of Cu@CS. Typically, 200 three diffraction peaks at 43.3, 50.5 and 74.2°, which
mg of Cu@CS was dispersed in a round-bottom flask contained corresponded to the characteristic diffraction peaks of (111),
2
3
0 mL of 1 M HNO with reflux condensation at 80 °C for 20 h. (200) and (220) lattice planes of the cubic phase metallic Cu
And then, the obtained carbon sheets were washed with (PDF No. 65-9026), respectively (Figure 1b). Transmission
deionized water for several times until the solution pH at 7. electron microscopy (TEM) image of the Cu@CS catalysts
Synthesis of Cu/C catalysts. Cu nanoparticles supported on C
2
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DOI: 10.1039/C8CY02079E
Figure 2 Catalytic hydrogen production from formaldehyde and water. (a) Plots of
hydrogen production vs reaction time under various conditions. Reaction conditions: 5
or 0 mg of the Cu@CS catalysts, 4.3 mL of aqueous HCHO solution (0 M/0.70 M) and 120
°
C, Ar. (b) Hydrogen release rates in aqueous HCHO solution with various concentrations.
Reaction conditions: 5 mg of the Cu@CS catalysts, 4.3 mL of aqueous HCHO solutions
with various concentrations and 120 °C, Ar. (c) Hydrogen production rates under various
reaction temperatures. Reaction conditions: 5 mg of the Cu@CS catalysts, 4.3 mL of
aqueous HCHO solution (0.70 M) and various temperatures, Ar.
Figure 1 Synthesis and characterization of catalysts (a) Schematic illustration of synthesis
of the Cu@CS catalysts. (b) XRD pattern, (c) TEM image and (d) HRTEM image of the
Cu@CS catalysts.
showed that Cu nanoparticles with an average size of 14.6 ± 4.0 catalysts (Figure S4a†). As a parallel, the carbon particles were
nm were uniformly embedded within carbon sheets (Figure 1c also synthesized through the direct pyrolysis of chitosan
2
+
and Figure S1a†). As shown in Figure 1d, the measured lattice without Cu ions by the identical synthetic procedure of the
fringe spacing of 1.806 Å could be well ascribed to the (200) Cu@CS catalysts (Figure S4b†). Both of the carbon sheets and
carbon particles delivered bare catalytic activity for the
hydrogen generation from formaldehyde and water under the
same conditions (Figure S5a† and Figure S5b†). Meanwhile, the
Cu@CS catalysts also catalyzed the hydrogen generation under
crystal face of metallic Cu, consistent with the XRD
measurements. Also, the Cu nanoparticles were surrounded by
amorphous carbon sheets, observed from the high resolution
TEM image. The actual Cu content in the Cu@CS catalysts was
2
air atmosphere. As shown in Figure S6a†, the H production was
5
2.8 wt%, determined by ICP-MS measurements. Meanwhile,
increased for initial 6 h reaction and then tend to balance under
the same reaction conditions. The disappeared catalytic activity
of Cu@CS during the hydrogen generation in the air
atmosphere can be attributed to the partial oxidized surface of
the specific surface area of Cu@CS could be measured as 107.7
2
-1
m g with average pore size of 1.13 nm from the Brunauer-
Emmett-Teller (BET) analysis (Figure S2†).
The Cu@CS catalysts were used to catalyze the hydrogen
generation through dehydrogenation from formaldehyde and
Cu to Cu
2
O obtained from the XRD pattern (Figure S6b † ).
Therefore, these control experiments suggested that the
water. In general reaction conditions, 5 mg of the Cu@CS metallic Cu nanoparticles in the Cu@CS catalysts served as the
catalysts were added into 4.3 mL of aqueous formaldehyde catalytic active components for the catalytic hydrogen
solution with various concentrations in air-tight glass bottles (30 generation from the formaldehyde and water system.
mL). After degassed with Ar for 30 min, the hydrogen
The effects of the dosage of catalysts, concentrations of
generation reactions were proceeded at 120 °C. In the presence formaldehyde and reaction temperatures were also
of only catalysts, formaldehyde and water, the Cu@CS catalysts investigated. Although the hydrogen production could be
gave a linearly increased hydrogen production with a rate of increased with the increase of catalyst dosage, the rates were
-
1
-1
decreased from 1.15 mol mol -1 -1 to 1.02 mol molCu-1 -1 and
Cu
h h
1
.15 mol molCu h (Figure 2a). On the contrary, there was no
-1
-1
hydrogen generation in the absence of the Cu@CS catalysts then to 0.65 mol molCu h for the 5 mg, 10 mg and 20 mg
under the same reaction conditions, indicating their catalytic catalysts, respectively, as shown in Figure S7†. Thus, the 5 mg
capability for dehydrogenation between formaldehyde and of Cu@CS was selected as the optimized catalyst dosage for the
water. Also, there was no hydrogen produced from the hot hydrogen generation. With the increase of the concentrations
water with or without the Cu@CS catalysts, suggesting of formaldehyde, the hydrogen generation rates initially
formaldehyde indeed involved in hydrogen production. The increased and then decreased, as shown in Figure 2b and Figure
-
1
possible influence of small amount methanol in formaldehyde S8†. The highest hydrogen generation rate of 1.15 mol molCu
-1
solution can be excluded by the no hydrogen generation from h could be yielded with the concentration of formaldehyde of
methanol solution with the Cu@CS catalysts under the same 0.7 M. Meanwhile, with the increase of the reaction
reaction conditions (Figure S3†). Importantly, no base and any temperatures from 100 °C, to 110 °C, 120 °C and then 130 °C,
-1
-1
other additives were required for this catalytic hydrogen the hydrogen release rates increased from 0.55 mol molCu h ,
-1
-1
-1 -1
production system.
to 0.88 mol molCu h , 1.15 mol molCu h and then 1.67 mol
In order to understand the role of Cu and carbon for hydrogen molCu h , respectively (Figure 2c and Figure S9†). In addition,
-1
-1
generation, the copper nanoparticles of the Cu@CS catalysts the hydrogen production could be occurred even at 30 °C by the
were removed by nitric acid (1 M) at 80 °C. The etched catalysts
left the carbon sheets with many bowl-like pits, also confirming
the embedded structural features of the Cu@CS
Cu@CS catalysts in the presence of base (Figure S10†).
To understand hydrogen generation through such a
dehydrogenation process of the aqueous formaldehyde
solution, the generated gases were analyzed by GC to monitor
their compositions and yields. Generally, the hydrogen release
from formaldehyde and water involves three steps: (1) the
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formation of methanediol in the aqueous formaldehyde
solution; (2) the conversion of methanediol into formic acid
with the release of one hydrogen molecule; and (3) subsequent
decomposition of formic acid with the release of one more
View Article Online
DOI: 10.1039/C8CY02079E
2
7
hydrogen molecule and one CO
complete dehydrogenation between formaldehyde and water
should give two molecules of H and one molecule of CO . For
the Cu@CS catalyzed reaction, both H and CO could be
released from the initial period (Figure 3a). However, the molar
ratio of H : CO was 4.27:1 much larger than the theoretical
value of 2:1. The phenomenon can be attributed to the
2
molecule.
Thus, the
2
2
2
2
2
2
3
6
dehydrogenation of methanediol to formic acid and the
dissolution of CO in formaldehyde and water at the initial stage
of the hydrogen generation. Afterwards, the molar ratios of
:CO could be fluctuated around 2:1, indicating the complete
2
H
2
2
dehydrogenation between formaldehyde and water.
Based on the above analysis, water should be involved in the
hydrogen generation to realize the complete dehydrogenation.
Detailed analysis of the dehydrogenation process exhibited that
one H atom of generated H
molecule. To confirm the origin of H
O for the hydrogen generation. As shown in Figure 3c and
2
molecule derived from H
2
O
2
, D O was used to replace
2
H
2
-1
-1
Figure 3d, the hydrogen generation rate of 0.29 mol molCu
h
in D O, 3.97 times lower than the rate in H O, indicated that
2
2
water played a crucial role in the dehydrogenation process.
Meanwhile, the gaseous products were analyzed by mass
spectrometry (MS). As shown in Figure 3e and Figure 3f, CO
2
Figure 3 Catalytic pathway for hydrogen production from formaldehyde and water by
molecules were detected in the gaseous phase products for the Cu@CS catalysts. (a) Plot of the mole of the generated H
2
and CO
as a function of reaction time.
production at 120 °C with H O or
O during 5 h reaction. Mass spectrogram of
the gases generated form formaldehyde (e) H O and (f) D O system. Reaction
O and formaldehyde was observed conditions: 5 mg of the Cu@CS catalysts, 4.3 mL of aqueous HCHO solution (0.70 M), and
2
vs reaction time.
(
b) Plot of the molar ratio of the generated H
Isotope-labelling experiments of D O and H O: (c) H
O. (d) H generation rates in H O and D
2 2
and CO
both H
catalytic pathways. By comparing the hydrogen generation
from H O and formaldehyde, the MS signal of m/z 3 for
hydrogen generated from D
and assigned to HD, revealing H
from water and another H atom from formaldehyde. While, the
can be attributed to the Cu@CS catalysts (1.15 mol molCu h-1) (Figure S14 † ). More
observation of the m/z 4.0 peak of D
exchange of H and D between formaldehyde and D
Therefore, the analysis on the gaseous phase products by MS
provided the direct evidences for both water and formaldehyde
as the source of hydrogen molecule and hydrogen generation
through the dehydrogenation between water and
formaldehyde.
2 2
O and D O as the reactants, suggesting their similar
2
2
2
2
D
2
2
2
2
2
2
2
2
generation with one H atom 120 °C, Ar .
2
-1
2
O. importantly, the hydrogen generation catalyzed by the Cu/C
catalysts tended to be deactivated after 180 min reaction, while
the hydrogen generation of the Cu@CS catalysts was linear
increased steadily.
2
To understand their different catalytic performance, the
catalysts were examined by XPS. Both of the Cu@CS and Cu/C
catalysts exhibited the metallic Cu from the XPS analysis of Cu
The embedded structure of Cu nanoparticles on the carbon
sheets in the Cu@CS catalysts is also expected to provide a
2
p peaks (Figure 4b and Figure S15†). However, the 932.1 eV
strong interaction between metal and supports, which binding energy of Cu 2p3/2 peak for the Cu@CS catalysts was
improves both the catalytic activity and structural stability of higher than that of the Cu/C catalysts at 931.3 eV, indicating the
catalysts during the reaction. In this case, the catalytic more electrons transition from Cu nanoparticles to carbon
performances of Cu nanoparticles with average size of 26.7 ±
.6 nm supported on the surface of carbon particles (Cu/C. TEM
sheet in the Cu@CS catalysts. The Cu 2p1/2 peaks also exhibited
the similar tendency. In this case, the surface Cu fraction of
6
δ+
images, size distribution and XRD pattern were shown in Figure
S11†, Figure S12a† and Figure S13†, respectively), and the Cu
content was 9.57 wt% according to the ICP-MS results. The
Cu/C samples were also tested as reference catalysts under the
identical reaction conditions. Figure 4a exhibited the catalytic
performance of the Cu@CS and Cu/C catalysts for the hydrogen
generation from formaldehyde and water system. Obviously,
the Cu@CS catalysts was higher than that of the Cu/C catalysts,
due to the stronger electronic metal-support interaction (EMSI)
in the Cu@CS catalysts with lager contact area between
embedded Cu nanoparticles and carbon sheets. Therefore, Cu
nanoparticles in the Cu@CS catalysts exhibited the lower
electronic density. Previous reports have proved that the
slightly positively charged Cu species in Cu nanoparticles are
more efficient for the dehydrogenation between formaldehyde
-1
-1
the initial hydrogen generation rate of 0.61 mol molCu h for
the Cu/C catalysts was 1.9 times lower than the rate of the
4
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and water.25 Therefore, it is easy to understand the higher In conclusion, the Cu@CS catalysts with unique embedded
View Article Online
DOI: 10.1039/C8CY02079E
catalytic activity of the Cu@CS catalysts for hydrogen
structures have been developed as heterogeneous catalysts for
the complete dehydrogenation of formaldehyde and water into
2 2
H and CO with a final molar ratio of 2:1 in the absence of base
media and any other additives under mild conditions. The
catalysts were synthesized through a facile and cost-effective
2
+
pyrolysis of Cu and chitosan mixture. The unique embedded
structure of Cu@CS can stabilize Cu nanoparticles compared
with the supported catalysts, which avoids the agglomeration
of Cu nanoparticles during the reaction. The embedded
structure also guarantees the strong electronic interaction
between Cu nanoparticles and carbon supports, which can
modulate the electronic structure of the active copper and
enhance their hydrogen generation activity. The exciting
demonstration of Cu@CS catalysts provides the high possibility
for practical applications of hydrogen generation from
formaldehyde solution.
Conflicts of interest
Figure 4 Catalytic stability. (a) Hydrogen production of the Cu@CS and Cu/C catalysts.
Reaction conditions: Cu@CS (5 mg) or Cu/C (20 mg), HCHO (0.70 M, 4.3 mL), and 120 °C, There are no conflicts to declare.
Ar. (b) Cu 2p XPS spectra of the Cu/C and Cu@CS catalysts. (c) Catalytic stability of
hydrogen release in the Cu@CS-HCHO-H O system (Insert image was TEM image of the
2
used Cu@CS catalysts). Reaction conditions: Cu@CS (5 mg), 4.3 mL of aqueous HCHO
solution (0.70 M), and 120 °C, Ar.
Acknowledgements
We acknowledge the financial support from the China
Postdoctoral Science Foundation Grant 2017M620453,
production through the dehydrogenation between
formaldehyde and water.
2
018T111067. Authors acknowledged the financial support
from the Xi’an Jiaotong University. We thank Miss Liu at
Instrument Analysis Center of Xi'an Jiaotong University for her
assistance with XPS tests.
In addition, the embedded structure of the Cu@CS catalysts
also benefit for their catalytic stability. To expose the catalytic
stability of Cu@CS catalysts for the hydrogen generation from
2
formaldehyde and H O system, the long-term durability
experiments were performed by using 5 mg of Cu@CS catalysts
in 4.3 mL of HCHO solution with a concentration of 0.7 M at 120
Notes and references
°
C under Ar atmosphere. As shown in Figure 4c, hydrogen could
1
2
3
4
5
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-1
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h
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Figure 4c and Figure S1b†) and phase (Figure S13†) of the used
Cu@CS catalysts indicated their structural robustness and
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Catalysis Science & Technology
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DOI: 10.1039/C8CY02079E
TOC
Base-free hydrogen generation through the completed dehydrogenation from formaldehyde and
water catalyzed by Cu nanoparticles embedded on carbon sheets.
1