G-C3N4 supported metal (Pd, Ag, Pt) catalysts for hydrogen-production from formic acid

Article abstract of DOI:10.1039/c8nj00404h

g-C₃N₄ supported metal (Pd, Ag, Pt) catalysts were synthesized, and their catalytic performances for hydrogen-production from formic acid were evaluated. The Pd catalyst can effectively turn formic acid into H₂ and CO₂ with 100% selectivity at room temperature or even at a lower temperature. The catalysts were characterized with TEM, XPS, PXRD, ICP, Chemisorption, IR spectra and Raman spectra. The results indicate that the good catalytic performance of the catalysts could be attributed to the interaction between g-C₃N₄ and the metal nanoparticles: that is, the overlap between the d-orbitals of Pd and the π-conjugated system of g-C₃N₄. The effect of the interaction was verified by analyzing the contrasting catalytic performances of Pd/g-C₃N₄, Ag-Pd/g-C₃N₄, Pt-Pd/g-C₃N₄ and Pd/HTNTs (hydrogen titanate nanotubes) for hydrogen-production from formic acid.

Full text of DOI:10.1039/c8nj00404h

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ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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g-C3N4 supported metal (Pd, Ag, Pt) catalysts for hydrogen-
production from formic acid
Xiaotong Liu a, Penghe Su a, Ya Chen a, Baolin Zhu a,c, Shoumin Zhang a,c and Weiping Huang a,b,c*
Received 00th January 20xx,
Accepted 00th January 20xx
ABSTRACT: g-C3N4 supported metal (Pd, Ag, Pt) catalysts were synthesized, and their catalytic performances for hydrogen-
production from formic acid were evaluated. The Pd catalyst can effectively turn formic acid into H2 and CO2 with 100%
selectivity at room temperature or even lower temperature. The catalysts were characterized with TEM, XPS, PXRD, ICP,
Chemisorption, IR spectra and Raman spectra. The results indicate that good catalytic performance of the catalyst was
attributed to the interaction between g-C3N4 and metal nanoparticles that is the overlap between d-orbits of Pd and π-
conjugated system of g-C3N4. The effect of interaction was verified by the contrast analyzing the catalytic performances of
Pd/g-C3N4, Ag-Pd/g-C3N4, Pt-Pd/g-C3N4 and Pd/HTNTs (hydrogen titanate nanotubes) for hydrogen-production from formic
acid.
DOI: 10.1039/x0xx00000x
www.rsc.org/
hydroxyapatite,17 graphite,18 TiO2-nanotubes (TNTs) and other
supporters. g-C3N4 of large π-conjugated system is an
interesting support, which is applied in several fields, such as
Introduction
A limited amount of fossil fuel in the earth drives people to
develop new and renewable energy, because the fossil fuel will
be used up in the foreseeable future. H2 energy, a renewable
energy, is becoming high attracting attention.1 One of the
processes of H2 energy utilization is the hydrogen-generation.
In terms of generation of H2, besides traditional water-gas shift
process etc. there are various developing methods, such as
photocatalytic decomposition of water2, biological hydrogen
production,3 catalytic decompositions of organic compounds4, 5
and so on. Among those methods, catalytic decomposition of
organics should be a more practical one in view of the fact that
organics used can be carried conveniently, synthesized
massively and decomposed efficiently. Formic acid (FA) is
widely used as hydrogen source because of its hydrogen
content (4.4 wt.%), nontoxicity, stability under ambient
condition6, easy-to-gain7 and so on. The FA can be selective
catalytically decomposed into H2 and CO2 by using
homogeneous8 and heterogeneous catalysts, such as metals
(e.g. Ru,9 Rh,10 Au,11 Pd,12 Cu13 Ag-Pd Alloys14 and Pt-Cu
Alloys15) and supported metals16. Among them the Pd shows
high activity. To make use of Pd more efficiently and increase
its catalytic activity as well as selectivity for H2, supports of
supported-Pd catalysts are extensively investigated, including
decomposition of water,19 chemical hydrogen storage20, 21
,
transfer hydrogenation22 and so on. Furthermore, g-C3N4 and
its modified products are also used in hydrogen-production
from formic acid 23-26
With a great template, mesoporous g-
.
C3N4 can be synthesized. Using this mpg-C3N4, metal like Pd
can be separated as single atoms.27
It has been reported that the assistant of sodium formate (SF)
is needed for increasing the reaction rate in the Pd catalysing
dehydrogenation of FA, in which the formate ion (HCOO-)
binds Pd NPs firstly.28,29 In view of the reference 30, the
promotion effect originates in the electron donation ability of
HCOONa toward the Pd surface, based on which it should be
theoretically reasonable and attracting to design and
synthesize Pd catalyst supported by the support with π-
conjugated system for the catalytically dehydrogenation of FA.
In such catalyst, the electron density on Pd NPs may be
reduced through the interaction between Pd and support. As
the result of it, HCOO- ions bind Pd NPs more smoothly, and
catalytic activity of catalyst, in turn, is enhanced.
In the present contribution, we design and synthesize g-C3N4
supported metal (Pd, Ag, Pt) catalysts, in which the large π-
conjugated system of g-C3N4 can accept the electron transfer
of palladium etc. nanoparticles by d-pπ action. The interaction
between Pd NPs and g-C3N4 not only effectively disperse Pd
NPs, but also obviously promote electron flowing. As a result,
the catalyst can catalyse hydrogen-production from formic
acid at room temperature with a high selectivity.
Experimental section
Synthesis of catalyst
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(1) Synthesis of g-C3N4. g-C3N4 was synthesized by direct (9) Synthesis of Ag-Pd/HTNTs. Silver nanoparticles were
pyrolysis of carbamide according to the previous report.31 The deposited on the Pd/HTNTs by same procedure as synthesis of
procedure is described as follows: 10 g of carbamide power Ag/g-C3N4, besides that 0.5
was put into a crucible with a cover and then heated at 500 Pd/HTNTs, and xenon lamp was replaced by the mercury lamp.
(with a heating rate 10
min-1) for 2 h in a muffle furnace. The Product was labeled as Ag-Pd/HTNTs.
product was washed with deionized water and dried at 80 Scheme 1. Schematic Representation for the Synthesis and
g g-C3N4 was replaced by
℃
℃
℃.
(2) Synthesis of Pd/g-C3N4. 1 g of g-C3N4 was dispersed in 15 Catalysis of Pd/g-C3N4 Catalyst
mL acetic acid, which was saturated solution of palladium
Characterizations of catalyst
diacetate. This mixture was stirred for
6 h at room
temperature. After centrifuged and dried, the solid was The metal contents in catalysts were determined by
dispersed and reduced in 20 mL 20% sodium formate (SF) inductively coupled plasma spectrometers (X7 Thermo Fisher
solution, and pH of the solution was adjusted to 10 with 1 M Scientific). Powder X-ray diffraction (XRD) measurements were
NaOH solution. After vigorous stirred for 3 h, the solid was performed on D/max-2500 X-ray diffraction analyzer of Rigaku
centrifuged, washed with deionized water, dried and labeled Corporation, with Cu K
as Pd/g-C3N4. nickel filter (18 KW 60 KV
(3) Synthesis of Pt/g-C3N4. Platinum nanoparticles were a scan rate of 0.02
s-1 and the 2
α
,
λ
= 0.154 nm radiation as source with
300 mA). Data were recorded at
range from 3 to 80 . X-
，
，
°
2
θ
θ
°
°
deposited on the g-C3N4 by photo-reduction.32 0.5 g g-C3N4 ray photoelectron spectroscopy (XPS) analysis was performed
powder was dispersed in 40 mL 90% ethanol solution, and 5 on Esalab 250Xi, using an Al X-ray source, and the binding
mL of H2PtCl6 solution (0.01 M) was added. Then the mixture energy was calibrated by taking C1s peak at 284.6 eV as
was irradiated by visible light from 500 W Xenon lamp for 2 h. reference. Transmission electron microscopy (TEM) image was
Solid was collected and washed with deionized water. After recorded using a JEOL Model JEM-2100 instrument at an
dried, product was labeled as Pt/g-C3N4.
accelerating voltage of 200 kV.
(4) Synthesis of Ag/g-C3N4. Silver nanoparticles were deposited Nitrogen adsorption–desorption isotherms were collected on
on the g-C3N4 by the same procedure as synthesis of Pt/g-C3N4, Autosorb-1-MP 1530VP automatic surface area and porosity
besides that 5 mL H2PtCl6 solution was replaced by 5 mL AgNO3 analyzer. The sample was degassed at 200 ℃ for 5 h and then
solution (0.01 M), and product was labeled as Ag/g-C3N4. analyzed at -196 . The relative pressure (P/P0) range used for
℃
(5) Synthesis of Pt-Pd/g-C3N4. Platinum nanoparticles were calculation of BET surface area was from 0.05 to 0.30. The H2
deposited on the Pd/g-C3N4 by the same procedure as chemisorption was carried out on Autosorb IQ C-XR
synthesis of Pt/g-C3N4, besides that 0.5 g g-C3N4 was replaced (Quantachrome Instruments). Prior to measurements, 0.410 g
by Pd/g-C3N4, and product was labeled as Pt-Pd/g-C3N4.
of Pd/g-C3N4 was thermally treated under a He stream at 100
℃ for 60 min to remove physically adsorbed water and other
(6) Synthesis of Ag-Pd/g-C3N4. Silver nanoparticles were
deposited on the Pd/g-C3N4 by the same procedure as impurities. The sample was cooled down to room temperature
synthesis of Pt-Pd/g-C3N4, besides that 5 mL H2PtCl6 solution and heated to 150 with a heating rate of 10
min-1 using
was replaced by 5 mL AgNO3 solution (0.01 M), and product pure H2 at 50 mL min-1. The oxides on the sample surface were
was labeled as Ag-Pd/g-C3N4 then reduced in a pure H2 flow at 150 for 60 min. After the
(7) Synthesis of Pd/HTNTs. Hydrogen titanate nanotubes reduction at 150 , the sample was purged with a He gas at
(HTNTs) are synthesized according to the previous report.33 To the same temperature for 30 min. After cooling to 40
, a
℃
℃
℃
℃
℃
obtain Pd/HTNTs, photo-reduction was applied. 0.5g HTNTs pure H2 was introduced for the combination of H2
powder was dispersed in 35 mL 90% ethanol solution, and 10 chemisorption and physical adsorption (the pressure range
mL of (NH4)2PdCl4 solution (0.05 M) were added. Then the was from 5332.89 to 106657.89 Pa), and after evacuated, He
mixture was irradiated by UV-light from 300 W mercury lamp was introduced for the physical adsorption. Then we can get
for 2 h. Product was labeled as Pd/HTNTs.
the H2 chemisorption data by using combined adsorption
(8) Synthesis of Pt-Pd/HTNTs. Platinum nanoparticles were minus weak adsorption (physical adsorption). The metal
deposited on the Pd/HTNTs by the same procedure as dispersion of Pd/g-C3N4 was then calculated from the amount
synthesis of Pt/g-C3N4, besides that 0.5 g g-C3N4 was replaced of H2 adsorbed, taking the stoichiometry factor (SF: Pd/H2) as
by Pd/HTNTs, and xenon lamp was replaced by the mercury 2. The metal dispersion could be calculated as follows:
lamp. Product was labeled as Pt-Pd/HTNTs.
ꢋꢌꢍꢎꢏꢐꢑꢏꢒꢓ
ꢈ
ꢉ
ꢀꢁꢂꢃꢄꢅꢂꢁꢆꢇ % ꢊ ꢐ ꢏꢕ ꢏꢗꢗ.ꢘꢙꢘ ꢏ 100%
(1)
ꢔ
ꢖ
where Vads is the cumulative volume of adsorbed H2 (cm3 at
STP). MW is the molecular weight of Pd metal (g mol-1). SW is
the weight of the sample, and Fn is the Pd fraction in relation
to the total catalyst sample weight.34
Fourier transform infrared (FTIR) spectra were recorded on a
Bio Rad FTS 6000 spectrometer, and the samples were
prepared as KBr pellets. Raman spectra were recorded on a
2 | J. Name., 2012, 00, 1-3
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Table 2. Metal dispersion and particle size of the Pd/g-C3N4 catalyst
Bruker RFS 100/S FT-Raman Spectrometer. The wavelength of
excitation light is 1064 nm.
a
Average particle size (nm)
Chemisorption a
Metal dispersion
(%)
Catalyst
TEM b
2.9
Evaluation of catalytic performance of catalyst.
Pd/g-C3N4 (before)
Pd/g-C3N4 (after)
72.7
50.4
1.54
4.28
0.1 g catalyst and 2 mL deionized water were mixed in a flask,
5.7
a.
b.
Calculated from the H2 chemisorption.
which was placed in a water bath at 25
℃. 15 mL buffer
Analyzed from the TEM images
solution, in which the ratio of SF to FA is 9 and the total
concentration is 6 mol/L, was added into the flask and the time
was recorded as starting point of reaction. The volume of
released gas was measured by displacement method and the
gas was analysed by gas chromatography (Beifen 3420A, with
thermal conductivity detector, and mixture of H2 and CO was
used as reference standard, nitrogen as the carrier gas).
Calculation method. The TOF and TON of catalytic reaction
were calculated based on the following formulas.
a: Pd/gꢀC3N4 (before reaction)
b: Pd/gꢀC3N4 (after reaction)
c: gꢀC3N4
c
a
b
⁄
⁄
ꢟꢠ
ꢟꢠ
ꢚꢛꢜ ꢊ ꢝꢋ
(2) ꢚꢛꢣ ꢊ ꢝꢋ
(3)
ꢞꢌꢎ
ꢞꢌꢎ
3184.82
801.10
3257.83
ꢡꢢꢍ
ꢤꢡꢢꢍ
1244.65
1640.68
4000
3200
2400
1600
800
0
where P is the atmospheric pressure (101325 Pa), Vgas is the
IR Shift (cmꢀ1
)
volume of H2 generated, R is the universal gas constant
(8.3145 m3 Pa mol− K−1), T =25
Figure 1. FTIR spectra of samples
1
℃ (298.15 K), nPd is the total
mole number of Pd atom in catalyst, and t is the time of gas
generation.
a: gꢀC3N4
b: Pd/gꢀC3N4
a
Result and discussion
1233.50
707.02
g-C3N4 was prepared by direct pyrolysis of carbamide and well-
dispersed Pd nanoparticles were anchored on g-C3N4 by an
impregnation method coupled with subsequent reduction with
HCOONa. Pt and Ag NPs were well dispersed on Pd/g-C3N4 by
photo-reduction method.
b
0
500
1000
1500
2000
2500
3000
3500
4000
Wavelength/nm
Composition and structure of catalyst
Figure 2. Raman spectra of gꢀC3N4 and asꢀprepared Pd/gꢀC3N4 (1064
nm)
The compositions of catalysts were determined by ICP and the
results are listed in Table 1. The SSA of catalysts are also listed
in Table 1. The SSA of catalysts are slightly reduced compared
with that of supports. Table 2 shows the metal dispersions and
metal surface areas of the as-prepared and used Pd/g-C3N4.
The dispersion degree of Pd NPs analyzed by static chemical
adsorption is 72.7% and the average particle size is 1.54 nm in
the as-prepared Pd/g-C3N4, which matches the result obtained
by TEM. However, the size of Pd particles increased in the used
Pd/g-C3N4.
Several methods were used to characterize catalysts; the
following discussion is mainly related to the catalysts that have
good catalytic performance. FT-IR spectra of the g-C3N4 and
catalysts are shown in Fig. 1. Both of pure g-C3N4 and as-
prepared Pd/g-C3N4 exhibit similar FT-IR vibration modes. The
peaks at 814 cm−1 and 1240-1640 cm−1 are the characteristic
breathing and stretching vibration modes of aromatic CN
heterocycles, confirming the existence of thiazine units; the
broad and weak bands at 3100–3250 cm−1 are typical signals of
N-H or C-H vibrations, which are attributable to the
uncondensed amino groups as the surface terminal groups.35 It
can be seen from Fig. 1a and b that the structure of g-C3N4 did
not change in the catalytic reaction process.
Table 1. Metal contents and SSA of catalysts.
Contents (%)
Sample
SSA (m2/g)
Pd
Pt
Ag
Pd/g-C3N4
Pt/g-C3N4
1.09
—
—
—
65.21
62.34
65.09
64.53
65.01
65.54
202.1
136.4
199.4
287.5
Fig. 2 displays Raman spectra of g-C3N4 and as-prepared Pd/g-
C3N4 (1064 nm). As is known to all, g-C3N4 of large π-
conjugated system has a band gap of 2.7 eV,36 it can absorb
visible light (457-532nm) and generate fluorescence. The
Raman spectrum of g-C3N4 (Fig. S1) using 532 nm laser source
as excitation light shows strong fluorescence. Using near
infrared laser source (1064 nm) as excitation light, the
fluorescence of g-C3N4 can be efficiently decreased. Two
Raman peaks at 707.02cm-1 and 1233.50cm-1 of g-C3N4 (Fig. 2a)
0.65
0.50
—
—
Pt-Pd/g-C3N4
Ag/g-C3N4
Ag-Pd/g-C3N4
g-C3N4
1.01
—
—
0.44
0.61
—
1.02
—
—
—
Pd/HTNTs
Pt-Pd /HTNTs
Ag-Pd /HTNTs
HTNTs
0.97
0.95
0.97
—
—
—
1.33
—
—
0.61
—
—
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are attributed to the D and G bands of a typical graphitic (111) and Pt (111). As is shown in Fig. 5e and 5f, HTNTs with a
structure.37 However, exciting Pd/g-C3N4 with the same diameter of about 8 nm has good tubular nanostructure and
excitation light, the Raman spectrum of Pd/g-C3N4 (Fig. 2b) the Pd NPs are well dispersed on the HTNTs. Though the SSA of
shows a strong broad fluorescence peak rather than D and G HTNTs is much larger than that of g-C3N4 (Table 1), all metallic
bands of the typical graphitic structure, which illustrates particles on the g-C3N4 are smaller than those on the HTNTs (S
clearly that as Pd NPs were introduced into g-C3N4, the V, ESI). Comparing Fig 5a and Fig. 5e, the Pd deposited on the
fluorescence appeared again. It may be explained that the g-C3N4 is highly dispersive, however, the Pd well-distributed on
interaction between Pd NPs and g-C3N4, that is, the electron the surface of the HTNTs shows graininess, which can be
transfers between Pd and g-C3N4 by the d-pπ interaction interpreted as that π-conjugated system in g-C3N4 makes a
between Pd and g-C3N4 increased the electron density of g- great deal of contribution to disperse electrons in Pd, as a
C3N4, which results in the fluorescence reappearance. We also result, the aggregation of Pd NPs becomes much more difficult
used HTNTs without π system as the support to explore the because of the feature of metal crystal formed maintained by
Raman spectrum. In the Raman spectrum of Pd/HTNTs, there metallic bond.
is no fluorescence, which confirms that Pd NPs themselves do
not cause the fluorescence if there is no d-pπ interaction
a: Pd/gꢀC3N4
between Pd NPs and support that does not have π-conjugated
b: AgꢀPd/gꢀC3N4
system. PXRD pattern of as-prepared Pd/g-C3N4 (Fig. 3a)
displays the typical diffraction peaks of g-C3N4 (110) and Pd
27.48
gꢀC3N4(110)
(111) at 27.48° (PDF#50-1512) and 40.02° (PDF#46-1043),
respectively. Ag-Pd/g-C3N4 (Fig. 3b) not only shows peaks of g-
40.02
Pd(111)
C3N4 and Pd, but also peak of Ag (111) at 38.68° and peak of Ag
(200) at 44.96° (PDF#04-0783), which interprets that no alloy
a
38.68
Ag(111)
forms in the bimetallic catalyst.
44.96
Ag(200)
b
XPS was used to characterize the chemical state of metal in
catalysts, as well as the interactions between metals or metal
and support (Fig. 4). The Pd in samples exists as Pd0 and Pd2+,
but the Pd0 is the dominant component based on the peak
0
20
40
60
80
2 Theta /degree
area ratio (S III, ESI). The peaks of Pd 3d5/2 and 3d3/2 located at
334.4 and 339.60 eV, respectively, in Pd/HTNTs (Fig. 4a) are
associated with normal Pd(0).38 Compared with Fig. 4a, Fig. 4b
shows that the binding energy of Pd 3d in as-prepared Pd/g-
C3N4 increases slightly, which means that the electron density
on Pd reduces and there is certainly an interaction between
the Pd NPs and g-C3N4, where electrons are transferred from
Pd NPs to g-C3N4 by the overlap of d-orbits of Pd and empty π-
conjugated orbits of g-C3N4, which is consistent with the strong
fluorescence in Raman spectra. Similarly, the shift of Pd 3d
peaks also exists in Fig. 4c and Fig. 4d. However, by
comparison with Fig. 4a and 4b, it can be found that the
presence of Ag and Pt affects the shift of Pd 3d peaks
differently, which can be interpreted by different work
functions of metals. The work functions of Ag, Pd and Pt are
4.26 eV, 5.12 eV and 5.65 eV, respectively. It is well known
that the electrons are inclined to flow from the lower work
function metal to the higher one when metals with different
work functions are fitted together.39 Accordingly, the binding
energies of Pd 3d5/2 and 3d3/2 in Pd-Ag/g-C3N4 (335.1 eV,
340.4eV) and Pd-Pt/g-C3N4 (335.35 eV, 340.65eV) are relatively
lower and higher, respectively, than that in as-prepared Pd/g-
C3N4 (335.20 eV, 340.5eV).
Figure 3. XRD partterns of asꢀprepared Pd/gꢀC3N4 and AgꢀPd/gꢀ
C3N4
TEM images of the catalysts are showed in Figure 5 and
supplymentary information S IV. HRTEM images (Fig. 5a inset)
show that the interlayer spacing of Pd NPs in Pd/g-C3N4 is 0.22
nm, which agrees with that of Pd (111). The interlayer spacings
of NPs in Ag-Pd/g-C3N4 (Fig. 5c inset) are agreement with those
of Pd (111) and Ag (111), and the interlayer spacings of NPs in
Pt-Pd/g-C3N4 (Fig. 5d inset) are agreement with those of Pd
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Figure. 5 TEM images of Pd/gꢀC3N4 (a, b), AgꢀPd/gꢀC3N4 (c), Ptꢀ
Pd/gꢀC3N4 (d), Pd/HTNTs (e), and HTNTs (f)
Pd/HTNTs
Pd 3d
334.40
339.60
Pd NPs are well dispersed on the HTNTs. Though the SSA of
HTNTs is much larger than that of g-C3N4 (Table 1), all metallic
particles on the g-C3N4 are smaller than those on the HTNTs (S
V, ESI). Comparing Fig 5a and Fig. 5e, the Pd deposited on the
g-C3N4 is highly dispersive, however, the Pd well-distributed on
the surface of the HTNTs shows graininess, which can be
interpreted as that π-conjugated system in g-C3N4 makes a
great deal of contribution to disperse electrons in Pd, as a
result, the aggregation of Pd NPs becomes much more difficult
because of the feature of metal crystal formed maintained by
metallic bond.
330
335
340
345
350
Pd/gꢀC3N4
Pd 3d
Binding Energy/eV
335.20
340.50
330
335
340
345
350
AgꢀPd/gꢀC
N
3
4
Binding Energy/eV
Pd 3d
Evaluation of catalysts
335.10
340.40
The released gas in the catalytic decomposition of FA was
detected by GC and no CO was found in the released gas (S VI,
ESI).
The catalytic performances of catalysts are listed in Table 3. As
shown in Table 3, Figure S16 and S17, for Pd, Pt and Ag, only
Pd can catalyse the dehydrogenation of FA efficiently; all g-
C3N4 supported catalysts (Entry 1-3, 7) show far higher activity
than HTNTs supported ones (Entry 4-6). The TOF of as-
prepared Pd/g-C3N4 (Entry 1) is more than 8 times that of
Pd/HTNTs (Entry 4). Compared with as-prepared Pd/g-C3N4,
the calcinated catalyst shows higher activity (Entry 7), which is
mainly ascribed to the enhanced interaction between metal Pd
and g-C3N4. These results clearly indicate that the π-
conjugated system of support, by which the electron density of
metal can be efficiently reduced, is a key factor that makes
catalysts have high activity, which should be utilized as much
as possible in developing high efficient catalyst for hydrogen-
production from formic acid.
330
335
340
345
350
PtꢀPd/gꢀC3N4
Binding Energy/eV
Pd 3d
335.35
340.65
330
335
340
345
350
Binding Energy/eV
Figure 4. XPS spectra of Pd/HTNTs (a), Pd/gꢀC3N4 (b), Agꢀ Pd/gꢀ
C3N4 (c) and PtꢀPd/gꢀC3N4 (d)
b
a
For the as-prepared catalysts that have the same support, g-
C3N4, the order of the catalytic activity is as follows: Pt-Pd/g-
C3N4>Pd/g-C3N4>Ag-Pd/g-C3N4 (Tab. 3), which agrees with the
binding energy order of Pd determined by XPS. This order
implies that anions e.g. HCOO- bind to Pd NPs firstly in the
catalytic processes. In the previous reports 19, 20, researchers
believe that the catalytic decomposition of FA proceeds a
transformation from bidentate formate combined with metal
NPs to monodentate one, followed by decomposition into CO2
and H atom. Consequently, reducing the electron density on
the surface of Pd NPs is benefit to the combination between
formate ions and catalyst, and then enhances the catalytic
activity of catalyst. Among all catalysts, Pt-Pd/g-C3N4 shows
the highest activity, for which two factors are responsible: one
is the flow of electron between Pt and Pd NPs because of the
different work functions; and the next is that the Pt has lower
hydrogen over potential than the Pd, which should be favour
to the H2-release.
c
d
e
f
The effect of FA/SF molar ratio on the catalytic activity of the
Pd/g-C3N4 for FA dehydrogenation was investigated. As pure
FA is used, the rate of gas generation is very slow (TOF=87 h-1).
However, increasing the molar percentage of SF (FA/SF = 1 and
0.1) may induce a rapid increase in rate of gas generation or
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the catalytic activity of Pd/g-C3N4 (TOF=142.17 h-1 and 189.56 the ratio of buffer solution, the lifetime of catalysts lasts for 8-
h -1), which further confirms that HCOO- binds Pd NPs firstly, SF 12 h in the reaction system.
is an important promoter. However, no matter how to change
Table 3. Evaluation of catalytic performances of catalysts at room temperaturea
Content
of Pd (%)
1.09
1.02
1.01
0.97
0.97
0.95
1.09
0
Volume of gas
Composition
Entry
Catalyst
TON
TOF (h-1
)
released (mL)
of gas
1
2
3
4
5
6
7
8
9
Pd/g-C3N4
96
60
111
10
0
H2
H2
H2
-
383.12
191.56
Ag-Pd/g-C3N4
Pt-Pd/g-C3N4
Pd/HTNTs
255.88
127.94
478.08
239.04
44.84
22.42
Ag-Pd/HTNTs
Pt-Pd/HTNTs
-
-
-
0
-
-
-
b
Pd/g-C3N4
102
0
H2
-
407.7
203.54
Pt/g-C3N4
-
-
Ag/g-C3N4
0
0
-
-
-
a The data were collected when the reaction lasted for 2 h; b The catalyst was calcinated at 150 ℃ for 1 h in H2 atmosphere.
12 Ruthven, D. M. and Upadhye, R. S. J. Catal., 1971, 21, 39.
13 Marcinkowski, M. D.; Murphy, C. J.; Liriano, M. L.; Wasio, N.
Conclusion
A.; Lucci, F. R. and Sykes E. C. H. ACS Catal., 2015,
14 Lan, Y.; Xing, H.; Jun, S.; Wei, L.; Shengli, C. and Gongzhen, C.
Applied Catalysis B: Environmental, 2015, 168-169, 423
15 Marcinkowski, M. D.; Liu, J.-L.; Murphy, C. J.; Liriano, M. L.;
Wasio, N. A.; Lucci, F. R.; Flytzani-Stephanopoulos, M. and
Sykes, E. C. H. ACS Catal., 2017, 7, 413.
16 Zhang, X. Y.; Shang, N. Z.; Zhou, X.; Feng, C.; Gao, S. T.; Wu, Q.
H.; Wang, Z.; and Wang, C. New J. Chem., 2017, 41, 3443.
17 Boukha, Z.; Ayastuy, J. L.; González-Velasco, J. R. and
Gutiérrez-Ortiz, M. A. Applied Catalysis B: Environmental,
2017, 201, 189.
18 Zhu, Q. L.; Tsumori, N. and Xu, Q. J. Am. Chem. Soc., 2015,
137, 11743.
19 Majeed, I.; Manzoor, U.; Kanodarwala, F. K.; Nadeem, M. A.;
Hussain, E.; Ali, H.; Badshah, A.; Stride, J. A. and Nadeem M.
A. Catal. Sci. Technol., 2018, 8, 1183.
5, 7371.
In this study, g-C3N4 supported metal (Pd, Ag, Pt) catalysts
were synthesize. Among them, the catalysts containing Pd
have high catalytic activity and selectivity in hydrogen-
generating from formic acid. The combination of Pd, supports
with π-conjugated system, and metals with higher work
function and lower hydrogen overpotential should be a good
option in developing high efficient catalyst for hydrogen-
production from formic acid. Though g-C3N4 supported
catalysts containing Pd show excellent catalytic performance in
hydrogen-generating from formic acid, improving their
reusability should be the next focus.
.
20 Shao, X. Z. AIChE, 2016, 62, 2410.
Acknowledgements
21 Lee, H. J.; Ryu, J.; Kim, J. Y.; Nam, S.-W.; Han, J. H.; Lim, T.-H.;
Gautam, S.; Chae, K. H. and Yoon, C. W. J. Mater. Chem. A,
2014, 2, 9490.
22 Cheng, S. S.; Meng, X. F.; Shang, N. Z.; Gao, S. T.; Feng, C.;
Wang, C. and Wang, Z. New J. Chem., 2018, 42, 1771
23 Oh, T. H. Energy, 2016, 112, 679.
This work is supported by the National Natural Science
Foundation of China (21373120, 21301098, 21071086 and
21271110), and project IRT13022, B12015.
24 Deng, Q.-F.; Zhang, Z.-F.; Cui, J.-F. and Jia, L.-H. International
journal of Hydrogen Energy, 2017, 42, 14865.
25 Wu, Y. M.; Wen, M. C.; Navlani-Garcia, M.; Kuwahara, Y.;
Mori, K. and Yamashita, H. Chem. Asian J., 2017, 12, 860.
26 Xu, L. X.; Zhang, J.; Cheng, D.-G.; Chen, F. Q.; An, Y.; Cui, P.
Notes and references
1
2
3
Cheng, J.; Gu, X. J.; Liu, P. L.; Zhang H.; Ma, L. L. and Su, H. Q.
Applied Catalysis B: Envrionmental, 2017, 218, 460.
Zong, X.; Yan, H. J.; Wu, G. P.; Ma, G. J.; Wen, F. Y.; Wang, L.
and Li, C. J. Am. Chem. Soc., 2008, 130, 7176.
Das, D. and Veziroglu, T. N. International Journal of Hy-
drogen Energy, 2001, 26, 13.
Haruta, M. Gold Bulletin, 2007, 37, 27.
and Wan, C. RSC Adv., 2016, 6, 46908.
27 Vilé, G.; Albani, D.; Nachtegaal, M.; Chen, Z.; Dontsova, D.;
Antonietti, M.; López, N. and Pérez-Ramírez, J. Angew. Chem.
Int. Ed., 2015, 54, 11265.
28 Quan, J. M.; Kondo, T.; Wang, G. C. and Nakamura, J. Angew.
Chem. Int. Ed., 2017, 56, 3496.
29 He, F.; Li, K.; Yin, C.; Wang, Y.; Jiao, M. G.; Tang, H. and Wu,
Z. J. Applied Surface Science, 2016, 387, 221.
30 Wang, P.; Steinmann, S. N.; Fu, G.; Michel, C. and Sautet, P.
4
5
Pingping, Z.; Nan, C.; Wei, L. and Gongzhen, C. J. Mater.
Chem. A, 2015,
3, 12468.
6
7
8
9
Bi, Q. Y.; Lin, J. D.; Liu, Y. M.; He, H. Y.; Huang, F. Q. and Cao,
Y. Angew. Chem. Int. Ed., 2016, 55: 11849.
Ciftci, A.; Ligthart, D.A.J. M.; Pastorino, P. and Hensen, E. J.M.
Applied Catalysis B: Environmental, 2013, 130, 325.
Mellmann, D.; Sponholz, P.; Junge, H. and Beller, M. Chem.
Soc. Rev., 2016, 45, 3954.
ACS Catal. 2017, 7, 1955.
31 Shi, Y. K.; Hu, X. J.; Zhao, J. T.; Zhou, X. J.; Zhu, B. L.; Zhang, S.
M. and Huang, W. P. New J. Chem, 2015, 39, 6642.
32 Jiang, L. B.; Yuan, X. Z.; Pan, Y.; Liang, J.; Zeng, G. M.; Wu, Z.
B. and Wang, H. Applied Catalysis B: Environmental, 2017,
217, 388.
Kübler, M.; Jurzinsky, T.; Ziegenbalg, D. and Cremers, C.
Journal of Power Sources, 2018, 375, 320.
10 Himeda, Y.; Miyazawa, S. and Hirose, T. ChemSusChem, 2011, 33 An, H. Q.; Zhu, B. L.; Li, J. X.; Zhou, J.; Wang, S. R.; Zhang, S.
M.; Wu, S. H. and Huang, W. P. J. Phys. Chem. C, 2008, 112,
18772.
4, 487.
11 Bi, Q. Y.; Du, X. L.; Liu, Y. M.; Cao, Y.; He, H. Y. and Fan, K. N.
J. Am. Chem. Soc., 2012, 134, 8926.
6 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/C8NJ00404H
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ARTICLE
34 Prakash, N.; Lee, M.; Yoon, S. and Jung, K.-D. Catalysis Today,
2017, 293, 33.
35 Yan, S. C.; Li, Z. S. and Zou, Z. G. Langmuir, 2009, 25, 10397.
36 Wang, X. C.; Maeda, K.; Thomas, A.; Takanabe, K.; Xin, G.;
Carlsson, J. M.; Domen, K. and Antonietti, M. Nature
Materials, 2009, 8, 76.
37 Papailias, I.; Giannakopoulou, T.; Todorova, N.; De-motikali,
D.; Vaimakis, T. and Trapalis, C. Applied Surface Science,
2015, 358, 278.
38 Tura J.M.; Regull P.; Victori L. and Dolors de Castellar M. Surf.
Interface Anal. 1988, 11, 447.
39 Ding, Y. J.; Sun, W. Z.; Yang, W. Y. and Li, Q. Applied Catalysis
B: Environmental, 2017, 203, 372.
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TOC
Graphic:
Text: Pd/gꢀC3N4 of dꢀπ interaction between Pd NPs and gꢀC3N4 with πꢀconjugated system shows high
catalytic activity in dehydrogenation of FA.