Anchoring and Upgrading Ultrafine NiPd on Room-Temperature-Synthesized Bifunctional NH2-N-rGO toward Low-Cost and Highly Efficient Catalysts for Selective Formic Acid Dehydrogenation

Article abstract of DOI:10.1002/adma.201703038

Hydrogen is widely considered to be a sustainable and clean energy alternative to the use of fossil fuels in the future. Its high hydrogen content, nontoxicity, and liquid state at room temperature make formic acid a promising hydrogen carrier. Designing highly efficient and low-cost heterogeneous catalysts is a major challenge for realizing the practical application of formic acid in the fuel-cell-based hydrogen economy. Herein, a simple but effective and rapid strategy is proposed, which demonstrates the synthesis of NiPd bimetallic ultrafine particles (UPs) supported on NH₂-functionalized and N-doped reduced graphene oxide (NH₂-N-rGO) at room temperature. The introduction of the ?NH₂?N group to rGO is the key reason for the formation of the ultrafine and well-dispersed Ni_0.4Pd_0.6 UPs (1.8 nm) with relatively large surface area and more active sites. Surprisingly, the as-prepared low-cost NiPd/NH₂-N-rGO dsiplays excellent hydrophilicity, 100% H₂ selectivity, 100% conversion, and remarkable catalytic activity (up to 954.3 mol H₂ (mol catalyst)^?1 h^?1) for FA decomposition at room temperature even with no additive, which is much higher than that of the best catalysts so far reported.

Full text of DOI:10.1002/adma.201703038

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Anchoring and Upgrading Ultrafine NiPd on Room-
Temperature-Synthesized Bifunctional NH -N-rGO
2
toward Low-Cost and Highly Efficient Catalysts for
Selective Formic Acid Dehydrogenation
Jun-Min Yan, Si-Jia Li, Sha-Sha Yi, Ba-Ri Wulan, Wei-Tao Zheng, and Qing Jiang*
lower the cost of the catalysts, it is urgent
Hydrogen is widely considered to be a sustainable and clean energy alterna-
tive to the use of fossil fuels in the future. Its high hydrogen content, non-
toxicity, and liquid state at room temperature make formic acid a promising
hydrogen carrier. Designing highly efficient and low-cost heterogeneous
catalysts is a major challenge for realizing the practical application of formic
acid in the fuel-cell-based hydrogen economy. Herein, a simple but effective
and rapid strategy is proposed, which demonstrates the synthesis of NiPd
to introduce non-noble metals (NNMs),
such as Co and Ni, to Pd to form the
[
6]
bimetallic NNM-Pd catalyst. However,
up to now, the activity/selectivity of NNM-
containing (even <40 at% of NNMs) Pd-
based catalysts is still very poor even at
elevated temperature, especially without
[
6]
extra additives. Thereafter, the develop-
ment of facile and effective strategy to syn-
thesize highly efficient catalysts with high
content of NNMs is highly desirable while
still very challenging for FA as a feasible
bimetallic ultrafine particles (UPs) supported on NH -functionalized and
2
N-doped reduced graphene oxide (NH -N-rGO) at room temperature. The
2
introduction of the NH N group to rGO is the key reason for the forma-
2
tion of the ultrafine and well-dispersed Ni Pd UPs (1.8 nm) with relatively
0
.4
0.6
H -storage material.
2
large surface area and more active sites. Surprisingly, the as-prepared low-
cost NiPd/NH -N-rGO dsiplays excellent hydrophilicity, 100% H selectivity,
In response, the fabrication of ultrafine
particles (UPs) could increase the surface
area and thus enhance the catalytic per-
formances of NNM-containing Pd-based
catalyst (NNM-Pd), while achieving good
dispersity and avoiding the intrinsic aggre-
gation of the UPs is still a big challenge,
due to the absence of efficient catalyst sup-
2
2
1
(
00% conversion, and remarkable catalytic activity (up to 954.3 mol H
2
−
mol catalyst) 1 h ) for FA decomposition at room temperature even with no
−1
additive, which is much higher than that of the best catalysts so far reported.
Low-cost and efficient storage and release of hydrogen (H2)
remain one of the most important challenges toward the fuel-
cell-based hydrogen economy.[ Formic acid (FA, HCOOH), a
liquid at room temperature, is one of the major products of bio-
mass processing, and has been identified as a safe and potential
port that holds both large surface area and, especially, suitable
interaction with the supported NNM-Pd UPs. Theoretically,
N-doped graphene (N-graphene) could be employed as an ideal
support, thanks to combined advantages of large surface area
and enhanced adsorption ability for metal ions of metal pre-
cursors, which not only could in situ anchor the active metal
nanoparticles, but also could offer more opportunity to tune the
electronic structure of the particles (through the strong metal-
to-support interaction (SMSI)) and thus enhance its catalytic
1]
H storage material due to its high hydrogen density (4.4 wt%),
2
[2]
nontoxicity, and excellent stability. To this end, FA should be
selectively decomposed via dehydrogenation (HCOOH → CO2
+
+
H ) pathway (not follow dehydration route: HCOOH → CO
2
2
[
3]
[7]
H O), which is still heavily rely on noble metal of Pd, and
activity. Unfortunately, the hydrophobicity of pristine NNM-
even so, the catalytic activity/selectivity is still far from satis-
fying even with the extra additives (HCOONa and/or triethyl-
Pd/N-graphene nanocatalyst is not good to be applied in FA
system due to the unavoidable aggregation and stacking in
aqueous solution, which cannot ensure the ultrafine sizes and
excellent dispersion of the NNM-Pd particles. In response, the-
[
4,5]
amine (NEt )) and under elevated temperature (323–363 K).
3
To significantly improve the activity/selectivity and, especially,
oretically, the introduction of polar groups, such as NH , to
2
N-graphene can endow the NNM-Pd/N-graphene with hydro-
Prof. J.-M. Yan, S.-J. Li, S.-S. Yi, B.-R. Wulan,
Prof. W.-T. Zheng, Prof. Q. Jiang
Key Laboratory of Automobile Materials
Ministry of Education
Department of Materials Science and Engineering
Jilin University
philicity, and the steric stabilization gained by NH groups
2
may further suppress the aggregate of NNM-Pd UPs. Further-
more, the presence of
to accelerate the cleavage of OH bond in FA, which is the

NH alkaline groups has the priority
2
[8]
initial step of the FA dehydrogenation. However, up to now,
Changchun 130022, China
E-mail: jiangq@jlu.edu.cn
to the best of our knowledge, there is no report on NH -func-
2
tionalized N-graphene (NH -N-graphene), to say nothing of
2
DOI: 10.1002/adma.201703038
being employed as a novel support for catalysts. Therefore, the
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development of a cost- and time-effective strategy to synthesize
Figure 1 shows the transmission electron microscopy (TEM)
images and the photographs of the as-prepared Ni0.4Pd0.6/NH2-
N-rGO, Ni0.4Pd0.6/N-rGO and Ni0.4Pd0.6/rGO. Obviously, the
novel NH -N-graphene-supported NNM-Pd UPs catalyst and
2
then exploring its catalytic performances for decomposition of
FA is highly desirable but very challenging.
Ni0.4Pd0.6 UPs anchored on NH -N-rGO (Figures 1a,d) demon-
2
Herein, we first propose and demonstrate a facile while
effective and rapid strategy to synthesize well-dispersed NiPd
strate very good dispersity and very small particle size (≈1.80 nm;
Figure S2a, Supporting Information). The accurate molar ratio
bimetallic UPs (1.8 nm) anchored on the novel NH -function-
of Ni:Pd in Ni0.4Pd0.6/NH -N-rGO is determined to be about
2
2
alized and N-doped reduced graphene oxide (NH -N-rGO) at
0.43:0.57 by inductively coupled plasma-atomic emission spec-
trometry (ICP-AES), which agrees very well with the appointed
value. The high-resolution TEM (HRTEM) image (Figure 1d,
inset) reveals the crystalline nature of Ni0.4Pd0.6 UPs, and the
lattice spacing is measured to be 0.220 nm, which is between
2
room temperature, wherein the metallic UPs and NH -N-rGO
2
are simultaneously one-step generated within 1 min, endowing
the resultant NiPd/NH -N-rGO catalyst with good hydrophi-
2
licity. Unexpectedly, when first used as novel catalyst for FA
[
11]
decomposition, the as-prepared low-cost NiPd/NH -N-rGO
the (111) planes of face-centered cubic Ni (0.203 nm) and Pd
2
[
12]
shows 100% H selectivity and excellent catalytic activity (up to
(0.224 nm). On the other hand, Ni0.4Pd0.6 nanoparticles sup-
2
−1
−1
9
54.3 mol H mol catalyst h ) at room temperature even with
ported on N-rGO without NH functionalization are also well
2
2
no additive, which is much more higher than that of the best
catalyst ever reported.
dispersed (Figure 1b) but with the larger average size of ≈6.0 nm
(Figure S2b, Supporting Information). However, Ni0.4Pd0.6 on
pure rGO is severely aggregated (Figure 1c), and the average
particle size is ≈10.2 nm (Figure S2c, Supporting Informa-
The design and fabrication processes of NiPd/NH -N-
2
rGO are illustrated in Scheme 1. Briefly, for the synthesis
[9]
of Ni0.4Pd0.6/NH -N-rGO,
the colorless (3-aminopropyl)
tion), which is larger than those supported on NH -N-rGO and
2
2
triethoxysilane (APTS, 0.2 mL) is mixed with the previously
prepared light brown and transparent GO aqueous solution by
sonicating and stirring at 298 K to form the dark brown col-
loidal solution (Figure S1, Supporting Information), which
N-rGO. As expected, the prepared Ni0.4Pd0.6/NH -N-rGO spec-
2
imen demonstrates the excellent hydrophilicity, which does not
sink in aqueous solution even after 40 h (Figure 1e). However,
both Ni0.4Pd0.6/N-rGO and Ni0.4Pd0.6/rGO show the obvious
phenomenon of sedimentation after only 20 min (Figure 1e).
Based on the above TEM and sedimentation images, it can be
reasonably believed that, after N doping, the resultant N-rGO
has an effect to increase the dispersion of nanoparticles, and
after further adding NH groups, the obtained NH -N-rGO
[
10]
indicates the strong interaction between APTS and GO. And
then aqueous solutions of NiCl2 and Na PdCl4 (with Ni:Pd
2
molar ratio of 0.4:0.6) are added to the above APTS-treated
GO solution with magnetic stirring. Finally, NaBH4 is dis-
solved into the above mixed solution, and the resultant black
2
2
Ni0.4Pd0.6/NH -N-rGO product can be rapidly obtained within
can make the catalyst to be hydrophilic and lead to the ultrafine
sizes and excellent dispersion of UPs. Moreover, the Brunner–
2
1
min. The product is separated and washed with water for the
following characterization and catalytic FA dehydrogenation at
Emmet–Teller surface area for Ni0.4Pd0.6/NH -N-rGO is meas-
2
2
−1
2
98 K without any additive. For comparison, Ni0.4Pd0.6/N-rGO
ured to be 286.1 m g , which is larger than that of Ni0.4Pd0.6/
and Ni0.4Pd0.6/rGO are also prepared.[ Moreover, the molar
9]
2
−1
rGO (225.8 m g ); namely, the addition of NH N groups
2
ratio of Ni:Pd in NiPd/NH -N-rGO system has been changed
on rGO is the key reason for the formation of the ultrafine
and well-dispersed Ni0.4Pd0.6 UPs with relatively large surface
2
by several values (0:1, 0.2:0.8, 0.4:0.6, 0.6:0.4, 0.8:0.2, and 1:0).
Scheme 1. Schematic representation of the rapid preparation process of the NiPd/NH -N-rGO catalyst.
2
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Figure 1. TEM images of: a,d) Ni0.4Pd0.6/NH -N-rGO, b)Ni0.4Pd0.6/N-rGO, and c) Ni0.4Pd0.6/rGO; e) photographs of newly prepared Ni0.4Pd0.6/NH -N-
2
2
rGO, Ni0.4Pd0.6/N-rGO, and Ni0.4Pd0.6/rGO specimens, and their corresponding photographs after keeping in aqueous solution for the indicated time.
−
1
area, which may lead to the great enhancement in the catalytic
activity of Ni0.4Pd0.6 active sites (vide infra).
To investigate the detailed crystal and chemical states of
the three specimens, X-ray diffraction (XRD), Fourier trans-
form infrared (FTIR) spectroscopy, X-ray photoelectron spec-
trometry (XPS), and Raman and UV–vis have been applied.
and 1636 cm , which could be ascribed to the out of plane and
[
18]
in-plane NH bending vibrations, respectively,
confirming
the existence of amine (NH ) group on the N-rGO of this
2
specimen. To further confirm the chemical states of N in
Ni0.4Pd0.6/NH -N-rGO and Ni0.4Pd0.6/N-rGO, the high-resolu-
tion XPS analyses have also been applied. As shown in Figures
2
Figure 2a shows the XRD patterns of the Ni0.4Pd0.6/NH -N-
2c,d, the remarkable peaks of N 1s at ≈398.9 and ≈399.2 eV have
2
rGO, Ni0.4Pd0.6/N-rGO and Ni0.4Pd0.6/rGO specimens. It can be
seen that the three specimens have the broad C (002) peaks at
around 24.8°, which proves the successful reduction of GO to
been observed for Ni0.4Pd0.6/NH -N-rGO and Ni0.4Pd0.6/N-rGO,
2
respectively, suggesting that the element of N has been success-
fully incorporated into the two products. The little difference of
the two N 1s peak positions may result from the different chem-
ical states of N in the two specimens, where the N (Figure 2c)
[
13]
rGO during the preparation process of the specimens, and
this has also been proved by the Raman, UV–vis, and XPS anal-
yses (Figures S3–S5, Supporting Information).[
7e,13,14]
Besides
in Ni0.4Pd0.6/NH -N-rGO is similar to the pyridinic N (398.7 eV)
2
[
18b,19,20]
the diffraction of C (002), the peaks between those of metallic
and amine N/pyrrolic N (399.7 eV),
while that in
Ni (111) (JCPDS: 65-2865)[ and Pd (111) (JCPDS: 65-2867)
11]
[13]
Ni0.4Pd0.6/N-rGO (Figure 2d) can be assigned to pyridinic N
[
20]
are also observed for the three specimens from Figure 2a,
which agrees very well with the HRTEM image of Ni0.4Pd0.6
(398.7 eV) and pyrrolic N (399.7 eV)
which are identified
[
20]
to be the doping N in atomic chain of graphene. Both con-
sidering the FTIR and XPS results, N in Ni0.4Pd0.6/N-rGO is
(Figure 1d, inset). The XRD and HRTEM results indicate that
Ni0.4Pd0.6 is formed in an alloy structure, and this can be further
proved to be the doping atoms on rGO, and N in Ni0.4Pd0.6/
confirmed by the XRD pattern of Ni0.4Pd0.6/NH -N-rGO after
NH -N-rGO is existed both as the doping atoms to rGO and
2
2
heat treatment at 873 K for 3 h in Ar atmosphere (Figure S6,
Supporting Information), where all the diffraction peaks are
located between those of metallic Ni and Pd. Figure 2b shows
the FTIR of the three specimens. For Ni0.4Pd0.6/rGO, only a
small peak corresponding to aromatic CC stretching vibra-
also in NH group on surface of rGO, which are schematically
2
shown in Figures 2e,f. Therefore, by considering the types of
N on rGO, the two specimens are named as Ni0.4Pd0.6/N-rGO
(doping N on rGO) and Ni0.4Pd0.6/NH -N-rGO (doping N and
2
amine N on rGO), respectively.
−
1
[15]
tion (≈1544 cm ) can be observed, namely, there is no other
To study the electronic effects of Ni to Pd and NH -N-rGO
2
element or group modification on the rGO of this specimen.
on Ni0.4Pd0.6 UPs, XPS analysis has been applied on speci-
mens of the Ni0.4Pd0.6/NH -N-rGO, Pd/NH -N-rGO, Ni/NH -
For Ni0.4Pd /N-rGO, besides the peaks of CC and COH
0.6
2
2
2
−
1
[16]
−1
(
1402 cm ),
a new band at 965 cm assigned to CN
N-rGO, and free Ni0.4Pd0.6, as shown in Figure 3. It can be
[17]
stretching vibration can also be found, which proves that N
element has been successfully doped in the rGO of this spec-
seen that Pd and Ni in Ni0.4Pd0.6/NH -N-rGO are mostly in
2
0
0
metallic Pd (Figure 3a, black trace) and Ni (Figure 3b, black
imen.[ While for Ni0.4Pd0.6/NH -N-rGO, except CC, COH,
17]
[4b,21]
II
II
trace), respectively
(a small amount of Ni and Pd can be
2
and CN,[
18a–b]
the appearance of another two bands at 894
attributed to the surface oxidation of Pd and Ni during sample
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Figure 2. a) XRD patterns and b) FTIR spectra of Ni0.4Pd0.6/NH -N-rGO, Ni0.4Pd0.6/N-rGO, and Ni0.4Pd0.6/rGO; c,d) high-resolution XPS spectra of N
2
1
s in Ni0.4Pd0.6/NH -N-rGO (c) and Ni0.4Pd0.6/N-rGO (d); e,f) schematic illustration of NH -N-rGO (e) and N-rGO (f).
2
2
Figure 3. High-resolution XPS spectra of: a) Pd 3d and b) Ni 2p in Ni0.4Pd0.6/NH -N-rGO, Pd/NH -N-rGO, Ni/NH -N-rGO. and Ni0.4Pd0.6 specimens.
2
2
2
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preparing for XPS[22]). However, comparing Ni0.4Pd0.6/NH2-
N-rGO with Pd/NH -N-GO, Ni/NH -N-rGO (Figures 3a,b), the
metal UPs through the strong SMSI effect. Through the above
two effects, the Pd active sites are electron-rich, which can
facilitate to produce H and CO due to the promotion of rate-
2
2
Pd 3d peaks are shifted to the lower binding energies, while
the Ni 2p peaks are shifted to the higher values. These shifts
might be attributed to a partial electron-transfer from Ni to Pd,
which can be easily understood by the lower electronegativity of
element Ni than Pd (Pd 2.2; Ni 1.8).[ In addition, comparing
2
2
determining step for the C–H scission in the absorbed HCOO*
[
8]
intermediate on the catalyst, and this has been immediately
proved by the following catalytic results.
23]
The catalytic performance of the as-prepared Ni0.4Pd0.6
/
/
Ni0.4Pd0.6/NH -N-rGO with unsupported Ni0.4Pd0.6, the Pd 3d
NH -N-rGO hybrid together with Ni0.4Pd0.6/N-rGO, Ni0.4Pd0.6
2
2
and Ni 2p peaks are both shifted to the lower binding energies,
rGO, and Ni0.4Pd0.6 nanoparticles prepared with/without APTS
(Ni0.4Pd0.6-APTS and Ni0.4Pd0.6) for H2 generation from FA
(1.0 m, 5 mL) decomposition at 298 K under ambient atmosphere
is shown in Figure 4a for comparison, in order to better observe
the effect of APTS and rGO on the catalytic performance. Obvi-
indicating that some electrons are transferred from the NH -N-
2
rGO substrate to the Ni0.4Pd0.6 UPs, and confirming the strong
interaction between the substrate and Ni0.4Pd0.6 UPs. Because
the XPS peak intensity is proportional to the concentration (the
molar ratio of Ni:Pd is 0.4:0.6 in Ni0.4Pd0.6/NH -N-rGO) and the
ously, Ni0.4Pd0.6/NH -N-rGO catalyst shows the highest activity
2
2
sensitivity factors (Ni is 4.044, and Pd is 5.356) of the element
among all the prepared catalysts, with which 245 mL of gas
can be released in only 4 min, corresponding to a 100% con-
version. Considering the actual molar number of the metal
is 0.1 mmol (nmetal = 0.1 mmol and metal loading = 20 wt%,
which are tested by ICP-AES), the initial turnover frequency
on the surface,[
23d]
and hence the peak of Ni is relatively weak
in Figure 3. Based on the above XPS analysis, it can be deduced
that the addition of Ni to Pd can adjust the electron structure
of Pd through the electron synergetic effect, while the support
[
9]
of NH -N-rGO can also modify the electron structure of the
(TOF; Equation (S2), Supporting Information) is measured to
2
Figure 4. a) Gas generation from the decomposition of FA (1.0 m, 5.0 mL) versus time in the presence of Ni0.4Pd0.6 with/without different supports
or APTS and b) the corresponding TOF value; c,d) gas generation from the decomposition of FA (1.0 m, 5.0 mL) versus time in the presence of NiPd/
NH -N-rGO with different Ni:Pd molar ratios (c) and the corresponding TOF value (nmetal/nFA = 0.02) (d).
2
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be 954.3 mol H mol catalyst−1 h−1 without additive at 298 K.
stability of Ni0.4Pd0.6/NH -N-rGO with a large amount of non-
2
2
As it is known, this value is one of the highest among all the
noble metal.
reported heterogeneous catalysts for this reaction without addi-
More interestingly, with different Ni:Pd molar ratios, the pre-
tive (Table S1, Supporting Information)[
1b,2d,5a-d,6b,7e,12a,24]
and
pared NiPd/NH -N-rGO composite shows the excellent catalytic
2
even comparable to most of those obtained with additive or/and
activity for the dehydrogenation of FA at 298 K, except Ni/NH2-
at elevated temperature.[
4,5e,6a,c,25]
Additionally, with catalyst of
rGO. As shown in Figure 4b, monometallic Pd/NH -N-rGO and
2
Ni0.4Pd0.6/NH -N-rGO, only the mixture of H2 and CO2 but
bimetallic Ni0.2Pd0.8/NH -N-rGO with low content of Ni have
2
2
no CO (detection limit: ≈10 ppm for CO; Figure S7, Supporting
Information) has been detected by GC (Figure S8, Supporting
Information) and MS (Figure S9, Supporting Information)
the similar activities, and the reaction can be completed within
6 min with the initial TOF of 462.5 and 513.9 mol H mol cata-
2
−
1
−1
lyst h , respectively. When Ni addition comes to 40 at%, the
analyses, which means that the present Ni0.4Pd0.6/NH -N-rGO
obtained Ni0.4Pd0.6/NH -N-rGO demonstrates the best activity.
2
2
hybrid has an excellent H selectivity for FA dehydrogenation.
Further increase in the Ni content to 60%, the activity of the
bimetallic system deceased slightly, with the initial TOF of
2
On the other hand, for catalyst of Ni0.4Pd0.6/N-rGO, only 74 mL
of gas can be released from FA even after 60 min, giving a con-
version of only 30%. And for Ni0.4Pd0.6/rGO, only 18 mL of gas
−
1
−1
355.8 mol H mol catalyst h . However, even when the Ni
2
content reaches 80 at%, the resultant Ni0.8Pd0.2/NH -rGO also
2
can be generated in 60 min, with conversion of 7%. Ni0.4Pd0.6
-
shows the excellent activity with full conversion and high ini-
−
1
−1
APTS can release the total 245 mL gas in 26 min, while pure
Ni0.4Pd0.6 or APTS (Figure S10, Supporting Information)
shows no catalytic activity without gas generation. The better
catalytic activity of Ni0.4Pd0.6-APTS than that of Ni0.4Pd0.6/rGO
may be due to the much smaller particle size and thus more
surface active sits of Ni0.4Pd0.6 prepared with APTS (≈1.8 nm;
Figure S11, Supporting Information) than those prepared
with rGO (≈10.1 nm, Figure 1c), and there is no bond formed
between Ni0.4Pd0.6 and APTS (Figure S12, Supporting Informa-
tion). However, the particle dispersity of Ni0.4Pd0.6-APTS is not
tial TOF (140.5 mol H mol catalyst h ). The actual molar
2
ratios of Ni:Pd in Ni0.2Pd0.8/NH -N-rGO, Ni0.6Pd0.4/NH -N-
2
2
rGO, and Ni0.8Pd0.2/NH -N-rGO are measured by ICP-AES
2
to be 0.22:0.78, 0.62:0.38, and 0.82:0.18, respectively, which is
consistent to nominal molar ratios of Ni:Pd in the samples. To
the best of our knowledge, this is the first report on catalyst
for hydrogen generation from FA with such a high NNM con-
tents (up to 80 at%) but excellent catalytic activities (Table S1,
Supporting Information). Due to the chemical instability and
catalytic inactivity of NNM (such as Ni and Co) in FA solution,
there is still no report on heterogeneous catalyst with content of
as good as that of Ni0.4Pd0.6/NH -N-rGO. Therefore, Ni0.4Pd0.6
/
2
[
6]
NH -N-rGO demonstrates the highest activity among all the
NNM higher than 40 at%.
2
specimens. Based on the above results, it can be concluded that
To better understand the superiority of the present
the use of NH -N-rGO can significantly improve the catalytic
Ni0.4Pd0.6/NH -N-rGO catalyst, in situ carbon dioxide infrared
2
2
activities of Ni0.4Pd0.6 UPs. Obviously, the significant enhance-
spectroscopy (CO-IR) has been applied to determine the
ment on the catalytic performance of Ni0.4Pd0.6/NH -N-rGO
surface adsorption properties of Ni0.4Pd0.6/NH -N-rGO,
2
2
may due to the presence of novel hydrophilic NH -N-rGO sup-
Ni/NH -N-rGO, and Pd/NH -N-rGO for comparison. As shown
2
2
2
port that leads to the ultrafine particle sizes, good dispersion,
and strong SMSI effect of alloyed Ni0.4Pd0.6 UPs with plentiful
and upgraded active sites. It should be noted that the activity
in Figure S16 (Supporting Information), intrinsic Ni displays
no adsorption to CO. The vibration bands for Pd/NH -N-rGO
2
−
1
appeared at 1951 cm , which can be assigned to bridged
CO adsorption. While after the addition of Ni, the bridge-
adsorption CO is presented at 1936 cm for the NiPd/NH -N-
[
26a]
of Ni0.4Pd0.6/NH -N-rGO almost has no relationship with the
2
−
1
dosage of APTS in the range of 0–0.6 mL, while for further
increase in the dosage higher than 0.6 mL, the activity will be
decreased (Figure S13, Supporting Information).
2
−
1
rGO catalyst, showing a significant redshift of about 15 cm
when compared to Pd/NH -N-rGO. The redshift is ascribed
2
The recycling stability of the Ni0.4Pd0.6/NH -N-rGO hybrid is
to that the neighboring Ni atoms could increase the electronic
density of Pd and change the surface performance of the cat-
alysts through geometric “ensemble effects” and electronic
2
also tested by adding an additional aliquot of FA to the reac-
tion vessel after the completion of the previous run. It can be
seen that there is no significant decrease in catalytic activity
[
26a,b]
“ligand effects,”
and thus enhance the catalytic activity. Moreover, for Ni0.4Pd0.6
NH -N-rGO, a new linear-bonded CO peak centered at
which is consistent with the XPS result,
th
after the 5 run (Figure S14, Supporting Information), and the
/
Ni0.4Pd0.6 particles also demonstrate the similar good disper-
sion and ultrafine sizes with no obvious sedimentation in the
reaction solution (Figure S14 (inset), Supporting Information),
2
−
1
2059 cm is appeared, which is caused by the low-coordi-
nated Pd sites in the catalyst, such as corners and defects.
[
26c]
indicating the good recycling stability of Ni0.4Pd0.6/NH -N-rGO
catalyst.
Up to now, there have been very few reports on the turnover
number (TON; Equation (S3), Supporting Information) of FA
decomposition over heterogeneous catalysts, which may be due
to the poor long-time stability of those catalysts. As shown in
Adsorbate is easy to desorb on low-coordinated Pd sites thanks
to the relatively low adsorption enthalpy, which may lead to
2
[
26d]
an improvement on the selectivity.
Hence, the as-prepared
Ni0.4Pd0.6/NH -N-rGO exhibits the outstanding catalytic activity
2
and 100% H selectivity. Therefore, in this work, the alloy struc-
2
ture of NiPd may facilitate to increase the stability of Ni in the
Figure S15 (Supporting Information), the TON over Ni0.4Pd0.6
/
reaction system, and the unique NH -N-rGO support can fur-
2
NH -N-rGO are calculated to be 334 and 585 within 1 and 3 h,
respectively, which are comparable to the values obtained by the
ther help to form plenty of upgraded reactive sites of NiPd UPs
on its surface. The above two factors may be responsible for the
2
noble metal catalysts even with additive (Table S2, Supporting
high efficiency of NiPd/NH -N-rGO for FA selective dehydro-
genation even with high Ni content.
2
Information),[
5e,24f]
demonstrating the relatively good long-time
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In summary, we have developed a facile one-step strategy
to simultaneously synthesize NiPd bimetallic UPs growing
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This work was supported in part by the National Natural Science
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