Bifunctional networked Ag/AgPd core/shell nanowires for the highly efficient dehydrogenation of formic acid and subsequent reduction of nitrate and nitrite in water

Article abstract of DOI:10.1039/c8ta00600h

Nitrate (NO₃^-) and nitrite (NO₂^-) pollution in water has increasingly become a serious environmental concern. The catalytic reduction of NO₃^- and NO₂^- to harmless N₂ by a reducing agent is considered to be one of the most promising methods to remove NO₃^- and NO₂^- from water. Herein, we report the one-pot synthesis of networked Ag/AgPd core/shell nanowires (CS-NWs) via seed-mediated growth in polyol solution. The shell thickness of the networked Ag/AgPd CS-NWs can be readily controlled by tuning the amount of precursors. The networked Ag/AgPd CS-NWs with a 0.9 nm shell thickness exhibited the highest activity towards the dehydrogenation catalysis of FA with an initial TOF of 1400 h^-1 at 50 °C, and the highest selectivity for the catalysis of NO₃^- and NO₂^- to N₂ in water and at room temperature. Their enhanced bifunctional catalytic performance could be attributed to more efficient electron transfer from PVPI and Ag to Pd. This work demonstrates a new way to prepare bifunctional nanocatalysts for the removal of NO₃^- and NO₂^- from water using FA as the in situ hydrogen source.

Full text of DOI:10.1039/c8ta00600h

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Bifunctional Networked Ag/AgPd Core/Shell Nanowires for
Highly Efficient Dehydrogenation of Formic Acid and Subsequent
Reduction of Nitrate and Nitrite in Water
Received 00th January 20xx,
Accepted 00th January 20xx
1
,2
2
1,2
2
1
1
Hu Liu , Xinyang Liu , Yongsheng Yu * Weiwei Yang *, Ji Li , Ming Feng
DOI: 10.1039/x0xx00000x
1
and Haibo Li
www.rsc.org/
ꢀ
ꢀ
Nitrate (NO
The catalytic reduction of NO
3
) and nitrite (NO
2
) pollution in water has increasingly become a serious environmental concern.
ꢀ
ꢀ
3
and NO
2
to harmless N
2
by the reducing agent is considered as one of the
ꢀ
ꢀ
most promising methods to remove NO
3
and NO in water. Herein, we report oneꢀpot synthesis of the
2
networked Ag/AgPd core/shell nanowires (CSꢀNWs) via a seedꢀmediated growth in polyol solution. The shell
thickness of the networked Ag/AgPd CSꢀNWs can be readily controlled by tuning the amount of the
precursors. The networked Ag/AgPd CSꢀNWs with 0.9 nm shell thickness exhibit the highest activity for
ꢀ
1
o
dehydrogenation catalysis of FA with an initial TOF of 1400 h at 50 C and the high selectivity for
ꢀ
ꢀ
catalyzing NO
3 2 2
and NO in water to N at room temperature. Its enhanced bifunctional catalytic performance
could be attributed to more efficient electron transfer from PVPI and Ag to Pd. This work demonstrates a new
ꢀ
ꢀ
3 2
way to prepare the bifunctional nanocatalysts for removing NO and NO from the water with FA as inꢀsitu
hydrogen source.
ꢀ
ꢀ
Nitrate (NO ) and nitrite (NO ) pollution, generating mainly from groundwater and to provide clean drinking water for
3
2
from agricultural, municipal and industrial activities, has healthy life.
1
,2
7
increasingly become
a
serious environmental concern
.
To meet drinking water standard, there are bioꢀreduction ,
ꢀ
ꢀ
8
9
10
Pollution of NO
3 2
and NO in water is a nearly colorless, ion exchange , reverse osmosis , catalytic reduction methods ,
ꢀ
ꢀ
transparent and neutral solution, which is hard to be observed etc. for NO
3
and NO
2
removing from drinking water. The bioꢀ
ꢀ
ꢀ
ꢀ
ꢀ
by the naked eye. Excessive contents of NO
3
and NO
2
are a reduction is available method for NO and NO removal, but
3 2
major cause of water eutrophication destructing the ecological drinking water supplies could lead to bacterial spillꢀover.
3
equilibrium in water . More seriously, once consumed and Compared with the expensive operation and maintenance cost
ꢀ
carried to a hypoxia environment in a human body, NO
3
can be of ion exchange and reverse osmosis methods, the catalytic
ꢀ
reduced to more toxic NO
hemoglobin (Hb) from Fe(II) to Fe(III), making it impossible water by converting NO
for Fe(II)ꢀHb to transfer oxygen (O ) and causing serious agent in water. However, the existing catalytic technology
biological consequences , especially for infants, who are among relies on the noble metal as the catalyst and hydrogen (H ) as a
the most delicate group and are easily affected by the nitrated reducing agent. Despite the demonstrated success of the
water to show “blue baby syndrome”, liver damage and various catalytic reaction process, the use of a large amount of H for
cancers . Hence, to ensure the health of people, Environmental the reduction purpose brings a separate safety issue in transport,
Protection Agency (EPA) around the world had set up the storage and use of H for largeꢀscale water purification. It has
in become imperative to develop a new catalyst that can convert
2
that oxidizes Feꢀcomplexes of reduction method more conveniently provides clean drinking
ꢀ
ꢀ
3
2 2
and NO to N using the reducing
2
4
2
2
5
2
ꢀ
ꢀ
maximum contaminant level (MCL) for NO
3
and NO
drinking water at 25 mg/L . It is, therefore, an urgent need to NO3 and NO to N without using pure H so that the safety
2
6
ꢀ
ꢀ
2
2
2
ꢀ
ꢀ
develop a highly efficient approach to remove NO3 and NO2 risks associated with H2 transportation and storage can be
eliminated.
Formic acid (FA) with a high volumetric capacity of 53 g
1 Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of
Education, Jilin Normal University, Changchun 130103, China
H /L demonstrates promise as a safe, convenient liquid
2
1
1
hydrogen carrier at ambient temperature . Under mild
condition, FA can produce and CO through the
2
MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion
H
2
2
and Storage, School of Chemistry and Chemical Engineering, Harbin Institute of
Technology, Harbin, Heilongjiang 150001, China
dehydrogenation process. Recently, Pdꢀbased alloy reported
efficiently catalyze FA decomposition to H2 in an aqueous
*
To
whom
correspondence
should
yongshengyu80@sohu.com and yangww@hit.edu.cn
be
addressed.
Email:
12ꢀ18
solution under mild condition
. There is a hydrogen spillꢀ
over based PdꢀH bond on the surface of Pdꢀbased catalyst
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during happening hydrogenation process. Much efforts have analyzed by the inductively coupled plasma optical emission
reported that the hydrogen spillover can be used various
spectroscopy (ICPꢀOES) (Table S1 in Supporting Information).
1
9,21
hydrogenation reaction
. In this regard, using FA as the inꢀ
situ reducing agent is one of the most promising methods to
ꢀ
ꢀ
22ꢀ26
reduce NO
3
and NO
2
to N
2
in existence of the catalyst
.
Therefore, it is desirable to develop a bifunctional catalyst
which can not only completely decompose FA by
dehydrogenation route without additive as inꢀsitu hydrogen
ꢀ
ꢀ
source, but also thoroughly catalyze NO
to N in water.
3 2
and NO converting
2
Herein, we describe a novel route to prepare networked
Ag/AgPd core/shell nanowires (CSꢀNWs) via a seedꢀmediated
growth in polyol solution (Scheme 1), which can completely
decompose FA by dehydrogenation route without additive and
ꢀ
ꢀ
3 2 2
subsequent convert NO and NO to harmless N with FA as
inꢀsitu hydrogen source at room temperature. The strategy
opens a new way to prepare the bifunctional nanocatalysts for
ꢀ
ꢀ
removing NO3 and NO2 from the water with FA as inꢀsitu
hydrogen source.
Figure 1.
different magnifications. (
The insert a and b of Figure 1C shows the lattice profiles of fcc Ag and fcc
AgPd in the Ag/AgPd CSꢀ0.9. (D-G) HAADFꢀSTEM and elemental
mapping of the Ag/AgPd CSꢀ0.9. (
(
A-B) Typical TEM images of the Ag/AgPd CSꢀ0.9 with
Scheme 1. The schematic illustration on oriented attachment of
Ag/AgPd NPs for the growth mechanism of networked Ag/AgPd CSꢀ
NWs.
C) HRTEM image of the Ag/AgPd CSꢀ0.9.
In a typical synthesis, polymerꢀpolyvinylpyrrolidine imine
H) XRD patterns of the AgPd alloy
(PVPI) solution of 1,3ꢀbutylene glycol (1, 3ꢀBG) was
NWs, Ag/AgPd CSꢀ0.9 and Ag NPs.
synthesized by the ketoamine condensation reaction between
The typical morphology and structure of Ag/AgPd CSꢀ0.9 were
characterized by transmission electron microscopy (TEM) with
2
7
polyvinylpyrrolidone (PVP) and NH ·H O . Then 0.1 mmol
3
2
3 2
AgNO was reduced to Ag nanoparticles (NPs) in Na S and
different magnifications (Figure 1A&B), which clearly show
PVPI solution of 1, 3ꢀBG and EG (Figure S1A in Supporting
Information). Ag/AgPd core/shell nanoparticles (CSꢀNPs) were
further obtained by depositing equivalent amount of Pd(NO3)2
the Ag/AgPd CSꢀ0.9 sample exhibits the networkꢀlike
morphology with unique convex/concave regions and kinks. As
shown in highꢀresolution (HR) TEM image (Figure 1C), the
3
and AgNO on Ag NPs. Finally, Ag/AgPd CSꢀNPs further
(
(
111) lattice fringe distances of faceꢀcentered cubic (fcc) Ag
0.24 nm) and fcc AgPd alloy (0.23 nm) accurately obtained
assembled into a networked Ag/AgPd CSꢀNWs. The asꢀ
synthesized networked Ag/AgPd CSꢀNWs with controlled shell
thickness were easily made by controlling the amount of
Pd(NO ) and AgNO . For example, 0.05 mmol of AgNO and
from the lattice profiles of the HRTEM image of the Ag/AgPd
CSꢀ0.9 are located in the centre and edge of NWs, respectively,
which does demonstrate the Ag/AgPd CSꢀ0.9 is coreꢀshell
structure. In addition, dense low coordination atoms and a mass
of defects distribute on the kink surface of Ag/AgPd CSꢀ0.9.
Meanwhile, high density of many steps form on surface of the
networked NWs. Elemental distribution of a representative
Ag/AgPd CSꢀ0.9 NW is investigated by STEMꢀEDS elemental
mapping analysis (Figure 1D-G). It can be clearly seen that Pd
and Ag distribute evenly across the NW. The ~4.5 nm diameter
of Ag/AgPd CSꢀ0.9 can been accurately obtained from the
3
3
2
2
3
3
Pd(NO
)
gave Ag/AgPd CSꢀNWs with a 0.3 nm shell,
designated as Ag/AgPd CSꢀ0.3 (Figure S1B), 0.075 mmol of
AgNO and Pd(NO resulted in a 0.6 nm AgPd shell,
designated as Ag/AgPd CSꢀ0.6 (Figure S1C), 0.1 mmol of
AgNO and Pd(NO formed a 0.9 nm AgPd shell, designated
as Ag/AgPd CSꢀ0.9 (Figure 1A ) and 0.125 mmol of
AgNO and Pd(NO yielded a 1.2 nm AgPd shell, designated
as Ag/AgPd CSꢀ1.2 (Figure S1D). The Ag/AgPd CSꢀNWs was
3
3 2
)
3
3 2
)
&
B
3
3 2
)
diffraction profiles of the HRꢀTEM image (Figure S2A&B). In
2
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order to further figure out whether the Ag and AgPd phases are IMs can been accurately obtained from the diffraction profiles
coexisting, the STEMꢀEDS line scan of the Ag/AgPd CSꢀ0.9 of the HRꢀTEM image (insert of Figure 2B), which is
NW was analyzed (Figure S2C), showing that Ag distributes consistent with the diameter of Ag/AgPd CSꢀ0.9 (Figure
throughout the entire NWs with a higher distribution in the S2A
core, and AgPd phase is observed in the edge region of the NWs, the IMs of CSꢀNWs and Ag NPs were also tested
whole NW, which indicates the formation of a core (Ag)/shell Figure 2C). Compared with the XRD patterns of the Ag Pd
AgPd) structure. Figure 1H and Figure S3 shows the XRD alloy NWs, the XRD patterns of Ag NPs and the IMs samples
patterns of the Ag Pd alloy NWs, CSꢀNWs and Ag NPs. have same diffraction peaks assigned to the (111) planes of Ag
&B). In addition, the XRD patterns of the Ag Pd alloy
5 5
(
5
5
(
5
5
Compared to the XRD patterns of the Ag Pd5 alloy NWs core in the IMs of CSꢀNWs. When the reaction stays at 1 min,
5
samples, the XRD patterns of Ag NPs and CSꢀNWs samples some Ag/AgPd CSꢀNPs were still observed, suggesting that the
have same diffraction peak assigned to the (111) planes of Ag nucleation of Ag/AgPd CSꢀ NPs and the growth of Ag/AgPd
core in the CSꢀNWs. In addition, the absorption spectra of the CSꢀNWs occurred simultaneously
(Figure 2D). With
Ag Pd5 alloy NWs and Ag/AgPd CSꢀNWs were tested in increasing the reaction time to 30 min, only Ag/AgPd CSꢀNWs
5
aqueous solution (Figure S4). Compared to the absorption band with distinct networkꢀlike structure were produced (Figure 2E
)
of the Ag Pd alloy NWs, there are the 330ꢀ550 nm absorption and no Ag/AgPd CSꢀNPs and short Ag/AgPd CSꢀNWs could
5
5
band for the Ag/AgPd CSꢀNWs, which may be contributed to be found. At this point, abundant convex/concave regions and
the surface plasmon resonance (SPR) effect of the Ag core in kinks are clearly seen on the surface of networked Ag/AgPd
Ag/AgPd CSꢀNWs. Those results indeed testify that Ag/AgPd CSꢀNWs. Further extension of the reaction time to 2 h, there
CSꢀNWs were successfully synthesized.
was no obvious morphological change (Figure 2F), retaining
.9 nm AgPd shell of the CSꢀNPs (Insert of Figure 2F). The
0
result of timeꢀdependent evolution clearly indicates that the
formation mechanism of networked Ag/AgPd CSꢀNWs
undergoes an process involving the following three steps
(
Scheme 1): i) the generation of Ag/AgPd CSꢀNPs within very
short reaction time through burst nucleation; ii) collision and
oriented attachment of the thermodynamically unstable
Ag/AgPd CSꢀNPs to generate short Ag/AgPd CSꢀNWs; and iii)
connection of the short Ag/AgPd CSꢀNWs via an endꢀtoꢀend
mode to generate longer Ag/AgPd CSꢀNWs and then
interweaving into networked Ag/AgPd CSꢀNWs. Thus, the
controllable reaction kinetic during the initial stage is crucial to
the formation of networked Ag/AgPd CSꢀNWs.
Figure 2 Typical TEM images of intermediates for synthesizing
Ag/AgPd CSꢀ0.9 at different reaction time: (
min and ( ) 2 h. The insert of Figture 2A
distribution of Ag/AgPd NPs and Ag/AgPd CSꢀ0.9, repectively. (
A
) 10 s, (
D) 1 min, (E) 30
F
&F
shows the diameter
B
)
HRTEM image and diffraction profile of the IMs. (
AgPd alloy NWs, the IMs and Ag NPs.
C) XRD patterns of
To elucidate the formation mechanism of networked Ag/AgPd
CSꢀNWs, the growth intermediates (IMs) of the CSꢀNWs at
different reaction durations were collected. As shown in Figure
S1A, Ag NPs with ~3.6 nm diameter were synthesized at the
seed growth stage (typically 20 min). As the reaction proceeded
for another 10 s after the adding 0.1 mmol of Pd(NO
3 2
) and
AgNO into the synthesis solution, Ag/AgPd core/shell
3
nanoparticles (CSꢀNPs) had been formed with 0.9 nm AgPd
Figure 3. A) High resolution XPS spectra of C1s and N1s for (a) PVPI and
shell (Figure 2A), and the CSꢀNPs grew into the short CSꢀ
(
b) Ag/AgPd CSꢀ0.9, respectively. (B-C) High resolution XPS spectra of
Ag NWs and Ag/AgPd CSꢀ0.9, respectively. (D)
IR spectra of PVPI and Ag/AgPd CSꢀ0.9, respectively.
NWs. Herein, the random IMs of the CSꢀNWs were tested the Ag 3d and Pd 3d for Pd
5
5
HRꢀTEM image (Figure 2B), and the ~4.5 nm diameter of the
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To further understand the electronic structures of C, N, Ag and
Pd in Ag/AgPd CSꢀ0.9, the XPS measurement was carried out
to confirm the electronic states of the elements in Ag/AgPd CSꢀ
0.9 catalyst. Figure S4 shows the representative survey XPS
spectrum of the Ag/AgPd CSꢀ0.9, which clearly verified the
existence of Ag, Pd, C, and N elements in Ag/AgPd CSꢀ0.9
catalyst. The electronic states of C and N in Ag/AgPd CSꢀ0.9
were also measured. it can be seen that, compared with pure
PVPI, the binding energies of C1s and N1s from Ag/AgPd CSꢀ
0.9 are shifted to the higher values (Figure 3A). For XPS
spectra of Ag 3d and Pd 3d, the binding energies of Ag 3d in
core/shell structure of Ag/AgPd CSꢀ0.9 shift to a higher value
than those of bulk Ag material and alloying structure in
2
8
networked Pd
of Pd 3d in coreꢀshell structure of Ag/AgPd CSꢀ0.9 shift to a
lower value than those of bulk Pd material and alloying the catalytic the dehydrogenation of FA at different temperatures and (
the related Arrhenius plot (ln TOF vs. 1/T). (C) CO + H volum generated
5 5
Ag NWs (Figure 3B) , while binding energies
2 2
Figure 4 (A) The volume of gas mixture (CO +H ) generated vs. time for
B)
2
9
2
2
structure in networked Pd Ag NWs (Figure 3C) . In addition,
5
5
vs. time for the catalytic the dehydrogenation of FA at different FA
concentrations and (D) the plot of gas generation rate vs. FA concentration.
we further studied the charge states of PVPI and Ag/AgPd CSꢀ
0
.9 by the FTIR spectra. The νC=N value for PVPI is
We further studied the effects temperature and FA
concentration on the FA dehydrogenation catalyzed by
Ag/AgPd CSꢀ0.9 catalyst. Firstly, the rate of FA
dehydrogenation was investigated in 1 M aqueous FA solution
ꢀ1
ꢀ1
monotonically redꢀshifted from 1693 cm to 1650 cm with
2
7,30
Ag/AgPd CSꢀ0.9 (Figure 3D
)
. These shifts testify that there
is more efficient electron transfer from PVPI and Ag to Pd in
core/shell structure of Ag/AgPd CSꢀ0.9 than alloying structure
at different temperatures. As shown in Figure 4A&B, the
in networked Pd
5 5
Ag NWs. Such electron transfer has the
decomposition percent of FA almost is 100 % at different
temperatures, and the value of TOF is 1400, 656, 366 and 316
potential to endow itself with boosting catalysis for
ꢀ
ꢀ
dehydrogenation of FA and reduction of NO
on the surface of Ag/AgPd CSꢀ0.9.
3 2 2
and NO to N
ꢀ1
o
o
o
o
h
at 50 C, 40 C, 30 C and 25 C, respectively. We plotted
the Arrhenius plot by the logarithmic TOF vs. 1/T (inset in
We first evaluated the catalytic activity of Ag/AgPd CSꢀNWs
toward the dehydrogenation of FA in a typical gas burette
system. The evaluation results of the Ag/AgPd CSꢀNWs with
different shell thickness were plotted into Figure S6A in 10 mL
FA aqueous solution (1 M) at 50 °C. Among the Ag/AgPd CSꢀ
NWs, it was found that the Ag/AgPd CSꢀ0.9 exhibited the
highest catalytic activity. The initial TOF of the Ag/AgPd CSꢀ
Figure 4B), and calculated the apparent activation energy
app
ꢀ1
(
Ea ) whose value is 41.1 KJ·mol . In addition, to study the
effect of FA concentration on the rate of FA dehydrogenation,
the concentration of Ag/AgPd CSꢀ0.9 was kept 10 mM at 50
°
C. The volume of gasꢀgeneration versus reaction time is
plotted at different FA concentrations (Figure 4C). Figure 4D
shows the initial TOFs versus corresponding FA concentration
plot. When the FA concentration raises from 0.25 M to 1.0 M,
the rate of FA dehydrogenation increases, and drops when the
FA concentration raises from 1.0 M to 10 M, but the TOF value
of FA dehydrogenation with FA concentrations as high as 10 M
0.3, Ag/AgPd CSꢀ0.6, Ag/AgPd CSꢀ0.9 and Ag/AgPd CSꢀ1.2
ꢀ1
catalysts is 312, 446, 1400 and 986 h at 50 °C, respectively.
As shown in Figure S6B, the TOF firstly increases and then
decreases with increasing shell thickness, which manifests that
the coreꢀshell structure with 0.9 nm AgPd shell thickness are
more active than other shell thickness in Ag/AgPd CSꢀNWs.
ꢀ1
stays about 600 h . This result verifies that Ag/AgPd CSꢀ0.9
catalyst achieves H production from high concentration FA
2
solutions without additive. The findings open a promising
avenue for guiding the rational design of novel catalysts for H2
production from high concentration FA solution.
4
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Due to the effect of undesired FA dehydration route, hence, we into the 9.1 mL water in 50 mL twoꢀneck flask under a
tested the evolving gas mixture by gas chromatograph (GC). magnetic stirring (600 rpm) for 15 min in the flask, and
The result shows that the evolving gas mixture is composed of thermostated to a desired temperature value. Then, 0.5 mL
−
−
H and CO , meanwhile there is no CO detected in the gas NaNO (3.2 g NO /L) or NaNO solution (2.5 g NO /L) and
2
2
3
3
2
3
mixture (detection limit for CO: ~2 ppm) (Figure 5E
Additionally, we measured the H volumes by gas mixture from the rubber stopper neck, respectively. During the
flowing into the NaOH trap (Figure S7), and then compared experiment, we extracted 0.5 mL suspension from catalytic
with gas mixture (CO + H ) volumes. The result further verify system at the regular time interval. The Ag/AgPd CSꢀ NWs
that the molar ratio of CO2 and H is 1. Importantly, these catalyst was separated from the suspension by centrifugation,
&F). 0.2 mL FA were rapidly rejected into the flask using a syringe
2
2
2
2
+
−
−
−
results demonstrate that COꢀfree H
2 4 3 2
can be released from our and the concentrations of NH , NO , NO , and HCOO in
catalytic system for practical applications.
the clear solution were detected by the ion chromatograph.
We first evaluated the catalytic activity of Ag/AgPd CSꢀNWs
ꢀ
ꢀ
toward the NO3 and NO2 reduction in 0.5 M FA aqueous at
5 °C. The evaluation results of the Ag/AgPd CSꢀNWs with
different shell thickness were plotted into Figure S8 9 and
2
＆
Figure 5A&B. Among the Ag/AgPd CSꢀNWs, it was found
that the Ag/AgPd CSꢀ0.9 exhibited the highest catalytic activity
ꢀ
ꢀ
toward the NO
3
and NO
2
reduction. As can be seen from
ꢀ
Figure 5A&B, during the FA hydrogenation process, the NO
3
can be reduced rapidly within 10 min, and the initial reduction
ꢀ
ꢀ
rate of NO2 was faster than the reduction rate of NO , but the
3
ꢀ
ꢀ
ꢀ
Figure 5
(
A
) The catalytic NO
3
and NO
2
reduction and (
B
) the catalytic NO3 reduction rate slowed down quickly after 10 min. The
FA decomposition of the Ag/AgPd CSꢀ0.9 catalyst vs. the reaction time in
ꢀ
ꢀ
NO
3 2
and NO can be completely reduced for 1 h and 0.3 h,
0
.5 M FA aqueous at 25 °C, respectively. (C) The ammonia nitrogen
ꢀ
ꢀ
content in the catalytic NO
time. (
NO
2
commercial pure N
CSꢀ0.9 at 25 C in FA (0.5 M, 10 mL) dehydrogenation system, respectively.
3
and NO
2
reduction system vs. the reaction respectively, before the FA dehydrogenation process is over. To
ꢀ
D
) The selectivity of Ag/AgPd CSꢀ0.9 catalyst toward NO
to meet its drinking water standard recommended by the EPA at
5mg/L. (E) GC spectrum using TCD for the evolved gas from (a) ammonia nitrogen concentration were detected by Nessler’s
3
and
+
−
−
4 3 2
test further the concentrations of NH , NO and NO , the
ꢀ
2
ꢀ
ꢀ
2
, the reduction of (b) NO
3
and (c) NO
2
over Ag/AgPd
reagent dectrophotometry at the regular time interval. It is
o
o
(
d) FA aqueous solution (0.5 M, 10 mL) over Ag/AgPd CSꢀ0.9 at 25 C. (F) found that the ammonia nitrogen concentration is always kept
GC spectrum using FIDꢀMethanator for the evolved gas from the
at about 10 mg/L in the first hour and dropped to 7 mg/L after 2
h reaction (Figure 5C), which further demonstrates that
Ag/AgPd CSꢀ0.9 catalyst has 100 % selectivity and high
activity toward FA dehydrogenation and 99.8 % selectivity for
ꢀ
ꢀ
o
reduction of (
a
)
NO
3
and (
b
)
NO
2
over Ag/AgPd CSꢀ0.9 at 25 C in FA
) Commercial
d) FA aqueous solution (0.5 M, 10 mL) over Ag/AgPd CSꢀ0.9
(0.5 M, 10 mL) dehydrogenation system, respectively. (
c
pure CO. (
o
at 25 C.
ꢀ
ꢀ
The above results show that Ag/AgPd CSꢀ0.9 could completely reduction of NO
3
and NO
2
2
to N (Figure 5D) at room
catalyze FA dehydrogenation reaction under mild condition, temperature. In addition, we tested the evolving gas mixture by
ꢀ
and our previous work have confirmed that NO
and Pd(NO ·2H
3
of the AgNO
3
2
gas chromatograph (GC) in this reaction system. The result
shows that the evolving gas mixture is composed of H , N and
3
)
2
2
O was thoroughly converted to harmless N
2
2
3
1
ꢀ
ꢀ
during synthetic process , inspiring us to use hydrogen CO , confirming reduction production of NO3 and NO2 is N2
2
ꢀ
spillover of FA dehydrogenation to reduce efficiently NO3 and
(Figure 5E&F). The experiment suggests that Ag/AgPd CSꢀ0.9
ꢀ
ꢀ
ꢀ
NO
2
on Ag/AgPd CSꢀNWs with FA as inꢀsitu hydrogen can efficiently catalyze NO3 and NO2 into harmless N2 to
ꢀ
ꢀ
ꢀ
source. Hence, we conducted the catalytic reduction of NO
3
alleviate the NO3 and NO2 pollution in water with FA as inꢀ
ꢀ
and NO
2
experiments in the typical FA dehydrogenation situ hydrogen source. Its enhanced bifunctional catalytic
o
system at 25 C. In this setup, one neck of twoꢀneck flask was performance could be attributed to more efficient electron
connected to a balloon, and the other neck was sealed rubber transfer from PVPI and Ag to Pd, both of which were beneficial
stopper, 0.1 mmol Ag/AgPd CSꢀ NWs catalyst was dispersed for the catalytic FA decomposition to provide the in situ
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ꢀ
sources of the reducing agent of H
2
for the catalytic NO
3
and (No. 2015M81436) and Heilongjiang Postdoctoral Science
Foundation (No. LBHꢀZ15065).
ꢀ
27
2
NO reduction process .
Finally, the cycle property of Ag/AgPd CSꢀ0.9 catalyst was
tested in the FA aqueous solution (10.0 mL, 0.5 M) with or
Notes and references
1
J. P. Van der Hoek, W. K. Van der Hoek, A. Klapwijk, Water Air
Soil Pollut. 1988, 37, 41ꢀ53.
ꢀ
ꢀ
o
without NO
3
and NO
2
at 25 C (Figure S10&11). The
2
3
A. Kapoor, T. J. Viraraghavan, Environ. Eng. 1997, 123, 371ꢀ380.
Ag/AgPd CSꢀ0.9 catalyst maintains its initial high activity
L.W. Canter, Nitrates in Groundwater, CRC Press, Boca Raton, FL
996
J. O. Lundberg, E. Weitzberg, M. T. Gladwin, Nature reviews Drug
2008 , 156ꢀ167.
D. M. Freedman, K. P. Cantor, M. H. Ward, K. J. Helzlsouer, Arch.
Environ. Health 2000, 55 326ꢀ329.
,
1
.
toward FA dehydrogenation (Figure S10) and the conversion
4
ꢀ
ꢀ
of NO
3
and NO
2
to N
2
(
Figure S11) at least the fourth run. We discovery
,
, 7
5
further investigated the morphology
(
Figure S12) and
composition (Table S3) of Ag/AgPd CSꢀ0.9 catalyst after the
fourth run using ICPꢀOES and TEM. There are no obvious
change on the Ag/Pd composition and Ag/AgPd CSꢀ0.9 catalyst
is still the networkꢀlike morphology. Therefore, these Ag/AgPd
CSꢀ0.9 catalyst are stable under the current FA
6
7
L. Bontoux, N. Bournis, D. Papameletiou, IPTS Rep. 1996, 6, 7.
V. Mateju, S. Cizinska, J. Krejci, T. Janoch, Enzyme Microbiol.
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O. K. Marquardt, Aqua 1987, 1, 39ꢀ44.
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ꢀ
8181.
rounds of the dehydrogenation reaction and reduction of NO
3
1
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ꢀ
and NO .
Angew. Chem. Int. Ed. 2013
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2
1
Conclusions
,
, 5
1
In summary, we demonstrate a novel route to prepare
networked Ag/AgPd CSꢀNWs via a seedꢀmediated growth in 2011
,
6
1
polyol solution as highly efficient bifunctional nanocatalysts for
catalyzing dehydrogenation reaction of FA and reduction of
,
6
1
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57ꢀ666.
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ꢀ
ꢀ
NO
3 2 2
and NO to harmless N with FA as inꢀsitu hydrogen
,
source at room temperature. The shell thickness of the
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,
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,
,
2
2
0 Ding, Y., Sun, W., Yang, W., Li, Q. Appl. Catal. B-Environ. 2017
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ꢀ1
o
1
400 h at 50 C and the high selectivity for efficiently 21 U. Prüsse, K. D. Vorlop, J. Mol. Catal. A: Chem. 2001, 173, 313ꢀ328.
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ꢀ
ꢀ
catalyzing NO
3 2 2
and NO in water to harmless N at room
2
temperature. Its enhanced bifunctional catalytic performance
could be attributed to more efficient electron transfer from
PVPI and Ag to Pd. The results presented here open a new way
2
Applied Catalysis B: Environmental
2
,
,
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Conflicts of interest
There are no conflicts of interest to declare.
9 C. J. Jenks, S. L. Chang, J. W. Anderegg, P. A. Thiel, D. W. Lynch,
1996 54, 6301ꢀ6306.
Acknowledgements
Phys. Rev. B
,
,
This work was supported by the National Natural Science 30 H. Tsunoyama, N. Ichikuni, H. Sakurai, T. Tsukuda, J. Am. Chem.
Soc., 2009
1 H. Liu, Y. Y. Yu, W. W. Yang, W. J. Lei, M. Y. Gao, S. J. Guo,
Nanoscale 2017 , 9305ꢀ9309.
, 131, 7086ꢀ7093.
Foundation of China under Grant (No. 51571072),
Fundamental Research Funds for the Central Universities (No.
AUGA5710012715), China Postdoctoral Science Foundation
3
,
, 9
6
| J. Name., 2012, 00, 1-3
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Table of contents (TOC) figure
Bifunctional Networked Ag/AgPd Core/Shell Nanowires for Highly Efficient
Dehydrogenation of Formic Acid and Subsequent Reduction of Nitrate and Nitrite in
Water
1
,2
2
1,2
2
1
1
1
Hu Liu , Xinyang Liu , Yongsheng Yu * Weiwei Yang *, Ji Li , Ming Feng and Haibo Li
The bifunctional catalytic networked Ag/AgPd core/shell nanowires (CSꢀNWs) with tunable shell
thickness exhibit the highest activity for dehydrogenation catalysis of FA and the high selectivity for
ꢀ
ꢀ
catalyzing NO and NO in water to N at room temperature.
3
2
2
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