Low temperature decomposition of hydrous hydrazine over FeNi/Cu nanoparticles

Article abstract of DOI:10.1016/j.apcata.2014.02.012

A simple, surfactant-free liquid-phase reduction of Cu, Ni and Fe salts (e.g. nitrates, chlorides) was used to prepare nanostructured FeNi/Cu catalysts for hydrous hydrazine (N₂H₄·H₂O) decomposition. The synthesis of nanomaterials includes reduction of copper salt using N₂H₄, followed by rapid reduction of iron and nickel salts by NaBH₄. The catalysts were characterized by XRD, BET, TEM, XPS, XANES/EXAFS techniques and their activity and selectivity was studied during hydrous hydrazine decomposition at temperatures ranging from 300 to 345 K. The selectivity to hydrogen increases to ～100% with increasing temperature up to ～345 K. The catalytic performance of these materials depends on the structure of NiFe layer formed over a Cu core, which may be controlled by changing of NiFe/Cu mass ratio. Investigation of the catalytic performance for bi- and tri-metallic materials show that main active metal is nickel but a NiFe alloy could be responsible for the increased selectivity. Alloying of nickel with iron coupled with a favorable dispersion on copper nanoparticles remarkably enhances the catalytic conversion and selectivity of hydrogen evolution.

Full text of DOI:10.1016/j.apcata.2014.02.012

Applied Catalysis A: General 476 (2014) 47–53
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Low temperature decomposition of hydrous hydrazine over
FeNi/Cu nanoparticles
a
a
b
c
Khachatur V. Manukyan , Allison Cross , Sergei Rouvimov , Jeffrey Miller ,
a
a,∗
Alexander S. Mukasyan , Eduardo E. Wolf
a
Department of Chemical & Biomolecular Engineering, University of Notre Dame, Notre Dame, IN 46556, United States
Department of Electrical Engineering, University of Notre Dame, Notre Dame, IN 46556, United States
Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, IL 60429, United States
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
A simple, surfactant-free liquid-phase reduction of Cu, Ni and Fe salts (e.g. nitrates, chlorides) was used to
prepare nanostructured FeNi/Cu catalysts for hydrous hydrazine (N2H4·H2O) decomposition. The synthe-
sis of nanomaterials includes reduction of copper salt using N2H4, followed by rapid reduction of iron and
nickel salts by NaBH4. The catalysts were characterized by XRD, BET, TEM, XPS, XANES/EXAFS techniques
and their activity and selectivity was studied during hydrous hydrazine decomposition at temperatures
ranging from 300 to 345 K. The selectivity to hydrogen increases to ∼100% with increasing temperature
up to ∼345 K. The catalytic performance of these materials depends on the structure of NiFe layer formed
over a Cu core, which may be controlled by changing of NiFe/Cu mass ratio. Investigation of the catalytic
performance for bi- and tri-metallic materials show that main active metal is nickel but a NiFe alloy could
be responsible for the increased selectivity. Alloying of nickel with iron coupled with a favorable disper-
sion on copper nanoparticles remarkably enhances the catalytic conversion and selectivity of hydrogen
evolution.
Received 31 October 2013
Received in revised form 4 February 2014
Accepted 7 February 2014
Available online 17 February 2014
Keywords:
Hydrous hydrazine
Catalytic decomposition
Hydrogen storage
NiFe/Cu nanoparticles
©
2014 Elsevier B.V. All rights reserved.
1
. Introduction
The decomposition pathway depends on the catalyst used and reac-
tion conditions (e.g. temperature) [4–9]. SiO -supported Ni, Pd, and
2
Development of hydrogen storage materials remains one of
Pt catalysts are active even at room temperature [1]. The hydrogen
selectivity increases with the reaction temperature in the range
of 310–390 K, and then quickly decreases as the reaction temper-
ature is further increased. It is suggested that the two competing
reactions (1) and (2) are occurring during hydrazine decomposition
over these supported catalysts. At higher temperatures (>670 K),
the difficult challenges on the way to a hydrogen energy based
technologies. The safe transportation of hydrogen, limitations on
volumetric and gravimetric hydrogen storage capacities, handling
conditions and recycling of byproducts are major technological bar-
riers preventing the widespread application of hydrogen in energy
technologies.
the hydrogen selectivity is ∼100% due to the decomposition of NH .
3
Hydrazine (N H ), a liquid at room temperature, has a hydrogen
The explosive nature of anhydrous hydrazine upon exposure to
metal catalyst surfaces, however, limits its application for hydrogen
generation.
2
4
content of 12.5 wt.%. Studies have shown that hydrazine can be
decomposed on supported metals [1], metal nitrides [2,3] or metal
carbides [4,5] in two ways: complete decomposition:
Hydrous hydrazine, on the other hand, such as hydrazine mono-
hydrate, N H ·H O, still contains a large amount of hydrogen,
2
4
2
N H → N + 2H
(1)
8.0 wt.%, which is available for hydrogen generation and is much
safer, although efforts need to be made to minimize its toxicity.
The distinct advantages of using hydrous hydrazine are: gener-
ation of only nitrogen as byproduct thus not requiring on-board
collection for recycling, and easy recharging using the current
infrastructure of liquid fuels. The key to exploit effectively the
hydrogen-storage properties of hydrazine is to develop efficient
and selective catalysts for H2 generation from hydrous hydrazine
[10–17].
2
4
2
2
and the incomplete decomposition:
N H → 4NH + N
3
(2)
2
4
3
2
∗ Corresponding author. Tel.: +1 574 631 5897.
E-mail address: ewolf@nd.edu (E.E. Wolf).
http://dx.doi.org/10.1016/j.apcata.2014.02.012
926-860X/© 2014 Elsevier B.V. All rights reserved.
0

4
8
K.V. Manukyan et al. / Applied Catalysis A: General 476 (2014) 47–53
Among the various unsupported monometallic nano-catalyst,
were adjusted to produce equimolar quantities of metals after full
reduction, as we found early that catalysts with such composition
may provide the highest selectivity of hydrazine decomposition
toward hydrogen [15]. Synthesis of iron and nickel particles by
NaBH4 reduction was performed under continuous nitrogen flow
(rate ∼50 ml/min) for about 2 h.
Rh is found to be the most selective (45%) for hydrogen release
from hydrous hydrazine decomposition at room temperature [12].
Other metals, such as Co, Ru and Ir, exhibited only 7% selectivity for
hydrogen, and Fe, Cu, Ni, Pt and Pd are inactive at room temperature
[
11]. Bimetallic Ni alloyed with noble metals such as NiRh, NiPt,
and NiIr catalysts show enhanced activity and hydrogen selectivity
at room temperature. The H2 selectivity is found to be strongly
dependent on the ratio of metals. For example, 100% H2 selectivity
at 298 K is reached when Ni/Rh mass ratio was 0.25 [18].
Graphene-supported NiRh catalyst has been also successfully
prepared and tested for hydrous hydrazine decomposition via a
facile co-reduction reaction [16]. Graphene plays a key role as a
dispersion agent and distinct support for the Rh-Ni nanoparticles.
The RhNi-graphene catalyst exhibits 100% H2 selectivity at room
temperature. Thus, noble metal containing nano-catalysts show
high catalytic activity and 100% selectivity for hydrous hydrazine
decomposition at room temperature.
In catalytic experiments, the total volume of metallic suspen-
sion was reduced to ∼1 ml and hydrous hydrazine (Alfa Aesar, 98%)
directly added to the suspension. The catalytic performance of the
nanomaterials was evaluated on the basis of the volumetrically
measured amount of gases released during the reaction. In these
experiments, the gases evolved during the reaction passed thought
a trap containing 1 M solution of hydrochloric acid to capture the
ammonia evolved. Thus, the volume of gas measured equals the
sum of nitrogen and hydrogen evolved during hydrous hydrazine
decomposition. The compositions of gases were also analyzed by an
online gas-chromatograph (Varian 290) using a HAYESEP D column
with Ar carrier gas.
Recently, emphasis has been placed on the development of
suitable reaction conditions for hydrous hydrazine decomposition
to hydrogen by using low-cost catalysts [15,17,19]. For example,
NiFe bimetallic nanoparticles have been studied as catalysts for
this reaction [13–15]. Bimetallic NiFe nanocatalysts are prepared
using a surfactant-aided (hexadecyltrimethylammonium bromide)
co-reduction process of metal salts in an aqueous solution. These
nanoparticles are active at 345 K, and addition of sodium hydrox-
ide is necessary for high H2 selectivity. A noble metal-free Raney
Ni catalyst has also shown high selectivity toward H2 for hydrous
hydrazine decomposition in a basic solution at temperatures of
The X-ray diffraction (XRD) patterns were obtained in a D8
Advance powder diffractometer (Bruker), using CuK␣ mono-
−
1
chromatized radiation (ꢀ = 0.1541 nm) at a scan speed of 10 min
.
The scanning angle (2ꢁ) range was varied from 20 to 80, operated
at 40 kV and 40 mA.
A Titan 80-300 (FEI, USA) transmission electron microscope with
resolution of 0.136 nm in STEM mode and about 0.1 nm informa-
tion limit in high resolution TEM mode was also used. The TEM is
equipped with energy dispersive X-ray spectroscopy (EDS, Oxford
Inca) system with a spectral energy resolution of 130 keV.
BET specific surface area determinations were made using N2
gas adsorption/desorption (∼77 K) using an ASAP 2020 apparatus
(Micromeritics). Before absorption analysis, the samples are dried
at room temperature and then vacuum degassed at 373 K for 6 h.
X-Ray photoelectron spectroscopy (XPS) measurements were
carried out in a PHI VersaProbe II spectrometer with an Al K␣
3
10–350 K [19]. A supported nickel catalyst has also been proposed
for selective decomposition of hydrous hydrazine [17]. In this case
Ni-Al hydrotalcite is co-precipitated from a solution of nickel and
aluminum salts, which annealed in hydrogen at 670 K results in
the formation of nickel nanoparticles on the surface of the sup-
◦
port. Although this catalyst exhibits ∼100% conversion and ∼90% H
X-ray source operating at 1486.6 eV and a 90 take-off angle for
2
selectivity, high reduction temperature during preparation hinder
its application for the decomposition of hydrous hydrazine.
near surface analysis of O 1s, Cu 2p , Fe 2p , and Ni 2p electronic
3 3 3
transitions. Catalyst powders were adhered to brass mounts using
a double-sided carbon tape, and loaded into the analysis cham-
ber. Samples were left to outgas overnight in the vacuum system
The above references indicate that Ni-based catalysts have
high potential for selective decomposition of hydrous hydrazine
toward hydrogen and nitrogen at low temperatures. We investi-
gated the possibility of preparing supported NiFe catalysts using
a surfactant-free low temperature synthesis process. As support
material, copper nanoparticles are selected, as a recent investiga-
tion [20] shows that copper may be an efficient “support” for nickel
in the water gas shift reaction. In this work we show that copper
helps to obtain NiFe nano-size domains during liquid phase reduc-
tion process. The NiFe/Cu catalysts show high activity, stability and
−
7
maintained at a pressure less than ∼10 Pa. Binding energy val-
ues were referenced to the C 1 s peak (284.8 eV) that resulted from
the adventitious contamination layer. The spectra were analyzed
using the Casa XPS software package with relative sensitivity fac-
tors obtained from the Kratos library.
XANES measurements of the hydrogen reduced catalysts (at
573 K for 2 h) were made using X-ray absorption spectroscopy
at the Advanced Photon Source at Argonne National Laboratory.
The measurements were obtained in transmission mode with
ionization chambers optimized for the maximum current with lin-
ear response (∼1010 photons detected/s). A cryogenically cooled
double-crystal Si (1 1 1) monochromator with resolution (ꢂE) bet-
ter than 2.5 eV at 8.979 keV (Cu K edge) was used in conjunction
with a Rh-coated mirror to minimize the presence of harmonics.
The integration time per data point was 1–3 s, and three scans
were obtained for each condition. Oxidation states were inferred
from XANES data obtained for reference metal oxides and pure
metals.
∼100% hydrogen selectivity at 330–340 K.
2
. Experimental
The catalysts were prepared in two stages. In the first stage,
copper nanoparticles were produced by solution reduction using
copper nitrate hydrate as precursor. 0.4 g of Cu(NO ) ·2.5H O was
3
2
2
dissolved in pure ethyl alcohol (20 ml), then a solution contain-
ing 1 M sodium hydroxide (3 ml) and hydrous hydrazine (0.15 ml)
is added drop-wise to the copper nitrate solution under vigorous
stirring conditions at temperatures of 300 to 350 K for 2 h.
In the second stage, the copper nanoparticles produced were
washed several times in deionized water without air exposure and
transferred into a three-necked flask. Then, 2 ml of a solution con-
taining iron (FeCl ·4H O) and/or nickel (Ni(NO ) ·6H O) salts were
3. Results and discussion
3.1. Synthesis and characterization of catalysts
2
2
3
2
2
added to the suspension of copper nanoparticles under vigorous
stirring, followed by rapid addition of 2 ml of sodium borohydride
The synthesis procedure of NiFe/Cu catalysts involves two
stages: copper nanoparticles preparation by hydrazine reduction
of copper nitrate and subsequent precipitation of nickel and iron
(
NaBH ) solution (1 M). The concentrations of iron and nickel salts
4

K.V. Manukyan et al. / Applied Catalysis A: General 476 (2014) 47–53
49
Fig. 1. XRD patterns of copper nano-powders prepared at 300 K (a) and 350 K (b) by
hydrazine reduction of copper nitrate hydrate (reaction time is 0.5 h).
Fig. 2. The XPS spectrum of dried copper powder.
optimized conditions of 0.5 h results in 30–50 nm sized copper
nanoparticles, which were employed as support for preparation of
NiFe catalyst in the next stage.
A typical TEM image of NiFe/Cu catalysts (mass ratio of 1) is
shown in Fig. 4. It can be seen that copper particles are covered
by a layer of NiFe with thickness of 5–20 nm. The selected area
diffraction (SAD) pattern (insert in Fig. 4) shows two different types
ofdiffractionspots:intensespotsforcopperparticlesandweakdots
corresponding to nano-crystalline Ni and Fe.
High resolution TEM and EDS analyses were used to further
characterize the microstructure of the NiFe layer. The results of
those analyses suggest that the microstructure of this layer may
be controlled by changing x = NiFe/Cu ratio (Fig. 5). Fig. 5a shows
that NiFe layer at x = 1.5 contains relatively large individual Fe and
Ni particles with sizes of 10–20 nm. The EDS analysis shows that
in between metal particles NiFe alloy is formed (Fig. 5d and 5e).
The HRTEM image for the sample with x = 1 indicates that the dis-
tribution of Fe and Ni is more uniform (Fig. 5b and 5f). Although
the NiFe layer in the catalyst with x = 0.5 is more uniform as com-
pared to x = 1.5, some individual Ni and Fe nanoparticles with sizes
∼8–10 nm may be seen in the matrix of NiFe alloy (Fig. 5c). The
local EDS analysis shows that all materials contain some amount
of oxygen, due to the air oxidation during sample transfer into the
TEM.
using reduction of the corresponding metals salts by sodium
borohydride. The characteristics of copper nanoparticles produced
in the first stage strongly depend on reduction temperature.
For example, reduction of copper at ∼300 K for two hours is
not complete, as a broad Cu O diffraction peak appears in the
2
XRD pattern (Fig. 1a). Higher reduction temperature (e.g. 350 K)
results in complete reduction (Fig. 1b). The XPS spectrum (Fig. 2)
of dried copper powder produced at 350 K with 0.5 h reaction
time shows some oxygen present (∼10%). Most likely copper is
oxidized during drying and transfer into the XPS analysis chamber
yielding a thin and/or amorphous oxide layer, not detected by
XRD.
We also studied the effect of reaction time on the microstructure
of copper nanopowders produced by hydrazine reduction. Fig. 3
shows TEM micrographs of Cu nanoparticles synthesized at 350 K
with reaction times of 0.5 and 2 h, respectively. It can be seen that at
shorter reaction time (0.5 h) the size of copper particles are ranging
from 30 to 50 nm. A longer reaction time (2 h) results in significant
growth of the primary copper particles into large aggregates with
sizes of several micrometers. The BET surface area measurements
of copper powders produced at 0.5 and 2 h of reaction time are
2
∼
25 and 10 m /g, respectively, consistent with the microstructures
shown in Fig. 3. Thus, hydrazine reduction of copper nitrate within
Fig. 3. TEM images of copper nano-powders prepared at 0.5 h (a) and 2 h (b) reaction times by hydrazine reduction of copper nitride hydride (reaction temperature is 350 K).

5
0
K.V. Manukyan et al. / Applied Catalysis A: General 476 (2014) 47–53
Ni/Fe intensity ratios indicate that the near surface composition of
the NiFe layer is 45% Fe and 55% Ni. It should be noted that BET
surface areas of NiFe/Cu catalysts with different NiFe/Cu ratios do
2
not vary too much (40–45 m /g).
X-ray adsorption spectroscopy (XAS) analysis of the dried cata-
lyst powders for the sample reduced in situ in hydrogen gas at 573 K
for 2 h was carried out. The results suggest that room temperature
drying in air significantly oxidizes the Ni and Fe catalyst compo-
nents. The Cu K-edge XANES, starting at 8.94 keV and reaching a
maximum at 9.01 keV for the dried powder, is presented in Fig. 7a.
Good agreement of the K-edge with a metallic copper standard
shows that drying does not oxidize the copper nanoparticles. This
may be due to the size of copper particles (above 10 nm) which are
covered by a NiFe layer that protect them from oxidation.
Analysis of the Ni K XANES edge suggests that air drying causes
some oxidation of nickel. Based on a linear interpolation of the
maximum edge height of the metal and oxide one can estimate a
composition of 0.7Ni (0) and 0.3Ni (II) (Fig. 7b). It is interesting that
even after hydrogen reduction some part of nickel is still oxidized,
as the estimated composition from Ni K-edge using the Fourier
transform of the EXAFS signal (Fig. 7c) is 0.85Ni(0) and 0.15Ni(II).
The spectrum for Fe is similar to the standard Fe O3 which sug-
2
gests that drying the catalyst result in almost full oxidation of iron.
The Fe K-edge Fourier transform of the EXAFS (Fig. 7d) indicate
that hydrogen reduction at 573 K is not able to reduce oxidized
iron.
Fig. 4. The results of TEM analysis for NiFe/Cu material with x = 1 ratio.
The XPS analysis (Fig. 6a) for the sample with x = 1 shows that the
ratio intensities of copper peak (932.5 eV) significantly decreased
as compared with pure Cu (Fig. 2) before deposition of NiFe layer.
This means that most of the copper particles become covered by
a NiFe layer during the second stage reduction of nickel and iron
3.2. Catalytic activity-selectivity
The catalytic activity of pure metals and Ni/Cu and Fe/Cu mate-
rials were studied for hydrous hydrazine decomposition at 343 K
salts by NaBH . XPS analysis also suggest that the surface of nickel is
4
partly oxidized (Fig. 6b). The surface of iron is fully oxidized, as the
iron peak (709 eV) corresponding to Fe O was found (Fig. 5c). XPS
(Fig. 8). The molar ratio between N H4 and metals is kept at 5:1.
The results show that the gas evolution rates (slope of the plot) for
2
2
3
Fig. 5. The results of HRTEM (a–c) and EDS (d–f) analyses for NiFe/Cu materials: x = 1.5 (a, d and e), x = 1 (b and f) and x = 0.5 (c).

K.V. Manukyan et al. / Applied Catalysis A: General 476 (2014) 47–53
51
The results of catalytic experiments for bimetallic Fe/Cu, Ni/Cu
and NiFe materials (with ∼50 wt.% of each constituents) are
also shown in Fig. 8. Hydrogen selectivity for Fe/Cu material is
closer to the individual iron and copper ((N + H )/N H = 0.2).
2
2
2
4
Hydrogen selectivity for Ni/Cu, however, is remarkably higher
(N + H )/N H ratio is ∼2.2) compared to monometallic cata-
(
2
2
2
4
lysts. The NiFe bimetallic catalysts also show significant catalytic
activity-selectivity as the n ratio is even higher (∼2.5). Fig. 8 indi-
cates that Ni, Ni/Cu and bimetallic unsupported NiFe catalysts
show similar gas evolution rates. Comparison of catalytic activ-
ity of monometallic and bimetallic materials indicates that both
copper and iron remarkably enhance the selectivity of hydrogen
evolution of Ni. Enhancement of catalytic activity of Ni throught
adding iron is primarily related to formation of a FeNi alloy
(see Fig. 5). On the other hand copper also enhances the hydro-
gen selectivity. High resolution scanning TEM analysis indicates
that copper nanoparticles helps to produce a thin (2–3 nm) uni-
form Ni layer (Fig. 9) on the surface, thus increasing activity
toward hydrogen. Therefore, the engineered NiFe/Cu tri-metallic
catalysts have enhanced catalytic activity toward hydrogen evolu-
tion.
The activity of NiFe/Cu catalysts with different NiFe:Cu mass
ratios (or x) was studied for hydrous hydrazine decomposition at
3
43 K. The mass ratio between Ni and Fe is kept as 50%:50%. The x
ratio has significant influence on the activity of NiFe/Cu catalysts
Fig. 10). Catalysts with x = 1.5 ratio (Ni content is 30 wt.%) exhibits
(
the lowest activity with the slowest gas evolution rate (slope of the
plot), and after 50 min no gas release is observed. The final n ratio,
is about 2.3.
When x = 1 (Ni content is 25 wt.%), a maximum value of 3 for
the n ratio is observed, which indicates that selectivity of hydrous
hydrazine decomposition toward hydrogen (and nitrogen) is 100%.
The decomposition rate in this catalyst is very high and it takes
∼
17 min to decompose all hydrous hydrazine. Note that the cat-
alytic activity of these nanoparticles is reproducible even after
repeating 15 similar experiments. The selectivity toward hydro-
gen decreases slightly (n = 2.8) for the catalyst with the x ratio of
0
.5 (Ni content is ∼17 wt.%).
These results show that alloying of nickel with iron has a critical
role in the selective decomposition of hydrous hydrazine. The cat-
alyst with the most uniform NiFe alloy layer on copper (x = 1, see
Fig. 5b and 5f) has high catalytic activity and ∼100% selectivity to
hydrogen. The selectivity decreases significantly when segregated
Ni and Fe particles are produced on copper (x = 1.5, Fig. 5a). The cat-
alytic performance of the catalyst with x = 0.5 (Fig. 4c), where some
individual Ni and Fe particles form with NiFe alloys on copper, is
in between catalytic performance of materials with x = 1 and x = 1.5
ratios.
To determine the effect of the hydrazine/catalyst ratio on the
catalytic activity of nano-materials, the molar ratio between N H4
2
and NiFe is changed from 5:1 to 15:1. The results show that gas
evolution rate is essentially the same compared to the 5:1 ratio.
The selectivity to hydrogen also is ∼100%.
We also studied the effect of temperature on the catalytic
activity of NiFe/Cu catalysts with x = 1 ratio and with the
hydrazine/catalyst ratio equal to 5:1. The results, summarized in
Fig. 11a, show that the selectivity to hydrogen decreases signifi-
cantly as the reaction temperature decreases with no significant
activity detected below 310 K. To calculate the activation energy,
the data in Fig. 8a are plotted in an Arrhenius plot of ln(k)
vs −1/T, where k is the slope of the gas evolution-time plot
(Fig. 11b). The results show a good linear approximation from
which an activation energy of 44 ± 3 kJ/mol is obtained. The cal-
culated activation energy is in good agreement with previously
reported [21] activation energies of hydrazine gas adsorption
on iron (45.95 ± 1.5 kJ/mol) and nickel (40.84 ± 1.2 kJ/mol). The
Fig. 6. The results of XPS analysis for NiFe/Cu powder (x = 1): copper (a), nickel (b)
and iron (c).
pure iron and copper catalysts are very low, and no gas release
are observed after 45 and 70 min, respectively. The final molar
n = (N + H )/N H ratio, where the number of moles are calcu-
2
2
2
4
lated from volumetric measurement is about ∼0.15 for both metals.
Pure Ni shows remarkably higher catalytic activity and selectivity
toward hydrogen, as the n ratio is ∼1.45 (Fig. 8).

5
2
K.V. Manukyan et al. / Applied Catalysis A: General 476 (2014) 47–53
Fig. 7. The results of XAS for NiFe/Cu material with x = 1: K-edge XANES of Cu (a) and Ni (b) and Fourier transform of the EXAFS for Ni K-edge of Ni (c) and Fe (d).
activation energy (24.36 ± 0.8 kJ/mol) of hydrazine adsorption on
pure copper is significantly lower compared to Ni and Fe [21]. How-
ever, the nature of hydrazine adsorption on the three metals is
different. Dissociative chemisorption of hydrazine occurs on Fe and
The application of three metals in one catalyst shows a synergetic
effect, e.g. gas evolution rates reaches a maximum and selectiv-
ity to hydrogen is ∼100% far superior than the mono-metallic
catalysts.
Ni films even at 243 K with liberation of NH , N and H gases, while
3
2
2
adsorption on a Cu film is molecular and reversible. These results
suggest that in the tri-metallic nano-catalyst the rate-limiting fac-
tor may be the dissociative-adsorption on the surface of a NiFe alloy.
Fig. 8. Time-course plots for the decomposition of hydrous hydrazine in the pres-
ence of different catalysts at 343 K.
Fig. 9. Scanning TEM image of Ni/Cu nanoparticles.

K.V. Manukyan et al. / Applied Catalysis A: General 476 (2014) 47–53
53
4. Summary and conclusions
In summary, we report a trimetallic catalyst containing Ni/Fe
supported on Cu that is active and selective for the production
of H2 from hydrous hydrazine at T = 343 K. The results indicate
that liquid-phase reduced Cu nano-particles may become effec-
tive seeds for nucleation of a bimetallic NiFe nanostructured layer
in a surfactant-free co-reduction of Ni and Fe salts by NaBH . The
4
copper core is not selective for hydrogen decomposition reaction,
while NiFe/Cu becomes highly active and selective for the pathway
to H2 production at temperatures 315–343 K. The catalytic perfor-
mance of these materials depends on the structure of the NiFe layer,
which may be controlled by changing the NiFe/Cu ratio. The cat-
alytic activity-selectivity of mono-, bi- and tri-metallic catalysts
show that a NiFe alloy could be responsible for selective decom-
position of hydrous hydrazine, with the main active metal being
nickel. Alloying of nickel with iron, coupled with a favorable dis-
persion on copper nanoparticles remarkably enhances the catalytic
conversion and selectivity of hydrogen evolution during hydrous
hydrazine decomposition.
Fig. 10. Gas evolution vs. time plots for the decomposition of hydrous hydrazine to
hydrogen and nitrogen in the presence of NiFe/Cu catalysts at 343 K.
Acknowledgements
Use of the Advanced Photon Source is supported by the U. S.
Department of Energy, Office of Science, Office of Basic Energy
Sciences, under Contract DE-AC02-06CH11357. Support for K.V.
Manukyan from ANL contract 0J 30521 of the Chemical Science
and Engineering Division is gratefully acknowledged. A. Cross was
supported by a grant from the Sustainable Energy Initiative (SEI)
of the Center for Sustainable Energy of Notre Dame CSEND. Par-
tial funding for J.T. Miller was provided as part of the Institute for
Atom-efficient Chemical Transformations (IACT), and Energy Fron-
tier Research Center funded by the US Department of Energy, Office
of Science, Office of Basic Energy Sciences.
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Fig. 11. Time-course plots (a) for the decomposition of hydrous hydrazine different
temperatures and dependence of gas release rate, k, on the T (b).
−
1
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