Easy access to Ni3N- and Ni-carbon nanocomposite catalysts

Article abstract of DOI:10.1002/chem.201400398

In the search for alternative materials to current expensive catalysts, Ni has been addressed as one of the most promising and, on this trail, its corresponding nitride. However, nickel nitride is a thermally unstable compound, and therefore not easy to prepare especially as nanoparticles. In the present work, a sol-gel-based process (the urea glass route) is applied to prepare well-defined and homogeneous Ni₃N and Ni nanoparticles. In both cases, the prepared crystalline nanoparticles (～25 nm) are dispersed in a carbon matrix forming interesting Ni₃N- and Ni-based composites. These nanocomposites were characterised by means of several techniques, such as XRD, HR-TEM, EELS, and the reaction mechanism was investigated by TGA and IR and herein discussed. The catalytic activity of Ni₃N is investigated for the first time, to the best of our knowledge, for hydrogenation reactions involving H₂, and here compared to the one of Ni. Both materials show good catalytic activities but, interestingly, give a different selectivity between different functional groups (namely, nitro, alkene and nitrile groups). A nickel for every time: Homogeneous Ni₃N and Ni nanoparticles embedded in a carbon matrix were prepared by the urea glass route. Their respective catalytic activities over different functional groups are reported for hydrogenation reactions using H₂ (see scheme).

Full text of DOI:10.1002/chem.201400398

DOI: 10.1002/chem.201400398
Full Paper
&
Catalysis
Easy Access to Ni3N– and Ni–Carbon Nanocomposite Catalysts
Guylhaine Clavel,* Valerio Molinari, Alexander Kraupner, and Cristina Giordano[a]
Abstract: In the search for alternative materials to current
expensive catalysts, Ni has been addressed as one of the
most promising and, on this trail, its corresponding nitride.
However, nickel nitride is a thermally unstable compound,
and therefore not easy to prepare especially as nanoparti-
cles. In the present work, a sol–gel-based process (the urea
glass route) is applied to prepare well-defined and homoge-
neous Ni3N and Ni nanoparticles. In both cases, the prepared
crystalline nanoparticles (~25 nm) are dispersed in a carbon
matrix forming interesting Ni3N- and Ni-based composites.
These nanocomposites were characterised by means of sev-
eral techniques, such as XRD, HR-TEM, EELS, and the reaction
mechanism was investigated by TGA and IR and herein dis-
cussed. The catalytic activity of Ni3N is investigated for the
first time, to the best of our knowledge, for hydrogenation
reactions involving H2, and here compared to the one of Ni.
Both materials show good catalytic activities but, interesting-
ly, give a different selectivity between different functional
groups (namely, nitro, alkene and nitrile groups).
halide, amides and fluoroacetylacetonates[4a,7] with ammonia.
This is the main route described in the literature for bulk[5a,6,7b]
and nanoparticles.[4a,5b,7a,c] Ni3N can be also prepared using the
highly reactive azide instead of ammonia, from NiBr2 by a solvo-
thermal[8] synthesis at 2008C or starting with metallic nickel at
high pressure and temperature.[9] Nickel nitride film prepara-
tions have also been reported through sputtering of nickel
films in N2 gas[10] as well as through N+ ion implantation[11] and
chemical vapour deposition using NH3.[12] While the bulk syn-
theses lead to Ni3N with hexagonal structure, Ni2N and Ni4N
stoichiometries have been obtained as films.[10c,13]
Introduction
Bulk metal nitrides are a well-known class of materials mainly
used for engineering purposes. Just recently with the develop-
ment of new synthesis pathways, which allow to access these
materials at the nanoscale and at milder conditions,[1] the inter-
est toward this field has been increasing and the attention has
moved to more fine applications, especially in the field of cat-
alysis. Up to now, most of the catalytic studies have been de-
voted to early transition metal carbides and nitrides, such as
MoC, MoN and WC.[1c,2] These nitrides and carbides are often
used as support catalysts for metallic nanoparticles, such as Co
and Ni,[1c,3] but surprisingly the corresponding nitrides of late
transition metals have been barely studied as compared to
their parental metals. Nickel nitride, for example, has been
mainly investigated as electrode material for lithium batteries[4]
whereas nickel nanoparticles are recognised catalysts. Howev-
er, it is true that up to now few synthesis routes have been re-
ported in the literature for late transition metal nitrides, such
as Fe, Ni, and Cu. These are indeed difficult to synthesise by
usual high-temperature methods as they take up nitrogen to
a small level and form metal-rich nitrides, which are metasta-
ble. Nickel nitride, for example, is stable only up to tempera-
tures of about 4008C and has been reported to begin to de-
compose at 2608C.[5]
The “urea glass route” is a simple, scalable and versatile ap-
proach for synthesising various metal carbides and nitrides[1a,14]
based on the formation of a metal–urea gel followed by its
thermal decomposition under inert atmosphere. In this work,
we adapted this route to synthesise nickel nitride. This synthe-
sis procedure uses the nontoxic and nonaggressive urea as ni-
trogen precursor. Its action is double, its decomposition pro-
vides the nitrogen to form the metallic nitride and, leads to
the development of a carboneous matrix, which directs the
formation of nanoparticles and prevents their aggregation. In
the case of nickel, the resulting material is a Ni3N@carbon
hybrid composite at 3508C and a Ni@C one at higher tempera-
ture. The crystalline nanoparticles of nickel nitride are embed-
ded in a carboneous matrix and have a size of around 25 nm.
The nickel particles, presenting a similar size, are surrounded
by a graphitic shell and do not show surface oxidation upon
storage in air. The catalytic properties of the Ni3N@C composite
for hydrogenation reactions with H2 have been investigated
and compared to those of Ni@C. Their respective activity and
selectivity in hydrogenation reactions of different functional
groups are presented and discussed.
Nickel nitride is usually synthesised by nitration at tempera-
tures between 200 and 4508C of metallic nickel,[4a,5a,b,6] nickel
[a] Dr. G. Clavel, V. Molinari, Dr. A. Kraupner, Dr. C. Giordano
Department of Colloid Chemistry
Max-Planck-Institute of Colloids and Interfaces
Am Mꢀhlenberg 1 OT Golm, 14476 Potsdam (Germany)
E-mail: guylhaine.clavel@mpikg.mpg.de
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201400398.
Chem. Eur. J. 2014, 20, 1 – 7
1
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
a slightly higher temperature, such as 4008C (Figure 3C and
D). This behaviour can result either from the incorporation of
carbon in the lattice of the nitride on the way to the formation
of the carbide or from a deficiency of nitrogen in the structure
due to the early decomposition of the nitride. Indeed, from
the XRD measurements, it is clear that the observed shifts, in
both samples, move toward the carbide and hexagonal nickel
diffraction regions. However, the lattice parameters of the hex-
agonal phase of Ni, Ni3C and Ni3N are too similar, the XRD pat-
terns just differ in a few and very close reflections (see refer-
ence patterns in Figure 3C and D),[15] to unequivocally ascer-
tain the cause of the shift.
Results and Discussion
The decomposition under nitrogen of a viscous starting mix-
ture of nickel acetate and urea readily produces, at low tem-
perature (350 to 4508C), foam-like black to greyish materials
(Figure 1). This foam-like material consists of crystalline nickel
nitride nanoparticles of around 25 nm embedded in a carbon
matrix at 3508C and of metallic nickel ones at 4508C as ascer-
tained by TEM (Figure 2). The specific surface area from N2 ab-
sorption measurements is approximately 20 and 50 m2 gÀ1 for
the nickel nitride and nickel composites, respectively.
At temperatures higher than 4508C cubic metallic nickel is
obtained (Figure 3B), and elemental analysis shows a lower
amount of nitrogen in those samples (Table 1). These nickel
nanoparticles do not exhibit any noticeable oxidation after sev-
eral months of storage under air. Along with the XRD peaks of
metallic cubic nickel, other diffractions are observed at 41.8,
47.6, 62.6 and 83.8 2q (corresponding to d-spacing of 2.16,
1.91, 1.48 and 1.15). These peaks could not be assigned to
a referenced phase of nickel nitride or carbide. This unknown
phase can be observed up to 8008C, and at 5008C its quantity
does not seem to decrease by increasing reaction time but in-
stead seems to be related to the initial amount of urea (Fig-
ure S1 in the Supporting Information). Furthermore, this phase
is also obtained with nickel acetylacetonate instead of nickel
acetate or by using 4,5-dicyanoimidazole instead of urea,
which rule out the possibility that this phase is due to impuri-
ties other that N or C (Figure S1 in the Supporting Informa-
tion). To our knowledge, none of the XRD patterns of substoi-
chiometric phase that could be intermediates in the formation
of nickel from the nitride/carbide (Ni8N or hexagonal Ni4N, for
example)[10a,13b,16] do really fit the features observed here at
high temperature. Interestingly, similar diffraction peaks have
been attributed to pure hexagonal nickel by Bolokang et al.[17]
and can be found in few other reports in which, unfortunately,
the nature of this phase was not discussed.[18] In order to un-
derstand the nature of this side phase, we are conducting fo-
cused investigations.
Figure 1. Photographs showing the precursor solution and the products ob-
tained after heating at 150, 250 and 3508C.
Figure 2. TEM images of nickel nitride nanoparticles synthesised at 3508C
(left) and metallic nickel obtained at 4508C (right).
The composition and structure of the final product are influ-
enced by the temperature but also by the urea-to-nickel ratio
(R=molar ratio of urea/Ni(ac)2). The XRD pattern of materials
prepared with different ratios of precursors and at different
temperatures are shown in Figure 3. At 3508C (Figure 3A), the
XRD peaks of the sample synthesised with a ratio R=4 match
the expected ones for hexagonal nickel nitride. Furthermore,
the broad diffraction peak at 26 (2q) indicates the presence of
carbon and carbonaceous residues. The elemental analysis
gives an amount of residual carbon after synthesis at 3508C of
around 16% (Table 1). Under this condition, traces of cubic
metallic nickel could also be observed by XRD. At the same
temperature, when a higher quantity of urea was used, no
crystalline phase was obtained, even with a longer calcination
time, while with a lower R ratio, the proportion of metallic
nickel increased sharply (Figure 3A). Additionally, for R=3, one
can observe a small shift of the XRD peaks (Figure 3C and D).
This shift is also observed if the synthesis is performed at
The morphology of the products was examined with trans-
mission electron microscopy (TEM). The nitride particles syn-
thesised at 3508C appear rather homogeneous in shape and
size and, are embedded in a carbon matrix (low-contrast
region around the particles; Figure 4A and C). The chemical
composition of the sample and especially the carbon matrix
was investigated by electron energy loss spectroscopy (EELS).
The spectrum recorded from the sole carbon matrix (Figure S3
in the Supporting Information), reveals the presence, beside
carbon, of a significant amount of nitrogen and oxygen in the
same quantity range. The presence of oxygen of the sample
was already expected from the results of elemental analysis
(Table 1). Surprisingly, also L2 and L3 nickel edges are visible in
EELS spectra recorded from this carboneous phase (Figure S3
in the Supporting Information), suggesting that at 3508C the
precursors and intermediates are not fully decomposed. While
the EELS spectrum recorded from a collection of particles
shows the same features as that of carboneous matrix, the
&
&
Chem. Eur. J. 2014, 20, 1 – 7
www.chemeurj.org
2
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
and structure of the carbon in
the immediate surroundings of
the particles is slightly different.
The morphology and size of the
metallic nickel phase synthesised
at 4508C are similar to the ni-
tride ones (Figure 4B and D),
suggesting that the metallic
phase is due to the further de-
composition of the Ni3N. At this
temperature, the carbon appears
as a graphitic shell around the
particles. The presence of
a graphitic shell around transi-
tion metal nitride and carbide
particles was already observed
with the urea route synthesis for
other metals.[1a,14a]
To examine the reaction
mechanism responsible for the
formation of the nitride, ther-
mogravimetry analyses as well
as IR spectra of starting materials
and intermediate products have
been recorded. The IR spectra of
the precursors and their respec-
tive mixture (after ethanol re-
moval) are presented in Figure 5
(see also Table S3 in the Sup-
porting Information). Urea is
a good complexing agent coor-
dinating metal centres through
either the oxygen or the nitro-
Figure 3. A) XRD of materials synthesised at 3508C with different R ratios. B) XRD of products synthesised with
R=4 at different temperatures. C), D) Enlargement of the XRD regions where a shift is observed for the samples
synthesised with R=3 (3508C) and at 4008C (R=4) compared to the one synthesised at 3508C (R=4). Light grey,
dark grey, black and dotted vertical lines represent the reference peaks of hexagonal Ni3C, Ni, Ni3N and, cubic Ni,
respectively.
Table 1. Mass% of CHN from elemental analysis and Ni from ICP-AES.
Samples
N
C
H
Ni
Sum
precursor mix
1508C
2508C
Ni3N 3508C R=3
Ni3N 3508C
3508C R=6
Ni3N 4008C
Ni 4508C
24
21.5
21.5
21.7
7.5
16.5
19.25
10.25
11
5
5
3.5
1.2
2
2
1.2
1
–
–
–
–
40
–
–
82.5
–
–
–
–
–
76
–
–
98.2
–
24.4
20.5
4.4
17.5
23.3
4.1
3.7
3
Ni 5008C
10.6
1
Figure 4. TEM images of nickel nitride nanoparticles synthesised at: A),
C) 3508C, and of nickel particles synthesised at: B), D) 4508C.
spectrum from a single particle exhibits some differences. First,
the oxygen edge is barely visible, which implies that the
oxygen is solely present in the carboneous phase. In addition,
the shape of the carbon edge is different. The reason for this
discrepancy might be either because the carbon edge account
for carbon inside the nickel nitride or more likely, due to the
intensity of the band and its likeness to amorphous carbon
fine structure (rather than carbide), because the composition
gen atoms. Generally, urea coordinates to transition metal
through the C=O.[19] The spectrum of the starting mix (labelled
precursors in the Figure 5) seems to be the superimposition of
the nickel acetate and urea ones. However, a slight change of
the C=O vibration, compared to pure urea, at 1587 cmÀ1 is
clearly visible, confirming the complexation of urea through
the carbonyl. The decomposition of this initial complex, fol-
lowed by TGA under N2, shows three main decomposition
Chem. Eur. J. 2014, 20, 1 – 7
www.chemeurj.org
3
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
2508C, the obtained sample is amorphous (Figure S2 in the
Supporting Information) and the IR measurement indicates the
decomposition toward the formation of cyano-type complexes
as intermediates. It is at this decomposition step that the sam-
ples start to present their foam-like appearance (Figure 1). Be-
tween 305 and 3908C, a third mass loss is observed. In this
range of temperature, the IR reveals the decomposition of the
intermediate cyano-product formed previously. At 3308C, the
obtained material is still amorphous, while at 3508C the nitride
is formed even though the current decomposition step carries
on until 3908C. Consequently, the nickel nitride composite syn-
thesised at 3508C still contains undecomposed products,
which explains the nickel still present in the carboneous matrix
as revealed by EELS. However, at this temperature the nickel
nitride decomposes readily to give metallic nickel. Indeed, TGA
analysis of nickel nitride synthesised at 3508C (Figure 6) sup-
ports the fact that nickel nitride starts to decompose just after
its formation between 350 and 4008C, which is in agreement
with the XRD data recorded at 350, 400 and 4508C that show
the early formation of metallic nickel in these ranges of tem-
perature (Figure 3B).
Figure 5. IR spectra of the different precursors and products formed at vari-
ous temperatures.
The catalysis activities of nitride and metallic nickel compo-
sites (synthesised with a ratio R=4 at 350 and 4508C, respec-
tively) have been studied for hydrogenation reactions by using
a continuous-flow system. Metallic nickel is known to be
a good catalyst and especially for hydrogenation of different
functional groups. It generates much interest as catalyst for
transfer hydrogenation reactions.[21] In contrast, few published
works report the catalytic activity of nickel nitride and none
about its reactivity in hydrogenation using H2. Baiker et al. ob-
served the formation of surface nickel nitride during nickel-cat-
alysed amination of alcohols and disproportionation of amine,
but found that the nitride deactivated the catalyst.[5a,22] Later
on, Egashira et al. examined the use of Ni3N, instead of metallic
nickel that oxidises rapidly, for the reaction between NO and
CO and observed that the catalyst suffers from oxidation in
this condition as for nickel.[6] Ni3N should be stable up to
1508C in H2 atmosphere.[5a,23] A preliminary stability test on our
nickel nitride composite was performed under the same condi-
tions as the catalytic experiments. No strong changes were ob-
served by elemental analysis and XRD after several hours in
the reactor under 25 bar of H2 at 758C (Table S2 and Figure S2
in the Supporting Information). Furthermore, in order to evalu-
ate safely the catalytic properties of the nickel nitride compo-
site, the catalytic tests were performed on the amorphous
sample synthesised at 3308C to ensure that the carbon matrix,
which contains nickel, does not interfere with the hydrogena-
tion reaction. According to these tests, the matrix does not ex-
hibit catalytic activity. The results of the hydrogenation of ni-
trobenzene, cyclohexene, benzonitrile and 4-nitroacetophe-
none by both composites are presented in Table 2. The nickel
nanocomposites exhibit a good catalytic activity at low tem-
perature for the hydrogenation of all functional groups tested,
that is, nitro, alkene and nitrile. A similar catalytic activity is ob-
served in the case of the nitride for the hydrogenation of nitro
groups. On the contrary, the hydrogenation of alkene was not
achieved with this catalyst. Thus, nickel nitride has a different
Figure 6. Thermogravimetry curves of a urea/nickel acetate (R=4) starting
mix (black line, the inset shows an enlargement of the region between 300
and 5008C) and of particles synthesised at 3508C (grey curve).
steps starting at 130, 300, 3808C (Figure 6). XRD and IR analysis
of syntheses quenched at 150, 250 and 3308C give some in-
sights on the decomposition pathway. Below 1308C, the small
mass loss is probably due to the removal of absorbed water
and ethanol. Indeed, the XRD pattern at 1508C (Figure S2 in
the Supporting Information) shows only urea as crystalline
phase while IR measurement displays a rather similar spectrum
to that of the starting mixture but with a broadening of the
bands and appearance of a new band at approximately
2193 cmÀ1. In this region lie the vibrational bands of cyana-
mide, cyanide and cyanato ligands,[20] however, an unambigu-
ous attribution was not possible due to the complexity of our
intermediates. The second step in the TGA curve between 130
and 3058C account for approximately 53% of mass loss. At
&
&
Chem. Eur. J. 2014, 20, 1 – 7
www.chemeurj.org
4
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
nation reactions but offer a differ-
ent selectivity between different
functional groups. Nickel nitride
Table 2. Catalysis results for hydrogenation of nitrobenzene, cyclohexene, benzonitrile and 4-nitroacetophe-
none by the Ni3N– and Ni–carbon nanocomposites.
Reactant[a]
Catalyst Volumetric
flow
Pressure T
Conv.
Products
nanoparticles,
compared
to
[bar]
[8C] [%]
those of nickel, show a compara-
ble activity for hydrogenation of
nitro-compounds but none for
hydrogenation of alkenes. In the
case of nitrile functions, the dif-
ferent reactivity of the catalysts
leads to distinct hydrogenation
pathways, and thus to different
hydrogenated products.
[mLminÀ1
]
Ni
Ni3N
Ni
Ni3N
Ni
Ni
0.5
0.5
0.3
0.3
0.3
0.5
0.5
0.5
25
25
25
25
12
12
12
12
50 >99
75 >99
75 >99
75 >99
25 >99
nitrobenzene
aniline
p-nitroacetophe-
none
4-aminoacetophenone
50
50
90
0
cyclohexene
cyclohexane
Ni3N
Ni3N
75 <10
benzylamine dibenzylimine dibenzylamine
Ni
Ni
Ni
Ni
Ni3N
Ni3N
Ni3N
0.3
0.5
0.5
0.5
0.3
0.3
0.5
25
25
25
25
25
25
25
55
75
0
48
–
–
8
–
–
–
92
–
–
8
92
>99
–
135 >99
150 >99
55 >99
75 >99
135 >99
Experimental Section
benzonitrile
–
>99
69
9
In a typical experiment, nickel(II)
22
88
8
4
acetate
tetrahydrate
(250 mg,
1.0 mmol, Ni(CH3CO2)2·4H2O, Al-
drich, 98%) and urea (240 mg,
4.03 mmol, CO(NH2)2, Aldrich 99%),
giving a molar ratio of urea/Ni(ac)2,
R=4, were dissolved in approxi-
[a] The concentration of reactant in ethanol was 0.05m.
selectivity than nickel regarding the functional group to hydro-
genate. In the case of the hydrogenation of nitrile functions,
the difference in the reaction kinetics between metallic and ni-
tride leads to the formation of different products. At low tem-
perature, the nickel nitride catalyst allows the dibenzylimine to
be obtained, produced by the condensation of the newly
formed benzylamines on the starting nitriles (Scheme 1), while
nickel in the same condition does not catalyse the reaction. By
increasing the temperature, the fast formation of the benzyl-
amine with the nitride catalyst does not any longer allow the
formation of the dibenzylimine, and thus the amine is the
main product obtained. With the nickel catalyst, the formation
of amine was never observed;
mately 1 mL of ethanol. After being stirred for a few hours, a clear
light-green solution was obtained. Subsequent heating at 3508C
for 3 h (heating rate ~58CminÀ1) under N2 led to a shiny-black
foam of Ni3N.
All the catalytic tests were performed using a H-Cube Pro continu-
ous flow system. The reactor columns were filled with approxi-
mately 4.33 mmol of either Ni3N (~630 mg) or Ni (~305 mg). Nitro-
benzene, cyclohexene, benzonitrile and 4-nitroacetophenone were
purchased from Sigma–Aldrich and used as received without fur-
ther purification. The chemical reactants were dissolved in EtOH to
get 100 mL of an approximately 0.05m solution. The reactions
were screened at different temperatures (25–1508C), pressures
(12–25 bar) and volumetric flows (0.3–0.5 mLminÀ1). The products
the reaction leads to the forma-
tion of the dibenzylimine as for
nickel nitride at lower tempera-
ture. Furthermore, at higher
temperature, the nickel compo-
site makes the further hydroge-
nation of the dibenzylimine
Scheme 1. Reaction mechanism of the formation of benzylamine, dibenzylimine, and dibenzylamine from benzo-
nitrile.
toward the dibenzylamine possi-
ble (Scheme 1).
were collected and analysed without further purification using
a GC-MS Agilent Technologies 5975 equipped with a capillary
column (HP-5MS, 30 m, 0.25 mm, 0.25 mm). The temperature pro-
gram started with an isothermal step at 508C for 2 min, the tem-
perature was then increased to 3008C with a rate of 308CminÀ1
and maintained for 1 min. The resulting spectra were analysed
with the MS library NIST MS Search 2.0.
Conclusion
Ni3N– and Ni–carbon composites were prepared at low tem-
perature by a urea route. The crystalline nanoparticles of nickel
nitride embedded in a carboneous matrix have a homogeneous
size, of around 25 nm, and shape. The nickel particles, present-
ing a similar size, are surrounded by a graphitic shell and show
no noticeable oxidation upon exposure to air. The catalytic
properties of Ni3N@carbon for hydrogenation reactions with
H2, never reported to date, were compared to those of Ni@car-
bon. Both materials show good catalytic activities for hydroge-
Characterisation details
X-ray powder diffraction (XRD) measurements were collected on
a D8 Bruker instruments Diffractometer (CuKa radiation, at 40 kV
Chem. Eur. J. 2014, 20, 1 – 7
www.chemeurj.org
5
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
[5] a) A. Baiker, M. Maciejewski, J. Chem. Soc. Faraday Trans. 1 1984, 80,
2331–2341; b) Z. Wang, W. Yu, J. Chen, M. Zhang, W. Li, K. Tao, J. Alloys
Compd. 2008, 466, 352–355; c) A. Fernꢁndez Guillermet, K. Frisk, Int. J.
Thermophys. 1991, 12, 417–431.
[6] Y. Egashira, H. Komiyama, Ind. Eng. Chem. Res. 1990, 29, 1583–1588.
[7] a) N. S. Gajbhiye, R. S. Ningthoujam, J. Weissmꢂller, Phys. Status Solidi A
2002, 189, 691–695; b) A. Leineweber, H. Jacobs, S. Hull, Inorg. Chem.
2001, 40, 5818–5822; c) S. Desmoulins-Krawiec, C. Aymonier, A. Loppi-
net-Serani, F. Weill, S. Gorsse, J. Etourneau, F. Cansell, J. Mater. Chem.
2004, 14, 228–232.
and 50 mA) equipped with a scintillation counter. The different
phases were identified by using the ICDD-PDF4 files [ICDD 04-011-
7280], [ICDD 04-001–9088], [ICDD 04-007-3753], [ICDD 04-008-
0901], [ICDD 01-089-7129] and [ICDD 00-055-0142] for Ni3N, Ni4N,
Ni3C, cubic and hexagonal Ni and, urea, respectively. FTIR spectra
were measured using a Varian FTS1000 spectrometer in the ATR
geometry. To determine the quantity of nickel in the sample,
a Varian Vista-MPX inductively coupled plasma optical emission
spectrometer (ICP-OES) was used (solutions of the samples were
prepared by calcination on air at 5008C and dissolved in HCl).
Transmission electron microscopy (TEM) was performed on a Zeiss
EM 912 W microscope operated at an acceleration voltage of
120 kV, and high resolution TEM and EELS measurements were re-
corded on a CM200FEG (Philips) microscope, operated at 200 kV
and equipped with a field-emission gun and a postcolumn EELS
spectrometer (GATAN Tridiem). Samples were prepared by deposit-
ing a drop of a dispersion of particles in ethanol on a copper grid
coated with an amorphous carbon film. Elemental analysis was per-
formed for nitrogen, carbon and hydrogen using a Vario EL Ele-
mentar. Nitrogen sorption isotherms were recorded, after degass-
ing at 1508C for about 20 h, with a Quantachrome porosimeter at
liquid nitrogen temperature. Thermogravimetric analyses were per-
formed under argon on a Netzsch STA 449C Jupiter instrument at
[8] J. Choi, E. G. Gillan, Inorg. Chem. 2009, 48, 4470–4477.
[9] C. Guillaume, J. P. Morniroli, D. J. Frost, G. Serghiou, J. Phys. Condens.
Matter 2006, 18, 8651–8660.
[10] a) G. J. W. R. Dorman, M. Sikkens, Thin Solid Films 1983, 105, 251–258;
b) M. Kawamura, Y. Abe, K. Sasaki, Vacuum 2000, 59, 721–726; c) A. I.
Linnik, A. M. Prudnikov, R. V. Shalaev, T. A. Linnik, V. N. Varyukhin, S. A.
Kostyrya, V. V. Burkhovetskii, Tech. Phys. Lett. 2013, 39, 143–146.
[11] H. Savaloni, M. Habibi, Appl. Surf. Sci. 2011, 258, 103–112.
[12] a) Z. Li, R. G. Gordon, V. Pallem, H. Li, D. V. Shenai, Chem. Mater. 2010,
22, 3060–3066; b) E. Lindahl, M. Ottosson, J.-O. Carlsson, Chem. Vap.
Deposition 2012, 18, 10–16.
[13] a) N. Terao, A. Berghezan, J. Phys. Soc. Jpn. 1959, 14, 139–148; b) P. N.
Terao, J. Phys. Soc. Jpn. 1960, 15, 227–230.
[14] a) C. Giordano, C. Erpen, W. Yao, B. Milke, M. Antonietti, Chem. Mater.
2009, 21, 5136–5144; b) Y. Qiu, L. Gao, J. Am. Ceram. Soc. 2004, 87,
352–357.
a heating rate of 5 KminÀ1
.
[15] a) L. He, J. Magn. Magn. Mater. 2010, 322, 1991–1993; b) K. Jack, Acta
Crystallogr. 1950, 3, 392–394.
[16] a) I. M. Neklyudov, A. N. Morozov, Physica B+C 2004, 350, 325–337;
b) Z. L. Schaefer, K. M. Weeber, R. Misra, P. Schiffer, R. E. Schaak, Chem.
Mater. 2011, 23, 2475–2480; c) C. M. Fang, M. H. F. Sluiter, M. A. van
Huis, H. W. Zandbergen, Phys. Rev. B 2012, 86, 134114–134117.
[17] A. S. Bolokang, M. J. Phasha, Mater. Lett. 2011, 65, 59–60.
[18] a) M. Richard-Plouet, M. Guillot, S. Vilminot, C. Leuvrey, C. Estournꢃs, M.
Kurmoo, Chem. Mater. 2007, 19, 865–871; b) M. Z. Figueroa-Torres, L. De
La torre Sꢁenz, C. Domꢄnguez Rꢄos, R. Torres-Sꢁnchez, A. Aguilar-Elguꢅ-
zabal, Top. Catal. 2011, 54, 568–571; c) S. Uhlig, R. Struis, H. Schmid-
Engel, J. Bock, A.-C. Probst, O. Freitag-Weber, I. Zizak, R. Chernikov, G.
Schultes, Diam. Relat. Mater. 2013, 34, 25–35.
Acknowledgements
S. Metzke, I. Shekova and K. Otte are acknowledged for experi-
mental assistance. The authors also thank the Fritz-Haber-Insti-
tute for instrumental help and the Max-Planck Society for fund-
ing.
Keywords: catalysts
nickel · nickel nitride
· hydrogenation · nanocomposites ·
[19] T. Theophanides, P. D. Harvey, Coord. Chem. Rev. 1987, 76, 237–264.
ˇ
ˇ
ˇ
ˇ
[20] a) Z. Smꢅkal, F. Brezina, Z. Sindelꢁr, R. Klicka, M. Nꢁdvornꢄk, Chem. Pap.
1997, 51, 95–98; b) S. Pagano, G. Montana, C. Wickleder, W. Schnick,
Chem. Eur. J. 2009, 15, 6186–6193.
[1] a) C. Giordano, M. Antonietti, Nano Today 2011, 6, 366–380; b) B. Ma-
zumder, A. L. Hector, J. Mater. Chem. 2009, 19, 4673–4686; c) A.-M.
Alexander, J. S. J. Hargreaves, Chem. Soc. Rev. 2010, 39, 4388–4401.
[2] a) S. T. Oyama, Catal. Today 1992, 15, 179–200; b) W. Yao, P. Makowski,
C. Giordano, F. Goettmann, Chem. Eur. J. 2009, 15, 11999–12004.
[3] a) J. A. Rodriguez, J. Evans, L. Feria, A. B. Vidal, P. Liu, K. Nakamura, F.
Illas, J. Catal. 2013, 307, 162–169; b) W. Yuhong, L. Wei, Z. Minghui, G.
Naijia, T. Keyi, Appl. Catal. A 2001, 215, 39–45; c) W.-F. Chen, K. Sasaki,
C. Ma, A. I. Frenkel, N. Marinkovic, J. T. Muckerman, Y. Zhu, R. R. Adzic,
Angew. Chem. 2012, 124, 6235–6239; Angew. Chem. Int. Ed. 2012, 51,
6131–6135.
[21] a) F. Alonso, P. Riente, M. Yus, Acc. Chem. Res. 2011, 44, 379–391; b) V.
Polshettiwar, B. Baruwati, R. S. Varma, Green Chem. 2009, 11, 127–131.
[22] A. Baiker, J. Kijenski, Catal. Rev. 1985, 27, 653–697.
[23] A. M. Alexander, J. S. J. Hargreaves, C. Mitchell, Top. Catal. 2012, 55,
1046–1053.
[4] a) F. Gillot, J. Oro-Sole, M. R. Palacin, J. Mater. Chem. 2011, 21, 9997–
10002; b) Y. Wang, Z.-W. Fu, X.-L. Yue, Q.-Z. Qin, J. Electrochem. Soc.
2004, 151, E162–E167.
Received: January 30, 2014
Published online on && &&, 0000
&
&
Chem. Eur. J. 2014, 20, 1 – 7
www.chemeurj.org
6
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
FULL PAPER
A nickel for every time: Homogeneous
Ni3N and Ni nanoparticles embedded in
a carbon matrix were prepared by the
urea glass route. Their respective cata-
lytic activities over different functional
groups are reported for hydrogenation
reactions using H2 (see scheme).
&
Catalysis
G. Clavel,* V. Molinari, A. Kraupner,
C. Giordano
&& – &&
Easy Access to Ni3N– and Ni–Carbon
Nanocomposite Catalysts
Chem. Eur. J. 2014, 20, 1 – 7
www.chemeurj.org
7
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ