Synthesis of Nickel Nanoparticles with N-Doped Graphene Shells for Catalytic Reduction Reactions

Article abstract of DOI:10.1002/cctc.201500848

The synthesis of novel nanoparticles is of general importance for the development of efficient heterogeneous catalysts. Herein, the preparation of carbon-supported nickel-based nanoparticles (NPs), modified by nitrogen-doped graphene layers, is reported for the first time. The resulting materials were characterized in detail by TEM, X-ray photoelectron spectroscopy (XPS), XRD, elemental analysis (EA), electron paramagnetic resonance (EPR), temperature-programmed reduction (TPR), BET, and Raman analysis. Initial catalytic tests revealed the potential of this class of compounds in hydrogenation reactions.

Full text of DOI:10.1002/cctc.201500848

DOI: 10.1002/cctc.201500848
Communications
Synthesis of Nickel Nanoparticles with N-Doped Graphene
Shells for Catalytic Reduction Reactions
Sabine Pisiewicz,[a] Dario Formenti,[a, b] Annette-Enrica Surkus,[a] Marga-Martina Pohl,[a]
Jçrg Radnik,[a] Kathrin Junge,[a] Christoph Topf,[a] Stephan Bachmann,[c]
Michelangelo Scalone,[c] and Matthias Beller*[a]
The synthesis of novel nanoparticles is of general importance
for the development of efficient heterogeneous catalysts.
Herein, the preparation of carbon-supported nickel-based
nanoparticles (NPs), modified by nitrogen-doped graphene
layers, is reported for the first time. The resulting materials
were characterized in detail by TEM, X-ray photoelectron spec-
troscopy (XPS), XRD, elemental analysis (EA), electron paramag-
netic resonance (EPR), temperature-programmed reduction
(TPR), BET, and Raman analysis. Initial catalytic tests revealed
the potential of this class of compounds in hydrogenation re-
actions.
cations,[6] such as the hydration of carbon dioxide,[7] dehydro-
genation of ammonium borane,[8] and transfer hydrogena-
tion.[9] Recently, we demonstrated that core–shell structured
nanocomposites based on iron and cobalt constitute highly se-
lective catalysts for the hydrogenation of nitroarenes,[10] reduc-
tive amination,[11] the synthesis of nitriles,[12] as well as oxida-
tion reactions of alcohols.[13] Notably, all active NPs, for exam-
ple, Fe2O3/NGr@C or Co-Co3O4/NGr@C, are encapsulated by
a nitrogen-enriched graphene-layer matrix. Based on this work
and our general interest in non-noble-metal catalysis, we envi-
sioned the synthesis of related Ni-NiO/NGr@C materials. In this
protocol, we demonstrate the preparation of this class of com-
pounds by impregnation of carbon (Vulcanꢀ XC72R) with a de-
fined nickel-phenanthroline complex and subsequent pyrolysis
(Figure 1). The resulting material was characterized in detail by
The synthesis of novel catalysts provides innovation for the
chemical- and life-science industries because catalysts are able
to specifically control both the selectivity and reaction rate of
many molecular transformations.[1] The synthesis of novel ma-
terials provides the basis for innovation in heterogeneous cat-
alysis, which is mainly applied for the production of petro-
chemicals as well as bulk and fine chemicals. Advantageously,
heterogeneous catalysts are easily recycled by filtration and
reutilized. Notably, in the last decades especially, metal nano-
particles (NPs) dispersed on different supports have found in-
creasing application as catalysts.[2] In general, these nanoparti-
cles are prepared by a range of different procedures, namely
precipitation, calcination, impregnation, ion exchange, hydro-
thermal transformations, or vapor deposition.[3] In addition, the
past decades have witnessed an explosion in new methods for
the synthesis of metal nanoparticles with controlled composi-
tion, size, shape, and structure.[4] Herein, we present the syn-
thesis of novel NPs covered by nitrogen-doped graphene
sheets (NGrs) from well-defined molecular nickel complexes.
Apart from the well-known Raney nickel,[5] nickel nanoparticles
have also found widespread interest for several catalytic appli-
Figure 1. Schematic representation of the Ni-NiO/NGr@C catalyst.
several analytical techniques [TEM, BET, X-ray photoelectron
spectroscopy (XPS), XRD, electron paramagnetic resonance
(EPR), elemental analysis (EA), and Raman spectroscopy] and
its catalytic activity was investigated in the reductive amination
of acetophenone and in the hydrogenation of nitroarenes.
The preparation was carried out by mixing Ni(OAc)2 (1.5 or
3 wt%) with 2 equivalents of 1,10-phenanthroline (phen) in ab-
solute ethanol at 708C. After stirring the solution for 1 h, the
complex formed in situ was impregnated on Vulcanꢀ XC72R.[14]
This type of carbon black represents an attractive support ma-
terial for the synthesis of redox catalysts because of its thermal
stability. After removal of the solvent, the remaining material
was pyrolyzed under argon at 600–8008C. In addition to com-
mercial Vulcanꢀ XC72R, activated carbon (pretreatment with
30% hydrogen peroxide), Al2O3 (alpha phase), TiO2 (mixture of
rutile and anatase, <100 nm particle size), and CeO2 (powder,
trace-metal basis) were used as the support. To increase the
concentration of the nitrogen species in the NGrs, pyrolysis
was also performed under an ammonia atmosphere.
[a] S. Pisiewicz, D. Formenti, Dr. A.-E. Surkus, Dr. M.-M. Pohl, Dr. J. Radnik,
Dr. K. Junge, Dr. C. Topf, Prof. Dr. M. Beller
Leibniz-Institut für Katalyse e.V. an der Universität Rostock
Albert-Einstein Strasse 29a, 18059 Rostock (Germany)
E-mail: matthias.beller@catalysis.de
[b] D. Formenti
Dipartimento di Chimica
Università degli Studi di Milano
Via Golgi 19, 20133 Milano (Italy)
[c] Dr. S. Bachmann, Dr. M. Scalone
F. Hoffmann-La Roche AG
Process Research and Development, CoE Catalysis
4070 Basel (Switzerland)
ChemCatChem 2016, 8, 129 – 134
129
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communications
Following the above-described procedure approximately 20
potential Ni catalysts were prepared and tested for the reduc-
tive amination of acetophenone and N-benzyl-ethyl amine and
also for the hydrogenation of aromatic nitro compounds. The
most active catalyst (Ni-NiO/NGr@C-800) was prepared by py-
rolysis of the in situ formed Ni/phen complex at 8008C. For
a better understanding of the composition and the structure
of this material, it was fully characterized by TGA, XRD, XPS,
TEM, Raman spectroscopy, EPR, BET and TPR. The sample com-
position of Ni-NiO/NGr@C-800 was determined by elemental
analysis in weight percentage of Ni (3.17%), N (2.31%), C
(81.8%), and H (0.32%).
The results of the thermogravimetric analysis of the unpyro-
lyzed Ni catalyst on Vulcanꢀ XC72R are displayed in Figure S1
in the Supporting Information. Apparently, the formation of
nickel nanoparticles and the accompanied carbonization pro-
ceeds in a multistage fashion. Initial dehydration of the materi-
al is indicated by the broad peak between 100 and 2508C of
the differential scanning calorimetry (DSC) graphs. The subse-
quent exothermic process at 2718C is assigned to the loss of
excess 1,10-phenanthroline as well as the initial decomposition
of the ligated nickel acetate. The third exothermic step, rang-
ing from 450 to 5008C, is accompanied by a significant loss of
mass (15%) and may be assigned to the decomposition of the
ligated nickel acetate, which culminates in the formation of
NiO and metallic nickel as well as the generation of the N-
doped graphene layers.
The powder XRD pattern of the prepared material is dis-
played in Figure S2. In accordance with existing data (JCPDS
file No. 65-2865), metallic nickel was detected by the character-
istic peaks at Bragg’s angle 44, 52, and 768. In contrast to the
TEM measurements (see below), surprisingly no nickel oxide
species could be detected. Apparently, the NiO concentration
is very low. Notably, the broad peak at approximately 258
arises from the amorphous structure of the carbonaceous
matrix.[15]
Figure 2. High-resolution XPS spectra of A) N1s and B) C1s of Ni-NiO/
NGr@C-800.
Transmission electron microscopy (TEM) measurements of
Ni-NiO/NGr@C-800 were deployed to elucidate the size of the
formed nickel nanoparticles and the texture of the surface of
the functionalized carbonaceous material. Additional energy
dispersive X-ray analysis (EDX) gave insight into the chemical
composition of the surface. As shown in Figure 3 the resulting
nickel particles are spread over the surface of the carbon sup-
port. They are of 10–50 nm size and consist mostly of a metallic
nickel core irregularly covered with nickel oxide, which is con-
firmed by further dispersive X-ray analysis (Figure 4).
To elucidate the detailed structure further, the binding
energy (BE) of the surface species was measured by XPS. The
high-resolution spectra of N1s exhibits three peaks that are
characteristic for nitrogen-doped graphene. The detection of
signals for pyridinic N (398.8 eV), pyrrolic N (400.5 eV), and qua-
ternary ammonium indicates the incorporation of different ni-
trogen species into the carbon matrix (Figure 2A). Further-
more, the C1s spectrum confirms the presence of various
carbon species. For example, the sharp C1s peak at 284.2 eV
indicates characteristic sp2 carbon atoms (Figure 2B). Besides,
smaller peaks at higher energy refer to carbon species with
triple bonds and the existence of oxygen-containing groups
such as CÀOH (285.2 eV), carbonyls (286.1 eV), and carboxy-
lates (289.7 eV) (Figure 2B).[16]
Interestingly, the corresponding bright field contrast imaging
shows that the nickel NPs are clearly encapsulated in a carbon-
layer matrix that results from decomposition of the 1,10-phen-
anthroline ligand (Figure 5).
Additional structural information of the carbon support and
the formed NGrs is provided by the Raman spectra. The amor-
phous character of the surface is underlined by the appearance
of the two peaks G (graphitic or graphene) and D (disordered
or defect) at 1589 and 1339 cmÀ1 for visible excitation (Fig-
ure S3). Both peaks arise from sp2 carbon bonds and corre-
spond to bond-stretching modes. More specifically, the G-band
refers to planar sp2-carbon modifications and the D-band is pe-
culiar for the “breathing” mode originating from sp2-carbon
rings.[19] Similar to the XRD analysis, no signals corresponding
to the presence of nickel oxide were detected. This again con-
The spectrum of Ni2p shows two characteristic peaks with
3
the corresponding satellites arising from NiO (2p = : 855.1 and
2
[17]
1
861.8 eV, 2p = : 872.5 and 879.2 eV, Figure 3A). The presence
2
of nickel oxide species is proven by a broad peak at 532.7 eV
in the high-resolution O1s spectra. This peak might also be as-
signed to adsorbed oxygen at the surface (Figure 3B).[18]
ChemCatChem 2016, 8, 129 – 134
www.chemcatchem.org
130
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communications
Figure 5. A) High-angle annular dark-field (HAADF); B) Bright-field (BF) con-
trast imaging of Ni-NiO/NGr@C-800. Scale bar=2 nm.
Another powerful tool for the elucidation of the nature of
the catalytic material is electron paramagnetic resonance spec-
troscopy (EPR). The spectrum reveals the typical ferromagnetic
character of bulk metal phase (g=2.21) according to the iso-
tropic symmetrical shape (Figure S4).
The determination of the specific surface of the Ni-NiO/
NGr@C-800 material was realized through BET measurements.
According to the IUPAC classification, the resulting isotherms
resemble an IV isotherm (Figure S5).[20] The isotherm shows
a hysteresis between the adsorption and desorption curves
and is typical for mesoporous materials[21] and also indicates
the formation of a gaseous monolayer. The BET surface of Ni-
NiO/NGR@C was calculated to be 76.5 m2gÀ1, the average pore
diameter amounted to 9.4 nm, and a single-point total pore
Figure 3. High-resolution XPS spectra of A) Ni2p and B) O1s of Ni-NiO/
NGr@C-800.
firms our assumption, that the major species of the nickel par-
ticles is metallic Ni0.
Figure 4. EDX mapping of Ni-NiO/NGr@C-800: A) Metallic nickel core; B) Nickel oxide layer.
ChemCatChem 2016, 8, 129 – 134
www.chemcatchem.org
131
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communications
volume of 0.18 cm3gÀ1 was obtained. In comparison, the sur-
face of pure carbon (Vulcanꢀ XC72R) features a surface area of
226.3 m2gÀ1, an average pore diameter of 5.4 nm and a single
point total pore volume of 0.30 cm3gÀ1. The diminished surface
and pore diameter as well as the pore volume of the metal-
based material may arise from the fact that the pores are filled
with Ni nanoparticles and covered by a carbon-layer matrix.
Temperature-programmed reduction (TPR) has been used to
understand the reducibility of the implicated Ni species. The
reduction profile shows a peak at 586.58C, which seems to be
very high compared to other reports (Figure S6).[22] Usually,
a peak at approximately 4508C is observed for pure nickel
oxide and for supported nickel at slightly elevated tempera-
ture. The relatively high-temperature measured in this case
may be assigned to nickel species strongly attached to the
support and/or the hydrogen spillover. Another reason for
a high-temperature peak could also be low nickel loading,
which is peculiar for distinct contact between support and
metal species. Calculations, based on the consumed hydrogen
amount, implicate the heterogeneous material to consist of
>90% reducible nickel species. This stands in contradiction to
XRD measurements, which revealed the nanoparticles to be
mainly of metallic nature. One obvious reason for this high hy-
drogen turnover may be assigned to hydrogen spillover. The
temperature-programmed desorption of hydrogen (H2-TPD)
shows two peaks (Figure S6). Only materials containing a metal
phase show the appearance of two peaks, whereas the peak at
high temperature is attributed to changes of functionalities of
the support (8018C). The peak at lower temperature refers to
the existence of a metallic portion.[22]
Table 1. Reductive amination with different nickel-based catalysts.
Entry
Catalyst
Yield[a] 3 [%]
1
2
3
4
5
6
7
8
Co3O4/NGr@C
46
44
40
30
42
10
traces
traces
Ni-NiO/NGr@C
Ni-NiO/NGr@C[b]
Ni-NiO/NGr@C[c]
Ni-NiO/NGr@C[d]
Ni-NiO/NGr@C[e]
Ni(phen)2@C[f]
Vulcanꢀ XC72R
[a] Isolated yields. [b] Pyrolysis at 6008C. [c] 1.5 wt%. [d] Carbon previous-
ly treated with H2O2 (aq., 30%). [e] Pyrolysis in the presence of ammonia.
[f] Homogeneous complex on Vulcanꢀ XC72R.
Table 2. Hydrogenation of nitrobenzene to aniline.
Entry
Ni cat. [mol%]
Time [h]
Yield[a] 5a [%]
1
3
3
3
5
5
5
4
4
8
4
4
8
18
44
80
35
79
98
2[b]
3[b]
4
5[b]
6[b]
The direct reductive amination reaction is a straightforward
method to synthesize amines, without the necessity of prior
isolation of the intermediate imine.[23] This process allows for
the formation of several substituted amines starting from
easily available carbonyl compounds. Usually, this procedure is
accomplished in a one-pot reaction, wherein the formed inter-
mediates such as imines, enamines, or iminium cations are
subsequently reduced. The initial experiments were performed
on the benchmark reaction shown in Table 1. The various cata-
lysts were tested for reductive amination under previously op-
timized conditions.[11a,b] To exclude the activity of the support,
the latter was tested separately (Table 1, entry 8). Compared to
the known cobalt catalyst (Co-Co3O4/NGr@C), the nickel ana-
logues prepared under the same conditions display similar ac-
tivity (Table 1, entries 1 and 2). Catalysts with lower metal load-
ing or those pyrolyzed at lower temperature showed slightly
reduced activity (Table 1, entries 3, 4). Furthermore, the use of
oxidatively pretreated carbon does not increase the activity
(Table 1, entry 5). No, or low activity was observed for the cata-
lyst prepared in the presence of ammonia and for the homo-
geneous nickel phenanthroline complex fixed on Vulcanꢀ
XC72R without pyrolysis (Table 1, entries 6 and 7).
[a] GC yield was determined using n-hexadecane as the internal standard.
[b] 1 equiv. of Et3N was added.
The employed reaction conditions were similar to those re-
ported in our previous publications.[10a] The catalytic tests clear-
ly show that prolonged reaction time (8 h) is beneficial for the
aniline yield (Table 2, entries 3 and 6). Furthermore, a higher Ni
loading of 5 mol% improved the formation of aniline. Finally,
addition of an equivalent of an organic base, such as Et3N, fur-
ther increased the efficiency of the system (Table 2, entries 2
and 3, 5, and 6) and the desired product was obtained in
quantitative yield. Then, with these optimal conditions in hand
(Table 2, entry 6), the scope of the reaction was investigated
with seven functionalized nitroarenes (Scheme 1). In all cases,
this catalytic system showed complete conversion and high se-
lectivities for the reduction of the nitro group, even in the
presence of other sensitive reducible functional groups. In fact,
carbonyl (5b) and conjugated olefin (5c) groups were success-
fully tolerated. In the case of substrate 4g, the yield is due to
the formation of 4-vinylaniline as the side product. Moreover,
for halogen-containing substrates (5d) and ether-containing
molecules (5e), no dehalogenation and no CÀO bond cleavage
occurred, respectively. In addition, this catalytic protocol allows
for the selective hydrogenation of nitropyridine affording the
corresponding heteroaryl amine (5 f) in good yield. Finally, for
In addition, this novel Ni catalyst was also active in the hy-
drogenation of nitroarenes to give the corresponding anilines.
The reduction of nitrobenzene to aniline was investigated and
the findings are summarized in Table 2.
ChemCatChem 2016, 8, 129 – 134
www.chemcatchem.org
132
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communications
für Bildung und Forschung (BMBF). The authors thank Dr. H. Atia,
Dr. W. Baumann, Dr. U. Bentrup, S. Buchholz, R. Eckelt, Dr. C.
Fischer, C. Heber, A. Koch, A. Lehmann, Dr. T. Peppel, Dr. J.
Rabeah, S. Rossmeisl, S. Schareina, and Dr. M. Schneider (all at
LIKAT) for their excellent technical and analytical support. The au-
thors also thank T. Stemmler for his helpful discussions and tech-
nical support. D.F. thanks Milan University and Erasmus+ Pro-
gramme for a fellowship.
Keywords: nickel
· graphene · heterogeneous catalyst ·
hydrogenation · nanoparticles
[1] a) G. Ertl, H. Knuzinger, J. Weitkamp, Handbook of Heterogeneous Cataly-
sis, Wiley-VCH, Weinheim, 2008; b) L. Lloyd, Handbook of Industrial Cat-
alysis, Springer, Berlin, 2011; c) M. Beller, R. A. van Santen, Catalysis-
From Principles to Applications, Wiley-VCH, Weinheim, 2012.
Scheme 1. Substrate scope for the hydrogenation of substituted nitroarenes.
[a] GC yield with hexadecane as the internal standard; [b] reaction time was
16 h; [c] small amounts (<5%) of 4-vinylaniline were detected.
[2] For excellent reviews, see: a) G. Centi, S. Perathoner, Coord. Chem. Rev.
2011, 255, 1480; b) H. Cong, J. A. Porco, ACS Catal. 2012, 2, 65; c) S.
Schauermann, N. Nilius, S. Shaikhutdinov, H.-J. Freund, Acc. Chem. Res.
2013, 46, 1673; d) D. S. Su, S. Perathoner, G. Centi, Chem. Rev. 2013, 113,
5782; e) C. Amiens, B. Chaudret, D. Ciuculescu-Pradines, V. Colli›re, K.
Fajerwerg, P. Fau, M. Kahn, A. Maisonnat, K. Soulantica, K. Philippot,
New J. Chem. 2013, 37, 3374.
[3] a) F. Pinna, Catal. Today 1998, 41, 129; b) P. Serp, P. Kalck, R. Feurer,
Chem. Rev. 2002, 102, 3085; c) K. P. de Jong, Synthesis of Solid Catalysts,
Wiley-VCH, Weinheim, 2009.
[4] a) H. Hahn, Nanostruct. Mater. 1997, 9, 3; b) F. E. Kruis, H. Fissan, A.
Peled, J. Aerosol Sci. 1998, 29, 511; c) D. B. Kittelson, J. Aerosol Sci. 1998,
29, 575; d) H. Schmidt, Appl. Organomet. Chem. 2001, 15, 331; e) A. T.
Bell, Science 2003, 299, 1688.
[5] For an excellent recent review about the spread applications of Raney
Ni, see: T.-K. Yang, D.-S. Lee, J. Haas in Encyclopedia of Reagents for Or-
ganic Synthesis John Wiley & Sons, Ltd, 2001.
[6] a) E. R. C. Leite, N. L. V. CarreÇo, E. Longo, A. Valentini, L. F. D. Probst, J.
Nanosci. Nanotechnol. 2002, 2, 89; b) S.-H. Wu, D.-H. Chen, J. Colloid In-
terface Sci. 2003, 259, 282; c) J. Park, E. Kang, S. U. Son, H. M. Park, M. K.
Lee, J. Kim, K. W. Kim, H. J. Noh, J. H. Park, C. J. Bae, J. G. Park, T. Hyeon,
Adv. Mater. 2005, 17, 429; d) A. Dhakshinamoorthy, K. Pitchumani, Tetra-
hedron Lett. 2008, 49, 1818; e) S. B. Sapkal, K. F. Shelke, B. B. Shingate,
M. S. Shingare, Tetrahedron Lett. 2009, 50, 1754–1756.
the reduction of 2,4-dinitrotoluene (4h) a prolonged reaction
time is beneficial to obtain the desired product (5h) in high
yield.
In conclusion, a novel mesoporous material prepared by im-
pregnation of Vulcanꢀ XC72R with an in situ generated nickel
acetate/1,10-phenanthroline complex and subsequent pyrolysis
of the adsorbed complex is presented. The character and
chemical composition of the heterogeneous material was elu-
cidated by the utilization of several analytic techniques. It was
shown that the supported material mainly consists of bulk
metallic nickel nanoparticles with NiO fractions on its surface.
Those nickel-based particles are spread over the support and
partly occupy the pores of the support and are also covered
with an N-doped graphene-layer matrix. Initial activity tests re-
vealed applicability in different hydrogenation reactions with
molecular hydrogen. More specifically, reductive amination re-
actions and hydrogenation of aromatic nitro compounds pro-
ceeded with high yield and selectivity.
[7] G. A. Bhaduri, L. Siller, Catal. Sci. Technol. 2013, 3, 1234.
[8] Ö. Metin, V. Mazumder, S. Özkar, S. Sun, J. Am. Chem. Soc. 2010, 132,
1468.
Experimental Section
[9] a) F. Alonso, P. Riente, J. A. Sirvent, M. Yus, Appl. Catal. A 2010, 378, 42;
b) F. Alonso, P. Riente, M. Yus, Acc. Chem. Res. 2011, 44, 379.
Preparation of the catalytically active material
Vulcanꢀ XC72R-supported nickel-based materials were prepared by
the impregnation method as previously reported.[10,11] Nickel ace-
tate tetrahydrate (1.0 equiv., Aldrich 98%) was dissolved in abso-
lute ethanol (20 mL). Afterwards, 1,10-phenanthroline (2.0 equiv.,
Aldrich ꢀ99%) was added and the resulting solution was stirred
for 1 h at 608C. The mixture was cooled to RT, Vulcanꢀ XC72R
(CABOT Corporation) was added and the resulting suspension was
stirred overnight at RT. Afterwards, the solvent was evaporated
carefully under reduced pressure to dryness and the obtained solid
was dried overnight in vacuo. To obtain the final nitrogen-doped
graphene-coated nickel nanoparticles on carbon, the material was
grinded and pyrolyzed in a crucible with a lid at 800 or 6008C for
2 h under Ar atmosphere.
[10] a) R. V. Jagadeesh, G. Wienhofer, F. A. Westerhaus, A.-E. Surkus, M.-M.
Pohl, H. Junge, K. Junge, M. Beller, Chem. Commun. 2011, 47, 10972;
b) F. A. Westerhaus, R. V. Jagadeesh, G. Wienhçfer, M.-M. Pohl, J. Radnik,
A.-E. Surkus, J. Rabeah, K. Junge, H. Junge, M. Nielsen, A. Brückner, M.
Beller, Nat. Chem. 2013, 5, 537; c) R. V. Jagadeesh, A.-E. Surkus, H. Junge,
M.-M. Pohl, J. Radnik, J. Rabeah, H. Huan, V. Schünemann, A. Brückner,
M. Beller, Science 2013, 342, 1073; d) F. A. Westerhaus, I. Sorribes, G.
Wienhçfer, K. Junge, M. Beller, Synlett 2015, 26, 313.
[11] a) T. Stemmler, A.-E. Surkus, M.-M. Pohl, K. Junge, M. Beller, Chem-
SusChem 2014, 7, 3012; b) T. Stemmler, F. A. Westerhaus, A.-E. Surkus,
M.-M. Pohl, K. Junge, M. Beller, Green Chem. 2014, 16, 4535; c) S. Pisie-
wicz, T. Stemmler, A.-E. Surkus, K. Junge, M. Beller, ChemCatChem 2015,
7, 62; d) R. V. Jagadeesh, T. Stemmler, A.-E. Surkus, H. Junge, K. Junge,
M. Beller, Nat. Protoc. 2015, 10, 548.
[12] R. V. Jagadeesh, H. Junge, M. Beller, Nat. Commun. 2014, 5, 4123.
[13] R. V. Jagadeesh, H. Junge, M.-M. Pohl, J. Radnik, A. Brückner, M. Beller, J.
Am. Chem. Soc. 2013, 135, 10776.
[14] For the preparation of related Fe-based electrocatalysts see: M. Lef›vre,
E. Proietti, F. Jaouen, J.-P. Dodelet, Science 2009, 324, 71.
Acknowledgements
[15] P. L. Walker Jr., A. F. Amington, ASTM Bull. 1955, 208, 52.
[16] a) J. R. Pels, F. Kapteijn, J. A. Moulijn, Q. Zhu, K. M. Thomas, Carbon
1995, 33, 1641; b) J. Casanovas, J. M. Ricart, J. Rubio, F. Illas, J. M. JimØ-
This research was funded by F. Hoffmann-La Roche AG, the State
of Mecklenburg-Western Pomerania, and the Bundesministerium
ChemCatChem 2016, 8, 129 – 134
www.chemcatchem.org
133
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communications
nez-Mateos, J. Am. Chem. Soc. 1996, 118, 8071; c) H. Wang, T. Maiyala-
gan, X. Wang, ACS Catal. 2012, 2, 781; d) L. Sun, L. Wang, C. Tian, T. Tan,
Y. Xie, K. Shi, M. Li, H. Fu, RSC Adv. 2012, 2, 4498.
[20] S. Brunauer, L. S. Deming, W. E. Deming, E. Teller, J. Am. Chem. Soc.
1940, 62, 1723.
[21] W. Wang, D. Yuan, Sci. Rep. 2014, 4, 5711.
´
[17] a) K. S. Kim, R. E. Davis, J. Electron. Spectrosc. Relat. Phenom. 1972, 1,
251; b) M. W. Roberts, R. S. C. Smart, J. Chem. Soc. Faraday Trans. 1984,
80, 2957; c) A. P. Grosvenor, M. C. Biesinger, R. S. C. Smart, N. S. McIntyre,
Surf. Sci. 2006, 600, 1771; d) M. A. Peck, M. A. Langell, Chem. Mater.
2012, 24, 4483.
[22] a) R. Wojcieszak, M. Zielinski, S. Monteverdi, M. M. Bettahar, J. Colloid In-
terface Sci. 2006, 299, 238; b) P. Kumar, Y. Sun, R. O. Idem, Energy Fuels
2008, 22, 3575.
[23] a) G. Mignonac, Compt. Rend. 1921, 172, 223; b) E. J. Schwoegler, H. J.
Adkins, J. Am. Chem. Soc. 1939, 61, 3499.
[18] R. Larciprete, S. Ulstrup, P. Lacovig, M. Dalmiglio, M. Bianchi, F. Mazzola,
L. Hornekær, F. Orlando, A. Baraldi, P. Hofmann, S. Lizzit, ACS Nano
2012, 6, 9551.
[19] a) A. C. Ferrari, Solid State Commun. 2007, 143, 47; b) J. Hodkiewicz,
Thermo Scientific Application Note, USA 2010; c) J. Lee, K. S. Novoselov,
H. S. Shin, ACS Nano 2011, 5, 608.
Received: July 29, 2015
Published online on October 23, 2015
ChemCatChem 2016, 8, 129 – 134
www.chemcatchem.org
134
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim