Mild-temperature hydrodeoxygenation of vanillin over porous nitrogen-doped carbon black supported nickel nanoparticles

Article abstract of DOI:10.1039/c7gc00531h

Porous nitrogen-doped carbon black (NCB) was synthesized by facile carbonization of carbon black (CB) coated with polypyrrole (CB@polypyrrole) and used as a support for Ni nanoparticles (NPs). The microstructure, reducibility and crystallinity of the as-synthesized materials were investigated by transmission electron microscopy (TEM), H₂-TPR/TPD, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). It was found that surface nitrogen species on NCB significantly promote the decomposition of the nickel precursor and the reduction of nickel oxide, and improve the stability of metallic Ni in ambient atmosphere. In the selective hydrodeoxygenation (HDO) of vanillin in the aqueous phase at low hydrogen pressure (0.5 MPa) and mild temperature (<150 °C), Ni/NCB shows much higher activity than N-free catalysts. This is ascribed to the higher reducibility, the lower oxidation state of Ni NPs and the enhanced hydrogen spillover of Ni to the support. Moreover, the Ni/NCB catalyst is relatively cheap and easy to scale-up the production of, thus achieving a low-cost transformation of biomass to bio-oils.

Full text of DOI:10.1039/c7gc00531h

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Heterogeneous catalytic oxidation for lignin valorization into valuable
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PAPER
Mild-temperature hydrodeoxygenation of vanillin over
porous nitrogen-doped carbon black supported nickel
nanoparticles †
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Renfeng Nie, Huanhuan Yang, Haifu Zhang, Xiaolong Yu, Xinhuan Lu, Dan Zhou* and Qinghua Xia*
www.rsc.org/
Porous nitrogen-doped carbon black (NCB) is synthesized by facile carbonization of carbon black (CB) coated with
polypyrrole (CB@polypyrrole) and used as support for Ni nanoparticles (NPs). Microstructure, reducibility and crystallinity
of as-synthesized materials are investigated by transmission electron microscope (TEM), H2-TPR/TPD, X-ray photoelectron
spectroscopy (XPS) and X-ray diffraction (XRD), respectively. It is found that surface nitrogen species on NCB significantly
promote the decomposition of the nickel precursor and the reduction of nickel oxide, and improve the stability of metallic
Ni in ambient atmosphere. In the selective hydrodeoxygenation (HDO) of vanillin in aqueous phase at low hydrogen
pressure (0.5 MPa) and mild temperature (<150 oC), Ni/NCB shows much higher activity than those of N-free catalysts,
which is ascribed to the higher reducibility, the lower oxidation state of Ni NPs and the enhanced hydrogen spillover of Ni
to the support. Moreover, the Ni/NCB catalyst is relatively cheap and easy scale-up production, thus achieving a low-cost
transformation of biomass to bio-oils.
representative of bio-oils. However, the non-noble-metal catalysts
usually exhibit relatively low activity, require higher temperatures
(150-300 oC) and hydrogen pressures (2-7 MPa), consume more
Introduction
Biomass represents renewable alternatives to fossil-fuel resources
for the green production of liquid fuels and valuable chemicals.1 For
example, lignin can be broken down to phenolic compounds (called
bio-oil) by various approaches.2 Bio-oil usually contains up to 60
wt% oxygen, an upgrading process is necessary to reduce the
oxygen content, and improve the heating value and the stability.3
Up to date, several approaches, hydrodeoxygenation (HDO),4-8
energy in the process. Additionally, the conventional Al2O3 is not a
good support because it tends to deactivate very fast (irreversibly
undergoes partial crystallization to form boehmite), in which water
is formed in the HDO reaction,23 and the presence of weak Lewis
acid sites on the alumina support benefits the coke formation.24
Therefore, alternative heterogeneous Ni catalysts with improved
performance for HDO of biomass under mild conditions are desired.
Carbon can offer many advantages as the support because of its
good resistance to acid and base media, low cost and high thermal
stability.25 Most importantly, carbon has less affinity to produce
coke as compared to the acidic supports for HDO reactions.21
However, the weak interaction of NPs with carbon can lead to
aggregation or leaching, which inevitably reduces the catalytic
activity. Moreover, it has hardly any surface species, making it a
non-preferred choice for reactions needing acid-base functionality,
such as the hydrogenolysis of carbon-oxygen bonds.26 To
overcome this limitation, the functionalization of carbons is
necessary in most cases.
9
10
cracking and aqueous-phase reforming
on zeolite have been
developed for the bio-oil upgrading. Among all practicable routes
mentioned above, catalytic HDO is a very promising process
because this route can achieve high conversion efficiency with low
emission.
Undoubtedly, the precious metal-based catalysts still remain
leading for HDO such as palladium,11, 12 platinum,13, 14 rhodium,15
4, 16
17, 18
ruthenium
and aurum-based
systems, even though their
widespread applications are limited by low earth-abundance and
high cost. Among the non-noble catalysts, a number of studies have
been reported on the activity of unmodified and modified (using
15, 19-22
alkaline and precious metals) Co-Mo and Ni-Mo catalysts
for
Recently, nitrogen-doped carbon materials with rich pore
structure and excellent electrical conductivity have been recognized
as superior candidates as catalyst supports and catalytic materials.27
It is envisioned that N-doped carbon supported metal NPs as the
catalyst for heterogeneous catalysis would exhibit enhanced
performance because of the following reasons. (1) The N-dopants
in the carbon skeleton can be usually regarded as favorable
anchoring sites or defects for enhancing the particle nucleation
and reducing the particle size.28 (2) The N doping results in an
HDO, dehydrogenation and hydrogenolysis of model molecules
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improvement in the hydrophilicity and basicity of supports,29
beneficial to the use of the prepared catalysts in aqueous
phase and the sufficient interaction of substrate with support.
(3) The introduction of N can modify the electronic structure of
carbon matrix, and tune the activity of the sp2 carbon and metal
NPs in the H2 activation by lowering down the dissociation
energy,30, 31 thus promoting the catalytic hydrogenation. However,
recent studies on the promoting effect of N-doped carbon support
have mainly focused on noble metals and on the comparison of
oxygen and nitrogen functional groups.11, 32 It is of great interest to
know whether the promoting effect can be applied to non-noble
metals, especially to those oxidized easily in air.
NCB-600
NCB-900
CB
300
250
200
150
100
50
(a)
AC
0
0.0
0.2
0.4
0.6
0.8
1.0
Relative pressure (p/p0)
As
a model molecule, vanillin (4-hydroxy-3-methoxyben-
zaldehyde, a common component of pyrolysis oil) can be effectively
hydrogenated into 2-methoxy-4-methylphenol (MMP), which is a
potential future biofuel.4, 11, 12, 33, 34 However, the HDO of vanillin
normally requires noble metal catalyst, high hydrogen pressure and
high temperature, and always forms by-product (4-hydroxymethyl-
2-methoxyphenol, HMP) as a result of incomplete hydrogenation
due to the low catalytic activity of catalysts. Herein, we have
synthesized porous N-doped CB for constructing supported Ni
catalyst for the HDO of vanillin. The type and amount of functional
groups on the surface of CB are tuned, and the properties and
catalytic performance of the supported Ni NPs for catalytic
hydrogenation are also discussed.
(b)
0.008
0.006
0.004
0.002
0.000
NCB-600
NCB-900
CB
AC
1
10
Pore width (nm)
Fig. 1 (a) Nitrogen sorption isotherms and (b) pore size distributions of the
Results and discussion
supports.
Characterizations of nanostructured N-doped carbon
materials
ꢀ
ꢂ
ꢁ
C
NiO
Ni
Firstly, the morphology and structure of NCB is studied. The SEM
images (Fig. S1) show no obvious differences in the morphology
between pristine CB and N-doped CB, suggesting the homogeneity
of N species on surface of CB. Nitrogen sorption analysis of CB and
NCB (Fig. 1) show H4 hysteresis loop on the isotherm and sharp rise
at relative pressure higher than 0.80, characteristic of textural
mesopores.35 As expect, the average pore sizes of NCB-900, NCB-
600, CB and AC are calculated to be 16.4, 16.8, 15.0 and 4.3 nm,
respectively (Table 1). It can be seen that, after N-doping of CB, the
SBET increases from 87.7 to 103.1 m2/g for NCB-600, and further
increases to 137.9 m2/g for NCB-900, probably owing to the
emission of many non-carbon or carbon elements and
enhancement of the burn off of CB@polypyrrole when the
carbonization temperature increases.36
ꢁ
ꢀ
ꢂ
ꢂ
ꢁ
ꢂ
(d)
(c)
(b)
(a)
10
20
30
40
2 Theta (degree)
50
60
70
NiO(101)
ꢂ
The FTIR spectra of NCB (Fig. S2) show characteristic peak at
1384 cm−1 related to C–N heterocycles,37 which fluctuates weakly
with increasing the temperature. The C1s peak of NCB (Fig. S3)
shows a tail peak at high binding energy of around 285-290 eV, is
assigned to the electron-deficient carbons bind to nitrogen/oxygen
(C=N/C-N and C-O).38 The percentages of nitrogen (Table S1) in
(d)
(c)
(b)
(a)
Table 1 Pore structure of the supports.
Supports
S
BET (m2/g) Vtotal (cm3/g) Average pore diameter (nm)
30
32
34
36
2 Theta (degree)
38
40
42
NCB-900 137.9
NCB-600 103.1
0.372
0.386
0.455
0.44
16.8
16.4
15.0
4.3
Fig. 2 The XRD patterns of (a) Ni/NCB-900, (b) Ni/NCB-600, (c) Ni/CB and (d)
CB
AC
87.7
Ni/AC.
718.5
2 | J. Name., 2012, 00, 1-3
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Table 2 Structural properties of N-doped carbon materials.
Particle size (nm)
Catalysts
Relative atomic percentage (%)
Relative atomic percentage (%)
N1/N2
XRD
TEM
N1 (398.5 eV)
N2 (400.5 eV)
Ni0
Niδ+
Ni/NCB-600
Ni/NCB-900
Ni/CB
8.1
7.7
8.3
8.4
8.7
8.1
9.1
9.7
50.1
49.9
1.0
15.6
13.3
3.8
84.4
86.7
96.2
97.0
63.6
36.4
1.75
-
-
-
-
-
-
Ni/AC
3.0
Ni/NCB-600 and Ni/NCB-900 are calculated from the XPS survey scattering,41 well agreed with the XRD results. As demonstrated by
spectra to be around 4.38 and 2.98 am%, respectively, implying XRD and Raman, clear decrease of the NiO intensity and increase of
the partial removal of N species from carbon skeleton.
metallic Ni dispersion occur due to the increase of nitrogen content
In order to characterize the Ni NPs on carbon surface, XRD, TEM from 0 to 4.38 at% on surface of CB (Table S1).
and XPS et. al have been carried out. Typical XRD patterns of Ni-
based catalysts are shown in Fig. 2. The broad characteristic peak at
around 24.3o is ascribed to the (002) plane reflection of carbon. The
intensive diffraction peaks at 44.5o and 51.8o are associated with
the (111) and (200) planes of the face-centered-cubic (fcc) structure
Ni (PDF# 04-0850), respectively.26 The crystallite sizes of Ni
calculated by Scherrer equation are also listed in Table 2. The
crystallite size of Ni supported on NCB is smaller than that of Ni
supported on AC, suggesting that the N-doping of CB can promote
the dispersion of Ni. Moreover, Ni/CB and Ni/AC catalysts show two
strong peaks at 2θ values of 37.3 and 43.3°, corresponding to the
(101) and (012) planes of NiO;26 while these NiO peaks weaken for
Ni/NCB-900 and even disappear for Ni/NCB-600. This result
indicates that higher reduction of NiO to metallic Ni could occur on
surface of nitrogen-doped supports.
The Raman spectra of Ni-based catalysts are presented in Fig.
3, in which the G band at
vibration of sp2 carbon atoms,39 while the D band at
defect-induced Raman feature representing the imperfect
∼
1590 cm−1 indicates the in-plane
∼
1350 cm−1 is
a
crystalline structure of carbon.40 Compared with the Ni/CB, the
ID/IG value shows an increase from 0.91 to 1.02 and 1.07 for
Ni/NCB-900 and Ni/NCB-600, respectively, indicating the
formation of much more structural defects on N-doped CB.
The Ni/CB and Ni/AC catalysts show multiple Raman peaks of NiO
between 500 and 1200 cm-1. The peaks observed at 568 and 1091
cm-1 are ascribed to one-phonon (1P) and two-phonon (2P) light
G
D
2P
1091 cm-1
1P
568 cm-1
(d)
(c)
(b)
(a)
200
400
600
800
1000 1200 1400 1600 1800
Raman shift (cm-1)
Fig. 4 TEM images of (a, b) Ni/NCB-600, (c, d) Ni/NCB-900, (e, f) Ni/CB and
(g) Ni/AC. The insets in images (b, d, f and g) are corresponding histograms
of Ni particle size distribution.
Fig. 3 The Raman spectra of (a) Ni/NCB-900, (b) Ni/NCB-600, (c) Ni/CB and
(d) Ni/AC.
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Fig. 6 The N1s spectra of (a) Ni/NCB-600 and (b) Ni/NCB-900
.
on the decomposition of nickel precursor.42 The second peak
centered at ca. 320-370 °C is found in four TPR profiles due to the
reduction of nickel oxides (formed through precursor
decomposition) to metallic Ni. In addition, the second peak for
Ni/AC centered at ca. 365.4 °C is higher than that of 342.9 °C for
Ni/CB. This peak is further shifted to lower temperature of ca. 338.2
and 324.4 °C for Ni/NCB-900 and Ni/NCB-600, respectively.
Comparatively, the relatively narrow peak for Ni/NCB-900 indicates
well-dispersed Ni species on surface of NCB. The electron-donating
effect of surface N species, as observed in several previous studies,
is assumed to be responsible for the promoting effect.45, 46 Besides,
the metal cations are believed to be preferably located on N-
containing sites on the carbon surface, which possess modified local
electronic structure likely favoring the reduction of supported Ni.42
In case of Ni/NCB-600 with a higher surface N content, the local
electronic structure can be more significantly modified, leading to a
more pronounced promoting effect.
324.4
338.2
258.0
259.6
(a)
(b)
(c)
342.9
274.4
365.4
277.4
(d)
100
150
200
250
300
T (oC)
350
400
450
Fig. 5 The H2-TPR spectra of (a) Ni/NCB-600, (b) Ni/NCB-900, (c) Ni/CB and
(d) Ni/AC.
Fig. 4 shows the TEM images and particle size distributions of Ni
catalysts. It can be seen that the particle size of Ni NPs is in range of
3-20 nm without substantial differences on these three CB
supports. However, Ni particles are not so well-dispersed and
agglomerate more or less on N-free CB support, whereas the
particle size on NCB seems to be more homogeneous, and large
particles are seldom detected, which can be attributed to the
strong anchoring effect of surface N groups in accordance with
previous reports.42, 43 Comparatively, the Ni NPs on AC seem to be
more uniform with a narrow size distribution than those on CB,
which can be ascribed to rich micropore structure for size
confinement.44 Statistical analysis of the particle size is carried out
by measuring the size of ca. 150 Ni NPs, which yields the histograms
shown in Fig. 4. It can be found that the average Ni sizes with
standard deviation in Ni/NCB-600, Ni/NCB-900, Ni/CB and Ni/AC are
8.7±2.9, 8.1±2.7 nm, 9.1±2.7 and 9.7±1.2, respectively, well agreed
with the XRD results.
TPR results can reveal the reduction behavior of Ni2+ species (Fig.
5). Two peaks are observed at temperature lower than 400 °C in
TPR profiles of the four dried samples. The first peaks in all samples
are very similar in terms of peak shape and peak intensity, ascribing
to the decomposition of nickel precursor. However, the position of
the first peak for Ni/NCB-600 and Ni/NCB-900 is shifted to a lower
temperature of ca. 258 °C, as compared to ca. 277.4 °C for Ni/CB
and Ni/AC, indicating the promoting effect of the surface nitrogen
The N envelope (Fig. 6) demonstrates that the nitrogen atoms
are mainly in form of pyridinic N (N1, 398.2 eV) and pyrrolic N/N-Ni
(N2, 400.4 eV).47 It can be seen that, for Ni/NCB-600, N1 and N2
account for 50.1 and 49.9 % in total N atoms, respectively. In terms
of Ni/NCB-900, the intensity of the N1 peak becomes much stronger
and its proportion is obviously higher (63.6 %) than that of Ni/NCB-
600, indicating the formed N1 is much more stable than N2 at high
temperatures.36 These results demonstrate that N atoms within the
pentagonal ring of polypyrrole are progressively converted to type
of N1 in the carbonization process, as previously found in other
materials.
The surface chemistry of the Ni-based samples after reduction at
400 °C is examined using XPS (Fig. 7). The main Ni 2p3/2 peaks for all
samples are found to be at 854.5 eV, revealing that surface Ni is
mainly in the oxidized state.48 In the case of Ni/NCB-900 and
Ni/NCB-600, a minor contribution is recorded at a lower binding
energy of 852.7 eV, which can be assigned to Ni in metallic state.
For example, the metallic Ni percentages (Table 2) in Ni/NCB-900
and Ni/NCB-600 are 13.3 and 15.6 %, respectively, much higher
than that of Ni/CB (3.8 %) and Ni/AC (3.0 %). The presence of
metallic Ni confirms the stabilization effect of the NCB support as
revealed by the XRD analysis.
Previous results in the literature suggested that pyridinic N sites
N1
N2
(d)
(c)
Shake up
N2+
(a)
(b)
N0
(b)
(a)
848
852
856
860
864
Binding Energy (eV)
392
394
396
398
400
402
404
406
408
Fig. 7 Ni2p spectra of (a) Ni/NCB-900, (b) Ni/NCB-600, (c) Ni/CB and (d)
Binding Energy (eV)
Ni/AC.
4 | J. Name., 2012, 00, 1-3
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graphitized carbon skeleton.53 Moreover, the signal peaks of
hydrogen desorption in Ni/NCB-600 and Ni/NCB-900 strengthen
obviously. In case of Ni/NCB-900, the TPD profile exhibits a more
strengthened shoulder at 424.8 oC, suggesting more obvious
spillover hydrogen in N-doped CB.54 It should be considered
whether the signal peak is caused by a size effect of Ni NPs, namely
that smaller Ni usually has stronger signal peak. In this work, the
size effect is unlikely to be the only origin of peak area. For example,
although Ni/NCB-600 has much stronger signal peak than Ni/CB, its
particle size of Ni is close to that of Ni/CB. Moreover, Ni/AC has a
stronger signal peak than Ni/CB, while its particle size is larger than
that of Ni/CB. And, there is no clear relationship between peak
intensity and Ni size. Therefore, the peak intensity can also be
attributed to spillover hydrogen of Ni to support.50 Here, it can be
found that N-doping pushes up the capacity of CB for hydrogen
spillover, and higher treatment of NCB owns stronger hydrogen
spillover ability.30
424.8 o
C
(a)
459.8 o
C
(b)
(c)
484.9 o
C
475.1 o
C
(d)
100 150 200 250 300 350 400 450 500 550
T (oC)
Fig. 8 The H2-TPD spectra of (a) Ni/NCB-900, (b) Ni/NCB-600, (c) Ni/CB and
(d) Ni/AC.
could facilitate both the coordination of metal ions and the
anchoring of metal NPs to their electron-withdrawn property.49 XPS
spectra show that pyridinic nitrogen atoms exist dominantly in NCB,
which are often associated with defect sites on edges of graphite
layers or on vacancy sites.50 It was reported that the interaction of
Co with pyridinic nitrogen atom would lead to the increased
electron density of the Co atoms through Co-N-C(III) structure as
compared to the Co-N(II) precursor.51 As expected, compared with
NCB-900 (Fig. S5), the N1 peak in Ni/NCB-900 becomes weak. For
instance, the N1 proportions in NCB-900 and Ni/NCB-900 are 81.5
and 63.6 %, respectively. This result indicates that the N1 atom
donates preferentially electron to Ni NPs, which leads to the shift of
N1 binding energy to high-energy side and the increase of N2
proportion in Ni/NCB-900.52 Therefore, it can be concluded that the
XPS-detectable metallic Ni arises mainly from the Ni atoms bonded
to pyridinic N atoms in the carbon skeleton.
Catalytic property of Ni catalysts
The HDO of vanillin in water is carried out as a model reaction.
Fig. 9 displays the evolution of the vanillin and products with the
time over Ni/NCB-900. In the initial stage of the reaction, vanillin is
transformed to HMP with a relatively moderate rate, and about
35.5 % conversion of vanillin is obtained within 0.5 h. When the
reaction time prolongs, the reaction is accelerated and almost 95.7
% conversion of vanillin is obtained at 3 h. As the reaction
continues, the concentration of HMP decreases gradually, while the
concentration of MMP increases correspondingly. Further reacting
for 2 h, HMP is converted completely with a 99.8 % MMP yield. It is
worth mentioning that no other product is observed during the
whole process. These results demonstrate that vanillin is mainly
reacted with H2 by hydrogenation of C=O bond to form HMP and
further deoxidized to form MMP in water.
H2-TPD tests of Ni catalysts are carried out (Fig. 8). The profiles of
o
The impact of solvent on hydrogenation of vanillin is investigated
under the similar condition (Fig. 10). Among these solvents
examined, the reaction in water shows the best activity for vanillin
hydrogenation, giving 74.4 % conversion of vanillin and 48.1 % yield
towards MMP after 2 h. We deduce that, doping with N atoms
increases the hydrophilic property of Ni/NCB-900, which might
all show a broad desorption peak centered between 300-550 C. As
for Ni/AC and Ni/CB catalyst, the peaks appear at 475.1 and 484.9
oC, respectively. Although the peak intensity of Ni/CB is fairly weak
o
compared to those in Ni/AC, a peak shoulder shows up at ~425 C
for Ni/CB, suggesting the spillover hydrogen on CB due to its high
100
Conv.
HMP sele.
MMP sele.
MMP yield
100
80
Conv.
80
60
40
20
0
HMP sele.
MMP sele.
MMP yield
60
40
20
0
0.5
0
1
2
3
4
5
t (h)
Ethyl acetate
water
THF
DMF
Cyclohexane
Fig. 9 Time-activity profile for the selective hydrogenation of vanillin over
Ni/NCB-900. Reaction conditions: Vanillin (228 mg), Ni/NCB-900 (20 mg),
H2O (10 mL), 0.5 MPa H2, 150 oC.
Fig. 10 Hydrogenation of vanillin in different solvents over Ni/NCB-900.
Reaction conditions: Vanillin (228 mg), Ni/NCB-900 (20 mg), solvent (10 mL),
0.5 MPa H2, 150 oC, 2 h.
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Table
catalysts.a
3
The aqueous phase HDO of vanillin over different Ni-based increases, the specific MMP yield of per Ni atom is enhanced
slightly from 10.1 to 11.6 h-1 as increasing the Ni loading from 4.95
to 7.41 wt %. Further increasing the Ni loading to 19.45 wt %,
however, leads to significant decrease of this value to 7.5 h-1.
Therefore, lower Ni loading could accelerate the transformation of
vanillin, while moderate Ni loading could give the highest efficiency
for MMP generation over single Ni atom.
Selectivity / %
HMP MMP
Conversion
/ %
MMP
Entry Catalysts
Using Ni/NCB-900 as catalyst, we can still achieve 51.2 %
conversion of vanillin and 42.8 % selectivity of MMP even
yield / %
1
No catalyst
Ni/NCB-600
Ni/NCB-900
Ni/CB
1.2
-
-
-
decreasing the temperature to 130 °C. When the hydrogenation of
2
52.9
74.4
37.8
35.9
0.3
39.4
35.4
49.4
75.2
-
60.6
64.6
50.6
24.8
-
32.1
48.1
19.1
8.9
vanillin is carried out under higher temperature (190 °C), the MMP
yield is 99.8 % (Fig. S6). High yield of MMP (>99.5 %) can also be
realized by decreasing the substrate dosage (from 228 to 76 mg,
Fig. S7) or increasing the hydrogen pressure (from 0.5 to 2.5 MPa,
Fig. S8). The Ni/NCB-900 catalyst can be easily separated by
extraction and recycled 5 times with a small fluctuation of activity
or MMP selectivity (Table 3, entries 9-12). ICP-AES analysis of the
reaction mixture and the used catalyst did not detect the leaching
of any metal during recycling, also proven by the characterization of
the reused catalyst (Fig. S9 and S10).
3
4
5
Ni/AC
6
Ni/SiO2
-
7
Ni/MgO
Ni/ZrO2
19.0
3.7
1.4
98.6
20.5
65.1
67.5
64.5
62.8
18.7
0.8
8
79.5
34.9
32.5
35.5
37.2
9
2nd reuse of entry 3 78.1
50.8
48.8
45.9
43.1
10
11
3rd reuse of entry 3
4th reuse of entry 3
5th reuse of entry 3
72.3
71.1
68.7
12
Based on these experimental results above, the improved
catalytic activity of Ni/NCB catalysts could be attributed to several
factors. Firstly, the rich surface nitrogen (Table S1) results in good
hydrophilic property that benefits the dispersion of catalyst in
water and the wettability of the substrate on support, hence
accelerating the diffusion and transformation of substrates.7
Secondly, the incorporated nitrogen facilitates the highly dispersion
and stabilization of Ni NPs on the surface of carbon supports (Fig.s 2
and 4). The electron-rich nitrogen donates electron to Ni NPs
preferably than carbons,26 leading to high electron density on Ni
surface (Fig. 7) and easy reduction of Ni species (Fig. 5). It is
confirmed that the catalytic activity and selectivity of the catalyst
can be ascribed to Ni(0) species. The stronger interaction between
Ni NPs and nitrogen species on surface of carbon affords
catalytically active sites for vanillin hydrogenation. Thirdly, the
hydrogen spillover effect of catalyst has been greatly enhanced
through the metal-support interface due to the N-doping of carbon
skeleton, as is confirmed by H2-TPD analysis. It is well known that
hydrogen spillover exerts a great influence on the catalytic activity
in hydrogenation reactions.30 In one word, the greatly improved
catalytic activity of Ni/NCB-900 can also be ascribed to its increased
interfacial sites, which enhance the hydrogen spillover effect (Fig.
S11).
a
Reaction conditions: vanillin (228 mg), catalyst (20 mg), H2O (10 mL), 0.5
MPa H2, 150 oC, 2 h.
enhance the catalyst dispersion in water and improve the exposure
of the catalyst to the substrates. The reaction in ethyl acetate, THF
and cyclohexane obtains relative low vanillin conversion (3.6-17.2
%) with the desired MMP selectivity of 26.9-33.4 %. Additionally,
the reaction in DMF exhibits nearly no transformation of vanillin.
The HDO of vanillin in water over different Ni catalysts is tested
and these results are summarized in Table 3. In blank test, when no
catalyst is used, nearly no vanillin is transformed (entry 1). Under
150 oC and low hydrogen pressure of 0.5 MPa for 2 h, the
conversion of vanillin reaches 52.9, 74.4, 37.8 and 35.9 % over
Ni/NCB-600, Ni/NCB-900, Ni/CB and Ni/AC, respectively (entries 2-
5), indicating the significant improvement towards activity via N-
doping of carbon. Although similar vanillin conversion can be
achieved over Ni/CB and Ni/AC, the desired MMP selectivity over
Ni/CB (50.6 %) is much higher than that of Ni/AC (24.8 %), which
might be ascribed to the micropore-free structure of CB that is
beneficial for smooth transformation of HMP. The calculated MMP
yield over Ni/NCB-900 is 5.4 times higher than that of Ni/AC. Other
frequently used heterogeneous Ni-based catalysts inclusive of
Ni/SiO2, Ni/MgO and Ni/ZrO2 (entries 6-8) achieve poor
hydrogenation activity or MMP selectivity under the same
condition. These results imply that the nature of support has a
noticeable impact on the catalytic activity of Ni for vanillin
hydrogenation and Ni/NCB-900 is a good hydrogenation catalyst in
water.
Conclusions
Porous nitrogen-doped carbon black is synthesized by facile
carbonization using CB as template and pyrrole as nitrogen source.
Using NCB as support for Ni NPs, the as-obtained catalyst exhibits
high performance for hydrogenation of vanillin to MMP under mild
conditions, which is significantly superior to other frequently-used
nickel-based catalysts. The high catalytic activity can be ascribed to
the specific characteristics of the nanostructure of Ni/NCB and the
intimate interaction of Ni NPs and N species, endowing Ni with the
higher reducibility, hydrogen spillover and the lower oxidation
state. Moreover, the Ni/NCB catalyst is not only cheap but also
easily separable, and therefore, this approach facilitates achieving
the cost-effective reduction of vanillin to bio-oils.
The NCB-900 supported Ni catalysts with different Ni content are
prepared and investigated for HDO of vanillin (as shown in Table
S2). It can be found that vanillin conversion is quickly increased
from 48.1 to 90.8 % after 2 h when the Ni loading is increased from
4.95 to 19.45 wt %. However, the TOF value based on total Ni atoms
exhibits a reverse variation trend with increasing the Ni loading
from 4.95 to 19.45 wt %, in which the maximal value of 21.4 h-1 is
achieved over 4.95 % Ni/NCB-900. Moreover, as the Ni loading
6 | J. Name., 2012, 00, 1-3
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Experimental
spectra were collected at room temperature from 100 to 4000 cm-1
with 514.5-nm argon ion laser (Rhenishaw Instruments, England).
The spectra were recorded at a resolution of 2 cm−1. X-ray
photoelectron spectra (XPS) were recorded on a Perkin-Elmer PHI
ESCA system. Scanning electron images (SEM) and surface
compositions were collected on JEOL (JSM6700F)) with an
accelerating voltage of 15 kV. Transmission electron microscope
(TEM) images were obtained using an accelerating voltage of 200
kV on a JEOL-135 2010F Transmission Electron Microscope.
Materials
The chemicals used included pyrrole (98 %, Sinopharm),
Ni(NO3)2•6H2O (98 %, Sinopharm), ammonium persulfate (APS,
98 %, Sinopharm), H2O2 (30 %, Sinopharm), vanillin (99.5 %,
Aladdin). Vulcan XC-72 carbon black (CB) was purchased from
Cabot Corporation. Active carbon (AC) was purchased from
Hunan Xiangda Chemical Reagent Co. All other chemicals were
of analytical purity if not otherwise noted.
TPR experiments were performed in a flow setup using 20 vol% H2
in N2 at a flow rate of 50 mL/min. The TPR of the calcined Ni/NCB
samples was performed from room temperature to 600 °C at a
heating rate of 5 °C/min. A thermal conductivity detector (TCD) was
used to monitor the H2 consumption. Before starting the TPR
procedure, the sample was pretreated at 200 °C for 30 min in a N2
flow of 100 mL/min and then cooled down to room temperature.
The H2 activation activity of the reduced catalysts was
detected via temperature-programmed desorption of H2 (H2-
Preparation of NCB
Ten grams of carbon black (CB) was first immersed in 250 mL
H2O2 (28 wt%) solution. The slurry was stirred and treated at
50 °C for 5 h. Then, the solid was recovered by filtration and
washed thoroughly with distilled water. The pretreated CB was
dried in a vacuum oven at 80 °C for 10 h, which is denoted as
H2O2-CB. In a typical synthesis of NCB, 500 mL of the 90.3
mmol/L pyrrole aqueous solution was added into 1.0 g H2O2-
CB followed by 30 min of sonication. The mixture was then
stirred for 60 min before it was transferred into a beaker.
Subsequently, 200 mL of aqueous APS solution (45.3 mmol/L)
was slowly added into the beaker under continuous stirring at
TPD). The sample was first reduced at 400
mL/min for 1 h, purged in purified N2, and further treated at
450 C for 0.5 h in N2. Then the reactor was cooled to 30 C in
°C in a H2 flow of 30
°
°
N2, exposed to 20% H2/N2 for 30 min, and purged with by N2
for 2 h at 30 °C in order to eliminate the physically adsorbed H2.
30 oC. After further stirring for
4 h, the product
H2-TPD was conducted by ramping to 650 °C at 5 °C/min and
H2 in effluent was detected and recorded by a thermal
CB@polypyrrole was separated by filtration, washed with
ethanol and water, and dried at 60 oC overnight under vacuum.
Finally, the CB@polypyrrole was annealed in a quartz tube
under N2 atmosphere with a 5 °C/min heating rate to
carbonization temperature (600 and 900 °C) for 2 h to obtain
the nitrogen-doped CB (NCB-600 and NCB-900).
conductivity detector (TCD).
Selective HDO of vanillin
The catalytic test was carried out in a 50 mL stainless
autoclave with a Teflon liner. In a typical procedure, 20 mg
catalyst was dispersed in 10 mL DI water, and then added with
228 mg vanillin. The autoclave was sealed, purged and
pressurized with hydrogen to 0.5 MPa, and then heated to 150
oC under magnetic stirring at a rate of 1000 rpm. After reaction,
the autoclave was quickly cooled down within cold water. The
organic compounds was extracted by ethyl acetate, the
catalyst was recovered from aqueous phase by centrifugation
and then washed several times with ethanol. The contents of
products and substrate were analyzed by gas-chromatogram
(Shimadzu 2010) with a 30 m capillary column (Rtx®-1) using a
flame ionization detector (FID). Interpolated calibration was
employed for product quantification using standard solutions
of vanillin, HMP and MMP. All the products were confirmed by
GC-MS (Agilent 6890).
Preparation of NCB supported Ni catalysts
NCB-supported Ni NPs were prepared by impregnation using
Ni(en)3(NO3)2 as precursor (en, ethylenediamine).56 Briefly, 50
mL of Ni(en)3(NO3)2 aqueous solution (0.034 mol/L) and 1 g of
NCB were mixed at 30 °C for 2 h. Dark powders were obtained
after removing water in a rotary evaporator, and the powders
were dried in a vacuum oven at 80 °C for 10 h. The sample was
subsequently calcined in nitrogen at 300 °C for 90 min,
followed by reduction in H2 atmosphere at 400 °C for 120 min,
yielding the Ni/NCB catalyst. Other two different samples with
the same nominal loading of 10 wt% (weight percent) were
prepared by using CB and AC as supports and designated as
Ni/CB and Ni/AC.
Catalyst characterization
Acknowledgements
Powder X-ray diffraction (XRD) was performed on a Bruker D8A25
This work was supported by National Natural Science Foundation of
China (21603066, 21673069, 21503074, 21571055), Natural Science
Fund for Creative Research Groups of Hubei Province
(2014CFA015), Natural Science Fund of Hubei Province
(2015CFB232), the 2014 Sci-tech Support Project of the Science and
Technology Department of Hubei Province (2014BAA098), Natural
Science Fund of the Education Department of Hubei Province
(Q2015009), and Hubei Provincial Outstanding Youth Foundation
(2016CFA040).
diffractometer with CuKα radiation (λ = 1.54184 Å) operating at 30
kV and 25 mA in the range of 10-80o 2
θ. N2 adsorption was carried
out at -196 °C using an auto-adsorption analyzer (Micromeritics,
TriStar II). Before adsorption measurements, the samples were
degassed at 250 °C overnight under vacuum. The total pore volume
was determined from the aggregation of N2 vapor adsorbed at a
relative pressure of 0.99. The specific surface area was calculated
by using the Brunauer−Emmeꢀ–Teller (BET) method, and the pore
size distributions were measured by using Barrett−Joyner−Halenda
(BJH) analysis from the desorption branch of the isotherms. Raman
Notes and references
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ARTICLE
Journal Name
1. R. Sharma and N. Bakhshi, Energy & Fuels 1993, 7, 306-314.
2. A. Singh, D. Pant, N. Korres, A. Nizami, S. Prasad and J. Murphy,
Bioresour. Technol., 2010, 101, 5003-5012.
29. E. Haque, J. W. Jun, S. N. Talapaneni, A. Vinu and S. H. Jhung, J.
Mater. Chem., 2010, 20, 10801-10807.
30. T. Fu, M. Wang, W. Cai, Y. Cui, F. Gao, L. Peng, W. Chen and W.
Ding, ACS Catal., 2014, 4, 2536-2543.
3. F. H. Mahfud, S. Bussemaker, B. J. Kooi, G. H. Ten Brink and H.
J. Heeres, J. Mol. Catal. A 2007, 277, 127-136.
31. Z. Wei, J. Wang, S. Mao, D. Su, H. Jin, Y. Wang, F. Xu, H. Li and
Y. Wang, ACS Catal., 2015, 5, 4783-4789.
4. S. Crossley, J. Faria, M. Shen and D. Resasco, Science 2010, 327,
68-72.
32. X. Cui, A.-E. Surkus, K. Junge, C. Topf, J. Radnik, C.
Kreyenschulte and M. Beller, Nat. Commun., 2016, 7, 11326-
11334.
5. H. Lee, H. Kim, M. J. Yu, C. H. Ko, J.-K. Jeon, J. Jae, S. H. Park, S.-
C. Jung and Y.-K. Park, Sci. Rep., 2016, 6, 28765-28773.
6. H. Lee, Y.-M. Kim, I.-G. Lee, J.-K. Jeon, S.-C. Jung, J. D. Chung, 33. M. T. Jimaré, F. Cazaña, A. Ramirez, C. Royo, E. Romeo, J. Faria,
W. G. Choi and Y.-K. Park, Korean J. Chem. Eng., 2016, 33,
3299-3315.
D. E. Resasco and A. Monzón, Catal. Today 2013, 210, 89-97.
34. X. Yang, Y. Liang, Y. Cheng, W. Song, X. Wang, Z. Wang and J.
Qiu, Catal. Commun., 2014, 47, 28-31.
7. H. W. Lee, B. R. Jun, H. Kim, D. H. Kim, J.-K. Jeon, S. H. Park, C.
H. Ko, T.-W. Kim and Y.-K. Park, Energy 2015, 81, 33-40.
35. A. Vinu, Adv. Funct. Mater., 2008, 18, 816-827.
8. E. H. Lee, R.-s. Park, H. Kim, S. H. Park, S.-C. Jung, J.-K. Jeon, S. 36. L.-F. Chen, ACS Nano 2012, 6, 7092-7102.
C. Kim and Y.-K. Park, J. Ind. Eng. Chem., 2016, 37, 18-21.
9. B. Puértolas, T. C. Keller, S. Mitchell and J. Pérez-Ramírez, Appl.
Catal. B 2016, 184, 77-86.
37. Q. Hu, M. C. Paau, Y. Zhang, X. Gong, L. Zhang, D. Lu, Y. Liu, Q.
Liu, J. Yao and M. M. F. Choi, RSC Adv., 2014, 4, 18065-18073.
38. G. P. Mane, S. N. Talapaneni, C. Anand, S. Varghese, H. Iwai, Q.
Ji, K. Ariga, T. Mori and A. Vinu, Adv. Funct. Mater., 2012, 22,
3596-3604.
10. T. Vispute and G. Huber, Green Chem., 2009, 11, 1433-1445.
11. X. Xu, Y. Li, Y. Gong, P. Zhang, H. Li and Y. Wang, J. Am. Chem.
Soc., 2012, 134, 16987-16990.
39. V. Chandra, J. Park, Y. Chun, J. W. Lee, I.-C. Hwang and K. S.
Kim, ACS Nano 2010, 4, 3979-3986.
12. Z. Zhu, H. Tan, J. Wang, S. Yu and K. Zhou, Green Chem., 2014,
16, 2636-2643.
40. H. Wang, X. Xiang and F. Li, J. Mater. Chem., 2010, 20, 3944-
3952.
13. X. Chen, L. Zhang, B. Zhang, X. Guo and X. Mu, Sci. Rep., 2016,
6, 28558-28571.
41. P. K. Nayak, C. Hsu, S. Wang, J. C. Sung and J. Huang, Thin Solid
Films 2013, 529, 312-316.
14. L. J. Durndell, C. M. A. Parlett, N. S. Hondow, M. A. Isaacs, K.
Wilson and A. F. Lee, Sci. Rep., 2015, 5, 9425-9434.
15. Y.-C. Lin, C.-L. Li, H.-P. Wan, H.-T. Lee and C.-F. Liu, Energy &
Fuels 2011, 25, 890-896.
42. P. Chen, F. Yang, A. Kostka and W. Xia, ACS Catal., 2014, 4,
1478-1486.
43. M. Shalom, V. Molinari, D. Esposito, G. Clavel, D. Ressnig, C.
Giordano and M. Antonietti, Adv. Mater., 2014, 26, 1272-1276.
44. R. Nie, H. Jiang, X. Lu, D. Zhou and Q. Xia, Catal. Sci. Technol.,
2016, 6, 1913-1920.
16. G. Yao, G. Wu, W. Dai, N. Guan and L. Li, Fuel 2015, 150, 175-
183.
17. Y. Zhu, H. Qian, B. A. Drake and R. Jin, Angew. Chem. Int. Ed.,
2010, 49, 1295-1298.
45. X.-H. Li and M. Antonietti, Chem. Soc. Rev., 2013, 42, 6593-
6604.
18. S. Zhu, Y. Xue, J. Guo, Y. Cen, J. Wang and W. Fan, ACS Catal.,
2016, 6, 2035-2042.
46. G. Zhang, S. Zang, L. Lin, Z.-A. Lan, G. Li and X. Wang, ACS Appl.
Mater. & Interfaces 2016, 8, 2287-2296.
19. J. Bredenberg, M. Huuska, J. Raty and M. Korpio, J. Catal.,
1982, 77, 242-247.
47. H. Jiang, X. Yu, X. Peng, H. Q. Zhang, R. Nie, X. Lu, D. Zhou and
Q. Xia, RSC Adv., 2016, 6, 69045-69051.
20. W. Wang, L. Li, S. Tan, K. Wu, G. Zhu, Y. Liu, Y. Xu and Y. Yang,
Fuel 2016, 179, 1-9
48. T. Zeng, H. Zhang, Z. He, J. Chen and S. Song, Sci. Rep., 2016, 6,
33348-33357.
21. S. Mukundan, M. Konarova, L. Atanda, Q. Ma and J. Beltramini,
Catal. Sci. Technol., 2015, 5, 4422-4432.
49. X. Ning, H. Yu, F. Peng and H. Wang, J. Catal., 2015, 325, 136-
144.
22. M. Ferrari, B. Delmon and P. Grange, Carbon 2002, 40, 497-
511.
50. Y. Zhou, K. Neyerlin, T. S. Olson, S. Pylypenko, J. Bult, H. N.
Dinh, T. Gennett, Z. Shao and R. O'Hayre, Energ. Environ. Sci.,
2010, 3, 1437-1446.
23. E. Furimsky and F. E. Massoth, Catal. Today 1999, 52, 381-495.
24. E. Laurent and B. Delmon, Stud. Surf. Sci. Catal., 1994, 88, 459-
466.
51. F. Chen, A.-E. Surkus, L. He, M.-M. Pohl, J. Radnik, C. Topf, K.
Junge and M. Beller, J. Am. Chem. Soc., 2015, 137, 11718-
11724.
25. J. Xia, G. He, L. Zhang, X. Sun and X. Wang, Appl. Catal. B 2016,
180, 408-415.
26. X. Kong, Y. Zhu, H. Zheng, X. Li, Y. Zhu and Y.-W. Li, ACS Catal., 52. D. A. Bulushev, M. Zacharska, E. V. Shlyakhova, A. L. Chuvilin, Y.
2015, 5, 5914-5920.
Guo, S. Beloshapkin, A. V. Okotrub and L. G. Bulusheva, ACS
Catal., 2016, 6, 681-691.
27. X. Wang, G. Sun, P. Routh, D.-H. Kim, W. Huang and P. Chen,
Chem. Soc. Rev., 2014, 43, 7067-7098.
53. P. A. Gordon and R. B. Saeger, Ind. Eng. Chem. Res., 1999, 38,
4647-4655.
28. R. Nie, M. Miao, W. Du, J. Shi, Y. Liu and Z. Hou, Appl. Catal. B
2016, 180, 607-613.
8 | J. Name., 2012, 00, 1-3
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Page 9 of 10
Journal Name
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ARTICLE
54. Z. Gao, M. Dong, G. Wang, P. Sheng, Z. Wu, H. Yang, B. Zhang,
G. Wang, J. Wang and Y. Qin, Angew. Chem. Int. Ed., 2015, 54,
9006-9010.
55. T. Mokrane, A. Boudjahem and M. M. Bettahar, RSC Adv.,
2016, 6, 59858-59864.
56. J. Wang, Z. Yuan, R. Nie, Z. Hou and X. Zheng, Ind. Eng. Chem.
Res., 2010, 49, 4664-4669.
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Graphic abstract
Porous nitrogen-doped carbon black (NCB) derived from carbon black
(CB) and pyrrole was used as support for Ni NPs. The catalyst exhibited
significantly higher activity than most of Ni-based catalyst for selective
HDO of vanillin in aqueous phase at mild conditions, which was ascribed
to the higher reducibility, the lower oxidation state of Ni NPs and the
enhanced spillover hydrogen of Ni to NCB due to the intimate interaction
of Ni and N species.