Hydrogenation of 3-nitro-4-methoxy-acetylaniline with H2 to 3-amino-4-methoxy-acetylaniline catalyzed by bimetallic copper/nickel nanoparticles

Article abstract of DOI:10.1039/c7nj00066a

Monometallic Cu, monometallic Ni, and bimetallic Cu_xNi_y nanoparticles were prepared by a wet chemical reduction method. A Cu-Ni alloy phase was formed in the bimetallic Cu_xNi_y nanoparticles. The bimetallic Cu_xNi_y nanoparticles exhibited higher catalytic activity for the hydrogenation of 3-nitro-4-methoxy-acetylaniline (NMA) to 3-amino-4-methoxy-acetylaniline (AMA) with H₂ than the sole Ni nanoparticles, which was ascribed to the effect of the Cu-Ni alloy phase. When the reaction was catalyzed over the bimetallic Cu_0.7Ni_0.3 catalyst at 140 °C for 2 h, the AMA selectivity was 99.4% when the NMA conversion was 95.7%. The reaction activation energy for NMA hydrogenation was 19.74 kJ mol^-1.

Full text of DOI:10.1039/c7nj00066a

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PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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Hydrogenation of 3-nitro-4-methoxy-acetylaniline with H2 to
3-amino-4-methoxy-acetylaniline catalyzed by bimetallic copper/nickel
nanoparticles
Chenchen Yang, Wuping Xue, Hengbo Yin*, Zhipeng Lu, Aili Wang*, Lingqin
Shen, Yunyan Jiang
Faculty of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang
212013, China
ABSTRACT
Monometallic Cu, monometallic Ni, and bimetallic CuxNiy nanoparticles were
prepared by a wetness chemical reduction method. CuꢀNi alloy phase was formed in
the bimetallic CuxNiy nanoparticles. The bimetallic CuxNiy nanoparticles exhibited
higher catalytic activity for the hydrogenation of 3ꢀnitroꢀ4ꢀmethoxyꢀacetylaniline
(NMA) with H2 to 3ꢀaminoꢀ4ꢀmethoxyꢀacetylaniline (AMA) than the sole Ni
nanoparticles, which was ascribed to the effect of CuꢀNi alloy phase. When the
reaction was catalyzed over the bimetallic Cu0.7Ni0.3 catalyst at 140 ºC for 2 h, the
AMA selectivity was 99.4% at the NMA conversion of 95.7%. The reaction activation
energy for NMA hydrogenation was 19.74 kJ/mol.
Keywords: 3ꢀNitroꢀ4ꢀmethoxyꢀacetylaniline;
3ꢀAminoꢀ4ꢀmethoxyꢀacetylaniline;
Bimetallic CuxNiy nanoparticles; Hydrogenation; Kinetics
Corresponding author: Tel.: +86ꢀ(0)511ꢀ88787591
Eꢀmail address: yin@ujs.edu.cn (H. Yin), alwang@ujs.edu.cn (A. Wang)

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Introduction
Anilines are valuable chemicals in the production of pharmaceuticals, agricultural
chemicals, dyes, polymers, photographic and rubber materials, and chelating agents.
1−3
3ꢀAminoꢀ4ꢀmethoxyꢀacetylaniline (AMA) is one of the most useful anilines in
great demand, which is widely used as a coupling component in many commercial
dyes because it can give high fastness properties to dyes on hydrophobic fibers and
deep shades.4 There are two methods for the production of AMA, selective acylation
of 2,4ꢀdiaminoanisole and reduction of 3ꢀnitroꢀ4ꢀmethoxyꢀacetylaniline (NMA).
There are some drawbacks in the acylation process. Byproducts, 4ꢀdiacetamidoanisole
and 3ꢀaminoꢀ6ꢀmethoxyꢀacetanilide, are formed and 2,4ꢀdiaminoanisole can be easily
oxidized, giving a low selectivity of AMA. Considering that NMA is commercially
available at a lower price, reduction of NMA is taken as a favorable process for AMA
production, in which the key point is the selection of effective reductant and catalyst.
Iron powder was used as a cheap reductant for the reduction of NMA to AMA
under acidic condition in industry. However, a large amount of ironꢀoxide sludge (1.2
kg sludge/kg product) was also produced, which is a heavy pollutant difficult to deal
with industrially.5−7 Hydrazine hydrate is commonly used as an efficient reductant for
the reduction of nitroꢀcompounds at 50–70 ºC and atmospheric pressure.8–10 The
selectivities and yields of products are significantly affected by the concentration of
hydrazine hydrate. At a low concentration of hydrazine hydrate, amines are favorably
formed. However, the reduction rate is very low. At a high concentration of hydrazine
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hydrate, many byꢀproducts are formed, such as diimide, azoxybenzene, and
hydrazobenzene.11 Sodium borohydride also exhibits good activity for the reduction
of NMA to AMA, catalyzed by copper nanoparticles.12 However, the prices of
hydrazine hydrate and sodium borohydride are very high, which are not suitable for
the reduction of NMA to AMA in industrial scale from the perspective of economy.
Catalytic hydrogenation of nitroꢀcompounds using molecular hydrogen as hydrogen
source is considered as the most economical and environmental friendly method for
the production of corresponding amines. Metallic catalysts, such as nano Ni,13‒17
AuꢀNi,18 Raney Ni,19,20 Pd/C,20 Pt/C,21‒23 and Ag,24 are reported active for the
hydrogenation reaction. There was hardly any byꢀproduct formed in this process,
giving a very high selectivity of amine. It is noteworthy that all of these researches
focused on the catalytic performances of noble metal and nickel catalysts, the
catalytic performances of copperꢀcontaining catalysts for the hydrogenation of NMA
were rarely investigated. It is wellꢀknown that metallic copper is a conventionally
used catalyst for hydrogenation reactions because of its high activity and stability as
well as cheap price.25,26 However, the monometallic copper catalysts are not so active
as noble metal and nickel catalysts for the hydrogenation of nitroꢀcompound at a
lower reaction temperature. The optimal active temperature of monometallic copper
catalyst is over 200 ºC, which causes energy consumption and side reactions at such
high reaction temperature. According to open literatures, Niꢀcontaining Cu/SiO2
catalyst exhibited good catalytic activity for the selective synthesis of ethanol via
hydrogenation of dimethyl oxalate.27,28 The catalytic performance of bimetallic CuꢀNi
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nanoparticles for the hydrogenation of NMA is worth of study.
In our present work, bimetallic CuxNiy nanoparticles were prepared by a wet
chemical reduction method in anhydrous ethanol using Tweenꢀ80 as the organic
modifier. The chemical structures of the bimetallic CuxNiy nanoparticles were
analyzed by XRD and HRTEM techniques. The asꢀprepared bimetallic CuxNiy
nanoparticles were used as the catalysts in the catalytic hydrogenation of NMA with
H2 to AMA. The effect of the Cu and Ni contents in CuxNiy nanoparticles and reaction
parameters on the catalytic hydrogenation of NMA was investigated in detail. A
power function type reaction kinetic model was used to evaluate the reaction kinetics
of NMA hydrogenation over the bimetallic Cu0.7Ni0.3 nanoparticle catalyst.
Experimental
Materials
The chemicals, copper nitrate (Cu(NO3)2·3H2O), nickel acetate (C4H6O4Ni·4H2O),
sodium
hydroxide
(NaOH),
hydrazine
hydrate
(N2H4·H2O,
85%),
polyoxyethylenesorbitan monooleate (Tweenꢀ80, C24H44O6), NMA, AMA, acetic acid,
and anhydrous ethanol were of reagent grade and were purchased from Sinopharm
Chemical Reagent Co., Ltd. China. Methanol was of chromatographic grade and was
purchased from Sinopharm Chemical Reagent Co., Ltd. China. All the chemicals were
used as received without further purification.
Preparation of CuxNiy nanoparticles
CuxNiy nanoparticles (x and y, mole fractions of Cu and Ni) were prepared by the wet
chemical reduction method using hydrazine hydrate as the reductant and Tweenꢀ80 as
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the organic modifier, respectively. Considering that Tweenꢀ80 could effectively
control the particle sizes of metallic Ni and Au nanoparticles and induce the
morphology evolution of metallic Ag nanoparticles due to the interaction between
Tweenꢀ80 molecules and metallic crystallites,29−31 Tween 80 was selected as the
organic modifier in our present work to control the particle sizes of CuxNiy
nanoparticles. To completely reduce Ni2+ to metallic Ni, a strong reductant, hydrazine
hydrate, was used. Typically, given amounts of copper nitrate and Tweenꢀ80 (0.38 g)
were dissolved in anhydrous ethanol with the Cu2+ concentration of 0.4 M. Prescribed
amount of nickel acetate ethanol solution (0.4 M) was added to the solution. After the
mixture was heated to 60 ºC, 40 mL of NaOH (1.8 M) ethanol solution was added
dropwise into it to adjust the pH value to ca. 10. Then, a hydrazine hydrate ethanol
solution (25 mL in 75 mL anhydrous ethanol) was added dropwise into the mixture
and the reaction mixture was refluxed for 4 h under mild stirring. After reduction with
hydrazine hydrate, the color of the reaction solution changed to black, indicating that
Cu2+ and Ni2+ were reduced to metallic Cu0 and Ni0, respectively. The resultant
CuxNiy nanoparticles were cooled to room temperature, centrifugated, washed with
anhydrous ethanol, and kept in anhydrous ethanol before they were characterized and
used as the catalysts for the hydrogenation of NMA. The preparation conditions of the
CuxNiy nanoparticles are listed in Table 1. The inductively coupled plasma (ICP)
analysis showed that the contents of Cu and Ni in the CuxNiy nanoparticles were close
to those calculated according to their precursors (Table 1).
For comparison, sole Cu and Ni nanoparticles were also prepared according to the
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aboveꢀmentioned procedures.
Characterization
The crystal phases of the asꢀprepared nanoparticle samples were determined by the
Xꢀray powder diffraction (XRD). The XRD spectra of the samples were recorded on a
diffractometer (D8 super speed BrukeꢀAEX Company, Germany) using Cu Kα
radiation (λ = 1.54056 Å) with a Ni filter at room temperature, scanning from 20º to
80º (2θ).
Transmission electron microscopy (TEM) and high resolution transmission electron
microscopy (HRTEM) images were obtained on a microscope (JEMꢀ2100) operated at
an acceleration voltage of 200 kV to characterize the morphologies and crystal
structures of the nanoparticle samples. Specimens for TEM analysis were prepared by
placing a drop of ethanol suspension of nanoparticle sample onto a copper grid coated
with a layer of amorphous carbon. The data used for the calculation of particle size
distribution for each sample were measured from the TEM images by counting at
least 100 individual particles. The average metal particle sizes of samples were
calculated by a weightedꢀaverage method according to the individual particle sizes of
the all counted particles. And the results are listed in Table 1.
The Cu and Ni contents of the CuxNiy nanoparticles were analyzed using
inductively coupled plasma (ICP) technique (VISTAꢀMPX).
Catalytic test
Catalytic hydrogenation of NMA with H2 was performed in a 500 mL capacity
stainless steel autoclave equipped with a magnetically driven impeller. The autoclave
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was charged with appointed amounts of NMA, methanol, and catalyst. Firstly, the
autoclave was purged with N2 for 10 min to replace the air inside. When the autoclave
was heated up to given reaction temperature at a stirring speed of 100 rpm, pure H2
was pressurized into the autoclave. After raising the pressure to the desired value, the
hydrogenation of NMA started at a stirring speed of 400 rpm. After reacting for a
certain time period, the autoclave was cooled to ambient temperature and
depressurized for product analysis.
The concentrations of products and remained NMA were analyzed on an Agilent
HPLC system equipped with a reverseꢀphase column (Innoval ASB C18, 5µm, 4.6
mm × 250 mm) and a UV detector (λ = 254 nm) at 30 ºC. A mixture of acetic acid
(0.5 wt.%) aqueous solution and methanol of chromatographic grade (v:v = 55:45)
was used as a mobile phase at a flow rate of 0.8 mL/min. The concentrations of
products and NMA were analyzed by the external standard method.
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Table 1 The catalytic activities of the CuxNiy nanoparticles for the catalytic hydrogenation of NMA with H2
Average
Raw materials (g)
Selectivities (%)
particle sizes
and size
NMA
Conversionsc
(%)
Cu/Ni atomic
ratiosa
TOFd
(h−1)
Catalysts
Cu(NO3)2 C4H6O4Ni
distributionsb
HAMA
AMA
·3H2O
·4H2O
(nm)
Cu
3.87
3.87
3.87
3.87
1.94
0
0
/
7.3, 4.0−11.2
5.3, 3.3−7.5
4.2, 2.8−6.1
4.6, 3.3−6.4
4.8, 3.4−6.7
3.8, 2.1−5.1
0
0
0
/
Cu0.9Ni0.1
Cu0.7Ni0.3
Cu0.5Ni0.5
Cu0.3Ni0.7
Nie
0.44
1.71
3.98
4.65
3.98
0.90:0.10
0.72:0.28
0.52:0.48
0.33:0.67
/
65.9
84.5
82.2
76.3
24.0
3.5
1.8
1.5
0.8
0.3
96.5
98.2
98.5
99.2
99.7
6.23
2.62
1.51
0.98
0.74
a The atomic ratios of Cu to Ni were determined by ICP.
b The metal particle sizes were determined from TEM images.
c Reaction conditions: NMA methanol solution, 150 mL, 0.2 mol L−1; H2 pressure, 0.8 MPa; reaction temperature, 120 ºC; reaction time, 2 h; catalyst loading, 1.0 g;
and stirring rate, 400 rpm.
d TOF = The moles of converted NMA divided by moles of Ni in CuxNiy catalysts and reaction time, assuming that pure Cu nanoparticles had no catalytic activity
under our present reaction conditions.
e The amount of monometallic Ni nanoparticles used in the catalytic reaction was the same as that present in the Cu0.7Ni0.3 catalyst.
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Results and discussion
XRD analysis
The XRD patterns of the monometallic Cu, monometallic Ni, and bimetallic CuxNiy
nanoparticles are shown in Fig. 1. The XRD pattern of the monometallic Cu
nanoparticle sample showed three diffraction peaks appearing at 2θ of 43.3, 50.4, and
74.1º, which are the characteristic peaks corresponding to the (111), (200), and (220)
planes of the faceꢀcenteredꢀcubic (fcc) copper (JCPDS 04ꢀ0836), respectively. For the
monometallic Ni nanoparticle sample, three peaks appearing at 2θ of 44.5, 51.8, and
76.4º corresponded to the (111), (200), and (220) planes of the faceꢀcenteredꢀcubic
(fcc) nickel (JCPDS 04ꢀ0850), respectively.32,33 No impurity diffraction peaks of
copper and nickel oxides were detected, indicating that phaseꢀpure monometallic Cu
and Ni nanoparticles were prepared under the present experimental conditions. For the
bimetallic Cu0.9Ni0.1, Cu0.7Ni0.3, and Cu0.5Ni0.5 samples, three diffraction peaks
appeared at 2θ of 43.4−43.6, 50.5−50.7, and 74.3−74.6o, respectively. These peaks
appeared between those of the monometallic Cu and Ni nanoparticles and the 2θ
shifted to large value upon increasing the Ni content, revealing that the Cu and Ni
components in the bimetallic Cu0.9Ni0.1, Cu0.7Ni0.3, and Cu0.5Ni0.5 samples formed
CuꢀNi alloy. However, For the Cu0.3Ni0.7 sample, in addition to the alloy diffraction
peaks, three diffraction peaks appearing at 2θ = 44.5, 51.8, 76.4º were indexed as the
(111), (200), and (220) planes of metallic Ni. When the mole fraction of Ni was
excessive in the bimetallic CuNi sample, in addition to CuꢀNi alloy, metallic Ni
nanoparticles were also formed.
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♦
♦
Ni
♦
Cu0.3Ni0.7
Cu0.5Ni0.5
Cu0.7Ni0.3
Cu0.9Ni0.1
•
•
•
Cu
*Cu0.7Ni0.3
Cu (JCPDS 04-0836)
Ni (JCPDS 04-0850)
10
20
30
40
50
60
70
80
2θ (°)
Fig.1. XRD patterns of Cu, Ni, and Cu−Ni samples. ●, Cu; ♦, Ni; *, spent catalyst.
TEM and HRTEM analysis
TEM and HRTEM were used to determine the morphologies, structures, and particle
sizes of the monometallic Cu, monometallic Ni, and bimetallic CuxNiy samples. The
TEM and HRTEM images are shown in Fig. 2. For the monometallic Cu sample, the
TEM image shows that spherical Cu nanoparticles were formed with the average
particle size of 7.3 nm and the particle size distribution of 4.0−11.2 nm (Fig. 2a1,
Table 1). The lattice fringes of the monometallic Cu nanoparticles were examined to
be 0.208 and 0.181 nm, being close to the (111) and (200) lattice spacings of fcc
metallic copper, respectively (Fig. 2a2). For the monometallic Ni sample, the
spherical Ni nanoparticles were formed with the average particle size of 3.8 nm and
the particle size distribution of 2.1−5.1 nm (Fig. 2f1). The lattice fringes of
monometallic Ni nanoparticles were examined to be 0.203 and 0.176 nm, which are
close to the (111) and (200) lattice spacings of fcc metallic nickel, respectively (Fig.
2f2).
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Fig. 2. TEM and HRTEM images of (a1,a2) Cu, (b1,b2) Cu0.9Ni0.1, (c1,c2) Cu0.7Ni0.3,
(d1,d2) Cu0.5Ni0.5, (e1,e2) Cu0.3Ni0.7 and (f1,f2) Ni samples.
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The TEM images (Figs. 2b1ꢀe1) of the bimetallic Cu0.9Ni0.1, Cu0.7Ni0.3, Cu0.5Ni0.5,
and Cu0.3Ni0.7 samples show that the asꢀprepared bimetallic nanoparticles had the
small average particle sizes of 4.2−5.3 nm and the narrow size distributions ranging
from 2.8 to 7.5 nm. The HRTEM images of the bimetallic Cu0.9Ni0.1, Cu0.7Ni0.3, and
Cu0.5Ni0.5 nanoparticles show that the individual nanoparticles were formed by the
coalesce of metallic Ni and Cu nanoparticles (Figs. 2b2ꢀd2). The lattice fringes of
0.208−210 nm were close to the (111) lattice spacing of fcc metallic copper while the
lattice fringes of 0.202 (or 0.203) and 0.175 (or 0.176) nm were close to the (111) and
(200) lattice spacings of fcc metallic nickel, respectively. The HRTEM results
certified the formation of CuꢀNi alloy in these bimetallic CuxNiy samples, being in
agreement with the results obtained by XRD analysis.
For the Cu0.3Ni0.7 sample, in addition to the CuꢀNi alloy nanoparticles, the
individual metallic Ni nanoparticles were also detected according to the HRTEM
analysis (Fig. 2e2).
Hydrogenation of NMA with H2 catalyzed by CuxNiy nanoparticles
The catalytic hydrogenation of NMA with H2 over the bimetallic CuxNiy nanoparticle
catalysts was carried out in a methanol solution at 120 ºC and 0.8 MPa H2 for 2 h. The
results are listed in Table 1. The monometallic Cu nanoparticles did not exhibit
activity for the hydrogenation of NMA. When the monometallic Ni nanoparticles
were used to catalyze the hydrogenation of NMA, the conversion of NMA was 24.0%
with the selectivity of AMA of 99.7%.
When the bimetallic Cu0.9Ni0.1, Cu0.7Ni0.3, Cu0.5Ni0.5, and Cu0.3Ni0.7 nanoparticles
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were used to catalyze the hydrogenation of NMA, the bimetallic Cu0.7Ni0.3 and
Cu0.5Ni0.5 catalysts exhibited high catalytic activities for the hydrogenation of NMA,
giving the NMA conversions of 84.5% and 82.2%, respectively. When the
hydrogenation of NMA was catalyzed by the bimetallic Cu0.7Ni0.3 and monometallic
Ni catalysts with the same Ni content, the conversion of NMA over the former was
more than 3.5 times that over the latter. The results revealed that the formation of
CuꢀNi alloy favored the hydrogenation of NMA.
Upon increasing the mole fraction of Ni in the bimetallic catalysts, the selectivities
of AMA slightly increased from 96.5% to 99.2% while the selectivities of the
intermediate product, 3ꢀhydroxaminoꢀ4ꢀmethylꢀacetylaniline (HAMA) decreased
from 3.5% to 0.8%. The monometallic Ni nanoparticles gave the highest selectivity of
AMA and the lowest selectivity of HAMA among all the tested catalysts. It could be
concluded that high Ni content in the catalyst favored the hydrogenation of HAMA to
AMA.
According to TOF values, it was interesting to find that the TOF values over the
bimetallic CuxNiy catalysts were higher than that of the monometallic Ni
nanoparticles (0.74 h–1). The bimetallic catalyst with a lower mole fraction of metallic
Ni gave higher TOF value. It was reasonable to suggest that the alloying interaction
between Cu and Ni in the bimetallic CuxNiy nanoparticles favored the hydrogenation
of NMA.
Considering that the Cu0.7Ni0.3 catalyst exhibited high catalytic activity for the
hydrogenation of NMA to AMA, it was selected as the model catalyst for
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investigating the effect of other reaction parameters on the catalytic hydrogenation of
NMA.
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Fig. 3. Effect of reaction temperature on the catalytic hydrogenation of NMA over the
bimetallic Cu0.7Ni0.3 nanoparticles. Reaction conditions: NMA methanol solution, 150
mL, 0.2 mol/L; H2 pressure, 0.8 MPa; catalyst loading, 1.0 g; and stirring rate, 400
rpm.
Effect of reaction temperature
Fig. 3 shows the conversions of NMA and the selectivities of HAMA and AMA in the
hydrogenation of NMA catalyzed by the bimetallic Cu0.7Ni0.3 catalyst at different
reaction temperatures. The NMA conversion and AMA selectivity increased while the
HAMA selectivity decreased upon increasing the reaction temperature. After reacting
o
at 140 C for 2 h, the selectivities of AMA and HAMA were 99.4% and 0.6% at the
NMA conversion of 95.7%. The results revealed that a high reaction temperature
favored the catalytic hydrogenation of NMA to AMA through HAMA because only
HAMA was detected as a byproduct.
Effect of NMA concentration
The NMA conversions and product selectivities in the hydrogenation of NMA over
the bimetallic Cu0.7Ni0.3 catalyst under different NMA concentrations are shown in
Fig. 4. When the reaction was carried out at 140 ºC and 0.8 MPa H2 for 2 h, the
conversions of NMA and the selectivities of AMA decreased from 99.1% to 82.7%
and from 99.9% to 92.5%, respectively, upon increasing the NMA concentrations
from 0.15 to 0.25 mol/L. NMA was efficiently hydrogenated to AMA under the NMA
concentration of less than 0.25 mol/L.
Effect of H2 pressure
When NMA was hydrogenated over the bimetallic Cu0.7Ni0.3 catalyst at different H2
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pressures and 140 ºC for 2 h, the NMA conversion and AMA selectivity reached 100%
and 99.9%, respectively, upon increasing the H2 pressure to 1.2 MPa (Fig. 5). High H2
pressure favored the catalytic hydrogenation of NMA to AMA.
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Fig. 4. Effect of NMA concentration on the catalytic hydrogenation of NMA over the
bimetallic Cu0.7Ni0.3 nanoparticles. Reaction conditions: NMA methanol solution, 150
mL; H2 pressure, 0.8 MPa; reaction temperature, 140 ºC; catalyst loading, 1.0 g; and
stirring rate, 400 rpm.
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Fig. 5. Effect of H2 pressure on the catalytic hydrogenation of NMA over the
bimetallic Cu0.7Ni0.3 nanoparticles. Reaction conditions: NMA methanol solution, 150
mL, 0.2 mol/L; reaction temperature, 140 ºC; catalyst loading, 1.0 g; and stirring rate,
400 rpm.
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Fig. 6. Effect of catalyst loading on the catalytic hydrogenation of NMA over the
bimetallic Cu0.7Ni0.3 nanoparticles. Reaction conditions: NMA methanol solution, 150
mL, 0.2 mol/L; H2 pressure, 0.8 MPa; reaction temperature, 140 ºC; and stirring rate,
400 rpm.
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Effect of catalyst loading
The conversions of NMA and the selectivities of HAMA and AMA in the
hydrogenation of NMA catalyzed by the bimetallic Cu0.7Ni0.3 catalyst at 140 ºC with
different catalyst loadings are shown in Fig. 6. When the catalyst loading was 1.4 g,
the NMA conversion was 99.9% with the AMA selectivity of 99.6%. The results
demonstrated that high catalyst loading favored the conversion of NMA to AMA.
Reaction kinetics
Experimental conditions for kinetic research
A powerꢀfunction type reaction kinetic equation was used to evaluate the effect of the
NMA concentration, H2 pressure, and reaction temperature on the reaction rate of
NMA hydrogenation. The bimetallic Cu0.7Ni0.3 nanoparticle catalyst was selected as
the model catalyst because it exhibited good catalytic performance for the
hydrogenation of NMA.
In order to eliminate the effect of diffusion, the bimetallic Cu0.7Ni0.3 catalyst with
different loadings in the range of 0.6–1.4 g was used for the catalytic hydrogenation
of NMA (0.2 mol/L) at 140 ºC for 0.5 h. Plotting catalyst loading vs NMA conversion
gave a straight line (Fig. S1). This result indicated that the initial hydrogenation rate
was controlled solely by chemical reaction rather than mass diffusion.34,35
The powerꢀfunction type reaction kinetic equation for the hydrogenation of NMA is
listed as follows.
a
b
r0
=
−
d
n
0/(d
t·W
cat) = kC0 P0
(1)
a and b are the reaction orders with respect to the
where
k
is the rate constant.
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concentration of NMA and H2 pressure.
r0 is the initial reaction rate of NMA, mol/h·g.
C
0 is the initial concentration of NMA, mol/L. P0 is the initial H2 pressure, MPa. Wcat
is the catalyst weight, g.
The rate constant
exp(−Ea RT
k
follows the Arrhenius equation Eq. (2).
k
=
A
/
) (2)
where
A
is the preꢀexponential factor and Ea is the activation energy, kJ/mol. R is the
10−3 kJ/mol·K. T is the reaction temperature, K.
ideal gas constant, 8.314
×
In the kinetic experiments, the H2 pressure is taken constant because the consumed
H2 mount is negligible as compared with the initial H2 feed at a lower NMA
conversion. The initial NMA concentration is used as the value of NMA concentration
variable considering that the plot of NMA conversion vs reaction time can be taken as
a straight line at a lower NMA conversion.
Determination of kinetic parameters
By taking the natural logarithm of both sides of the Eq. (1), a linear Eq. (3) is obtained
as follows.
ln
r
0 = ln(
−
d
n
0/(dt·Wcat)) = ln
k
+
a
lnC0
+
b
lnP0
(3)
To simulate the reaction orders of
a
and
b
according to Eq. (3), NMA methanol
solution with different concentrations was fed into the stainless steel autoclave and
then reacted over 1.0 g of Cu0.7Ni0.3 nanoparticle catalyst under different H2 pressures.
The conversions of NMA at the reaction temperatures of 100−140 ºC are listed in Fig.
S2. The initial reaction rates of NMA were calculated at the first 0.5 h.
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Fig. 7. Estimation of (a,b) the reaction orders and (c) the reaction activation energy
for the powerꢀfunction type reaction kinetic equation over the bimetallic Cu0.7Ni0.3
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catalyst.
Fig. 7a shows the lines by plotting lnr0 vs lnC0 while Fig. 7b shows the lines by
plotting lnr0 vs ln 0 at the reaction temperatures ranging from 100 to 140 ºC. All the
straight lines gave good linear correlations above 0.995. The slopes were close to each
other in each figure. The average values of the reaction orders, and , for NMA and
P
a
b
H2 were 0.45 and 1.15, respectively, which were calculated according to the slopes
(Table 2).
According to Eq. (3), the rate constants (
calculated by using the obtained values of the reaction orders,
A linear Eq. (4) is obtained by taking the natural logarithm of both sides of the Eq.
(2).
ln
k
) at different reaction temperatures were
a
and
b.
k
= lnA −
(Ea/R
)(1/T)
(4)
By plotting lnk vs 1/T, a straight line with the correlation coefficient of 0.9936 was
obtained (Fig. 7c). The reaction activation energy (Ea) of 19.74 kJ mol−1 and
preꢀexponential factor (A) of 13.59 were calculated according to the slope and
intercept of the straight line (Table 2).
Table 2 Reaction orders, activation energy, and preꢀexponential factor of the reaction
kinetics
Reaction orders
Reaction
temperatures
T /ºC
Preꢀexponential
Ea
/kJ·molꢀ1
ln k
factor
A
Average
Average
a
b
a
b
100
0.45
0.45
0.44
1.16
1.15
1.13
ꢀ3.77103
ꢀ3.40485
ꢀ3.15587
120
0.45
1.15
19.74
13.59
140
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The reaction kinetic equation for the catalytic hydrogenation of NMA over the
bimetallic Cu0.7Ni0.3 catalyst was written as follows.
1.15
C00.45P0
r0
=
−d
n
0/(d
t·W
cat) = 13.59 exp(
−
19.74/RT
)
mol/h·g
(5)
Catalyst recycling performance
The recycling performance of the bimetallic Cu0.7Ni0.3 catalyst for the catalytic
hydrogenation of NMA was also investigated and the results are shown in Fig. 8.
After reacting at 140 ºC for 2 h, the used catalyst was centrifugated and washed with
anhydrous ethanol before next recycling. The XRD pattern of the spent catalyst was
the same as that of the fresh one (Fig. 1). The conversion of NMA and the selectivity
of AMA over the fresh Cu0.7Ni0.3 nanoparticles were 95.7% and 99.4%, respectively.
After recycling for 4 times, the NMA conversion and AMA selectivity slightly
decreased to 93.5% and 96.8%, respectively. It is clear that the bimetallic Cu0.7Ni0.3
catalyst exhibited excellent recycling performance and stability for the catalytic
hydrogenation of NMA to AMA.
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100
80
60
40
20
0
ConvNMA
SelAMA
SelHAMA
1
2
3
4
5
Running Time
Fig. 8. Recycling performance of the bimetallic Cu0.7Ni0.3 catalyst for the catalytic
hydrogenation of NMA. Reaction conditions: NMA methanol solution, 150 mL, 0.2
mol/L; H2 pressure, 0.8 MPa; reaction time, 2 h; reaction temperature, 140 ºC; catalyst
loading, 1.0 g; and stirring rate, 400 rpm.
Conclusions
Monometallic Cu, monometallic Ni, and bimetallic CuxNiy nanoparticles with the
small particle sizes and narrow size distributions were successfully prepared by the
wet chemical reduction method using Tween as the organic modifier and hydrazine
hydrate as the reductant. CuꢀNi alloy phase was formed in the bimetallic CuxNiy
nanoparticles. The formation of CuꢀNi alloy phase in the bimetallic CuxNiy
nanoparticles favored the hydrogenation of NMA with H2 to AMA. The bimetallic
Cu0.7Ni0.3 catalyst exhibited good stability without obvious deactivation after
recycling for 4 times. A powerꢀfunction type reaction kinetic model over the
bimetallic Cu0.7Ni0.3 catalyst well fitted the experimental data, r0
= −dn0/(dt·Wcat) =
kC00.45P01.15, and the reaction activation energy was 19.74 kJ mol−1. The bimetallic
CuxNiy nanoparticle catalyst probably has potential application for catalytic
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hydrogenation of other reducible chemicals.
Acknowledgements
This work was financially supported by National Natural Science Foundation of
China (21506078 and 21506082 and), Research Foundation of Jiangsu University
(15JDG026), China Postdoctoral Science Foundation (2016M591786 and
2016M601739) and Jiangsu Planned Projects for Postdoctoral Research Funds
(1601084B).
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