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Promotion Effect of Mo in Amorphous Ni-P Catalystsfor the Liquid-Phase Catalytic Hydrogenation ofNitrobenzene to AnilineZu-zeng Qin a b , Zi-li Liu a b & Yan-hua Wang ba School of Chemistry and Chemical Engineering, Guangxi University , Nanning , Guangxi ,Chinab School of Chemistry and Chemical Engineering, Guangzhou University , Guangzhou ,Guangdong , ChinaAccepted author version posted online: 02 Aug 2013.
To cite this article: Chemical Engineering Communications (2013): Promotion Effect of Mo in Amorphous Ni-P Catalystsfor the Liquid-Phase Catalytic Hydrogenation of Nitrobenzene to Aniline, Chemical Engineering Communications, DOI:10.1080/00986445.2013.773422
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Promotion Effect of Mo in Amorphous Ni-P Catalysts for the Liquid-phase Catalytic
Hydrogenation of Nitrobenzene to Aniline
Zu-zeng Qin1,2,, Zi-li Liu1,2,, Yan-hua Wang2
1School of Chemistry and Chemical Engineering, Guangxi University, Nanning, Guangxi, China 2School of Chemistry and Chemical Engineering, Guangzhou University,
Guangzhou, Guangdong, China
Corresponding author. , Tel: +86 20 39366506, Fax: +86 20 39366903 E-mail: [email protected] (Prof. Z-l Liu), [email protected] (Dr. Z-z Qin)
Abstract Amorphous Ni-P catalysts were prepared via a chemical reduction method, and the promotional effects of Mo on the hydrogenation of nitrobenzene to aniline on Ni-P catalyst were investigated. However, the two crystallization temperatures of the 1% Ni-Mo-P catalyst were 644 K and 723K, which were 15 K and 43 K higher, respectively, than those of the Ni-P catalyst itself; these results indicate that the presence of Mo increased the thermal stability of the Ni-P catalysts. SEM results showed that the particle size of the active component of Ni-P in the 1.0% Ni-Mo-P catalyst was smaller than that in the amorphous Ni-P catalyst. The N2 adsorption isotherms for the amorphous Ni-Mo-P catalysts were the III-type, and the N2 isothermal adsorption-desorption curves exhibited H3-type hysteresis loops. H2-TPR results showed that the addition of Mo had no effect on the reduction of NiO in the catalyst but negatively affected the reduction of Ni-P-O. H2-TPD results showed that the hydrogen adsorption capacity of the amorphous Ni-P catalysts can be enhanced through the addition of Mo, and the optimal amount of Mo was determined to be 1.0%. The XPS results indicated the presence of a small amount of free metallic Mo in the amorphous Ni-Mo-P catalysts in addition to the Mo in MoO3. The use of the 1% amorphous Ni-Mo-P catalyst at 383 K and under 1.0 MPa of hydrogen for 3.0 h resulted in a nitrobenzene conversion rate and aniline selectivity of 64.5% and 98.8%, respectively.
KEYWORDS: Amorphous Ni-Mo-P catalyst; Nitrobenzene; Aniline; Hydrogenation
INTRODUCTION
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Aniline, an important intermediate in synthetic chemistry, is widely used in the
manufacture of polyurethanes, dyes, rubber chemicals, explosives, pharmaceuticals and
pesticides (Travis, 2007; Zhang et al., 2007). The main methods for production of aniline
are the reduction of nitrobenzene by Fe powder and/or hydrogenation methods, reactions
of phenol ammonia soda (Zhang, 2007), selective photoreduction on TiO2 nanoparticles
(Huang et al., 2010), selective hydrogenation in condensed-phase carbon dioxide over
Ni/γ-Al2O3(Meng et al., 2009), catalytic reduction of nitrobenzene on Ru3(CO)12 by
CO/H2O (Ragaini et al., 2001), catalytic hydrogenation over a Cu/SiO2 (Diao et al.,
2005), Pt/RGO(Nie et al., 2012), C60(Li et al., 2009), Ni-5/SiO2(Wang et al., 2010), or
Cu-Zr amorphous alloy (Jiang et al., 2003) catalyst. Among these methods, the catalytic
hydrogenation of nitrobenzene to aniline is of special interest to researchers in this field
because the starting materials are easily obtained and inexpensive and because the
production process is simple (Lee et al., 2000a; Meng et al., 2009).
Because of their structural characteristics of short-range order and long-range disorder,
amorphous alloy catalysts are a promising class of catalyst for commercial applications.
Such catalysts often exhibit high catalytic activity (Wu et al., 2005; Zhao et al., 2006).
Metal-B catalysts, which are typically prepared using KBH4 as a reducing agent, have
been investigated to a greater extent than metal-P catalysts (Li et al., 2004; Liu et al.,
2007). However, the latter have a significant cost advantage because they are prepared
using relatively inexpensive phosphate compounds as reducing agents.
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Lee et al. (Lee et al., 2000b) and Okamoto et al. (Okamoto et al., 1980) have studied the
hydrogenation of nitrobenzene on Ni-P ultrafine materials. The authors prepared
amorphous Ni-P alloy catalysts supported on carbon nanofibers, which exhibited high
catalytic activity in the liquid-phase hydrogenation of nitrobenzene to aniline (Xie et al.,
2009). The addition of small amounts of other metals affected the catalytic activity of the
amorphous catalysts (Sun et al., 2006; Yan et al., 2006).
In our previous study (Liu et al., 2010; Liu et al., 2012), we used Ni-P amorphous alloy
as a catalyst for the hydrogenation of nitrobenzene to aniline. The nitrobenzene
conversion was only 55%, and the aniline yield was only 53%. In the present study, to
improve the conversion of nitrobenzene and the yield of aniline, we added Mo to
investigate its effect on the catalytic activity of the amorphous Ni-P catalyst. The
Mo-enhanced catalysts were characterized with respect to nitrogen adsorption, X-ray
diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron
spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR),
temperature-programmed desorption (TPD), differential scanning calorimetry (DSC), and
hydrogenation activity. The Ni-P catalyst prepared previously (Liu et al., 2010) was
included in this study for comparison.
MATERIAL AND METHODS
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Preparation And Characterization Of Catalysts
Amorphous Ni-P and Ni-Mo-P catalysts were prepared using chemical reduction methods.
Mixtures of NaH2PO2·H2O, NiCl2·6H2O, and CH3COONa (used as a dispersant) at molar
ratios of nP:nNi:nNa=8:4:1, and Mo (xMo=nMo/(nMo+nNi), where xMo, nMo and nNi are the
mole fraction of Mo, and the moles of Mo and Ni, respectively, were added to 100 mL of
distilled water. The pH of the solution was adjusted to 11 by the addition of 5 mol·L-1
NaOH while stirring at 363 K. After an induction reaction period, a black precipitate was
formed and was accompanied by the evolution of gas bubbles. When the bubbles were no
longer generated in the solution, the reaction in mixture solution was stopped, and the
precipitate was collected by filtration of the solution. The precipitate was washed with
NH3·H2O solution and distilled water until no chloride ion was detected in the filtrate;
0.5-mol·L-1 AgNO3 solution was used as the chloride-ion indicator. The precipitate was
then washed with ethanol several times and stored in ethanol.
The amorphous Ni-P catalysts modified by 1% Ca, Mg, Mn, Fe, Co, Cu, Zn, La, or Ce
were followed the preparation method of the amorphous Ni-Mo-P catalysts (xMo=1%).
Nitrobenzene Catalytic Hydrogenation To Aniline On Amorphous Ni-Mo-P Catalysts
Two hundred milligrams of amorphous Ni-Mo-P catalyst (nP/nNi=4, xMo=1.0%), 2.0 g of
nitrobenzene and 8.0 g of anhydrous ethanol were added to a 100 mL high-pressure
reaction vessel equipped with a magnetic stirrer. Air in the vessel was displaced by
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hydrogen, and then additional hydrogen was added to a pressure of 1.0 MPa. The vessel
was subsequently heated to 383 K, and the components were allowed to react for 3 h at a
stirring speed of 600 r·min-1. After removal of the reaction mixture from the vessel, the
catalyst was recovered by filtration, and the product solution was analyzed by gas
chromatography (Agilent 6890). The gas chromatograph was configured as follows: a
DB-1 column was used; the injection port temperature was 523 K; the detector
temperature was 553 K; the column temperature was programmed (initial temperature of
363 K, maintained 1.5 min, and then heated to 423 K at 6 K·min-1, and held for 3 min).
The target product, aniline, was quantitatively analyzed using the peak-area internal
standard method with toluene as the internal standard.
Characterization Of Catalysts
Samples of the synthesized catalysts were characterized by X-ray diffraction (XRD)
(Beijing Purkinje General Instrument Co., XD-3), scanning electron microscopy (SEM)
(JEOL JSM-6360LA, 10 kV), N2 adsorption-desorption (Micromeritics Instrument
Corporation, ASAP 2020), and differential scanning calorimetry (DSC) (TA Instruments,
SDT Q600). Based on the adsorption branches of the N2 sorption isotherms, the
Brunauer-Emmett-Teller (BET) method was used to calculate the specific surface area
and the Barrett-Joyner-Halenda (BJH) model was used to calculate the pore volume and
average pore radius of the catalyst under study. The H2-TPR and H2-TPD experiments
were conducted on a TP-5000 multi-function adsorption instrument (Tianjin Xianquan
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Industry and Trade Development Co.) equipped with a TCD detector. The oxidation state
and surface composition were analyzed using an X-ray photoelectron spectrometer (XPS)
(Kratos Ultra Axis DLD), equipped with an Al Kα radiation source. The energy resolution
of the spectrometer was 0.48 eV. The peak positions were corrected for sample charging
by setting the C1s binding energy at 284.8 eV. The XPS analysis was conducted at 150 W
and at a pass energy of 40 eV.
RESULTS AND DISCUSSION
The effects of metal-modified amorphous Ni-P catalyst on hydrogenation of
nitrobenzene
A screening process was conducted to confirm the effects of metal-modified on the
catalytic activities of amorphous Ni-P catalysts. After modified by 1% (mol) metal,
amorphous Ni-M-P was applied in the hydrogenation of nitrobenzene to aniline, the
results were shown in Table 1, as a comparison, the results of amorphous Ni-P (Liu et al.,
2010) used as catalyst was also list. After modified by Al, Ca, Mg, Fe, Cu, La, and Ce,
the conversion of nitrobenzene and yield of aniline were decreased to some extent, which
indicated these metal have negative effect on the activity of amorphous Ni-P catalyst. In
the other hand, using the Ni-P modified by Mn, Co, Zn, and Mo as hydrogenation
catalysts, the conversion of nitrobenzene and yield of aniline were increased, and the
order of promoting effect was: Mo> Co> Zn ≈ Mn. From the above data, Mo was
selected as a promoter in the following study.
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The Effects Of Mo On The Catalytic Reduction Of Nitrobenzene To Aniline Using
Amorphous Ni-Mo-P Catalysts
The influence of the Mo content on the catalytic reduction of nitrobenzene to aniline
using amorphous Ni-Mo-P catalysts is shown in Table 2, as a comparison, the results of
amorphous Ni-P (Liu et al., 2010) used as catalyst was also list.
As evident from the results in Table 2, the amount of Mo had very little effect on the
hydrogenation selectivity of nitrobenzene to aniline (approximately 98%) in this study.
When the amount of Mo was equal to 1.0% or less, the conversion of nitrobenzene and
the yield of the aniline increased as the amount of Mo was increased from 0 to 0.5% to
1%, at which point the conversion of nitrobenzene and the yield of aniline peaked 64.5%
and 63.7%, respectively. These values are 9.3 and 9.9 percentage points higher than those
achieved with the amorphous Ni-P catalyst alone. As the amount of Mo was increased
further from 1.5% to 3.0% to 5.0%, the conversion of nitrobenzene and the yield of
aniline decreased. At 5% Mo, the conversion of nitrobenzene and the yield of the aniline
were 34.6% and 34.2%, respectively, which were actually less than the values achieved
with the amorphous Ni-P catalyst itself. These data clearly indicated that the addition of
an appropriate amount of Mo would significantly improve the catalytic activity of the
amorphous Ni-P catalyst when used in the catalytic hydrogenation of nitrobenzene to
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aniline and show that the best-performing catalyst is that in which the amount of added
Mo is 1.0%.
XRD Patterns Of Amorphous Ni-Mo-P Catalysts
The crystalline structures of the prepared catalysts were analyzed by XRD. The XRD
patterns of the prepared catalysts with different Mo contents are shown in Fig. 1.
Figure 1 shows that no sharp diffraction peaks were observed in the XRD patterns of the
catalysts; only a single and dispersion peak, which was attributed to metallic Ni, was
found at 2θ approximately 45o; the presence of this peak indicated that the Ni-Mo-P
catalysts retained an amorphous structure (van Wonterghem et al., 1986). With increasing
amounts of Mo beyond 1.5%, the intensity of the dispersion peaks at 2θ approximately
45o merely increased, and obvious diffraction peaks were not found. These results
indicate that although the amorphous nature of the catalysts decreased, no crystal phases
were found; these results also suggest that the addition of Mo had little effect on the
amorphous nature of the Ni-P catalysts.
SEM Study Of The Amorphous Ni-Mo-P Catalyst
The size, size distribution and morphology of the catalyst particles are important
parameters that affect catalytic activity. Therefore, the morphology of the amorphous
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Ni-P and Ni-Mo-P catalysts (nP/nNi=4, xMo=1.0%) were studied by scanning electron
microscopy (SEM), and some of the resulting images are shown in Fig. 2.
The amorphous Ni-P catalyst consisted of agglomerated spherical particles with
diameters of approximately 0.4-0.8 µm. A layer of white matter, which was MoO3(Liu et
al., 2012), was found on the amorphous Ni-Mo-P (nP/nNi=4, xMo=1.0%) catalyst, and the
particle diameter of the Ni-P spheroids was approximately 0.2-0.5 µm; i.e., smaller than
the spheres in the pure amorphous Ni-P catalyst. These images reveal that the amorphous
Ni-Mo-P catalyst has more surface area than that of amorphous Ni-P catalyst and which
allows for more active sites. The increased number of active sites may be one the reason
that helps account for the higher catalytic activity of the Ni-Mo-P catalyst when used for
the hydrogenation nitrobenzene to aniline.
DSC Analysis Of Amorphous Ni-Mo-P Catalysts
Differential scanning calorimetry (DSC) was used to investigate the thermal stability of
the amorphous Ni-Mo-P catalysts. The results are shown in Fig. 3.
These data show that when the amount of Mo was increased from 0 to 0.5% to 1.0%, the
crystallization temperature of the amorphous Ni-Mo-P catalyst also increased, reaching
644 K and 723 K, respectively, when the amount of Mo was 1.0%. These crystallization
temperatures are 16 K and 43 K higher than those observed in the case of the amorphous
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Ni-P catalyst. This increase indicates that the introduction of Mo improved the thermal
stability of the amorphous Ni-P catalyst. After Mo was added, Mo adhered to the active
sites in the form of MoO3 on the amorphous Ni-P bulk, which could effectively disperse
the active components on the catalyst (Chen et al., 2002), thereby preventing the
agglomeration of the active components of the catalysts and thereby enhance the thermal
stability of the amorphous Ni-P catalyst(Shi et al., 2006). When the amount of Mo added
was 1.5%, the crystallization temperature was approximately the same as that of the
catalyst that contained 1.0% of added Mo. When the amount of Mo was increased to
3.0% and 5.0%, broad exothermic peaks were observed at 715 K and 659 K, respectively.
As the amount of Mo was increased, the active components of the amorphous Ni-Mo-P
catalyst, such as MoO3, were well dispersed, which led to the crystallization process
becoming slower with increasing of the temperature. On the other hand, there may be
interactions between Mo and Ni-P amorphous alloy(Qi et al., 2012), the atomic radius of
Mo element is larger than that of Ni, which would reduce the diffusion rate of Ni atoms
and make it difficult to be crystallization(Walter, 1981; Zhang et al., 2001). Therefore,
added Mo, the thermal stability of the amorphous Ni-P alloy will be improved. However,
at even higher levels of Mo, e. g. the amount of Mo added was above 1.0%, the active
sites on the amorphous Ni-Mo-P catalyst will be hindered, which will lead to a decrease
of the catalytic activity. In summary, these experiments show that 1% added Mo is the
optimal amount of Mo to maximize both the thermal stability and the catalytic activity
toward the conversion of nitrobenzene to aniline.
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The N2 Sorption Isotherms And The Pore Distributions Of Amorphous Ni-Mo-P
Catalysts
To investigate the N2 sorption, the surface area, and the pore size distribution, N2
adsorption-desorption experiments were conducted with the results shown in Fig. 4.
As shown in Fig. 4, the N2 adsorption isotherms of the amorphous Ni-Mo-P catalysts
with different amount of Mo exhibit type III isotherms. At low relative pressures, the
isotherm plots exhibit a region of mildly increasing N2 adsorption, which is related to
monolayer adsorption becoming multi-layer adsorption (Rouquerol et al., 1999).
Combined with the desorption curve, an obviously H3-type hysteresis loop (He et al.,
2004) was observed between the low-pressure section and the saturation vapor pressure
for all of the catalysts. These hysteresis loops indicated that the added Mo did not destroy
the pore structure of the amorphous Ni-Mo-P catalysts. The inset of Fig. 4 shows the pore
size distribution curve calculated for the desorption branch of the N2 isotherm based on
the BJH method. These data show that the amorphous Ni-Mo-P catalysts, independent of
their Mo content, contain a large number of small microspores (2-3 nm), which suggests
that the diameter of most of the pores in the catalysts is also independent of the amount of
Mo.
The BET surface area, the cumulative desorption pore volume determined using the BJH
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method and the average pore radius of the amorphous Ni-Mo-P catalysts are shown in
Table 3. With increasing amounts of Mo, the surface area, pore volume, and average pore
radius increased, which was a result of the increased amount of Mo oxide in the catalyst.
Based on the previously discussed results, the optimal amount of Mo in the catalyst for
the hydrogenation of nitrobenzene is 1.0%. The fact that the yield of aniline decreases
when the amount of Mo is greater than 1%, despite the fact that the surface area
continues to grow, suggests that the additional Mo results in the formation of Mo oxide
which fouls the catalytic surface (Chen et al., 2002).
H2-TPR Analysis Of Amorphous Ni-Mo-P Catalysts
Temperature-programmed reduction (TPR) experiments were conducted to investigate
the reduction performance of the amorphous the Ni-Mo-P catalysts. The results are
shown in Fig. 5.
Two hydrogen consumption peaks were observed in the profile of the amorphous Ni-P
catalyst (curve “a” in Fig. 5) at 388 K and 616 K, which were attributed to the reduction
peaks of the NiO and Ni-P-O species (Zong et al., 1991a; Zong et al., 1991b),
respectively. The peak at 390 K was also observed in the profiles of all of the Mo-Ni-P
catalysts, which indicated that the addition of Mo had little effect on the reduction of NiO.
A new consumption peak was observed at approximately 580 K in the profiles of these
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Mo-modified catalysts and was attributed to the reduction of Mo oxide in the catalysts;
the areas of the peaks increased with the increasing amounts of Mo in the catalysts. The
third consumption peak in the profiles of these catalysts was attributed to an
up-temperature shift of the peak for the reduction of the Ni-P-O species between 616 K
and 672 K, and the temperature and peak area increased with increased amounts of Mo in
the catalysts. This observation indicated that the reduction of the Ni-P-O species was
became more difficult after the Mo was added and that the amounts of these Ni-P-O
species increased with increasing amounts of Mo.
In this regard, the additional Mo negatively affected the catalytic hydrogenation activity
of the amorphous Ni-P catalysts. However, the reduction peak of NiO at approximately
390K in the profile of the 1.0% amorphous Ni-Mo-P catalyst became obviously weaker,
which indicates that this catalyst contains less NiO and more Ni-P active compounds
because the additional Mo increases the dispersion of the precursor of the active
component that makes the Mo fully reduced. Therefore, the addition of 1.0% Mo
improved the catalytic hydrogenation performance of the amorphous Ni-P catalyst.
H2-TPD Profiles Of Amorphous Ni-Mo-P Catalysts
To investigate the hydrogen adsorption properties of the amorphous Ni-Mo-P catalysts,
the H2 temperature-programmed desorption (H2-TPD) of the catalysts was examined. The
results are shown in Fig. 6.
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As shown in Fig. 6, a desorption peak was observed near 406 K in the H2-TPD curve of
the amorphous Ni-P catalyst. After the Mo was added to the amorphous Ni-P catalyst, no
new desorption peaks appeared in the H2-TPD curve. The position of the desorption peak
shifted continuously to higher temperatures as the amount of Mo was increased, which
indicated that the properties of hydrogen adsorption were enhanced with the addition of
Mo (Lei et al., 2007) and that no new active sites were formed. However, for the 5% Mo
catalyst, the peak became a shoulder peak, which indicated that the adsorbed hydrogen on
the catalyst could not be desorbed. At lower Mo contents, such as 0.5%, the intensity of
the hydrogen adsorption peak was somewhat weak. In contrast, the intensity of hydrogen
adsorption peak was so high at higher Mo amounts, such as 1.5%, 3.0%, and 5%, that the
desorption of the adsorbed hydrogen was difficult. In general, the stronger or weaker
adsorption of reactants on catalysts is detrimental to the catalytic activity. Therefore, in
the present study, the catalytic hydrogenation of the amorphous Ni-P catalysts was
adjusted through the addition of Mo to change the strength of the hydrogen adsorption,
and the optimal Mo content in the present study was found to be 1.0%.
XPS Analysis Of Amorphous Ni-P And Ni-Mo-P Catalysts
To obtain information about the distribution of Mo and the promoter on the support, the
amorphous Ni-P and Ni-Mo-P (nP/nNi=4, xMo=1.0%) catalysts were studied by XPS. The
results are shown in Fig. 7.
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From the XPS spectrum of Ni 2p, the binding energy of Ni 2p was 853.8 eV, even after
the Mo was added, which was attributed to the Ni 2p3/2 of Ni metal. The binding-energy
peaks at 870.8 eV (amorphous Ni-P catalyst) and 870.3 eV (amorphous 1% Ni-Mo-P
catalyst) were attributed to the Ni 2p 1/2 of Ni metal (Li et al., 1999; Liu et al., 2005; Xie
et al., 2005), The binding energy of the Ni 2p 1/2 decreased by 0.5 eV in the Ni-Mo-P
catalyst, which indicated that the Ni in the catalyst was in an electron-loss state. The
binding energy peaks at 859.3 eV and 859.7 eV were attributed to the 2p 3/2 of Ni; these
peaks resulted form the formation of Ni-P alloys. These results show that the
modification with Mo changed the alloys formed between Ni and P (Thube et al., 1986).
The peak position and peak intensity of the peaks at a binding energy of 854.0 eV, which
were attributed to the Ni 2p 3/2 in Ni-O, remained unchanged, which indicated that the
combination of Ni and O was less affected by the modification with Mo(González-Elipe
et al., 1989; Khawaja et al., 1989).
From the XPS spectrum of P 2p, the binding energy of the P 2p 3/2 increased from 130.8
eV to 131.3 eV after Mo was added to the catalyst. This 0.5 eV increase in the binding
energy indicated that the P in the catalyst was in an electron-gain state after Mo
modification. Therefore, in the amorphous Ni-Mo-P catalyst, the method of activation of
the H-H bond in the hydrogen molecules might be heterolysis, i.e., the H-H bond may
break into H+ and H- active groups with an asymmetric distribution of electrons between
the two protons(Liu et al., 2008; Sakamoto et al., 2009).
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Based on the XPS spectrum of Mo 3d, the binding energies of the Mo 3d electrons were
226.2 eV, 230.2 eV, and 233.3 eV, which were attributed to the Mo 3d 5/2 of Mo metal
and to the Mo 3d5/2 and Mo 3d3/2 of MoO3 (Parks et al., 2007; Chen et al., 2009; Wang
et al., 2009), respectively. These data show that in addition to the Mo in MoO3, a small
amount of free Mo metal was present in the amorphous Ni-Mo-P catalysts. The standard
binding energy of Mo 3d 5/2 was 227.7 eV(Parks et al., 2007), which is a 1.5 eV higher
than that of Mo metal in the amorphous Ni-Mo-P catalysts. This result indicates that the
Mo mental was in an electron-loss state in the catalyst.
In summary, after the addition of Mo, although an overall balance of electrons is achieved
in the system, a defect potential that results from the uneven local charge distribution that
was formed in the amorphous Ni-Mo-P catalysts is present. This uneven defect potential
results in a condition that is conductive to the adsorption of O atoms in the N=O bonds of
the nitrobenzene. In addition, the polarization between Mo6+ in MoO3 and the N=O group
(Liu et al., 2007) in active nitrobenzene will lead to an advanced effect on the catalytic
hydrogenation reaction(Ren et al., 2008). Therefore, the nitrobenzene catalytic
hydrogenation to aniline on the amorphous Ni-P catalysts is promoted by an alteration of
the electronic structure of the amorphous Ni-P catalyst induced by the addition of Mo,
which results in the generation of the optimal amount of MoO3.
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Conclusions
In this study, the addition of Mo increased the conversion of nitrobenzene and improved
the overall catalytic activity of the amorphous Ni-P catalyst; the optimal amount of Mo
was determined to be 1% (mole fraction). When such a 1% amorphous Ni-Mo-P catalyst
was used at 383 K and under 1.0 MPa of hydrogen for 3.0 h, the conversion of
nitrobenzene and the selectivity for aniline were 64.5% and 98.8%, respectively. The
introduction of a small amount of Mo can increase the crystallization temperature of the
amorphous Ni-P catalyst, which improves the thermal stability of the catalyst. New
hydrogen adsorption centers that exhibited higher adsorption intensity were formed in the
presence of the added Mo, which can enhance the activation capability of the metal
center of the catalyst. In the catalysts, Mo was found in an oxidized state, and a smaller
proportion was present as metallic Mo.
ACKNOWLEDGEMENT
This work was supported by National Natural Science Foundation of China (No.
21006013).
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Table 1 Performance of amorphous Ni-P catalyst modified with different metal for
nitrobenzene hydrogenation to aniline
Catalysta Conversion of
nitrobenzene/ %
Selectivity of
aniline/ %
Yield of aniline
/ %
Ni-Pb 55.2 97.5 53.8
Ni-Al-P 19 98.6 18.7
Ni-Ca-P 50.4 98.6 49.7
Ni-Mg-P 49.5 98 48.5
Ni-Mn-P 57.9 98.3 56.9
Ni-Fe-P 32.8 97.8 32.1
Ni-Co-P 61.9 99.1 61.3
Ni-Cu-P 21.6 98.6 21.3
Ni-Zn-P 57.8 98.9 57.2
Ni-La-P 33.3 98.7 32.9
Ni-Ce-P 29.8 98.1 29.2
Ni-Mo-P 64.5 98.8 63.7
a. metal amounts in the Ni-P catalysts was 1%.
b. the results of Ni-P catalyst was reported in literature (Liu et al., 2010)
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Table 2 Effects of Mo amounts on nitrobenzene hydrogenation to aniline on amorphous
Mo/Ni-P catalyst
Mo
content/%
Conversion of
Nitrobenzene/%
Selectivity of
aniline/%
Yield of aniline/%
0a 55.2 97.5 53.8
0.5 58.9 98.2 57.7
1.0 64.5 98.8 63.7
1.5 59.4 98.7 58.6
3.0 52.6 98.7 51.9
5.0 34.6 98.8 34.2
a. the results of Ni-P catalyst was reported in literature (Liu et al., 2010)
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Table 3 Textural properties of amorphous Mo/Ni-P catalysts with different Mo content
Mo content
/%
BET Surface Area/
m2·g-1
Total pore volume
/ 10-2 mL·g-1
Average pore
Radius / nm
0 13.7 5.43 15.0
0.5 17.0 5.82 15.5
1.0 24.6 8.74 15.8
1.5 29.7 11.0 16.0
3.0 33.1 12.3 16.1
5.0 132.9 32.4 17.4
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Figure. 1.
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Figure. 2.
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Figure. 3.
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Figure. 4.
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Figure. 5.
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Figure. 6.
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Figure. 7.
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Figure. 8.
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