Catalytic performance of Ni/Γ-Al2O3 for hydrogenation of 2-ethyl-2-hexenal

Article abstract of DOI:10.1016/j.catcom.2017.09.023

The effect of reaction conditions on the catalytic performance of Ni/γ-Al₂O₃ was investigated and the result showed that Ni/γ-Al₂O₃ showed excellent catalytic activity. However, the catalytic performance of the recovered Ni/γ-Al₂O₃ catalyst declined dramatically. The fresh and the recovered catalysts were comparatively analyzed by means of XRD, XPS and FT-IR techniques. The result demonstrated that the main reason for the activity decline of the recovered Ni/γ-Al₂O₃ catalyst is that the surface Ni has been reoxidized to NiO. After calcination and reduction, the recovered Ni/γ-Al₂O₃ catalyst could be reused four times without a significant decrease in its catalytic performance.

Full text of DOI:10.1016/j.catcom.2017.09.023

Accepted Manuscript
Catalytic performance of Ni/γ-Al2O3 for hydrogenation of
2-ethyl-2-hexenal
Lili Zhao, Yi Wang, Hualiang An, Xinqiang Zhao, Yanji Wang
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DOI:
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doi:10.1016/j.catcom.2017.09.023
CATCOM 5205
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28 August 2017
26 September 2017
Please cite this article as: Lili Zhao, Yi Wang, Hualiang An, Xinqiang Zhao, Yanji Wang ,
Catalytic performance of Ni/γ-Al2O3 for hydrogenation of 2-ethyl-2-hexenal. The address
for the corresponding author was captured as affiliation for all authors. Please check if
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ACCEPTED MANUSCRIPT
Catalytic Performance of Ni/γ-Al2O3 for Hydrogenation of 2-Ethyl-2-hexenal
Lili Zhao, Yi Wang, Hualiang An, Xinqiang Zhao* zhaoxq@hebut.edu.cn, Yanji Wang
Hebei Provincial Key Lab of Green Chemical Technology and Efficient Energy Saving,
School of Chemical Engineering and Technology,
Hebei University of Technology,
Tianjin 300130, China
*Corresponding author.
Abstract: The effect of reaction conditions on the catalytic performance of Ni/γ-Al2O3 was
investigated and the result showed that Ni/γ-Al2O3 showed excellent catalytic activity. However,
the catalytic performance of the recovered Ni/γ-Al2O3 catalyst declined dramatically. The fresh
and the recovered catalysts were comparatively analyzed by means of XRD, XPS and FT-IR
techniques. The result demonstrated that the main reason for the activity decline of the recovered
Ni/γ-Al2O3 catalyst is that the surface Ni has been reoxidized to NiO. After calcination and
reduction, the recovered Ni/γ-Al2O3 catalyst could be reused four times without a significant
decrease in its catalytic performance.
Keywords: 2-Ethyl-2-hexenal, 2-Ethylhexanol, Hydrogenation, Deactivation, Regeneration
1. Introduction
2-Ethylhexanol (2-EHO)，an important plasticizer alcohol，is mainly used in the production of
plasticizers, coatings, adhesives and inks, etc. Nowadays, 2-EHO is produced via gas-phase
hydrogenation of 2-ethyl-2-hexenal in the presence of ZnO-CuO catalyst [1], which is in high
energy consumption. Therefore, development of economic and environmentally benign
2-ethyl-2-hexenal hydrogenation process and its catalyst is of academic and practical significance.
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Mattos et al. [2] investigated the effect of Ni loading on the catalytic performance of Ni/γ-Al2O3
in liquid-phase hydrogenation of 2-ethyl-2-hexenal using a slurry reactor at atmospheric pressure.
They found that Ni2+ species in the octahedral coordination was beneficial to the formation of
2-ethylhexanal and its selectivity was 100 % over the Ni/γ-Al2O3 with 7.3 (wt) % Ni. Yang et al. [3]
studied the effect of Ni loading and reduction temperature of Ni/γ-Al2O3 on the hydrogenation of
crude 2-ethylhexanol (the main byproducts were 2-ethylhexanal, 2-ethylhexenal and
2-ethylhexenol) in a fixed-bed reactor under the conditions of a reaction temperature of 120 ℃, a
reaction pressure of 2.5 MPa and a liquid space velocity of 3.0 h-1. The result indicated that the
conversion of 2-ethylhexanal, 2-ethyl-2-hexenal and 2-ethylhexenol were separately 98.6 %,
99.99 % and 99.99 % using the Ni/γ-Al2O3 catalyst with Ni loading of 19.2 (wt) % prepared at the
reduction temperature of 800 ℃. Deng et al. [4] studied the hydrogenation of 2-ethyl-2-hexenal
catalyzed by Cu-Ni catalyst supported on silica gel and found that the mass fraction of 2-EHO
could reach 99 % at the reaction temperatures of 90-125 ℃ and the pressures of 3-4 MPa.
It is obvious that the supported Ni-based catalysts, especially Ni/γ-Al2O3, shows excellent
catalytic performance for the hydrogenation of 2-ethyl-2-hexenal. However, the reusability of
catalyst especially the reason for deactivation and approach to regeneration has not been
investigated in the above studies. In this paper, Ni/γ-Al2O3 was used to catalyze 2-ethyl-2-hexenal
hydrogenation reaction. We aimed to clarify the reason for deactivation of Ni/γ-Al2O3 and the
approach to its regeneration. Therefore, we investigated the effect of reaction conditions on the
catalytic performance of Ni/γ-Al2O3 for hydrogenation of 2-ethyl-2-hexenal first and then the
reusability of Ni/γ-Al2O3 catalyst.
2. Experimental
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The whole details of experimental part were depicted in the Supplementary information.
3. Results and discussion
3.1. Effect of reaction conditions on the catalytic performance of Ni/γ-Al2O3
3.1.1. Effect of catalyst amount
The effect of the amount of Ni/γ-Al2O3 with a Ni loading of 10 wt. % on 2-ethyl-2-hexenal
hydrogenation reaction was investigated and the results are listed in Table S1. It can be seen that
the conversion of 2-ethyl-2-hexenal was kept at 100 % while the yield of 2-EHO increased first
and then decreased with the increase of Ni/γ-Al2O3 amount from 10 wt. % to 20 wt. %. When
Ni/γ-Al2O3 amount was 10 wt. %, the yield of 2-EHO was lower (14.6 %) while the yield of
2-ethyhexanal was higher (76.8 %). The results suggest that the hydrogenation of C=C bond is
easier than that of C=O bond. When Ni/γ-Al2O3 amount was 15 wt. %, the hydrogenation of C=O
bond was promoted and the yield of 2-EHO was significantly increased to 93.8 %. When
Ni/γ-Al2O3 amount was 20 wt. %, the yield of 2-EHO decreased slightly, possibly because
excessive hydrogenation activity sites promoted side reactions. As a result, the formation of
byproduct 2-ethylhexyl-2-ethylhexanoate caused the decrease in the yield of 2-EHO. Therefore,
the suitable Ni/γ-Al2O3 amount was 15wt. %.
3.1.2. Effect of reaction temperature
The effect of reaction temperature on 2-ethyl-2-hexenal hydrogenation reaction was
investigated. As can be seen from Table S2, the conversion of 2-ethyl-2-hexenal was also kept at
100 % while the yield of 2-EHO increased first and then decreased slightly at a reaction
temperature ranging from 170 ℃ to 190 ℃. The yield of 2-ethyhexanal was higher but the yield of
2-EHO was lower at a reaction temperature of 170 ℃, suggesting that C=C bond hydrogenation
requires lower temperature for its lower energy barrier. With the increase of reaction temperature,
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the hydrogenation rate of C=O bond was significantly improved. 2-Ethylhexanal did not exist in
the system and the yield of 2-EHO was 93.8 % at a reaction temperature of 180 ℃, indicating that
C=O bond could be completely hydrogenated. However, the yield of 2-EHO decreased to 92.3 %
with a continued increase of reaction temperature to 190 ℃, possibly due to the promotion of side
reactions. In fact, 2-ethylhexylbutyrate, 2-ethylhexyl-2-ethylhexanoate and other byproducts
increased by consuming some of 2-EHO, leading to the decrease in the yield of 2-EHO. Therefore,
the suitable reaction temperature was 180 ℃. The experimental results also suggest that the
hydrogenation of C=C bond is more preferential than that of C=O bond.
3.1.3. Effect of reaction pressure
The effect of reaction pressure on 2-ethyl-2-hexenal hydrogenation reaction was investigated. As
can be seen from Table S3, 2-ethyl-2-hexenal was completely converted while the yield of 2-EHO
increased first and then decreased with the increase of reaction pressure. The yield of
2-ethyhexanal was 80.1 % but the yield of 2-EHO was only 19.9 % at a reaction pressure of 1
MPa due to incomplete hydrogenation of the C=O bond. The hydrogenation rate of the C=C bond
and the C=O bond was obviously improved at the reaction pressure of 2 MPa; 2-ethyl-2-hexenal
was completely hydrogenated and the yield of 2-EHO reached the maximum of 93.8 %. The
reaction pressure had no effect on the conversion of 2-ethyl-2-hexenal while the yield of 2-EHO
decreased slightly with a continued increase of reaction pressure. That is probably because the
larger reaction pressure aggravated the Tishchemko reaction of 2-ethyhexanal [5]. Therefore, the
suitable reaction pressure was 2.0 MPa.
3.1.4. Effect of reaction time
The effect of reaction time on 2-ethyl-2-hexenal hydrogenation reaction was investigated and the
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results are shown in Table S4. The conversion of 2-ethyl-2-hexenal and the yield of 2-EHO
increased while the yield of 2-ethyhexanal increased first and then decreased. There were a lot of
2-ethyhexanal and a small amount of 2-EHO in the product at the reaction time of 20 min,
indicating that the main reaction was the C=C bond hydrogenation of 2-ethyl-2-hexenal. When the
reaction time was prolonged to 40 min, 2-ethyl-2-hexenal was completely converted. Meanwhile,
the yield of 2-ethylhexanal decreased and the yield of 2-EHO increased. With a continued increase
of reaction time to 60 min, 2-ethylhexanal was completely converted into 2-EHO. When the
reaction time was prolonged to 80 min, the yield of 2-EHO increased slowly and reached the
maximum of 93.8 %. However, the yield of 2-EHO leveled off roughly
with the increase of reaction time longer than 6 h. Therefore, the suitable reaction time was 80
min.
3.2. Reusability of Catalyst
The recovered Ni/γ-Al2O3 catalyst was treated in two ways. The first one was that the recovered
Ni/γ-Al2O3 catalyst was washed with ethanol for three times and then dried at 110 ℃ for 8 h while
the second one was that the recovered Ni/γ-Al2O3 catalyst was washed with ethanol for three times,
dried at 110 ℃ for 8 h, calcinated at 500 ℃ for 4 h and reduced at 550 ℃ for 4 h. The catalytic
performance of the recovered Ni/γ-Al2O3 catalyst separately treated in the two ways was evaluated
and the results are listed in Table 1. It can be seen that the catalytic performance of the recovered
catalyst treated by the first way declined significantly in the second run. However, the catalytic
performance of the recovered catalyst treated by the second way did not decrease and the yield of
2-EHO remained unchanged even after reused for four times.
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Table 1 Reusability of Ni/γ-Al2O3
Catalyst
Fresh
Run
1
X2E2H / %
100
Y2EH/ %
0
Y2EHO / %
93.8
Recovered and treated
by the first way
2
16.5
4.1
0
2
3
100
100
0
0
93.7
94.2
Recovered and treated
by the second way
4
5
100
100
0
0
94.8
93.9
Reaction conditions：T=180 ℃, P=2.0 MPa, t=80 min and a weight percentage of catalyst =15 %.
X2E2H: conversion of 2-ethyl-2-hexenal; Y2EHO: yield of 2-ethylhexanol; Y2EH: yield of 2-ethylhexanal.
The fresh catalyst and the recovered Ni/γ-Al2O3 sample treated by the first way were analyzed
by means of XRD and XPS techniques and the results are given in Figs. 1 and 2. As can be seen
from Fig. 1, the intensity of characteristic diffraction peak of Ni in the recovered catalyst became
weakened, possibly due to reoxidation of Ni to NiO. In order to analyze the change of diffraction
peak of the fresh and recovered Ni/γ-Al2O3, XRD pattern of NiO/γ-Al2O3 was also given in Fig. 1.
The peaks located at 2 theta = 37.25°, 43.24° and 62.88° were attributed to NiO [6]. However, the
characteristic diffraction peaks of γ-Al2O3 and NiO were overlapped and could not be clearly
distinguished. Through comparison of the diffraction peaks of a, b and c, we found that the
characteristic diffraction peaks of the recovered Ni/γ-Al2O3 catalyst increased significantly but the
characteristic diffraction peaks of Ni became weaker, suggesting that a part of Ni in the recovered
Ni/γ-Al2O3 was reoxidized to NiO. In order to confirm the above speculation, XPS analyses of the
fresh and recovered Ni/γ-Al2O3 were conducted and the result is showed in Fig. 2. According to
the literatures [7-10], the binding energy of Ni2p3/2 in Ni0 is 852.4±0.2 eV, the binding energy of
Ni2p3/2 in Ni2+ is 856.7 eV and the binding energies of Ni2p1/2 in Ni2+ are 873 eV and 863 eV.
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As can be seen from Fig. 2, there was no Ni0 but Ni2+ onthe surface of the fresh and the recovered
Ni/γ-Al2O3 catalysts, indicating that Ni on the surface of the fresh Ni/γ-Al2O3 was oxidized to NiO
in the cooling stage of the reduction process and Ni in the recovered Ni/γ-Al2O3 was also
reoxidized to NiO in the process of hydrogenation reaction.
●
a: fresh Ni/Al2O3
a: fresh
b: recovered
856.8
856.3
Ni2p3/2
b: recovered
c: fresh NiO/Al2O3
Ni2p1/2
873
863
●
a
b
c
●
a
b
850
860
Binding Energy(ev)
870
880
20
40
60
80
2Theta(deg.)
Fig. 1. XRD patterns of the fresh and the recovered
Fig. 2. XPS spectra of Ni 2p in the fresh and the
Ni/γ-Al2O3 catalysts
●：Ni
recovered Ni/γ-Al2O3 catalysts
The fresh Ni/γ-Al2O3 catalyst was analyzed by TG-DTG technique and the result
is illustrated in Fig. S1. The weight loss percentage was 3.0 % at 300 ℃, being attributed to the
desorption of adsorbed water and volatile substances. The weight gain percentage was 0.6 % at
330 ℃ due to the oxidation of Ni to NiO. In addition, the mass change was not obvious at 530 ℃
and above, indicating that the catalyst was stable at a calcination temperature of 550 ℃. In this
sense, the analysis result of H2-TPR was not affected if the reduction temperature was higher than
550 ℃. Fig. 3 shows H2-TPR curve of the calcined NiO/γ-Al2O3 catalyst while Fig. 4 shows
H2-TPR curves of the fresh catalyst and the recovered Ni/γ-Al2O3 catalyst treated by the first way.
By comparing the H2-TPR profile of the calcined catalyst (NiO/γ-Al2O3) with the fresh one
(Ni//γ-Al2O3), it can be seen that the fresh Ni/γ-Al2O3 catalyst had obvious reduction peaks at
161.8 ℃ and 218.1 ℃. The two reduction peaks were attributed to the reduction of the dispersed
NiO particles formed from the oxidation of Ni particles in the cooling stage in the reduction
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furnace. This kind of the dispersed NiO particles could be in situ reduced in the reaction process.
For the recovered catalyst, however, there were not only the lower-temperature reduction peaks
but also reduction peaks at 300~400℃ assigned to the reduction of NiO with large grains [11-13].
This kind of NiO was difficult to be in situ reduced.
Fig. 5 shows FT-IR spectra of the fresh and recovered Ni/γ-Al2O3 treated by the first way. There
existed the infrared peaks of organic compounds in the recovered catalyst while there were no
such infrared peaks in the fresh catalyst and the recovered catalyst after calcination. The weak and
broad characteristic peaks at 3200～3700 cm-1 were assigned to water molecules or surface
hydroxyl bond. The characteristic peak at 1630 cm-1 was assigned to hydroxyl group of water
molecules. The absorption peak of alkyl group at 2800～2960 cm-1 in the recovered catalyst
suggested that some kinds of organic compounds were adsorbed on the catalyst surface after
reaction. The active sites were occupied by the adsorbed organic compounds and could not be
effectively removed by ethanol washing and drying, thus lowering the catalytic performance.
In summary, the main reasons for the decrease in the catalytic performance of the recovered
Ni/γ-Al2O3 catalyst treated by the first way are that the surface Ni has been reoxidized to NiO
which cannot be in situ reduced and that the active sites are occupied by the adsorbed organic
compounds. Therefore, the recovered catalyst needs to be calcinated and reduced in order to
restore its catalytic performance.
a: fresh
b: recovered
b
a
200
400
600
800
1000
100
200
300
400
500
Temperature/℃
Temperature/oC
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Fig. 3. H2-TPR curve of the calcined NiO/γ-Al2O3
catalyst
Fig. 4. H2-TPR curves of the fresh and the
recovered Ni/γ-Al2O3 catalysts
a: recovered and calcination
a: recovered and calcination
b: fresh NiO/Al2O3
b: fresh NiO/Al2O3
c: fresh Ni/Al2O3
d: recovered
c: fresh Ni/Al2O3
d: recovered
a
a
b
b
c
c
d
d
4000
3500
3000
2500
2000
1500
1000
Wavenumber(cm-1
)
3200
3000
2800
Wavenumber(cm-1
)
Fig. 5. FT-IR spectra of the fresh and the recovered Ni/γ-Al2O3 catalysts
4. Conclusion
The suitable reaction conditions for the hydrogenation of 2-ethyl-2-hexenal catalyzed by
Ni/γ-Al2O3 were obtained as follows: a weight percent of Ni/γ-Al2O3 = 15 %, a reaction
temperature of 180 ℃, a reaction pressure of 2.0 MPa and a reaction time of 80 min. Under the
above reaction conditions, the conversion of 2-ethyl-2-hexenal and the yield of 2-EHO were
100 % and 93.8 %, respectively. The main reasons for the decline of hydrogenation activity of the
recovered Ni/γ-Al2O3 catalyst are that the surface Ni has been oxidized to NiO and the active sites
are occupied by some kinds of organic substances. The recovered Ni/γ-Al2O3 catalyst could be
reused four times without a significant change in its catalytic performance after calcination and
reduction.
Acknowledgments
This work was financially supported by National Natural Science Foundation of China (Grant
No. 21476058 and 21506046) and Natural Science Foundation of Tianjin City (Grant No.
16JCQNJC06100). The authors are gratefully appreciative of their contributions.
Appendix A. Supplementary data
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Materials and reagents; catalyst preparation; catalyst characterization; 2-ethyl-2-hexenal
hydrogenation reaction; product analysis; effect of reaction conditions on the catalytic
performance of Ni/γ-Al2O3; TG-DTG curves of the fresh Ni/γ-Al2O3 catalyst.
Supplementary data
Supplementary material
References
[1] J.Q. Ma, L. Xu, L. Xu, H. Wang, S. Xu, H. Li, S. Xie, H. Li, Highly dispersed Pd on Co−B amorphous alloy:
facile synthesis via galvanic replacement reaction and synergetic effect between Pd and Co, ACS Catal. 3
(2013) 985-992.
[2] A.R.J.M. Mattos, S.H. Probst, J.C. Afonso, M. Schmal, Hydrogenation of 2-ethyl-hexen-2-al on Ni/Al2O3
catalysts, J. Brazil. Chem. Soc. 15 (2004) 760-766.
[3] R.C. Yang, X.G. Li, J.S. Wu, X. Zhang, Z.H. Y.F. Zhang, J.T. Guo, Hydrotreating of crude 2-ethylhexanol over
Ni/Al2O3 catalysts:surface Ni species-catalytic activity correlation, Appl. Catal. A Gen. 368 (2009) 105-112.
[4] D. Deng, X. Zhang, Industrial appication domestic catalyst for liquid phase hydrogenation of 2-ethyl-hexanal,
Science & Technology in Chemical industry (Chinese) 10 (2002) 34-37.
[5] W.J. Xu, X.H. Liu, J.W. Ren, P. Zhang, Y. Wang, Y. Guo, Y. Guo, G. Lu, A novel mesoporous Pd/cobalt
aluminate bifunctional catalyst for aldol condensation and following hydrogenation, Catal. Commun. 11
(2010) 721-726.
[6] A. Fouskas, M. Kollia, A. Kambolis, Ch. Papadopoulou, H. Matralis, Boron-modified Ni/Al2O3 catalysts for
reduced carbon deposition during dry reforming of methane, Appl. Catal. A Gen. 474 (2014) 125-134.
[7] M.H. Amina, S. Putlaa, S.B.A. Hamid, S.K. Bhargave, Understanding the role of lanthanide promoters on the
structure–activity of nanosized Ni/γ-Al2O3 catalysts in carbon dioxide reforming of methane, Appl. Catal. A
Gen. 492 (2015) 160-168.
[8] F. Pompeo, D. Gazzoli, N. N. Nichio, Stability improvements of Ni/α-Al2O3 catalysts to obtain hydrogen from
methane reforming, Int. J. Hydrogen Energ. 34 (2009) 2260-2268.
[9] C. C. Torresa, J. B. Alderete, C. Mella, B. Pawelec, Maleic anhydride hydrogenation to succinic anhydride
10

ACCEPTED MANUSCRIPT
overmesoporous Ni/TiO2 catalysts: Effects of Ni loading and temperature, J. Mol. Catal. A Chem. 423 (2016)
441-448.
[10] D. Dissanayake, M. P. Rosynek, K. C. C. Kharas, J. H. Lunsford, Partial oxidation of methane to carbon
monoxide and hydrogen over a Ni/AI2O3 catalyst, J. Catal. 132 (1991) 117-127.
[11] K.V.R. Chary, P.V.R. Rao, V.V. Rao, Catalytic functionalities of nickel supported on different polymorphs of
alumina, Catal. Commun. 9 (2008) 886-893.
[12] P. Kim, H. Kim, J.B. Joo, W. Kim, I.K. Song, J. Yi, Effect of nickel precursor on the catalytic performance of
Ni/Al2O3 catalysts in the hydrodechlorination of 1,1,2-trichloroethane, J. Mol. Catal. A Chem. 256 (2006)
178-183.
[13] N. Liang, X. Zhang, H. An, X. Zhao, Y. Wang, Direct synthesis of 2-ethylhexanol via n-butanal aldol
condensation-hydrogenation reaction integration over a Ni/Ce-Al2O3 bifunctional catalyst, Green Chem. 17
(2015) 2959-2972.
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The highlights of the manuscript can be described as follows:


Ni/γ-Al2O3 shows excellent catalytic activity in hydrogenation of 2-ethyl-2-hexenal.
The main reason for the activity decline of the recovered Ni/γ-Al2O3 is that Ni is oxidized to
NiO.

Ni/γ-Al2O3 has good stability after calcination and reduction of the recovered Ni/γ-Al2O3.
12