Effect of preparation method on the catalytic performance of Ni/H-ZSM-5 for the reductive deoxygenation of cyclohexanone

Article abstract of DOI:10.1007/s11164-012-0798-0

The effect of the impregnation and co-precipitation-kneading methods on the catalytic performance of the Ni/H-ZSM-5 catalyst was evaluated via catalytic reductive deoxygenation of cyclohexanone in a fixed bed. The catalysts were characterized by X-ray diffraction, nitrogen adsorption, and NH ₃-temperature programmed desorption. A sharply acidic and textural change was observed on the catalysts prepared by the different methods, while the metal active phase structure was almost the same. The results of the cyclohexanone reductive deoxygenation reaction indicated that the catalyst based on the co-precipitation-kneading method afforded a higher yield of cyclohexane, and thus proved that the co-precipitation-kneading method is suitable for the preparation of a bi-functional catalyst.

Full text of DOI:10.1007/s11164-012-0798-0

Res Chem Intermed (2013) 39:2795–2800
DOI 10.1007/s11164-012-0798-0
Effect of preparation method on the catalytic
performance of Ni/H-ZSM-5 for the reductive
deoxygenation of cyclohexanone
•
Guangyuan Wang Yifan Duan Xilong Yan
•
Received: 20 July 2012 / Accepted: 29 August 2012 / Published online: 12 September 2012
Ó Springer Science+Business Media B.V. 2012
Abstract The effect of the impregnation and co-precipitation-kneading methods
on the catalytic performance of the Ni/H-ZSM-5 catalyst was evaluated via catalytic
reductive deoxygenation of cyclohexanone in a fixed bed. The catalysts were
characterized by X-ray diffraction, nitrogen adsorption, and NH3-temperature pro-
grammed desorption. A sharply acidic and textural change was observed on the
catalysts prepared by the different methods, while the metal active phase structure
was almost the same. The results of the cyclohexanone reductive deoxygenation
reaction indicated that the catalyst based on the co-precipitation-kneading method
afforded a higher yield of cyclohexane, and thus proved that the co-precipitation-
kneading method is suitable for the preparation of a bi-functional catalyst.
Keywords Impregnation Á Co-precipitation-kneading Á Ni/H-ZSM-5 Á
Reductive Á Deoxygenation
Introduction
As is well known, the reductive deoxygenation of ketones to corresponding alkanes is
an important reaction in fine chemical engineering, but the traditional Clemmensen
reaction and Wolff–Kishner–Huangminlon reaction are environmentally unfriendly.
So far, there have been rare reports on the hydrogenation reduction of the aliphatic
ketones over H-ZSM-5-supported catalyst. H-ZSM-5 possesses tunable acidity, three-
dimensional porosity, short pore pathway, high thermal stability, and the capability to
stabilize active metal clusters; thus, it has been widely applied in a series of fields like
oil refining [1], organic synthesis, fine chemistry, environmental protection [2, 3], etc.
G. Wang Á Y. Duan Á X. Yan (&)
School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072,
People’s Republic of China
e-mail: yan@tju.edu.cn
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G. Wang et al.
H-ZSM-5 is also important in acid catalysis because of its acid sites (Lewis and
¨
Bronsted acid) and specific properties. The metal/acid bi-functional catalyst is one
of the successful applications with the consideration that it makes use of the acidity
of the zeolite molecular sieve. Usually, bi-functional catalysts use shaped zeolite as
the support, and the impregnation method is a widely used method for preparation
of this kind of catalyst [4]. Generally, the active species loading on the support via
the impregnation method are no more than 10 wt% because even more loading may
block the pores system of the support, which could lead to the decrease of the
catalytic activity. However, in some cases, more than 10 wt% active species are
always required. In our previous works [5, 6], a co-precipitation-kneading method
has proved to be effective for the preparation of a bi-functional catalyst with high
metal content. Bai et al. [7] also reported the effect of preparation on the catalytic
performance. This encouraged us to apply the co-precipitation-kneading method to
the preparation of Ni20/H-ZSM-5-supported catalyst (the content of nickel on the
catalyst is 20 wt%).
In this paper, the catalysts were prepared by impregnation and co-precipitation
methods. The effect of the preparation was studied by the characterizations of the
catalysts, using X-ray diffraction (XRD), nitrogen adsorption [Brunauer–Emmett–
Teller (BET)], and NH3-temperature programmed desorption (NH3-TPD). Reduc-
tive deoxygenation of the cyclohexanone to cyclohexane was carried out to evaluate
the performance of the catalysts. The aim was to explain the differences and find a
better way to prepare bi-functional catalysts for reduction of aliphatic ketones.
Experimental
Materials and catalysts
Shaped H-ZSM-5 support and H-ZSM-5 powder (with a Si/Al ratio of 25) were
purchased from the catalyst plant of Nankai University, Tianjin, China. The 1,4-dioxane
and cyclohexanone were obtained from Tianjin Jiangtian Chemical Technology,
Tianjin, China. All the solvents and reagents were used without further purification.
The catalyst prepared by the wet-impregnation method was named as Ni20/H-
ZSM-5-IM, while the catalyst prepared by the co-precipitation-kneading method
was referenced as Ni20/H-ZSM-5-CP. The Ni20/H-ZSM-5-IM was prepared as
follows: 23.2 g H-ZSM-5 were impregnated with 64.0 mL aqueous solution of
29.9 g Ni(NO3)2Á6H2O at ambient temperature for 4 h. Then, the catalysts were
dried at 110 °C for 8 h and calcined at 500 °C for 4 h. Ni20/H-ZSM-5-CP was
prepared as follows: under mechanical stirring, a solution of 29.9 g Ni(NO3)2Á6H2O
in 200.0 mL H2O and a solution of 10.6 g Na2CO3 in 200.0 mL H2O were added
dropwise into a beaker at ambient temperature over 1 h and aged for 1 h. The pH
was controlled around 8 during the process. The precipitate was filtered and washed
with deionized water several times until a pH range of 7.0–7.5 was obtained. Then,
the filter cake was dried at 110 °C and pulverized. The dried samples were kneaded
with a mixture of 23.2 g H-ZSM-5 and 30 mL 2 wt% nitric acid, followed by
molding to bars with an extruder. The bars were dried at 110 °C for 6 h and then
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Effect of preparation method on the catalytic performance of Ni/H-ZSM-5
2797
calcined at 500 °C for 4 h. All the catalysts prepared above were reduced at 360 °C
for 4 h in a hydrogen stream (1.0 MPa) before use.
Catalysts characterization
Powder XRD was performed at ambient temperature on a Rigaka D/max 2000
diffractometer using the Ni b-filtered Cu Ka radiation (k = 0.15418 nm). Analysis
were performed on the specimen reduced at 360 °C for 4 h and registered in the 2h
range of 20–70° at a scan speed of 5°/min. Diffraction peaks were compared with
the JCDS data file.
Textual properties of the samples were determined by N2 adsorption–desorption
isotherms on an ASAP 2405 apparatus. The specific surface areas were calculated
by the Brunauer–Emmett–Teller (BET) equation.
NH3-TPD data were acquired on a TP-5000 instrument. The dried samples
(50 mg) were heated at a linear rate of 10 °C/min from 120 to 700 °C.
Experiment
The reaction was performed in a fixed-bed reactor, and a solution of cyclohexanone in
1,4-dioxane was dosed into the reactor with a syringe pump. The reaction mixture was
condensed in a cold trap (-2 °C) and analyzed without preliminary separation by an
offline gas chromatograph (OV-1701 capillary column: 30 m 9 0.32 mm, 1.0 lm
film thickness). Moreover, the composition of samples were identified by GC/MS
(HP-1 capillary column: 30 m 9 0.25 mm, 0.2 lm film thickness) equipped with an
ion-trap MS detector.
Results and discussion
Phase structure of the catalyst
As shown in Fig. 1, two typical diffraction lines at 44.4° and 51.8° were observed
on the XRD curves of reduced Ni20/H-ZSM-5-IM and Ni20/H-ZSM-5-CP, which
could be assigned to the element Ni. Moreover, no diffraction line of NiO was
detected on either of the two reduced catalysts, which indicated that NiO had been
completely reduced to Ni0 on both the samples. These results also demonstrated that
the reduction conditions used in this work are effective for both kinds of catalysts.
Textual properties
As shown in Table 1, Ni20/H-ZSM-5-CP has a larger surface area than
Ni20/H-ZSM-5-IM. This phenomenon is caused by the impregnated metal, which
may locate on the surface and pore system of the H-ZSM-5 support and thus lead to
the pore blockage. This blockage could also change the distribution of the pores as
displayed by the mean pore diameter data of the two kinds of catalysts.
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G. Wang et al.
♦ Ni
(a)
(b)
♦
?
♦
♦
♦
20
40
60
2θ°
Fig. 1 XRD patterns of H-ZSM-5 supported nickel samples: a Ni20/H-ZSM-5-IM, b Ni20/H-ZSM-5-CP
Table 1 Textural properties of Ni-based catalysts prepared by the impregnation and co-precipitation-
kneading methods
c
SBET (m2 g-1 a
)
VpN2 (cm3 g-1 b
)
˚
Dp (A)
Catalyst
Ni20/H-ZSM-5-IM
143.7
241.6
0.42
0.34
115.9
56.1
Ni20/H-ZSM-5-CP
a
The surface area was calculated by the BET equation
BET cumulative desorption pore volume
Mean pore diameter = 4 Vp N2/SBET
b
c
NH3-TPD
The results of the NH3-TPD profiles are shown in Fig. 2. The results can be used to
indicate the strength of the acid by the desorption peaks [8]. The curves of the
reduced Ni20/H-ZSM-5-IM and Ni20/H-ZSM-5-CP both have a double-peak. The
peak at the low temperature (237–243 °C) is for the weak acidic site while the peak
at high temperature (550 °C) is for the strong acidic site. The areas of the desorption
peaks are listed in Table 2 and the data can be taken as a criterion of the distribution
of the acidic sites [9, 10]. It is obvious that the total acidity of Ni20/H-ZSM-5-IM is
much lower than that of Ni20/H-ZSM-5-CP. Combined with the BET results, it can
be concluded that the catalysts prepared by the impregnation method have got their
acidic sites covered by the metal. So they exhibited low activity.
Catalytic activity of the catalyst
Reductive deoxygenation of the cyclohexanone to cyclohexane was carried out to
evaluate the performance of the two catalysts, and the obtained results are summarized
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Effect of preparation method on the catalytic performance of Ni/H-ZSM-5
2799
(b)
(a)
200
400
600
Temperature(
)
Fig. 2 NH3-TPD of the catalysts prepared by the impregnation and co-precipitation-kneading methods:
a Ni20/H-ZSM-5-IM, b Ni20/H-ZSM-5-CP
Table 2 Theareas of the desorptionpeaks of the catalysts preparedbythe impregnationand co-precipitation-
kneading methods
Catalyst
Tdes
(°C)a
Peak area
(a.u.)c
Tdes
(°C)c
Peak area
(a.u.)c
Total peak
area (a.u.)c
Ni20/H-ZSM-5-IM
243
237
1,707.3
550
550
221.7
1,929.0
Ni20/H-ZSM-5-CP
19,064.8
4,168.7
23,233.5
a
Lower temperature peak for weak acid sites
Higher temperature peak for strong acid sites
b
c
The peak area was calculated by the Gaussian fitting method
O
OH
[H]
-H2O
[H]
Acdic sites
Metal sites
Metal sites
Cyclohexanone
Cyclohexanol
Cyclohexene
Cyclohexane
Scheme 1 The main reaction process for the reductive deoxygenation of cyclohexanone
in Table 3. The reaction mixture were collected and detected by GC/MS, based on
the obtained results and some other previous reports, and the main reaction of the
reductive deoxygenation of the cyclohexanone is shown in Scheme 1. The reaction
starts with the hydrogenation of the cyclohexanone to cyclohexanol on metal active
sites, followed by the dehydration of the cyclohexanol to the corresponding olefin
over the acidic sites and the hydrogenation of the cyclohexene to the cyclohexane
on metal active sites. As shown in Table 3, the Ni20/H-ZSM-5-CP exhibited better
hydrogenation activity and dehydration activity than Ni20/H-ZSM-5-IM, and the
high yield of the cyclohexanol over Ni20/H-ZSM-5-IM indicates that the acidity of
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G. Wang et al.
Table 3 The yield of the catalytic reductive deoxygenation of the cyclohexnone (catalysts prepared by
the impregnation and co-precipitation-kneading methods)
Catalysts
Conversion (%)
Selectivity (%)
Cyclohexane
Cyclohexene
Cyclohexanol
Other
Ni20/H-ZSM-5-IM
Ni20/H-ZSM-5-CP
88.7
93.5
45.9
84.0
4.4
8.1
48.4
3.6
1.3
4.3
Reaction conditions: temperature 240 °C; hydrogen pressure 2.0 MPa; flow rate: 0.2 mL/min; cyclo-
hexanone concentration in 1,4-dioxane: 20.0 wt%
the catalysts do affect the dehydration reaction. However, these results were quite in
agreement with those discussed before. Thereafter, it can be concluded that the co-
precipitation-kneading method is better than the impregnation method for the
preparation of a high metal content H-ZSM-5-supported bi-functional catalyst.
Conclusion
The impregnation and co-precipitation-kneading methods were employed to prepare
Ni/H-ZSM-5 bi-funictional catalysts with high metal content. The catalysts were
characterized by XRD, nitrogen adsorption, and NH3-TPD. The results obtained
indicated that the catalyst prepared by the co-precipitation-kneading method have
more acidity sites and larger BET surface areas than the catalyst prepared by the
impregnation method, and led to a better catalytic performance for the model
reaction, and thus proved that the co-precipitation-kneading method is suitable for
the preparation of bi-functional catalysts.
Acknowledgment Financial support was provided by the National Natural Science Foundation of
China (Grant No. 20706043 and 20976123).
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