e-Journal of Surface Science and Nanotechnology 23 June 2012-Study on Synthesis of NixZn1−xAl2O4/γ-Al2O3 x=0, 0.5, 1 Spinel Catalysts by Hydrothermal Method and Their Catalytic Activity
Trang 1e-Journal of Surface Science and Nanotechnology 23 June 2012
-Study on Synthesis of NixZn1−xAl2O4/γ-Al2O3 (x=0, 0.5, 1) Spinel Catalysts by
Hydrothermal Method and Their Catalytic Activity in Aromatic Hydrocarbon
Conversion∗
Nguyen Thanh Binh, Hoa Huu Thu,† Le Thanh Son, Tran Thi Nhu Mai, and Nguyen Hong Vinh
Department of Petroleum Chemistry, Faculty of Chemistry, Hanoi University of Science, 334 Nguyen Trai, Thanh Xuan, Hanoi, Vietnam
(Received 6 December 2009; Accepted 21 December 2011; Published 23 June 2012)
The spinel oxides NixZn1−xAl2O4/γ-Al2O3 (x = 0, 0.5, 1) were synthesized by hydrothermal method Oxides
obtained were characterized by XRD and SEM The XRD result showed principal spinel phase over all samples In
addition, NiO phase appeared for two cases of x = 0.5 and 1 Using XRD results, the Rietveld Refinement method
indicated that the sample ZnAl2O4/γ-Al2O3 consisted of wt 80% of ZnAl2O4 and 20% of γ-Al2O3 with crystal size of 60 nm and 40 nm, respectively This one was in accordance with SEM image which showed quite uniform particles with the side from 50 to 80 nm Catalytic activity was evaluated by methylation of toluene by methanol and dehydrogenation of ethylbenzene to styrene For methylation reaction, the results showed high selectivity in xylene In case of Ni0.5Zn0.5Al2O4/γ-Al2O3, at 400◦C, the result showed the best toluene conversion of 25.46% and selectivity in xylene was 88.33% In case of ethylbenzene dehydrogenation reaction, sample ZnAl2O4 synthesized
by coprecipitation method used as a reference catalyst We observed, after 180 min of time reaction, a double conversion of ethylbenzene on ZnAl2O4/γ-Al2O3 in comparison with ZnAl2O4reference In addition, working time
of ZnAl2O4/γ-Al2O3 was longer than this one of ZnAl2O4 reference [DOI: 10.1380/ejssnt.2012.259]
Keywords: Nano spinel; Ethylbenzene; Dehydrogenation
Spinels are blulk catalysts that have small total surface
area [1] But they have high thermal, hydrothermal
sta-bility, and acid, base, mechanical resistance The most
advantage of spinels that they are able to form the solid
solution with active components can be changed easily [1]
In fact, the spinels that active components are transition
metallic oxides usually present high catalytic activity in
oxidation reactions
Spinels were synthesized by many techniques For
ex-ample, the ancient techniques as coprecipitation of
mix-ture of metallic ions or by solid state reaction of mixmix-ture
of metallic oxides formed spinels with large crystal size
and small total surface area [2–4] Recently, the spinels
were synthesized by new techniques as sol-gel techniques,
hydrothemal method or decomposition of complexes as
precursors showed that obtained spinels had nano-crystal
size and large total surface area [5, 6]
NixZn1−xAl2O4/γ-Al2O3 (x = 0, 0.5, 1) by hydrothermal
method using active gel Al(OH)3 that obtained from
neutralization a solution of aluminum nitrate by
ammo-niac and acetates of bivalent metals, as Ni 2+, Zn2+
During the treatment in an autoclave at 250◦C, the ions
of bivalent metals form the precursors Al–O–M (M=Ni,
Zn) after the reaction:
Al≡ Al–O–H + M2+ + CH3COO−⇌
≡ Al–O–M(precursor) + CH3COOH (1)
Concurrently, in these conditions ion nitrate in solution
oxidize the acetic acid formed to help this chemical
Ad-vanced Materials and Nanotechnology 2009 (IWAMN2009), Hanoi
University of Science, VNU, Hanoi, Vietnam, 24-25 November, 2009.
Figure 1: SEM images of catalysts The SEM images of catalysts shower particle size distribution of these catalysts was
g
g
g
FIG 1: SEM images of catalysts
librium to move to right forming precursors When the precursors were calcined at 600◦ C, spinel phases on
γ-Al2O3was formed
A solution of aluminum nitrate 1.5 M was neutralized
by ammonia solution to pH = 5.5-6 In the obtained gelatinous precipitate, the zinc acetate and nickel ac-etate were dissolved with ratios calculated The mixture was stirred and treat at 250◦C in an autoclave for 15 h.
Obtained precursors were washed with water distillated, dried at 160◦C for 12 h, then obtained solids were
cal-cined at 600◦C for 4 h to form catalysts Used catalysts
had particle size of 0.5-1 mm
The phase composition and the structure of the cat-alysts were analyzed by XRD using SIEMEN D5005
Diffractometer with Cu Kα radiation (λ = 1.5406 ˚A) The calculation of content of crystal phases and crystal size by Rietveld Refinement method using Fullprof 200 and BGMN software based on RXD results of ZnAl2O4
/γ-Al2O3sample was carried out according to Ref [7] The observation of the catalysts surface and estimation particle size of catalysts were using SEM-5410LV with the enlargement of 20000 times
The influence of reaction temperature and catalyst
ISSN 1348-0391 ⃝ 2012 The Surface Science Society of Japanc (http://www.sssj.org/ejssnt) 259
Trang 2Volume 10 (2012) Nguyen, et al.
Figure 2: Results of calculation of content of crystal phase and crystal size of ZnAlFIG 2: Results of calculation of content of crystal phase and crystal size of ZnAl2O4/γ-Al2O3 sample by Rietveld Refinement
method using Fullprof 2000 and BGMN software
composition to catalytic activity were investigated using
methylation of toluene by methanol Reaction were
car-ried out in a reactors of gaseous phase, reaction
temper-ature from 290-400◦C, volume rate of toluene of 2.5 h−1,
ratio of reagents of: toluene: methanol: water= 1:4:1.5,
after 30 minutes the products were taken out to analyze
by GC-MS
The comparison of catalysts activity of ZnAl2O4
/γ-Al2O3 sample and ZnAl2O4 sample synthesized by
co-precipitation, and influence of reaction time to catalytic
activity were carried out using oxidation dehydrogenation
of ethybenzene to styrene using oxygen of air The
reac-tion was carried out at 450◦C, volume rate of 1 h−1, rate
of air flow of 10 ml/minute
The liquid products were analyzed using
GCMS-HP6890 equipment with HP5 capillary column, carrious
gas of helium, MS detector, temperature of column top
was 50◦C, temperature of column end was 270◦C.
The SEM images of catalysts were represented in Fig 1
The SEM images of catalysts shower particle size
distri-bution of these catalysts was quite uniform Estimation
of particle size in samples synthesized by hydrothermal
method from 50 nm to 80 nm For the sample obtained by
coprecipitation, particle size was approximately 130 nm
We have recorded XRD patterns of the catalysts
The XRD patterns of catalysts confirmed that spinel
phases and γ-Al2O3 phase were formed very well For
Ni0.5Zn0.5Al2O4/γ-Al2O3 and NiAl2O4/ γ-Al2O3
sam-ples, beside spinels and γ-Al2O3phases, formation of NiO
phase was observed
On XRD patterns of catalysts, an enlargement of picks
was observed This effect was generated by small crystal
size
The results of calculation of content of crystal phases
tent in catalysts reaction yield at reaction temperature of
Figure 5: Influence of temperature to reaction
on catalysts Ni
0 5 10 15 20 25 30
Content Zn (%)
FIG 3: Influence of Zn content in catalysts reaction yield at reaction temperature of 400◦C
and crystal size of ZnAl2O4/γ-Al2O3sample by Rietveld refinement method using fullprof 2000 and BGMN soft-ware was shown in Fig 2 The result showed that this sample consisted of 80% of NiAl2O4 with crystal size of
60 nm, and 20% of γ-Al2O3 with crystal size of 40 nm
This result was corresponding to SEM images of the cat-alysts
The results of study on methylation of toluene by methanol were shown in Figs 3, 4 and 5 The re-sults showed that xylene was formed with high se-lectivity When increasing the reaction temperature, the conversion of toluene increased but the selectivity
of xylene decreased Methylation reaction of toluene
on Ni0.5Zn0.5Al2O4/γ-Al2O3 showed the highest toluene conversion of 25.46% with xylene selectivity of 88.33% at
400◦C, a little amount of benzene and trimethylbenzene
was formed from secondary reactions
The composition of catalysts also influenced on
Trang 3e-Journal of Surface Science and Nanotechnology Volume 10 (2012)
0 10 20 30 40 50 60 70 80 90 100
0 10 20 30 40 50 60 70 80 90 100
Content Ni (%)
tent in catalysts reaction yield at reaction temperature of
Figure 4: Influence of Ni content in catalysts reaction yield at reaction temperature of 400 C
Temperature ( C)
/ -Al 2 O 3
/ -Al 2 O 3
Figure 5: Influence of temperature to reaction
O and
g
0
0
Content Zn (%)
FIG 4: Influence of Ni content in catalysts reaction yield at reaction temperature of 400◦C
0 5 10 15 20 25 30
200 250 300 350 400 450 500
Temperature ( o C)
Ni 0.5 Zn 0.5 Al 2 O 4 /g-Al 2 O 3
ZnAl 2 O 4 /g-Al 2 O 3
Figure 5: Influence of temperature to reaction
/Al O and
g
FIG 5: Influence of temperature to reaction yield on catalysts
Ni0.5Zn0.5Al2O4/Al2O3 and ZnAl2O4/Al2O3
alytic activity Figure 3 showed influence of Zn content in catalysts to reaction yield, at temperature of 400◦C (Zn
content = nZn/(nZn+nNi) A maximum yield attained on
Ni0.5Zn0.5Al2O4/γ-Al2O3catalysts at Zn content of 54%
Increasing of Ni content in catalysts effected to decrease xylem selectivity, and increase content of secondary prod-ucts from parasite reaction Figure 4 showed influence of
Ni content in catalysts on selectivity of xylene, at temper-ature of 400◦C The results showed that when the absence
of water in the first material, the conversion of toluene was very low, about 8.14% on Ni0.5Zn0.5Al2O4/γ-Al2O3 cata-lysts at 400◦C This permitted to predict that alkylation
of toluene was mainly catalyzed by OH groups link with metal ion as Bronsted acid centers that the water had the role to form them
The results of study on oxidative dehydrogenation of ethylbenzene to styrene were represented in Figs 6 and 7
The results showed that styrene selectivity was very high
on both of two samples The ethylbenzene conversion on ZnAl2O4/γ-Al2O3sample was about two times more than
on ZnAl2O4 sample synthesized by coprecipitation after react time of 180 minutes This can be explained by small crystal size and large total surface area of ZnAl2O4
/γ-Al2O3 sample
The catalytic activity decreased slowly according to the reaction time ZnAl2O4/γ-Al2O3 sample contained
Al2O3 as solid acid and it had porous structure effected
0 5 10 15 20 25 30 35 40
0 20 40 60 80 100 120 140 160 180 200
Time (mins)
ZnAl 2 O 4 /g-Al 2 O 3
ZnAl 2 O 4
ence of reaction time to styrene
g
g
g
FIG 6: Influence of reaction time to styrene selectivity on catalysts ZnAl2O4/γ-Al2O3and ZnAl2O4
ZnAl 2 O 4
60 65 70 75 80 85 90 95 100
Time (min)
ZnAl 2 O 4 /g-Al 2 O 3
ZnAl 2 O 4
ence of reaction time to styrene Figure 7: Influence of reaction time to
ethylbenzene conversion on catalysts
g
g
g
g
g g
FIG 7: Influence of reaction time to ethylbenzene conversion
on catalysts ZnAl2O4/γ-Al2O3 and ZnAl2O4
secondary reactions involving cracking reaction, dealky-lation conducting to form little amount of benzene, ben-zaldehyde, benzofurane as second products observed on GCMS diagram The cock content on ZnAl2O4/γ-Al2O3
sample was of 85.8 mg/1g catalyst, on ZnAl2O4 sample was 57.9 mg/1g catalyst after 3 h of reaction
The catalysts of spinels on gamma aluminium oxide
- NixZn1−xAl2O4/γ-Al2O3 (x = 0, 0.5, 1) were
synthe-sized using hydrothermal method XRD patterns of
cat-alysts confirmed that spinel phases and γ-Al2O3 phase were formed very well
Calculation of content of crystal phases and crystal size
by Rietveld Refinement method using Fullprof 2000 and BGMN software based on XRD results of ZnAl2O4
/γ-Al2O3 sample showed that this sample consisted of 80%
of ZnAl2O4 with crystal size of 60 nm, and 20% of
γ-Al2O3 with crystal size of 40 nm These results were corresponding with SEM images
For methylation of toluene by methanol on catalysts, xylene was formed with high selectivity Ni content in catalysts influenced to toluene conversion and xylene se-lectivity
Trang 4Volume 10 (2012) Nguyen, et al.
For oxidation dehydrogenation of ethylbenzene to
styrene, ZnAl2O4/γ-Al2O3 sample was better than
ZnAl2O4 sample synthesized by coprecipitation with
higher catalytic activity and longer life time
These results contributed to study to synthesize and
catalytic activity of nanostructure materials
Acknowledgments
The authors gratefully acknowledge financial support from the National Foundation for Science and Technology Development of Vietnam (NAFOSTED)
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