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FeOx catalysts for the oxidative coupling of methane
621
CatalyGsToduy,13 (1992)621-624
Elsevier Science Publishers B.V., Amsterdam
Synergestic effect between NaCl and B203 in the NaC1/&03/FeOx catalysts for the oxidative coupling of methane X. -R. Xia”, G. -X. Xiong’ and X. -X. Guo Lab for Catalysis, Dalian Institute of Chemical Physics, Dalian 116023, China *Lab for Catalysis, Department of Chemistry, Jilin University,
Changchun 130023, China
JNTRODUCTION Alkali chloride doped transition metal oxides, especially modified by B& or P&,
have
high ethylene selectivity. Most of the papers were focused on the improvement of catalyst performance and the optimization of reaction conditions. However, there were few detailed basic researches on such catalysts [l , 21. In this paper several techniques, such as, flow-reaction, XRD, HrTPR , &-TPD and in-situ Moasbauer , were employed to investigate the properties of the titled catalysts at different stages of preparation,
periods of reaction and approaches of
treatment. EXPERIMENTAL
The NaCI/B203/FeO, catalysts were prepared by two-step impregnations. belling was as fohows, e.g. , pure Fe(X-FlOO, Cl/15(at)%BrO~/FeO,~FBN1525.
15(at)%B&/Fe0,-FB15,
The sample la25(at)%Na-
The methane conversion was performed in a conven-
tional fixed-bed reactor. The general reaction conditions were as follows: T=75O’C, 24g
l
s
l
cmm3, Pc~,/Po~=4,
P,,=32kPa,
r=O.
and balanced to atmospheric pressure by helium.
The reactant and product analyses were performed by on-line gas chromatography
(GC) as
described elsewhere [3]. XRD measurements were performed with a Rigaku D/MAX-RB
X-ray diffractometer us-
ing a copper target at 40 KVx lOOmA and scanning speed of 8 Deg. /min. were obtained with a AME-
meter after catalyst in-situ treatment.
recorded at a programmed temperature velocity of lGC/min flow at 700% for 30 min. Gr-TPD
Hz-TPR
Mossbauer data profiles were
after samples were treated in Ar
measurements were performed with a HP-5980 GC-
MC meter. The TPD profiles were recorded at a programmed temperature velocity of 16-C/
min. When the programmed temperature reached 8OO’C, it was stopped and held for 10 min. * To whom correspondence should be addressed.
0920~5661/92/$05.00 0 1992- Elsevier Science Publishers B.V. All rightsreserved.
622 REXJLTS AND DISCUSSION
In the flow-reaction, FQ(FB15)
pure FeO,(FlOO)
has high activity but produces only Coz. B.&J
has poor activity and selectivity. NaCl/FeO#N25)
selectivity.
has high activity but poor
Only when NaCl and B& co-modify FeO, (FBN1525) , the catalyst can have
high activity and selectivity (Table).
The catalyst performance becomes better as ~content
increases. When the additive approaches 15 (at) %Bzo3, the CZyield and selectivity reach their maxima,
17% and 76%.
Table
respectively (Table).
Synergestic effect of NaCl and B&S on F&surface
~@w FlOO
Conversion ( % ) 02 c&
13. 5
Selectivity ( % ) CO
(-332
100
100
czE4
a%
0
0
FB20 49.8 I%.‘0 4% 3;54 ::: 2 8 BN* 15.7 13.7 18. 2 l% PN25 49 17.5 24.2 l62.55 27: PBNO525 5. 5 54.6 21. 2 22.1 18.7 PBN1025 5. 5 58.1 18. 2 22. 7 18.2 FBN1525 5. 8 56.9 18. 6 21. 4 G 18.8 FBN2025 6. 0 56.0 9. 2 19.9 21.5 FBN3025 T=750%, r=O. 24g s cmm3, Por,/Poz=32kPa except BN t . l
c2
0
0
4:82 29. 4 66.5 75. 8 76. 3 75: 5 65.2
;:: 5.4 16. 1 16.8 17. 4 16. 1 13. 0
l
EN+ denotes 8(wt%)BzoS/NaCl crnd3, Pm,/%=4
yield (%) c2
under reaction conditions:
T=750’(!,
~=l.
In the HZ-TPR profiles of the modified FeOx(Fig. 1) , the two peaks (490%, pure FeO,((FlOO) shift to higher temperature as B&is BzQ, the first peak of Bzo3/FeO&%15) Bfi/Fe9,
2Og
l
s
l
and Pp,=32kPa. 780-C) of
added. When the additive is 15(at) %
shiits from 490% to 755%.
by NaCl makes the first peak more narrow.
The modification of
In the TPR profiles of NaCl/BrOr/
FeO, catalysts (Fig. 2)) it is noted that the peak height ratio between the first and second peaks increases as the BzoScontent increases. The peak height ratio reaches a maximum when 15 (at) %l3& is added. This indicates that the NaCl mcdified BzO&?eO, catalyst has high reduction rate at 15(at) %BrCb content and at about 750%. Based on in-situ Mossbauer results @ii. 3)) it is noted that there are a-Fefi pure FeO,(FlOO)
and B&/F&(FB15>
after treating in flowing methane at 750% for 20
min. But there is only FeaO, in NaCl/B&FeO,
catalyst (FBN1525)
ment. This also shows that the NaCl/B&/Fe~catalyst In the Or-TPD profile of pure F-two
and Fe804 in
after the same treat-
has high W-reduction
peaks appear at 630% and 800%.
rate. The latter is re-
lated with the evaporation of the lattice oxygen, which is formed by experimental operation
623
400 500 600 700 800 go0 Temp.(%) Fig.1 HP-TPR profiles of the modified FeOx a:FlOO, brFBl5, ctFBNl525. 300
400
500 600 700 800 900 Temp. ( 'C) Fig.2 H2-TPR profiles of the FBN catalysts asFN25, brFBN0525, c:FBNl525, drFBN3025.
20
157 308 457 607 759 Temp.(%)
Fig.3 In-situ Hossbauer profiles Fig.4 02-TPD profiles of the of the modified Fe& modifies Feq( aMlOO,
brFB15, c:FBNl525.
azFlO0, brFB15, crFRXl525; MS Ion 32, Senei.r 1%09.
624
because the programmed temperature was stopped and held at 8OO.C for 10 min. The first peak disappears in the profile of B&r/ FeO, (FB15 ).
The profile of NaCl/ &OS/ FeC&
(FBN1525) is complicated before 6OOC, but the most attentive is that the last peak is much higher than that of pure FeO, or B&/FeO,
(Fig. 4).
This indicates that the NaCl/B&/
FeQ catalyst has high lattice oxygen evaporation rate. The relation of the catalyst performance and the so-called synergestic effect can be summerized as follows : (1) The BzC&content at which the CZyield and selectivity reach their maxima and that at which the TFW peak height ratio reaches its maximum are same, i. e. , 15(at) % BZG3. (2) The NaCl/BzOs/FeCLcatalyst evaporation rates at about 750°C.
(FBN1525) has
high reduction and lattice oxygen
Ibis catalyst has high activity and selectivity, and (3)
this temperature is the optimum reaction temperature of the catalyst in the oxidative wupling of methane. The XRD results show that NaCl can not well disperse on the surface of FeQ or BrO3/ Fea.
The addition of NaCl to Fa(F100,
FN25) and &Or/FeO,(FB15,
FBN1525)
do
change their Hz-TPR profiles, but with different changing pattern (Fig. 1, Fig. 2). Adding C&Q
to the feeding gas the performance of FeO, and B&/FeO,
the performance of Na@/Br03/Fe0,is
improved significantly.
is improved slightly, but
These results indicate that the
synergestic effect of NaCl and B&I3is critical to the catalyst performance although the pub lished argument inclined that the chloride compound participate the methane activation processes over metal chloride doped catalysts [ 41. XPS and CH&&-injection-reaction
results
show the chemisorption of chloride on the catalyst surface, which would be the reason why the chloride compound improves the catalyst performance. CONCLUSIONS (1) There is a synergestic effect between NaCl and B&3 on FeQ, surface. B203modifies the
redox ability of Fe%, the first Hrreduction
peak of FeQ. shifts from 49O’C to 755%.
The
NaCl modified B203/FeGx has high reduction and lattice oxygen evaporation rates at 750°C. (2) The high activity and selectivity of the NaCl/B203/FeG,catalyst
are close related with
this synergestic effect. REFERENCES 1 J. S. Lee and S. T. Gyama, Catal. Rev. -Sci. Eng. , 30(1988) 2 Y. Amenomiya,
et al. , Catal. .Rev. -Sci. Eng. 32(1990)
249.
163.
3 X. -R. Xia , G. -X. Xiong and X. -X. Guo. Proceedings of the Symposium on Novel Methods of Producing Olefins and Aromatics, April 1990, Boston, USA. 4 K. Otsuka , Methane Conversion Symposium,
1987, New Zealand.
CatalyGsToduy,13 (1992)621-624
Elsevier Science Publishers B.V., Amsterdam
Synergestic effect between NaCl and B203 in the NaC1/&03/FeOx catalysts for the oxidative coupling of methane X. -R. Xia”, G. -X. Xiong’ and X. -X. Guo Lab for Catalysis, Dalian Institute of Chemical Physics, Dalian 116023, China *Lab for Catalysis, Department of Chemistry, Jilin University,
Changchun 130023, China
JNTRODUCTION Alkali chloride doped transition metal oxides, especially modified by B& or P&,
have
high ethylene selectivity. Most of the papers were focused on the improvement of catalyst performance and the optimization of reaction conditions. However, there were few detailed basic researches on such catalysts [l , 21. In this paper several techniques, such as, flow-reaction, XRD, HrTPR , &-TPD and in-situ Moasbauer , were employed to investigate the properties of the titled catalysts at different stages of preparation,
periods of reaction and approaches of
treatment. EXPERIMENTAL
The NaCI/B203/FeO, catalysts were prepared by two-step impregnations. belling was as fohows, e.g. , pure Fe(X-FlOO, Cl/15(at)%BrO~/FeO,~FBN1525.
15(at)%B&/Fe0,-FB15,
The sample la25(at)%Na-
The methane conversion was performed in a conven-
tional fixed-bed reactor. The general reaction conditions were as follows: T=75O’C, 24g
l
s
l
cmm3, Pc~,/Po~=4,
P,,=32kPa,
r=O.
and balanced to atmospheric pressure by helium.
The reactant and product analyses were performed by on-line gas chromatography
(GC) as
described elsewhere [3]. XRD measurements were performed with a Rigaku D/MAX-RB
X-ray diffractometer us-
ing a copper target at 40 KVx lOOmA and scanning speed of 8 Deg. /min. were obtained with a AME-
meter after catalyst in-situ treatment.
recorded at a programmed temperature velocity of lGC/min flow at 700% for 30 min. Gr-TPD
Hz-TPR
Mossbauer data profiles were
after samples were treated in Ar
measurements were performed with a HP-5980 GC-
MC meter. The TPD profiles were recorded at a programmed temperature velocity of 16-C/
min. When the programmed temperature reached 8OO’C, it was stopped and held for 10 min. * To whom correspondence should be addressed.
0920~5661/92/$05.00 0 1992- Elsevier Science Publishers B.V. All rightsreserved.
622 REXJLTS AND DISCUSSION
In the flow-reaction, FQ(FB15)
pure FeO,(FlOO)
has high activity but produces only Coz. B.&J
has poor activity and selectivity. NaCl/FeO#N25)
selectivity.
has high activity but poor
Only when NaCl and B& co-modify FeO, (FBN1525) , the catalyst can have
high activity and selectivity (Table).
The catalyst performance becomes better as ~content
increases. When the additive approaches 15 (at) %Bzo3, the CZyield and selectivity reach their maxima,
17% and 76%.
Table
respectively (Table).
Synergestic effect of NaCl and B&S on F&surface
~@w FlOO
Conversion ( % ) 02 c&
13. 5
Selectivity ( % ) CO
(-332
100
100
czE4
a%
0
0
FB20 49.8 I%.‘0 4% 3;54 ::: 2 8 BN* 15.7 13.7 18. 2 l% PN25 49 17.5 24.2 l62.55 27: PBNO525 5. 5 54.6 21. 2 22.1 18.7 PBN1025 5. 5 58.1 18. 2 22. 7 18.2 FBN1525 5. 8 56.9 18. 6 21. 4 G 18.8 FBN2025 6. 0 56.0 9. 2 19.9 21.5 FBN3025 T=750%, r=O. 24g s cmm3, Por,/Poz=32kPa except BN t . l
c2
0
0
4:82 29. 4 66.5 75. 8 76. 3 75: 5 65.2
;:: 5.4 16. 1 16.8 17. 4 16. 1 13. 0
l
EN+ denotes 8(wt%)BzoS/NaCl crnd3, Pm,/%=4
yield (%) c2
under reaction conditions:
T=750’(!,
~=l.
In the HZ-TPR profiles of the modified FeOx(Fig. 1) , the two peaks (490%, pure FeO,((FlOO) shift to higher temperature as B&is BzQ, the first peak of Bzo3/FeO&%15) Bfi/Fe9,
2Og
l
s
l
and Pp,=32kPa. 780-C) of
added. When the additive is 15(at) %
shiits from 490% to 755%.
by NaCl makes the first peak more narrow.
The modification of
In the TPR profiles of NaCl/BrOr/
FeO, catalysts (Fig. 2)) it is noted that the peak height ratio between the first and second peaks increases as the BzoScontent increases. The peak height ratio reaches a maximum when 15 (at) %l3& is added. This indicates that the NaCl mcdified BzO&?eO, catalyst has high reduction rate at 15(at) %BrCb content and at about 750%. Based on in-situ Mossbauer results @ii. 3)) it is noted that there are a-Fefi pure FeO,(FlOO)
and B&/F&(FB15>
after treating in flowing methane at 750% for 20
min. But there is only FeaO, in NaCl/B&FeO,
catalyst (FBN1525)
ment. This also shows that the NaCl/B&/Fe~catalyst In the Or-TPD profile of pure F-two
and Fe804 in
after the same treat-
has high W-reduction
peaks appear at 630% and 800%.
rate. The latter is re-
lated with the evaporation of the lattice oxygen, which is formed by experimental operation
623
400 500 600 700 800 go0 Temp.(%) Fig.1 HP-TPR profiles of the modified FeOx a:FlOO, brFBl5, ctFBNl525. 300
400
500 600 700 800 900 Temp. ( 'C) Fig.2 H2-TPR profiles of the FBN catalysts asFN25, brFBN0525, c:FBNl525, drFBN3025.
20
157 308 457 607 759 Temp.(%)
Fig.3 In-situ Hossbauer profiles Fig.4 02-TPD profiles of the of the modified Fe& modifies Feq( aMlOO,
brFB15, c:FBNl525.
azFlO0, brFB15, crFRXl525; MS Ion 32, Senei.r 1%09.
624
because the programmed temperature was stopped and held at 8OO.C for 10 min. The first peak disappears in the profile of B&r/ FeO, (FB15 ).
The profile of NaCl/ &OS/ FeC&
(FBN1525) is complicated before 6OOC, but the most attentive is that the last peak is much higher than that of pure FeO, or B&/FeO,
(Fig. 4).
This indicates that the NaCl/B&/
FeQ catalyst has high lattice oxygen evaporation rate. The relation of the catalyst performance and the so-called synergestic effect can be summerized as follows : (1) The BzC&content at which the CZyield and selectivity reach their maxima and that at which the TFW peak height ratio reaches its maximum are same, i. e. , 15(at) % BZG3. (2) The NaCl/BzOs/FeCLcatalyst evaporation rates at about 750°C.
(FBN1525) has
high reduction and lattice oxygen
Ibis catalyst has high activity and selectivity, and (3)
this temperature is the optimum reaction temperature of the catalyst in the oxidative wupling of methane. The XRD results show that NaCl can not well disperse on the surface of FeQ or BrO3/ Fea.
The addition of NaCl to Fa(F100,
FN25) and &Or/FeO,(FB15,
FBN1525)
do
change their Hz-TPR profiles, but with different changing pattern (Fig. 1, Fig. 2). Adding C&Q
to the feeding gas the performance of FeO, and B&/FeO,
the performance of Na@/Br03/Fe0,is
improved significantly.
is improved slightly, but
These results indicate that the
synergestic effect of NaCl and B&I3is critical to the catalyst performance although the pub lished argument inclined that the chloride compound participate the methane activation processes over metal chloride doped catalysts [ 41. XPS and CH&&-injection-reaction
results
show the chemisorption of chloride on the catalyst surface, which would be the reason why the chloride compound improves the catalyst performance. CONCLUSIONS (1) There is a synergestic effect between NaCl and B&3 on FeQ, surface. B203modifies the
redox ability of Fe%, the first Hrreduction
peak of FeQ. shifts from 49O’C to 755%.
The
NaCl modified B203/FeGx has high reduction and lattice oxygen evaporation rates at 750°C. (2) The high activity and selectivity of the NaCl/B203/FeG,catalyst
are close related with
this synergestic effect. REFERENCES 1 J. S. Lee and S. T. Gyama, Catal. Rev. -Sci. Eng. , 30(1988) 2 Y. Amenomiya,
et al. , Catal. .Rev. -Sci. Eng. 32(1990)
249.
163.
3 X. -R. Xia , G. -X. Xiong and X. -X. Guo. Proceedings of the Symposium on Novel Methods of Producing Olefins and Aromatics, April 1990, Boston, USA. 4 K. Otsuka , Methane Conversion Symposium,
1987, New Zealand.