- Email: [email protected]
Catalytic performance of mesoporous silica SBA-15-supported noble metals for thiophene hydrodesulfurization
Studies in Surface Science and Catalysis 142 R. Aiello, G. Giordano and F. Testa (Editors) 9 2002 Elsevier Science B.V. All rights reserved.
739
Catalytic p e r f o r m a n c e of m e s o p o r o u s silica S B A - 1 5 - s u p p o r t e d noble metals for thiophene h y d r o d e s u l f u r i z a t i o n M. Sugioka*, T. Aizawa, Y. Kanda, T. Kurosaka, Y. Uemichi and S. Namba* Department of Applied Chemistry, Muroran Institute of Technology, 27-1 Mizumoto-cho, Muroran 050-8585, Japan +Department of Materials, Teikyou University of Science and Technology, Unohara-machi, Kitatsuru-gun, Yamanashi 409-0913, Japan
The Pt/AISBA-15
catalyst showed
high
hydrodesulfurization of thiophene at 350~
and
stable
catalytic
activity for
the
and this activity was higher than those of
Pt/SBA-15 and commercial CoMo/A1203 catalysts. The Pt/A1SBA-15 catalyst has high sulfur-tolerant property toward hydrogen sulfide formed in hydrodesulfurization of thiophene. The Broensted acid sites of A1SBA-15 and the spillover hydrogen formed on Pt particle in Pt/A1SBA- 15 catalyst play an important roles for the hydrodesulfurization of thiophene.
1. I N T R O D U C T I O N Hydrodesulfurization (HDS) of petroleum feedstocks is one of the important processes in the petroleum industry to produce clean fuels. The CoMo/AI203 catalyst has been widely used in the HDS process of petroleum. However, recently, the development of highly active HDS catalysts, which exhibit higher activity than commercial CoMo/AI203 HDS catalyst, have been claimed in the petroleum industry to produce lower sulfur content fuels. It has been accepted that metal-zeolite catalysts have high possibility as a new HDS catalyst for petroleum [1, 2]. The authors have also investigated the development of highly active HDS catalysts based on zeolites [3-5]. Recently, mesoporous silicate materials such as MCM-41 and FSM-16 with large pore diameter are attracting wide attention as new materials for catalysts and catalyst supports. Some
740 attempts have been done to develop new HDS catalyst using Mo, Co(Ni)-Mo(W) and MCM-41 [6, 7]. In the previous papers [8, 9], we have reported that noble metals, especially platinum, supported on FSM-16 and MCM-41 showed high and stable activity in the HDS of thiophene. However, these mesoporous silicas have weak points with thin wall and mechanically unstable for use of industrial HDS catalyst. In the present work, we investigated the catalytic performance of noble metals supported on mesoporous silicates SBA-15 and AISBA-15, which have thicker wall than those of FSM-16 and MCM-41, for the HDS catalyst in order to develop much more highly active and mechanically stable mesoporous silicate-based HDS catalysts. 2.
EXPERIMENTAL
HDS of thiophene over noble metals supported on SBA-15 and A1SBA-15 was carried out at 350~ under 1 atm by using a conventional fixed-bed flow reactor. Thiophene was introduced into the reactor by passing hydrogen through a thiophene trap cooled at 0~
The dehydration of
2-propanol and cracking of cumeme on SBA-15 and AISBA-15 were performed at 200~ and 400~
respectively, using 30mg of catalysts by pulse reactor.
Noble metals supported on SBA-15 and A1SBA-15 (Si/AI=15) were prepared by an impregnation method using noble metal chloride aqueous solutions; the amount of metal loading was 5 wt%. All catalysts were calcined at 500~ for 4 hrs in air and were reduced at 450~ for 1 hr prior to the HDS reaction. XRD analysis of the catalyst was carried out by using Rigaku diffractmeter with CuK a radiation. Infrared spectra of pyridine adsorbed on SBA-15 and A1SBA-15 were observed by using Jasco b-T-IR spectrometer. We used SBA-15 with surface area; 847 m2/g and channel diameter; 53 A, and A1SBA-15 with surface area; 666
mZ/gand channel diameter; 55 A.
3. R E S U L T S AND D I S C U S S I O N 3.1. Catalytic activities of noble metals supported on SBA-15 and A I S B A - 1 5
The catalytic activities of transition metals supported on SBA-15 were examined at 350~ for the HDS of thiophene. It was found that the catalytic activities of transition metals/SBA-15 such as Ni(Co)/SBA-15, Mo/SBA-15 (5wt% loading), 15wt% Mo/SBA-15 and 5wt% Co(Ni) -15wt% Mo/SBA-15 showed low activity and their activity values were lower than that of commercial CoMo/AlzO3 catalyst. Thus, we examined the catalytic activities of noble metals/SBA-15 for the HDS of thiophene at 350~
It was revealed that the catalytic activities of
741 noble metals/SBA-15 varied remarkably with the kind of noble metals as shown in Figure 1. The order of the activities of these catalysts for the HDS of thiophene after 2 hrs reaction was as follows: Pt/SBA- 15 >Pd/SBA- 15 >Rh/SBA- 15 >Ru/SBA- 15.
100 ,
.
.
.
.
.
.
.
.
.
.
80
.
.
.
.
Presulfided CoMo/AI,03
60 I~ O
40
5wt%Pd/S
~ 2O t
5
%Pt/SBA- 15
5wt%Rh/SBA- 15
5wt%Ru/SBA- 15
|
/'~'7.~
0
~
~:z~
1
~
.
~ -
....
!
....
I
2 3 4 Time. on stream(hour)
W/F = 87.9 g. hr/mol,
.
I
5
I-I=/Thlophene = 30
Figure 1. Hydrodesulfurization of thiophene over noble metal/SBA-15 catalysts at 350~ The activity of Pt/SBA-15 was the highest among noble metals/SBA-15 catalysts and this activity was almost the same as that of commercial CoMo/AIzO3 catalyst. The reaction products in the HDS of thiophene over Pt/SBA-15 were mainly C4 hydrocarbons (butane 90%, butenes 9%) and small amount of CI-C 3 (1%) hydrocarbons. These results indicate that Pt/SBA-15 catalyst has high hydrogenating ability for unsaturated C 4 hydrocarbons and low hydrocracking activity for hydrocarbons in the presence of hydrogen sulfide. As the activity of Pt/SBA-15 catalyst was almost the same as that of CoMo/A1203 catalyst, we examined the catalytic activities of noble metals supported on AISBA-15 for the HDS of thiophene at 350~
in order to develop much more highly active SBA-15 based HDS catalysts.
It was found that the catalytic activities of noble metals/A1SBA-15 were higher than those of noble metals/SBA-15. Pt/A1SBA-15 showed the highest activity among noble metals/AlSBA-15 catalysts as shown in Figure 2. The Pt/A1SBA-15 catalyst showed high and stable activity and this activity was higher than that of CoMo/AI203 catalysts.
742
100 AISBA-15
80 P, 9 60 40
5wt%Pd/Ak~A-15 '1,,..~_=_..
O
-_ ~_ -_ _~ _= " _ - - _ ! '
\
20
5
II
m
m
_an
|
.,.i
. .....
_n
_-
V A-15
5wI~FIu/NSBA-15 -,
0
,.-,-~
:.. "
1
~.=
+
--~
2
"
I. . . .
3
4
I.
.
!
5
Time on stream(hour) Figure 2. Hydrodesulfurization of thiophene over noble metal/AlSBA- 15 ~talysts at 350"C.
3.2.
Properties of Pt/AISBA-15 catalyst
As the Pt/A1SBA-15 catalyst showed high and stable activity for the HDS of thiophene, we studied in detail the catalytic properties of Pt/A1SBA-15 for the HDS of thiophene in order to clarify the cause of high activity of Pt/AISBA-15 for the HDS of thiophene. The effect of introduction of hydrogen sulfide on the catalytic activity of Pt/A1SBA-15 was examined in order to learn more about the origin of high and stable activity of Pt/A1SBA-15 catalyst. The introduction of hydrogen sulfide (3ml/min) was performed using a microfeeder with a glass syringe; the concentration of hydrogen sulfide in the hydrogen stream was ca.5 vol%. The catalytic activity of Pt/A1SBA-15 was remarkably decreased by the introduction of hydrogen sulfide in the course of HDS reaction. However, the decreased activity was almost restored after cutting off the introduction of hydrogen sulfide as shown in Figure 3. This shows that hydrogen sulfide is reversibly adsorbed on Pt/AISBA-15 and Pt/AISBA-15 catalyst has high sulfur-tolerant properties for the HDS of thiophene as well as Pt/FSM-16 and Pt/MCM-41 catalysts described in the previous paper [8, 9]. By this reason, Pt/AISBA-15 shows high and stable activity for the HDS of thiophene. We also examined the effect of introduction of ammonia on the catalytic activity of Pt/A1SBA-15 in the HDS of thiophene in order to clarify the role of acidic properties of Pt/A1SBA-15 in the HDS of thiophene. The introduction of ammonia (3ml/min) was carried out using microfeeder with glass syringe as well as that of hydrogen sulfide. It was revealed that
743 the catalytic activity of Pt/A1SBA-15 was decreased by the introduction of ammonia (ca.5 vol%) in the course of HDS reaction and the decreased activity was completely regenerated after cutting off the introduction of ammonia as shown in Figure 3. This result indicates that the acid site of Pt/A1SBA- 15 catalyst play an important role for the HDS of thiophene. 100
90 - ~ 80
NH~ Introduction (3 ml/min)
Introduction ~
70
v I::
o
60
(
= 50
>
)
oo 40 30
20 10 0
2
4
6
"lime on stream (hour)
8
10
Figure 3. Effect of introduction of hydrogen sulfide and ammonia on the catalytic acdvity of Pt/AISBA-15 in the hydrodesulfurization of thiophene at 350~
3.3. XRD analysis of Pt/SBA-15 and Pt/AISBA-15 catalysts Figure 4 shows the XRD analysis of A1SBA-15 and noble metal/AlSBA-15 catalysts before reduction. Almost the same XRD patterns as that of A1SBA-15 were obtained before and after loading of noble metals. This indicates that the structure of A1SBA-15 was maintained after loading of noble metals. In the case of SBA-15 before and after loading of noble metals, the situation was quite similar to that of AISBA- 15. Furthermore, almost the same XRD patterns of noble metals were observed in noble metals supported on SBA-15 and A1SBA-15 except platinum. No peaks of Pt were observed in the XRD analysis of Pt/A1SBA-15 but the sharp peaks of Pt were observed in the XRD analysis of Pt/SBA-15 as shown in Figure 4. These results indicate that Pt particles in Pt/A1SBA-15 are loaded on A1SBA-15 with high dispersion but Pt in Pt/SBA-15 is loaded on SBA-15 with relatively large particle size. Since we have reported that the acid site of HZSM-5 zeolite enhances the dispersion of Pt on HZSM-5 in our previous paper [5], high dispersion of Pt on AISBA-15 may be due to high acidity of A1SBA-15. By these results, it can be assumed that Pt/AISBA-15 has higher ability of activation of hydrogen, that is, the formation of spillover hydrogen, on highly dispersed Pt particles than Pt/SBA-15.
744
l i~ I~
a)AISEIA-- 15 b)RIVAISBA--- 15 c) Pd/AISBA-- 15
-" ~
;-;~:~
d) Ru/AISBA--- 15 e) Pt/AISBA-- 15 f)Pt/SBA-- 15
;:,,~='C'~~
9
_==
O)
o
c)
I 5
10 15 20 25 30 35 40 45 50 5 5 ' 6 0 2 0/degree
65 70 75 80 85 90
Figure 4. XRD patterns for noble metallAlSBA-15eatalystsbefore reduction.
3.4.
Mechanism of HDS of thiophene on Pt/AISBA-15 Catalyst
Pt/A1SBA-15 catalyst showed higher activity for the HDS of thiophene than Pt/SBA-15 and commercial CoMo/A1203 catalysts. We also studied the active sites and reaction mechanism in the HDS of thiophene over Pt/AISBA-15 catalyst. 100 90 8O vI:: 70
El 2-Propanol dehydration I= Cumene cracking
o
"~ 60 o
> g: 50 oo 40 30
20 10
Low activity SBA--15
AISBA-- 15
Figure 5. Catalytic activities of SBA-15 and AISBA-15 for the dehydration of 2-propanol (200~
and cracking of cumeme (400"C).
745 We evaluated the acidic properties of SBA-15 and A1SBA-15 by the reactions of 2-propanol dehydration (200~
and cumene cracking (400~
using pulse reactor. It was revealed that
SBA-15 showed very low activity for both reactions but AISBA-15 showed remarkably high activity for these reactions as shown in Figure 5. These results indicate that AISBA-15 has high acidity and there exists the Broensted acid sites on A1SBA-15. We also confirmed the existence of the Broensted acid sites at 1547 cm -1 on A1SBA-15 by the observation of b-T-IR spectra of pyridine adsorbed on AISBA-15 as shown in Figure 6. Thus, we supposed that the Broensted acid site of A1SBA- 15 acts as active site for the activation of thiophene in the HDS of thiophene.
ID
o r-co
b)AISBA-15
x~ 0
1700
1600
1500
1400
1300
Wavenumber (cm -I) SBA- 15and AISBA- 15 were evacuated at 500~ for 2 hrs. Pyridine was
adsorbed at 150~ followed by evacuation at 150,"C for 0.5 hr. Figure 6. Infrared spectra of pyridine adsorbed on SBA-15 and A1SBA-15.
On the basis of these results, we propose a possible mechanism for the HDS of thiophene over Pt/A1SBA-15 as shown in Scheme 1. In the proposed mechanism, the Broensted acid site in the Pt/AISBA-15 acts as active site for the activation of thiophene and Pt acts as active site for the activation of hydrogen to form spillover hydrogen. The spillover hydrogen formed on Pt attacks the activated thiophene on the Broensted acid site on A1SBA-15.
746
HzS + C4Hydrocarbon
H
H~
H-~Hydmg~_
f~[
Activated thiophene ] , 4 - - - -
Pt
.
~
.
.
.
.
.
H+ Br~nsted ,
0 9
|
acid site 9
.
[~
"' '
~ ~ d , e ~ AISBA-15
. . . . . . . .
Acid" sltef " '
............
Scheme 1. The possible mechanism of hydrodesulfurization of thiophene over
Pt/AISBA-15 catalyst. 4. C O N C L U S I O N It was revealed that the Pt/A1SBA-15 catalyst showed high and stable activity for the HDS of thiophene and this activity was higher than that of commercial CoMo/AI203 HDS catalyst. Therefore, it is concluded that there is a possibility for using Pt/AISBA-15 as highly active new HDS catalyst for bulky organic sulfur compounds in the petroleum feedstocks. ACKNOWLEDGEMENT
This work was partly supported by KAWASAKI STEF.I~21 Century Foundation, Japan and Petroleum Energy Center of Japan. REFERENCES
1. M. Laniecki and W. Zmierczak, Zeolites, 11(1991)18. 2. Y. Okamoto, Catal. Today, 39(1997)45. 3. M. Sugioka, Erdol & Kohle, Erdgas, Petrochemie, 48(1995)128. 4. M. Sugioka, F. Sado, T. Kurosaka and X. Wang, Catal. Today, 45(1998)327. 5. T. Kurosaka, M. Sugioka and H. Matsuhashi, Bull. Chem. Soc. Jpn, 74(2001)747. 6. K. M. Reddy, B. Wei and C. Song, Catal. Today, 43(1998)261. 7. A. Wang, Y. Wang, T. Kabe, Y. Chen, A. Ishihara and W. Qian, J. Catal., 199(2001)19. 8. M. Sugioka, L. Andalaluna, S. Morishita and T. Kurosaka, Catal. Today, 39(1997)61. 9. M. Sugioka, S. Morishita, T. Kurosaka, A. Seino, M. Nakagawa and S. Namba, Stud. Surf. Sci. Catal., 125(1999)531.
739
Catalytic p e r f o r m a n c e of m e s o p o r o u s silica S B A - 1 5 - s u p p o r t e d noble metals for thiophene h y d r o d e s u l f u r i z a t i o n M. Sugioka*, T. Aizawa, Y. Kanda, T. Kurosaka, Y. Uemichi and S. Namba* Department of Applied Chemistry, Muroran Institute of Technology, 27-1 Mizumoto-cho, Muroran 050-8585, Japan +Department of Materials, Teikyou University of Science and Technology, Unohara-machi, Kitatsuru-gun, Yamanashi 409-0913, Japan
The Pt/AISBA-15
catalyst showed
high
hydrodesulfurization of thiophene at 350~
and
stable
catalytic
activity for
the
and this activity was higher than those of
Pt/SBA-15 and commercial CoMo/A1203 catalysts. The Pt/A1SBA-15 catalyst has high sulfur-tolerant property toward hydrogen sulfide formed in hydrodesulfurization of thiophene. The Broensted acid sites of A1SBA-15 and the spillover hydrogen formed on Pt particle in Pt/A1SBA- 15 catalyst play an important roles for the hydrodesulfurization of thiophene.
1. I N T R O D U C T I O N Hydrodesulfurization (HDS) of petroleum feedstocks is one of the important processes in the petroleum industry to produce clean fuels. The CoMo/AI203 catalyst has been widely used in the HDS process of petroleum. However, recently, the development of highly active HDS catalysts, which exhibit higher activity than commercial CoMo/AI203 HDS catalyst, have been claimed in the petroleum industry to produce lower sulfur content fuels. It has been accepted that metal-zeolite catalysts have high possibility as a new HDS catalyst for petroleum [1, 2]. The authors have also investigated the development of highly active HDS catalysts based on zeolites [3-5]. Recently, mesoporous silicate materials such as MCM-41 and FSM-16 with large pore diameter are attracting wide attention as new materials for catalysts and catalyst supports. Some
740 attempts have been done to develop new HDS catalyst using Mo, Co(Ni)-Mo(W) and MCM-41 [6, 7]. In the previous papers [8, 9], we have reported that noble metals, especially platinum, supported on FSM-16 and MCM-41 showed high and stable activity in the HDS of thiophene. However, these mesoporous silicas have weak points with thin wall and mechanically unstable for use of industrial HDS catalyst. In the present work, we investigated the catalytic performance of noble metals supported on mesoporous silicates SBA-15 and AISBA-15, which have thicker wall than those of FSM-16 and MCM-41, for the HDS catalyst in order to develop much more highly active and mechanically stable mesoporous silicate-based HDS catalysts. 2.
EXPERIMENTAL
HDS of thiophene over noble metals supported on SBA-15 and A1SBA-15 was carried out at 350~ under 1 atm by using a conventional fixed-bed flow reactor. Thiophene was introduced into the reactor by passing hydrogen through a thiophene trap cooled at 0~
The dehydration of
2-propanol and cracking of cumeme on SBA-15 and AISBA-15 were performed at 200~ and 400~
respectively, using 30mg of catalysts by pulse reactor.
Noble metals supported on SBA-15 and A1SBA-15 (Si/AI=15) were prepared by an impregnation method using noble metal chloride aqueous solutions; the amount of metal loading was 5 wt%. All catalysts were calcined at 500~ for 4 hrs in air and were reduced at 450~ for 1 hr prior to the HDS reaction. XRD analysis of the catalyst was carried out by using Rigaku diffractmeter with CuK a radiation. Infrared spectra of pyridine adsorbed on SBA-15 and A1SBA-15 were observed by using Jasco b-T-IR spectrometer. We used SBA-15 with surface area; 847 m2/g and channel diameter; 53 A, and A1SBA-15 with surface area; 666
mZ/gand channel diameter; 55 A.
3. R E S U L T S AND D I S C U S S I O N 3.1. Catalytic activities of noble metals supported on SBA-15 and A I S B A - 1 5
The catalytic activities of transition metals supported on SBA-15 were examined at 350~ for the HDS of thiophene. It was found that the catalytic activities of transition metals/SBA-15 such as Ni(Co)/SBA-15, Mo/SBA-15 (5wt% loading), 15wt% Mo/SBA-15 and 5wt% Co(Ni) -15wt% Mo/SBA-15 showed low activity and their activity values were lower than that of commercial CoMo/AlzO3 catalyst. Thus, we examined the catalytic activities of noble metals/SBA-15 for the HDS of thiophene at 350~
It was revealed that the catalytic activities of
741 noble metals/SBA-15 varied remarkably with the kind of noble metals as shown in Figure 1. The order of the activities of these catalysts for the HDS of thiophene after 2 hrs reaction was as follows: Pt/SBA- 15 >Pd/SBA- 15 >Rh/SBA- 15 >Ru/SBA- 15.
100 ,
.
.
.
.
.
.
.
.
.
.
80
.
.
.
.
Presulfided CoMo/AI,03
60 I~ O
40
5wt%Pd/S
~ 2O t
5
%Pt/SBA- 15
5wt%Rh/SBA- 15
5wt%Ru/SBA- 15
|
/'~'7.~
0
~
~:z~
1
~
.
~ -
....
!
....
I
2 3 4 Time. on stream(hour)
W/F = 87.9 g. hr/mol,
.
I
5
I-I=/Thlophene = 30
Figure 1. Hydrodesulfurization of thiophene over noble metal/SBA-15 catalysts at 350~ The activity of Pt/SBA-15 was the highest among noble metals/SBA-15 catalysts and this activity was almost the same as that of commercial CoMo/AIzO3 catalyst. The reaction products in the HDS of thiophene over Pt/SBA-15 were mainly C4 hydrocarbons (butane 90%, butenes 9%) and small amount of CI-C 3 (1%) hydrocarbons. These results indicate that Pt/SBA-15 catalyst has high hydrogenating ability for unsaturated C 4 hydrocarbons and low hydrocracking activity for hydrocarbons in the presence of hydrogen sulfide. As the activity of Pt/SBA-15 catalyst was almost the same as that of CoMo/A1203 catalyst, we examined the catalytic activities of noble metals supported on AISBA-15 for the HDS of thiophene at 350~
in order to develop much more highly active SBA-15 based HDS catalysts.
It was found that the catalytic activities of noble metals/A1SBA-15 were higher than those of noble metals/SBA-15. Pt/A1SBA-15 showed the highest activity among noble metals/AlSBA-15 catalysts as shown in Figure 2. The Pt/A1SBA-15 catalyst showed high and stable activity and this activity was higher than that of CoMo/AI203 catalysts.
742
100 AISBA-15
80 P, 9 60 40
5wt%Pd/Ak~A-15 '1,,..~_=_..
O
-_ ~_ -_ _~ _= " _ - - _ ! '
\
20
5
II
m
m
_an
|
.,.i
. .....
_n
_-
V A-15
5wI~FIu/NSBA-15 -,
0
,.-,-~
:.. "
1
~.=
+
--~
2
"
I. . . .
3
4
I.
.
!
5
Time on stream(hour) Figure 2. Hydrodesulfurization of thiophene over noble metal/AlSBA- 15 ~talysts at 350"C.
3.2.
Properties of Pt/AISBA-15 catalyst
As the Pt/A1SBA-15 catalyst showed high and stable activity for the HDS of thiophene, we studied in detail the catalytic properties of Pt/A1SBA-15 for the HDS of thiophene in order to clarify the cause of high activity of Pt/AISBA-15 for the HDS of thiophene. The effect of introduction of hydrogen sulfide on the catalytic activity of Pt/A1SBA-15 was examined in order to learn more about the origin of high and stable activity of Pt/A1SBA-15 catalyst. The introduction of hydrogen sulfide (3ml/min) was performed using a microfeeder with a glass syringe; the concentration of hydrogen sulfide in the hydrogen stream was ca.5 vol%. The catalytic activity of Pt/A1SBA-15 was remarkably decreased by the introduction of hydrogen sulfide in the course of HDS reaction. However, the decreased activity was almost restored after cutting off the introduction of hydrogen sulfide as shown in Figure 3. This shows that hydrogen sulfide is reversibly adsorbed on Pt/AISBA-15 and Pt/AISBA-15 catalyst has high sulfur-tolerant properties for the HDS of thiophene as well as Pt/FSM-16 and Pt/MCM-41 catalysts described in the previous paper [8, 9]. By this reason, Pt/AISBA-15 shows high and stable activity for the HDS of thiophene. We also examined the effect of introduction of ammonia on the catalytic activity of Pt/A1SBA-15 in the HDS of thiophene in order to clarify the role of acidic properties of Pt/A1SBA-15 in the HDS of thiophene. The introduction of ammonia (3ml/min) was carried out using microfeeder with glass syringe as well as that of hydrogen sulfide. It was revealed that
743 the catalytic activity of Pt/A1SBA-15 was decreased by the introduction of ammonia (ca.5 vol%) in the course of HDS reaction and the decreased activity was completely regenerated after cutting off the introduction of ammonia as shown in Figure 3. This result indicates that the acid site of Pt/A1SBA- 15 catalyst play an important role for the HDS of thiophene. 100
90 - ~ 80
NH~ Introduction (3 ml/min)
Introduction ~
70
v I::
o
60
(
= 50
>
)
oo 40 30
20 10 0
2
4
6
"lime on stream (hour)
8
10
Figure 3. Effect of introduction of hydrogen sulfide and ammonia on the catalytic acdvity of Pt/AISBA-15 in the hydrodesulfurization of thiophene at 350~
3.3. XRD analysis of Pt/SBA-15 and Pt/AISBA-15 catalysts Figure 4 shows the XRD analysis of A1SBA-15 and noble metal/AlSBA-15 catalysts before reduction. Almost the same XRD patterns as that of A1SBA-15 were obtained before and after loading of noble metals. This indicates that the structure of A1SBA-15 was maintained after loading of noble metals. In the case of SBA-15 before and after loading of noble metals, the situation was quite similar to that of AISBA- 15. Furthermore, almost the same XRD patterns of noble metals were observed in noble metals supported on SBA-15 and A1SBA-15 except platinum. No peaks of Pt were observed in the XRD analysis of Pt/A1SBA-15 but the sharp peaks of Pt were observed in the XRD analysis of Pt/SBA-15 as shown in Figure 4. These results indicate that Pt particles in Pt/A1SBA-15 are loaded on A1SBA-15 with high dispersion but Pt in Pt/SBA-15 is loaded on SBA-15 with relatively large particle size. Since we have reported that the acid site of HZSM-5 zeolite enhances the dispersion of Pt on HZSM-5 in our previous paper [5], high dispersion of Pt on AISBA-15 may be due to high acidity of A1SBA-15. By these results, it can be assumed that Pt/AISBA-15 has higher ability of activation of hydrogen, that is, the formation of spillover hydrogen, on highly dispersed Pt particles than Pt/SBA-15.
744
l i~ I~
a)AISEIA-- 15 b)RIVAISBA--- 15 c) Pd/AISBA-- 15
-" ~
;-;~:~
d) Ru/AISBA--- 15 e) Pt/AISBA-- 15 f)Pt/SBA-- 15
;:,,~='C'~~
9
_==
O)
o
c)
I 5
10 15 20 25 30 35 40 45 50 5 5 ' 6 0 2 0/degree
65 70 75 80 85 90
Figure 4. XRD patterns for noble metallAlSBA-15eatalystsbefore reduction.
3.4.
Mechanism of HDS of thiophene on Pt/AISBA-15 Catalyst
Pt/A1SBA-15 catalyst showed higher activity for the HDS of thiophene than Pt/SBA-15 and commercial CoMo/A1203 catalysts. We also studied the active sites and reaction mechanism in the HDS of thiophene over Pt/AISBA-15 catalyst. 100 90 8O vI:: 70
El 2-Propanol dehydration I= Cumene cracking
o
"~ 60 o
> g: 50 oo 40 30
20 10
Low activity SBA--15
AISBA-- 15
Figure 5. Catalytic activities of SBA-15 and AISBA-15 for the dehydration of 2-propanol (200~
and cracking of cumeme (400"C).
745 We evaluated the acidic properties of SBA-15 and A1SBA-15 by the reactions of 2-propanol dehydration (200~
and cumene cracking (400~
using pulse reactor. It was revealed that
SBA-15 showed very low activity for both reactions but AISBA-15 showed remarkably high activity for these reactions as shown in Figure 5. These results indicate that AISBA-15 has high acidity and there exists the Broensted acid sites on A1SBA-15. We also confirmed the existence of the Broensted acid sites at 1547 cm -1 on A1SBA-15 by the observation of b-T-IR spectra of pyridine adsorbed on AISBA-15 as shown in Figure 6. Thus, we supposed that the Broensted acid site of A1SBA- 15 acts as active site for the activation of thiophene in the HDS of thiophene.
ID
o r-co
b)AISBA-15
x~ 0
1700
1600
1500
1400
1300
Wavenumber (cm -I) SBA- 15and AISBA- 15 were evacuated at 500~ for 2 hrs. Pyridine was
adsorbed at 150~ followed by evacuation at 150,"C for 0.5 hr. Figure 6. Infrared spectra of pyridine adsorbed on SBA-15 and A1SBA-15.
On the basis of these results, we propose a possible mechanism for the HDS of thiophene over Pt/A1SBA-15 as shown in Scheme 1. In the proposed mechanism, the Broensted acid site in the Pt/AISBA-15 acts as active site for the activation of thiophene and Pt acts as active site for the activation of hydrogen to form spillover hydrogen. The spillover hydrogen formed on Pt attacks the activated thiophene on the Broensted acid site on A1SBA-15.
746
HzS + C4Hydrocarbon
H
H~
H-~Hydmg~_
f~[
Activated thiophene ] , 4 - - - -
Pt
.
~
.
.
.
.
.
H+ Br~nsted ,
0 9
|
acid site 9
.
[~
"' '
~ ~ d , e ~ AISBA-15
. . . . . . . .
Acid" sltef " '
............
Scheme 1. The possible mechanism of hydrodesulfurization of thiophene over
Pt/AISBA-15 catalyst. 4. C O N C L U S I O N It was revealed that the Pt/A1SBA-15 catalyst showed high and stable activity for the HDS of thiophene and this activity was higher than that of commercial CoMo/AI203 HDS catalyst. Therefore, it is concluded that there is a possibility for using Pt/AISBA-15 as highly active new HDS catalyst for bulky organic sulfur compounds in the petroleum feedstocks. ACKNOWLEDGEMENT
This work was partly supported by KAWASAKI STEF.I~21 Century Foundation, Japan and Petroleum Energy Center of Japan. REFERENCES
1. M. Laniecki and W. Zmierczak, Zeolites, 11(1991)18. 2. Y. Okamoto, Catal. Today, 39(1997)45. 3. M. Sugioka, Erdol & Kohle, Erdgas, Petrochemie, 48(1995)128. 4. M. Sugioka, F. Sado, T. Kurosaka and X. Wang, Catal. Today, 45(1998)327. 5. T. Kurosaka, M. Sugioka and H. Matsuhashi, Bull. Chem. Soc. Jpn, 74(2001)747. 6. K. M. Reddy, B. Wei and C. Song, Catal. Today, 43(1998)261. 7. A. Wang, Y. Wang, T. Kabe, Y. Chen, A. Ishihara and W. Qian, J. Catal., 199(2001)19. 8. M. Sugioka, L. Andalaluna, S. Morishita and T. Kurosaka, Catal. Today, 39(1997)61. 9. M. Sugioka, S. Morishita, T. Kurosaka, A. Seino, M. Nakagawa and S. Namba, Stud. Surf. Sci. Catal., 125(1999)531.