Abstract accepted for poster presentation in ZMPC-Totttori(2006)

1. Catalytic Isomerization of n-butane and n-pentane over Sulfided AgHMordenite Zeolite
Lebong Andalaluna1,2,* and Masatoshi Sugioka1
Department of Applied Chemistry, Muroran Institute of Technology, 27-1 Mizumoto-cho,
Muroran-shi 050-8585, Japan 2DTIEML,BPPT.
*
Corresponding author, e-mail andalalu@inn.bppt.go.id, fax +62-21-8297433
Catalytic isomerization of n-butane and n-pentane proceeded predominantly via bimolecular
pathway over sulfided AgHMordenite zeolite (SAHMOR), as well as in HMordenite zeolite
(HMOR). It was revealed that SAHMOR showed particular high enhanced activity which was
remarkably higher than that of parent HMOR in n-butane isomerization. However, the catalyst only
showed comparable catalytic activity with that of HMOR in n-pentane isomerization. It is proposed
that the formation of C10+ intermediate in n-pentane isomerization was inhibited by zeolite channel
narrowing as the result of silver-sulfide species (AgSx) formation in the sulfiding of AgHMordenite.
Introduction
In the previous works, we have reported that sulfiding of metal ion-exchanged zeolites and
mesoporous material with hydrogen sulfide resulted remarkable activity enhancement for some
acid-catalyzed reactions [1,2]. Mordenite is applied commercially as alkanes isomerization catalyst
which is an important process for producing high quality of automotive fuel. In current study, the
catalytic activities of sulfided AgHMordenite zeolite (SAHMOR) in the isomerization of n-alkanes
(n-butane and n-pentane) was examined. The catalytic performance of the catalyst was associated
with surface active sites and pore character generated over SAHMOR in the sulfiding.
Experimental
HMordenite (HMOR) was prepared using 0.1 mol/l HCl aqueous solution and AgHMordenite
(AHMOR) was prepared by ion exchanging HMOR using 0.1 mol/l aqueous solution of AgNO3.
All samples were calcined in air at 500ºC for 4 hours. Isomerization of n-butane and n-pentane were
carried out on a conventional closed circulating reactor at 250ºC and 220ºC, respectively. AHMOR
were sulfided with 40 Torr of hydrogen sulfide at 300ºC for one hour and evacuated for 0.5 hour at
the same temperature to obtain SAHMOR. Infrared spectroscopic study of pyridine adsorption and
deuterium exchange were also performed by Jasco FT-IR 230S using an in-situ cell
Results and Discussions
Skeletal isomerization of n-butane proceed via bimolecular reaction route over acidic zeolite,
involving the formation of C8 carbenium ion [3]. Mordenite has a one-dimensional micropore
system with opening channel of 6.5 x 7.0 Å. The one-dimensional pore of Mordenite [4] and
inclusion of metal particle inside the zeolite channel [5] was proposed inhibit sterically the
bimolecular pathway of the reaction.
Figure 1 shows the catalytic isomerization of n-butane over HMOR and SAHMOR at 250ºC. It
was observed that SAHMOR showed remarkable high catalytic activity in the isomerization, which
was much higher than that of its parent HMOR. SAHMOR showed twice of HMOR n-butane
conversion after 4 hours reaction. Furthermore, SAHMOR was revealed exhibiting significant
catalytic activity at 200ºC with much shorter induction period than HMOR (figure not shown).
The isomerization of n-pentane over HMOR and SAHMOR at 220ºC is shown in Figure 2. The
isomerization products was mainly C2-C5 hydrocarbons with low selectivity to iso-pentane which
showed that the isomerization predominantly occured through bimolecular mechanism via C10+
intermediate formation [6]. It was observed that SAHMOR showed high catalytic activity in the
isomerization. However, in contrast with result in n-butane isomerization, the activity was only
slightly higher than that of HMOR. Moreover, an induction period was observed over SAHMOR
in the isomerization. The initial product was predominantly iso-pentane which indicated that
monomolecular reaction might occured in the initial reaction over SAHMOR. We assumed that
C10+ intermediate formation of bimolecular route in n-pentane isomerization was suppresed over
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2. 25 25
C1 C1
Amount of product (%)
Amount of product (%)
20 C3 20 C3
i-C4 i-C4
i-C5 i-C5
15 15 n-C5
n-C5
10 10
5 5
0 0
0 120 240 360 480 0 120 240 360 480
Reaction time (min) Reaction time (min)
Figure 1: Catalytic isomerization of n-butane over HMOR and SAHMOR zeolites, respectively.
20 20
C3 C3
Amount of product (%)
Amount of product (%)
i-C4 16 i-C4
16 n-C4
n-C4 i-C5
12 i-C5 12
8 8
4 4
0 0
0 60 120 180 240 0 60 120 180 240
Reaction Time (min) Reaction Time (min)
Figure 2: Catalytic isomerization of n-pentane over HMOR and SAHMOR zeolites, respectively.
SAHMOR. This kind of inhibition might occured as the result of narrowing of mordenite zeolite
pore system due to formation of silver-sulfide species inside one-dimensional channel of mordenite
zeolite. Such as inhibition was apparent in the isomerization of n-pentane but not in the case of
n-butane isomerization, possibly due to bulkier size of C10+ intermediate of n-pentane isomerization
than C8 carbenium ion intermediate of n-butane isomerization.
Conclusion
Sulfided AgHMordenite zeolite (SAHMOR) showed remarkable high activity for n-butane
isomerization which was much higher than that of HMOR. On the other hand, the catalytic activity
of for n-pentane isomerization was affected by suppression of C10+ intermediate formation as the
result of formation of silver-sulfide species (AgSx-) inside the mordenite zeolite pore system.
References
[1] M. Sugioka and L. Andalaluna, Stud. Surf. Sci. Catal., 105 (1997) 1995.
[2] M. Sugioka, L. Andalaluna and J.K.A. Dapaah, Stud. Surf. Sci. Catal., 129 (2000) 823.
[3] R.A. Asuquo, G. Eder-Mirth, J.A. Lercher, J. Catal. 135 (1992) 115.
[4] H. Liu, G.D. Lei, W.M.H. Sachtler, Appl. Catal. A, 137, 167(1996).
[5] P. Canizares, A. de Lucas, F. Dorado, D. Perez, Appl. Catal. A, 190 (2000) 233.
[6] N. Essayem, Y. Ben Taarit, C. Feche, P.Y. Gayraud, G. Sapaly, C. Naccache, J. Catal., 219
(2003) 97.
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