210
S.-H. Lee et al. / Journal of Catalysis 223 (2004) 200–211
the conditions in which a considerable amount of coke has
already built up on the outer surface of H-FER crystals, as
well as near the 8-ring pore mouths. This indicates that the
rate of coke formation on H-FER differs significantly ac-
cording to the intrazeolitic location of acid sites. If such is
the case, it should then be noted here that the amount (5.6%)
of coke deposited on H-FER-L is considerably smaller than
that (8.9%) on H-FER-S, while no significant differences
in the amount (∼ 6%) of coke formed are observed for H-
ZSM-5-L and H-ZSM-5-S (Table 1). Recall that these two
pairs of zeolites with small and large crystal sizes have sim-
ilar bulk Si/Al ratios, respectively. It is thus appears that the
rate of coke formation on zeolites can also depend on the
crystal size of these microporous materials, as well as on
their pore architecture and acidity [44,45], although there
is currently little understanding of the correlation between
coke formation and zeolite crystal size. Considering that the
general catalytic behavior of H-CLI is similar to that of H-
FER, on the other hand, one cannot claim that pore mouth
catalysis is unique with H-FER among the already known
10-ring zeolites. Based on the overall catalytic results of our
study, however, we believe that the 10-ring pores of H-FER
may have a more suitable degree of ellipticity of 10-ring
channels in more effectively chemisorbing n-butene mole-
cules near the pore mouths than the other 10-ring zeolites
studied here.
Acknowledgment
Funding for this work was provided by the Korea Sci-
ence and Engineering Foundation under Grant R02-2003-
000-10087-0 to S.B.H.
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4. Conclusions
The catalytic activities of the proton form of a series of
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