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JOURNAL OF CATALYSIS 171, 449–456 (1997)
ARTICLE NO. CA971810
Location of Active Sites for 3-Pentanone Formation during Ethene
Hydroformylation on Rh/Active-Carbon Catalysts
Hirotoshi Sakagami, Naoki Ohta, Shunsuke Endo, Teruyuki Harada, Nobuo Takahashi,1
and Takeshi Matsuda
Department of Materials Science, Kitami Institute of Technology, 165 Koencho, Kitami, Hokkaido 090, Japan
Received February 10, 1997; revised June 24, 1997; accepted June 24, 1997
decreased with an increase in CO partial pressure, while
r3-P increased; (iv) r3-P decreased when the catalyst was ex-
posed to CO at >433 K, whereas rPA was enhanced by this
treatment; and (v) the active sites for 3-pentanone forma-
tion required the presence of chlorine to be formed but
those for propanal formation did not. These results indi-
cate that the active sites for 3-pentanone formation are
different from those for propanal formation. It was al-
ready reported that the propanal formation is accelerated
by the presence of rhodium metal particles (5, 6). Chuang
et al. have proposed Rh+ sites at the surface of supported
rhodium metal particles as the active sites for the propanal
formation on Rh/SiO2 (7–9). The Rh/active-carbon cata-
lyst which showed high activity for 3-pentanone forma-
tion adsorbed a considerable amount of CO, and it showed
a CO desorption peak at almost the same position with
Rh6(CO)16-like species formed on Y-zeolite (10). In addi-
tion, EXAFS analysis of this sample suggested the presence
of Rh6(CO)16-like species (11). On the basis of the results
obtained, we suggested an important role of the Rh–CO
speciesin formingthe active speciesfor 3-pentanone forma-
tion.
In ethene hydroformylation over Rh/active carbon prepared
from RhCl3, 3-pentanone was formed in addition to propanal,
which was a common product in the reaction. In the case of propene
hydroformylation, however, butanal was exclusively formed and
no appreciable formation of ketones was observed. On the catalyst
treated with CO at 473 K, both activities for propanal and butanal
formation were observed to be higher than those on the catalyst
untreated. An approximate linear relation between the activity for
propanal formation and that for butanal formation was observed,
indicating that the active sites for aldehyde formation can catalyze
the reaction for both ethene and propene. On the other hand, the ac-
tivity for 3-pentanone formation was reduced by the CO treatment.
These results indicate that the transformation of active species for
3-pentanone formation into the active species for aldehyde forma-
tion was induced by the CO treatment. On the catalyst treated with
CO, a value for n/iso- ratio in butanal formed was observed to be
higher than that on the catalyst untreated. These results suggest
the formation of new active Rh particles in the narrower pores. On
the basis of the results obtained, the active species for 3-pentanone
formation was thought to be located in the narrow pores, where the
formation of reaction intermediates of C7-ketones from propene
would be strongly suppressed because of their bulky structure com-
c
pared with that for 3-pentanone.
1997 Academic Press
Formation of C7-ketones was reported by Rode et al.
in propene hydroformylation over Rh supported Y-zeolite
catalysts (12). If the Rh/active carbon could catalyze prop-
ene hydroformylation, n-butanal and isobutanal would be
formed. In addition, three kinds of ketones (4-heptanone,
2-methyl-3-hexanone, and 2,4-dimethyl-3-pentanone) are
expected to be produced. Active carbon is one of the
typical microporous materials. If the active sites for ke-
tone formation were located in the narrow pores, a ra-
tio of (ketone)/(aldehyde) would be small in propene
hydroformylation compared with that in ethene hydro-
formylation, since the intermediates of ketones are more
bulky than those for aldehydes. The ratio of (n-butanal)/
(isobutanal) may also reflect the location of active sites for
aldehyde formation, since the intermediate of isobutanal is
more bulky than that for n-butanal. In the present work,
the catalytic behavior of Rh/active carbon for propene
hydroformylation has been compared with that for ethene
INTRODUCTION
Rhodium supported on active carbon can catalyze ethene
hydroformylation as well as other supported rhodium cata-
lysts (1–4). In the reaction over the former catalyst, how-
ever, 3-pentanone is formed in addition to propanal, which
is a common hydroformylation product from ethene. The
following results were obtained in the previous work: (i)
an increase in the temperature for the pretreatment of the
catalyst with H2 reduced the activity for 3-pentanone for-
mation (denoted by r3-P), while the activity for propanal
formation (denoted by rPA) was enhanced; (ii) although r3-P
rapidly decreased with time on stream at reaction temper-
atures >413 K, rPA slowly decreased even at 453 K; (iii) rPA
1 To whom correspondence should be addressed.
449
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1997 by Academic Press
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