Vapor-phase synthesis of symmetric ketone from alcohol over CeO2-Fe2O3 catalysts

Article abstract of DOI:10.1246/cl.2000.232

Formation of 3-pentanone via oxidative dimerization of 1-propanol was investigated over CeO₂-based solid solution with various metal oxides. An addition of Fe₂O₃ into CeO₂ greatly enhanced the 3-pentanone formation, and both 1-propanol conversion and 3-pentanone selectivity were maximized at Fe content of 20 mol%. It was found that the CeO₂-Fe₂O₃ effectively works as a catalyst for the formation of symmetric ketones such as 3-pentanone, 4-heptanone, 5-nonanone, etc.

Full text of DOI:10.1246/cl.2000.232

232
Chemistry Letters 2000
Vapor-Phase Synthesis of Symmetric Ketone from Alcohol over CeO2-Fe2O3 Catalysts
Yoichiro Kamimura, Satoshi Sato,* Ryoji Takahashi, Toshiaki Sodesawa, and Masahiro Fukui†
Department of Materials Technology, Faculty of Engineering, Chiba University, Yayoi, Inage-ku, Chiba 263-8522
†Group Planning-Performance Products, Chisso Co. , 2-7-3 Marunouchi, Chiyoda-ku, Tokyo 100-8333
(Received November 2 , 1999; CL-990935)
Formation of 3-pentanone via oxidative dimerization of l-
propanol was investigated over CeO2-based solid solution with
various metal oxides. An addition of Fe2O3 into CeO2 greatly
enhanced the 3-pentanone formation, and both l-propanol con-
version and 3-pentanone selectivity were maximized at Fe con-
tent of 20 mol%. It was found that the CeO2-Fe2O3 effectively
works as a catalyst for the formation of symmetric ketones such
as 3-pentanone, 4-heptanone, 5-nonanone, etc.
CeO2 is an attractive catalyst for various reactions such as
hydrogenation of CO1 and alkylation of phenol.2-4 In the alky-
lation of phenol using l-propanol, we found that 3-pentanone
was observed as a by-product over CeO2-MgO solid solution
catalyst, and that the yield of 3-pentanone increased with
increasing CeO2 content in the CeO2-MgO.4 We have speculat-
ed that the total reaction proceeds as follows: l-propanol is
dehydrogenated to propanal, followed by aldol addition to pro-
duce 3-hydroxy-2-methylpentanal, and finally it is decomposed
to 3-pentanone.
In this work, we examine catalytic tests of l-propanol con-
version over CeO2-based solid solution with various metal
oxides (MOx), and discuss what in the catalyst essentially
affects the 3-pentanone formation. Furthermore, we examine
syntheses of symmetric ketones from the other alcohols.
All reagents were supplied by Wako Pure Chemical indus-
tries, Ltd. (Japan). CeO2-based solid solution (CeO2-MOx)
samples were prepared by using cerium (III) nitrate hexahy-
drate, another metal (M) nitrate, and citric acid monohydrate.
The preparation procedure has been described elsewhere.3 After
the citrate precursor had been heated in air at 170 °C for 2 h, it
was calcined in air at 550 °C for 2 h to provide a CeO2-MOx
sample. The content of MOx was defined as a mol percent of
metal ion.
tests at 450 °C, every catalyst we examined showed no decay in
the catalytic activity with process time. Conversion levels of 1-
propanol over CeO2 modified with alkaline earth oxides (M=
Mg, Ca, Sr, and Ba) and acidic oxides (M = B and Al) were
lower than that of pure CeO2, while the product distribution
was similar to that of pure CeO2. This indicates that the addi-
tion of the oxides into CeO2 decreases the catalytic activity of
pure CeO2 because it dilutes the surface Ce concentration in the
solid solution. Although the conversion levels over CeO2 mod-
ified with transition metal oxides (M = Co, Ni, Cu, and Zn)
were higher than that of pure CeO2, selectivities to 3-pentanone
were lower than that of pure CeO2. Over the catalysts, propanal
is not dimerized, whereas l-propanol is readily dehydrogenated
to propanal. In contrast, not only 1-propanol conversions but
also 3-pentanone selectivities of CeO2-Fe2O3 and CeO2-Mn2O3
catalysts were higher than those of pure CeO2. The gaseous
hydrocarbons such as methane, ethane, ethene, propane and
propene were observed in the reaction effluent (Table l): ca.
50% of them was propane in case of CeO2-Fe2O3. In addition,
propyl propionate was detected as another by-product.
The reaction of 1-propanol was carried out in a usual fixed
bed flow reactor under atmospheric pressure of N2 at 450 °C.
Prior to the reaction, a catalyst sample (0.15 g) was preheated
in a glass tube reactor at 500 °C for 1 h. l-Propanol was fed
into the reactor at 450 °C at the rate of 23 mmol h-1, together
with N2 flow of 73 mmol h-1. An effluent collected in an ice
trap was extracted every an hour, and analyzed by FID-GC with
a packed column of Silicon OV-17 (2 m) at temperatures con-
trolled from 50 to 220 °C at a heating rate of 5 K min−1
.
Gaseous hydrocarbons such as propane and propene were ana-
lyzed by FID-GC with a packed column of either PEG-HT (1
m) or VZ-7 (6 m) at a constant temperature of 40 °C. The cat-
alytic activities are estimated by the average conversion of 1-
propanol for 5 h. Most of catalysts tested showed stable activi-
ties and/or an inductive period for the initial 3h.
TPD experiments of adsorbed CO2 and NH3 have revealed
that the CeO2 has only weak basic sites without acidic sites.3 In
the present system, it was ascertained that the addition of Fe2O3
into CeO2 did not change the basic strength (profiles not
shown). Although it is known that aldol condensation is usual-
Table 1 summarizes catalytic activities of various CeO2-
MOx catalysts containing MOx of 10 mol%. In the catalytic
Copyright © 2000 The Chemical Society of Japan

Chemistry Letters 2000
233
ly catalyzed by strong base,5 the modification of CeO2 with
alkaline earth oxides with strong basic sites3 has little effect on
the product distribution (Table 1). Because strong basic sites
are not always effective for aldol addition at a temperature as
high as 450 °C, weak basic sites of CeO2 efficient for the
dimerization process of propanal. It is speculated that the sur-
face property of CeO2 is suitable for the redox processes such
as the dehydrogenation of l-propanol to propanal and the
decomposition of 3-hydroxy-2-metylpentanal to 3-pentanone.4
Gaseous products like CO and CO2 were also observed in the
reaction: the major was CO2 over the CeO2-Fe2O3. Thus, the
decomposition of 3-hydroxy-2-metylpentanal into 3-pentanone
probably proceeds via oxidative-decarboxylation6 rather than
via deformylation.4 It is reported that lanthanoide oxides,
except for CeO2, catalyze both the aldol addition of propanal
and the following oxidative-decarboxylation into 3-pentanone
under H2 flow conditions,6 whereas the present CeO2 system is
deactivated in H2 flow. It is speculated that oxygen atom,
which may be produced by decomposion of 1-propanol into
propane, can be supplied for the oxidative-decarboxylation. In
addition, neither propanoic acid as an oxidation product nor
unsaturated aldehyde such as 2-metylpent-2-enal produced by
dehydration of 3-hydorxy-2-methylpentanal was observed in
the reaction.
CeO2-Fe2O3 (20 mol%) catalysts even after 48 h.
Table 2 also summarizes the specific surface area and
turnover frequency (TOF) value defined as a space time yield
of 3-pentanone based on unit surface area. Although the specif-
ic surface area varied with Fe content, the variation was not
correlated to the 1-propanol conversion. The TOF value was
maximized at Fe content around 10-20 mol%, while the specific
surface area was maximized at Fe content of 30 mol%.
Table 3 summarizes the catalytic results of other alcohols
In XRD patterns of CeO2-Fe2O3 samples (profiles not
shown), only peaks of fluorite-type structure of CeO2 were
observed up to the Fe content of 50 mol%, whereas the struc-
ture of pure Fe2O3 (100 mol%) was α-Fe2O3. This means that
the CeO2-Fe2O3 catalysts consist of solid solution. The dehy-
drogenation of 1-propanol to propanal was accelerated over the
CeO2 modified with transition metal oxides (Table 1). In par-
ticular, the addition of Fe and Mn enhanced the activity of pure
CeO2 for the dehydrogenation and the decomposition of 3-
hydroxy-2-metylpentanal into 3-pentanone without losing the
ability for aldol addition of CeO2. However, it is not clear
whether Fe and Mn themselves in the CeO2-MOx solid solution
act as active sites for both the dehydrogenation of 1-propanol
and the decomposition of 3-hydroxy-2-metylpentanal or not.
over CeO2-Fe2O3 (20 mol%) at 450 °C. As has been examined
in 1-propanol, several primary alcohols with straight chain pro-
vided the corresponding symmetric ketones. However, in a
branched alcohol such as 2-methylpropanol, the conversion of
alcohol and the selectivity to symmetric ketone were lower than
those in the straight-chain alcohols. 2-Phenylethanol also pro-
vides a symmetric ketone, 1,3-diphenylacetone, with poor
yield, whereas no symmetric ketone was observed in phenyl-
methanol which has no α-hydrogen. This surely indicates that
this reaction proceeds via aldol addition. The CeO2-Fe2O3 (20
mol%) provides yields of symmetric ketones higher than those
of pure CeO2 and pure ZrO2, which has been used for a com-
mercial production of 2,4-dimetyl-3-pentanone from 2-methyl-
1-propanol.7 The reaction rate of 3-pentanone formation over
the CeO2-Fe2O3 is roughly 10 times as high as that of pure
ZrO2.
In conclusion, catalytic activity of CeO2-Fe2O3 for the 3-
pentanone formation from 1-propanol was found to be the high-
est among the other CeO2-MOx, and the highest space time
yield of 3-pentanone was obtained at Fe content of 20 mol%.
Both weak basic sites and redox property are needed to catalyze
the stepwise reaction for the formation of symmetric ketone
such as 3-pentanone.
References and Notes
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2
For the most active CeO2-Fe2O3, variations in the conver-
sion and selectivity were examined with different Fe content
(Table 2). The l-propanol conversion together with the 3-pen-
tanone selectivity was maximized at Fe content of 20 mol%.
The higher the l-propanol conversion is, the higher selectivity
to 3-pentanone formation is provided. Although the 1-propanol
conversion steeply decreased with process time over pure
Fe2O3, no degradation in the conversion was observed over the
3
4
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