FULL PAPER
the propene yield reached ap-
proximately 60% at 30% par-
tial pressure of ethanol.[14] It is
important to note that the the-
oretical maximum yield of pro-
pene based on Equation (4)
(carbon basis) was 75%, due
to the side production of
carbon dioxide, and therefore
the 60% yield corresponded to
80% of the theoretical maxi-
mum value and was sufficient-
ly high. The reaction pathways
were also suggested based on
the change in the products and
the reactivity of possible inter-
mediate compounds.
Figure 1. The catalytic activity of In2O3 (the upper row, U) and Sc3/In2O3 (the lower, L) as a function of the re-
action time and temperature. Reaction conditions: catalyst weight, 2.0 g; total flow rate, 12.8 mLminꢀ1 (GHSV
687 hꢀ1); 1 atm; PEtOH, 30 vol%; PH O, 0 (U) or 8.5 vol% (L); PH , 0 (U) or 30 vol% (L); N2 balance.
Experimental Section
2
2
General:
Indium
oxide,
In2O3
(4.2 m2 gꢀ1 BET surface area after
yield decreased, whereas the yields of acetone and acetalde-
hyde increased. The yield of propene at 723–823 K greatly
diminished as the reaction time increased. In contrast, the
acetone yield gradually increased at 723–773 K and subse-
quently decreased at 823 K with reaction time, whereas the
yield of acetaldehyde significantly increased at 823 K (ap-
proximately 60%). It follows that the incipient stage of de-
activation made the catalysis for Equation (3) weak and fur-
ther deactivation caused the lower activity for Equation (2)
(or 2’). Therefore, only Equation (1) progressed. The appa-
rent changes in the catalysts before and after the reaction
were the partial reduction of In2O3 to indium metal and the
accumulation of carbon on the catalyst. The former is de-
picted in Figure 2, which shows the XRD patterns of indium
metal after the reaction.
Figure 1 indicated that there were two disadvantages on
the In2O3 catalysts; the deactivation and the low selectivity
of propene. They were caused by the reduction of In2O3 to
In metal as shown in Figure 2, the coke formation as shown
later, and the by-production of acetone. The effect of vari-
ous metals in the In2O3 was next examined to improve the
stability and enhance the activity.
calcination at 1073 K for 5 h), was commercially obtained from Kanto
Chemical Co. Japan. Metal-loaded In2O3 samples were prepared by a
conventional impregnation method by using mainly nitrate salts. The de-
tailed preparation method is described in the Supporting Information.
Metal loadings were 1–20 atom%, which were determined by induced
coupled plasma analysis after the samples were dissolved in HF solutions.
All catalysts were calcined at 1023 K for 5 h and the respective grain
sizes were adjusted to 300–600 mm for use in catalytic runs. The structure
of the resulting metal-loaded In2O3 was confirmed by X-ray diffraction
analysis. The catalyst was designated as for example Sc3/In2O3, where “3”
was the amount of loaded scandium (atomic% to that of In).
General procedure: The catalytic reaction was carried out using a fixed-
bed flow reactor at an atmospheric pressure. The catalyst (0.05–2.0 g)
was loaded into the reactor made of quartz, heated in N2 at 673 K, and
EtOH (PEtOH =30%, N2 balance, total flow rate of 10–300 mLminꢀ1) was
subsequently let into the reactor at the desired temperature using a mass
flow controller for liquid. Water and/or hydrogen were added into the re-
actant flow as necessary. The product distribution was determined by on-
line gas chromatographs with thermal-conductivity (TCD) and flame-ion-
ization (FID) detectors or a mass spectrometer. The yield and selectivity
were calculated on the carbon basis. The detailed methods are described
in the Supporting Information.
Results and Discussion
Catalytic activity of the parent In2O3: The catalytic activity
of the parent In2O3 was studied as a function of temperature
and reaction time in the absence of water and hydrogen and
is summarized in Figure 1. The conversion degrees of EtOH
were 94–100% at 623–823 K. The major byproducts were
ethene, butenes (mostly isobutene), acetone, and acetalde-
hyde. Ethene formation indicated the undesirable competi-
tion of EtOH dehydration. As shown in Figure 1, the cata-
lytic activity greatly changed with the reaction time, indicat-
ing the severe deactivation of the catalyst. In the compari-
son of the “initial” activity at each temperature, the yield of
propene was maximized at 723 K (29%). Above 773 K, the
Modification of In2O3 with various metal additives: Figure 3
and S1 (the Supporting Information) summarize the results
at 773 and 823 K in the absence of water and hydrogen after
45 and 140 min with 10 atom% metal additive, the numeri-
cal values of which are summarized in the Supporting Infor-
mation. The C3 and C4 compounds are in the upper portion
of the Figure, and the C2 compounds are in the lower.
Among 28 kinds of metals, the addition of Sc, Zr, V, Cr, Mo,
Co, Ni, and Cu increased propene production, whereas Li,
K, Ca, Ba, Y, La, Ce, Ti, Fe, Al, Sn, and Sb increased the
yield of acetone. The addition of Er, Nb, W, Mn, Pd, Zn,
Ga, and Bi had no effect on propene or acetone production.
Chem. Eur. J. 2013, 19, 7214 – 7220
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
7215