Supporting Information
Influence of the support on the reaction network of ethanol steam
reforming at low temperatures over Pt catalysts
M. Kourtelesis, P. Panagiotopouloua, S. Ladas and X.E. Verykios*
Department of Chemical Engineering
University of Patras, GR-26504 Patras, Greece.
Tel. / Fax. No: +30 2610 991527; e-mail: verykios@chemeng.upatras.gr
a
present address: School of Environmental Engineering, Technical University of Crete,
GR-73100 Chania, Greece
* To whom correspondence should be addressed.
1
S1. Product distribution of pure supports as a function of temperature
The primary products detected in the case of γ-Al2O3 carrier (Fig. S1A) are diethyl
ether, acetaldehyde and ethylene, produced via ethanol etherification, dehydrogenation and
dehydration reactions, respectively [1, 2]. Selectivity toward diethyl ether and ethylene
increases from 50 to 83% and from 2 to 21%, respectively, with increasing temperature,
whereas the opposite is observed with selectivity toward acetaldehyde formation, indicating
that dehydration reactions are enhanced on the surface of γ-Al2O3 support with increasing
temperature or ethanol conversion. Interestingly, neither carbon oxides (CO, CO2) nor CH4
were detected in the gas phase when the reaction was carried out over γ-Al2O3. Molecular
hydrogen was not detected in the gas phase either. This is probably due to the fact that atomic
hydrogen cannot recombine into molecular hydrogen on Al2O3 and thus it cannot desorb. It
probably stays on the surface in the form of hydroxyl radicals and may desorb at higher
temperatures as water.
When the reaction is taking place on CeO2, ethanol is dehydrogenated at low
temperatures producing H2 and CH3CHO, with their selectivities decreasing between 48–37%
and 31-14%, respectively, with increasing temperature from 350 to 430oC (Fig.S1B). In
contrast to what is observed on Al2O3, acetaldehyde is further decomposed on CeO2 surface
producing CO and CH4, exhibiting selectivities between 4-16%. Carbon dioxide formation
implies the occurrence of the WGS reaction which is known to be enhanced over cerium
dioxide [3-5]. Ethanol dehydration is also taking place at higher temperatures, producing
ethylene, which is further hydrogenated by the produced H2 toward ethane. Interestingly,
significant amounts of acetone as well as smaller amounts of propylene are also produced,
with the sum of their selectivities increasing from 26 to 43% with increasing temperature. The
formation of acetone accompanied by high selectivity of hydrogen has been previously
observed over CeO2 based catalyst [6-9]. The reaction proceeds in the following three
2
sequential steps: dehydrogenation of ethanol to acetaldehyde, aldol condensation from two
molecules of acetaldehyde, and the reaction of the aldol with the lattice oxygen of CeO2 to
form a surface intermediate, followed by its dehydrogenation and decarboxylation [6, 10].
The overall reaction can be expressed as follow:
2CH3CH2OH +H2O → CH3COCH3 + CO2+ 4H2
ΔHo= 100.7 kJ/mol
(Eq. 1)
Alternatively, the produced acetaldehyde is transformed into acetone either via acetic acid
formation [8, 10-13] or via direct decarbonylation [9, 14, 15]. The formation of acetone has
been proposed to be enhanced over metal oxides having both surface acidity and basicity
[16].
Propylene is produced from ethanol either via acetone hydrogenation and subsequent
dehydration [17] or via intermediate production of ethylene followed by oligomerizationcracking [18, 19] or via cracking and dehydration of the intermediate produced oxygenates
[20].
Ethanol steam reforming on pure ZrO2 gives rise to acetaldehyde and hydrogen
formation, with their selectivities decreasing from 50 to 7% and from 37 to 25%, respectively,
with increasing temperature from 365 to 417 oC (Fig.S1C). Results indicate that although
ethanol conversion is more or less the same for all supports examined at ca 370 oC, ethanol
dehydrogenation is favored on ZrO2, compared to Al2O3 or CeO2. Acetaldehyde is
decomposed giving rise to CO and CH4 formation on ZrO2 support, with their selectivities
being lower than 5% in the whole temperature range. Increasing temperature results in a
significant increase of C2H4 (from 14-48%) and C3Hx (from 19-33%) selectivities, indicating
that ethanol dehydration and oligomerization-cracking of intermediate compounds are
enhanced at higher temperatures compared to ethanol dehydrogenation. Carbon dioxide
selectivity varies between 11-15% and is most probably due to cracking of produced
oxygenated compounds.
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Selectivity (%)
100
(A)
γ-Al2O3
(C2H5)2O
80
60
CH3CHO
40
C2H4
20
0
300
325
350
375
400
425
0
Temperature ( C)
Selectivity (%)
100
(B)
CeO2
80
60
H2
CH3CHO
40
CH4
20
0
C2H6
C3HxOy
C2H4
CO2
CO
300 325 350 375 400 425
o
Temperature ( C)
Selectivitiy (%)
100
(C)
ZrO2
80
CH3CHO
60
C2H4
H2
40
C3HX
CO2
20
0
CO
300
325
350
CH4
375
400
425
o
Temperature ( C)
Figure S1. Selectivity toward reaction products as a function of reaction temperature over (A)
γ-Al2O3, (B) CeO2 and (C) ZrO2 supports. Experimental conditions: same as in Fig. 1.
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SCH3CHO (%)
100
(A)
80
60
40
20
0
0.5% Pt
Al2O3
CeO2
ZrO2
4
6
8
10
12
14
16
Ethanol conversion (%)
SCO, SCH4 (%)
100
(B)
0.5% Pt
Al2O3
80
CeO2
ZrO2
60
40
20
0
4
6
8
10
12
14
16
Ethanol conversion (%)
Figure S2. Selectivities toward (A) CH3CHO and (B) CH4 and CO as a function of ethanol
conversion obtained from Pt/Al2O3, Pt/CeO2 and Pt/ZrO2 catalysts under differential reaction
conditions. Experimental conditions: same as in Fig.3.
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Concentration (ppm)
12500 (Α)
10000
7500
H2
CH3CHO
5000
CO2
2500
0
C3H6
100
200
CO
CH4
CH3COCH3
300
400
500
600
o
Temperature ( C)
Concentration (ppm)
12500 (Β)
H2
10000
CH3CHO
CO2
7500
5000
C3H6
CH4
CO
CH3COCH3
2500
0
100
200
300
400
500
600
o
Temperature ( C)
Figure S3: Transient-MS spectra obtained over the (A) Pt/CeO2 and (B) Pt/ZrO2 catalysts
following interaction with the reaction mixture 0.8% CH3CHO-2.4% H2O at 25 oC and
subsequent linear heating at 600 oC (β=15 οC/min).
7