Hydrogen production via steam reforming of ethanol on ceria-containing catalysts

Full text of DOI:10.1134/S0012500809080035

ISSN 0012-5008, Doklady Chemistry, 2009, Vol. 427, Part 2, pp. 190–193. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © M.S. Yakimova, V.K. Ivanov, O.S. Polezhaeva, A.S. Lermontov, Yu.D. Tretyakov, 2009, published in Doklady Akademii Nauk, 2009, Vol. 427, No. 5,
pp. 633–636.
CHEMISTRY
Hydrogen Production via Steam Reforming
of Ethanol on Ceria-Containing Catalysts
b
a
a
M. S. Yakimova , V. K. Ivanov , O. S. Polezhaeva ,
b
c
A. S. Lermontov , and Academician Yu. D. Tretyakov
Received April 20, 2009
DOI: 10.1134/S0012500809080035
The key problem of hydrogen power engineering is thus ensuring that oxidation of the carbon fragments be
the search for available inexpensive and environmen- as complete as possible. In addition, it is important to
tally safe hydrogen sources. In modern industry hydro- minimize the acidity and the hydrogenating activity of
gen is produced by steam reforming of coal or natural the catalyst, because methane and ethylene evolution
gas, i.e., non-renewable natural resources, which brings should be reduced [8]. The above requirements are sat-
to nought most of the favorable environmental effects isfied for supported metal ceria-based catalysts [9];
4
+
3+
of the use of hydrogen as a fuel [1, 2]. The difficulties owing to reversibility of the Ce
Ce transition,
associated with storage of large volumes of hydrogen ceria is able not only to accumulate or release oxygen
stimulated development of methods for hydrogen pro- during redox reactions but also, in the presence of
duction from organic compounds immediately before appropriate promoter and reducing agent, to detach
use in the electric motor cars or home electronic oxygen from water at relatively low temperature [10].
devices [3]. Methanol is the key organic feedstock for However, most of researchers [11, 12] focus attention
in situ hydrogen production. This is due first of all to on the catalysts containing noble metals, which sharply
relative ease of methanol conversion into a hydrogen- increases the cost of the whole process.
containing gas [4]. However, methanol is toxic and
In this work, we carried out the first systematic
industrial methods for its production are based on con-
study of the activity of both nanocrystalline ceria and
version of non-renewable resources [5]. Ethanol pro-
ceria-based catalysts with applied transition metal
duced by biomass fermentation is free from many of
oxides. As a result, we prepared a catalyst that allows
these drawbacks not being a poison and being available
conversion of water–ethanol mixtures into a hydrogen-
everywhere [6].
containing gas with a low content of byproducts, first of
Steam reforming of ethanol into a hydrogen-con- all, carbon monoxide and other oxygenates.
taining gas is a more complex process than methanol
2
Ceria with a surface area of more than 200 m /g was
reforming, first of all, due to the necessity of activation
precipitated from a solution of cerium(III) nitrate in an
and cleavage of the C–C bond. The process of ethanol
isopropanol–water mixture with aqueous ammonia
reforming is accompanied by a number of side reac-
[
13, 14]. The precipitate was dried and annealed in air
tions such as partial oxidation of ethanol to give acetal-
dehyde, acetone, or CO; methanation of CO with
excess hydrogen; ethanol dehydration to give ethylene;
and hydrogenation of ethylene [7].
at 400 to 700°C for 2 h. According to transmission elec-
tron microscopy data, the particle size increased with
an increase in the annealing temperature from 3–4 to
2
5
0 nm. The supported catalysts based on CeO with
% contents of transition metals were prepared by
2
Catalysts for steam reforming of ethanol should
activate both ethanol molecules and water molecules
incipient wetness technique.A calculated amount of the
metal nitrate was dissolved in a water volume corre-
sponding to the volume of pores in ceria annealed at
4
00°C (0.6 mL). After deposition of the active compo-
a
Kurnakov Institute of General and Inorganic Chemistry,
nent, the samples were annealed at 400°C. Binary cata-
Russian Academy of Sciences, Leninskii pr. 31, Moscow,
lysts were prepared stepwise: to prepare the catalyst
119991 Russia
b
c
(5%Ni, 5%Cu)–CeO , the samples were first impreg-
2
Topchiev Institute of Petrochemical Synthesis,
nated with copper nitrate, then annealed at 400°C, and
Russian Academy of Sciences, Leninskii pr. 29, Moscow,
119991 Russia
then the procedure was repeated with nickel nitrate.
The catalyst (5%Cu, 5% Ni)–CeO was prepared in a
Moscow State University, Vorob’evy gory, Moscow,
19992 Russia
2
1
similar way but with opposite order of component dep-
1
90

HYDROGEN PRODUCTION VIA STEAM REFORMING OF ETHANOL
Degrees of water and ethanol conversion, %
191
1
00
Annealing temperature
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
EtOH–CeO (400°ë)
2
EtOH–CeO (500°ë)
2
EtOH–CeO (600°ë)
2
EtOH–CeO (700°ë)
2
H O–CeO (400°ë)
2
2
H O–CeO (500°ë)
2
2
H O–CeO (600°ë)
2
2
H O–CeO (700°ë)
2
2
–
–
10
20
4
00 450 500 550 600 650 700
Temperature, °ë
Fig. 1. Reforming of water–ethanol mixtures (3 : 1) on ceria annealed at different temperatures.
osition. The ethanol reforming was carried out in a con- The composition of products formed on unpromoted
tinuous flow fixed bed reactor with 0.5 g catalyst load. CeO depends on the reforming temperature. At 400°C,
2
The ethanol–water mixture (1 : 3 molar ratio) prepared up to 45% acetone and considerable amounts of ethyl-
beforehand was fed to the reactor at atmospheric pres- ene (up to 10%) are formed, while the yield of hydro-
–
1
sure at a velocity of 3000 h . The reforming products gen is one mole per mole of reformed ethanol. As the
were analyzed on a Kristall 2000M chromatograph temperature is raised to 550–600°C, the yield of hydro-
(
3 mm × 3 m column, Porapak Q phase, helium as the gen increases to 2–3 moles per mole of ethanol, the
carrier gas).
Pure ceria can catalyze various transformations of
major byproducts being methane (7–12%) and
ethane/ethylene (10–20%). Note that the content of CO
does not exceed 1–2% over the whole temperature
range. Since the best results for steam reforming of eth-
anol were attained using a sample annealed at 400°C,
the subsequent experiments were carried out on the cat-
alysts prepared from this sample.
ethanol in the temperature range of 400 to 600°C, the
degree of ethanol conversion being almost independent
of the annealing temperature (Fig. 1). On the contrary,
the degree of water conversion increases with a
decrease in the CeO annealing temperature. For sam-
2
ples annealed at 600 and 700°C, even water evolution
As a result of ceria promotion by transition metal
as a result of ethanol dehydration to give acetone is oxides, the degree of ethanol conversion somewhat
observed at the reforming temperature of 400–450°C. increases and the composition of reformed products
Reforming of water–ethanol mixtures (3 : 1) on ceria and ceria-based catalysts
Degree of
T, °C EtOH con-
version, %
Contents of major reaction products, vol %
Catalyst
H2
CO
CH4
CO2
C2H4
C2H6 CH3CHO CH3COCH3
CeO (400°C)
450
50
450
50
450
50
450
50
450
50
450
50
69.7
54.2
78.3
98.7
46.9
67.8
23.9
81.0
30.0
49.1
28.3
81.7
30.0
47.0
52.0
53.5
63.0
63.5
62.5
62.5
61.5
66.5
59.5
65.5
0.0
1.5
0.1
0.9
1.3
2.9
1.5
2.8
1.4
7.0
1.1
7.0
3.9
13.9
4.0
6.0
3.7
6.5
2.5
2.4
13.2
8.5
19.2
20.2
23.0
22.6
22.9
20.9
22.3
20.5
23.5
18.0
20.5
17.3
13.8
12.7
6.0
5.4
2.2
3.2
4.2
4.4
0.1
0.0
9.1
1.6
2.5
1.7
10.8
11.0
0.2
0.2
3.4
2.0
0.0
2.0
0.0
0.9
0.1
0.8
0.5
0.3
0.7
0.1
0.0
1.1
0.4
22.7
1.7
2.3
0.0
5.7
1.9
2.7
4.3
0.2
0.0
4.0
0.8
2
5
5
5
5
5
%Cu–CeO2
%Co–CeO2
%Fe–CeO2
%Ni–CeO2
5
5
5
5
0.0
0.3
0.3
5%Ni, 5%Mg–CeO2
2.2
6.9
5
DOKLADY CHEMISTRY Vol. 427 Part 2 2009

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92
YAKIMOVA et al.
Degrees of water and ethanol conversion and yield of hydrogen, %
1
00
9
8
7
6
5
4
3
0
0
0
0
0
0
0
EtOH–(5%Ni, 5%Cu)–CeO2
H O–(5%Ni, 5%Cu)–CeO
2
2
H –(5%Ni, 5%Cu)–CeO
2
2
EtOH–(5%Cu, 5%Ni)–CeO
2
H O–(5%Cu, 5%Ni)–CeO
2
2
H –(5%Cu 5,%Ni)–CeO
2
2
4
00
450
500
550
600
Temperature, °ë
Fig. 2. Reforming of water–ethanol mixtures (3 : 1) and yield of hydrogen on binary Ni–Cu catalysts supported on CeO2.
Yield of carbon-containing products, %
3
2
2
1
1
0
5
0
5
0
5
0
CO–(5%Ni, 5%Cu)–CeO2
CH –(5%Ni, 5%Cu)–CeO
4
2
CO –(5%Ni, 5%Cu)–CeO
2
2
C O H –(5%Ni, 5%Cu)–CeO
x
y
z
2
CO–(5%Cu, 5%Ni)–CeO2
CH –(5%Cu, 5%Ni)–CeO
4
2
CO –(5%Cu, 5%Ni)–CeO
2
2
C O H –(5%Cu, 5%Ni)–CeO
x
y
z
2
4
00
450
500
550
600
650
700
Temperature, °ë
Fig. 3. Yield of byproducts in the reforming of water–ethanol mixtures (3 : 1) on binary Ni–Cu catalysts supported on CeO2.
somewhat changes depending on the nature of the order deposition of active components has an effect on
introduced oxide (table). The most significant effects the properties of the obtained catalysts. The same is
are caused by introduction of copper or nickel oxides. true for the selectivity to hydrogen. This is apparently
In the former case, the degree of ethanol conversion due to the fact that copper oxide interacts with CeO2
increases to 98% and low selectivity to CO is retained
but the yield of other byproducts remains high. On the
contrary, nickel oxide promotion of ceria results in
rather low degrees of ethanol conversion, almost zero
surface [15], thus preventing the subsequent formation
of NiO–CeO contacts. The activity of binary catalysts
2
in ethanol reforming is much higher than that of cata-
lysts promoted by either copper or nickel alone. Analy-
sis of the composition of carbon-containing products
content of acetone and C hydrocarbons, but rather high
2
amounts of CO and methane. For other oxides, interme-
diate values of conversion were found. Therefore, com-
bined deposition of copper and nickel oxides on CeO2
was used subsequently for preparing an effective cata-
lyst for the reforming of water–ethanol mixtures.
(
Fig. 3) shows that, at 400°C, considerable amounts of
methane (8–12%), CO (1–6%), acetone (2–6%), and
ethylene (3%) are present apart from CO . Neverthe-
2
less, upon temperature rise, almost all products con-
taining two or more carbon atoms disappear and meth-
Data on the activity of copper–nickel–cerium oxide ane concentration decreases. At 600°C, the concentra-
catalysts are presented in Fig. 2. It can be seen that a tion of CO sharply increases (to 10–12%). These results
considerable amount of water are involved in the reac- imply that the optimal ratio of hydrogen to byproducts
tion even at 400°C, the activity being much higher for in the reforming on binary catalysts is attained in the
the catalyst (5%Cu, 5%Ni)–CeO , indicating that the temperature range of 450–550°C.
2
DOKLADY CHEMISTRY Vol. 427 Part 2 2009

HYDROGEN PRODUCTION VIA STEAM REFORMING OF ETHANOL
193
Thus, it was shown that CeO -based catalysts are
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active toward reforming of water–ethanol mixtures to
hydrogen-containing gas. The activity of pure ceria can
be considerably increased by transition metal oxide
additives. In particular, the addition of nickel oxide
decreases the yield of ethylene and acetone and the
addition of copper oxide results in overall increase of
the catalytic activity accompanied by a decrease in the
selectivity to CO. Stepwise deposition of copper and
nickel oxides yielded catalysts having high activity in
steam reforming of ethanol to hydrogen-containing gas
and distinguished by low selectivity to byproducts.
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Science, 2003, vol. 301, pp. 935–938.
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DOKLADY CHEMISTRY Vol. 427 Part 2 2009