Synthesis gas production from bio-oil: Steam reforming of ethanol as a model compound

Article abstract of DOI:10.1039/c4ra05948d

Using original hydrothermal technology honeycomb corundum monoliths with a peculiar porous structure and high water-adsorbing capacity facilitating procedures of active component loading have been produced. The detailed study of ethanol steam reforming over Ru/Ce_0.5Zr_0.5O ₂(CZ), Ru/Ce_0.4Zr_0.4Sm_0.2O ₂-(δ + γ)Al₂O₃ (granulated) and Ru/Ce_0.4Zr_0.4Sm_0.2O₂/α-Al ₂O₃ (monolithic) has been performed. It has been revealed that the main route of the reaction over Ru/CZ is ethanol dehydrogenation while ethanol dehydration into ethylene mainly occurs over Ru/CZS-Al₂O ₃. Variation of the H₂O-EtOH ratio, contact time and temperature allows hydrogen and CO yield to be governed. The monolithic catalyst has shown a high performance and stability at short contact time (0.1-0.4 s) and low water concentration (H₂O-EtOH ～ 1-3). the Partner Organisations 2014.

Full text of DOI:10.1039/c4ra05948d

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Synthesis gas production from bio-oil: steam
reforming of ethanol as a model compound
Cite this: RSC Adv., 2014, 4, 37964
a
S. Pavlova, P. Yaseneva,b V. Sadykov,a V. Rogov,a S. Tikhov,a Yu. Bespalko,a
*
S. Belochapkinec and J. Rossd
Using original hydrothermal technology honeycomb corundum monoliths with a peculiar porous structure
and high water-adsorbing capacity facilitating procedures of active component loading have been
produced. The detailed study of ethanol steam reforming over Ru/Ce0.5Zr0.5O2(CZ), Ru/
Ce0.4Zr0.4Sm0.2O2–(d + g)Al2O3 (granulated) and Ru/Ce0.4Zr0.4Sm0.2O2/a-Al2O3 (monolithic) has been
performed. It has been revealed that the main route of the reaction over Ru/CZ is ethanol
dehydrogenation while ethanol dehydration into ethylene mainly occurs over Ru/CZS–Al2O3. Variation of
the H2O–EtOH ratio, contact time and temperature allows hydrogen and CO yield to be governed. The
monolithic catalyst has shown a high performance and stability at short contact time (0.1–0.4 s) and low
water concentration (H2O–EtOH ꢀ 1–3).
Received 19th June 2014
Accepted 12th August 2014
DOI: 10.1039/c4ra05948d
www.rsc.org/advances
out for typical examples of an individual compound class such
as ethanol, acetic acid, acetone, glycerol et.11–15 A wide range of
1. Introduction
supported active metals (Ni, Co, Cu,13,14,16–23 Pt, Pd, Rh, Ru15,24–28
)
Currently, the major sources for energy and chemical produc-
tion are fossil fuels: crude, natural gas or coal. Biomass, being a
renewable feedstock, is an attractive alternative source with the
advantages of its availability throughout the world and reduc-
tion of greenhouse emissions.1,2 Fast pyrolysis of biomass is
now a mature technology producing bio-oils (biodiesel) which
can be converted by their catalytic treatment to hydrogen or
synthesis gas.3–5 Bio-hydrogen and bio-syngas could be feed-
stocks for liquid fuels (gasoline, diesel) and valuable chemicals
production and they are cleanest fuels for the different types of
fuel cells, gas turbine, internal combustion engine as well.6–8
Hence, this technology to produce syngas or hydrogen can be
the most promising process for a clean and renewable fuel
generation.
The most promising processes of bio-oil catalytic trans-
formation into synthesis gas are known to be the steam and
combined oxidative reforming. However, rapid deactivation of
current catalysts in these processes is a signicant technolog-
ical barrier, and design of highly stable, selective and active
catalysts for novel, highly oxygenated feedstocks is a key option
in solving this problem.6–12
were used for the bio-oil reforming processes. However, they are
subjected to strong coking being supported on traditional inert
oxides,14–18,24 while a high stability to coking and catalytic
activity of metals is achieved when their nanoparticles are
stabilized in the matrix of ceria–zirconia uorite-like mixed
oxides with high oxygen mobility that is due to participation of
support oxygen in gasication of coke precursors.21–23,25–28
Incorporation of low-valence cations (such as La, Gd, Pr) into
the lattice of ceria–zirconia solid solution improves the lattice
oxygen mobility29,30 that could increase coking stability of
catalysts.
The catalysts are usually studied in reforming reactions as
pellets obtained from corresponding powders which are
unsuitable for practical applications because of pressure drop.
Compared with them, catalysts loaded on structured supports
have advantages such as lower pressure drop and larger external
surface area per unit volume. However, there are only several
works in which conversion of bio-oil or its components into
synthesis gas or hydrogen has been studied over monolithic
catalysts.31–36 Thus, Ni/La2O3 and Ru/g-Al2O3 supported on
cordierite honeycomb and alumina–zirconia foam monoliths
have shown good catalytic performance in partial oxidation of
ethanol.31,32 Pt(Rh)/Ce0.5Zr0.5O2 supported on cordierite mono-
lith35 and Rh–CeO2/g-Al2O3 loaded on a-Al2O3 foam monolith
have been tested in steam reforming of real bio-oil.36
Since bio-oils are complex mixtures of oxygenated hydro-
carbons including aliphatic and aromatic acids, aldehydes,
ketones, alcohols, esters, the catalytic studies are usually carried
In previous work using combinatorial approach,37 we studied
in ethanol steam reforming (ESR) a large number of catalysts
based on Al2O3 loaded with Ce–Zr mixed oxides doped by La,
Sm, Pr and different active metals (Cu, Cu–Ni, Ru, Pt, etc.). The
aBoreskov Institute of Catalysis, Pr. Lavrentieva, 5, 630090, Novosibirsk, Russia.
E-mail: pavlova@catalysis.ru
bUniversity of Cambridge, UK
cMaterials & Surface Science Institute, Limerick, Ireland
dUniversity of Limerick, Limerick, Ireland
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results revealed that the most effective catalyst composition is stage (HTT) by a proprietary procedure. The mixture of
Ru/Ce0.4Zr0.4Sm0.2–Al2O3. Herein, we report the detail study of aluminium and its hydroxide loaded into the special die was
ESR for production of synthesis gas over Ru supported on ceria– subjected to HTT at 100 ꢁC followed by calcination in air at
ꢁ
zirconia and Ce0.4Zr0.4Sm0.2–Al2O3. The catalyst Ru/Ce0.4Zr0.4Sm0.2 1200 C. During these procedures the total oxidation of metal
was also tested being supported on a corundum monolith. The aluminum occurs. The total pore volume of the monolith was
inuence of a support nature and such ESR process parameters as estimated from the values of true and apparent densities. Its
feed composition, contact time and temperature is studied to true density was measured using a helium pycnometer – Auto-
achieve a high yield of syngas with a given composition.
pycnometer 1320 (Micromeritics). The share of micropores and
mesopores as well as a specic surface area were determined
from adsorption isotherms of nitrogen recorded at 77 K using
the ASAP-2400 Micromeritics instrument.
2. Experimental
2.1. Catalysts
The monolithic catalyst containing 1%Ru – 8%Ce0.4Zr0.4
-
Sm0.2O2 was prepared by subsequent loading of the mixed oxide
and Ru using impregnation of the support with corresponꢁding
water solutions followed by drying and calcination at 800 C.
As supports, Ce0.5Zr0.5O2 (CZ) and 10%Ce0.4Zr0.4Sm0.2–Al2O3
(CZS–Al2O3) were used. CZ was prepared by modied sol–gel
method.38 An aqueous solution of Ce(NO3)3$6H2O (20 ml) was
added to the zirconium butoxide Zr(OC4H9)4 dissolved in 20 ml
of butanol. A pseudogel formed was dried and calcined in air at
2.2. Catalystic tests
ꢁ
900 C for 2 h.
ESR over catalysts pellets were carried out in U-shaped tubular
quartz plug-ow reactor (4.5 mm i.d.) at atmospheric pressure.
Usually 0.18 g of pelletized catalyst (fraction 0.5–0.25 mm)
diluted in a 1 : 10 weight ratio with quartz sand was takeꢂn1.
Reaction was performed at 300–800 ꢁC and 3300–50 000 h
GHSV (0.07–1 s contact time) using the gas feed containing
10 vol% C2H5OH, 15–50 vol% H2O (the corresponding molar
ratio H2O : C2H5OH ¼ 1.5 O 5), N2 balance. Before testing the
catalysts were pre-treated for 1 hour at 400 ꢁC in the ow of
10% H2 in N2. Three on-line gas chromatographs (GC) “LHM-8”
equipped with thermal conductivity detectors and a ame
ionization detector were used for the analysis of reactants and
products. Hydrocarbons (CH4, C2H6, C2H4, etc.) and oxygenates
(EtOH, CH3OH, acetone, diethyl ether, etc.) were analyzed using
a Porapak T column; N2, O2, CH4 and CO were analyzed with a
molecular sieve column, and H2, N2, CO, CO2, CH4 – with an
active carbon “SYT” column. Ar and He were used as carrier
gases.
To prepare CZS–Al2O3, g-Al2O3 (CONDEA Puralox SBa – 150,
150 m2 gꢂ1) stabilized by 5 wt%. of La was impregnated with
mixed solution of Ce, Sm nitrates and ZrO(NO3)2, dried over-
night in air at 85 C and then calcined at 800 C.37
ꢁ
ꢁ
The catalysts 1.4% Ru/Ce0.5Zr0.5 (Ru/CZ) and 1.4%Ru/10%
Ce0.4Zr0.4Sm0.2–Al2O3 (Ru/CZS–Al2O3) were synthesized by the
standard wet impregnation of supports with a water solution of
ꢁ
RuOHCl3 followed by drying and calcination at 800 C in air.
Main characteristics of these catalysts were reported
elsewhere.37
The specic surface area (BET area) was determined by the
express BET method using Ar thermodesorption data obtained
on a SORBI-M instrument. The XRD patterns were recorded
using a URD-6M diffractometer with Cu Ka radiation in the
range of 2q angles 10–90ꢁ.
Honeycomb corundum monoliths of 50 mm diameter and
25 mm length with a peculiar porous structure (Fig. 1) were
obtained using original hydrothermal technology (HTT).39 The
aluminum powder (a commercial PA-4 grade) and aluminum
hydroxide were used as raw materials. To form the transport
microchannels along the monolith, easily burned organic bers
were inserted into the matrix before hydrothermal treatment
Ethanol conversion (XEtOH), selectivity to carbon products (Si)
and hydrogen yield (YH ) were calculated according to the next
2
equations:
in
mol
EtOH
out
EtOH
ꢂ mol
xEtOH
¼
ꢃ 100%;
in
mol
EtOH
nimoli
Si ¼
ꢃ 100%;
n
P
nimoli
i
molH
2
YH
¼
ꢃ 100%;
2
in
EtOH
6 mol
where ni is the number of carbon atoms in “i” product.
The monolithic catalyst was tested in a pilot reactor in the
gas feed with C2H5OH concentration of 13 vol%, H2O concen-
tration of 14–60 vol% corresponding to H2O–C2H5OH molar
ꢁ
ratio of ꢀ1.1–4.7 at 700–750 C and contact time of 0.03–0.1 s.
Fig. 1 The monolith prepared by hydrothermal treatment (HTT) and
extrusion after thermoshocks.
The temperature of the monolithic catalyst has been measured
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at its exit. The analysis of the main reaction products (H2, CO,
CO2, CH4) was carried out with on-line GC.
3. Results and discussion
3.1. Characterization of catalysts
The BET surface area of CZ calcined at 900 ꢁC was 9 m2 gꢂ1
while in the case of Ru/CZS–Al2O3 it is equal 110 m2 gꢂ1. Thus,
successive deposition of CZS and Ru on g-Al2O3 having the
initial surface area 150 m2 gꢂ1 led to a moderate decrease of the
surface area.
Fig. 3 Raman spectrum of Ce0.5Zr0.5O2 calcined at 900 ꢁC.
The BET surface of the corundum monolith was ꢀ2.6 m2 gꢂ1
.
The total pore volume was close to 0.4 cm3 gꢂ1. The absence of
hysteresis on the nitrogen adsorption isotherm evidences that
micropores are missing. The volume of mesopores is substan-
tially small (ꢀ0.005 cm3 gꢂ1). Thus, the pore structure of
corundum monoliths is namely formed by macropores and
ultramacropores with a size of 1 mm and more that provides a
high diffusion permeability of the monolith walls. Ultra-
admixture of d-Al2O3. For both Ru-containing catalysts, the
reections of RuO2 phase (JCPDS 71-2273) are observed.
3.2. Steam reforming of ethanol
3.2.1. Blank experiments. The data of the blank experiment
macropores of the size in the range from 1 to 10 mm with the without a catalyst allow evaluation of the thermal decomposi-
average value of 1–2 mm are clearly visible in SEM images of the tion of ethanol. Its thermal conversion is low at temperatures
monolith cross-section (Fig. 2b and c). The surface of channel below 750 ꢁC and substantially increases only at and above
walls is highly rough (Fig. 2a): a height difference reaches tens 750 ꢁC (Fig. 4). The yield of H2 in the blank experiment is low in
of mm. Thus, these peculiarities of porous structure gives the whole temperature range with main products being CO,
sufficiently high water-absorbing capacity, keeps
a high CH4, acetaldehyde, C2H4 and C2H6 (Fig. 4 and 5). A sufficiently
dispersion of supported active component and provides a high selectivity to CO and CH4 at all temperatures evidences
higher thermal shock stability of cermet monoliths as ethanol cracking while a high selectivity to acetaldehyde at
ꢁ
compared with honeycombs prepared by extrusion (Fig. 1). A temperatures below 750 C and to C2H4 at temperatures above
high water absorption capacity simplies procedures of the 750 ꢁC shows realization of the gas-phase dehydrogenation and
active component loading on the monolith support: a common dehydration, respectively, catalyzed by quartz reactor walls.
method of incipient wetness impregnation was used instead of
washcoating requiring repeated supporting of the catalyst support nature on ESR parameters has been studied in the feed
suspension on the substrate. with H2O–EtOH molar ratio being equal 1 : 4 at the contact time
3.2.2. Inuence of support nature. The inuence of a
According to XRD data, Ce0.5Zr0.5O2 is a mixture of of 0.07 s. Temperature dependence of ethanol conversion,
Ce0.76Zr0.24O2 and Ce0.45Zr0.55O2 cubic solid solutions with hydrogen yield and product selectivity over CZS–Al2O3, Ru/CZS–
˚
lattice parameters 5.354 and 5.248 A, respectively. Raman Al2O3, Ru/CZ is presented in Fig. 4 and 6. Over all catalysts, the
spectroscopy being a very sensitive to the structure shows that a conversion of ethanol changes with temperature depending on
metastable tetragonal phase t00 is present along with a cubic the catalyst support. For Ru/CZ, ethanol conversion continu-
phase. Indeed, in the Raman spectrum, the main band at ously increases from 37% up to 100% at temperature rising
472 cmꢂ1 corresponding to a cubic solid solution is asymmet- from 650 to 825 ꢁC. In the case of Ru/CZS–Al2O3, the conversion
rical with a shoulder at 535 cmꢂ1 and, additionally, a low being equal 100% at 650 ꢁC passes through the minimum at
intensity band at 310 cmꢂ1 is observed (Fig. 3). As shown 700–750 ꢁC and reaches again the value of 100% at 800 ꢁC. Such
earlier,37 for CZS–Al2O3, the main phases are uorite-like cubic a behavior is conditioned by the participation of a support in
solid solution (JCPDS 43-1002) and mixed d- and g-Al2O3. The ESR. Indeed, the similar temperature dependence of the
monoliths are mainly comprised of a-Al2O3 with a small ethanol conversion is observed for CZS–Al2O3 with
a
Fig. 2 SEM images of a monolith face plane near a channel (a) and an inner spall of monolith at different magnification (b and c).
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Fig. 4 Temperature dependence of ethanol conversion and hydrogen yield in the blank experiment and in the presence of CZS–Al2O3, Ru/CZS–
Al2O3, Ru/CZ. Reaction mixture EtOH–H2O–N2 ¼ 1 : 4 : 5, contact time 70 ms.
Fig. 5 Product selectivity in the blank experiment.
ꢁ
pronounced drop at 700 C and continuously increasing up to
90% at 825 ꢁC.
It is known that ethanol conversion over Al2O3 could be close
to 100% already at 350 ꢁC with C2H4 as a main product of
ethanol dehydration on acid centers.40,41 Ethanol adsorbs on the
surface of Al2O3 with formation of ethoxy species which are
transformed into highly stable acetate species at increasing
temperature up to 700 ꢁC thus sharply decreasing ethanol
conversion. At further temperature rising, acetate species are
decomposed and the ethanol conversion increases. It may be
stated that the same processes occur over CZS–Al2O3. For Ru/
CZS–Al2O3, acetate species hinder the migration of ethoxide
species toward Ru particles where they are decomposed. As a
Fig. 6 Temperature dependence of the product selectivity in ESR for
result, only the minor decrease of ethanol conversion is
observed due to facile decomposition of ethoxide and acetate
species on the metal-support boundary.26,41,42
CZS–Al2O3, Ru/CZS–Al2O3 and Ru/CZ. Contact time 0.07 s, H2O–
EtOH ¼ 4.
The high C2H4 selectivity over CZS–Al2O3 and Ru/CZS–Al2O3
at 650–700 ꢁC evidences preferential realization of ethanol decomposition at high temperature.11,26 The extremal temper-
dehydration, while for Ru/CZ the high selectivity to acetalde- ature dependence of selectivity to acetaldehyde for Ru/CZS–
hyde and methane (at 650ꢁ ꢀ30 and ꢀ20%, correspondingly) is Al2O3 (CZS–Al2O3) is determined by the parameters of catalyst
a result of ethanol dehydrogenation followed by decarbon- testing in ESR as demonstrated in our experiments with a
ylation of acetaldehyde.11 The temperature dependence of higher H2O–EtOH ratio and a longer contact time (see below).
selectivity to acetaldehyde is different for Ru/CZ and Ru/CZS–
Hydrogen yield over CZS–Al2O3 is low. Ru-containing cata-
Al2O3 (CZS–Al2O3): it decreases gradually when temperature lysts show practically the same high values independent on the
increases and passes through the maximum, correspondingly. support type while selectivity to C-products is strongly inu-
Dependences similar to the case of Ru/CZ are usually observed enced by the support nature (Table 1 and Fig. 4, 6). Thus, H2/CO
for the catalysts where reaction mechanism includes ethanol values and CO2 selectivity are higher for Ru/CZ in the whole
dehydrogenation with formation of acetaldehyde and its temperature range. Note that in the case of CZS–Al2O3, CO2 is
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ꢁ
Table 1 H2/CO ratio in ESR over Ru/CZS–Al2O3 and Ru/CZ catalysts at
different contact times and H2O–EtOH ratio
60% at 700 C for the contact time of 1 s (Fig. 8). The temper-
ature dependence of the selectivity to C-products shows that at
the short contact time, the main product is ethylene up to
700 ꢁC. For contact time of 1 s, selectivity to ethylene passes
through the maximum (ꢀ90%) at 400 ꢁC and decreases to zero
at 600 ꢁC. Selectivity to CO gradually increases with the
temperature rise while selectivity to CO2 and methane reaching
maximum at 600 ꢁC decreases at further temperature rising that
is due to occurring RWGS and steam reforming of methane,
respectively, which are facilitated at long contact times and high
temperature.6,11
Temperature, ꢁ
C
Catalyst
Contact time, s H2O–EtOH 650 700 750 800 825
Ru/CZS–Al2O3 0.07
Ru/CZ 0.07
Ru/CZS–Al2O3 0.1
Ru/CZ 0.1
4
4
3
3
3.5 2.8 2.0 2.0 2.2
3.5 3.4 2.6 2.4 2.4
—
3
2
1.8 1.7
4.1 3.2 2.4 2.3 2.4
ꢁ
Thus, these results show that at temperatures below 650 C
absent in the reaction products. The same effect was observed
for CeZrO2 in ref. 22. Using DRIFTS, the authors had shown that
at high temperature, over CeZrO2, in contrast to the results
observed for Pt/CeZrO2, signicant amounts of acetate species
were detected at the surface and there was no CO2 formation
over CeZrO2 alone. Thus, the presence of Ru active metal
promotes acetate decomposition and carbonate formation at
high temperature, which could occur at the metal–support
interface.
Selectivity to methane, in the case of CZS–Al2O3 support,
being low at 650 ꢁC gradually increases with temperature rising
up to 825 C as a result of thermal decomposition of ethanol
which is in agreement with a low selectivity to target products
(H2, CO, CO2) (Fig. 6). Over Ru/CZS–Al2O3, it passes through the
maximum at 750 ꢁC due to methane conversion via steam
reforming at high temperature. For Ru/CZ, at 700–825 ꢁC
methane selectivity is close to one over Ru/CZS–Al2O3 while at
650 ꢁC its value is much higher due to decarbonylation of
acetaldehyde.6,11
the yield of hydrogen and syngas strongly determines by the
contact time value: it is sufficiently high at the longer contact
time.
Above 650ꢁ, the inuence of the contact time on the catalyst
performance has been studied at H2O–EtOH molar ratio
equals 6 when ethanol conversion is complete (Fig. 9). The
intermediate product – acetaldehyde is absent under these
conditions, while selectivity to ethylene decreases at longer
contact times and higher temperatures being close to zero at
800 ꢁC for all contact times. Hydrogen yield slightly varies witꢁh a
contact time depending on the temperature. Thus, at 700 C,
hydrogen yield passes through a small maximum at the contact
time 0.1 s, while at 750–800ꢁ it increases up to ꢀ94–97% at the
longest contact time (Fig. 9). Variation of CO selectivity with the
contact time also depends on the temperature: at 700–750ꢁ it
goes through the maximum at 0.1 s and decreases at 800 ꢁC with
the rise of the contact time. Selectivity to CO2 increases with the
contact time rising at all temperatures. These variations
observed for H2, CO and CO2 selectivities are due to parallel
occurrence of water gas shi (WGS) and reverse WGS reactions
whose shares in the overall ESR process depend not only on
ꢁ
3.2.3. Effect of contact time and water–EtOH ratio.
Temperature dependence of ethanol conversion, hydrogen yield
and ꢁproducts selectivity in the low temperature region (350–
700 C) at contact times of 0.46 and 1 s is presented in Fig. 7
and 8. The data show that though ethanol conversion is already
high (80–100%) at 400 ꢁC and slightly dependent on contact
time, the yield of hydrogen strongly changes with the contact
time. At contact time of 0.46 s, the yield is low in the tempera-
ture range of 350–600 ꢁC and reaches ꢀ28% only at 700 ꢁC,
reaction thermodynamics43,44 but kinetic factors as well.45,46
A
gradual rise of methane selectivity with the contact time at
ꢁ
700 C is mainly controlled by methanation which is favoured
over Ru-based catalysts in the presence of water.47 At higher
temperatures, steam reforming of methane leads to decrease of
methane selectivity with longer contact times.
Temperature dependences of ethanol conversion, hydrogen
yield and products selectivity at different H2O–EtOH ratio and
0.07 s contact time over Ru/CZS–Al2O3 are presented in Fig. 10
and 11. At H2O–EtOH ¼ 4–5 ethanol conversion (Fig. 10) passes
through the minimum at 700–750 ꢁC that is conditioned by
formation of highly stable acetate groups on the CZS–Al2O3
surface which hinder the decomposition of ethoxide at the Ru/
support interface. The increase of H2O–EtOH ratio up to 6 leads
to 100% ethanol conversion in the whole temperature range due
to facile reforming of adsorbed intermediate carbonaceous
species.40–42
ꢁ
while its value is equal to ꢀ30% at 500 C and increases up to
The values of hydrogen yield for H2O–EtOH molar ratio ¼ 4–5
ꢁ
are close at 700–750 C being somewhat higher when it is equal
to 5. However, at increasing temperature above 750 ꢁC, the
hydrogen yield is noticeably higher for H2O–EtOH ¼ 5. At H2O–
EtOH ¼ 6, the hydrogen yield is the highest in all temperature
range, especially at 700–750 ꢁC (Fig. 11). The same trends are
observed for CO2 selectivity while CO selectivity is practically
Fig. 7 Temperature dependence of ethanol conversion (1, 2) and
hydrogen yield (3, 4) at contact time of 0.46 (2, 4) and 1 s (1, 3). 10 vol%
EtOH + 40 vol% H2O, N2 – balance.
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Fig. 8 Influence of contact time on products selectivity: a – 0.46 s, b – 1 s. 10 vol% EtOH + 40 vol% H2O, N2 – balance.
Fig. 10 Influence of the ratio H2O–EtOH on the ethanol conversion.
Ru/CZS–Al2O3, contact time 0.07 s, reaction mixture 10 vol% EtOH +
40–60 vol% H2O, N2 – balance.
reforming which rate is high even at H2O–EtOH ¼ 3 as was
shown in.48 Selectivity to acetaldehyde formed by dehydroge-
nation of ethanol is rather low not exceeding 7% and appre-
ciably varies with values of H2O–EtOH ratio. At H2O–EtOH ¼ 4–5
it goes through the maximum at 700–750 ꢁC and falls to zero at
800 ꢁC being practically absent in the reaction products at H2O–
EtOH ¼ 6 in the whole temperature range. Thus, dehydroge-
nation route of ESR could be competitive with dehydration
reaction to ethylene depending on reaction parameters. The
similar results were observed for NiZnAl and NiMgAl catalysts
derived from layered double hydroxides: at H2O–EtOH ¼ 3 and
close contact time, the temperature dependence of selectivity to
acetaldehyde passed through the maximum of 20% being equal
to zero at high water concentration.49
Fig. 9 Influence of the contact time on the product selectivity in ESR.
Catalyst – Ru/CZS–Al2O3. Contact time 0.07–0.2 s, reaction mixture
10 vol% EtOH + 60 vol% H2O, N2 – balance.
independent on the H2O–EtOH ratio (Fig. 11). At all water
concentrations, selectivity to methane passes through the
ꢁ
maximum at 750–800 C being lower at H2O–EtOH ¼ 6 due to
steam reforming which is more effective at high water concen-
trations and temperatures according to thermodynamics.43,44
Selectivity to ethylene, which is formed via dehydration of
ethanol over CZS–Al2O3 support, is practically independent on
3.2.4. Testing of the monolithic catalyst. The monolithic
catalyst was tested in ESR without any pretreatment and was
directly activated in the reaction mixture at the process
temperature. The effect of water to ethanol ratio and contact
time on the monolith performance was studied.
ꢁ
the water concentration being high at 650–700 C (ꢀ50–80%)
and gradually decreases as the temperature increases dropping
to zero at 800 ꢁC. Such dependence is due to ethylene steam
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Fig. 13 Products concentration vs. contact time over the monolithic
catalyst. 12 vol% EtOH + 36% H2O, N2 – balance, 750 ꢁC.
were H2, CO, CO2 and CH4. The concentration of CO2 and H2
gradually increases with rising of the ratio H2O–EtOH up to 6
while variation of CO concentration is opposite. In the whole,
these dependences go with thermodynamic data (Fig. 12).
However, if experimental CO2 concentration is only slightly
lower as compared to equilibrium one, the values of H2 and CO
concentration is appreciably below corresponding thermody-
namic values (Fig. 12). The latter could be due to consumption
of H2 and CO in the methanation reaction.47 The methane
concentration higher than the equilibrium value conrms its
occurring. In addition, the high methane concentration could
be caused by ethanol cracking in the monolith channels.
The effect of contact time on the performance of the
monolithic catalyst in ESR was studied at H2O–EtOH ¼ 3 and
exit temperature 750 ꢁC. The variation of the main products
concentration with the contact time (Fig. 13), in general,
corresponds to that for the grain catalyst Ru/CZS–Al2O3 (Fig. 9).
H2 and CO2 concentration increases with longer contact time
while concentrations of CO and CH4 go down. As mentioned
above, at 750ꢁ, if the change in concentrations of H2, CO and
CO2 are mainly affected by water gas shi (WGS) and reverse
WGS reactions, decreasing of CH4 content in the exit reaction
mixture is conditioned by its steam reforming.
Fig. 11 Influence of H2O–EtOH ratio on the yield of hydrogen and
selectivity of products in ESR. Catalyst – Ru/CZS–Al2O3. Contact time
0.07 s, Reaction mixture 10 vol% EtOH + 40–60 vol% H2O, N2
–
balance.
The effect of H2O–EtOH ratio in the range from 1 to 6 on ESR
over the monolithic catalyst ꢁwas examined at the constant
ethanol concentration at 720 C and the contact time of 0.4 s
(Fig. 12). At all values of H2O–EtOH ratio, the main products
Fig. 12 Products concentration vs. H2O–EtOH ratio over the mono- Fig. 14 H2 and CO concentration vs. time-on-stream over the
lithic catalyst. 12 vol% EtOH, 720 ꢁC, contact time 0.4 s. Solid line – monolithic catalyst. EtOH concentration – 12 vol%, H2O–EtOH ¼ 3,
experimental data, dash line – thermodynamic data.
750 ꢁC, contact time 0.4 s.
37970 | RSC Adv., 2014, 4, 37964–37972
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The long-time testing of the monolithic catalyst was con- 14 X. Hu and G. Lu, Appl. Catal., B, 2009, 88, 376.
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0.4 s. The concentrations of H2 and CO during 30 hours time-
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stability of the monolithic catalyst to coking.
E. A. Blekkan, Top. Catal., 2008, 49, 38.
17 J. Comas, F. Marino, M. Laborde and N. Amadeo, Chem. Eng.
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4. Conclusions
18 A. N. Fatsikostas and X. E. Verykios, J. Catal., 2004, 225, 439.
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the monolith support.
G. J. Burtron, H. Davis, L. V. Mattos and F. B. Noronha, J.
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The study of ethanol steam reforming reveals that the main 23 L. O. O. Costa, A. M. Silva, F. B. Noronha and L. V. Mattos,
route of the reaction over the catalyst Ru/CZ is dehydrogenation
Int. J. Hydrogen Energy, 2012, 37, 5930.
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G. J. Burtron, H. Davis, L. V. Mattos and F. B. Noronha,
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28 I. A. C. Ramos, T. Montini, B. Lorenzut, H. Troiani,
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Acknowledgements
This work is supported by Integration Project 8 of SB RAS-NAN 29 M. E. Doukkali, A. Iriondo, P. L. Arias, J. F. Cambra,
Belarus, Russian Fund of Basic Research Project RFBR-CNRS
12-03-93115.
I. Gandarias and V. L. Barrio, Int. J. Hydrogen Energy, 2012,
37, 8298.
ˇ
30 J. Kaspar and P. Fornasiero, in Catalysis by Ceria and Related
Materials, ed. A. Trovarelli, Catalytic Science Series, Imperial
College Press, London, UK, 2002, vol. 2, p. 217.
31 T. Montini, L. D. Rogatis, V. Gombac, P. Fornasiero and
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