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Faculty of Chemistry, Vietnam National University Hanoi, 19 Le Thanh Tong ST, Hanoi, 10999, Viet Nam
Received 15 June 2016
Accepted 28 July 2016
Available online 18 August 2016
Keywords:
CO hydrogenation
Metal dispersion
CueCo
Perovskite
La(CoCuO3) nanoperovskites have been prepared by the mechano-synthesis method and treated with
hydrogen to yield a high dispersion of bimetallic CoeCu sites. The reduced LaCo1-xCuxO3samples were
characterized by XRD, H2-TPR, CO and H2chemisorption and tested for CO dissociation and for alcohol
synthesis from syngas. The experimental results indicated that the activities in CO dissociation and
hydrogenation on copper-cobalt metals extracted from perovskite lattice crystals are significantly
different from those in the extra-perovskite lattice. The overall catalytic activity in syngas conversion is
correlated with the CoeCu metal surface, but the alcohol productivity e productivity of alcohols
de-creases in the order of LaCo0.7Cu0.3O3> LaCo0.4Cu0.6O3> Cu2O/LaCoO3> LaCo0.9Cu0.1O3> LaCoO3. The
highest catalytic activity and alcohol productivity was obtained over sample of the reduced LaCo0.7
-Cu0.3O3perovskite catalyst.
© 2016 The Authors. Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi.
This is an open access article under the CC BY license ( />
1. Introduction
Perovskites, mixed oxides of the general formula ABO3, have
extensively been applied in many fields due to their particular
compositional structure [1]. In principle, the ideal perovskite
structure is cubic with the space-group Pm3m-Oh in which the A
cation occupies at the body center, the cation (B) is at the cube
corner, and the oxygen stays at the midpoint of the cube edges[1,2].
By this way, the perovskite derivatives may be synthesized by the
replacement of another element in A and/or B position[1,3,4]. In
the present work, we have partially substituted Co3ỵin
lanthanum-cobaltate by Cu2ỵ to obtain La(Co,Cu)O3 perovskite catalyst
pre-cursors. The partial reduction of La(Co,Cu)O3 perovskites may
further produce metallic copper-cobalt metals those originate
intentionally from the perovskite lattice. As a result, a finely
dispersed metal catalyst from perovskite precursors would be
ex-pected to use for several applications[2,4]. In experimental, Crespin
and Hall[5]had produced Co0/La2O3from the reduction of LaCoO3
under hydrogen atmosphere. Fierro et al.[6]received the Ni/La2O3
after the complete reduction of LaNiO3at 705 K. Bedel et al.[4]only
carried out the partial reduction of La(Co,Fe)O3 orthorhombic
perovskites at 723 K, producing a small amount of metallic cobalt
while the perovskite lattice still preserved. Thus, the perovskite
product has exhibited a high catalytic activity in many applications
such as CO oxidation[7]hydrogenation of ethylene[8], reforming
of CO2 [9], and conversion of syngas (H2/CO) into many useful
chemicals and liquid fuels[10,11]. The latter conversion is a very
important process since a mixture of alcohols is a crucial gasoline
additive or green vehicle fuel today[12e14].
In our previous work, we have reported some novel
character-istics of lanthanum-cobaltate nanoperovskites prepared by
mechano-synthesis method[10,11,14]. The reduction of such
ma-terials leads to the formation of a well-homogenized supported
bimetallic alloy. Furthermore, the co-existence of two transition
metal ions in the solid lattice results in the formation of dual sites
which are active for many oxidation-reduction applications
[4,15e19]. This article is to present a way for the preparation of
metals supported catalysts for the conversion of carbon monoxide
into oxygenated compounds.
2. Experimental
2.1. Catalyst preparation
A series of CoeCu bases perovskites were synthesized by
mechano-synthesis method. The stoichiometric proportions of
commercial lanthanum, copper, and cobalt oxides (99%, Aldrich)
* Corresponding author. Fax: ỵ84 (04) 3824 1140.
E-mail address:(N. Tien Thao).
Peer review under responsibility of Vietnam National University, Hanoi.
Contents lists available atScienceDirect
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j s a m d
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were mixed together with three hardened steel balls
(diameter¼ 11 mm) in a hardened steel crucible (50 mL). A SPEX
high energy ball mill working at 1000 rpm was used for
mechano-synthesis. Milling was carried out for 8 h prior to a second milling
step with an alkali additive. Then, the resulting powder was mixed
to 50% sodium chloride (99.9%) and further milled under the same
conditions for 12 h before washing the additives with distilled
water. A sample was added into a beaker containing 1200 mL water
and stirred by magnetic stirring for 90 min prior to being
sedi-mented for 3e5 h. After the clean water is removed, the slurry was
dried in oven at 60e80<sub>C before calcination at 250</sub><sub>C for 150 min.</sub>
2.2. Characterization
The elemental chemical analysis of copper and cobalt in the
perovskites was performed by atomic absorption spectroscopy
using a PerkineElmer 1100B spectrometer. Phase analysis and
crystal domain size determination were performed by powder
X-ray diffraction (XRD) using a SIEMENS D5000 diffractometer with
CuKaradiation (l¼ 1.54059 Å). Bragg's angles between 15 and 75
were collected at a rate of 1/min.
To measure the real surface area of the reduced perovskites, two
other BET experiments were performed using aflow system
(RXM-100, Advanced Scientific Designs, Inc., ASDI). First, 70e100 mg of
catalyst was calcined at 773 K (ramp of 5 K/min) under 20 mL/min
of O2/He (20 vol. %) for 90 min and then evacuated at 723 K for
90 min (P<sub> 8.5 10</sub>8mmHg). Nitrogen adsorption was carried
out at 77 K. Each point of the adsorption isotherm was established
by introducing a given amount of nitrogen from the reaction
manifold into the reactor. Temperature Programmed Reduction
(TPR) experiments were carried out after evacuating N2adsorption
(BET measurement). TPR of the catalysts was then carried out by
ramping under 4.65 vol.% of H2/Ar (20 mL/min) from room
tem-perature to 773 K (5 K/min) for 90 min. The second BET
measure-ment of the sample after reduction was also done in situ.
Chemisorption performance with H2at 373 K and CO at room
temperature was carried out after the second BET measurement.
The H2-chemisorption performance was similar to steps for BET
measurement of nitrogen. After the first isotherm that contains
both physical adsorption and chemisorption was collected, the
sample was evacuated at adsorption temperature for 5e10 min in
order to remove all physically adsorbed species prior to do the
second adsorption. The difference between the<sub>first and the second</sub>
isotherm gives the chemisorption isotherm. H2-and CO-uptake
were determined by extrapolating the straight-line portion of the
adsorption isotherms to zero pressure as represented inFig. 1.
CO dissociation tests on the reduced samples were carried out
using a RXM-100 system. Prior to pretreatment, 40e50 mg of
catalyst was ramped at 10 K/min up to the calcination temperature
(773 K) under 20 vol.% O2/He (20 mL/min) for 90 min and then
cooled down to room temperature under aflow of 20 mL/min He
for 60 min in order to remove the physically adsorbed gas. The
pretreatment of the catalysts was then carried out from room
temperature up to 798 K (5 K/min) for 90 min under 4.65 vol. % of
H2/Ar (20 mL/min) and then cooled down to reaction temperature
under a<sub>flowing 20 mL/min of He. A number of CO/He (0.586 vol. %)</sub>
pulses (0.25 mL) were then injected and passed through the reactor
prior to on line analysis using mass spectrometer (UTI-100). The m/
z signals 2, 18, 28, 44 were collected.
2.3. Catalytic activity
The catalytic tests were carried out in a stainless-steel
contin-uous fixed-bed flow micro-reactor (BTRSeJr PC, Autoclave
Engi-neers). The reaction pressure was controlled using a back-pressure
regulator. The syngas mixture (H2/CO¼ 2/1) was diluted in helium
(20 vol. %). A mixture of reactants and inert gas was supplied from a
pressurized manifold via individual mass flow controllers. The
catalyst pellet size was 40 mesh. Catalysts were pretreated in situ
underflowing 5 vol.% of H2/Ar (20 mL/min) prior to each reaction
test. The temperature was kept at 523 K (3 h), and 773 K (2h30)
with a ramp of 2 K/min. Then, the reactor was cooled down to the
reaction temperature while pressure was increased to 69 bars by
feeding a reaction mixture of gases. The products were analyzed
using a gas chromatograph equipped with two capillary columns
and an automated online gas sampling valve maintained at 443 K.
The temperature of transfer line between the reactor and the valves
was kept at 493 K in order to avoid any product condensation.
Carbon monoxide and carbon dioxide were separated using a
capillary column (Carboxen™ 1006 PLOT, 30 m 0.53 mm)
con-nected to the TCD. Quantitative analysis of all organic products was
carried out using the second capillary column (Wcot fused silica,
60 m 0.53 mm, Coating Cp-Sil 5CB, DF ¼ 5.00
FID detector (Varian CPe 3800) and mass spectrometer (Varian
Saturn 2200 GC/MS/MS).
3. Results and discussion
3.1. Catalyst characteristics
The physical properties of all fresh catalyst samples are
measured and shown inTable 1. X-ray diffraction spectra of all
samples were collected (but not shown) and the crystal phase is
presented inTable 1 [10]. Although Table 1 shows each sample
contains at least two components, but it is noted that the main
phase is perovskite a long with a very small amount of starting
metal oxide material(s) as impurities [10]. Both LaCoO3 and
La(Co,CuO)O3 perovskites are presented as the well-structured
<b>0.00</b>
<b>0.20</b>
<b>0.40</b>
<b>0.60</b>
<b>0.80</b>
<b>1.00</b>
<b>1.20</b>
<b>1.40</b>
<b>0</b> <b>10</b> <b>20</b> <b>30</b> <b>40</b> <b>50</b>
<b>Pressure (torr)</b>
<b>H2</b>
<b>)g/</b>
<b>l</b>
<b>m(</b>
<b>e</b>
<b>ka</b>
<b>t</b>
<b>p</b>
<b>u</b>
<b>de</b>
<b>bo</b>
<b>ro</b>
<b>si</b>
<b>me</b>
<b>h</b>
<b>C</b>
<b></b>
<b>-Total adsorption</b>
<b>Chemisorption</b>
<b>Physisorption</b>
Fig. 1. H2e Chemisorption at 373 K over LaCo0.4Cu0.6O3reduced at 773 K.
Table 1
Properties of the synthesized perovskites.
Nominal Sample XRD analysisa <sub>BET surface</sub>
area (m2<sub>/g)</sub>b
Chemical
composition
Co Cu
LaCoO3 P, Co3O4 60 21.1 e
LaCo0.9Cu0.1O3 P, Co3O4 20 19.3 1.9
LaCo0.7Cu0.3O3 P, Co3O4,CuO 22 18.6 5.8
LaCo0.4Cu0.6O3 P, Co3O4,CuO 21 9.8 11.6
Cu2O/LaCoO3 P, Cu2O, CuO 16.8 20.0 3.3
a<sub>XRD spectra were compared to JCPDS</sub><sub>files: P: Perovskite (JCPDS No. 48e0123);</sub>
Co3O4(JCPDS No. 42e1467); CuO(JCPDS No. 45e0937).
rhombohedral perovskite as shown inFig. 1 [3e5,10]. The crystal
surface area, ranging from 20 to 60 m2/g.Fig. 2.
The reducibility of the ground perovskites is interpreted
through the H2-TPR analysis as represented inFig. 3. It is clearly
observed that the copper efree perovskite sample shows two
distinct visible peaks at 670 and 960 K. The low temperature peak is
firmly ascribed to the reduction of Co3ỵ<sub>to Co</sub>2ỵ<sub>and the other broad</sub>
peak is attributed to the complete reaction of cobalt divalent to
metallic phase, in good harmony with the results reported by
several groups [1,4<sub>e6,9,10]</sub>. A similar H2-TPR feature is also
observed for LaCo0.9Cu0.1O3, the profile slightly shifts to the lower
temperature (Fig. 3). Thus, the first shaped-peak is observed at
650 K while the second is at 840 K. It is worthily noted that the H2
-TPR baseline was completely recovered at 950 K showing that the
reduction is essentially terminated at much lower temperature as
compared with the case of LaCoO3 [10,12]. The calculation of H2
consumed amount balance indicates that the reduction of Co3ỵand
Cu2ỵto Co2ỵand Cu0below 671 K, whereas that of Co2ỵto Co0at
840 K [4,11,15]. An increased amount of intra-perovskite lattice
copper leads to a significant affect on the perovskite reducibility
[15]. For LaCo0.7Cu0.3O3sample, the lower peak is visible, but the
other is very broadening from 643 to 943 K. When a larger amount
of intra-lattice cobalt is replaced by copper ions, the two distinct
peaks in H2-TRP trace of the perovskite sample seems to coalesce
into a single peak at 687 K while that of the physical mixture of
Cu2O/LaCoO3still preserves two visible peaks at 670 and 1018 K.
This is interpreted by the assumption of mutual interaction
be-tween cobalt and copper ions in the reduced form; the reduced
copper metal is to promote the reducibility of cobalt ions in the
framework when copper was essentially extracted from the
perovskite lattice at lower reduction temperature as demonstrated
by H2-TPR results[1,10,15,19]. Moreover, hydrogen is well known to
be easily dissociated to hydrogen atoms on metallic copper sites.
Consequently, the reduction of cobalt ions (Co3ỵ and Co2ỵ) by
atomic hydrogen is presumably taken place at lower temperatures
[1,10,15]. Thus, the reduction of La(Co,Cu)O3is to provide afinely
dispersed CoeCu atoms on the catalyst surface and the formation of
bimetallic alloy is not ruled out[19].
To determine the dispersion of metals formed, we have
measured both H2and CO chemisorptions for the reduced
perov-skite forms. Unfortunately, the determination of each individual
component dispersion level is a very difficult task due to a synergic
interaction between two metals after the partial reduction of
perovskites[10,11,15,19]. In this case, we have recorded total H2and
CO chemisorbed volume (mL/g) of each sample (Fig. 1). The volume
of H2and CO uptake of all reduced samples is in turn presented in
Table 2.
The reduced samples were investigated the ability of CO
chemical composition and dissociation temperatures[15,17,20]. The
presence of copper component gives rise to slight decreased CO
dissociation conversion in the temperature range of 500e798 K. The
CO dissociation conversion decreases with the order of LaCoO3> CuO/
LaCoO3> LaCo0.7Cu0.3O3> LaCo0.4Cu0.6O3 LaCo0.9Cu0.1O3(Fig. 4). It
is well known that cobalt metal has shown a very good activity in the
dissociation of CO while copper is inactive for the CO splitting
[17,21,22]. In this case, copper plays an important role in the synthesis
of alcohols through the protection of the OH functional groups during
the hydrogenation conditions[11,20,22]. Thus the higher CO
con-versions over the cobalt-rich samples are certainly comprehensive
[4,21]. Based on the ability of the reduced samples to dissociate CO
molecule, we are firmly expected that the reduced copper-free
perovskite is active for the synthesis of hydrocarbons while the
perovskite containing copper may act as promising catalysts for the
3.2. Catalytic activity in hydrogenation of carbon monoxide
All the prepared samples are pretreated under hydrogen
flow-rate at 798 K prior to test for the hydrogenation of carbon monoxide
at 548 K, 68.9 bars and space velocity VVH¼ 5000 h1(H2/CO/
He¼ 8/4/3). The products contain a mixture of linear primary
al-cohols and n-alkane in addition to small amounts of secondary
alcohols and isoparafins and the formation of products is believed
to be associated with the catalyst metal surface[22].
Thus, we presented the correlation between CO conversion and
product selectivity versus the CO-chemisorbed volume uptake.
With the exception of mixture Cu2O/LaCoO3sample,Fig. 5shows
an increased CO conversion with the CO chemisorbed-volume in
order of LaCo0.7Cu0.3O3 > Cu2O/
LaCoO3> LaCoO3> LaCo0.4Cu0.6O3> LaCo0.9Cu0.1O3. The selectivity
to alcohols obtained over these catalyst samples are presented in
more insight into the catalytic behavior[10,22]. Undoubtedly,Fig. 6
<b>0</b>
<b>300</b>
<b>600</b>
<b>900</b>
<b>1200</b>
<b>1500</b>
<b>1800</b>
<b>20</b> <b>30</b> <b>40</b> <b>50</b> <b>60</b>
<b>Li</b>
<b>n </b>
<b>(C</b>
<b>ps</b>
<b>)</b>
<b>LaCo Cu O</b>
<b>LaCo Cu O</b>
<b>LaCo Cu O</b>
<b>LaCoO</b>
<b>2θ (degree)</b>
Fig. 2. XRD patterns of all catalyst precursor samples.
<b>0</b>
<b>5</b>
<b>10</b>
<b>15</b>
<b>20</b>
<b>25</b>
<b>300</b> <b>450</b> <b>600</b> <b>750</b> <b>900</b> <b>1050</b>
<b>Temperature (K)</b>
<b>T</b>
<b>C</b>
<b>D</b>
<b> S</b>
<b>ign</b>
<b>al</b>
<b> (a.u</b>
<b>)</b>
<b>LaCoO3</b>
<b>LaCo0.7Cu0.3O3</b>
<b>LaCo0.4Cu0.6O3</b>
<b>Cu2O/LaCoO3</b>
<b>LaCo0.9Cu0.1O3</b>
shows the productivity of alcohols decreases monotonically with
CO uptake in the order of LaCo0.7Cu0.3O3> LaCo0.4Cu0.6O3> Cu2O/
LaCoO3 > LaCo0.9Cu0.1O3 > LaCoO3. This observation is not with
respect to the order of CO chemisorbed volume, but in good
agreement with the ratio of H2volume uptake/BET surface area of
the sample after reduction (Fig. 7). This phenomenon is explained
by the composition of the catalyst surface and the available
abun-dance of bimetallic cobalt-copper sites on the catalyst surface after
reduction[11,16,22e24].
Certainly, the presence of intra-lattice copper (LaCo0.7Cu0.3O3)
has a promotional effect on the formation of alcohols as compared
with the extra-lattice copper (Cu2O/LaCoO3) or the copper-free
perovskite sample [11,23]. The formation of La(Co,Cu)O3
perov-skite precursors would provide intimidate dual copper-cobalt sites
which are prerequisite for the formation of alcohols from CO and H2
[17,19,25]. This issue is further supported by the examination of the
catalytic activity at different pretreatment conditions.Table 2
dis-plays the alcohol selectivity/productivity versus the reduction
temperatures obtained on LaCo0.7Cu0.3O3. It is noted that the
alcohol productivity gradually increases and reaches a maximal
value at 773 K and then sharply decreased at higher reduction
temperatures. This observable trend is explained by the fact that
the surface composition is strongly associated with pretreatment
temperature because of the reduction of CoeCu based perovskites
happening in a multiple-step process at different temperatures
[1,2,4,8,10]. The surface concentration of cobalt and copper metals
is very sensitive to the reduction temperatures[4,5,9,11,15,21,25].
As an increased in H2-reduction temperature, the (Cu0eCo0)surface/
(CueCo)totalmolar surface ratio is varied and probably approached
a highest value around 773 K as elucidated by hydrogen
chemi-sorption data (Table 2)[23].
A higher reduction temperature gives rise to a sintering of
atomic copper metals and as consequence the active sites for the
formation of OH alcohol functional group gradually decreases.
Indeed, it was widely reported that the reduction of perovskites can
be described either by the contrasting-sphere model or by the
Table 2
Effect of hydrogen pretreatment temperature on alcohol productivity over sample LaCo0.7Cu0.3O3in CO hydrogenation at 548 K (VVH¼ 5000 h1, 69 bar, H2/CO/He¼ 8/4/3).
Reduction temperature (K) H2evolume (mL/gcat) CO conversion (%) Alcohol selectivity (%) Alcohol productivity (mg/gcat/h)
623 0.78 17.5 27.2 43.0
723 0.93 16.1 41.9 49.4
773 0.84 25.1 42.9 70.1
823 0.56 8.7 43.5 33.4
<b>20</b>
<b>30</b>
<b>450</b> <b>500</b> <b>550</b> <b>600</b> <b>650</b> <b>700</b> <b>750</b> <b>800</b>
<b>Temperature (K)</b>
<b>)</b>
<b>%(</b>
<b>noi</b>
<b>tai</b>
<b>co</b>
<b>si</b>
<b>d</b>
<b>O</b>
<b>C</b>
LaCoO3
CuO/LaCoO3
LaCo0.7Cu0.3O3
LaCo0.9Cu0.1O3
<b>LaCoO3</b>
<b>CuO2/LaCoO3</b>
<b>LaCo0.7Cu0.3O3</b>
<b>LaCo0.9Cu0.1O3</b>
<b>LaCo0.4Cu0.6O3</b>
Fig. 4. CO dissociation ability at different temperatures on the reduced samples after
pre-treatment at 798 K in H2/Ar (0.586 vol. % CO/He pulses (0.25 mL) were then
injected through the catalyst).
<b>5</b> <b>15</b> <b>25</b> <b>35</b> <b>45</b> <b>55</b> <b>65</b> <b>75</b>
<b>CO Conversion (%) and Alcohol productivity (mg/gcat/h)</b>
<b>0.012</b>
<b>0.014</b>
<b>0.016</b>
<b>0.018</b>
<b>0.028</b>
<b>g/</b>
<b>L</b>
<b>m(</b>
<b>ek</b>
<b>at</b>
<b>pu</b>
<b>de</b>
<b>br</b>
<b>osi</b>
<b>me</b>
<b>h</b>
<b></b>
<b>C-O</b>
<b>C</b>
<b>ca</b>
<b>t </b>
<b>h)</b>
<b>Conversion</b>
<b>Alcohols</b>
<b>Cu2O/LaCoO3</b>
<b>LaCo0.4Cu0.6O3</b>
<b>LaCo0.7Cu0.3O3</b>
<b>LaCo0.9Cu0.1</b>
<b>LaCoO3</b>
Fig. 5. Correlation between the volume of CO chemisorbed uptake and CO
hydroge-nation activity at 548 K (VVH¼ 5000 h1<sub>, 69 bar, H</sub>
2/CO/He¼ 8/4/3).
<b>0</b> <b>10</b> <b>20</b> <b>30</b> <b>40</b> <b>50</b> <b>60</b> <b>70</b> <b>80</b> <b>90</b> <b>100</b>
<b> Alcohol and hydrocarbon selectivity (wt.%)</b>
<b>0.012</b>
<b>0.014</b>
<b>0.016</b>
<b>0.018</b>
<b>0.028</b>
<b>)t</b>
<b>ac</b>
<b>g/</b>
<b>L</b>
<b>m(</b>
<b>e</b>
<b>ka</b>
<b>t</b>
<b>p</b>
<b>u</b>
<b>de</b>
<b>br</b>
<b>osi</b>
<b>me</b>
<b>h</b>
<b></b>
<b>C-O</b>
<b>C</b>
<b>Hydrocarbons</b>
<b>Alcohols</b>
<b>Cu2O/LaCoO3</b>
<b>LaCo0.4Cu0.6O3</b>
<b>LaCo0.7Cu0.3O3</b>
<b>LaCo0.9Cu0.1O3</b>
<b>LaCoO3</b>
Fig. 6. Correlation between the volume of CO chemisorbed uptake and CO
hydroge-nation activity at 548 K (VVH¼ 5000 h1<sub>, 69 bar, H</sub>
2/CO/He¼ 8/4/3).
<b>0.01</b>
<b>0.02</b>
<b>0.03</b>
<b>0.04</b>
<b>0.05</b>
LaCoO3 Cu2O/LaCoO3
<b>Perovskite catalysts</b>
<b>Vo</b>
<b>lum</b>
<b>e o</b>
<b>f H</b>
<b>2</b>
<b> </b>
<b>-upt</b>
<b>ak</b>
<b>e / S</b>
<b>BET</b>
<b> (m</b>
<b>L</b>
<b>.g</b>
<b>/m</b>
<b>2)</b>
<b>LaCoO3LaCo0.9Cu0.1O3LaCo0.7Cu0.3O3LaCo0.4Cu0.6O3Cu2O/LaCoO3</b>
nucleation mechanism[1,2,5,8,9]. Thus, the total metal surface area
is strongly dependant on the pretreatment conditions[8,10,18,20].
In the present study, the LaCo0.7Cu0.3O3is reduced at 773 K gives
the most effective catalyst for the formation of higher alcohols from
CO hydrogenation reaction.
The alcohol product distribution is presented inFig. 8which
contains a mixture of linear primary alcohols from methanol to
heptanol [10,22]. The product distribution is recalculated as
Anderson-Schulz-Flory (ASF) rule and the plot between ln(wt.%/n)
versus carbon number (n) is drawn in Fig. 9 [20,22]. Since the
carbon chain growth factor of alcohols (designated as
par with that of hydrocarbons (
one (a2) excluding methanol because methanol may be
indepen-dently produced by different pathways[11,19,26e30]. In the case,
the alcohol chain growth factor (
value between
skeletal carbons of primary alcohols occurs parallel to that of
hy-drocarbons on cobalt catalyst surface[20,22,24e27]. A close
dis-tance between cobalt and copper sites on catalyst surface has
steered the formation of hydrocarbons into primary alcohols by
insertion of undissociated CO molecule absorbed on copper sites
[11,19,20,22,28e30].
4. Conclusions
A set of La(Co,Cu)O3perovskite samples prepared by grounding
method was pretreated in H2prior to test for the CO hydrogenation
reaction. The presence of copper ions in the perovskite lattice
results in a signi<sub>ficant effect on the perovskite reducibility. Under</sub>
the same pretreatment conditions the LaeCoeCu based perovskites
is easily reduced, yielding metallic cobalt and copper sites
dispersed over a La2O3matrix. The CO dissociation ability of cobalt
is remarkably affected by the presence of neighboring copper
atoms. The overall activity of the catalysts in syngas conversion
strongly depends on pretreatment temperature and the metal
surface area. The intra-framework copper increases the formation
of higher alcohols. Alcohol and hydrocarbon productivity are
strongly dependant on reducing conditions. The highest alcohol
productivity was about 0.07 galcohol/gcat/h on the LaCo0.7Cu0.3O3
perovskite precursor.
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M
et
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M
et
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nol
M
et
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M
et
ha
<b>623</b> <b>723</b> <b>773</b> <b>823</b>
<b>Temperature (K)</b>
<b>)</b>
<b>%(</b>
<b>noi</b>
<b>tu</b>
<b>bi</b>
<b>rts</b>
<b>i</b>
<b>Dl</b>
<b>oh</b>
<b>ocl</b>
<b>A</b>
Fig. 8. Effect of hydrogen pretreatment temperature on alcohol distribution over
sample LaCo0.7Cu0.3O3in CO hydrogenation at 548 K (VVH¼ 5000 h1, 69 bar, H2/CO/
He¼ 8/4/3).
<b>-4</b>
<b>-3</b>
<b>-2</b>
<b>-1</b>
<b>0</b>
<b>1</b>
<b>2</b>
<b>3</b>
<b>4</b>
<b>5</b>
<b>0</b> <b>1</b> <b>2</b> <b>3</b> <b>4</b> <b>5</b> <b>6</b> <b>7</b> <b>8</b> <b>9</b> <b>10</b> <b>11</b>
<b>Carbon number</b>
<b>Ln</b>
<b> [(w</b>
<b>t.%)/</b>
<b>n]</b>
<b>α3 = 0.43</b>
<b>α2 = 0.42</b>
<b>α1 = 0.38</b>
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