Dehydration of 2-Octanol over Ca-doped CeO2 Catalysts

Article abstract of DOI:10.1002/cctc.201601076

Vapor-phase catalytic dehydration of 2-octanol was investigated over Ca-doped CeO₂ at 375 °C and atmospheric pressure. Ca doping up to 0.15 wt % was found to increase the dehydration activity for 2-octanol, whereas further increases in Ca conte

Full text of DOI:10.1002/cctc.201601076

Accepted Article
Title: Dehydration of 2-octanol over CeO2-CaO mixed oxides
Authors: Muthu Kumaran Gnanamani, Gary Jacobs, Wilson D Shafer,
and Burtron Davis
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Dehydration of 2-octanol over Ca-doped CeO2 catalysts
Muthu Kumaran Gnanamani, Gary Jacobs, Wilson D. Shafer, Burtron H. Davis*
Center for Applied Energy Research, University of Kentucky, 2540 Research Park Dr,
Lexington, KY 40511, USA
Abstract
Vapor-phase catalytic dehydration of 2-octanol was investigated over Ca-doped CeO2 at
375°C and atmospheric pressure. Ca doping up to 0.15 wt% was found to increase the
dehydration activity for 2-octanol, while further increases in Ca content (0.50 and 1.25 wt%)
detrimentally affected the conversion. Catalyst surface area and pore volume increased with
increasing Ca content in Ca-doped CeO2. Hydrogen TPR profiles indicate that the partially
reduced state of surface ceria (i.e., Ce3+), which increases with increasing Ca loading up to 0.15
wt%, might play an important role in promoting dehydration.
Key words: Ceria; Ca-doped ceria; alcohol dehydration; 2-octanol; dehydrogenation; octenes
*Corresponding author. Tel.: +859 257 0251.
E-mail address: davis@caer.uky.edu
1.0 Introduction
Dehydration of alcohols to olefins or ethers is known to be catalyzed by metal oxides.[1-5]
Alumina has been extensively studied for this reaction.[1-10] Other oxides such as ZrO2,[11,12] and
rare earth oxides[13-20] have been examined as well. Chokkaram and Davis[21] found that the
activity of ZrO2 resembles thoria for both dehydration and 1-alkene selectivity for 2-octanol.
The authors concluded that the pretreatment of ZrO2 influenced the dehydration selectivity but
the activity and selectivity are essentially independent of the zirconia crystal phase. In another
study, Davis compared olefin selectivity obtained from the dehydration of 2-octanol over thoria
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with acidic and non-acidic alumina;[15] the conclusion was that a single mechanism of “cis
elimination” is sufficient to describe the dehydration selectivity of secondary alcohols over both
thoria and alumina.
Although the mechanism of catalytic dehydration has been studied for many years, it is
not yet fully understood.[5-10] Some have agreed that dehydration proceeds through an E2-like
reaction intermediate which exhibits a certain degree of ionic character; with increasing reaction
temperature, the structure of the transition state changes from E2-like to E1-like.[22,23] The E2
elimination involves a synchronous weakening of the C-O bond by an acid site and extraction of
β-hydrogen atom by a basic site. However, the mode of elimination differs with different oxides
leading to changes in product selectivity. Siddhan and Narayanan[14] revealed from the study of
dehydration of threo-3-methyl-2-pentanol over gamma-alumina and thoria that the tendency
toward anti elimination is greater in the case of gamma alumina whereas, for thoria, syn
elimination is favored. In this respect, ceria is a more versatile rare earth oxide, because of the
dynamic nature of its surface; oxygen vacancies can be created at high temperature and activated
by molecules such as H2, CO, or hydrocarbons, as shown below:[24,25]
2CeO2 (s) → 2CeO2-y (s) + yO2 (g)
CeO2 (s) + yCO (g) → CeO2-y (s) + yCO2 (g)
Ceria also possesses acid-base properties, depending on the nature and temperature of the
pretreatment.[26,27] Bernal and Trillo[13] compared the selectivity to 1-olefins among various rare
earth oxides, such as La2O3, CeO2, Pr6O11, Sm2O3, Eu2O3, Dy2O3, Ho2O3, and Yb2O3 for
dehydration of 2-propanol, 1-butanol and 2-butanol. The authors emphasized that the reaction
temperature affects the product distribution, which may significantly restrict the validity of
correlations made between alkene distribution and catalyst properties. Haffad et al.[28] suggest
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that the redox properties and highly labile lattice oxygen contribute to product formation
involving oxygen vacancies on CeO2 for 2-propanol dehydration.
Recently, Mullins et al.[16] found from a study of the adsorption of C1-C3 alcohols on
CeOx(111) thin films that the reduced surface can break the C-O bond much easier than that of
the O-substrate (Ce) bond; in other words, reduced ceria should promote dehydration moreso
than oxidized ceria. Reddy et al.[29] investigated dehydration of 4-methylpentan-2-ol using
CeO2-SiO2 and CeO2-ZrO2 prepared by a rapid microwave-assisted combustion synthesis
method. The authors claimed that the presence of additional oxygen vacancies and lattice
defects in CeO2-ZrO2 were responsible for the higher conversion and selectivity for 4-
methylpent-1-ene relative to CeO2. In this work, Ca-doped CeO2 catalysts were investigated for
dehydration of 2-octanol with the aim of producing more partially reduced ceria after H2
pretreatment at elevated temperatures and thereby promote the dehydration activity for 2-octanol.
2.0 Experimental
2.1 Catalyst preparation
CeO2, CaO, and Ca-doped CeO2 were prepared via a homogeneous co-precipitation of
cerium and calcium nitrates using a urea decomposition method. In this method, appropriate
amounts of Ce(NO3)3.6H2O (Alfa Aesar, 99.5%) and Ca(NO3)2.4H2O (Aldrich, 99%) were first
dissolved simultaneously in deionized water at room temperature. In a separate beaker, the
required quantity of urea (usually ~4 times that of the molar equivalent of metal nitrates) was
dissolved in deionized water and mixed with the solution of metal nitrates. The solution was
refluxed at 85-90°C with constant stirring (500 rpm) for 15 h. The resulting precipitate was
filtered and washed three times using deionized water. It was then dried in a static oven at
120°C and calcined in air in a muffle furnace at 500°C for 3 h. In the case of pure calcium oxide
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(CaO), the dried CaCO3 was decomposed in air overnight at 950°C. The amount of calcium
present in the calcined samples was determined by ICP and corresponding theoretical values
calculated based on the amount of metal salts that were added to the synthesis mixture are shown
in Table 1. Also, the Ce/Ca X-ray fluorescence signal ratio was estimated at the Soft X-ray
Microcharacterization beamline (SXRMB) at the Canadian Light Source, Inc. using Ca Kα1 and
Ce Lβ1 lines. As shown in Table 1 and using the 0.15%Ca-CeO2 catalyst as a basis of
comparison, the relative ratios for 0.50%Ca-CeO2 and 1.25%Ca-CeO2 were 1 and 2,
respectively, indicating that the 1.25%Ca-CeO2 catalyst had double the Ca content in the surface
shell relative to the 0.15%Ca and 0.50%Ca catalysts. This is different from the relative ratios
estimated by ICP, which gave an increasing trend; using the 0.15%Ca-CeO2 catalyst as a basis of
comparison, the relative ratios for the 0.5%Ca-CeO2 and 1.25%Ca-CeO2 catalysts were 3.5 and
10, respectively. Thus, relatively speaking, the bulk dopant concentration of Ca increases
moreso than the surface shell concentration with increasing Ca content for the catalyst prepared
by the co- precipitation of Ce-Ca oxides. Furthermore, with the preparation conditions used,
only a fraction of the calcium was precipitated with CeO2. Catalysts are designated based on the
concentrations found experimentally by ICP (i.e., 0.15%, 0.50%, and 1.25%).
2.2 BET surface area and porosity
BET surface area and porosity characteristics were measured using a Micromeritics 3-
Flex system. Before performing the test, the temperature was gradually ramped to 160°C and the
sample was evacuated at this temperature for 12 h to approximately 50 mTorr. The BET surface
area, single point pore volume, and single point average pore diameter were obtained. The
Barrett-Joyner-Halenda (BJH) method was also used to estimate pore volume and average pore
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diameter, as well as to provide an estimate of the pore size distribution as a function of pore
radius using the relation dV / d (log R).
2.3 X-ray diffraction (XRD)
Powder X-ray diffractograms of calcined CeO2, CaO, Ca-doped CeO2 were recorded
using a Philips X’Pert diffractometer with monochromatic Cu Kα radiation (λ = 1.5418). XRD
scans were taken over the range of 2θ from 10 - 90°. The scanning step was 0.01, the scan speed
was 0.0025 s-1, and the scan time was 4 s.
2.4 Scanning electron microscopy (SEM)
The morphology of the calcined samples of CeO2, Ca-doped CeO2 and CaO was studied
by scanning electron microscopy (SEM). The scanning electron microscope (Hitachi S-4800
model) was operated at 300 kV in the SE display mode. For characterization prior to analysis,
samples were gold coated in a sputter coating unit (Edwards Vacuum Components Ltd., Sussex,
England).
2.5 Temperature programmed reduction (TPR)
Temperature programmed reduction (TPR) profiles of undoped ceria, CaO, and Ca-doped
CeO2 were recorded using a Zeton-Altamira (AMI-200) unit which employs a thermal
conductivity detector (TCD). The calcined samples were first purged at 350°C in flowing argon
to remove traces of water. TPR was performed using a 10%H2/Ar mixture and referenced to
argon at a flow rate of 30 cm3/min. The sample was heated from 50 to 920°C using a heating
ramp of 10°C/min.
2.6 Catalytic testing
The reaction was performed in a plug-flow catalytic micro reactor system (stainless steel
fixed-bed tubular reactor, 1.13 cm ID) capable of operating at high temperatures. About 15-20
ml of the reactor volume above the catalyst bed contained Pyrex glass beads to serve as a
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preheater zone. Approximately 1.0 g of previously calcined CeO2 or Ca-doped CeO2 or pure
CaO (40-100 microns) are mixed with 1.0 g of powdered glass beads (100 microns) and the
mixture was heated in situ in flowing hydrogen at 500°C for 2 h. A liquid feed of 2-octanol was
introduced at 0.6 ml/h using a syringe pump via an 0.16 cm needle with a side port hole. The
temperature of the catalyst bed was monitored by a thermocouple (Fe–Cr) and maintained by a
temperature controller (OmegaCN3251-R). Liquid products were collected using a trap
maintained at 20°C. The percent conversion of 2-octanol and the selectivity for various alkenes
were determined by offline GC analysis of liquid products using a gas chromatograph (HP
Agilent, model no. 7890A) with a DB-5 capillary column and a flame ionization detector (FID).
Reaction products were identified by GC-MS.
3.0 Results and discussion
3.1 BET surface area and porosity
BET surface area and porosity measurements are reported in Table 2. The surface area
of undoped CeO2 after calcination at 500°C was found to be 89 m2/g. The BET surface area
increased from 89 to 95 and 100 m2/g with increases the weight percent of Ca in CeO2 from 0 to
0.15, and further to 0.50, respectively. However, an additional increase of Ca in CeO2 (1.25
wt%) resulted in a decrease in the BET surface to 91 m2/g (still higher than CeO2). The BET
surface area of CaO was 2.7 m2/g. The single point pore volume of the calcined samples
exhibited a similar trend as that of the surface area as shown in Table 2. The BJH pore size
distributions of the calcined samples for the desorption branch are shown in Figure 1. The BJH
pore volume increased from 0.036 to 0.068 cm3/g with increases in the weight percent of Ca in
CeO2 from 0 to 1.25%. The results suggest that Ca addition enhanced the surface area of CeO2
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by incorporating into the cubic fluorite type lattice of CeO2. The pure CaO exhibited only
macropores and very low pore volume.
3.2 X-ray diffraction
Figure 2 shows XRD patterns of pure CeO2, CaO, and Ca-doped CeO2 (0.15%Ca-CeO2,
0.50%Ca-CeO2, and 1.25%Ca-CeO2). The diffraction lines corresponding to the fluorite-type
structure of ceria and Ca-doped ceria are clearly observed, consistent with our previous work.[30]
Line broadening occurs for diffraction peaks corresponding to (111) and (200) planes with
increases in the weight percent of Ca in Ca-doped CeO2; a similar trend was reported by
others.[30-33] The XRD pattern of pure CaO displays the cubic structure.
3.3 Scanning electron microscopy
The effect of Ca dopant on the morphological changes of ceria was studied by scanning
electron microscopy (SEM) and the corresponding images are shown in Figure 3. The particles
of undoped cerium oxide were polyhedron shaped typical of the cubic fluorite structure of ceria
with varying length and diameter. Doping of calcium up to 0.15 wt% to CeO2 decreased the
particle size for CeO2 overall with particles remaining cuboid in shape. Irregularities in sizes as
well as shapes developed with further increases in dopant concentration (1.25 wt% Ca) in CeO2
suggesting that Ca decreases the particle sizes of CeO2 probably by affecting their crystal growth
during co-precipitation. The SEM image of pure CaO obtained by the calcination of CaCO3 at a
temperature of 950°C displays a cubic morphology and has a less porous structure.
3.4 Temperature programmed reduction
The H2-TPR profiles for CeO2, CaO, and Ca-doped CeO2 are shown in Figure 4. In
general, surface ceria reduced at a lower temperature of around 400 - 600°C and bulk reduction
of CeO2 to Ce2O3 began at ~750°C.[34] In our system, the reduction peak maximum
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corresponding to surface reduction of ceria was observed at 515°C, whereas the maximum for
bulk reduction of ceria was 860°C. A shoulder peak developed at 350-385°C, and the peak area
appeared to increase with increasing Ca content in CeO2; the peak maxima of that particular
shoulder peak tended to shift to higher temperature with increasing Ca doping level. The surface
ceria reduction (i.e., the peaks at ~500-515oC) increased by adding 0.15% by wt%, while further
increases in Ca (0.50 and 1.25 wt%) tended to decrease the low temperature peaks (i.e., partial
reduction of surface ceria). On the other hand, bulk reduction of ceria (i.e., the peaks at 835-
860°C) decreased continuously with Ca loading. This suggests that calcium doping of CeO2 at
low levels (e.g., 0.15 wt%) promotes the formation of partially reduced ceria, which presumably
provides the active sites for dehydration.
3.4. Catalytic reaction
The conversion of 2-octanol plotted against time on-stream for various catalysts is shown
in Figure 5. Undoped CeO2 displayed a conversion of 2-octanol of about 41 % up to 40 h of
time on-stream, and the conversion decreased to 35% within another 30 h. However, Ca-doped
CeO2 catalysts exhibited less deactivation overall and showed an improvement in the conversion
of 2-octanol with Ca doping of 0.5 wt%; above that level, the conversion was even lower than
that of ceria alone. For the purpose of comparison, the reactivity data for pure calcium oxide is
included in the same figure; it displayed about 14.5% conversion initially and then dropped to
8.0% within a few hours.
2-octanol mainly undergoes dehydration over ceria. In addition, 2-octanone was also
obtained, and it is known to be a dehydrogenation product; in addition, products of cracking
were also observed, including methane, ethane, hexane and heptanes (<2%). The dehydration
selectivities expressed as the selectivity to enes plotted against time on-stream for various CeO2,
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CaO, and Ca-doped CeO2 are shown in Figure 6. The selectivity to enes does not vary (~52%)
with the catalyst composition of Ca-doped CeO2 except 1.25%Ca-CeO2 which exhibited a
slightly higher (~56%) selectivity to enes (octenes). Pure calcium oxide (CaO) displayed a much
lower selectivity for octenes (16-26%); however, the selectivity increased with increasing time
suggesting that the redox functionality of CaO might change with time. Kobune et al.[35]
investigated the particle size effect of CeO2 for various catalytic reactions, in which the
selectivity to enes for dehydration of 2-heptanol was found to vary in the range of 70-80% at
intermediate conversions (25-40%). The authors claimed that the dehydration reaction is
structure-insensitive, as it did not vary with the particle size of CeO2. In the present system, we
do not see any significant changes in the selectivity for octenes with Ca addition to CeO2 while
some indication of the variation in particle size from SEM analyses revealed that the dehydration
reaction is structure insensitive.
The selectivity to 1-olefin as a function of time on-stream for various catalysts is shown
in Figure 7 and the distribution of octenes is given in Table 3. Ca doping to CeO2 up to 0.5
wt% did not result in any significant changes in selectivity. In contrast, 1-olefin selectivity for
1.25%Ca-CeO2 catalyst was significantly lower (~74.9%) in comparison with other Ca-doped
CeO2 catalysts (90.1% for 0.15%Ca-CeO2 and 89.8% for 0.5%Ca-CeO2). The 1-octene
selectivity for pure CaO was found to be 37.8%, which is only half of the selectivity observed
with CeO2-based catalysts. This indicates that the acid-base properties of the catalyst influence
olefin formation from the dehydration of 2-octanol. In an earlier study, Davis[15] compared the
selectivity for 1-octene between acidic and nonacidic alumina. The study suggests that 1-octene
selectivity for nonacidic alumina is slightly lower (30-40%) than that of acidic alumina (40-
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45%). In this case, the introduction of Ca might have increased the surface basicity of the CeO2
catalysts without significantly affecting the formation of 1-octene.
3.5 Reaction pathway
Dehydration of alcohols has been known for centuries but the mechanism of olefin and
ether formation from alcohols is not yet fully understood. Acidic and basic sites of the oxide
catalyst are believed to be involved in this reaction. Alcohols react over metal oxides and often
produce a mixture of dehydration and dehydrogenation products depending on the reaction
conditions and the selection of the catalyst.[36-38] Davis[39] reported that alumina is sensitive to
pretreatment conditions; based on the results of the dehydration reaction of 2-octanol over
alumina prepared from different sources, alumina has both dehydrogenation as well as
dehydration activity. In another study, Davis and Ganesan[12] showed changes in the selectivity
from dehydrogenation to dehydration with time on-stream for oxidized ZrO2 for the reaction of
2-octanol. On the other hand, hydrogen pretreated ZrO2 exhibited greater stability and higher
selectivity to dehydration relative to the dehydrogenation reaction. Titania and hafnia were
found to be selective for dehydration whether pretreated with air or hydrogen. Ceria and ceria-
based mixed oxides possess redox properties and are known to catalyze the conversion of diols
such as 1,3- and 1,5-diols,[40] while they do not catalyze the dehydration of the primary alcohol
into olefin and ether even at high temperatures > 400°C. The literature study on the active sites
of ceria for dehydration of alcohols proposed that the redox cycle of Ce4+ - Ce3+ on the surface
plays a role in the dehydration concerning the activation of diols. Zaki et al.[41] found that
doping of ceria with Na+ ions suppresses alcohol dehydration while Al3+ doping improves the
dehydration activity. The authors proposed that the surface reactivity is associated with Ce4+-
OH- pair sites and these active sites are poisoned by Na+, indicating the acidic site is similar to
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that involved in dehydration. In our current study, Ca-doped ceria catalysts (0.15%Ca-CeO2 and
0.5%Ca-CeO2) exhibited more dehydration activity than undoped ceria after pretreatment in
hydrogen at elevated temperatures. The H2-TPR study indicates that doping of Ca promotes the
surface reduction of ceria from Ce4+ to Ce3+. The oxygen vacancies in ceria could possibly act
as adsorption sites for 2-octanol as shown in Scheme 1, where a plausible reaction pathway for
2-octanol on reduced ceria is shown. The oxidation state of ceria should not change, but rather
remain in the 3+ oxidation state for either pathway (dehydration or dehydrogenation).
Scheme 1 A plausible reaction pathway for 2-octanol over partially reduced ceria.
As the dopant concentration (Ca) for CeO2 was increased to 1.25 wt%, the activity for
dehydration of 2-octanol fell below that of CeO2 alone, indicating that the possibility of forming
a separate calcium oxide phase above 0.5 wt% loading adversely affects the activity of ceria.
Similarly, in the steam reforming of ethanol over metal/ceria catalysts, defect sites (i.e., oxygen
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vacancies) provided a synergy, resulting in high catalytic activity.[42] Ichikawa et al.[43]
investigated the adsorption of 1,3-butanediol on oxygen-defect sites of a CeO2 (111) surface
using density functional theory (DFT) and paired interacting orbital (PIO) calculations. The
authors speculated that 1,3-butanediol preferentially adsorbs on the oxygen-defect sites of the
CeO2 (111) surface and is dehydrated at the defect site. The authors mentioned that differences
in adsorption structure between mono-alcohols and 1,3-diols at the oxygen-defect site result in
differences in their reactivity. In our work, the hydrogen pretreated Ca-doped ceria was found to
promote the dehydration reaction for 2-octanol moreso than undoped ceria under similar reaction
conditions.
4.0 Conclusions
The dehydration of 2-octanol catalyzed by undoped and Ca-doped CeO2 was
investigated. The dehydration activity for 2-octanol was found to increase with increasing Ca
content in CeO2 up to 0.5 wt%; however, the selectivity of the catalyst did not change. The
surface area and pore volume of the catalysts increased with increases in Ca content in Ca-doped
CeO2. H2-TPR reveals Ca dopant promoted the surface reduction of Ca-doped ceria (Ce4+ to
Ce3+), which in turn catalyzes the dehydration reaction. Pure CaO exhibits lower selectivity for
1-octene (37.8%) as compared to CeO2 and Ca-doped CeO2 catalysts (> 89%).
Acknowledgements
This work was supported by the Commonwealth of Kentucky. The authors thank Dr. Yongfeng
Hu and Ms. Aimee MacLennan for the XRF analysis of catalyst samples which was carried out
at the Soft X-ray Microcharacterization beamline (SXRMB) at the Canadian Light Source, Inc.
The Canadian Light Source, Inc., is funded by the Canada Foundation for Innovation, the Natural
Sciences and Engineering Research Council of Canada, the National Research Council Canada,
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the Canadian Institutes of Health Research, the Government of Saskatchewan, Western
Economic Diversification Canada, and the University of Saskatchewan.
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15
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10.1002/cctc.201601076
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Table 1. Elemental analysis
Elemental analysis by ICP wt%
XRF signal
Ca Kα1/CeLβ1
Catalyst
description
(Ca/Ce)n
(Ca/Ce)i
(Ca/Ce)n
(Ca/Ce)i
Ce
Ca
-
Ca/Ce
-
CeO2
93.7(81.4)*
-
0.15%Ca-CeO2 93.0(78.6) 0.15(2.50)* 0.0056
1†
3.5
10
0.0045
0.0044
0.0089
-
1†
1
2
0.50%Ca-CeO2 89.5(73.4)
1.25%Ca-CeO2 77.7(61.4) 1.25(17.56) 0.0562
CaO 71.78(71.47)
0.50(7.00)
0.0195
-
-
i = results for the 0.15%Ca-CeO2 catalyst
*The value in the parentheses indicates theoretical weight percent calculated based on the amount of metal salts were
added for synthesis.
† Basis for the relative comparison.
1X-ray fluorescence was carried out at at the Soft X-ray Microcharacterization beamline (SXRMB) at the Canadian
Light Source, Inc. The photon energy was set to 6500 eV and the dwell time was 10 sec.
Table 2. Textural characterization of the calcined sample of CeO2, CaO and Ca-doped CeO2
BJH
Single Point
Average Pore
Diameter
(nm)
BJH
Desorption
Pore Diameter
(nm)
BET
S.A.
Single Point
Pore Volume
(cm3/g)
Desorption
Pore
Catalyst
description
(m2/g)
volume
(cm3/g)
CeO2
89
95
100
91
2.7
0.071
0.086
0.096
0.091
0.024
3.2
3.6
3.8
4.0
35.0
0.036
0.054
0.061
0.068
0.024
6.8
6.3
7.0
5.3
31.7
0.15%Ca-CeO2
0.50%Ca-CeO2
1.25%Ca-CeO2
CaO
16
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Table 3. Conversion of 2-octanol over CeO2, CaO, and Ca-doped CeO2
Olefin distribution, %
Temp,
°C
Time,
min
Conversion,
%
Catalyst
1
t-2
5.5
5.9
5.2
6.5
14.8
c-2
4.0
CeO2
375
375
375
375
375
42
42
41
43
26.5
40.4
48.7
48.7
30.4
8.1
90.5
90.1
89.8
74.9
37.8
0.15%Ca-CeO2
0.50%Ca-CeO2
1.25%Ca-CeO2
CaO
4.0
5.0
18.6
47.4
17
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Figure 1. BJH pore size distributions of the calcined sample of CeO2, CaO, and Ca-doped CeO2
18
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Figure 2. X-ray diffraction profiles of CeO2, CaO, and Ca-doped CeO2 calcined in static air at
500°C (CaO was obtained by the calcination of CaCO3 at 950°C).
19
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Figure 3. SEM images of CeO2, CaO, and Ca-doped CeO2 calcined in static air at 500°C (CaO
was obtained by the calcination of CaCO3 at 950°C).
20
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10.1002/cctc.201601076
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Figure 4. H2-TPR profiles for CeO2, CaO, and Ca-doped CeO2.
21
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Figure 5. Conversion of 2-octanol over CeO2, CaO, and Ca-doped CeO2 catalysts. (Reaction
conditions: 375°C, 1 atm, no inert, feed rate = 0.6 ml/h).
22
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Figure 6. Effect on the selectivity for enes (octenes) as a function of time for the conversion of 2-
octanol over CeO2, CaO, and Ca-doped CeO2 catalysts. (Reaction conditions: 375°C, 1 atm, no
inert, feed rate = 0.6 ml/h).
23
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10.1002/cctc.201601076
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Figure 7. The selectivity for 1-octene as a function of time on-stream for the conversion of 2-
octanol over CeO2, CaO, and Ca-doped CeO2 catalysts. (Reaction conditions: 375°C, 1 atm, no
inert, feed rate = 0.6 ml/h).
24
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