Isopropanol decomposition on carbon based acid and basic catalysts

Article abstract of DOI:10.1016/j.cattod.2010.04.043

Chemical activation of biomass waste with different activating agents allows the preparation of activated carbons with a relatively highly porous development and different surface chemistry properties. Acidic and basic carbon based catalysts have been prepared by chemical activation of olive stone waste with H₃PO₄ and H₂SO₄ of acid character and Ca(OH)₂ and Ba(OH)₂ of basic character. The carbons have been tested as catalysts for the isopropanol decomposition reaction. The acidic carbons show higher steady state conversions than those corresponding to the basic carbons. The highest conversions were obtained using the carbon activated with phosphoric acid as catalyst. In the absence of oxygen acidic carbon based catalysts dehydrate isopropanol to propylene. In the case of the basic carbon catalysts, the carbon activated with Ba(OH)₂ mainly dehydrogenates isopropanol to acetone, with low production of propylene. The carbon activated with Ca(OH)₂ presents acid and basic surface sites and propylene and acetone are obtained on this catalyst. In the presence of oxygen, the acidic carbons show higher conversion values and part of the isopropanol suffers oxidative dehydrogenation yielding acetone as well as propylene, although at high isopropanol steady state conversion values only propylene is obtained.

Full text of DOI:10.1016/j.cattod.2010.04.043

Catalysis Today 158 (2010) 89–96
Contents lists available at ScienceDirect
Catalysis Today
journal homepage: www.elsevier.com/locate/cattod
Isopropanol decomposition on carbon based acid and basic catalysts
J. Bedia, J.M. Rosas, D. Vera, J. Rodríguez-Mirasol, T. Cordero∗
Chemical Engineering Department, School of Industrial Engineering, University of Málaga, Campus de Teatinos s/n, 29071 Málaga, Spain
a r t i c l e i n f o
a b s t r a c t
Keywords:
Isopropanol
Dehydration
Dehydrogenation
Carbon catalyst
Chemical activation of biomass waste with different activating agents allows the preparation of activated
carbons with a relatively highly porous development and different surface chemistry properties. Acidic
and basic carbon based catalysts have been prepared by chemical activation of olive stone waste with
H3PO4 and H2SO4 of acid character and Ca(OH)2 and Ba(OH)2 of basic character. The carbons have been
tested as catalysts for the isopropanol decomposition reaction. The acidic carbons show higher steady
state conversions than those corresponding to the basic carbons. The highest conversions were obtained
using the carbon activated with phosphoric acid as catalyst. In the absence of oxygen acidic carbon
based catalysts dehydrate isopropanol to propylene. In the case of the basic carbon catalysts, the carbon
activated with Ba(OH)2 mainly dehydrogenates isopropanol to acetone, with low production of propylene.
The carbon activated with Ca(OH)2 presents acid and basic surface sites and propylene and acetone are
obtained on this catalyst. In the presence of oxygen, the acidic carbons show higher conversion values
and part of the isopropanol suffers oxidative dehydrogenation yielding acetone as well as propylene,
although at high isopropanol steady state conversion values only propylene is obtained.
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
coproduct phenol from this process. Therefore, there is a needing
of alternative acetone production routes. In the isopropyl alcohol
Flash pyrolysis of biomass produces liquid oil (bio-oil) consti-
tuted mostly by oxygenated compounds, which are of great interest
as fuel [1,2]. Like the biomass precursor, this bio-oil contains almost
negligible amount of nitrogen, sulfur and metals. However, trans-
formation of bio-oil is necessary to reach a quality similar to that of
the conventional fuel. Studies have been conducted to improve the
quality of bio-oil as fuel through catalytic processes with inorganic
acid solids [3–5]. Gayubo et al. [4] studied the catalytic transfor-
mation of several model components of biomass pyrolysis oil, such
as phenols and alcohols (1-propanol, isopropanol, 1 and 2-butanol,
etc), over HZSM-5 zeolite obtaining mainly light olefins and aro-
matics.
Nowadays, nearly 90% of acetone is coproduced with phenol
by the cumene route. This technique is the preferred technology
because of its lower cost. The main process for manufacturing
cumene involves the reaction of propylene and benzene in the pres-
ence of phosphoric acid-based catalysts or, more recently, zeolite
catalysts. The cumene is oxidized in the liquid phase to cumene
hydroperoxide, which is then cleaved in the presence of sulfuric
acid to phenol and acetone. About 0.62 tons of acetone is pro-
duced per ton of phenol obtained. The production of acetone from
only cumene would require a balancing of the market with the
route, the alcohol is dehydrogenated to acetone over a metal, metal
oxide or salt catalyst. Acetone could be obtained from isopropanol
alcohol by either dehydrogenation or air oxidation.
Propylene is a key building block for the petrochemical industry
used for the production of polypropylene, acrylonitrile, propylene
oxide, cumene, oxo-alcohols and other intermediates. Propylene
demand has grown from 16.4 million tons in 1980 to 69.0 million
tons in 2006 and the demand is expected to increase faster than
supply up to 350 million tons in 2020 [6]. Nowadays propylene
is obtained from non-renewable sources mainly as by-product of
ethylene production in stream crackers and from refinery in FCC
streams. Therefore, the finding and developing of new processes for
propylene production from renewable sources is of great interest
from economical and environmental point of views.
Activated carbons are mainly used as adsorbents and catalyst
supports. However, the special characteristics of these materials
related to their porous structure and surface chemistry make them
suitable to be used also as catalysts per se [7]. Activated carbons
show some important advantages to be used as catalysts [8], such as
high specific surface area, high thermal and chemical stability and
the possibility to be obtained from many diverse materials includ-
ing different types of lignocellulosic waste [9–15]. Carbon materials
can be used as catalysts for acid/base reactions due to the presence
of surface oxygen groups of acidic and/or basic character [16,17].
Alcohol decomposition is also used as test reaction for the
evaluation of the acid–base properties of catalysts. Alcohol dehy-
∗
Corresponding author. Tel.: +34 952132038; fax: +34 952132038.
E-mail address: cordero@uma.es (T. Cordero).
0920-5861/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.cattod.2010.04.043

90
J. Bedia et al. / Catalysis Today 158 (2010) 89–96
Table 1
Notation and activation conditions (impregnation ratio and carbonization temper-
ature) for the different carbons obtained.
Nomenclature
N
apparent surface area (m2/g)
2
ABET
Carbon catalyst
Impregnation
ratio
Activating agent
Activation
AtN
2
external surface area (m2/g)
temperature (◦C)
Ea
apparent activation energy (kJ/mol)
PAC-550
SAC-600
SAC-900
CaAC-900
BaAC-700
1
1
1
3
3
H3PO4
H2SO4
H2SO4
Ca(OH)2
Ba(OH)2
550
600
900
900
700
FoIPA
FTIR
IPA
k
isopropanol molar flow rate (mol s−1
)
Fourier transform infrared spectroscopy
isopropanol
apparent rate constant (mol atm−1 g−1 s−1
)
ko
preexponential factor (mol atm−1 g−1 s−1
nitrogen relative pressure
)
P/Po
PoIPA
Py
when H3PO4, H2SO4, Ba(OH)2 and Ca(OH)2 were used as activat-
ing agents, respectively, followed by the activation temperature in
degrees Celsius.
isopropanol inlet partial pressure (atm)
pyridine
r
isopropanol reaction rate (mol IPA s−1 g−1
)
R
impregnation ratio (weight of activating agent rela-
tive to that of dry precursor)
2.2. Catalyst characterization
Sa
Selectivity to acetone
Sp
STP
T
Selectivity to propylene
standard temperature pressure conditions
temperature (K)
The porous structure of the carbons was characterized by N2
adsorption–desorption at −196 ◦C, carried out in a 2020 ASAP
model of Micromeritics. Samples were previously outgassed during
at least 8 h at 150 ◦C. From the N2 adsorption/desorption isotherm,
TPD
Vads
temperature-programmed desorption
N
nitrogen volume adsorbed (cm3 STP g−1
)
the apparent surface area (ABET) was determined applying the BET
2
VtN
micropore volume (cm3 g−1
catalyst weight (g)
)
equation [20], the micropore volume (VtN ) and the external surface
2
2
area (ANt ) were calculated using the t-method [21].
2
W
W/FoIPA isopropanol space-time (g s mol−1
)
The surface chemistry of the samples was analyzed by
temperature-programmed desorption (TPD), X-ray photoelectron
spectroscopy (XPS) and Fourier transform infrared spectroscopy
(FTIR). TPD profiles were obtained in a custom quartz tubular reac-
tor placed inside an electrical furnace. The samples were heated
from room temperature up to 900 ◦C at a heating rate of 10 ◦C/min
in a helium flow (200 cm3 STP/min). The amounts of CO and CO2
desorbed from the samples were monitored with non-dispersive
infrared (NDIR) gas analyzers (Siemens ULTRAMAT 22). X-ray
photoelectron spectroscopy (XPS) analyses of the samples were
obtained using a 5700C model Physical Electronics apparatus, with
MgK␣ radiation (1253.6 eV). For the analysis of the XPS peaks, the
C1s peak position was set at 284.5 eV and used as reference to posi-
tion the other peaks. Infrared (FTIR) spectra were obtained using a
Bruker Optics Tensor 27 FTIR spectrometer by adding 256 scans
in the 4000–400 cm−1 spectral range at 4 cm−1 resolution. Pressed
KBr pellets at a sample/KBr ratio of around 1:250 were used.
The type of surface acidity (Brönsted or Lewis) was studied by
FTIR of the carbons with pyridine (Py) chemisorbed at 100 ◦C. The
inlet partial pressure of the organic base was 0.02 atm and it was
established saturating He with pyridine in a saturator at controlled
temperature. After saturation of the carbon, desorption is carried
out at the adsorption temperature in helium flow.
X
XPS
isopropanol conversion
X-ray photoelectron spectroscopy
drogenation products (aldehydes and ketones) are preferentially
formed on basic catalysts, while dehydration products (olefins and
ethers) are favored when acidic sites are present [18]. It is generally
accepted that isopropanol decomposition over basic sites proceeds
through an elimination reaction yielding acetone. Over acid sites,
isopropanol dehydrates to propylene and to di-isopropyl ether [19].
In this study, home-made acid and basic carbons were studied as
catalysts for the selective catalytic decomposition of isopropanol
(as model compound of bio-oil). Activated carbons with surface
acidity were obtained by chemical activation of a biomassic mate-
rial with H3PO4 and H2SO4. Activated carbons with surface basicity
were obtained by chemical activation of a biomassic material with
Ca(OH)2 and Ba(OH)2. The effect of the presence of oxygen in the
isopropanol decomposition was also analyzed.
2. Experimental
2.1. Catalysts synthesis methods
The carbon catalysts were obtained from olive stone waste.
The raw olive stone waste shows a negligible porous struc-
ture. The olive stone was impregnated at room temperature
with the different activating agents, namely, H3PO4 (85 wt.% in
H2O, Aldrich), H2SO4 (95.0–98.0%, Sigma–Aldrich), Ca(OH)2 (≥95%,
Sigma–Aldrich) and Ba(OH)2 (∼95%, Aldrich), at different impreg-
nation ratios (R = weight of activating agent relative to that of dry
precursor). The impregnated samples were activated under contin-
uous N2 flow (150 cm3 STP/min), in a conventional tubular furnace
at different temperatures. These temperatures were reached at a
heating rate of 10 ◦C/min and maintained for 2 h. The activated
samples were cooled inside the furnace, maintaining the N2 flow
and then washed with distilled water at 60 ◦C. The resulting car-
bon catalysts were dried at 100 ◦C. Table 1 reports the notation
and activation conditions (impregnation ratio and carbonization
temperature) of the different carbons obtained. The nomenclature
used for the carbon based catalysts was PAC, SAC, BaAC and CaAC
2.3. Isopropanol dehydration
The activities of the catalysts were measured by the decompo-
sition of isopropanol (IPA) performed at atmospheric pressures, in
a quartz fixed bed microreactor (4 mm i.d.) placed inside a verti-
cal furnace with temperature controlled, using 100 mg of catalyst
(100–300 ␮m particle size) dispersed in quartz. Nitrogen or air was
saturated with isopropanol (Sigma–Aldrich, 99.5%, HPLC grade)
vapor by contact in a saturator at 10 ◦C resulting in a partial pres-
sure of 0.0185 atm. To avoid the condensation of isopropanol or any
reaction product, all the lines from the saturator to the chromato-
graph were heated above 120 ◦C. The gas reaction mixture feeds
the reactor at 100 cm3 STP/min, corresponding to a space-time of
W/FoIPA = 0.073 g s ␮mol−1. Reactant and products concentrations
were measured by gas chromatography (Perkin-Elmer Autosystem
GC with a 50 m HP-1 methyl silicone capillary column and flame
ionization detector).

J. Bedia et al. / Catalysis Today 158 (2010) 89–96
91
Fig. 1. N2 adsorption–desorption isotherms at −196 ◦C of the carbon catalysts
(adsorption: closed symbols; desorption: open symbols).
The reaction rate, r, was defined as the mol number of iso-
propanol transformed in one second per gram of catalyst. The
conversion was defined as the ratio of the amount of isopropanol
converted to the amount of isopropanol supplied to the reactor.
The selectivity (in mol%) was defined as the molar ratio of a spe-
cific hydrocarbon product to all the hydrocarbons products formed.
The carbon balance was reached with an error lower than 3%.
3. Results and discussion
Fig. 2. TPD spectra for different carbons: (a) CO evolution; (b) CO2 evolution.
Fig. 1 presents the N2 adsorption–desorption isotherms at
−196 ◦C of the different carbon catalysts. Carbons SAC-600, CaAC-
900 and BaAC-700 show type I isotherms characteristic of solids
with to a predominantly microporous structure. The isotherms of
these carbons have an almost negligible hysteresis cycle which
indicates the lack of a developed mesoporosity. The increase of
the activation temperature from 600 to 900 ◦C when using sulfuric
acid as activating agent results in a carbon which adsorbs much
more nitrogen as a consequence of a more developed porous struc-
ture. Carbon SAC-900 shows a modified type I isotherms with a
slight increase of the N2 adsorbed with the relative pressures and a
well developed H4 hysteresis cycle, associated to type I isotherms,
which closes at a relative pressure value of 0.4, indicative of capil-
lary condensation in mesopores. This isotherm is characteristic of
an essentially microporous solid with a slightly developed meso-
porosity. Finally, the carbon prepared by activation with H3PO4,
PAC-550, shows an isotherm with an open knee, which extends
up to increasingly higher relative pressures characteristic of wide
microporosity. It is noticeable the presence of the hysteresis cycle
up to high relative pressures. The isotherm is characteristic of a
well-developed microporous structure with a significant contribu-
tion of mesoporosity. During the activation process, phosphoric
acid is combined with organic species to form phosphate and
polyphosphate bridges that separate and expand the organic struc-
ture. After removal of the acid, the carbon matrix results in an
expanded state with an accessible pore structure [17,22].
surface areas between 68 m2/g for that obtained by activation with
Ba(OH)2 to 830 m2/g for that prepared by activation with H3PO4 at
a activation temperature of 550 ◦C. Most of the carbons, except for
PAC-550 and SAC-900, show low external surface areas, ANt , indica-
2
tive of their predominantly microporous structure. PAC-550 and
SAC-900 carbons display higher values of external surface area and
micropore volumes, VtN , as a consequence of their more developed
2
porous structure.
TPD analysis was used to characterize the different oxygen sur-
face groups of the activated carbons, whose nature and amount
depend on the starting material and the activation treatment [23].
Carbon–oxygen groups of acidic character (carboxylic, lactonic)
evolve as CO2 upon thermal desorption, whereas the non-acidic
(carbonyl, ether, and quinone) and phenol groups give rise to CO.
Anhydride surface groups evolve as both CO and CO2. Fig. 2a and
b depict the CO and CO2 profiles, respectively, obtained from TPD
experiments. All the carbons desorb most of the CO at high tem-
peratures (T > 700 ◦C). The carbon PAC-550 desorbs a high amount
of CO. It is reported that phosphoric acid activation generates a
significant amount of groups of high thermal stability, which des-
orb as CO in the TPD experiments at high temperatures [16,24]. A
lower amount of CO is desorbed at lower temperatures (T < 700 ◦C)
as a consequence of decomposition of anhydride, phenol and ether
groups. Carbons SAC-900 and CaAC-900 show the lowest amount
of CO desorbed as a consequence of the high carbonization temper-
ature used in their preparation.
Table 2 summarizes the structural parameters obtained from the
N2 adsorption–desorption isotherms. The carbons show apparent
Table 2
Porous structural parameters, obtained from N2 isotherms, and amount of CO and CO2 evolved from TPD analyses.
Carbon catalyst
N2 isotherm
TPD
N
ABET (m2/g)
ANt (m2/g)
VtN (cm3/g)
CO (␮mol/g)
CO2 (␮mol/g)
2
2
2
PAC-550
SAC-600
SAC-900
CaAC-900
BaAC-700
830
194
754
338
68
130
10
112
24
5
0.318
0.085
0.301
0.150
0.029
4070
3520
500
610
2180
270
220
20
110
410

92
J. Bedia et al. / Catalysis Today 158 (2010) 89–96
Fig. 3. FTIR spectra of the carbon catalysts.
Fig. 4. FTIR spectra resulted from the subtraction of the spectra of the original
catalysts from those of the catalysts after adsorption of Py.
CO2 profiles show lower desorbed amounts compared to those
for CO, indicating a lower presence of carboxyl, lactonic and anhy-
dride groups on the surface of the different carbon catalysts. For the
catalysts PAC-550 and SAC-600, it is noteworthy the evolution of
CO2 at around 800 ◦C that seems to be related to the evolution of CO
at this temperature [24]. Evolution of CO2 at this high temperature
may be due to secondary reactions between CO and oxygen surface
complexes [25].
surface groups. The presence of aliphatic structures is suggested
by the low intensity peaks at around 2950, 2910 and 2840 cm−1
.
These peaks are due to methyl C–H asymmetric stretch vibration
of aliphatic C–H and to the asymmetric/symmetric stretch vibration
of methylene C–H, respectively [27]. The spectra of most of the car-
The amount of CO and CO2 evolved during the TPD experiments
obtained by the integration of the areas under the TPD curves is
summarized in Table 2. As previously mentioned, the amount of CO
evolved is higher than that of CO2. The high amount of CO2 evolved
during the TPD of the Ba containing sample may probably be con-
nected with carbonates formation on this sample during drying
in air. Additionally, some oxygen surface groups of acidic charac-
ter (carboxylic and lactones) may be formed during the activation
process that would evolve as CO2 in the TPD. Decomposition of car-
bonate formed during the activation step may be responsible for
the CO2 evolution at about 700 ◦C. The literature shows examples
of decomposition of the alkaline metal carbonates at temperatures
below the melting point when heating carbonate–carbon mixtures
[26]. The highest amount of oxygen surface groups (CO + CO2) cor-
responds to the carbon activated with phosphoric acid PAC-550.
Fig. 3 shows the FTIR spectrum of the carbon catalysts. Infrared
spectroscopy (IR) provides information about the chemical struc-
ture of carbon catalysts. All spectra show an absorption band at
3600–3200 cm−1, with a maximum at about 3420 cm−1. This band
is characteristic of the stretching O–H vibration of carbon hydroxy
compounds, with the broadening of the band indicating an exten-
sive hydrogen bonding and could also be associated to the presence
of adsorbed water, although there is not a clear band at 1640 cm−1
to confirm this. This suggests that the analyzed carbons contain
hydroxyl groups from carboxyls, phenols or alcohols as previously
seen in the TPD analyses. The higher intensity of this band, observed
for PAC-550, CaAC-900 and BaAC-700, may result also from the
presence of OH corresponding to phosphate, Ca(OH)2 and Ba(OH)2
bons, but BaAC-700, show bands in the range of 1550–1570 cm−1
,
characteristic of the aromatic ring stretching mode and a wide band
between 1300 and 900 cm−1 with the maximum at 1160 cm−1
,
which is generally attributed to C–O stretching vibrations in acids,
alcohols, phenol, ethers, and esters [28,29], although in the case
of PAC-550 carbon it could also be associated to the O–C stretch-
ing vibrations in the P–O–C (aromatic) linkage [30–32]. In the
case of the carbons activated with sulfuric acid, the bands in the
1000–1200 cm−1 range are characteristic of the vibration of the S–O
bonds [33]. The broad bands observed at about 1620 and 1440 cm−1
in the IR spectra of CaAC-900 and BaAC-700 can be ascribed to the
presence of calcium and barium carbonate surface groups, respec-
tively. The peak at 875 cm−1 corroborates the presence of calcium
carbonate groups on the surface of the CaAC-900 carbon.
Chemisorption of basic molecules such as pyridine (Py) is often
used to probe the acidity of solids [34–37]. Pyridine interacts with
acidic sites because it has a lone electron pair at the nitrogen atom
available for donation to a Lewis acidic site and because it can accept
a proton from Brönsted sites. Fig. 4 shows the spectra resulted from
the subtraction of the spectra of the original catalysts from those of
the catalysts after adsorption of Py. Only the carbons obtained by
activation with acid precursor, H3PO4 and H2SO4, show peaks asso-
ciated to the vibration of adsorbed pyridine. Interaction of pyridine,
via the nitrogen lone-pair electrons, with aprotic (Lewis) and pro-
tonic (Brönsted) acid sites can be analyzed by following the ring
vibration modes 8a and 19b, respectively [38]. The interaction of
Py with Lewis type acid sites produces 8a vibration mode usually
observed at around 1624 cm−1 and 19b vibration mode at around
Table 3
Mass surface concentration of the carbon catalysts prior and after Py chemisorption at 100 ◦C obtained by XPS quantitative analysis.
C (%)
N (%)
O (%)
S (%)
P (%)
Ba (%)
Ca (%)
PAC-550
SAC-600
SAC-900
BaAC-700
CaAC-900
82.3
83.1
87.0
69.9
71.2
0.3
0.5
0.5
0.5
0.5
12.9
11.9
7.9
17.7
19.2
–
4.5
–
–
–
–
–
–
–
11.9
–
–
–
–
–
4.5
4.6
–
–
9.1
PAC-550 (Py)
SAC-600 (Py)
SAC-900 (Py)
BaAC-700 (Py)
CaAC-900 (Py)
85.1
84.7
87.9
70.2
83.1
0.8
0.8
0.9
0.8
0.9
10.0
10.5
7.0
17.8
11.5
–
4.1
–
–
–
–
–
–
–
11.2
–
–
–
–
–
3.8
4.1
–
–
4.5

J. Bedia et al. / Catalysis Today 158 (2010) 89–96
93
Fig. 6. Steady state conversion of isopropanol on the different carbon based catalysts
in the absence of oxygen (PoIPA = 0.0185 atm, W/FoIPA = 0.073 g s ␮mol−1).
Table 3 summarizes the mass surface concentrations of the carbon
catalysts prior and after pyridine chemisorption at 100 ◦C. The main
elements found on the surfaces of the carbons were carbon and oxy-
gen. Lower amount of phosphorus, sulfur, calcium and barium was
retained in the structure during the activation procedure, depend-
ing on the activating agent used in the preparation of the carbon,
H3PO4, H2SO4, Ca(OH)2 and Ba(OH)2, respectively. Nitrogen, usu-
ally present in the biomassic materials, was also detected, although
in a very low concentration. During the activation these elements
are retained into the structure of the activated carbons, either com-
bined with the organic structure or physically entrapped. In the
case of the activation with sulfuric acid, the increase of the activa-
tion temperature (from 600 up to 900 ◦C) results in a lower oxygen
atomic surface concentration (observed also in the TPD experi-
ments), due to the removal of the oxygen surface groups at higher
temperatures. The differences observed between the oxygen con-
centration in TPD and XPS analyses indicate a non-homogeneous
distribution of the oxygen on the carbon material surface, given that
XPS provides information only of the external surface, while TPD
analyses provide information of both external and internal surface.
Adsorption of Py on PAC-550 results in a slight increase of N and C
and in the reduction of O and P, probably due to Py adsorption on
the H of the surface phosphate groups, as it was indicated by the
FTIR study.
The values of Table 3 for BaAC-700 confirm the absence of
adsorption of Py on this basic catalyst. However, an increase of the
amount N and C and a significant decrease of Ca and O are observed
for CaAC-900 after Py adsorption. This result seems to indicate that
this catalyst also presents acid sites. Fig. 5 represents the C(1s) (a),
O(1s) (b) and Ca(2p) (c) XPS region spectra for CaAC-900 catalyst.
As in the case of the catalysts obtained by acid activation (PAC-550,
SAC-600 and SAC-900) the decrease of the signal intensity in the Ca
spectrum and that of the O(1s) at 532.0 eV, with an increase of the
signal intensity in the C(1s) spectrum suggest that Py is adsorbed
on Ca␦+–O site, i.e., calcium with positive electronic density, as a
consequence of the formation of substequiometric surface specie.
This specie, which may act as acid surface site, could be formed by
decomposition of part of the surface carbonates at the high car-
bonization temperature (900 ◦C) used in the preparation of this
carbon. The presence of acid sites on the surface of the CaAC-900
catalyst is supported by the production of propylene during the
decomposition of isopropanol on this catalyst, as it will be seen
later.
Fig. 5. C(1s) (a), O(1s) (b) and Ca(2p) (c) XPS region spectra for CaAC-900 catalyst
before and after Py adsorption.
1452 cm−1. Neither of them is observed in the spectra of SAC-600,
SAC-900, CaAC-900 and BaAC-700, suggesting negligible presence
of Lewis acid sites on the surface of these carbons. However, the
presence of Lewis acid sites seems to be possible on the surface of
PAC-550 carbon base on its FTIR spectrum. The pyridine interaction
with Brönsted acid sites is observed at 1587 cm−1 for 8a vibra-
tion mode and at 1437 cm−1 for 19b vibration mode. Both peaks
are clearly observed in the Py-adsorbed spectra of SAC-600 and
PAC-550 carbon, indicating that the acid sites of the carbon surface
are predominantly of Brönsted type. The vibration peaks are more
clearly observed in the carbon SAC-600 than in the carbon SAC-900,
suggesting that the increase in the activation temperature from 600
to 900 ◦C seems to decrease the surface acidity of the resulting car-
bon. The band at 1484 cm−1, observed in the PAC-550 and SAC-600
spectra, could be associated to 19a vibration of pyridine ions.
X-ray photoelectron spectroscopy (XPS) analyses were per-
formed to analyze the surface chemical composition of the carbons.
Fig. 6 represents the steady state conversion of isopropanol
on the different carbon based catalysts in the absence of oxygen
(PoIPA = 0.0185 atm, W/FoIPA = 0.073 g s ␮mol−1). As expected, iso-
propanol conversion increases with the reaction temperature. The
acidic carbons PAC-550, SAC-600 and SAC-900 show higher steady
state conversions than those corresponding to the basic carbons

94
J. Bedia et al. / Catalysis Today 158 (2010) 89–96
Fig. 8. Steady state conversion of isopropanol (X) and selectivity to acetone (Sa)
and propylene (Sp) on BaAC-700 carbon based catalysts in the absence of oxygen
(PoIPA = 0.0185 atm, W/FoIPA = 0.073 g s ␮mol−1).
Fig. 7. Steady state conversion of isopropanol (X) and selectivity to acetone (Sa)
and propylene (Sp) on CaAC-900 carbon based catalysts in the absence of oxygen
(PoIPA = 0.0185 atm, W/FoIPA = 0.073 g s ␮mol−1).
for a catalyst with a basic surface. In the case of CaAC-900 catalyst, a
selectivity to about 40% for acetone is observed at low reaction tem-
peratures and conversions. An increase of the reaction temperature
increases both the conversion and propylene selectivity. The forma-
tion of acetone, through the dehydrogenation of isopropanol, takes
place on the basic sites of these two catalysts. The relatively high
production of propylene on the CaAC-900 is due to the presence of
surface acid sites, as evidenced by the IR results.
The influence of the presence of oxygen in the inlet stream
(21 vol.%) has been analyzed. In the case of the basic carbon cat-
alysts, CaAC-900 and BaAC-700, these carbons begin to burn out
at a significant rate at temperatures of around 300 ◦C, before
isopropanol begins to react. Figs. 9 and 10 represent the evo-
lution of isopropanol steady state conversions and selectivities
as a function of the reaction temperature in air flow (21%
O2) using PAC-550 and SAC-900 as catalysts (PoIPA = 0.0185 atm,
BaAC-700 and CaAC-900. The increase of the temperature, from
600 to 900 ◦C, during the activation of the carbon with sulfuric
acid shows very little influence in the isopropanol steady state con-
version. The highest conversions were obtained using PAC-550 as
catalyst. The activation of lignocellulosic residues with phosphoric
acid has proven to yield acid carbon catalysts in a single step with
a high activity in the alcohol decomposition [19,39,40]. The –OH
groups of phosphates and polyphosphate esters, formed during the
activation step, can act as Brönsted acid sites (in agreement with
the Py-FTIR analysis), giving up protons (H+) during the isopropanol
dehydration reaction [19].
The differences in the surface chemistry of the carbon catalysts
obtained with acidic or basic activating agents are clearly observed
analyzing the selectivity of the isopropanol decomposition in a
helium flow. In a previous study [19], we have shown that the high
activity of different acid carbon catalyst in the isopropanol decom-
position is due to their high acidity, as revealed the ammonia TPD,
and not by their porous structure development. Table 4 presents
the selectivity to propylene (Sp) and acetone (Sa) for the different
catalysts at a isopropanol conversion of 0.6, as well as the reac-
tion temperature at which this conversion is reached. In the case
of the acidic carbons, PAC-550, SAC-600 and SAC-900, isopropanol
decomposition reaction yields only propylene and water as reac-
tion products (Sp = 100%). This is a consequence of the acidity of the
surface of these carbons, since it is well known that isopropanol
dehydrates to propylene over solid acid catalysts. On the other
hand, Figs. 7 and 8 represent the evolution of isopropanol con-
versions and selectivities at the steady state as a function of the
reaction temperature in a helium flow using CaAC-900 and BaAC-
700 as catalysts (PoIPA = 0.0185 atm, W/FoIPA = 0.073 g s ␮mol−1). In
the case of these carbons, besides to propylene as dehydration
product, acetone is also obtained as isopropanol dehydrogenation
product. For BaAC-700 catalyst the selectivity to acetone is always
higher than 80% for the steady state conversion studied, as expected
Fig. 9. Steady state conversion of isopropanol (X) and selectivity to acetone (Sa)
and propylene (Sp) on PAC-550 carbon based catalysts in the presence of oxygen
(PoIPA = 0.0185 atm, W/FoIPA = 0.073 g s ␮mol−1).
Table 4
Selectivity to propylene (Sp) and acetone (Sa) and reaction temperature for the different catalysts at a isopropanol conversion of 0.6.
Sample
Gas
Sp (%)
Sa (%)
TX=0.6 (◦C)
PAC-550
SAC-600
SAC-900
BaAC-700
CaAC-900
He
He
He
He
He
100
100
100
13
0
0
0
87
27
300
365
354
505
556
73
PAC-550
SAC-900
BaAC-700
CaAC-900
Air
Air
Air
Air
92
90
–
8
10
–
255
258
Burn out
Burn out
–
–

J. Bedia et al. / Catalysis Today 158 (2010) 89–96
95
Fig. 10. Steady state conversion of isopropanol (X) and selectivity to acetone (Sa)
and propylene (Sp) on SAC-900 carbon based catalysts in the presence of oxygen
Fig. 11. Arrhenius plots for isopropanol decomposition using air and helium as
reaction gas.
(PoIPA = 0.0185 atm, W/FoIPA = 0.073 g s ␮mol−1).
W/FoIPA = 0.073 g s ␮mol−1). The presence of oxygen produces a
higher reaction rate and a change in the product distribution for
the acid catalysts PAC-550 and SAC-900 (see Figs. 9 and 10 and
Table 4). Furthermore, in the presence of oxygen, acid carbon cata-
lysts produce acetone by oxidative dehydrogenation of isopropanol
and propylene by dehydration of the alcohol.
These results are in agreement with the previously reported by
Grunewald and Drago [41] who studied the conversion reactions
of ethanol catalyzed by carbon. In the absence of oxygen, ethanol
transformation was catalyzed at 230 ◦C mainly to ethylene. How-
ever, in the presence of oxygen, acetaldehyde and ethyl acetate
were the major products. These authors indicated that the carbon
surface active sites were reduced by ethanol and regenerated by
the oxygen. In a similar sense, Carrasco-Marin et al. [42] stated
that when using surface-treated activated carbons as catalysts for
the decomposition of ethanol, the presence of air in the reactant
mixture cleaned some of carbon surface sites, increasing the dehy-
drogenation activity and decreasing the dehydration one.
decomposition reaction. The literature shows a broad spectrum
of activation energy values for this reaction, ranging from 12 to
133 kJ/mol [18,43,44]. This large variation in the activation energy
values could be due to the different type of interaction between
isopropanol molecules and the catalyst surface active sites. Also dif-
fusional limitations due to different experimental conditions may
reduce the value of the apparent activation energy.
4. Conclusions
Chemical activation of biomass waste with different activating
agents allows the preparation of activated carbons with a relatively
highly porous development and different surface chemistry prop-
erties. Acidic and basic carbon based catalysts have been prepared
by chemical activation of olive stone waste with H3PO4 and H2SO4
of acid character and Ca(OH)2 and Ba(OH)2 of basic character. In the
absence of oxygen acidic carbon catalysts dehydrate isopropanol to
propylene with 100% of selectivity. In the case of the basic carbon
catalysts, BaAC-700 mainly dehydrogenate isopropanol to acetone,
with low production of propylene. CaAC-900 carbon presents acid
and basic surface sites and propylene and acetone are obtained on
this catalyst. The presence of oxygen produces a higher reaction
rate and a change in the product distribution for the acid catalysts
PAC-550 and SAC-900. Furthermore, in the presence of oxygen, acid
carbon catalysts produce acetone by oxidative dehydrogenation of
isopropanol and propylene by dehydration of the alcohol.
It can be assumed that isopropanol decomposition reaction
follows a global first-order kinetics described by the following
equation in the absence of diffusional effects:
ꢀ
ꢁ
1
W
ln
= k · PoIPA
·
1 − X
FoIPA
where k is the apparent rate constant, W is the catalyst weight,
FoIPA is the reactant molar flow rate, PoIPA is the reactant partial
pressure and X is the conversion. The activation energy is derived
from the Arrhenius equation. Table 5 summarizes the values of the
kinetic parameters (ko is the preexponential factor and Ea is the
activation energy) for all the catalysts, obtained from the Arrhe-
nius plots represented in Fig. 11. Values from 63 to 88 kJ/mol have
been obtained, which are in the same range than those previously
obtained for carbon based acid catalysts prepared from biomass by
phosphoric acid activation for the dehydration of isopropanol [19].
It seems that the nature and amount of acid/basic sites affect the
catalytic activity and the product distribution for the isopropanol
Acknowledgements
We gratefully acknowledge to the Spanish DGICYT, Projects
CTQ2006-11322 and CTQ2009-14262.
References
[1] C. Branca, P. Giudicianni, C. Di Blasi, Ind. Eng. Chem. Res. 43 (2003) 3190.
[2] A.E. Pütün, A. Özcan, H.F. Gerc¸ el, E. Pütün, Fuel 8 (2001) 1371.
[3] J.D. Adjaye, S.P.R. Katikaneni, N.N. Bakhshi, Fuel Process. Technol. 48 (1996)
115.
[4] A.G. Gayubo, A.T. Aguayo, A. Atutxa, R. Aguado, J. Bilbao, Ind. Eng. Chem. Res.
43 (2004) 2610.
[5] A.G. Gayubo, A.T. Aguayo, A. Atutxa, R. Aguado, M. Olazar, J. Bilbao, Ind. Eng.
Chem. Res. 43 (2004) 2619.
[6] H. Koempel, W. Liebner, Stud. Surf. Sci. Catal. 167 (2007) 261–267.
[7] L.R. Radovic, F. Rodríguez-Reinoso, in: P.A. Thrower(Ed.), Chemistry and Physics
of Carbon, vol. 25, Marcel Dekker, New York, 1997, pp. 243–358.
[8] R.W. Coughlin, Ind. Eng. Chem. Prod. Res. Dev. 8 (1964) 23.
[9] F. Rodríguez-Reinoso, M. Molina-Sabio, Carbon 30 (1992) 1111.
[10] O. Ioannidou, A. Zabaniotou, Renewable Sustainable Energy Rev. 11 (2007)
1966.
Table 5
Apparent kinetic parameters for isopropanol conversion.
Sample
Gas
Ea (kJ/mol)
ln ko
PAC-550
SAC-600
SAC-900
CaAC-900
BaAC-700
PAC-550
SAC-900
He
He
He
He
He
Air
Air
75
77
70
70
88
86
63
19.6
20.3
16.9
13.8
15.0
23.8
18.0
[11] N. Tancredi, T. Cordero, J. Rodríguez-Mirasol, J.J. Rodríguez, Fuel 75 (1996) 1701.
[12] J. Rodríguez-Mirasol, T. Cordero, J.J. Rodríguez, Carbon 31 (1993) 87.

96
J. Bedia et al. / Catalysis Today 158 (2010) 89–96
[13] F. Marquez-Montesinos, T. Cordero, J. Rodríguez-Mirasol, J.J. Rodríguez, Fuel 81
(2002) 423.
[29] P. Vinke, M. van der Eijk, M. Verbree, A.F. Voskamp, H. van Bekkum, Carbon 32
(1994) 675.
[14] J.M. Rosas, J. Bedia, J. Rodríguez-Mirasol, T. Cordero, Fuel 88 (2009) 19.
[15] J.M. Rosas, J. Bedia, J. Rodríguez-Mirasol, T. Cordero, Ind. Eng. Chem. Res. 47
(2008) 1288.
[16] C.A. Leon y Leon, L.R. Radovic, in: P.A. Thrower (Ed.), Chemistry and Physics of
Carbon, vol. 25, Marcel Dekker, New York, 1992, pp. 213–310.
[17] G.S. Szyman´ ski, G. Rychlicki, Carbon 31 (1993) 247.
[18] J.M. Campelo, A. Garcia, J.F. Herencia, D. Luna, J.M. Marinas, A.A. Romero, J. Catal.
151 (1995) 307.
[30] L.J. Bellamy, The Infrared Spectra of Complex Molecules, Wiley, New York,
1954.
[31] D.E.C. Corbridge, J. Appl. Chem. 6 (1956) 456.
[32] G. Socrates, Infrared Characteristic Group Frequencies, Wiley, New York,
1994.
[33] M. Waqif, J. Bachelier, O. Saur, J.-C. Lavalley, J. Mol. Catal. 72 (1992) 127.
[34] F.M. Bautista, J.M. Campelo, A. Garcia, D. Luna, J.M. Marinas, A.A. Romero, M.R.
Urbano, J. Catal. 172 (1997) 103.
[19] J. Bedia, J.M. Rosas, J. Márquez, J. Rodríguez-Mirasol, T. Cordero, Carbon 47
(2009) 286.
[35] H.A. Benesi, J. Catal. 28 (1973) 176.
[36] H. Knözinger, H. Krietenbrink, P. Ratnasamy, J. Catal. 48 (1977) 436.
[37] A. Corma, C. Rodellas, V. Fornes, J. Catal. 88 (1984) 374.
[38] G. Turnes Palomino, J.J. Cuart Pascual, M. Rodríguez Delgado, J. Bernardo Parra,
C. Otero Areán, Mater. Chem. Phys. 85 (2004) 145.
[39] J. Bedia, R. Ruiz-Rosas, J. Rodríguez-Mirasol, T. Cordero, AIChE J. 271 (2010)
33.
[20] S. Brunauer, P.H. Emmett, E. Teller, J. Am. Chem. Soc. 60 (1938) 309.
[21] B.C. Lippens, J.H. de Boer, J. Catal. 4 (1965) 319.
[22] M. Jagtoyen, F. Derbyshire, Carbon 36 (1998) 1085.
[23] R.C. Bansal, J.B. Donnet, F. Stoeckli, Active Carbon, Marcel Dekker, New York,
1988 (Chapter 2).
[24] X. Wu, L.R. Radovic, Carbon 44 (2006) 141.
[25] P.J. Hall, J.M. Calo, Energy Fuels 3 (1989) 370.
[40] J. Bedia, R. Ruiz-Rosas, J. Rodríguez-Mirasol, T. Cordero, J. Catal. 271 (2010) 33.
[41] G.C. Grunewald, R.S. Drago, J. Am. Chem. Soc. 113 (1991) 1636.
[42] F. Carrasco-Marín, A. Mueden, C. Moreno-Castilla, J. Phys. Chem. B 102 (1998)
9239.
[43] W. Turek, J. Haber, A. Krowiak, Appl. Surf. Sci. 252 (2005) 823.
[44] P. Trens, V. Stathopoulos, M.J. Hudson, P. Pomonis, Appl. Catal. A: Gen. 263
(2004) 103.
[26] F. Kapteijn, G. Abbel, J.A. Moulijn, Fuel 63 (1984) 1036.
[27] A.M. Puziy, O.I. Poddubnaya, A. Martínez-Alonso, F. Suárez-García, J.M.D.
Tascón, Carbon 43 (2005) 2857.
[28] J. Zawadzki, in: P.A. Thrower (Ed.), Infrared Spectroscopy in Surface Chemistry
of Carbons, Marcel Dekker, New York, 1989, pp. 147–386.