selective catalytic reduction of no by nh3 over copper-hydroxyapatite catalysts: effect of the...
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Selective catalytic reduction of NO by NH3 overcopper-hydroxyapatite catalysts: effect of the increaseof the specific surface area of the support
Jihene Jemal • Carolina Petitto • Gerard Delahay •
Zouheir Ksibi • Hassib Tounsi
Received: 19 May 2014 / Accepted: 15 July 2014
� Akademiai Kiado, Budapest, Hungary 2014
Abstract The influence of the increase of the specific surface area of the support
Ca-HAp on the dispersion of copper species and their activity in the NO-SCR by
NH3 has been studied. The copper ion exchange does not alter the Ca-HAp structure
whatever the copper concentration. The increase of the specific surface area of the
support changed the dispersion and the reducibility of copper species. The high NO
conversion in the whole temperature range for the catalyst with the lowest specific
surface area (35 m2/g) was related to the highly dispersed CuO particles that are
easily reduced. Nevertheless, the increase of the specific surface area of the support
(76 m2/g), induces an increase of the size of CuO particles that become less active
in NO-SCR by NH3. The addition of 2.5 % of H2O to the reaction gas feed strongly
affects the NO conversion in the whole temperature range. This deactivation can be
related to the change of the nature of copper species rather than to the destruction of
the Ca-HAp structure.
J. Jemal � Z. Ksibi
Laboratoire de Chimie de Materiaux et Catalyse, Faculte des Sciences de Tunis, Universite Elmanar,
Tunis, Tunisie
C. Petitto � G. Delahay
Institut Charles Gerhardt, UMR 5253 CNRS/UM2/ENSCM/UM1; Equipe ‘‘Materiaux Avances pour
la Catalyse et la Sante’’ Ecole Nationale Superieure de Chimie de Montpellier, 8 rue de l’Ecole
Normale, 34296 Montpellier Cedex, France
H. Tounsi
Laboratoire de Chimie Industrielle, Ecole Nationale d’Ingenieurs de Sfax, Universite de Sfax,
B. P N� 1173, 3038 Sfax, Tunisie
Present Address:
H. Tounsi (&)
Departement de Chimie, Faculte des Sciences de Sfax, Universite de Sfax, B. P N� 1171, 3000 Sfax,
Tunisie
e-mail: hassibtounsi@yahoo.fr
123
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DOI 10.1007/s11144-014-0762-7
Keywords NO-SCR � NH3 � Surface properties � Ethanol � Hydroxyapatite
Introduction
The burning of fossil fuels in stationary and mobile sources emits nitrogen oxides
(NOx), which cause serious environmental problems such as photochemical smog,
acid rains, ozone depletion and greenhouse effect [1, 2]. With more and more
stringent regulations such as stage VI Euro, concerning NOx emissions [3], the
development of an active and stable catalyst for the removal of NOx emitted by
diesel engines is still a very challenging problem. Unfortunately, the traditional
three-way catalysts are effective for gasoline-powered engines, but cannot be used
for diesel vehicles because of the oxygen-rich atmosphere where NOx reduction
cannot be achieved easily [1, 2]. The selective catalytic reduction (SCR) of NOx by
NH3 in the presence of oxygen is one of the most effective methods of reducing
NOx levels in gaseous emissions [4–6]. The conventional V2O5-WO3/TiO2 catalysts
have been widely accepted as an industrial catalyst and are efficient within a narrow
temperature window (300–400 �C) [2, 7]. However, there are some drawbacks in
terms of toxicity of vanadium, catalyst deterioration, NH3-slip and ammonia sulfate
formation. Recent studies have shown small-pore zeolites such as Cu-SSZ-13
(CHA) and Cu-SSZ-16 (AFX) to be efficient NH3-SCR catalysts with higher
activity and selectivity at low temperatures and improved hydrothermal stability
over existing Cu-zeolites [8, 9].
We reported previously [10–12], for the first time, the excellent catalytic
properties of copper loaded hydroxyapatite (Cu-HAp) catalysts in the selective
catalytic reduction of NO by NH3 (NO-SCR) under oxidizing atmosphere despite
the low specific surface area (SBET) of the support. Thus, this work was devoted to
study the effect of the increase of the specific surface area of the support Ca-HAp on
the dispersion of copper species and the catalytic activity of Cu(x)-HAp catalysts in
the NO-SCR by NH3. Therefore, two series of Cu(x)-HAp catalysts have been
prepared with supports issued from different preparations. The first one with the
highest specific surface area (SBET = 76 m2/g) was prepared in ethanol–water
mixture and the second one with SBET = 35 m2/g was prepared in aqueous medium.
The prepared catalysts were tested in the selective catalytic reduction of NOx by
NH3 (NH3-SCR-NO) under oxidizing atmosphere and characterized with XRD,
UV–vis spectroscopy, N2 sorption and H2-TPR techniques.
Experimental
The mesoporous hydroxyapatite Ca-HAp was synthesized in ethanol–water medium
following a modified chemical wet method reported elsewhere [13]. 7.48 g of
Ca(OH)2 was first dissolved in a 100 mL of an ethanol–water mixture (50:50 %,
v/v) and stirred for 3 h at room temperature (RT). A quantity of 6.7 g
NH4H2PO4 was dissolved in 100 mL of water and then added to the Ca(OH)2
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solution over a period of 24 h. The amount of reagents in the solution was
calculated to obtain a Ca/P molar ratio equals to a 1.67 value, corresponding to a
stoichiometric hydroxyapatite Ca10(PO4)6(OH)2. The pH of the slurry was measured
during the precipitation reaction, reaching a final value of ca. pH 11. The
precipitated crystals were aged for 24 h, filtered and dried at 100 �C overnight and
finally calcined at 500 �C in air for 2 h. The obtained support was called Ca-HApE,
with E referring to ethanol.
Copper-hydroxyapatite catalysts were obtained by varying the concentration of
copper nitrate in the exchange solution: 5 9 10-3, 0.01, 0.025, 0.10 and 0.15 M
with an exchange time of 15 min. The catalysts were prepared at RT by introducing
1.5 g of Ca-HAp into 50 cm3 of copper nitrate solution under magnetic stirring. The
solids recovered after filtration were washed with water, dried at 70 �C for 7 h and
finally calcined at 500 �C in air for 2 h. The obtained catalysts were called Cu(x)-
HApE, with x the copper amount in wt%.
The hydrothermal treatment of catalysts was carried out in quartz fixed-bed
microreactor. 1 g of catalyst was placed in the reactor and heated to the desired
temperature in flowing air. Then water was injected by circulating the airflow
through a bubbler containing deionized water at a specified temperature during
12 h. All gas lines were heated to prevent water condensation. Two different
hydrothermal procedures were used: (i) ht500: temperature: 500 �C, water vapor
pressure: 23,756 torr (% 3 %) (resulting solid labeled Cu(2.26)ht500 W) and (ii)
ht750: temperature: 750 �C, water vapor pressure: 23,756 torr (% 3 %) (resulting
solid labeled Cu(2.26)ht750W).
Elemental analyses were performed by ‘‘Service Central d’Anlayse’’ of the
‘‘Centre National de la Recherche Scientifique; CNRS’’ in Vernaison FRANCE
(www.sca.cnrs.fr). The textural properties of the samples were determined by
adsorption and desorption of N2 at -196 �C, using Micromeritics ASAP 2020.
The BET method was used to determine the specific area whereas the pore size
and volume were estimated using the Barret-Joyner-Halenda (BJH) approximation.
The crystallinity of the catalysts was established by a Philips Powder X-ray
diffractometer DATA-MP SIEMENS D 501 using Cu Ka (k = 0.15418 nm)
incident radiation equipped with a Si detector.
The nature of the Cu species was determined by UV–visible spectroscopy.
Diffuse reflectance spectra were recorded in the UV–vis region (200–900 nm) with
a Jasco V-570 spectrometer equipped with an integrating sphere for solid samples
and using BaSO4 as reference.
The redox properties of the catalysts were studied by the temperature-
programmed reduction method (H2-TPR). The experiments were carried out with
a Micromeritics AutoChem II Chemisorption Analyser using H2/Ar (3/97, v/v) gas
at a total flow-rate of 30 cm3 min-1 and by heating the samples from room
temperature to 500 �C (10 �C min-1). In each case, 0.051 g of the catalyst was
previously activated at 550 �C for 30 min under air, and then cooled to room
temperature under the same gas. The TPR with H2/Ar (3/97, v/v) was then started
and the thermal conductivity detector monitored H2 consumption continuously.
The selective catalytic reduction of NO with NH3 was studied in a catalytic
microflow reactor operating at atmospheric pressure. An aliquot of the catalyst
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(0.022 g) was activated in situ at 550 �C for 1 h under a flow of O2/He (20/80, v/v)
and then cooled to room temperature. A feed mixture of 400 ppm NO, 400 ppm
NH3 and 8 % O2 in He was then charged to the catalyst at a flow rate of 100 cm3
min-1. The influence of H2O on the course of the NH3-SCR reaction was studied by
the addition of 2.5 % H2O to the feed. The SCR was carried out on programmed
temperature from 100 to 500 �C with the heating rate 6 �C. min-1. The reactants
and products were analyzed by a quadruple mass spectrometer (Pfeiffer Omnistar)
equipped with Channeltron and Faraday detectors (0–200 amu) following these
characteristic masses: NO (30), N2 (14, 28), N2O (28, 30, 44), NH3 (17, 18), O2 (16,
32) and H2O (17, 18).
Results and discussion
The chemical analyses and the textural properties of the studied catalysts and some
selected catalysts from Ref. [11] are reported in Table 1. The chemical analysis of
the Ca-HApE host structure shows a calcium deficit with a Ca/P close to 1.61
(Ca.wt% = 36.60 and P.wt% = 17.57), whereas the support prepared in aqueous
medium Ca-HApW has a Ca/P close to 1.55 (Ca.wt% = 38.40 and P.wt% = 19.16)
[11]. From Table 1, it is clearly shown that with the increase of the SBET, there is an
increase of the exchangeable sites on Ca-HAp surface and consequently, the
increase of the retained quantity of copper cations. Indeed, by using an initial copper
solution of 0.10 M, the sorbed copper amount for the catalyst prepared from Ca-
HApW was 1.12 wt% s, whereas it was 3.12 wt% from Ca-HApE with SBET of
76 m2/g. On the other hand, the amounts of sorbed copper cations increased with the
increase of initial solution concentrations.
Fig. 1 depicts the N2 adsorption–desorption isotherms of Ca-HApE and Cu(3.97)-
HApE samples. The isotherms were typical type IV with H1 hysteresis loop
according to IUPAC classification. The sharpness of the isotherms and the presence
Table 1 Chemical analysis of copper, SBET, pore diameter and pore volume of the prepared catalysts in
ethanol–water mixture and some selected catalysts from ref. [11] prepared in aqueous medium
Catalysts [Cu2?] (M) Cuexp wt% Exchange time
(min)
SBET
(m2/g)
BJH
(nm)
Vl(cm3/g)
Ca-HApw – 35 18 0.40
Cu(0.33)-HApW 0.025 0.33 15 27 25 0.11
Cu(1.12)-HApW 0.10 1.12 15 34 17 0.10
Cu(2.26)-HApW 0.15 2.26 60 33 22 –
Ca-HApE – – – 76 35 0.31
Cu(0.89)HApE 5 9 10-3 0.89 15 73 37 0.36
Cu(2.01) HApE 0.01 2.01 15 68 39 0.36
Cu(2.27) HApE 0.025 2.27 15 80 37 0.40
Cu(3.12) HApE 0.10 3.12 15 65 36 0.36
Cu(3.97) HApE 0.15 3.97 15 61 38 0.33
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of hysteresis loop at p/p0 [ 0.87 suggest that the tested catalyst is mostly
mesoporous [11]. In Table 1, the BET surface area (SBET) and micropore volume
(Vl) of the prepared catalysts are reported. The micropore volume of the support is
in agreement with those reported in the literature (0.30–0.40 cm3 g-1) [12].
Compared to the classic method [10, 11], the use of ethanol–water mixture
enhanced the SBET of support from 35 m2/g for the Ca-HApW prepared in aqueous
medium to 76 m2/g. This is in agreement with the study of El Hammari et al. [13]
suggesting that the entrapped ethanol plays a major role in the aggregation of the
apatite particles. This is due to both smaller nanocrystallite size and more compact
crystallite aggregation.
In Fig. 2, we report the X-ray diffraction patterns powder of Ca-HApE and the
prepared catalysts Cu(x)-HApE. The observed positions of diffraction lines are in
0,0 0,2 0,4 0,6 0,8 1,00
100
200
300
400
500 Cu(3.97)-HApE Ca-HApE
Vol
(N
2)ad
s (cm
3)
p/p0
Fig. 1 N2 adsorption–desorption isotherms of the carrier Ca-HApE and Cu(3.97)-HApE catalyst
20 25 30 35 40 45 50
Ca-HApE
Cu(0.89)-HAp E
Cu(2.01)-HAp E
Cu(2.27)-HAp E
Cu(3.12)-HAp E
Cu(3.97)-HAp E
Inte
nsit
y (
a . u
)
2 teta (°)
Fig. 2 XRD patterns of the carrier Ca-HApE and Cu(x)-HApE catalysts
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full agreement with the corresponding values reported for hexagonal Ca-HAp (PDF
Ref. 09-0432) [14]. The sharp diffraction peaks of the Ca-HApE compared to the
Cu(x)-HApE catalysts suggested that aqueous copper exchange induced a slight
decrease of the crystallinity of the carrier. No detectable CuO crystallites superior to
4 nm at 35,7� and 38.6� 2h were observed in all catalysts. Therefore CuO
crystallites are either amorphous and/or well dispersed in the external surface or in
the channels of CaHApE.
Fig. 3 shows the diffuse reflectance UV–visible spectra of the support Ca-HApE,
Cu(x)-HApE and Cu(2.26)HApW catalysts. The support showed a band at 205 nm
assigned to O2- ? Ca2? charge transfer [15]. For Cu(x)HApE catalysts, new bands
appeared, which can be related to copper species. For all catalysts, there is an
absorbance band centered at about 255 nm assigned to low energy charge transfer
O2- ? Cu2? of Cu2? ions in tetrahedral coordination [16, 17]. For Cu(2.26)HApW
catalyst, there is a broad peak in the 550–900 nm range which correspond to d–d
transitions of Cu2? in tetrahedral coordination surrounded by oxygen in CuO [16,
17]. The increase of the SBET of the support changed the dispersion and the nature of
copper species. Indeed, for all Cu(x)-HApE catalysts, there is an the increase of the
intensity of the band between 300–700 nm which is absent in sample Cu(2.26)HapW
[11]. The spectra showed many peaks at 324, 332, 342, 350 and 370 nm, which can
be assigned to O2- ? Cu2? charge transfer transition of polynuclear copper–
oxygen deposited on the outer surface of the support. On the other hand there is an
absorption edge between 400–800 nm due to the energy gap of large particles of
CuO.
The H2-TPR profiles of pure Ca-HApE, Cu(x)-HApE and Cu(2.26)HApW
catalysts are reported in Fig. 4. As seen, the reduction of the support do not
interfered with the reduction of copper species at temperatures below 500 �C. For
200 300 400 500 600 700 800 900
Cu(2.26)-HApW
Ca-HApE
255
Cu(3.12)-HApE
Cu(2.27)-HApE
Cu(2.01)-HApE
Cu(0.89)-HApE
Abs
orba
nce
( a
. u
)
Wavelength (nm)
Fig. 3 UV-Vis spectra of the carrier Ca-HApE, Cu(x)-HApE catalysts and Cu(2.26)HApW selected fromRef. [11]
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Cu(x)-HApE catalysts, the reduction profiles can be divided into low temperature
(LT) region (T \ 300 �C) and HT region (300 \ T (�C) \ 550). For
Cu(0.89)HApE, the LT reduction profiles contain mainly one peak at 248 �C,
which can be attributed to the reduction particles of CuO to Cu0 and eventually
small quantity of Cu2? to Cu?. The presence of isolated Cu2? cations in this catalyst
cannot be excluded. The broad HT peaks at around 380 �C, which is ascribed to the
reduction of Cu? to Cu0; formed from the reduction of Cu2? at LT; confirm the
presence of isolated Cu2?. The increase of copper amount results in the appearance
of a new peaks at temperature below 250 �C, which can be attributed to the
reduction of smaller CuO particles deposited on the surface of the carrier. The
intensity of these peaks increased with the increase of copper content. For example,
Cu(3.97)-HApE catalyst contains three peaks at 198, 217 and 248 �C. The first one
can be related to the reduction of fine particles of CuO to Cu0.
The reduction profile of Cu(2.26)-HApW catalyst contains two overlapping
reductions peaks at 200 and 213 �C. The low temperature at which the reduction
rate is maximum (Tm) indicates the presence of CuO species that are highly
dispersed on Ca-HApE surface. On the other hand, the increase of the SBET of the
support changed the dispersion and the reducibility of copper species. Indeed, the
H2-TPR profile of Cu(2.27)-HApE contains besides the peak at 213 �C, two other
ones at 230 �C and 270 �C, which are related to the reduction of bigger sized CuO
particles.
Fig. 5 shows the NO conversion profiles of Ca-HApE and Cu(x)-HApE catalysts.
The reduction of NO in the presence of NH3 and an excess of O2, the standard
reaction, occurred according to the following Eq. 1:
4NO þ 4NH3 þ O2 ! 4N2 þ 6H2O ð1Þ
100 150 200 250 300 350 400 450 500 550 600
Cu(2.26)-HApW
H2 r
educ
tion
rat
e (
a . u
)
Ca-HApE
Cu(3.97)-HApE
Cu(3.12)-HApE
Cu(2.27)-HApE
Cu(2.01)-HApE
Cu(0.89)-HApE
Temperature (°C)
Fig. 4 H2-TPR profiles of the carrier Ca-HApE,Cu(x)-HApE catalysts and Cu(2.26)HApW selected fromRef. [11]. Conditions: H2/Ar (3/97 vol./vol.), flow rate = 30 cm3 min-1, ramp: 10 �C min-1, catalystmass = 0.051 g
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The incorporation of copper in Ca-HApE produces marked changes in the
catalytic behavior. For all Cu(x)-HApE catalysts, NO conversion increases with
temperature to reach a maximum and then decreases at high temperatures. As can be
seen for Cu(3.97)-HApE catalyst, which exhibited excellent catalytic properties over
a broad temperature range, the NO conversion is about 31 % at around 175 �C,
reached 80 % at 325 �C and then decreased progressively to 0 % at 475 �C.
Moreover, the tested Cu(x)-HApE catalysts exhibited NH3 conversion very close to
NO conversion until its maximum then continues to grow up above it. This behavior
reveals a competition between reduction of NO by NH3 and NH3 oxidation into NO
or/and N2O as shown in reactions 2, 3 and 4.
4NH3 þ 3O2 ! 2N2 þ 6H2O ð2Þ
2NH3 þ 2O2 ! N2O þ 3H2O ð3Þ
4NO þ 4NH3 þ 3O2 ! 4N2O þ 6H2O ð4Þ
On the other hand, with the increase of copper content, there was an increase of
NO conversion in the whole temperature range.
The light-off temperature (T50), the maximum NO conversions and the related
temperatures of Cu(2.26)-HApw and Cu(x)-HApE catalysts were reported in
Table 2. It can be seen that Cu(2.26)-HApw catalyst is more active and has the
lower light-off temperature than the other catalysts. Furthermore, with the increase
of copper content for Cu(x)-HApE catalysts, there was a decrease of the T50 and an
increase of the maximum NO conversions. This behavior can be related to the
nature of copper oxide species. As demonstrated with the H2-TPR technique, there
is an increase of the quantity of the highly dispersed CuO clusters that are easily
150 200 250 300 350 400 450 5000
20
40
60
80 Cu(0.89)-HApE
Cu(2.01)-HApE
Cu(2.27)-HApE
Cu(3.12)-HApE
Cu(3.97)-HApE
NO
Con
vers
ion
(%)
Temperature (°C)
Ca-HApE
Fig. 5 NH3-SCR of NO in oxidizing atmosphere of the support Ca-HApE and the Cu(x)HApE catalysts.TPSR protocol: ramp = 6 �C. min-1, flow rate = 100 cm3 min-1, catalyst mass = 0.022 g,[NO] = [NH3] = 400 ppm, [O2] = 8 % balanced with He
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reduced with the increase of copper content. It seems that the increase of SBET
induced an increase of the size of CuO particles that become less active in NO-SCR
by NH3 compared to the catalysts prepared from carrier prepared in water by the
classic method [11].
The effect of water vapor on the catalytic performances of the prepared catalysts
has been studied with 2.5 % of H2O added to the reaction gas feed. Fig. 6 reports
the NO conversion without H2O and in the presence of 2.5 % of H2O for Cu(2.26)-
HapW, Cu(2.01)-HApE and Cu(3.97)-HApE. For all catalysts, the presence of H2O
strongly affects the NO conversion in the whole temperature range. The
deactivation of the catalyst is very likely associated with competitive adsorption
between H2O and reactants (NH3 and/or NO) molecules on the active Cu sites of the
catalysts.
In Fig. 7, we represent the NO conversions of the catalysts: Cu(2.26)-HApw, after
the hydrothermal treatments (Cu(2.26)ht500W and Cu(2.26)ht750W) and in the
Table 2 The light of temperatures, the maximum NO conversions and the related temperatures of
prepared catalysts
Catalysts T50 (�C) NO Con (%) T max (�C)
Cu(0.89)-HApE 270 59 325
Cu(2.01)-HApE 239 73 325
Cu(2.27)-HApE 224 82 325
Cu(3.12)-HApE 215 75 300
Cu(3.97)-HApE 200 80 325
Cu(2.26)-HapW 140 87 321
150 200 250 300 350 400 450 500
0
20
40
60
80
100Cu(2.26)-HApW
Cu(2.01)-HApE
Cu(3.97)-HApE
NO
Con
vers
ion
(%)
Temperature (°C)
Fig. 6 NH3-SCR of NO in oxidizing atmosphere of Cu(2.26)-HApw, Cu(2.01)-HApE and Cu(3.97)-HApE catalysts, without (full symbol) and in the presence of 2.5 % of H2O (open symbol). TPSRprotocol: ramp = 6 �C min-1, flow rate = 100 cm3 min-1, catalyst mass = 0.022 g,[NO] = [NH3] = 400 ppm, [H2O] = 2.5 %, [O2] = 8 % balanced with He
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presence of 2.5 % of H2O Cu(2,26)-HapW ? 2.5 % H2O). One can conclude that
whatever the deactivation process (hydrothermal treatment or 2.5 % of water in the
feed) there is a strong decrease of NO conversion in the entire range of temperature.
On the other hand, it seems that the hydrothermal treatment at 750 �C leads to the
same extend of deactivation as the addition of 2.5 % of water in the reaction feed.
To reveal the causes of deactivation of our catalysts in the reduction of NO by
NH3 oxygen-rich atmosphere, two ex situ hydrothermal treatments have been
chosen at 500 and 750 �C. This study was carried out for the most active catalyst
Cu(2.26)HApW and the related results are reported in Figs. 8 and 9. From XRD
150 200 250 300 350 400 450 5000
20
40
60
80
100 Cu(2,26)-HapW
Cu(2,26)-ht500W
Cu(2,26)-ht750W
Cu(2,26)-HapW+ 2.5% H2O
NO
Con
vers
ion
(%
)
Temperature (°C)
Fig. 7 NH3-SCR of NO in oxidizing atmosphere of Cu(2.26)-HApw, hydrotreated at 500 �CCu(2.26)ht500 W, hydrotreated at 750 �C Cu(2.26)ht750W and in the presence of 2.5 % of H2OCu(2,26)-HapW ? 2.5 % H2O)
20 25 30 35 40 45 50 55 60
Cu(2.26)-HApht750W
Cu(2.26)-HApht500W
Cu(2.26)-HapW
Inte
nsit
y (
a .
u )
2 Theta (°)
Fig. 8 XRD patterns of fresh catalyst Cu(2.26)-HApW; hydrotreated at 500 �C Cu(2.26)-HApht500W
and hydrotreated at 750 �C Cu(2.26)-HApht750W
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profiles of the fresh and hydrotreated catalysts at 500 and 750 �C, one may conclude
that the presence of 3 % of water vapor in the flowing air enhanced the crystallinity
of Ca-HAp support. On the other hand, the comparison between the H2-TPR profiles
(Fig. 9) of the fresh Cu(2.26)HApW and hydrotreated sample Cu(2.26)HApht500 W
clearly proved that the deactivation of the catalyst is very likely associated to the
change of the nature of copper species rather than to the destruction of the Ca-HAp
structure. Indeed, the H2-TPR profile of Cu(2.26)HApht500 W shows the presence
of two supplementary reduction peaks at 225 �C and 290 �C compared to the fresh
catalyst. This feature demonstrated that the presence of water vapor induced the
sintering of the active and highly dispersed CuO particles to bigger sized CuO ones
which are less active in the NO-SCR by NH3.
Conclusion
The influence of the increase of the specific surface area of the support Ca-HAp on
the dispersion of copper species and their activity in the NO-SCR by NH3 has been
studied. The Ca-HAp host structure, prepared in water–ethanol medium, has a molar
ratio Ca/P close to 1.61 and SBET of 76 m2/g. The copper ion exchange does not
alter the Ca-HAp structure whatever the copper concentration. The increase of the
SBET of the support changed the dispersion and the reducibility of copper species.
The high NO conversion at the whole temperature range for the catalyst prepared
from the carrier with low SBET Cu(2.26)HApW was related to the highly dispersed
CuO particles that are easily reduced. Whereas for Cu(2.27)HApE, the increase of
SBET induced an increase of the size of CuO particles that become less active in NO-
SCR by NH3. The addition of 2.5 % of H2O to the reaction gas feed strongly affects
100 200 300 400 500 600
291
225
210
Cu(2.26)-HApht500W
Cu(2.26)-HApW
H2 r
educ
tion
rat
e (
a . u
)
Temperature (°C)
Fig. 9 H2-TPR profiles of fresh catalyst Cu(2.26)-HApW and hydrotreated at 500 �C Cu(2.26)-HApht500W
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the NO conversion in the whole temperature range. This deactivation can be related
to the change of the nature of copper species rather than to the destruction of the Ca-
HAp structure.
References
1. Skalska K, Miller JS, Ledakowicz S (2010) Sci Total Environ 408:3976
2. Roy S, Hegde MS, Madras G (2009) Appl Energ 86:2283
3. Dieselnet http://www.dieselnet.com, 20114. Liu ZM, Woo SI (2006) Catal Rev Sci Eng 48:43
5. Brandenberger S, Krocher O, Tissler A, Althoff R (2008) Catal Rev 50:492
6. Harold MP (2012) Curr Opin Chem Eng 1:1
7. Zaihua W, Xinjun L, Wenji S, Jinfa C, Tao L, Ziping F (2011) React Kinet Mech Cat 103:353
8. Fickel DW, D’Addio E, Lauterbach JA, Lobo RF (2011) Appl Catal B 102:441
9. Kwak JH, Tran D, Szanyi J, Peden CHF, Lee JH (2012) Catal Lett 142:295
10. Tounsi H, Djemel S, Petitto C, Delahay G (2011) Appl Catal B 107:158
11. Jemal J, Tounsi H, Chaari K, Petitto C, Delahay G, Djemel S, Ghorbel A (2012) Appl Catal B
113–114:255
12. Jemal J, Tounsi H, Djemel S, Pettito C, Delahay G (2013) React Kinet Mech Catal 109:159
13. El Hammari L, Merroun H, Coradin T, Cassaignon S, Laghzizil A, Saoiabi A (2007) Mater Chem
Phys 104:448
14. International Centre for Diffraction Data. Powder Diffraction File, 09-0432
15. Rulis P, Ouyang L, Ching WY (2004) Phys Rev B 70:155104
16. Praliaud H, Mikhailenko S, Chajar Z, Primet M (1998) Appl Catal B 16:359
17. Araujo VD, Bellido JDA, Bernardi MIB, Assaf JM, Assaf EM (2012) Int J Hydrog Energ 37:5498
Reac Kinet Mech Cat
123
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