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.

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