Journal de la Société Chimique de Tunisie,

2007

,

9

, 85-96 85

H. Tounsi

et al.

CHARACTERIZATION AND PERFORMANCEOF OVER-EXCHANGED Cu-ZSM-5 CATALYSTSPREPARED BY SOLID-STATE ION EXCHANGE

FOR THE SELECTIVE CATALYTIC REDUCTION OF NO BY

n

-DECANE

H. Tounsi

a *

, S. Djemel

a

, A. Ghorbel

a

, G. Delahay

b

a

Laboratoire de Chimie des Matériaux et Catalyse, Département de Chimie,Faculté des Sciences de Tunis, Campus Universitaire, 1060 Tunis, Tunisie

b

Laboratoire de Matériaux Catalytiques et Catalyse en Chimie Organique, UMR 5618CNRS ENSCM,8 rue de l’École Normale, 34053 Montpellier Cedex, France

(Reçu le 26 Avril 2006, accepté le 11 Mai 2007)

*

correspondant

RESUME. Des catalyseurs Cu-ZSM-5 ont été préparés par échange ionique en phase solide à 500 °C sous flux d’azote à partir d’un mélange de CuCl et de NH

4-ZSM-5. La diffraction des rayons X a montré que la structure

zéolithique a été légèrement modifiée pour les teneurs accrues en cuivre. La nature des espèces de cuivre suite à

l'échange en phase solide dépend de la teneur en cuivre. Le cuivre se trouve majoritairement sous forme de Cu2+

pour

les catalyseurs ayant un taux d'échange inférieur à 100 %. Pour des teneurs accrues en cuivre, en plus des cations Cu2+

,

des espèces types Cu+ et des agrégats de CuO bien dispersées sur les surfaces et dans les canaux de la zéolithe, non

détectables par DRX ont été identifiés. Les catalyseurs préparés présentent une bonne activité dans la réduction

catalytique sélective de NO par le n-décane en atmosphère oxydante indépendamment de la teneur en cuivre.

L’augmentation de la teneur en cuivre décale la conversion de NO et l’oxydation de n-C10H22 vers les basses

températures. La présence de 25 ppm de SO2 dans le mélange réactionnel inhibe légèrement la conversion de NO pour

tous les catalyseurs à l’exception de Cu(136)-Z dont la conversion de NO est améliorée dans la plage de température

320-425 °C.

Mots clés : Cu-ZSM-5, NO-SCR, n-decane, échange ionique en phase solide, sur-échange.

ABSTRACT. Cu-ZSM-5 catalysts have been prepared by solid-state ion exchange at 500°C using CuCl and NH4-ZSM-5 mixture in presence of nitrogen flux. X-ray diffraction technique indicates that zeolite lattice is slightly modified

for high copper loadings. The nature of copper species depends on copper exchange levels. For under exchanged

catalyst, copper is mainly present as isolated Cu2+

. For higher loadings, Cu+ and dispersed CuO-like species with

different sizes and environments were detected besides Cu2+

ions. CuO-like species are located in the zeolite channels

such as Cu2+

-O-Cu2+

dimers or on the surface of zeolite crystals. Copper oxide clusters are not detectable by XRD

technique, which indicates that they are amorphous and/or well dispersed on the external surface of the zeolite. The

prepared catalysts show good activity in the selective catalytic reduction of NO by n-decane in oxidizing atmosphere

independently of copper exchange level. The increase of copper content has an effect on the operating temperature

window by decreasing the temperature of maximum NO conversion and total n-C10H22 oxidation. The presence of 25

ppm of SO2 in the reaction feed has a slight inhibiting effect for all catalysts excepting Cu(136)-Z for which NO

conversion was enhanced in the temperature range of 320-425 °C.

Key Words: Cu-ZSM-5, NO-SCR, n-decane, solid-state ion-exchange, over-exchange.

86 H. Tounsi

et al.

,

J. Soc. Chim. Tunisie

,

2007

,

9

, 85-96

I. INTRODUCTION

Cu-ZSM-5 zeolites, especially over-exchanged ones, have been pointed out as effective

catalysts for NO decomposition and NO selective catalytic reduction (NO-SCR) in the presence of

hydrocarbons in rich oxygen atmosphere [1-24]. Most of the hydrocarbons are more or less active

for the reduction of NO on Cu-zeolites, except for methane [10]. Lighter hydrocarbons (C6 or lower)

were traditionally chosen as reducing agent especially propane and propene. Heavier hydrocarbons

such as: n-C8H18 (i-C8H18) [21], n-C10H22 [13-20] and n-C16H34 [24] have also been reported in few

studies. Among heavy hydrocarbons, n-C10H22 was reported to be efficient on Cu-ZSM-5 [14, 16-

18] catalysts and other catalytic systems for the reduction of NO in oxidizing atmosphere [13, 15,

16]. It is interesting to note that for lighter hydrocarbons the presence of water vapor leads to

significant catalytic inhibition while heavier hydrocarbons maintain catalytic activity over Cu-ZSM-

5 even in the presence of water vapor [17].

The high performance of over-exchanged Cu-ZSM-5 catalysts (Cu/Al > 0.5) in NO-SCR by

hydrocarbons may be correlated with the availability of extra-lattice oxygen (ELO) species. The

identity of the ELO is not clear. Various proposals for copper structures bearing ELO have been put

forward: Cu2+

-O-Cu2+

dimers [25, 26], small zeolite-hosted copper oxide clusters [27-30]. Sarkany

et al. [26] revealed that over-exchanged, O2-calcined 3.1 wt% Cu(II)ZSM-5, mainly contained three

copper species, i.e., isolated Cu2+

ions (40%), Cu2+

-O-Cu2+

complex ions (35%) and non-ionic CuO

(25%). Grunert et al. [28] clearly proved that isolated Cu ions in low-symmetry environments and

intra-zeolite CuO clusters provide active sites for the reduction of NO with propene [8]. Capek et al.

[14] proposed that the most active and stable ions in NOx-SCR-C10H22 under lean burn conditions

appeared to be those located in vicinity of two Al atoms in one ring coordinated the cation.

On the other hand, over-exchanged Cu-ZSM-5 catalysts were usually prepared by repeated

aqueous ion exchange using diluted solution of copper salt; preferably copper (II) acetate [3, 31-35].

As a consequence, ion exchange frequently involves the handling and recycling of large volumes of

solution and time loss. In order to avoid these disadvantages, solid-state ion exchange (SSIE)

method has attracted increasing attention in recent years. Reported in 1973 by Rabo [36] and

Clearfield [37], this method consists of heating in vacuum [37, 38] or in flow of inert gas [4, 40-44]

a mechanical mixture of the zeolite and cation precursor. The highest exchange degrees were

reached using copper chlorides [40, 44-46] and the ammonium or protonic form of the zeolite [4,

40-42, 44-48]. In this case, hydrochloric acid (HCl) is released into the gas phase under the

preservation of the zeolite structure. The major advantage over conventional exchange is the

significantly higher degree of exchange reached in a one-step treatment compared to the procedure

in aqueous solution, which has to repeated between two to five times.

In this study, we prepared over-exchanged Cu-ZSM-5 catalysts by solid-state ion exchange

(SSIE) for NO-SCR in rich oxygen atmosphere using heavy hydrocarbon: n-C10H22, which is the

main component of diesel fuel. XRD and BET techniques have checked the stability of the zeolite

structure after the SSIE. H2-TPR and NO-TPD were used to identify copper species.

II. EXPERIMENTAL

Copper was introduced via solid-state ion exchange. The parent ZSM-5 (NH4+ form; Si/Al= 15;

Zeolyst) was ground with the required amount of CuCl (Prolabo Extra pure) in agate mortar for 15

min. The resulting mixture was heated to 500 °C at 7.5 °C min-1

in dry N2 and was maintained at

this temperature for 2 hours. The resulting samples were cooled to ambient temperature, washed

chloride-free and finally dried overnight at 100 °C.

Elemental analyses were performed by atomic absorption at the centre of CNRS in Vernaison

FRANCE. The catalysts were labelled as Cu(x)-Z, x being the copper theoretical exchange level

(TEL) which is defined as: 2 Cu/Al (mol. /mol.) ×100.

H. Tounsi

et al.

,

J. Soc. Chim. Tunisie

,

2007

,

9

, 85-96 87

Specific surface area (SBET) and pore volume distribution were measured by the nitrogen

method in Accursorb 2100 E Micrometrics Adsorption Analyser. Samples were degassed for 12

hours at 250 °C before adsorption. The BET method was used to determine the specific area at -196

°C.

The crystallinity of the catalysts and the presence of copper oxides were established by X-ray

diffraction on a Siemens D 500 diffractometer operating with a Cu- Kα radiation in the 4 ≤ 2θ° ≤

50 range at room temperature.

Temperature programmed reduction was carried out with a Micromeritics 2910 apparatus using

H2/Ar (3/97, vol. /vol.) gas at a total flow-rate of 30 cm3 min

-1 and by heating the samples from 50

to 700 °C (7.5 °C min-1

). In each case, 0.103 g of the catalyst was previously activated at 400 °C for

30 min under air, and then cooled to 50 °C under the same gas. The TPR with H2/Ar (3/97 vol.

/vol.) was then started and H2 consumption was monitored by the thermal conductivity detector.

The TPD experiments were performed in a Pyrex U-reactor with 0.104 g of catalyst. The sample

was pre-treated under air flow (100 cm3

min-1

) at 500 °C for 30 min and then cooled to room

temperature. After flushing with He until no oxygen was detected in the effluent, NO was adsorbed

at room temperature using a flow of NO/He mixture (0.1/99.9, vol. /vol.) at a total flow-rate of 50

cm3 min

-1 for 30 min. Afterwards, the system was purged with He (100 cm

3 min

-1) until no NO was

detected in the effluents. Thereafter, the TPD run was started from room temperature to 500 °C at a

heating rate of 7.5 °C min-1

in He flow (50 cm3

min-1

). The gas composition was monitored by

sampling on line with quadruple mass spectrometer (Pfeiffer Omnistar QMS 200) calibrated with

standard mixtures and following the masses 28, 30, 44, and 46.

The selective catalytic reduction of NO by n-decane (SCR-NO) was carried out at atmospheric

pressure in a fixed bed flow reactor with 0.104 g of catalyst. The flow-rates were adjusted using

Brooks mass flow controller units. The composition of the effluents was monitored continuously by

sampling in line to a quadruple mass spectrometer (Pfeiffer Omnistar QMS 200) equipped with

SEM detector (0-200 amu) and following the masses 28, 30, 44, 46, 57. The reaction gas containing

1000 ppm of NO, 300 ppm of n-decane, eventually 25 ppm of SO2 and 9 % O2 diluted with He was

switched on. The total flow rate was 120 cm3/min (VVH = 42,000 h

-1) and the temperature ramped

from 25 to 500 °C (7.5 °C min-1

). At 170 °C, n-decane was introduced to prevent its pre-adsorption

[15, 16].

III. RESULTS AND DISCUSSION

III.1 Chemical analysis

The chemical analyses of the studied catalysts are reported in Table I. The data show that SSIE

allows the introduction of the desired amount of copper in one step. Copper exchange level

exceeding 100 % for over-exchanged solids suggests the presence of oxygen-bridged copper species

such as Cu2+

-O-Cu2+

or copper oxide clusters beside isolated Cu2+

cations. According to Halasz et

al. [49], it is possible in ZSM-5 zeolite that Z-O-Cu-O-Z and Z-O-Cu-O-Cu-O-Z (with Z: zeolite)

bridges will be formed between two opposites Al-O sites in the double rings formed by 2×10

oxygen-bridged metal (Si, Al). The probability of such bridges is higher in ZSM-5 samples, which

have Si/Al ratio inferior to 24, because some of their double rings necessarily contain two or more

Al-O units. On the other hand, chemical analysis reveals the presence of chloride in spite of

washing catalysts several times with distilled water after SSIE. The remainder chloride was

probably located in the zeolite channels or strongly adsorbed on the external surface of the zeolite.

88 H. Tounsi

et al.

,

J. Soc. Chim. Tunisie

,

2007

,

9

, 85-96

copper loadings. The incorporation of copper affects the intensity of low angles reflections,

confirming the occupancy of distinct sites in the channel system of the ZSM-5 zeolite [50]. On the

other hand, the stability of the zeolite framework after the SSIE was checked by calculating the

crystallinity of the catalysts. The degree of crystallinity was estimated by taking the ratio of the sum

of the main peak intensities of CuZ samples at 2θ from 22 5 to 24 4° and those of the parent zeolite

In table I, were reported the BET surface area (SBET) and micropore volume (µV) of the

prepared catalysts. The µV of the support is in agreement with those reported in the literature for

ZSM-5 zeolites (0.126-0.148 cm3 g

-1) [55, 56]. The introduction of copper induced a decrease in the

SBET and the µV of the support. This decrease can be attributed to the blocking of ZSM-5 pore

10 20 0 40 50

Cu(348)-Z

Cu(230)-Z

Cu(136)-Z

Cu(56)-Z

NH4-ZSM-5

I n

t e

n s

i t

y /

a . u

2 theta / deg

y

In Figure 1 are reported the XRD patterns of the prepared Cu(x)-Z catalysts with different

copper loadings. The incorporation of copper affects the intensity of low angles reflections,

confirming the occupancy of distinct sites in the channel system of the ZSM-5 zeolite [50]. On the

other hand, the stability of the zeolite framework after the SSIE was checked by calculating the

crystallinity of the catalysts. The degree of crystallinity was estimated by taking the ratio of the sum

of the main peak intensities of CuZ samples at 2θ from 22.5 to 24.4° and those of the parent zeolite

NH4-ZSM-5. Accordingly, the crystallinities of NH4-ZSM-5, Cu(56)-Z, Cu(136)-Z, Cu(230)-Z and

Catalyst Si

(wt. %)

Al

(wt. %)

Cu

(wt. %)

Cl

(wt. %)

Cu/Al

(mol/mol)

TEL

(%)

SBET (m

2 g

-1)

µV

(cm3 g

-1)

H2/Cu

(mol/mol)

NH4-ZSM-5 40.01 2.35 367 0.140

Cu(56)-Z 38.80 2.30 1.50 0.28 56 334 0.112 1.08

Cu(136)-Z 35.45 2.00 3.21 0.17 0.68 136 298 0.095 1.06

Cu(230)-Z 35.90 2.11 5.68 1.15 230 287 0.097 0.98

Cu(348)-Z 35.40 1.98 8.08 0.62 1.74 348 249 0.088 0.96

III.2 X-ray diffraction

In Figure 1 are reported the XRD patterns of the prepared Cu(x)-Z catalysts with different

copper loadings. The incorporation of copper affects the intensity of low angles reflections,

confirming the occupancy of distinct sites in the channel system of the ZSM-5 zeolite [50]. On the

other hand, the stability of the zeolite framework after the SSIE was checked by calculating the

crystallinity of the catalysts. The degree of crystallinity was estimated by taking the ratio of the sum

of the main peak intensities of CuZ samples at 2θ from 22.5 to 24.4° and those of the parent zeolite

NH4-ZSM-5. Accordingly, the crystallinities of NH4-ZSM-5, Cu(56)-Z, Cu(136)-Z, Cu(230)-Z and

Cu(348)-Z are 100, 99, 98, 96 and 97, respectively. These results show that the crystallinity of the

copper-loaded ZSM-5 did not significantly change after the SSIE. No detectable CuO crystallites

superior to 4 nm at 35,7 ° and 38.6 ° 2θ were observed in all catalysts. Therefore CuO crystallites

are either amorphous and/or well dispersed in the external surface or in the channels of the zeolite.

III.2 X-ray diffraction

In Figure 1 are reported the XRD patterns of the prepared Cu(x)-Z catalysts with different

copper loadings. The incorporation of copper affects the intensity of low angles reflections,

confirming the occupancy of distinct sites in the channel system of the ZSM-5 zeolite [50]. On the

other hand, the stability of the zeolite framework after the SSIE was checked by calculating the

crystallinity of the catalysts. The degree of crystallinity was estimated by taking the ratio of the sum

of the main peak intensities of CuZ samples at 2θ from 22.5 to 24.4° and those of the parent zeolite

NH4-ZSM-5. Accordingly, the crystallinities of NH4-ZSM-5, Cu(56)-Z, Cu(136)-Z, Cu(230)-Z and

Cu(348)-Z are 100, 99, 98, 96 and 97, respectively. These results show that the crystallinity of the

copper-loaded ZSM-5 did not significantly change after the SSIE. No detectable CuO crystallites

superior to 4 nm at 35,7 ° and 38.6 ° 2θ were observed in all catalysts. Therefore CuO crystallites

are either amorphous and/or well dispersed in the external surface or in the channels of the zeolite.

In Figure 1 are reported the XRD patterns of the prepared Cu(x)-Z catalysts with different

copper loadings The incorporation of copper affects the intensity of low angles reflections

Table I: Chemical analysis, textural parameters and H2/Cu ratio of the prepared catalysts.

Figure 1: XRD patterns of the studied catalysts prepared by solid-state ion exchange.

H. Tounsi

et al.

,

J. Soc. Chim. Tunisie

,

2007

,

9

, 85-96 89

channels by copper species. In comparison with the parent zeolite, the loss of µV of the most loaded

sample, Cu(348)-Z, was around 37 %.

III.4 Temperature-programmed reduction (TPR) analysis

According to previous works [7, 16, 26, 30, 57-61], the reactions involved in the reduction

process of copper exchanged zeolites are the following:

CuO + H2 → Cu° + H2O (I)

Cu2+

+ H2 → Cu+ + 2 H

+ (II)

Cu+ + H2 → Cu

0 + 2 H

+ (III)

Figure 2 shows the H2-TPR profiles of Cu(x)-Z catalysts prepared via SSIE. The reduction

profile of Cu(56)-Z contains two reduction peaks. The first at around 240 °C, which is assigned to

the reduction of Cu2+

to Cu+ and the second at 492 °C is ascribed to the reduction of the formed Cu

+

to Cu°. With increasing copper contents supplementary peaks and shoulders are detected. For

example, Cu(136)-Z catalyst presents three reduction peaks located at 174, 230 and 374 °C. The

low temperature was assigned to the reduction of Cu2+

to Cu+. The central peak was attributed to

Cu2+

in dispersed undefined CuO species reduced in one-step process directly to Cu° [26, 60, 61].

In the last one, reduction of Cu+ to Cu° occurs. For the higher copper content catalysts, Cu(238)-Z

and Cu(348)-Z, the peak assigned to the reduction of CuO-like species increases in intensity

compared to Cu(136)-Z sample. Thus this peak should be attributed to the reduction of CuO clusters

inside the zeolite channels and on the outer surface of the samples. The shoulders observed for these

solids underline the fact that they contain isolated Cu+ species and eventually CuO clusters in

different environments [61].

On the other hand, the first and the third peak are shifted to lower temperatures when copper

loading increases. This suggests that Cu2+

and Cu+ ions are easier to reduce when Cu content is

increased which is in agreement with previous reports on Cu-zeolites [16, 62]. The amounts of

hydrogen uptake show that H2/Cu molar ratio are very close to unity which corresponds to the

stoichiometric reduction of Cu2+

to Cu° (Table I).

100 200 00 400 500 600

Cu(348)-Z

Cu(230)-Z

Cu(136)-Z

Cu(56)-Z

H2 r

e d

u c

t i

o n

r

a t

e /

a .

u

Figure 2: H2-TPR profiles of prepared catalysts.�Conditions: H2/Ar (3/97 vol./vol.), flow rate = 120 cm3 min

-1,

ramp: 7.5 °C min-1

, catalyst mass = 0.103 g.

Temperature / °C

90 H. Tounsi

et al.

,

J. Soc. Chim. Tunisie

,

2007

,

9

, 85-96

III.5 Temperature programmed desorption (TPD) analysis

NO desorption experiment on NH4-ZSM-5 reveals that small amount of NO (Table II) is

adsorbed. As it would be expected, the amount of adsorbed NO is significantly enhanced by

introduction of copper into the zeolite. NO-TPD profiles of Cu-Z prepared are in good agreement

with profiles reported in literature [63-68] except those of Cu(230)-Z and Cu(348)-Z which show a

second O2 desorption peaks at 450 and 434 °C, respectively. In Figure 3, the TPD profiles of the

desorbed species from Cu(230)-Z, after saturation with NO at 25 °C, are reported. Two distinct

desorption peaks of NO are observed at 108 and 367 °C:

(i) the first peak is ascribed to the decomposition of Cu+-NO

+ species leading to Cu

2+ and

NO (gas) [63-67] and;

(ii) the second peak, accompanied by oxygen desorption, is attributed to the decomposition

of nitrate (NO3-), nitrite (NO2

-) or NO2

+ adsorbed species on both isolated Cu

2+ sites and

CuO aggregates [66].

The second oxygen broad peak, was observed at 450 and 434 °C for Cu(230)-Z, Cu(348)-Z,

respectively, is probably due to the desorption of oxygen-bridged copper species located on the

external surface of ZSM-5 crystallites. Furthermore, the small peak at around 260 °C could be

associated to NO adsorption on copper species in different positions of the zeolite structure or with

different oxidation state. For Cu(136)-Z catalyst, the first desorption peak of NO presents a shoulder

at around 230 °C. According to the assignment of Torre-Abreu et al. [61] the shoulder was assumed

to be related to NO desorption from Cu+ species. Taking into account this result, the peak at around

260 °C, observed for the most loaded catalysts Cu(230)-Z and Cu(348)-Z, may be attributed also to

NO desorption from Cu+ species. Moreover, the quantities of NO2 and N2O desorbed during the

experiments are not significant. The evolution of N2O can also be related to the presence of Cu+

species [67].

The amounts of desorbed species from the catalysts and the NO accessibility NO/Cu are

reported in table. II. The first noteworthy feature is that the NO desorption increases with copper

amount for Cu(56)-Z and Cu(136)-Z and then drops for the other catalysts. Assuming that the

stoichiometry NO/Cu at the surface is unity whatever the adsorbed species, accessibility less than

the unity was found for all the catalysts. This NO/Cu ratio confirms the occurrence of clustered

cationic copper species with increasing copper loadings. A value of 0.14 was assessed for Cu(230)-

Z and Cu(348)-Z, which explains the drop of NO desorption from these two catalysts.

Table II: Amounts of desorbed species from the studied catalysts (µmol/g) and NO/Cu ratio (mol/mol).

Catalyst

NO total

NOLT

NOHT

O2

total

O2

1st peak

O2

2nd

peak

N2O total

NO2

total

NO/Cu

NH4-ZSM-5 11 11 0 0 0 0 1 2 -

Cu(56)-Z 74 42 33 6 6 0 8 2 0.61

Cu(136)-Z 192 157 35 47 47 0 3 3 0.38

Cu(230)-Z 122 96 26 39 30 9 3 1 0.14

Cu(348)-Z 134 110 24 41 23 13 20 1 0.14

H. Tounsi

et al.

,

J. Soc. Chim. Tunisie

,

2007

,

9

, 85-96 91

Figure : TPD profiles of NO and O2 after the adsorption of NO at room temperature for Cu(230)-Z catalyst.

Conditions: NO adsorption: NO/He (0.1/99.9 vol./vol.), flow rate=50 cm3

min-1

, catalyst mass=0.104 g.

NO Desorption: ramp=7.5°C min-1

, flow rate=50 cm3 min

-1 of He gas.

III.6 Selective catalytic reduction of NO by n-decane

Cu-free-catalyst (NH4-ZSM-5) shows no NO conversion and the color of the sample changes

from white to black, which points out a strong deactivation of the catalyst by coke. For the Cu-

catalysts (Figures 4 and 5), the NO conversion rapidly increases with the temperature, reaches a

maximum and then decreases more slowly with the temperature. The oxidation of n-C10H22 starts around 200 °C and becomes total above the temperature at which NO maximum conversion is

achieved [10]. This behavior reveals a competition between two reactions. The first correlated to

NO reduction and the second to n-C10H22 oxidation to CO2 by the oxygen present in the reaction

mixture. At high temperatures, the diminution of n-C10H22 concentration by excessive oxidation

decreases the NO reduction rate which explain the low NO conversion at 500 °C. On the other

hand, it seems that increasing copper content does not have influence on the NO maximum

conversion and a value about 84 % has been assessed for all the catalysts. The increase of copper

content has an effect on the operating temperature window by decreasing the temperature of

maximum NO conversion and total n-C10H22 oxidation. Torre-Abreu et al. [61] related the shifting

of temperature window to lower temperature to the easier reducibility of copper species by

increasing copper content.

The impact of addition of 25 ppm of sulphur dioxide (SO2) to the reaction mixture gas was also

studied (Table III, Figures 6 and 7). For under-exchanged Cu(56)-Z catalyst, the introduction of

SO2 has no effect; whereas for higher loaded catalysts: Cu(230)-Z and Cu(348)-Z, there is a slight

inhibition of NO conversion (< 5%) in the whole temperature range. For Cu(136)-Z catalyst, Fig. 6

100 200 00 400 500

NO

O2

I n

t e

n s

i t

y /

a . u

Temperature / °C

92 H. Tounsi

et al.

,

J. Soc. Chim. Tunisie

,

2007

,

9

, 85-96

Figure 4: NO-SCR by n-C10H22 in oxidizing atmosphere of the studied catalysts. Catalytic experiments were

performed using: [NO]=1000 ppm, [C10H22]=300 ppm, [O2]= 9% and He as balancing gas, flow rate = 120 cm3

min-1

,

ramp = 7.5°C min-1

, catalyst mass= 0.104 g.

200 250 00 50 400 450 500

0

20

40

60

80

100

Cu(56)-Z

Cu(136)-Z

Cu(230)-Z

Cu(348)-Z

N O

C

o n

v e

r s

i o

n /

%

Temperature / °C

clearly shows that SO2 addition enhance the NO conversion in the 320-425 °C temperature range.

For temperatures lower than 320 °C, NO-SCR slightly decreases but at higher temperature (T > 425

°C), the decrease of NO conversion was appreciable. For example, the conversion of NO was 43 %

at 500 °C in absence of SO2 while it was 23 % in its presence. Concerning n-C10H22 oxidation, SO2

displaces slightly the oxidation profile to low temperature.

One may conclude that SO2 has only a slightly inhibiting effect on catalysts having copper oxide

clusters on the surface of zeolite crystals by forming sulphate species linked to copper. In fact, Centi

et al. [69] demonstrated that SO2 was strongly adsorbed on copper as sulphate when SO2 was

adsorbed on CuO-Al2O3 catalyst (4.8 wt % CuO).

Table III: The maximum NO conversions and the related temperatures of prepared catalysts for NO-SCR with and

without SO2.

NO-SCR without SO2 NO-SCR with 25 ppm SO2

Catalyst NOmax Conv (%) Tmax (°C) NOmax Conv (%) Tmax (°C)

Cu(56)-Z 84 423 85 423

Cu(136)Z 85 360 94 360

Cu(230)-Z 83 329 82 326

Cu(348)-Z 84 316 80 315

H. Tounsi

et al.

,

J. Soc. Chim. Tunisie

,

2007

,

9

, 85-96 93

150 200 250 00 50 400 450 500

0

20

40

60

80

100

Cu(56)-Z

Cu(136)-Z

Cu(230)-Z

Cu(348)-Z

n

-C 1

0 H

22

C o

n v

e r

s i

o n

/

%

Temperature / °C

Figure 5: n-C10H22 oxidation of the studied catalysts. (For conditions see Figure 4).

Figure 6: NO-SCR by n-C10H22 in oxidizing atmosphere of Cu(136)-Z catalyst in presence and absence of SO2.

Catalytic experiments conditions: [NO]=1000 ppm, [C10H22]=300 ppm, [SO2]=25 ppm, [O2]= 9% and He as balancing

gas, flow rate =120 cm3 min

-1, ramp = 7.5°C min

-1, catalyst mass = 0.104 g.

250 00 50 400 450 500

0

20

40

60

80

100

Cu(136)-Z with SO2

Cu(136)-Z without SO2

N

O C

o n

v e

r s

i o

n /

%

Temperature / °C

94 H. Tounsi

et al.

,

J. Soc. Chim. Tunisie

,

2007

,

9

, 85-96

200 250 00 50 400 450 5000

20

40

60

80

100

Cu(136)-Z without SO2

Cu(136)-Z with SO2

n-C

10 H

22 C

o n

v e

r s

i o

n /

%

Temperature / °C

IV. CONCLUSION

Over-exchanged Cu-ZSM-5 catalysts were prepared using SSIE. This method allows the

introduction of the desired amount of copper in one step. The zeolite structure did not significantly

change after the SSIE as shown by XRD technique. The nature of copper species depends on copper

exchange levels. For under exchanged catalyst, copper is mainly present as isolated Cu2+

. For

higher loadings, Cu+ and dispersed CuO-like species with different size and environment were

detected beside Cu2+

ions. CuO-like species are located in the zeolite channels such as Cu2+

-O-Cu2+

dimers or on the surface of zeolite crystals. CuO particles are not detectable by XRD technique

which indicates that they are amorphous and/or well dispersed on the external surface of the zeolite.

The prepared catalysts show good activity in the selective catalytic reduction of NO by n-decane in

oxidizing atmosphere independently of copper exchange level. The increase of copper content has

an effect on the operating temperature window by decreasing the temperature of maximum NO

conversion and total n-C10H22 oxidation. The presence of 25 ppm of SO2 in the reaction feed has a

slight inhibiting effect for all catalysts excepting Cu(136)-Z for which NO conversion was

enhanced in the temperature range of 320-425 °C.

ACKNOWLEDGMENT

The authors gratefully acknowledge the Comité Mixte Franco-Tunisien pour la Coopération

Universitaire (CMCU 03G1203) for the financial support.

Fig.7. n-C10H22 oxidation for NO-SCR of Cu(136)-Z catalyst in presence and absence of SO2. (For conditions see

Figure 6).

H. Tounsi

et al.

,

J. Soc. Chim. Tunisie

,

2007

,

9

, 85-96 95

REFERENCES

[1] M. Iwamoto, H. Hamada, Catal. Today, 1991, 10, 57.

[2] W. Held, A. Konig, T. Richter, L. Puppe, SAE Paper N° 900496, 1990.

[3] S. Sato, Y. Yu- u, H. Yahiro, N. Mizuno, M. Iwamoto, Appl. Catal., 1991, 70, L1.

[4] N. N. Sazonova, O. V. Komova, E. V. Rebrov, A. V. Simakov, N. A. Kulikovskaya, V. A.

Rogov, R. V. Olkhov, G. B. Barannik, React. Kinet. Catal. Lett., 1997, 60 (2), 313.

[5] V. A. Bell, J. S. Feeley, M. Deeba, R. J. Farrauto, Catal. Lett., 1994, 29, 15.

[6] C. Torre-Abreu, M. F. Ribero, C. Henriques, F. R. Ribeiro, Appl. Catal. B., 1997, 11, 407.

[7] C. Torre-Abreu, C. Henriques, F. R. Ribero, G. Delahay, M. F. Ribeiro, Catal. Today, 1999, 54,

407.

[8] T. Liese, W. Grunert, J. Catal., 1997, 172, 34.

[9] R. Burch. S. Scire, Appl. Catal. B., 1994, 3, 295.

[10] H. Yahiro, M. Iwamoto, Appl. Catal. A. 2001, 222, 163.

[11] Z. Schay, V. S. James, G. Pal-Borbely, A. Beck, A. V. Ramaswamy, L. Guczi, J. Mol. Catal.

A., 2000, 162, 191.

[12] J. O. Petunchi, W. K. Hall, Appl. Catal. B., 1994, 3, 239.

[13] G. Delahay, E. Ensuque, B. Coq, F. Figueras, J. Catal., 1998, 175, 7.

[14] L. Capek, J. Dedecek, B. Wichterlova, L. Cider, E. Jobson V. Tokarova, Appl. Catal. B., 2005,

60, 151.

[15] B. Coq, D. Tachon, F. Figueras, G. Mabilon, M. Prigent, Appl. Catal. B., 1995, 6, 271.

[16] G. Delahay, B. Coq, L. Broussous, Appl. Catal. B., 1997, 12, 49.

[17] L. Capek, K. Novoveska, Z. Sobalik, B. Wichterlova, L. Cider and E. Jobson, Appl. Catal. B.,

2005, 60, 201.

[18] H. Tounsi, S. Djemel, A. Ghorbel, G. Delahay, L. C. de Menorval, B. Coq, React. Kinet. Catal.

Lett., 2004, 81(1), 33.

[19] K. Sato, T. Yoshinari, Y. Kintaichi, M. Haneda, H. Hamada, Appl. Catal. B., 200 , 44, 67.

[20] V. Houel, D. James, P. Millington, S. Pollington, S. Poulston, R. Rajaram, R. Torbati, J. Catal.

2005, 230, 150.

[21] K. Shimizu, A. Satsuma, T. Hattori, Appl. Catal. B., 2000, 25, 239.

[22] Y. Traa, B. Burger, J. Weitkamp, Microp. Mesopor. Mater., 1999, 30, 3.

[23] F. Witzel, G. A. Sill W. K. Hall, J. Catal., 1994, 149, 229.

[24] T. Inui, S. Iwamoto, S. Kojo, T. Yoshida, Catal. Lett., 1992, 13, 87.

[25] M. Iwamoto, H. Yahiro, N. Mizuno, W.X. Zhang, Y. Mine, H. Furukawa, S. Kagawa, J. Phys.

Chem., 1992, 96, 9360.

[26] J. Sarkany, J. L. d’Itri, W. M. H. Sachtler, Catal. Lett., 1992, 16, 241.

[27] J. Valyon, W. K. Hall, Catal. Lett., 199 , 19, 109.

[28] W. Grunert, N.W. Hayes, R.W. Joyner, E.S. Shpiro, M. Rafio, H. Siddiqui et G.N. Baeva, J.

Phys. Chem., 1994, 98, 10832.

[29] B. Wichterlova, Z. Sobalik, Vondrova, Catal. Today, 1996, 29, 149.

[30] T. Beutel, J. Sarkany, G. D. Lei, J. Y. Yan, W. M. H. Sachtler, J. Phys. Chem., 1996, 100, 845.

[31] R. Gopalakrishan, P. R. Stafford, J. E. Davidson, W. C. Hecher, C. H. Bartholomew, Appl.

Catal. B., 199 , 2, 165.

[32] W. Zhang, H.Yahiro, N. Mizuno, J. Izumi, M. Iwamoto, Langmuir, 199 , 9, 2337.

[33] M. Iwamoto, H.Yahiro, Y. Mine, S. Kagawa, Chem. Lett., 1989, 213.

[34] M. Iwamoto, H.Yahiro, S. Shundo, Y. Yu-u, N. Mizono, Appl. Catal., 1991, 69, L15.

[35] M. Iwamoto, H.Yahiro, Y. Torikai, T. Yoshoka, N. Mizono, Chem. Lett., 1991,1967.

[36] J.A. Rabo, M.L. Poutsma, G.W. Skeels, in: J.W. Hightower (Ed.), Proceedings of the 5th

International Congress on Catalysis, North Holland, New York, 197 , p. 1353.

96 H. Tounsi

et al.

,

J. Soc. Chim. Tunisie

,

2007

,

9

, 85-96

Fin[37] A. Clearfield, C.H. Saldarriaga, R.C. Buckley, J. B. Uytterhoeven (Ed.); 3rd International Conference on Molecular Sieves, Paper N° 130, University of Leuwen Press, Leuwen, 197 , p.

241.

[38] W. Grunert, T. Liese, C. Schobel, Stud, Surf. Sci. Catal., 1997, 105, 1517.

[39] H.G. Karge, B. Wichterlova, H.K. Beyer, J. Chem. Soc., Faraday Trans., 1992, 88(9), 1345.

[40] W. Grunert, N. W. Hayes, R. W. Joyner, E. S. Shpiro, M. Rafio, H. Siddiqui, G.N. Baeva, J.

Phys. Chem., 1994, 98, 10832.

[41] G. L. Price, V. Kanazirev, D. F. Church, J. Phys. Chem., 1995, 99, 864.

[42] I. Schay, H. Knozinger, L. Guezi, G. Pal-Borbily, Appl. Catal. B., 1998, 18, 263.

[43] J. Varga, J. Halasz, D. Horvath, D. Mefin, J.B. Nagy, Gy. Schobel, I. Kiricsi, Stud. Surf. Sci.

Catal., 1998, 116, 367.

[44] I. Halasz, G. Pal-Borbely, H.K. Beyer, React. Kinet. Catal. Lett., 1997, 61(1), 27.

[45] F.-S. Xiao, W. Zhang, M. Jia, Y. Yu, C. Fang Guoxingbatu, S. Zheng, S. Qiu, R. Xu, Catal.

Today, 1999, 50, 117.

[46] M. J. Jia, W. X. Zhang, T. H. Wu, J. Mol. Catal. A., 2002, 185, 151.

[47] J. Varga, A. Fudala, J. Halasz, G.Y. Schobel, I. Kiriesi, Stud. Surf. Sci. Catal. 1995, 94, 665.

[48] Z. Schay, L. Guczi, Catal. Today, 199 , 17, 175.

[49] I. Halasz, A. Brenner, Catal. Lett., 1998, 51, 195.

[50] A. Lassoued, J. Deson, C. Lalo, A. Gedeon, P. Batamack, J. Fraissard, R. Birjega, R. Ganea, C.

Nenu, Micropor. Mesopor. Mater., 2001, 43, 1.

[51] S. M. Campbell, D. M. Bibby, J. M. Coddington, R. F. Howe, R. H. Meinhold, J. Catal., 1996,

161, 338.

[52] A. Maijanen, E. G. Derouane, J. B. Nagy, Appl. Surf. Sci., 1994, 75, 204.

[53] P. Budi, E. Curry-Hyde, R. F. Howe, Catal. Lett., 1996, 41, 47.

[54] M. Muller, G. Harvey, R. Prins, Micropor. Mesopor. Mater., 2000, 34, 135.

[55] M. J. Remy, G. Poncelet, J. Phys. Chem., 1995, 99, 773.

[56] P. Voogd, J. J. F. Scholten, H. van Bekkum, Colloids Surf., 1991, 55, 163.

[57] C. Torre- Abreu, M.F. Ribeiro, C. Henriques, F. R. Ribeiro, G. Delahay, Catal. Lett., 1997, 43,

31.

[58] J. Sarkany, W.M.H. Sachtler, Zeolites, 1994, 14, 7.

[59] J. Sarkany, W.M.H. Sachtler, Stud. Surf. Sci. Catal., 1995, 94, 649.

[60] R. Bulanek, B. Wichterlova, Z. Sobalik, J. Tichy, Appl. Catal. B., 2001, 31, 13.

[61] C. Torre-Abreu, M.F. Ribeiro, C. Henriques, G. Delahay, Appl. Catal., 1997, 12, 249.

[62] H. Exner, F. Fetting, Chem. Eng. Technol., 1991, 14, 428.

[63] Y. Li, J. N. Armor, Appl. Catal. A., 1991, 76, L1.

[64] M. Shimokawabe, N. Hatakeyama, K. Shimada, K. Tadokoro, N, Takezawa, Appl. Catal. A.,

1992, 87, 205.

[65] A. Gervasini, Appl. Catal. B., 1997, 14, 147.

[66] W. Zhang, H. Yahiro, N. Mizuno, J. Izumi, M. Iwamoto, Langmuir, 199 , 9, 2337.

[67] R. Hierl, H. P. Urbach, H. Knozinger, J. Chem. Soc. Faraday Trans., 1992, 88 (3), 355.

[68] G. P. Ansell, A. F. Diwell, S. E. Golunski, J. W. hayes, R. R. Rajaram, T. J. Truex, A. P.

Walker, Appl. Catal. B., 199 , 2, 81.

[69] G. Centi, N. Passarini, S. Perathoner, A. Riva, Ind. Eng. Chem. Res., 1992, 31, 1947.