www.elsevier.com/locate/apcatb

Applied Catalysis B: Environmental 69 (2006) 43–48

In/Co-ferrierite: A highly active catalyst for the

CH4-SCR NO process under presence of steam

A. Kubacka a,b,*, J. Janas a, B. Sulikowski a

a Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, 30-239 Krakow, Polandb Instituto de Catalisis y Petroleoquımica, CSIC, Campus Cantoblanco, 28049 Madrid, Spain

Received 30 March 2006; received in revised form 16 May 2006; accepted 23 May 2006

Available online 7 July 2006

Abstract

A series of monometallic (In, Co) and bimetallic (In/Co and Co/In) catalysts supported on ferrierite type zeolite were tested in the selective

catalytic reduction of nitric oxide, in the presence of methane and excess of oxygen. All the catalysts were prepared by contact-induced ion

exchange. A strong synergistic effect was observed for the catalysts containing both indium and cobalt, in comparison with the monometallic

samples. For these bimetallic catalysts, a very high selectivity to nitrogen and rather efficient fuel economy were observed under the standard

reaction conditions (NO = 1000 ppm, CH4 = 2000 ppm, O2 = 4%, H2O = 2500 ppm). Moreover, the In/Co-ferrierite catalyst displays significant

stability under a prolonged test (�200 h) in the presence of 2.5% of steam: the activity dropped rather moderately but was completely restored if

steam supply was cut off, while the selectivity of the reaction was not affected in the whole temperature range scanned (300–500 8C). The study

suggests that a redox-type promotional effect of Co species on NO oxidation may be responsible of the strong synergistic effect detected in

bimetallic In–Co formulations.

# 2006 Elsevier B.V. All rights reserved.

Keywords: Selective catalytic reduction; Nitric oxide; Ferrierite; Methane; Cobalt; Indium; Contact-induced ion exchange

1. Introduction

The catalytic elimination of NOx is a major challenge in

order to protect the environment and human health in modern

societies [1]. In this respect, the pioneering work of Iwamoto

et al. opened a way to solve this problem by using hydrocarbons

as reducing agents [2]. Several metals, like Ag, Sn, In, Co and

noble metals (Pt, Pd) have been shown potential to selectively

reduce NOx [3,4]. While noble metals display significant de-

NOx activity from low temperatures, �200 8C, the simulta-

neous formation of N2O, a powerful green house gas, limits

their application under real conditions [5,6]. Base metals like

Ag, Sn, In or Co does not present such problem, showing high

N2 selectivity but typically at much higher temperatures, above

400 8C [5,6]. Zeolite-supported base-metal species were found

to have superior activity and N2 selectivity as compared with

* Corresponding author. Tel.: +48 12 6395126; fax: +48 12 4251923.

E-mail addresses: nckuback@cyf-kr.edu.pl, a.kubacka@icp.csic.es

(A. Kubacka).

0926-3373/$ – see front matter # 2006 Elsevier B.V. All rights reserved.

doi:10.1016/j.apcatb.2006.05.014

alternative supports like Al2O3 in the selective catalytic

reduction with hydrocarbons (HC-SCR) under dry conditions;

e.g. in the absence of water [7]. However, high concentration of

water present in effluents induces a significant deactivation of

most zeolite-type catalysts and therefore can limit their

application, particularly at high temperature where stability

of the zeolite support and/or exchanged species are rapidly

deteriorated [1,5,6].

The use of methane in the form of readily available natural

gas is very attractive from an environmental point of view [8]. A

few examples of potential markets for zeolite based CH4-SCR

are treatment of flue gases from nitric acid factories, small size

boilers installations, combined cycle devices, caprolactam

production and lean-burn gas engines and transformers. Its use

is however restricted due to the fact that C–H activation

requires high reaction temperature. In spite of this, zeolite-

supported cobalt (Co), palladium (Pd) and indium (In) are

among the most capable systems explored to date in the CH4-

SCR [9–13]. In addition ferrierite-supported catalyst has shown

a significant stability under hydrothermal conditions, display-

ing no loss of activity over a 50 h run [12]. On the other hand, In

A. Kubacka et al. / Applied Catalysis B: Environmental 69 (2006) 43–4844

Table 1

Modification degree (indium and cobalt) and surface area of the catalysts

studied

Catalyst Modification

degree (%)

wt.% BET

(m2/g)

Co In Co In

0.5Co-FER 50 – 2.13 – 273.6

0.6In-FER – 60 – 3.28 262.3

0.6In/0.5Co-FER 50 60 2.13 3.28 236.6

0.5Co/0.6In-FER 50 60 2.13 3.28 238.6

[13,14] and Co [10] zeolite-supported catalysts have also

shown promising properties in the presence of water.

In this work we analyze the use of In and Co on the ferrierite-

supported catalysts under both an extended period of time at

high temperature and in the presence of water vapor in order to

test the catalytic properties and potential use of such systems in

conditions approaching the broad use in the application area

mentioned above. We will see that although the monometallic

In and Co catalysts display moderate activity, combinations of

both metals boost the activity of the system without appreciable

detrimental (or even improved) effect in N2 selectivity and fuel

economy. These bimetallic novel catalysts display high activity,

N2 selectivity and fuel economy over a broad range of

temperatures (325–500 8C) under both almost dry and wet

conditions. Various details of catalysts preparation, e.g. order of

contacting of zeolite support with the metal source, affect the

catalytic performance, particularly at low temperature, and will

be studied by using XPS.

2. Experimental

2.1. Catalysts preparation

Ferrierite type zeolite was synthesized hydrothermally by

using Ludox AS-40 as the silica source and piperidine (pip) as

the organic templates. The gel with the molar composition of

22.7 SiO2:9.0 pip:6.8 Na2O:1.0 Al2O3:385 H2O has been

homogenized for few hours and allowed to crystallize in the

Teflon-lined stainless-steel autoclaves under autogenous

pressure for 4 days at 200 8C. After calcination at 550 8Cferrierite was ion-exchanged with ammonium nitrate (four

times at ambient temperature) and transformed into the

hydrogen form (H-FER) by calcination at 550 8C. The Si/Al

ratio of H-FER was 8.8 and BET (Ar) = 320.4 m2/g.

The hydrogen form of FER was modified further by Co2+

and/or In3+ ions using the contact-induced ion exchange

(c.i.i.e.) procedure [15]. The Co-containing catalysts were

obtained by mixing cobalt acetate (Merck, p.a.) with the

hydrogen forms of zeolite followed by calcination in the helium

flow at 550 8C for 2 h. The modification level with the metal

cations is showed by a fraction inserted before the ion symbol.

For example, 0.5Co-FER refers to a sample of ferrierite with the

50% modification level of cobalt (Scheme 1).

The In-FER samples were prepared by careful grinding of

ferrierite and indium(III) oxide, heating in He to 400 8C and

followed by reduction with hydrogen at this temperature for

2 h. The catalyst containing simultaneously the two types of

ions (Co2+ and In3+) was also prepared by c.i.i.e. method. The

In/Co-form of ferrierite was prepared from the Co-FER sample

by applying the additional c.i.i.e. procedure to the cobalt form.

Scheme 1. Catalyst prep

Thus Co-form of ferrierite was ground with In2O3, heated in the

helium flow to 400 8C, reduced with hydrogen for 2 h and

cooled to ambient temperature in He [16]. Similarly, the Co/In-

FER was prepared from In-FER sample by applying the

additional c.i.i.e. procedure to the indium form. Therefore In-

form of ferrierite was ground with cobalt acetate, calcinated in

the helium flow at 550 8C for 2 h and cooled to ambient

temperature in He (Scheme 1) [16].

The indium–, cobalt– and indium–cobalt forms of ferrierite

were prepared to give the catalysts shown in Table 1. The

amounts of Co and In were calculated in proportion to

aluminum content in a zeolite.

100%Co! 1Co2þ=2Alð�Þ !Co=Al ¼ 0:5

100%In! 1In3þ=3Alð�Þ ! In=Al ¼ 0:33

2.2. Catalysts characterization

The surface area of the samples was determined by using the

BET method (Chromosorb-1 Quantachrome) using nitrogen as

adsorbate at 77.5 K. XRD patterns were obtained with a

Siemens D5005 using Ni filtered Cu Ka radiation. XPS

analyses were performed with a SSI X-probe (SSX-100/206)

spectrometer from Surface Science Instrument working with a

monochromatic Al Ka radiation (1.0 kV, 22 mA). Charge

compensation was achieved by using an electron flood gun

adjusted at 8 eV. Energy pass for the analyzer was 50 eVand the

spot size was 1 mm in diameter, corresponding to a FWHM

(full width at half maximum) of 1.1 eV for the Au 4f7/2 band of

a gold standard.

As-prepared samples were subjected to XPS analysis. For

these experiments, O 1s, C 1s, Si 2p, Al 2p, Co 2p and In 3d

bands were recorded. For all experiments, the binding energies

were calibrated by fixing the C–(C, H) contribution of the C 1s

adventitious carbon at 284.8 eV. Peaks were considered to be

combinations of gaussian and lorentzian functions in a 85–15

ratio, working with a Shirley baseline. For the quantification of

aration procedures.

A. Kubacka et al. / Applied Catalysis B: Environmental 69 (2006) 43–48 45

Fig. 1. X-ray diffraction patterns of the ferrierite support and the In/Co-FER

bimetallic catalyst.

the elements, sensibility factors provided by the manufacturers

were used.

2.3. Catalytic tests

The catalytic tests were performed in a continuous-flow

laboratory unit consisting of a fixed bed reactor operating at

atmospheric pressure. The standard reaction conditions were:

NO = 1000 ppm, CH4 = 2000 ppm, O2 = 4%, H2O = 2500 ppm

(feed composition); He (carrier gas); T = 300–500 8C;

GHSV = 10 000 h�1. All the samples were pelletized without

a binder and the 0.2–0.5 mm fraction was used for the catalytic

tests. The analysis of NO was performed by a Photovac 10S50

gas chromatograph equipped with a photoionization detector

and a KCl-Alumina column. The other products were analyzed

by a Chrom-5 gas chromatograph. Methane, O2, N2 and CO was

analyzed using a column packed with zeolite 5A. CO2, N2O and

water were analyzed using a HayeSep R packed column. In

both cases a TCD was used as a detector. NO2 content in the

product mixture was analyzed by a colorimetric method. All the

catalytic data are related to steady-state conditions, which were

established usually after 2 h time-on-stream.

The 0.6In/0.5Co-FER catalyst has been tested in the

prolonged experiments (up to 200 h), applying either

2500 ppm of H2O (standard conditions, first 6 days), or using

2.5% of steam added to the feed (from 7th to 9th day). The

temperature inside the reactor was kept constant (425 8C)

during all the experiments. Additionally, during the 1st, 6th and

8th days of the experiment the catalyst was tested in the full

temperature range (300–500 8C).

The NO (to N2) and methane conversions were calculated

using the following equations:

XNO ¼½NO�0 � ½NO�½NO�0

� 100

XNO to N2¼ ½NO�0 � ½NO� � ½NO2� � 2½N2O�

½NO�0� 100

XCH4¼ ½CH4�0 � ½CH4�

½CH4�0� 100

where [NO]0 � NO concentration in the feed inlet; [NO] � NO

concentration in the outlet; [NO2] � NO2 concentration in the

outlet; [N2O] � N2O concentration in the outlet; [CH4]0 � CH4

concentration in the feed inlet; and [CH4] � CH4 concentration

in the outlet.

3. Results and discussion

3.1. Standard catalytic tests

The monometallic In-, Co- and bimetallic In/Co- and Co/In-

catalysts supported on ferrierite display high surface areas in all

cases and modification degrees of 60/50 for In/Co and 50/60 for

Co/In (Table 1). After modification with indium and/or cobalt

ions the prepared samples maintain the structure of the ferrierite

used as support (see Fig. 1) and show absence of dealumination

(MAS NMR; results not shown). The catalysts were obtained

by using the contact-induced ion exchange technique (a solid-

state reaction in presence of noble o reducing gases) which in

the case of In and its bimetallic catalysts has shown superior

performance with respect to traditional methods like ion

exchange, leading to the presence of InO+ species at exchange

positions [9,12]. Concerning Co, previous studies have shown

its presence mostly at ferrierite cationic positions [9]. The state

of active metal components in our catalysts will be further

discussed below on the basis of a XPS study.

The catalytic behaviour of our catalysts under the here called

‘‘standard test conditions’’ (2500 ppm of water) are illustrated

in Fig. 2. Monometallic In and Co catalysts give moderate

conversions of NO with a different thermal evolution; while In

shows decreasing level with temperature, Co shows an

improved performance when temperature increases [9,12].

More interestingly, both bimetallic catalysts have a clear

synergistic effect independently of the preparation conditions.

The sequence of contacting the support with the active metal

source does however introduce a differential behaviour

between bimetallic catalysts, particularly evident at low

temperature in Fig. 2A. While In/Co gives higher conversion

levels below 400 8C, it shows a slightly lower conversion above

450 8C. Interesting to stress is, in any case, the significant

improvement of the NO conversion obtained using the In/Co

and Co/In catalysts with respect to their metallic counterparts

from �325 8C. Additionally, the bimetallic systems also

improve the selectivity to N2, being NO2 the other product

detected (N2O below 10 ppm) and responsible for the

differences in NO (total) and NO to N2 conversions plotted

in Fig. 2A. The following graph (Fig. 2B) proves that such NO

elimination enhanced activity (with respect to monometallic

catalysts) is reached with practically no increment in the fuel

consumption, giving evidence that the selectivity of the

catalytic reduction reaction is notably enhanced.

A. Kubacka et al. / Applied Catalysis B: Environmental 69 (2006) 43–4846

Fig. 2. Comparison of the CH4-SCR NO process on the mono- and bimetallic catalysts: 0.6In-FER (*), 0.5Co-FER (^), 0.6In/0.5Co-FER (&) and 0.5Co/0.6In-

FER (~). Total conversion of NO (– – –), conversion of NO to N2 (—) (A), and conversion of CH4 (B) vs. temperature.

3.2. Prolonged catalytic test in the presence of steam

The outstanding performance of our bimetallic catalysts is

further proved by performing catalytic tests in extended periods

of time-on-stream with additional presence of 10 times higher

amount of water vapour. Fig. 3 displays the results obtained

during a 200 h run with the In/Co-FER catalyst; in the first 6

days under our standard conditions no deactivation is observed

in the selective NO conversion to N2. To confirm this, Fig. 4

shows the NO conversion in the whole temperature range

studied, without and with steam in the feed (Fig. 4A) giving

strong evidence of the stability of our system working at

10 000 h�1 (standard conditions), but also at 15 000 and

20 000 h�1 (insert in Fig. 4A). This happens again with no

penalty or even a small improvement in the fuel economy of the

SCR process (Fig. 4B). The presence of high level (2.5%) of

steam between the 7th and 9th days produces a rather moderate

decrease of NO conversion level of ca. 10% at the beginning

Fig. 3. Study of the catalyst stability vs. time-on-stream with and without steam

in the feed. The CH4-SCR NO process on the 0.6In/0.5Co-FER catalys

(T = 425 8C, GHSV = 10 000 h�1).

t

and ca. 5% at the end of the experiment (Fig. 3). In our case,

Fig. 3 additionally proves that the water effect is reversible and

likely produced by competitive adsorption of reactants [17].

When analyzed in the whole temperature range, it can be seen

that the activity drop is larger at lower temperatures (Fig. 4A),

as can be expected from literature reports [17–22]. However the

In/Co-FER sample maintains a significant activity at tempera-

tures where other In-based metallic formulations fail to do it

[18,20,22]. The presence of water leads typically to reversible,

detrimental effects in metal exchanged-zeolite systems,

affecting NO conversion particularly at low temperatures

(<450 8C) [17–22]. For Co on ferrierite, the water effect seems

however to be rather limited [11], as also is the case for the In/

Al2O3 systems [13]. These monometallic catalysts however

show the ‘‘poor’’ performance displayed in Fig. 2, giving

typical plots with limited NO conversion to N2 at low and high

temperatures and in a lot of cases poor maximum activity

values [1,2,5,6]. Figs. 3 and 4 were therefore able to provide

evidence that the bimetallic In–Co catalyst would yield high

NO conversion from low temperature (�325 8C) with a rather

efficient methane consumption (feed: 1000 ppm NO, 2000 ppm

CH4) irrespective of the dry/wet conditions.

3.3. Active metal state

The last point deserving comment is the synergistic effect

detected in the bimetallic systems. Of particular interest is the

metal order of contact with the ferrierite support, which makes

a significant impact on the low temperature behaviour; below

�325 8C (Fig. 2). This point was investigated by using XPS.

Table 2 summarizes XPS results on Co 2p, In 3d, Si 2p, Al 2p

and O 1s measurements. Si, Al and O show values as in the

ferrierite support (also included) although a small variation can

be noticed in the Al 2p peak. In 3d peak has binding energies in

the 445.5–445.8 eV interval, in between typical values for

In2O3 (444.8–445.3 eV) and In(OH)3 (445.9–446.4 eV) [23].

The above mentioned binding energies are characteristic of

ionic InO+ type species on zeolites, indicating as already

discussed, the non-aggregated state of indium in our catalysts.

Co 2p peaks display values around 780 eV for Co(III) species,

while the presence of a shake up line at higher binding energies

A. Kubacka et al. / Applied Catalysis B: Environmental 69 (2006) 43–48 47

Fig. 4. Comparison of the CH4-SCR NO process on the 0.6In/0.5Co-FER catalyst during the 1st (&) and the 6th (*) day under standard conditions (2500 ppm H2O)

and during the 8th (~) day in the presence of steam (2.5% H2O). Conversion of NO to N2 (A) and conversion of CH4 (B). Insert in (A) corresponds to a study of the

CH4-SCR NO process during the 6th day under varying space velocities.

Table 2

XPS results for the monometallic and bimetallic catalysts

Catalyst Binding energy (eV)

Co 2p In 3d Si 2p Al 2p O 1s

Main line ‘‘Shake up’’ line

H-FER – – – 102.8 74.0 532.0

0.6In-FER – – 445.8 102.8 74.3 531.9

0.5Co-FER 779.9 n.p. – 103.0 74.6 532.2

0.6In/0.5Co-FER 780.7 (88.9%) 786.1 (11.1%) 445.5 102.8 74.6 532.0

0.5Co/0.6In-FER 780.1 n.p. 445.6 102.6 74.5 532.1

The results for the H-form of ferrierite type zeolite used as support are also included. n.p., not present.

are indicative of the presence of Co(II) species [24]. This means

that Co and Co/In samples show a dominant Co(III) state while

In/Co contains Co(II) species. Note however that the intensity

of satellite line (shake up; Table 2) may in fact indicate the

presence of both Co(II) and Co(III) species. Exchanged or

isolated Co2+ are believed to provide active and selective

species, oxidized in contact to NO-containing mixtures, while

aggregated, oxide species and particularly Co3O4 are con-

sidered active for HC oxidation but not for the SCR due to their

relative redox inertness [5,25].

Promotion of In CH4-SCR activity by oxidic Ir [18,19], Fe

[20] and Ce [21,22] species has been previously reported. In

presence of water vapor the bimetallic synergistic effect is

however mostly observed at temperatures above 450 8C [18–

22]. In our case, Figs. 2 and 4 give evidence that such promotion

effect is obtained above 300 8C and that water presence does

not greatly influence the behaviour of the In/Co catalyst. Ir, Fe

and Ce oxides main role in the reaction mechanism is to provide

a sufficient NO2 supply (on the basis of NO oxidation) to In

species [18–22]. This appears capital in the presence of water

and here is achieved by presence of Co(II) species. It may thus

appear that NO oxidation on Co(II) containing oxide phases

competes favorably with water adsorption in a redox-type

process which may enhance NO and/or O2 activation giving

negatively charged species and (formally) Co(III) species. NO2

production and desorption may revert cobalt to the Co(II)

oxidation state allowing complection of the catalytic cycle.

4. Conclusions

To conclude, in this paper has been described a binary In–Co

catalyst highly active in the CH4-SCR NO reduction in a wide

temperature interval of ca. 180 8C (325–500 8C) in almost dry

as well as wet conditions. The highly active systems seem to be

composed of ionic InO+ and Co(II) species, although Co(III)

can also give a synergistic effect with the InO+ type species for

temperatures above 375 8C. The study suggests that a redox-

type Co promotioned effect on NO oxidation may be

responsible of the synergistic bimetallic effect. A forthcoming

structural study will be devoted to further analyze the physico-

chemical basis underlying this catalytic effect.

Acknowledgements

We are grateful to the Ministry of Education and Science,

Warsaw, Poland, for financial support (project no. PBZ-KBN-

116/T09/2004). We also thank Dr. Fabrice Bertinchamps (Unite

de Catalyse et chimie des materiaux divises-UCL, Louvain-la-

Neuve, Belgium) for XPS measurements and Dr. Ewa Wloch

for the help in the catalyst preparation.

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