A highly distributed CuxAuy-deposited nanotube carbon for selective reduction of NO in the presence of NH3 at very low temperature

Article abstract of DOI:10.1002/cctc.201300777

Cu_xAu_y Deposited on carbon nanotubes prepared by solution plasma sputtering was used for first time as a catalyst for selective reduction of NO, in the presence of NH₃, at low temperature. N ₂ and H₂O are desirable during the NO reduction process; however, N₂O is totally absent from the obtained products. Copyright

Full text of DOI:10.1002/cctc.201300777

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DOI: 10.1002/cctc.201300777
A Highly Distributed Cu Au -Deposited Nanotube Carbon
x
y
for Selective Reduction of NO in the Presence of NH at
3
Very Low Temperature
Rachid Amrousse* and Said El Moumni
[a]
[b]
Cu Au Deposited on carbon nanotubes prepared by solution
higher activities in SCR of NO with NH , H , CO, and hydrocar-
3 2
x
y
plasma sputtering was used for first time as a catalyst for selec-
bons.
tive reduction of NO, in the presence of NH , at low tempera-
The aim of this work is to study SCR of NO with NH over
3
3
ture. N and H O are desirable during the NO reduction pro-
novel Cu Au /CNTs catalysts synthesized by solution plasma
2
2
x
y
cess; however, N O is totally absent from the obtained prod-
sputtering (SPS) process and the detailed preparation condi-
tions and characterization results are given in the Supporting
Information.
2
ucts.
Moreover, the measurements of the SCR activity were per-
[15]
Selective catalytic reduction (SCR) is considered to be the most
formed in a self-designed SCR reactor.
Four gas steams,
efficient technology for reducing NO emissions from station-
700 ppm of NO, 4% of O and 10% of H O steam and with He
x
2
2
ary sources. The reaction can be achieved efficiently by con-
in balance were used to simulate the flue gas. Mass flow con-
troller was used to control NO, and gas rotameters were used
to control the stream of NH and O . In all the runs, the total
[
1]
ventional catalysts such as V O -WO /TiO [Eq. (1)]:
2
5
3
2
3
2
ꢀ
1
2
NO þ 2 NH þ 1=2 O ! 2 N þ 3 H O
ð1Þ
3
2
2
2
gas flow rate was maintained at 300 mLmin over 1 g of cata-
ꢀ3
ꢀ1
lyst to adjust W/F as 3.2ꢀ10 g/(mLmin ), where W denotes
the weight of catalyst and F denotes the flue of the feed
gases. The feed gases were mixed in a chamber and then pre-
heated before entering the reactor. Catalytic activity data was
collected at low temperature range of about 30–658C. The NO
concentrations at the inlet and outlet of the reactor were
monitored by using an on-line Flue Gas Analyzer KM900
equipped with NO sensor. To avoid the effect of the adsorption
characters, the catalysts were purged with reaction gas for 2 h
at first.
The most effective reaction temperature for this process is
[
2,3]
known to be in the range of 300–4008C.
However, many
studies have been performed to develop new low temperature
SCR catalysts that can work well around 2508C or even below.
In this case the SCR unit could be placed behind the electric
precipitation and desulfurizer in a power plant to efficiently
remove NO over a wider temperature range and for NO con-
x
x
[
4]
trol in diesel engines. According to our literature overview,
[
5]
many catalysts, e.g., modified carbon fibers and metal-acti-
[
6]
vated carbon, have been tested for the SCR of NO at low
temperatures (<2508C), however, such catalysts exhibited
lower catalytic activity for a commercial process. On the other
hand, catalysts containing transition metals such as Mn, V, Fe,
Here we report a rare example of SCR of NO using Cu Au /
x
y
CNTs catalysts. Figure 1 shows the catalytic activities of Cu Au /
x
y
[
7–10]
and Rh-Sn
exhibited good low-temperature SCR activity.
Among them, the nano-MnO catalyst has been studied exten-
x
sively, as it contains various types of labile oxygen species re-
[
4,11]
quired for low-temperature SCR.
Several accounts have
been reported for the SCR of NO conversion; Cu/CeO , Cu-Fe
2
[
12–14]
and Au/MgO, Au/SiO , and Au/Al O
3
catalysts display
2
2
[a] Dr. R. Amrousse
Japan Aerospace Exploration Agency (JAXA)
Chemical Engineering
3
-1-1 Yoshinodai Chuo-ku, Sagamihara 252-5210 Kanagawa (Japan)
Fax: (+81)42-759-8284
E-mail: rachid.amrousse@jaxa.jp
rachid.amrousse@yahoo.fr
[b] S. E. Moumni
University of Chouaib Doukkali
Department of Chemistry
2
4000 El Jadida (Morocco)
Figure 1. Catalytic activity of Cu
x y
Au /CNTs catalysts calcined at different tem-
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201300777.
peratures. Reaction conditions: 700 ppm of NO, 750 ppm of NH
3
, 4% of O
2
ꢀ3
ꢀ1
and 10% of H
2
O steam, He to balance, W/F=3.2ꢀ10 g/(mLmin ).
ꢁ
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CNTs catalysts calcined at different temperatures. As expected,
Cu Au /CNTs catalyst calcined at 4608C catalyst displays
x
y
a much higher activity than that calcined at 420 and 5008C. In
fact, the Cu Au /CNTs (4608C) catalyst achieved totally NO con-
x
y
version to 100% at very low temperature range 30–658C. The
NO conversion on Cu Au /CNTs catalysts decreased in the
x
y
order: Cu Au /CNTs (4608C)>Cu Au /CNTs (4208C)>Cu Au /
x
y
x
y
x
y
CNTs (5008C). Based on our literature overview, when copper
and gold salt precursors were calcined at different tempera-
tures, the main states of both noble metals were Au, Cu, and
CuO, whereas for the samples calcined at 4608C, the main
[
16]
states would appear to be Cu and Au.
To further investigate the effect of Cu/Au mass contents on
NO conversion, seven different loadings of copper and gold
have been prepared on Cu Au /CNTs catalysts and calcined at
x
y
4608C. These catalysts have the same total mass content of
1
%. The NO conversion as a function of temperature, in the
range of 30–658C, is shown in Figure 2 over different mass
Figure 3. Effect of initial NH
3
concentration on the catalytic performance on
Cu0.2Au0.8/CNTs catalyst calcined at 4608C. Reaction conditions: T=658C,
7
00 ppm of NO, 4% of O
2
and 10% of H
2
O steam, He to balance,
ꢀ
3
ꢀ1
W/F=3.2ꢀ10 g/(mLmin ).
of SCR of NO with NH , NH in excess should be treated to
3
3
[19,20]
avoid secondary pollution.
Figure 4 shows the effects of initial NO concentration on the
NO conversion. There is a lesser effect of initial NO concentra-
tion on the NO conversion. With initial NO concentration be-
Figure 2. Catalytic activity of Cu
mass contents. Reaction conditions: 700 ppm of NO, 750 ppm of NH
O and 10% of H O steam, He to balance, W/F=3.2ꢀ10 g/(mLmin ).
2 2
x
Au
y
/CNTs catalysts with different Cu and Au
, 4% of
3
ꢀ1
ꢀ
3
contents of Cu Au /CNTs catalysts. Among these catalysts,
x
y
Cu Au /CNTs (4608C) catalyst shows the highest NO conver-
0.2
0.8
sion of 100% at 658C and it was the most suitable for this ap-
plication. Then, the Cu/CNTs catalyst is more active at low tem-
perature but less selective in comparison with Au/CNTs cata-
lyst, which exhibits a lower activity at low temperature, but
which is more selective at high temperature. The catalytic ac-
Figure 4. Effect of NO concentration on the catalytic performance on
Cu0.2Au0.8/CNTs catalyst calcined at 4608C. Reaction conditions: T=658C,
750 ppm of NH and He to balance, W/F=3.2ꢀ10 g/(mLmin ).
3
tivity of Cu Au /CNTs catalysts was much higher than those re-
x
y
[
4,7–9,17,18]
ꢀ3
ꢀ1
ported in literature overview,
such as catalysts contain-
ing transitional metal: Fe, V, Cr, Cu, Co, and Mn.
The effect of the initial NH concentration on the NO conver-
3
sion is shown in Figure 3. The NO conversion increased with
the NH concentration. When the initial NH concentration was
tween 600 and 800 ppm, NO conversion remained constant at
100%. With the initial NO concentration of 400 ppm, the SCR
of NO attained more than 97% conversion of NO. Moreover, it
3
3
400 ppm, the SCR of NO attained 96% conversion of NO. The
NO conversion tended to be a constant value with further in-
was previously reported that O presents significant effect on
2
crease of NH concentration. Therefore, in practical application
SCR performance. Indeed, the effect of O concentration on
3
2
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Figure 5. Effect of O
Cu0.2Au0.8/CNTs catalyst calcined at 4608C. Reaction conditions: T=658C,
00 ppm of NO, 750 ppm of NH and 10% of H O steam, He to balance,
2
concentration on the catalytic performance on
x y
Figure 7. Long-term durability test of catalytic activity of Cu Au /CNTs for
SCR of NO.
7
3
2
ꢀ
3
ꢀ1
W/F=3.2ꢀ10 g/(mLmin ).
slightly decreased (about 4%), after ten tests, from 100 to
9
6%, demonstrating a good re-startability of Cu Au /CNTs cata-
x y
the NO conversion has been performed and is shown in
Figure 5.
lysts at 30–658C temperature range.
As shown in Figure 7, the NO conversion was very slightly
decreases from its original level 100% to 98.08% after 10 h of
NO conversion, but the NO conversion almost stabilizes. When
the catalyst was heated for 2 h at 5008C in Ar, the activity
quickly restores to its initial level. This indicates that the
Cu Au /CNTs catalyst is resistant to water vapor. The decreased
When the O concentration was less than 4%, the NO con-
2
version increased; however, NO conversion decreased slightly
when O concentration was above 4%. This can be explained
2
by the oxidation of NH to NO. With the O concentration of 2,
3
2
4
9
, 7, and 10%, the NO conversion reached 92, 100, 97, and
x
y
[
21]
4%, respectively. Gongshin et al. also found a similar obser-
activity in the process is mainly caused by the competing ad-
vation that the NO conversion increased sharply when a low
sorption of H O and reaction gases on the catalyst.
2
O concentration (less than 4%) was introduced to the initial
2
The carbon nanotubes and Cu Au /CNTs catalysts were also
x
y
reactants in SCR evaluation.
characterized by scanning electron microscopy (SEM) and
transmission electron microscopy (TEM). The obtained results
were presented in the Supporting Information.
For SCR of NO conversion, re-startability is another key pa-
rameter to be considered. Figure 6 shows that the activity
In conclusion, the current study reveals that novel highly dis-
tributed Cu Au /CNTs catalysts can act as encouraging catalysts
x
y
for very low temperature for SCR of NO and it is also resistant
to water vapor.
Acknowledgements
Dr. Rachid Amrousse would like to thank Japan Aerospace Explo-
ration Agency (JAXA) especially Department of Space Flight Sys-
tems for the financial support for this research work.
Keywords: copper · gold · low temperature · NO · nanotubes ·
reduction · solution plasma sputtering
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Received: September 16, 2013
Published online on November 15, 2013
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