Applied Catalysis B: Environmental 187 (2016) 259–268
Contents lists available at ScienceDirect
Applied Catalysis B: Environmental
j ourna l h om epage: www.elsevier.com/locate/apcatb
N
2
O decomposition over ceria-promoted Ir/Al
2
O
3
catalysts: The role
of ceria
E. Pachatouridou
a,b
, E. Papista
c
, A. Delimitis
b
, M.A. Vasiliades
d
, A.M. Efstathiou
d,∗
,
M.D. Amiridis
e
, O.S. Alexeev
f
, D. Bloom
g
, G.E. Marnellos
b,c
, M. Konsolakis
a,∗
,
E. Iliopoulou
b,∗
a
School of Production Engineering and Management, Technical University of Crete, GR-73100 Chania, Crete, Greece
b
Chemical Process & Energy Resources Institute (CPERI), Centre for Research & Technology Hellas (CERTH), 6th km. Charilaou—Thermi Rd., P.O. Box 60361,
GR-57001, Thermi, Thessaloniki, Greece
c
Department of Mechanical Engineering, University of Western Macedonia, Bakola & Sialvera, GR-50100, Kozani, Greece
d
Heterogeneous Catalysis Laboratory, Department of Chemistry, University of Cyprus, P.O. Box 20537, 1678 Nicosia, Cyprus
e
University of Illinois at Chicago, IL, 60607 Chicago, USA
f
Department of Chemical Engineering, University of South Carolina, SC, 29208 Columbia, USA
g
Electron Microscopy Center, University of South Carolina, SC, 29208 Columbia, USA
a r t i c l e i n f o
Article history:
Received 13 October 2015
Received in revised form 14 January 2016
Accepted 20 January 2016
Available online 22 January 2016
Keywords:
N2O decomposition
Ir/Al2O3 catalysts
Ceria promotion
HAADF-STEM/EELS
CO-DRIFTS
a b s t r a c t
The impact of CeO
2
in the Al
2
O
3
-20 wt% CeO
2
support prepared by the co-precipitation method on the Ir
particle size, morphology and oxidation state, and in turn on the deN
2
O catalytic activity (1000 ppm N
2
O)
of supported Ir catalysts were investigated in the absence and presence of excess O
2
(2 vol%) conditions.
It was demonstrated that the deN
2
O activity of Ir/Al
2
O
3
is notably suppressed by the presence of oxygen
in the feed stream, namely, the N
2
O conversion at 600
◦
C is declined to 65% in the presence of oxygen
as compared to 100% in the absence of oxygen. A similar detrimental catalytic effect was also observed
for the Ir/CeO
2
solid. On the contrary, the deN
2
O performance of CeO
2
-modified Ir/Al
2
O
3
catalyst is only
slightly affected by the presence of oxygen. An extensive characterization study involving surface texture
analysis (N
2
adsorption-desorption at −196
◦
C), temperature-programmed reduction in H
2
(H
2
-TPR), X-
ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), scanning transmission
electron microscopy (STEM), electron energy loss spectroscopy (EELS) and diffuse reflectance infrared
Fourier transform spectroscopy of CO adsorption and desorption (CO-DRIFTS) was carried out to gain
insight into the origin of the CeO
2
-induced promotional effect. The characterization results revealed the
existence of IrO
2
phase (H
2
-TPR, XRD, HRTEM, EELS and CO-DRIFTS) as well as of very small isolated
particles of Ir on the Al
2
O
3
, CeO
2
and CeO
2
-Al
2
O
3
supports (STEM) but to a notably different extent. The
coexistence of large IrO
2
particles of perfect crystallite structure and very small Ir particles located at the
Ir-ceria interface was revealed only in Ir/AlCe. The establishment of a certain Ir
+
/Ir
0
ratio and oxygen
vacant sites (V
O
) concentration in ceria around very small Ir particles under oxidative reaction conditions
seem to largely promote N
2
O adsorption and subsequent decomposition into N
2
and O
2
over the CeO
2
-
promoted Ir/Al catalyst. In the case of Ir/Al, a different deN
2
O decomposition mechanism occurs, where
the site reactivity of Ir
+
/Ir
0
established under oxidizing conditions is reduced significantly.
© 2016 Elsevier B.V. All rights reserved.
1. Introduction
Nitrous oxide (N
2
O) has long been considered as a relatively
harmless substance. However, during the last years a growing con-
∗
Corresponding authors.
E-mail addresses: efstath@ucy.ac.cy (A.M. Efstathiou), mkonsol@science.tuc.gr
(M. Konsolakis), eh@cperi.certh.gr (E. Iliopoulou).
URL: http://www.tuc.gr/konsolakis.html (M. Konsolakis).
cern has been developed focusing on its abatement, since N
2
O has
been recognized as a powerful greenhouse gas with a long lifetime
(∼150 years in the atmosphere) and a Global Warming Potential
(GWP) of ∼300 times higher than that of CO
2
[1,2]. Furthermore,
it has been well established that nitrous oxide participates in the
chemical cycle leading to the destruction of ozone layer [1–4].
Due to the negative effects of N
2
O on the global environment,
its emissions control from anthropogenic sources, such as the com-
bustion of fossil fuels and biomass in stationary and transport
applications, and the nitric and adipic acid chemical production,
http://dx.doi.org/10.1016/j.apcatb.2016.01.049
0926-3373/© 2016 Elsevier B.V. All rights reserved.