Applied
Catalysis
B:
Environmental
121–
122 (2012) 162–
170
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at
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Applied
Catalysis
B:
Environmental
jo
u
r
n
al
hom
ep
age:
www.elsevier.com/locate/apcatb
Activity,
selectivity
and
stability
of
praseodymium-doped
CeO
2
for
chlorinated
VOCs
catalytic
combustion
B.
de
Rivas
a
,
N.
Guillén-Hurtado
b
,
R.
López-Fonseca
a
,
F.
Coloma-Pascual
b
,
A.
García-García
b
,
J.I.
Gutiérrez-Ortiz
a
,
A.
Bueno-López
b,∗
a
Department
of
Chemical
Engineering,
Faculty
of
Science
and
Technology,
University
of
the
Basque
Country,
PO
Box
644,
E-48080
Bilbao,
Spain
b
Department
of
Inorganic
Chemistry,
University
of
Alicante,
Campus
Sant
Vicent
s/n,
PO
Box
99,
E-03080
Alicante,
Spain
a
r
t
i
c
l
e
i
n
f
o
Article
history:
Received
28
January
2012
Received
in
revised
form
24
March
2012
Accepted
27
March
2012
Available online 4 April 2012
Keywords:
Chlorinated
VOC
combustion
1,2-Dichloroethane
Ce
x
Pr
1−x
O
2
Cerium–praseodymium
mixed
oxide
a
b
s
t
r
a
c
t
Ce–Pr
mixed
oxides,
namely
Ce
0.8
Pr
0.2
O
2
,
Ce
0.5
Pr
0.5
O
2
and
Ce
0.2
Pr
0.8
O
2
,
were
prepared
by
conventional
coprecipitation
and
evaluated
for
the
catalytic
combustion
of
1,2-dichloroethane,
which
was
selected
as
a
model
reaction
for
chlorinated
VOC
abatement.
For
comparison
purposes,
the
pure
oxides
were
also
prepared
and
catalytically
tested.
A
certain
decrease
in
catalytic
activity
was
observed
after
three
consec-
utive
temperatures
cycles
from
150
to
500
◦
C
for
all
catalysts,
except
for
Ce
0.5
Pr
0.5
O
2
.
This
deactivation
was
particularly
noticeable
for
pure
praseodymia
and
Ce
0.2
Pr
0.8
O
2
,
while
Ce
0.8
Pr
0.2
O
2
and
Ce
0.5
Pr
0.5
O
2
exhib-
ited
a
superior
stability.
The
catalysts
deactivation
was
attributed
to
bulk
and/or
surface
chlorination,
as
revealed
by
X-ray
diffraction,
Raman
spectroscopy
and
X-ray
photoelectron
spectroscopy.
Interestingly,
the
Ce
0.5
Pr
0.5
O
2
mixed
oxide,
which
converted
the
chlorinated
feed
at
the
lowest
temperature
due
to
its
substantial
resistance
to
chlorination,
showed
a
constant
activity
in
a
115
h
lifetime
test
at
335
◦
C.
© 2012 Elsevier B.V. All rights reserved.
1.
Introduction
The
release
of
volatile
organic
compounds
(VOCs)
to
the
atmo-
sphere
results
in
tangible
environmental
damage.
These
pollutants
can
contribute
to
atmospheric
processes
which
can
have
detri-
mental
effects
on
human
health.
For
example,
VOCs
have
been
implicated
in
the
formation
of
ground
level
ozone,
ozone
deple-
tion
and
they
often
act
as
greenhouse
gases.
In
September
2005,
the
Commission
of
the
European
Communities
in
the
Framework
of
the
“Clean
Air
for
Europe”
(CAFE)
Programme
published
its
Thematic
Strategy
on
Air
Pollution
[1].
This
strategy
sets
health
and
envi-
ronmental
objectives
and
emission
reduction
targets
for
the
main
pollutants.
More
specifically,
its
aim
is
to
cut
the
annual
number
of
premature
deaths
caused
by
air
pollution
by
40%
in
2020,
with
regard
to
the
2000
level,
and
to
reduce
the
continuing
damage
of
the
Europe’s
ecosystems.
To
achieve
these
objectives,
emissions
of
sulphur
dioxide
must
be
reduced
by
82%,
nitrogen
oxides
by
60%,
volatile
organic
compounds
by
51%,
ammonia
by
27%
and
fine
particulate
matter
by
59%.
A
number
of
VOCs
with
different
chemical
composition
are
emitted
by
different
sources
(off-gases
from
chemical
plants,
groundwater
decontamination
by
air
stripping,
odour
emission
∗
Corresponding
author
at:
Inorganic
Chemistry
Department,
University
of
Ali-
cante,
Ap.
99,
E03080,
Alicante,
Spain.
Tel.:
+34
600948665;
fax:
+34
965903454.
E-mail
address:
agus@ua.es
(A.
Bueno-López).
control,
and
contaminated
air
in
solvent
evaporation
processes).
Chlorohydrocarbons
are
among
the
most
difficult
to
abate
by
catalytic
combustion.
Chlorinated
compounds
require
special
attention
due
to
their
toxicity,
high
stability
and
widespread
appli-
cation
in
industry
[2].
Consequently,
to
develop
efficient
catalysts
for
low-temperature
complete
destruction
of
chlorinated
VOCs
is
a
challenging
task
of
ongoing
interest
[3].
As
an
alternative
to
noble
metals
and
transition
metal
oxides,
cerium-based
oxides
are
promising
catalysts
[4–6].
Ceria-based
materials
are
able
to
undergo
a
rapid
and
reversible
Ce
4+
/Ce
3+
redox
cycles
at
moder-
ate
temperatures
due
to
the
high
oxide-ion
mobility
in
the
solid
state
from
surface
to
bulk
and
vice
versa.
In
many
cases,
the
redox
properties
and
chemical
activity
of
pure
ceria
could
be
enhanced
by
introducing
dopant
cations
into
the
oxide
lattice.
In
this
sense,
con-
siderable
attention
has
been
paid
to
incorporate
variable
valence
ions
into
the
ceria
lattice
to
recognise
their
role
on
defect
chem-
istry.
The
oxygen
atoms/vacancies
attached
to
reducible
elements
are
mobile,
which
could
contribute
to
the
oxygen
storage/release
capability
of
mixed
oxides
[7].
Among
the
reducible
elements,
praseodymium
is
particularly
suitable
to
obtain
solid
solutions
with
ceria.
The
structure
of
Pr
6
O
11
is
fluorite
type,
and
the
ionic
radius
of
Pr
4+
(0.096
nm)
is
close
to
that
of
Ce
4+
(0.097
nm).
In
the
mixed
oxide,
it
can
form
mixed
oxidation
states
with
both
Pr
3+
and
Pr
4+
cations.
Further,
in
ceria–praseodymia
solid
solutions,
both
ele-
ments
can
adopt
3+
and
4+
oxidation
states,
and
the
anion
vacancies
are
much
mobile
in
this
system
[8].
In
summary,
the
insertion
of
praseodymium
within
the
fluorite
host
lattice
of
CeO
2
provides
new
0926-3373/$
–
see
front
matter ©
2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.apcatb.2012.03.029