Catalysis Today 230 (2014) 61–66
Contents lists available at ScienceDirect
Catalysis Today
j our na l ho me page: www.elsevier.com/locate/cattod
Photocatalytic and photochemical decomposition of N
2
O on ZnS-MMT
catalyst
L. Obalová
∗
, M.
ˇ
Sihor, P. Praus, M. Reli, K. Koˇ cí
V
ˇ
SB – Technical University of Ostrava, 17 listopadu 15, Ostrava, Czech Republic
a r t i c l e i n f o
Article history:
Received 11 July 2013
Received in revised form
16 September 2013
Accepted 25 September 2013
Available online 23 October 2013
Keywords:
N2O
Photocatalysis
Photolysis
Decomposition
ZnS
Montmorillonite
a b s t r a c t
ZnS nanoparticles stabilized by cetyltrimethylammonium bromide were deposited on montmorillonite
forming the ZnS-MMT nanocomposite. The nanocomposite was characterized by UV–vis DRS, SEM-EDAX,
FTIR, XRD and nitrogen physisorption and tested for N
2
O photocatalytic decomposition in an annular
batch reactor illuminated with an 8 W Hg lamp (254 nm wavelength). Photolysis of N
2
O was tested at
the same conditions.
The N
2
O conversion in inert gas was 79% after 24 h of illumination and was attributed to the simul-
taneous N
2
O photocatalytic and photochemical decomposition. The presence of water vapor inhibited
photocatalytic reaction pathway while N
2
O photolysis was improved. Photocatalytic performance was
higher with catalyst in fluidized bed than in fixed bed. The reason is that both mass and photon transfer
to the photocatalyst was maximized. Better results were obtained with Zn-MMT compared to Evonic P25
catalyst.
© 2013 Elsevier B.V. All rights reserved.
1. Introduction
Nitrous oxide (N
2
O) is a compound that during the last decade
has been recognized as a contributor to the destruction of the
ozone in the stratosphere and acknowledged as a relatively strong
greenhouse gas. The continuous increase of its concentration, both
due to natural and anthropogenic sources (use of synthetic fer-
tilizers, adipic acid production, nitric acid production, fossil fuels
and biomass burning) and long atmospheric residence time (150
years), entails the need of developing efficient method for its abate-
ment. N
2
O decomposition into nitrogen and oxygen offers simple
solution for its conversion to natural components of air. The ther-
mal catalytic decomposition of N
2
O requires temperatures higher
then approximately 200
◦
C, because the produced molecular oxy-
gen is tightly bound to the catalyst surfaces at temperatures lower
than 200
◦
C [1]. Thermal catalytic N
2
O catalytic decomposition has
been extensively investigated during last decades and nowadays,
first large scale installations are tested e.g. for N
2
O abatement from
HNO
3
plants [2]. However, catalysts often suffer from oxygen, water
vapor or NO
x
inhibition, deactivation or low selectivity. Therefore,
a need for further research in this area still exists.
Relatively little attention has been paid to the N
2
O decom-
position initialized by UV light. Both photochemical [3–5] and
∗
Corresponding author. Tel.: +420 596991532.
E-mail address: lucie.obalova@vsb.cz (L. Obalová).
photocatalytic decomposition [6] have been reported. While ther-
mal catalytic decomposition of N
2
O is suitable mainly for N
2
O
abatement from waste gases from industry and combustion, N
2
O
photoinduced decomposition might help to reduce its concentra-
tion also in indoor and outdoor environments [6]. Compared to
N
2
O thermal catalytic decomposition, photoinduced reactions are
suitable for treatment of low-concentration gases and have some
advantages: the reaction proceeds at ambient temperature, and if
sunlight was utilized, it would lead to energy savings.
N
2
O photocatalytic decomposition (Eq. (1)) under wavelength
higher than 254 nm has been reported on Cu and Ag ion-
exchanged powder zeolite [8,9], Cu
I
ion anchored on various oxides
(SiO
2
·Al
2
O
3
, Al
2
O
3
, SiO
2
) [10,11], un-modified TiO
2
[10] or TiO
2
doped by Pt [12] and Ag [13–16]. Trapping of the photoformed elec-
tron by the N
2
O molecule to form N
2
O-ion is believed to be key
process in N
2
O photocatalytic decomposition over semiconductor
catalysts [7].
N
2
O
h,catalyst
-------→N
2
+
1
2
O
2
(1)
It is important to mention, that although N
2
O photolysis is
known process, none of the above cited papers dealing with N
2
O
photocatalytic decomposition (including our previous papers) took
it into account or distinguished between N
2
O conversion caused by
photolysis and photocatalysis.
Photocatalysts for N
2
O decomposition were typically tested as
a powdered material which was simply placed on the bottom of
the reactor [13,17], spread on adhesive tape [14] or immobilized in
0920-5861/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.cattod.2013.09.047