Applied Catalysis B: Environmental 30 (2001) 163–172
Effect of the silver loading and some other experimental
parameters on the selective reduction of NO with
C
3
H
6
over Al
2
O
3
and ZrO
2
-based catalysts
F.C. Meunier
a,∗
, R. Ukropec
b
, C. Stapleton
b
, J.R.H. Ross
b,1
a
Institut für Technische Chemie-2, Technische Universität München, Lichtenbergstrasse 4, D-85747 Garching, Germany
b
Centre for Environmental Research, University of Limerick, Limerick, Ireland
Received 26 March 2000; received in revised form 21 August 2000; accepted 3 September 2000
Abstract
The present work reports data on the activity of silver, alumina and zirconia based-catalysts for the C
3
H
6
-SCR of NO.
The optimum silver loading for Ag/-Al
2
O
3
catalysts for the C
3
H
6
-SCR of NO was about 8.7 × 10
−5
g
silver
m
−2
alumina
, which
gave the best compromise between a higher activity at low temperatures (favoured on high loading materials) and a high
selectivity to N
2
(favoured on low loading materials). The effect of the residence time was also investigated on a 1.2wt.%
Ag/-Al
2
O
3
. The use of low space velocities enabled to obtain high conversion to N
2
at low temperatures and significantly
reduced the amount of propene wasted by unselective combustion. The resistance of Ag, Ni, Co and In/-Al
2
O
3
catalysts
to ex situ exposure to 100 ppm of SO
2
was studied. The silver sample was the most inhibited by SO
2
whereas the other
samples were deactivated to a lower extent and showed partial regeneration with time on SO
2
-free stream. The effect of a
large concentration of water on the activity of these materials was investigated. All these catalysts showed a significant loss
of activity in the presence of 12% water but this inhibition was fully reversible. Interestingly, the activity of the silver sample
appeared to increase with time on wet stream. The activity of zirconia-based materials for the C
3
H
6
-SCR of NO was compared
to that of alumina and zeolite-based catalysts. Silver-promoted ZrO
2
catalysts were active at lower temperatures but displayed
greater selectivities to N
2
O than that of the alumina-based samples. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Silver; Alumina; Zirconia; NO reduction; Propene; Loading; SO
2
; Water
1. Introduction
The selective catalytic reduction of NO
x
by hydro-
carbons (HC-SCR) has received much attention as
a possible means of controlling the emissions from
stationary sources (for example, to replace for the
∗
Corresponding author. Present address: School of Chemistry,
David Keir Building, The Queen’s University of Belfast, Belfast
BT9 5AG, UK. Tel.: +44-28-9027-4420; fax: +44-28-9038-2117.
E-mail address: f.meunier@qub.ac.uk (F.C. Meunier).
1
Co-corresponding author. Fax: +353-61-202602.
ammonia-SCR process) and from vehicles of which
the engine operates in oxygen-rich conditions (e.g.
diesel and lean-burn engine). The utilisation of
methane is of particular interest for power plant ap-
plications as it is usually available on site. Catalysts
such as Co/ZSM-5 and Ga/ZSM-5 have been demon-
strated to be effective for the CH
4
-SCR of NO at
reasonable temperatures [1], ca. 400
◦
C. However, the
hydrothermal resistance of most zeolitic materials
is unsatisfactory at the higher temperatures for rea-
sons that still remain unclear but which are likely to
be associated with the zeolite [2]. Recent results by
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