Applied Catalysis B: Environmental 31 (2001) 133–143
Catalytic conversion of CO, NO and SO
2
on supported sulfide catalysts
II. Catalytic reduction of NO and SO
2
by CO
S.-X. Zhuang
1
, M. Yamazaki, K. Omata, Y. Takahashi, M. Yamada
∗
Department of Applied Chemistry, Graduate School of Engineering, Tohoku University, 07 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan
Received 29 February 2000; received in revised form 7 November 2000; accepted 7 November 2000
Abstract
To investigate the possibility of simultaneous catalytic reduction of NO and SO
2
by CO, reactions of NO, NO–CO, and
NO–SO
2
–CO were performed on
␥
-alumina-supported sulfides of transition metals including Co, Mo, CoMo and FeMo.
NO was decomposed into N
2
O and N
2
accompanied with the formation of SO
2
; this serious oxidation of lattice sulfur
resulted in the deactivation of the catalysts. The addition of CO to the NO stream suppressed SO
2
formation and yielded
COS instead. A stoichiometric conversion of NO and CO to N
2
and CO
2
was observed above 350
◦
C on the CoMo and the
FeMo catalysts. Although the CO addition lengthened catalyst life, it was not enough to maintain activity. After the NO–CO
reaction, an XPS analysis showed the growth of Mo
6+
and SO
4
2−
peaks, especially for the sulfided FeMo/Al
2
O
3
; the FeMo
catalyst underwent strong oxidation in the NO–CO reaction. The NO and the NO–CO reactions proceeded non-catalytically,
consuming catalyst lattice sulfur to yield SO
2
or COS.
The addition of SO
2
in the NO–CO system enabled in situ regeneration of the catalysts; the catalysts oxidized through
abstraction of lattice sulfur experienced anew reduction and sulfurization through the SO
2
–CO reaction at higher temperature.
NO and SO
2
were completely and catalytically converted at 400
◦
C on the sulfided CoMo/Al
2
O
3
. By contrast, the sulfided
FeMo/Al
2
O
3
was easily oxidized by NO and hardly re-sulfided under the test conditions.
Oxidation states of the metals before and after the reactions were determined. Silica and titania-supported CoMo catalysts
were also evaluated to study support effects. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: NO; SO
2
; CO; Catalytic reduction; Sulfide catalysts; Cobalt molybdenum catalyst
1. Introduction
In a previous paper [1], we have reported a com-
plete catalytic reduction of SO
2
by CO on a sulfided
CoMo/␥-Al
2
O
3
. In the SO
2
–CO reaction, a carbonyl
∗
Corresponding author. Tel.: +81-22-217-7214;
fax: +81-22-217-7293.
E-mail address: yamada@erec.che.tohoku.ac.jp (M. Yamada).
1
Present address: Department of Chemical Physics, University
of Science and Technology of China, Hefei, Anhui 230026, PR
China.
sulfide (COS) intermediate produced by abstraction
of catalyst lattice sulfur works as stronger reductant
than CO. Although the catalyst seems to be tem-
porarily oxidized and lose its activity through the
COS-forming reaction, it is assumed that the oxidized
catalyst is in situ regenerated by elemental sulfur
produced by the COS–SO
2
reaction. The nature of
catalyst metal–sulfur bond therefore strongly influ-
ences catalytic performances of sulfide catalysts in the
SO
2
–CO reaction. Sulfided CoMo/Al
2
O
3
catalysts, a
well-known HDS catalyst, have the CoMoS structure
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