Low-temperature water-gas shift reaction on Au/CeO
2
catalysts – the
influence of catalyst pre-treatment on the activity and deactivation
in idealized reformate
A. Karpenko,
a
Y. Denkwitz,
a
V. Plzak,
b
J. Cai,
a
R. Leppelt,
a
B. Schumacher,
a
and R. J. Behm
a,
*
a
Institute of Surface Chemistry and Catalysis, Ulm University, D-89069 Ulm, Germany
b
Centre for Solar Energy and Hydrogen Research, Helmholtzstr. 8, D-89081 Ulm, Germany
Received 27 March 2007; accepted 31 March 2007
The effect of the pre-treatment temperature and atmosphere on the surface composition and on the activity and stability of well
defined Au/CeO
2
catalysts in the low-temperature water-gas shift reaction in dilute water gas was investigated by X-ray
photoelectron spectroscopy, kinetic measurements and in-situ IR spectroscopic (DRIFTS) measurements, comparing different
reductive and oxidative conditioning procedures. Reductive conditioning at 200 °C yields the most active catalyst. Physical origin
and consequences of the resulting differences in the reaction behavior are discussed.
KEY WORDS: water-gas shift reaction; Au catalyst; catalyst conditioning; deactivation; Au/CeO
2
; GC; DRIFTS; XPS.
1. Introduction
In the recent decades oxide supported gold catalysts
have attracted increasing interest as highly active cata-
lysts for a number of oxidation and reduction reactions,
including also the water-gas shift (WGS) reaction [1–4].
The latter reaction is particularly attractive due to its
possible application for CO removal from CO contam-
inated H
2
-rich feed gases for Polymer Electrolyte Fuel
Cells (PEFCs), as they are produced by partial oxidation
and/or steam reforming of fossil fuels or biomass
derived fuels [5,6]. High WGS activities reaction have
been reported for Au/ZrO
2
[7], Au/Co
3
O
4
[8], Au/TiO
2
[9,10], Au/Fe
2
O
3
[11–14] and Au/CeO
2
[3,14–20] cata-
lysts, with the activity decreasing in the order Au/
Fe
2
O
3
@ Au/TiO
2
@ Au/ZrO
2
> Au/Co
3
O
4
[3]. It is
tempting and plausible to assume a similar reaction
mechanism for these catalysts; a comprehensive and
more quantitative understanding of the reaction on
these catalysts is hindered, however, by the widely
varying procedures and parameters for catalysts syn-
thesis and catalyst pre-treatment (‘activation’), and also
by the very different reaction conditions.
This is topic of the present paper, where we report on
the effect of the catalyst pre-treatment, specifically the
procedure and parameters of the activation process, on
the activity, deactivation and reaction/deactivation
behavior of Au/CeO
2
catalysts in the WGS reaction. We
will apply different oxidative, reductive or thermal
activation procedures on the same raw catalyst precur-
sor. This report is part of an extensive study on the
WGS reaction on Au/CeO
2
catalysts, which were pre-
pared by a deposition-precipitation method [21,22].
First results on the kinetics and mechanism of the
reaction and on the effects of catalyst loading for reac-
tion in idealized gas mixtures have been reported
recently in ref. [23], results on the effect of increasing
CO
2
and H
2
contents and on the influence of the surface
area of the support on the activity and in particular on
the deactivation behavior were presented in refs. [24]
and [25], respectively.
In previous studies three different general procedures
have been applied for the activation of Au/CeO
2
cata-
lysts: reductive pre-treatment, calcination or thermal
treatment in an inert atmosphere. In most cases reduc-
tive pre-treatment in H
2
(1–10% H
2
in inert gas as
balance at different temperatures) was used to activate
Au/CeO
2
catalysts for the WGS reaction [18,26–28].
Reductive pre-treatment with CO was also investigated
[27]. Since we wanted to avoid a possible blocking of
active sites with carbonates and formates, whose gen-
eration could be observed in the presence of CO with
DRIFTS [24], we did not test CO as reducing agent.
Another possible conditioning procedure is calcination,
which has also been reported for Au/CeO
2
catalysts
[12,14,15,19,28]. It should be noted that in some cases
the measurement temperatures exceeded the condition-
ing temperatures [14,26,28], which can lead to further
catalyst modification during the reaction. Thermal
treatment in inert atmosphere was chosen as one con-
ditioning procedure, since several groups reported a
*To whom correspondence should be addressed.
E-mail: juergen.behm@uni-ulm.de
Catalysis Letters, Vol. 116, Nos. 3–4, August 2007 (Ó 2007) 105
DOI: 10.1007/s10562-007-9111-z
1011-372X/07/0800–0105/0
Ó
2007 Springer Science+Business Media, LLC