Journal of Chromatography A, 1087 (2005) 158–168
Inverse gas chromatographic investigation of the effect of hydrogen in
carbon monoxide adsorption over silica supported Rh and Pt–Rh
alloy catalysts, under hydrogen-rich conditions
Dimitrios Gavril
∗
, Vassilios Loukopoulos, Aglaia Georgaka,
Aristea Gabriel, George Karaiskakis
Physical Chemistry Laboratory, Department of Chemistry, University of Patras, 26504 Patras, Greece
Available online 31 May 2005
Abstract
Selective CO oxidation (SCO) has attracted scientific and technological interest due to its application to the operation of proton electrolyte
membrane fuel cells (PEM-FCs). CO adsorption, being an elementary step of SCO, is studied over silica supported monometallic Rh and
Rh
0.50
+ Pt
0.50
alloy catalysts, under various hydrogen atmospheres, namely: 25% H
2
+ 75% He, 50% H
2
+ 50% He and 75% H
2
+ 25% He
carrier gas mixture compositions. The investigation of CO adsorption is done by utilizing reversed-flow gas chromatography (RF-GC). As
a result rate constants for the adsorption (k
1
), desorption (k
−1
) and irreversible CO binding (k
2
) over the studied catalysts as well as the
respective activation energies are determined. The variation of the rate constants and the activation energies against the nature of the used
catalyst (monometalic or alloy) and the amount of hydrogen in the carrier gas gives useful information for the selectivity as well as the activity
of CO oxidation over group VIII noble metals. At low temperatures and under H
2
-rich conditions compatible with the operation of PEM fuel
cells the activity of the monometallic and the alloy catalysts is expected to be similar, however the selectivity of Rh
0.50
+ Pt
0.50
alloy catalyst is
expected to be higher, making Pt–Rh alloy catalyst as a better candidate for CO preferential oxidation (PROX). The low energy barrier values
found in the present work, most likely are referred to high surface amounts of CO. The desorption barriers determined are in any case much
lower than the respective activation energies found for CO desorption in the absence of hydrogen indicating a H
2
-induced desorption, which
can explain the observed in the literature rate enhancement of SCO oxidation.
© 2005 Elsevier B.V. All rights reserved.
Keywords: Inverse gas chromatography; Physicochemical measurements; PEM fuel-cells; Platinum–Rhodium alloy catalysts; Selective CO oxidation (SCO);
Preferential oxidation (PROX); Activity; Selectivity
1. Introduction
Fuel cells are developed as a viable alternative for clean
energy generation. Fuel cell technology applications vary
from portable/micro power and transportation through to sta-
tionary power for buildings and distributed generation. Vari-
ous fuel cells applications operating at different temperatures
have been developed [1]. A series of advantages such as: low
operating temperature (343–373 K), low weight, compact-
ness, long stack life, suitability to discontinuous operation as
Presented at the 25 ISC, Paris, October 4–8, 2004.
∗
Corresponding author. Fax: +30 2610997144.
E-mail address: d.gavril@upatras.gr (D. Gavril).
well as potential for low cost make proton exchange mem-
brane (PEM) fuel cells leading candidates for mobile power
and/or for small power units’ applications.
The rational operation of the fuel cell units is closely re-
lated to the development of very active poison-resistant and
selective catalysts, which result in small catalytic volumes,
durability under steady-state and transient conditions, low
cost and versatility to variations in fuel/feed composition.
Pure hydrogen is the ideal fuel for the PEM fuel cell.
However, there is no available technology for safely storing
enough hydrogen to give a PEM fuel cell powered vehicle
acceptable range. PEM fuel cells utilize the hydrogen pro-
duced by external reforming using steam, air or a combination
of both. Steam reforming, catalytic partial oxidation and au-
0021-9673/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.chroma.2005.04.065