Effect of aging time and calcination on the preferential oxidation of CO over Au supported on doped ceria Abhishek Jain, Xin Zhao, Shane Kjergaard, and Susan M. Stagg-Williams* Chemical and Petroleum Engineering Department, University of Kansas, 1530 W. 15th Street, 4132 Learned Hall, Lawrence, KS, 66045 USA Received 10 February 2005; accepted 22 July 2005 Au/CeLaO x mixed oxide catalysts containing 0.6–1.0 wt% Au were prepared by co-precipitation with Na 2 CO 3 . BET surface areas ranged from 15 to 45 m 2 /g depending on aging time (precipitation time) and calcination conditions. The differences in the activity of the catalysts for preferential oxidation (PROX) of CO are ascribed to the differences in the metal loading, Ce/La ratio and support crystallinity, chloride content, and the resultant effect on the reduction properties of the catalysts. The catalysts did not require activation in H 2 prior to reaction. The temperature at which the catalysts exhibit significant activity correlates with the temperature of reduction, indicating that reduction of the metal and support is important for high activity. KEY WORDS: PROX of CO; gold catalyst; La doped Ceria; aging; calcination. 1. Introduction PROX of CO in hydrogen-rich mixtures is an important reaction in fuel cell technology. The hydro- gen used as fuel in a polymer electrolyte membrane fuel cell (PEMFC) should be essentially free of CO to avoid poisoning of the Pt anode catalyst [1] which substan- tially decreases the fuel cell performance. Pure hydro- gen is an ideal fuel for PEMFC with the advantage of simple system integration, high efficiency, and zero emissions; however the poor storage capacity, safety problems, and lack of hydrogen infrastructure are major disadvantages. To overcome the difficulties with hydrogen distribution and storage, research into the onboard production of H 2 in a fuel-processing unit has increased. H 2 would be generated through reforming or partial oxidizing liquid fuels, such as LPG, gasoline, and methanol and then further processed by a water– gas shift catalyst to maximize the yield of H 2 . How- ever, the CO concentration from a reformer/water–gas shift unit is typically about 1 mol%, which is set by the thermodynamic equilibrium of the water–gas shift reaction and must be removed or converted to a compound inert for the anode reaction before being fed into the fuel cell. Even with advances in the anode materials for a PEM fuel cell, the CO levels must be below 100 ppm to maintain efficiency. Thus, CO removal plays a significant role in the feasibility of mobile or small scale (gas station), local hydrogen generation. Among various methods for removing CO from the H 2 rich feed gas, the selective CO oxidation has been recognized as one of the most straightforward and cost-effective ones to reduce CO concentration down to acceptable levels [2–4]. The catalytic performance of gold has received sig- nificant attention since supported Au catalysts were found to exhibit exceptional CO oxidation activity at low temperatures [5]. More recently, their use as selec- tive materials has been explored for selective oxidation of CO in H 2 rich fuels for fuel cells. Several studies have indicated that the rate of CO oxidation over supported Au catalysts exceeds that of H 2 oxidation [5,6], making Au based catalysts attractive for the selective oxidation of CO. A wide range of oxide supported gold catalysts have been investigated for PROX of CO. In compara- tive studies, it has been shown that the support material employed can have a significant effect on the activity of Au/MeO x catalysts for the selective CO oxidation reaction [7–11]. The activity difference among the vari- ous catalysts is ascribed to the difference in the sizes of the gold clusters and the varying ability of the supports to supply oxygen to facilitate the CO oxidation reaction in presence of H 2 . Previous studies have shown that Au/CeLaO x is very active for the low temperature water-gas shift reaction [12–14] and more recently is active and has good selectivity for selective CO oxidation [15–16]. In this paper, we report on the activity and selectivity of Au/CeLaO x for the PROX of CO. Specifically, we have investigated the effect of aging (precipitation time) and calcination on the catalyst morphology and the activity and selectivity of the catalysts in the temperature range of 95–150 °C. The results of this work demonstrate that even preparation steps which may appear trivial can have a significant impact cat- alytic performance. * To whom correspondence should be addressed. E-mail: smwilliams@ku.edu Catalysis Letters Vol. 104, Nos. 3–4, November 2005 (Ó 2005) 191 DOI: 10.1007/s10562-005-7950-z 1011-372X/05/1100–0191/0 Ó 2005 Springer Science+Business Media, Inc.