Microfibrous entrapment of small catalyst or sorbent particulates for high contacting-efficiency removal of trace contaminants including CO and H2S from practical reformates for PEM H2-O2 fuel cells

The four catalyst systems, Pt-Co/Al2O3, Pt/Al2O3, Au/alpha-Fe2O3, and CuO-CeO2, which demonstrated promising catalytic activity among more than 150 catalysts investigated for the preferential oxidation (PROX) of CO from practical reformate in our previous studies [B. Chang, L. Chen, B.J. Tatarchuk, unpublished work], were further examined in differential reactor in the absence of heat and mass transfer limitations in order to compare their specific activities. Differential reactor studies reveal that the cobalt promoted Pt/Al2O3 (Pt-Co/Al2O3) is the best candidate among those four catalyst systems for the preferential oxidation (PROX) of CO from practical reformate for PEM fuel cells. A high void and tailorable sintered microfibrous carrier consisting of 5 vol% 4 and 8 mu m diameter Ni fibers was used to entrap 15 vol% 150-250 mu m Al2O3 particulates. SEM images showed the microstructures of the thin microfibrous entrapped alumina support particles. The alumina support particulates were uniformly entrapped into a well sinter-locked three-dimensional network of 4 and 8 mu m Ni fibers. Cobalt and platinum were then dispersed onto the microfibrous entrapped alumina support particles by impregnation method so as to prepare microfibrous entrapped Pt-Co/Al2O3 catalysts. The composite catalysts possessed 80 vol% voidage. The microfibrous entrapped Pt-Co/Al2O3 catalysts showed stable long-term activity for the preferential CO oxidation in wide temperature range. A microfibrous entrapped H2S sorbent layer was then placed upstream of a microfibrous entrapped PROX catalyst layer to remove both H2S and CO from a sulfur-contaminated practical reformate stream. Operating in this fashion, an outermost H2S sorbent layer promotes the activity maintenance of a secondary non-poison tolerant PROX CO catalyst, which ultimately serves to provide activity maintenance to CO-intolerant precious metal-based MEA assemblies in PEM fuel cells. (c) 2005 Elsevier B.V. All rights reserved.