Microfibrous entrapment of small catalyst or sorbent particulates for high contacting-efficiency removal of trace contaminants including CO and H ₂S from practical reformates for PEM H₂-O₂ fuel cells

The four catalyst systems, Pt-Co/Al₂O₃, Pt/Al ₂O₃, Au/α-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oxidation (PROX) of CO from practical reformate in our previous studies [B. Chang, L. Chen, B.J. Tatarchuk, unpublished work], were further examined in differential reactor in the absence of heat and mass transfer limitations in order to compare their specific activities.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 μm diameter Ni fibers was used to entrap 15 vol% 150-250 μm Al₂O ₃ 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 μm 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/Al ₂O₃ 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.