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 H_2-O_2 fuel cells

摘要

The four catalyst systems,Pt-Co/Al_2O_3,Pt/Al_2O_3,Au/alpha-Fe_2O_3,and CuO-CeO_2,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the preferential oxidation(PROX)of CO from practical reformate in our previous studies [B.Chang,L.Chen,B.J.Tatarchuk,unpublished work],were further examined in differential reactor in the absence of heat and mass transfer limitations in order to compare their specific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/Al_2O_3(Pt-Co/Al_2O_3)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 mum diameter Ni fibers was used to entrap 15vol% 150-250 mum Al_2O_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 mum 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_2O_3 catalysts.The composite catalysts possessed 80 vol% voidage.The microfibrous entrapped Pt-Co/Al_2O_3 catalysts showed stable long-term activity for the preferential CO oxidation in wide temperature range.A microfibrous entrapped H_2S sorbent layer was then placed upstream of a microfibrous entrapped PROX catalyst layer to remove both H_2S and CO from a sulfur-contaminated practical reformate stream.Operating in this fashion,an outermost H_2S 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.