Microfibrous Entrapment of Small Catalyst Particulates for High Contacting Efficiency Removal of Trace CO From Practical Reformates for PEM H2-O2 Fuel Cells

Preferential oxidation (PROX) of CO in H2 is the most efficient way to remove CO from a practical reformate stream for PEM H2-O2 fuel cells. Pt/Al^sub 2^O3 has long been known as a suitable catalyst for this purpose. Over the conventional Pt/Al^sub 2^O3 catalyst, however, PROX of CO in H2 has been known to occur at temperatures above 150°C, and the maximum CO conversion usually takes place at about 200°C. In this study, the promotion of Pt/Al^sub 2^O3 with a transition metal results in significantly enhanced catalytic performance in the temperature range of 25 to 150°C. The active reaction temperature window is enlarged to 25 to 200°C compared with a narrow window at about 200°C over the conventional Pt/Al^sub 2^O3. A high void and a tailorable sintered microfibrous carrier consisting of 5 vol.% of 4 and 8 µm diameter Ni fibers is used to entrap 15 vol.% 150 to 250 µm diameter Al^sub 2^O3 particulates. The alumina support particulates are uniformly entrapped into a sinter-locked, three-dimensional network of 4 and 8 µm Ni fibers. Promoter and Pt are then dispersed onto the microfibrous entrapped alumina support particles by the incipient-wetness impregnation method. The composite catalysts possess 80 vol.% voidage. At equivalent bed volumes, microfibrous entrapped catalysts achieve complete CO reduction (GC detection limit 40 ppm CO) at five times the higher gas hourly space velocity value compared with packed beds of 1 to 2 mm catalyst particles demonstrating ultrahigh contacting efficiency provided by the microfibrous entrapped catalysts.[PUBLICATION ABSTRACT]