Microfibrous entrapment of small catalyst particulates for high contacting efficiency removal of trace CO from practical reformates for PEM H2-O2 fuel cells

摘要

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/Al2O3 has long been known as a suitable catalyst for this purpose. Over the conventional Pt/Al2O3 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/Al2O3 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/Al2O3. 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 Al2O3 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.