Microfibrous Entrapment of Small Catalyst Particulates for High Contacting Efficiency Removal of Trace CO From Practical Reformates for PEM H_2-O_2 Fuel Cells

摘要

Preferential oxidation (PROX) of CO in H_2 is the most efficient way to remove CO from a practical reformate stream for PEM H_2-O_2 fuel cells. Pt/Al_2O_3 has long been known as a suitable catalyst for this purpose. Over the conventional Pt/Al_2O_3 catalyst, however, PROX of CO in H_2 has been known to occur at temperatures above 150 deg C, and the maximum CO conversion usually takes place at about 200 deg C. In this study, the promotion of Pt/Al_2O_3 with a transition metal results in significantly enhanced catalytic performance in the temperature range of 25 to 150 deg C. The active reaction temperature window is enlarged to 25 to 200 deg C compared with a narrow window at about 200 deg C over the conventional Pt/Al_2O_3. A high void and a tailorable sintered microfibrous carrier consisting of 5 vol. percent of 4 and 8 urn diameter Ni fibers is used to entrap 15 vol. percent 150 to 250 mu m diameter Al_2O_3 particulates. The alumina support particulates are uniformly entrapped into a sinter-locked, three-dimensional network of 4 and 8 mu m 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. percent voidage. At equivalent bed volumes, microfibrous entrapped catalysts achieve complete CO reduction (GC detection limit approx 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.