Highly Active Catalyst for Preferential Oxidation of CO in H2-Rich Gas Mixture

Abstract

Abstract: Preferential oxidation is one of the most effective methods for CO clean-up from the reformate stream prior to its introduction in the PEM fuel cell. In this work, Cu-Ce/γ-Al₂O₃ as a base catalyst promoted with Pt and Rh was prepared for the low temperature selective oxidation of CO in hydrogen rich syn gas mixture. Seven catalysts with atomic ratio of 100: 20: 3: 1 for Cu: Ce₂O₃: Pt: Rh were prepared with Cu loading in the range of 0.5 to 6%. Also, four catalysts were prepared to investigate the role of Pt and Rh in the catalyst activity. The effects of stoichiometric ratio of O₂/CO and water vapor on the selective oxidation of CO as a function of temperature were investigated. The prepared catalysts were characterized by using gas sorption analyzer and temperature programmed reduction (TPR). Slight decrease in surface area and pore volume was observed with increasing metal loadings. The TPR results indicate shift towards higher temperature when Pt and Rh were added to Cu–Ce/γ-Al₂O₃ catalyst. Moreover, TPR result showed that there is a correlation between reduction temperature and the activity and selectivity of the catalyst. The loading of Cu, Ce, Pt, Rh metals for maximum activity and selectivity were 2.0, 0.657, 0.183, 0.0324 wt % respectively, which decreased CO concentration in the product to 4 ppm (99.96%). A synergistic effect of addition of Pt or/and Rh was observed to enhancement the activity and selectivity of the base catalyst (Cu-Ce/γ-Al₂O₃). The CO conversion was increased from 24.7 to 96.77% with addition of 0.183 wt% Pt to the base catalyst, while the addition of 0.0324 wt% Rh increased the CO conversion to 44.1%. Addition of 10 vol% of water vapor to the feed resulted in higher conversion at lower temperature. The CO conversion was increased whereas the temperature of maximum conversion was decreased by 20 ºC.