Selective oxidation of carbon monoxide in fuel processor gas

The trace amount of CO present in the hydrogen-rich stream coming from fuel reformers poisons the platinum anode electrode of proton exchange membrane (PEM) fuel cells and reduces the power output. Removal of low levels of CO present in the reformed gas must take place before the gas enters the fuel cell. The tolerable level of CO is around 10 ppm. We investigated the performance of single step sol-gel prepared Pt/alumina catalyst and Pt supported on sol gel made alumina. The effect of water vapor, carbon dioxide, CO and oxygen concentrations, temperature, and Pt loading on the activity and selectivity are presented. Our results showed that a 2%Pt/alumina sol-gel catalyst can selectively oxide CO down to a few ppm with constant selectivity and high space velocity. Water vapor in the feed increases the activity of catalysts dramatically and in the absence of water vapor, CO₂ in the feed stream decreases the activity of the catalysts significantly. We also found that the presence of potassium as an electron donor did not improve the performance of Pt/alumina catalyst to the selective CO oxidation.; For Pt supported on sol gel made alumina, we found that the combination of CO₂ and H₂O in the gas feed has a strong effect on selective CO oxidation over Pt/Al₂O₃. It could be a positive or negative effect depending upon Pt loading in the catalyst. With high Pt loading, the CO₂ effect tends to dominate the H₂O effect resulting in the decrease in CO conversion. Moreover, the presence of CeO₂ as an oxygen storage compound promotes the performance of Pt supported on alumina at low temperature ∼90°C when Pt loading was 5%. Amongst the examined catalysts, the 5%Pt/15%CeO₂/Al ₂O₃ catalyst showed the highest selectivity, with high CO conversion at a low temperature ∼90°C. The beneficial effect of the addition of CeO₂ is most likely due to spillover of O₂ from CeO₂ to Pt at the Pt sites at the interface of Pt and CeO ₂.