Promotion of platinum/gamma-aluminum oxide for preferential oxidation of carbon monoxide in hydrogen for PEM fuel cells by cerium promoter and by preparation of stable platinum nanoparticles using a water-pretreatment

The hydrogen fuel for Polymer Electrolyte Fuel Cells (PEFC) can be produced by reforming hydrocarbons. To avoid deactivation of the PEFC anode by CO from the reforming gas, preferential oxidation (PROX) of CO is used to purify the hydrogen. The Pt/γ-Al₂O₃ catalyst is promoted for the PROX reaction using a Ce promoter and a special water-pretreatment.; The selectivity of CO over H₂ oxidation on a 5 wt% Pt/γ-Al ₂O₃ was highest at low temperatures (100°C) and low O ₂/CO ratios. However, the conversion was rather low and could be improved only by increasing the contact time. Over Ce promoted 5 wt% Pt/γ-Al ₂O₃, CO conversion and selectivity were significantly improved in simulated reformate gases due to enhanced oxygen-supply to the highly dispersed metallic Pt. This also resulted in lower hydrogen oxidation.; The water-pretreatment, reduction in the presence of water, was applied to 5 wt% Pt/γ-Al₂O₃. Its CO oxidation activity and selectivity were much improved over a large temperature range (−17–200°C) in the simulated reformate gases. A reversible deactivation was observed below 100°C by water adsorption from the H₂ oxidation and H ₂O in the feed gas.; Water-pretreatment stabilizes small metallic Pt particles on γ-Al ₂O₃, after H₂ reduction step against sintering. It can regenerate big sintered Pt particles to active small metallic Pt particles.; Water pretreated Pt/γ-Al₂O₃ has partial-positively charged small (∼2 nm) metallic Pt particles with a high number of Pt-alumina interface sites. They have a raft-like shape and Pt-Al alloy characteristics with a low CO interaction due to strong metal-support interaction (SMSI). Thus, they have more (reversible) H₂ spillover for formation of hydroxyl groups and carbonates for the PROX reaction at both high and low reaction temperatures. However, non-water pretreated Pt/γ-Al₂O ₃ has bigger metallic Pt particles (∼16 nm) with a small number of Pt-alumina interface sites. They have lower SMSI for less (reversible) H₂ spillover. Thus, the formation rates of hydroxyl groups and carbonates are low, resulting in lower selective CO oxidation.; After the water-pretreatment, the alumina is rich in hydroxyl groups. This increases the H₂ spillover and SMSI between the Pt and Al. Stabilization and redispersion of Pt nanocrystal result.