High Selectivity Preferential Oxidation (PROX) Catalysts for CO Removal from Hydrocarbon Derived Reformates for PEM Fuel Cells

摘要

Preferential oxidation (prox) catalysts for CO removal are important for the reformer-PEM fuel cell system. For ruthenium on promoted alumina catalysts, both high selectivity (99.9%) CO removal and low (<5%) hydrogen conversions were measured with synthetic reformates, typical of hydrocarbon partial oxidation (pox) products. Optimum excess air ratios (A02) and wide operating windows for gas hourly space velocities (GHSV) were defined. A two step reaction mechanism based on chloride in the support, redox properties of ruthenium and onstream observations is suggested. XPS analyses of fresh and deactivated catalysts (860 to 1700 hours) support the proposal. With hydrocarbon derived reformates, the selectivity was maintained only for gaseous hydrocarbons (C_1-C_3). Reformates from liquids e.g. isooctane, platformate, allowed 99.9% CO removal but H2 conversions rose to 17%, even with an active carbon adsorbent. Optimisation of catalyst and process parameters is required.