Development of A zeolites-supported noble-metal catalysts for CO preferential oxidation: H2 gas purification for fuel cell

Even traces of CO in the hydrogen-rich feed gas to proton exchange membrane fuel cells (PEMFC) poison the platinum anode electrode and dramatically decrease the power output. In this work, a variety of catalytic materials consisting of noble metals supported on A zeolites were synthesised, characterised and tested under realistic conditions in the quest of a catalyst for the removal of CO via the CO preferential oxidation (CO-PROX) reaction. Pt, Pd and Ru-based catalysts, prepared by wet impregnation and characterised by XRD and HRTEM, were investigated in a fixed bed reactor, by determining CO conversion and selectivity through the outlet concentrations of CO and O2. In contrast to supported Pd and Ru catalysts, Pt-catalysts showed complete CO-conversion and a comparatively high selectivity. The 1% Pt-3A catalyst showed the best performance: it kept the complete CO-conversion in a wide temperature range, showing the highest selectivity for CO oxidation with minimal involvement in side reactions, such as H2 oxidation and RWGS reaction. Experimental data proved that the RWGS outcome is directly related to the support structure. The rather high temperature (≈260 °C) at which complete CO conversion is achieved by the 1% Pt-3A catalyst enables to locate the CO-PROX unit immediately after the low temperature water-gas shift unit of the fuel processor converting hydrocarbons into hydrogen-rich gas.