Preferential CO oxidation in the presence of H2 over Au-based catalysts

Abstract

Traces amount of CO dramatically reduce the PEM fuel cell efficiency. Therefore, the removal of CO via preferential CO oxidation (PROX) is a potential method to remove CO from the EE-rich stream. Au-based catalysts are very active and selective to convert CO to CO2 at low temperatures. In this work, the Au-based catalysts were developed on various support for PEM fuel cells applications. The development of PROX efficiency can be divided into two parts; which are the development of the catalytic performance and the process performance. In the process development section, the addition of the second stage significantly reduced the H2 loss. The selectivity towards CO oxidation greatly increased from 48 to 58%. In the catalyst development section, the Au/ZnO catalyst prepared by deposition- precipitation technique calcined at 500°C displayed superior activity, giving complete CO conversion with the highest selectivity (-75%) at 50°C, whereas the Au/ZnO-Fe2O3 showed a marked improvement in activity under CO2 and H2O surroundings. After that, the photodeposition technique was used to prepare catalyst and the results indicated that Au/ZnO and Au/ZnO-Fe2O3 catalysts can be successfully prepared via the photodeposition under UV-vis light irradiation in order to obtain Au particles that are in nanometer size (1-6 nm). The catalysts exhibited high catalytic activity (without heat treatment step), where it achieves a complete conversion of the CO at 30°c and 50-73% CO selectivity. Finally, double-stage PROX reactor and Au/Zn0-Fe203 prepared by photodeposition were utilized in a fuel processor system. This process consists of 2 reactions; which are methanol steam reforming over ShiftMax 240 (commercial catalyst) and PROX reaction over Au catalyst. The results revealed that ShiftMax 240 showed the 100% methanol conversion at 250°c with high stability and obtained the average hydrogen production rate at 136 L/day. Moreover, the PROX unit can remove the CO content in a H2-rich stream to less than 100 ppm.