Accelerated Deactivation of Mesoporous Co3O4-Supported Au-Pd Catalyst through Gas Sensor Operation

High activity of a catalyst and its thermal stability over a lifetime are essential for catalytic applications, including catalytic gas sensors. Highly porous materials are attractive to support metal catalysts because they can carry a large quantity of well-dispersed metal nanoparticles, which are well-accessible for reactants. The present work investigates the long-term stability of mesoporous Co3O4-supported Au-Pd catalyst (Au-Pd@meso-Co3O4), with a metal loading of 7.5 wt% and catalytically active mesoporous Co3O4 (meso-Co3O4) for use in catalytic gas sensors. Both catalysts were characterized concerning their sensor response towards different concentrations of methane and propane (0.05-1%) at operating temperatures ranging from 200 °C to 400 °C for a duration of 400 h. The initially high sensor response of Au-Pd@meso-Co3O4 to methane and propane decreased significantly after a long-term operation, while the sensor response of meso-Co3O4 without metallic catalyst was less affected. Electron microscopy studies revealed that the hollow mesoporous structure of the Co3O4 support is lost in the presence of Au-Pd particles. Additionally, Ostwald ripening of Au-Pd nanoparticles was observed. The morphology of pure meso-Co3O4 was less altered. The low thermodynamical stability of mesoporous structure and low phase transformation temperature of Co3O4, as well as high metal loading, are parameters influencing the accelerated sintering and deactivation of Au-Pd@meso-Co3O4 catalyst. Despite its high catalytic activity, Au-Pd@meso-Co3O4 is not long-term stable at increased operating temperatures and is thus not well-suited for gas sensors.