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

Abstract

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.

Co3O4-Based Materials as Potential Catalysts for Methane Detection in Catalytic Gas Sensors

“…reported that three-dimensionally ordered, mesoporous Co 3 O 4 is not appropriate for application in pellistors due to the high instability of its structure under pellistor operation conditions. Especially, the mesoporous Co 3 O 4 catalyst functionalized with Au-Pd nanoparticles exhibited strong deactivation because of strong metal oxide sintering [ 32 ]. Thus, the suitable structure and morphology of the metal oxide had a crucial impact on performance of the catalytic sensors.…”

“…Thus, the suitable structure and morphology of the metal oxide had a crucial impact on performance of the catalytic sensors. Despite the high interest in metal oxides as catalysts for catalytic combustion, metal oxide materials have hardly been tested for use in catalytic gas sensors [ 32 , 33 ]. Although the catalytic oxidation of target gases underlies the sensor’s response, the results of standard catalyst studies using reactors cannot be easily transferred to catalytic gas sensors because the catalysts are prepared for examination according to the requirements for the catalytic bed reactors, e.g., by dilution with other components, pelletization, etc.…”

Differential thermal analysis techniques as a tool for preliminary examination of catalyst for combustion

“…The basis experimental investigations were performed on spinel cobalt oxide (Co 3 O 4 ) catalyst because previous works showed its high stability which is important for correct method evaluation. Moreover, Co 3 O 4 with variable valence states (Co 2+ /Co 3+ ) has attracted increasing attention as a very active non-noble metal catalyst for the catalytic combustion of CH 4 2 , 10 or as a support for noble metal catalyst 37 . With the focus on the sensor application, the temperature range between 250 and 450 °C was chosen for the investigations.…”