Co 3 O 4 -Based Materials as Potential Catalysts for Methane Detection in Catalytic Gas Sensors.

The present work deals with the development of Co 3 O 4 -based catalysts for potential application in catalytic gas sensors for methane (CH 4 ) detection. Among the transition-metal oxide catalysts, Co 3 O 4 exhibits the highest activity in catalytic combustion. Doping Co 3 O 4 with another metal can further improve its catalytic performance. Despite their promising properties, Co 3 O 4 materials have rarely been tested for use in catalytic gas sensors. In our study, the influence of catalyst morphology and Ni doping on the catalytic activity and thermal stability of Co 3 O 4 -based catalysts was analyzed by differential calorimetry by measuring the thermal response to 1% CH 4 . The morphology of two Co 3 O 4 catalysts and two Ni x Co 3-x O 4 with a Ni:Co molar ratio of 1:2 and 1:5 was studied using scanning transmission electron microscopy and energy dispersive X-ray analysis. The catalysts were synthesized by (co)precipitation with KOH solution. The investigations showed that Ni doping can improve the catalytic activity of Co 3 O 4 catalysts. The thermal response of Ni-doped catalysts was increased by more than 20% at 400 °C and 450 °C compared to one of the studied Co 3 O 4 oxides. However, the thermal response of the other Co 3 O 4 was even higher than that of Ni x Co 3-x O 4 catalysts (8% at 400 °C). Furthermore, the modification of Co 3 O 4 with Ni simultaneously brings stability problems at higher operating temperatures (≥400 °C) due to the observed inhomogeneous Ni distribution in the structure of Ni x Co 3-x O 4 . In particular, the Ni x Co 3-x O 4 with high Ni content (Ni:Co ratio 1:2) showed apparent NiO separation and thus a strong decrease in thermal response of 8% after 24 h of heat treatment at 400 °C. The reaction of the Co 3 O 4 catalysts remained quite stable. Therefore, controlling the structure and morphology of Co 3 O 4 achieved more promising results, demonstrating its applicability as a catalyst for gas sensing.