Impact of particle size and morphology of cobalt oxide on the thermal response to methane examined by thermal analysis

Differential thermal analysis (DTA) was used to examine the effect of the particle size and morphology of cobalt (III/IV) oxide (Co3O4) on its thermal response under exposure to methane (1 vol % in dry synthetic air), which is a relevant gas for the detection of combustible gases. The DTA response results from the catalytic oxidation of methane, and its characteristics should correlate with the pellistor response. Co3O4 samples differing in particle size and morphology were produced by ball milling (top-down technique) or were synthesized from precursor molecules by precipitation (bottom-up technique). The investigations carried out in dry air and a temperature range between 250 and 450 ∘C reveal that both particle size and particle shape have a considerable effect on thermal response, since the resulting layer structures and the associated surface area available for gas interaction differ. The Co3O4 catalyst, with small particles and an irregular shape, exhibits significantly higher response than milled Co3O4 samples. Comparison of DTA with the mass spectroscopy signal of CO2 evolved by the reaction verified a certain analogy between DTA measurements and the response produced by a pellistor.