Electrical Behavior of a Catalyst Composed of Laminar Manganese Oxide Supported on γ-Al₂O₃

The electrical characterization of catalysts composed of layered manganese oxide in the form of birnessite supported on γ-Al₂O₃, which have been successfully used in the combustion of soot, is presented. The results indicate that the electrical conduction and ion conduction processes are influenced by the amount of the active phase. There was also evidence of Grotthuss-type proton conductivity favored by the presence of surface water on the exposed alumina surface. The above is supported by the porous nature of the catalyst in which the surface area varied between 125.2 ± 1.2 and 159.0 ± 1.1 m²/g, evidencing changes in the alumina surface. The conductivity, determined from measurements of impedance spectroscopy, at low frequency showed changes associated with the amount of the active phase. The values ranged from 2.61 × 10^-8 ± 2.1 × 10^-9 Ω^-1·cm^-1 (pure alumina) to 7.33 × 10^-8 ± 5.9 × 10^-9 Ω^-1·cm^-1, 7.21 × 10^-8 ± 5.8 × 10^-9 Ω^-1·cm^-1 and 4.51 × 10^-7 ± 3.6 × 10^-8 Ω^-1·cm^-1 at room temperature for catalysts with nominal active phase contents of 5.0, 10.0 and 20.0%, respectively. Such results indicate that it is possible to modulate the electrical properties with variations in the synthesis parameters.