Combustion of Methane in Lean Mixtures over Bulk Transition-Metal Oxides: Evaluation of the Activity and Self-Deactivation

Different bulk transition-metal oxides (NiO, CuO, Mn2O3, Cr2O3, and Co3O4) were prepared, by precipitation from nitrate precursors, and tested for the combustion of methane−air lean mixtures (1000−5000 ppmv of CH4). Catalyst performances were compared in terms of both intrinsic activity and resistance to self-deactivation. Methane combustion experiments were carried out at ambient pressure and a space velocity of 62 h−1 [weight hourly space velocity (WHSV)]. The activity of the studied catalysts (determined by the recording of light-off curves in the interval of 250−600 °C) decreases in the order: Co3O4 > Mn2O2 > Cr2O3 > CuO > NiO. However, deactivation studies, carried out both at constant temperature (620 °C) and in hysteresis experiments, reveal that Mn2O3 is the most stable catalyst.