Effect of lean/rich cycling on catalytic activity of a methane oxidation catalyst

Natalia  Diaz Montenegro, University of Virginia

Current natural gas engine exhaust aftertreatment systems struggle to fully oxidize methane emissions, causing the release of unburned methane into the atmosphere. In order to comply with regulations, an improved catalytic aftertreatment system is needed for complete methane oxidation at low temperatures, as well as to simultaneously reduce CO and NOx emissions and be resistant to common catalyst poisons, such as SO₂. In this work, the effects of SO₂ exposure and lean/rich cycling on methane oxidation and NOx reduction performance were investigated on a layered precious metal and spinel metal oxide catalyst. Lean/rich cycling lowered the methane light-off temperature by 100°C due to the ability of the spinel metal oxide layer to release oxygen during oxygen-deficient periods. Under cycling conditions, NOx conversion improved and steadied at ~50% at high temperatures. The amplitude between λ_lean and λ_rich, and duration of the cycle were found to impact the magnitude of the effect of lean/rich cycling on performance. To understand the effect of SO₂ on cycling, the catalyst was subjected to two different SO₂ treatments: pre-saturation and co-fed. Under pre-saturation SO­₂ conditions, methane oxidation activity was not severely affected, and after regeneration, the catalyst regained most of its catalytic activity. Under SO₂ co-feed conditions, methane oxidation at low temperatures was promoted possibly due to increased levels of oxygen from sulfate decomposition.

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