A detailed study on regeneration of SO2 poisoned exhaust gas after-treatment catalysts: In pursuance of high durability and low methane, NH3 and N2O emissions of heavy-duty vehicles

Abstract

Utilization of natural gas fuels in heavy duty vehicles offers an effective solution to reduce global warming and improve urban air quality. However, there are problems related to catalyst durability and release of unburned methane (methane slip). Catalyst durability can be achieved through clever designs of both catalyst material and its regeneration process. In this paper, we studied extensively low temperature regeneration strategies of a commercial methane oxidation catalyst (MOC), a three-way catalyst (TWC) and a diesel oxidation catalyst (DOC) as well as two coupled catalysts; TWC-MOC and DOC-MOC. Methane and propane conversion along with NO2, NO, SO2, CO, N2O and NH3 formation were recorded and analyzed in a laboratory setup using a FTIR multigas analyzer. According to our findings, the MOC and the DOC can be regenerated under a broader range of O2 concentrations whereas the TWC requires a very low O2 concentration or anoxic conditions for efficient regeneration. The conversion increase ranged between 0 and 20 percentage points for methane and 0–45 percentage points for propane depending on the catalyst and regeneration technique. The coupled catalysts were highly effective in methane conversion and possessed higher tolerance against SO2 poisoning compared to single catalysts. The study further revealed that 10 ppm regulation limit of NH3 emission is plausible to exceed during the regeneration of a catalyst. By controlling the exhaust gas composition during the regeneration and length of the regeneration, the NH3 and N2O emissions can be minimized.