A system includes an exhaust aftertreatment system configured to treat emissions from a combustion engine. The exhaust aftertreatment system includes a first catalyst assembly having an outlet. The exhaust aftertreatment system also includes an ammonia slip catalyst (ASC) assembly configured to receive a fluid from the first catalyst assembly and to convert ammonia (NH3) within the fluid into nitrogen (N2), wherein the ASC assembly has an inlet. The exhaust aftertreatment system further includes a silencer disposed between the outlet of the first catalyst assembly and the inlet of the ASC assembly, wherein the silencer is configured to receive the fluid and an oxidant for mixing with the fluid provide sufficient oxygen in the fluid flowing into the inlet of the ASC assembly to enable the catalytic activity in the ASC assembly that coverts NH3 into N2, and the silencer is configured to mix the fluid and the oxidant.