An exhaust system for an engine comprises a selective catalytic reduction (“SCR”) device having a NOx reducing selective catalytic reduction composition disposed thereon. A particulate filter is disposed in the rigid shell or canister downstream of the selective catalytic reduction device. An ammonia dosing system comprising a controller in signal communication with NOx sensors located upstream and downstream of the selective catalytic reduction device for injection of ammonia into the exhaust gas upstream of the SCR device based on information collected from the NOx sensors to thereby optimize the reduction of NOx in the exhaust gas. An ammonia-neutral oxidation catalyst compound is disposed on the wall-flow substrate of the particulate filter device and is configured to pass through ammonia constituents of the exhaust gas exiting the selective catalytic reduction device with little or no conversion of the ammonia constituents to N2, N2O and NOx.