Def dosing for selective catalytic reduction catalysts

A method to reduce NOX breakthrough when the SCR is increasing in temperature, the method comprising the steps of:

• monitoring a plurality of parameters of an exhaust gas feed stream upstream of an ammonia-selective catalyst reduction device;
• identifying one of a temperature increase at an SCR inlet or an exhaust gas flow increase at an SCR inlet;
• identifying a new lower ammonia set-point;
• determining an NH3 consumption rate on the SCR brick, an estimated ammonia storage concentration on the SCR, and a percentage of NH3 consumed by sequentially determining a change in ammonia storage for a plurality of discrete substrate elements on the SCR brick;
• comparing the new lower ammonia set point against the estimated ammonia storage concentration to determine if a transient phase status exists;
• and
• providing a percentage of DEF dosage equivalent to the percentage of NH3 consumed during the transient phase to prevent NOx breakthrough and to prevent NH3 slip until the expiration of the intervening phase and steady state is achieved
• wherein the percentage of DEF dosage does not deviate from the percentage of NH3 consumption during the transient phase.