US Patent 10450925 Exhaust gas purification apparatus for an internal combustion engine

In cases where an adsorption amount of ammonia in the SCR catalyst is smaller than a predetermined target adsorption amount, when a condition of NOX being assumed not to flow into the SCR catalyst is satisfied, and when the temperature of the SCR catalyst falls within a temperature range (effective range) which is equal to or higher than a desorption temperature of ammonia adsorbed to the weak adsorption sites and which is less than a desorption temperature of ammonia adsorbed to the active sites, the adsorption of ammonia to the active sites is carried out, while suppressing the adsorption of ammonia to the weak adsorption sites, by supplying the additive agent to the SCR catalyst from a supply device.