Exhaust gas control apparatus and reductant dispensing method for internal combustion engine

An internal combustion engine exhaust gas control apparatus characterized by comprising:

• a selective reduction type NOx catalyst disposed in an exhaust passageway of an internal combustion engine, wherein a state of adsorption of NH3 on the selective reduction type NOx catalyst includes a weakly adsorbed state in which NH3 adsorbed on the NOx catalyst is useful for a reduction reaction of NOx, and a strongly adsorbed state in which NH3 adsorbed on the NOx catalyst is not useful for the reduction reaction of the NOx unless the state of adsorption of NH3 is changed into the weakly adsorbed state;
• a reductant dispensation portion that is disposed in the exhaust passageway upstream of the selective reduction type NOx catalyst and that dispenses a reductant for supplying NH3 to the selective reduction type NOx catalyst;
• an actual weakly adsorbed amount calculation portion that calculates an actual weakly adsorbed amount of NH3 that is adsorbed on the selective reduction type NOx catalyst in the weakly adsorbed state;
• and
• a dispensation control portion that performs a dispensation control of the reductant dispensed by the reductant dispensation portion, according to the actual weakly adsorbed amount calculated by the actual weakly adsorbed amount calculation portion.