Patent ID: 8580215

Claim:
An exhaust gas control apparatus for an internal combustion engine comprising: a NOx selective reduction catalyst disposed in an engine exhaust gas passage; and a supply device that supplies ammonia to the NOx selective reduction catalyst to cause the NOx selective reduction catalyst to adsorb the ammonia, wherein: the exhaust gas control apparatus is configured to selectively reduce NOx in exhaust gas using the ammonia adsorbed; the ammonia is adsorbed by the NOx selective reduction catalyst in at least two states, including: a first adsorption state of the ammonia that occurs if the ammonia is adsorbed by the NOx selective reduction catalyst while a temperature of the NOx selective reduction catalyst is in a lower side temperature range, and an amount of desorption of the ammonia in which state is maximized in the lower side temperature range as the temperature of the NOx selective reduction catalyst increases, and a second adsorption state of the ammonia that occurs if the ammonia is adsorbed or has already been adsorbed by the NOx selective reduction catalyst while the temperature of the NOx selective reduction catalyst is in a higher side temperature range higher than the lower side temperature range, and an amount of desorption of the ammonia in which state is maximized in the higher side temperature range as the temperature of the NOx selective reduction catalyst increases; and the exhaust gas control apparatus further includes a controller that estimates an amount of adsorbed ammonia that is in the first adsorption state to control the amount of adsorbed ammonia that is in the first adsorption state, and estimates an amount of adsorbed ammonia that is in the second adsorption state to control the amount of adsorbed ammonia that is in the second adsorption state, with the use of at least relations, stored in advance, between the temperature and a proportion of the amount of ammonia that is adsorbed in the first adsorption state and a proportion of the amount of ammonia that is adsorbed in the second adsorption state.