Exhaust purification control device for internal combustion engine

A control device for an exhaust gas control apparatus provided to an internal combustion engine, the exhaust gas control apparatus including

• a first NOx catalyst provided in an exhaust passage of the internal combustion engine,
• a hydrocarbon addition valve configured to add hydrocarbon to exhaust gas flowing into the first NOx catalyst,
• a second NOx catalyst provided in a downstream of the first NOx catalyst, and
• a urea addition valve provided between the first NOx catalyst and the second NOx catalyst in the exhaust passage,
• the first NOx catalyst having characteristics in which NOx in the exhaust gas is reduced when a hydrocarbon concentration in the exhaust gas flowing into the first NOx catalyst changes to fluctuate with an amplitude within a prescribed range at a time interval within a prescribed range and a storage amount of NOx increases when the time interval becomes longer than a value within the prescribed range,
• the control device comprising
• an electronic control unit configured to
• i) execute a first purification process, the first purification process being a process of purifying NOx by intermittently adding the hydrocarbon into the exhaust gas from the hydrocarbon addition valve and changing the hydrocarbon concentration in the exhaust gas flowing into the first NOx catalyst to fluctuate with the amplitude within the prescribed range at the time interval within the prescribed range,
• ii) execute a second purification process, the second purification process being a process of purifying NOx by use of the second NOx catalyst by adding urea water into the exhaust gas from the urea addition valve, and
• iii) execute a hydrocarbon poisoning recovery stand-by process, the hydrocarbon poisoning recovery stand-by process being a process of, at a time when an execution request of the second purification process is generated during execution of the first purification process, reducing an additive amount per once from the hydrocarbon addition valve as compared with an additive amount per once before the execution request is generated, prior to start of execution of the second purification process.