Generation and delivery of ammonia gas in an exhaust gas system

An exhaust gas system for an engine producing an exhaust gas includes an exhaust gas tube configured to receive the exhaust gas. A particulate filter is in fluid communication with the exhaust gas tube and configured to undergo thermal regeneration when the exhaust gas in the particulate filter is heated above a regeneration temperature. A generator unit is positioned downstream of the particulate filter and includes a first catalyst. A tank is configured to store a precursor material. The generator unit is configured to employ the precursor material and the heat generated for the thermal regeneration of the particulate filter to generate an ammonia gas from the precursor material. The system includes a controller having a processor and tangible, non-transitory memory on which is recorded instructions for executing a method of controlling generation of ammonia gas in the generator unit and injection of ammonia gas in the exhaust gas tube.