Method and system for purifying the exhaust gases of a combustion engine.

SCR method for_purifying the exhaust gases of an internal combustion engine of a vehicle, according to which ammonia gas is exclusively metered in the exhaust gases, the method comprising a step of releasing ammonia gas from at least one solid absorbing matrix where it is stored by sorption and a step of metering the released ammonia gas in the exhaust gases. The method is such that it comprises a step of regenerating the solid absorbing matrix that consists in: - generating a refilling ammonia gas by chemically decomposing a ammonia precursor in a biochemical decomposition unit (3) mounted on board the vehicle and storing at least one protein component adapted to decompose said ammonia precursor; - directing the refilling ammonia gas to the solid absorbing matrix where it is stored thereon.