Internal combustion engine having variable valve control system and NOx catalyst

An apparatus is provided which includes an internal combustion engine (1) of a lean-burn type, an NOx catalyst (46) disposed in an exhaust passage of the engine so as to remove nitrogen oxides contained in exhaust gas emitted from the engine, and a variable valve control system (30, 31, 30a, 31a) capable of changing the opening and closing timing and/or a lift of the intake valve and/or the exhaust valve for each cylinder of the engine. The variable valve control system is controlled so as to place the exhaust valve in an open position before a moment of initiation of an exhaust stroke of a corresponding one of the cylinders, when an exhaust gas emitted from the corresponding cylinder is desired to contain a reducing component for reducing NOx. A method of purifying an exhaust gas emitted from the above engine is also provided.