Abstract: An apparatus for reducing NOx comprising an exhaust conduit (101) of an IC engine (not shown) in which is placed a urea hydrolysis reactor (102) supplied with aqueous urea from urea storage tank (103). Flow of the hot exhaust gas through the exhaust conduit (101) heats the reactor (102) and causes the temperature of the urea therein to rise, promoting its hydrolysis and producing gaseous hydrolysis products. A pressure control valve (106) controls the release of the gaseous hydrolysis products from the reactor to a condenser (107). The condenser (107) is provided with a heat exchanger (108) which has an inlet (109) and an outlet (110) for connection to a coolant supply. When the gaseous hydrolysis gas enters the condenser (107) it is cooled by heat exchange with the engine cooling fluid and the ammonia and steam condense to form a pool of liquid in the bottom of the condenser (107).