Abstract: A converter for purifying exhaust gases from lean-burn engines, in particular for controlling the amount of NOx and soot from a diesel engine in transient operation such as a vehicle. The converter contains a catalyst bed with a catalyst effective for NOx reduction with a chemical reductant when the catalyst bed is with a certain temperature window and when the ratio between the molar amount of chemical reductant and NOx is above a certain minimum ratio. The catalyst bed is heated or cooled to a temperature within the temperature window and a switching valve is provided for reverse flowing the exhaust gases through the converter to maintain the catalyst bed at a temperature within the temperature window for a longer time than is possible with a conventional non-flow-reversing converter.

Abstract: A purification system and a method for controlling exhaust gas emissions from internal combustion engines during start-up and restart, as well as during normal engine operation is disclosed. A method for controlling emissions during low load operation of a diesel engine fueled with a diesel fuel/methane mixture is also provided. Exhaust gases are contacted with a gas permeable solid material containing an adsorbent and a catalyst capable of converting the noxious components into innocuous materials. The flow of the gases through the gas permeable solid material is reversed in a series of continuing cycles to bring or to maintain the catalyst in a temperature range suitable for controlling the noxious components, below which temperature the noxious materials are adsorbed by the adsorbent.