Plasma assisted catalytic treatment of gases

A reactor for the plasma-assisted processing of effluent gases such as exhaust gases from an internal combustion engine or effluent gases from industrial processes or incineration to reduce the emission of noxious combustion products therefrom, comprising a reactor chamber adapted to be connected to a source of effluent gas and including a central axial duct at least a portion of which is gas permeable, a first gas permeable bed of a material adapted to perform a first stage treatment including where necessary the removal of carbonaceous combustion products from gases passing therethrough, the said first gas permeable bed surrounding the gas permeable region of the central duct, means for establishing a non-thermal plasma in gases in the interstices of the first gas permeable bed, and also surrounding the axial duct at least one other gas permeable bed of a material adapted to catalyse the reduction of nitrogen oxides in gases passing therethrough and a flow diverter adapted in one state to constrain gases to pass initially through the first region of active material surrounding the central duct and then through at least one other region of active material surrounding the central duct and in a second state to allow the gases to pass directly through the central duct of the reactor.