The invention relates to a reactor for dielectric barrier discharge plasma catalysis, comprising a reactor housing (B) able to receive a plurality of DBD cells (C1, C2, C3 . . . ) removably mounted inside this housing.

According to a first aspect of the present invention, there is provided an apparatus for forming NOx from nitrogen and oxygen, the apparatus comprising: a gliding arc discharge, GAD, device arranged to generate a plasma; a passageway including an inlet for a feed gas comprising nitrogen and oxygen and an outlet for the NO.sub.x, wherein the passageway extends, at least in part, through the GAD device wherein, in use, the nitrogen and oxygen are reacted in the generated plasma, thereby forming the NO.sub.x from at least some of the nitrogen and oxygen; and a post-discharge container for adjusting the NO.sub.2/NO ratio in the formed NO.sub.x to from 1:2 to 2:1.