The device comprises: a dielectric conduit (2) having a gas input and a gas output； a lamp (3) that generates an UV radiation and is placed in the conduit； a first electrode (4) arranged against an outer wall of the conduit； a second electrode (5) disposed within the conduit； and a removable photocatalytic element (6) that is disposed against an inner wall of the conduit and comprises a support that supports a photocatalyst. The second electrode is formed by helical wire coils that press the photocatalytic element against the inner wall of the conduit. The device comprises: a dielectric conduit (2) having a gas input and a gas output； a lamp (3) that generates an UV radiation and is placed in the conduit； a first electrode (4) arranged against an outer wall of the conduit； a second electrode (5) disposed within the conduit； and a removable photocatalytic element (6) that is disposed against an inner wall of the conduit and comprises a support that supports a photocatalyst. The second electrode is formed by helical wire coils that press the photocatalytic element against the inner wall of the conduit. The photocatalytic element is in the form of a flexible sheet. The lamp is arranged within a quartz tube. The conduit and the coils of the second electrode are circular. The lamp is of elongated shape and is centered on a longitudinal axis of the conduit. Independent claims are included for: (1) a system for treating gas； and (2) a method for treating gas.Ce dispositif (1) de traitement de gaz, comprend :- un conduit diélectrique (2) comportant une entrée (E) et une sortie (S) de gaz,- une lampe (3) générant un rayonnement au moins en partie ultraviolet, placée dans le conduit (2),- une première électrode (4), disposée contre une paroi extérieure (22) du conduit (2),- une deuxième électrode (5), disposée à l'intérieur du conduit (2),- un élément photocatalytique amovible (6), disposé contre une paroi intérieure (21) du conduit (2) et comprenant un support qui
