A catalytic reactor (22) comprising a central axis (A) and a stack of catalytically active sheets (10), wherein the catalytically active sheets (10) are stacked in the axial direction. Each of the catalytically active sheets (10) comprises a central opening (17) and at least some of the catalytically active sheets (10) comprise an axially extending flange (18) arranged at least partially around said central opening (17), wherein the flange (18) of one catalytically active sheet (10) extends into the central opening (17) of an adjacent catalytically active sheet (10). Disclosed is also a method for providing a catalytic reaction.