Apparatus for substantially blocking flames and spreading heated gases emitted from a broiler flue. The apparatus includes a riser placed above the broiler flue for defining a pathway along which heated gases are exhausted from the flue, a catalyst support on the riser for supporting a catalyst in the pathway for flow of heated gases through the catalyst from a bottom surface of the catalyst to a top surface of the catalyst, and a plurality of baffles in the riser extending across the pathway below the catalyst support. The baffles have the shape of inverted troughs.