Abstract: In a gas turbine installation having an enclosure for passing cooling air therethrough and around the gas turbine, provision is made for a mixing of the cooling air with the exhaust gases being emitted from the gas turbine to thereby reduce the temperature thereof prior to its passing into the exhaust stack, but only after the primary air has passed through a catalyst bed which is disposed in a position over the gas turbine exhaust opening. The shape of the catalyst bed is preferably A-shaped in cross-section to thereby increase the surface area thereof. In this way, the temperature at the catalyst bed is maintained at an elevated level to obtain superior performance while a subsequent mixing of the primary air with the cooling air results in lower temperatures of the gases passing through the exhaust stack.