Catalyst for use in cleansing of inside of polymer film production furnace, and method for cleansing inside of polymer film production furnace

The present invention addresses the problem of providing: a highly durable catalyst which can be used in a decomposition treatment of a volatile organic compound (VOC) or a sublimatable organic substance, which is a substance generated in a polymer film production furnace, at a high conversion rate; and a method for cleansing a gas in a polymer film production furnace with the catalyst. A catalyst for use in the cleansing of a gas in a polymer film production furnace, said catalyst comprising an oxide mixture containing a manganese-containing oxide and copper oxide, wherein the manganese-containing oxide contains manganese and potassium and has a cryptomelane structure. A method for cleansing a gas in a polymer film production furnace, said method comprising: step 1 of bringing hot air that contains a volatile and/or a sublimatable organic substance each generated during the production of a polymer film in a polymer film production furnace into contact with the catalyst placed on the inside or outside of the furnace at a temperature of 200 to 350°C to oxidatively decompose the organic substance; and step 2 of allowing the whole or a portion of a decomposed gas, which is produced in the precedent step, to reflux into the polymer film production furnace.