TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Process: The gas having carbon dioxide as main component and/or air is pre-heated, and then supplied to the catalyzed-combustion device. The gas having carbon dioxide as a main component is cooled, and introduced into the catalyzed-combustion device. The gas having carbon dioxide as main component after removal of mercury is introduced into the catalyzed-combustion device. A catalyst layer containing metal oxide and noble metal is formed on the surface of the substrate. A metal oxide layer containing metal oxide is formed in the inner surface of the air flow passage in the honeycomb structure substrate. Preferred Component: The gas having carbon dioxide as main component is gas discharged from an acidic-gas separation apparatus, separated and recovered by contacting acidic gas in natural gas produced from gas field and a liquid solvent, or is an exhaust gas after reducing hydrogen sulfide with hydrogen-sulfide concentration apparatus provided in the latter stage of acidic-gas separation apparatus, a sulfur recovery unit and/or a tail-gas processing apparatus.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Properties: The metal oxide has specific surface area of 10-300 m2/g. The noble metal adhered to the surface layer portion of the metal oxide layer has density of 0.1-10 mg/cm2. The oxidative decomposition treatment is carried out at 250-650 degrees C. Preferred Composition: The substrate contains ceramics, metal oxide or metal alloy. Preferred Component: The combustion catalyst has a honeycomb structure, pellet or spherical-type substrate and a catalyst layer formed in the surface of the substrate.    TECHNOLOGY FOCUS - MECHANICAL ENGINEERING - Preferred Component: The catalyzed-combustion device is equipped with a catalyzed-combustion region in which combustion catalyst and gas, air and/or water are supplied between catalyzed-combustion regions. The combustion catalyst filled in the catalyzed-combustion device is substrate or honeycomb structure substrate having air flow passages. The catalyzed-combustion device is a container in which an outlet is formed in an end at the inlet, and the other end. The combustion catalyst units are mutually arranged at intervals between the inlet and outlet in the container. The combustion catalyst unit is honeycomb structure substrate having air flow passages which allows the carbon-dioxide off gas to pass through. Preferred Property: The internal diameter of vent hole of fuel catalyst unit near the outlet is larger than the internal diameter of fuel catalyst unit near the inlet.