Abstract: A reducing gas, such as, carbon monoxide (CO) or unsaturated hydrocarbons, is oxidized by contacting a mixture of the gas and oxygen with a catalyst or reagent which includes palladium sulfate and ammonium molybdate adsorbed on silica gel. The reducing gas is oxidized by the reagent and simultaneously reduces the reagent from a first oxidation state to a second, with an accompanying color change, which indicates the presence of the reducing gas. If the reducing gas is an unsaturated hydrocarbon it can be converted to an oxygenated hydrocarbon. A salt of a transition metal (such as, copper, iron, or nickel) is included in the reagent so it is oxidized back to the first state (regenerated) by atmospheric oxygen. The catalyst also promotes the synthesis of oxygenated hydrocarbons from the reaction of unsaturated hydrocarbons with other hydrocarbons.