PURPOSE: To improve the selectivity and prolonged stability of catalyst by reacting at least one selected from the group consisting of yttrium chloride and chlorides of rare earth metals with at least one selected from the group consisting of alkali carbonates and alkali bicarbonates.

CONSTITUTION: An aqueous solution of sodium hydroxide is added dropwise to an aqueous solution of silver nitrate to precipitate silver oxide which is filtered off and washed with water. The silver oxide is added to sodium carbonate solution to which formalin is added dropwise to react. The formed reduced silver is dried. The reduced silver is added to an aqueous solution of yttrium chloride and/or one or more chlorides of rare earth metals ranging from lanthanum to lutetium. To the resulting mixture is added dropwise an aqueous solution of an alkali carbonate to form a precipitate which is dried. The resulting mixture of the reduced silver and yttrium carbonate and/or one or more rare earth metal carbonates is added to an aqueous solution of an alkali metal compound to form a slurry. The slurry is mixed with a catalyst carrier. The resulting mixture is dried to produce the desired catalyst composition.