PURPOSE: To prepare quickly and easily such catalyst having high activity and causing no deterioration for a long period by exchanging ions between salt of a metal having catalytic activity and metallic manganese.

CONSTITUTION: Ion exchange reaction is caused by charging specified molar ratio of metallic Mn powder to aq. soln. of salt of a metal having catalytic activity such as NiCl2. The precipitate is washed and dried after completing the reaction. The catalyst prepd. by this method exhibits high activity. It does not cause spontaneous ignition nor deterioration of activity even if it is allowed to contact with air. Accordingly, it can be held in dry state and preserved for a long period.