PURPOSE: To avoid handling of a strongly basic carbonate solution, facilitate the treatment of basic wastewater and obtain a catalyst with high activity by carrying an alkali metal hydrogencarbonate on activated carbon and producing methyl decomposition catalyst as an alkali metal carbonate by thermal treatment.

CONSTITUTION: A methyl formate decomposition catalyst is prepared as an alkali metal salt by carrying an alkali metal hydrogencarbonate on activated carbon and carrying out thermal decomposition. For example, in the case a catalyst is prepared by carrying potassium hydrogencarbonate which is a catalyst suitable to produce carbon monoxide from methyl formate on activated carbon, potassium hydrocarbonate is dissolved in ion-exchanged water, activated carbon is thrown to be impregnated with the hydrogencarbonate, heated until the temperature becomes a prescribed level by a heat source and left at the temperature. After a prescribed time, the activated carbon is taken out of the solution, dried under reduced pressure, a reaction tube made of a stainless steel is packed with the obtained activated carbon, and while an inert gas is introduced into the tube, thermal decomposition is carried out under atmospheric pressure, and thus an activated carbon carrying potassium carbonate is obtained in the reaction tube.