Abstract: A catalyst comprising 10 to 30 wt.% of nickel as nickel oxide, 20 to 60 wt.% of calcium as calcium oxide, 10 to 70 wt.% of aluminum as aluminum oxide and containing less than 1 wt.% of silicon dioxide. The catalyst is prepared by using: as the starting material for the nickel component, fine particles of nickel oxide obtained by heating a nickel compound which is decomposed to nickel oxide by heating at a temperature in the range of 400.degree. to 800.degree. C in the presence of oxygen; as the starting material for the calcium component, calcium oxide per se or a calcium compound which is decomposed to calcium oxide by heating and; as the starting material for the aluminum component, alumina cement of a high purity. The catalyst is prepared by mixing and kneading the starting materials with water, molding the same, then keeping the catalyst composition under a highly humid atmosphere at a temperature in the range of 5.degree. to 35.degree.