TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Component: The catalyst comprises zinc oxide. An element(s) having an average particle diameter of not greater than 50 nm from ruthenium, rhodium, iridium, platinum, gold, silver, palladium, nickel, cobalt, copper, iron, zinc, vanadium, or manganese is supported on the clay mineral. Preferred Composition: The catalyst comprises clay mineral (1-50 wt.%). EXAMPLE - Metal-containing solution (600 ml) prepared by dissolving magnesium dinitrate hexahydrate (Mg(NO3)2.6H2O) (75.3 g), aluminum trinitrate nonahydrate (Al(NO3)3.9H2O) (28.3 g), and nickel dinitrate hexahydrate (Ni(NO3)2.6H2O) (9.0 g), and mixed alkali solution (400 ml) prepared by dissolving sodium hydroxide (14 mol/L) (58 ml) of NaOH and sodium carbonate (Na2CO3) (9.6 g) were prepared. The metal-containing mixed solution containing the magnesium salt, the aluminum salt, and the nickel salt was added to the mixed alkali solution, and the resultant mixed solution was aged at 90degreesC for 5.5 hour to obtain a composite hydroxide. The thus obtained composite hydroxide was separated by filtration from the reaction solution, and then dried to obtain particles. The resultant particles were granulated into 3 mmphi, and further subjected to heat treatment and then to reducing treatment, obtaining a nickel catalyst having beads shape. Separately, copper nitrate was sprayed over 3 mmphi alumina beads to support copper in 10.6 wt.% in terms of metallic copper, and the obtained product was heat-treated at 400degreesC for 1 hour. The thus obtained copper-supporting alumina beads were mixed with the above nickel catalyst to prepare a catalyst containing the alumina beads in 20 wt.% on the based on the weight of nickel catalyst. At this time, the copper-supporting alumina beads and the nickel catalyst beads were intimately mixed with each other such that the alumina beads were uniformly dispersed in the nickel catalyst beads. The amount of copper contained in the thus obtained catalyst was 20.4 wt.% in terms of metallic copper based on the weight of nickel contained. Steam-reforming reaction was conducted at 700degreesC for 3 hours. The reactor was purged with nitrogen to decrease a temperature to 100degreesC. Next, a mixed gas having a chemical equilibrium gas composition which was obtained by conducting the steam-reforming reaction at 650degreesC and a ratio of steam to carbon (S/C) of 3, was flowed through a reaction tube of the reactor at a gas hourly volumetric space velocity of 1000 hour-1 for 30 minutes. Then, the reaction tube was sealed with a valve, and allowed to stand at 100degreesC for 1 hour. The reaction tube was cooled to room temperature and taken out from the reactor. After allowing the reaction tube to stand for 3 days, quantitative determination of nickel carbonyl produced during the reaction was performed. As a result, it was confirmed that the amount of the nickel carbonyl produced was less than the lower detection limit and, thus, a sufficient effect of removing the metal carbonyl was attained.