TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Catalyst: The catalyst has chlorine, nitrogen and a sulfur content of not greater than 500 parts per million (ppm), not greater than 500 parts per million and not greater than 600 ppm respectivelyThe catalyst further contains fine particles which comprise at least one element selected from gold, silver, platinum, palladium, rhodium, iridium, rhenium, ruthenium, copper, iron, cobalt, manganese, chromium, vanadium and titanium having average particle diameter of 5 - 50 nm.The fine particles are present in an amount of 0.025 - 10 wt.% calculated as each metal element based on the weight of the metallic nickel contained in the catalyst.Preferred Components: The molar ratio of the metallic nickel to whole-metal ions contained in the catalyst is 0.0007 - 0.342.The fine metallic nickel particles have average particle diameter of 1 - 20 nm.Preferred Method: The low-temperature decomposition step is conducted at 250 - 650degreesC; and the high-temperature decomposition step is conducted at 300 - 850degreesC. EXAMPLE - Magnesium sulfate heptahydrate (221.8 g) and aluminum sulfate (72.93 g) were dissolved in water to prepare a 1000 ml solution. To the solution sodium carbonate (24.12 g), sodium silicate (6.104 g), sodium hydroxide (310 ml) were added to prepare a mixed alkali solution (2000 ml). The prepared mixed solution containing magnesium salt and aluminum salt was added to the mixed alkali solution and the resultant mixed was aged at 80degreesC for 6 hours to obtain composite hydroxide core particles. The pH of obtained reaction solution was 8.3. The resultant alkaline suspension was mixed with mixed solution (500 ml) containing magnesium salt, a nickel salt and an aluminum salt, which was prepared by dissolving magnesium sulfate heptahydrate (18.48 g), nickel sulfate (65.71 g) and aluminium sulfate (6.078 g) to adjust pH of reaction solution to 11.5. The reaction solution was aged at 95degreesC for 3 hours, thereby topotactically growing a composite hydroxide on the surface of the composite hydroxide core particles. The obtained reaction solution was filtered, separated and was washed with chemical solution composed of 55degreesC 1N sodium hydroxide in an amount of 25 g/1 kg of the composite hydroxide particles. The molar ratio of sum of magnesium, aluminum, nickel and silicon added upon growth reaction to sum of magnesium and aluminum added upon production of core particles was 0.250. The formed particles had average-plate surface diameter of 0.215 microns, crystallite size D006 of 0.042 microns and BET surface area of 78.2 m2/g. The resultant composite hydroxide particles were molded into spherical beads, having a diameter of 3 mm, were calcined in air at 1370degreesC for 8 hours to obtain oxide particles (beads shape), which were subjected to reducing treatment at 880degreesC for 2 hours in a gas flow containing hydrogen and argon at a volume ratio of 20/80, to obtain a hydrocarbon-decomposing catalyst having nickel content of 20.39 wt.%. The fine metallic nickel particles had particle size of 1 nm. The obtained catalyst had silicon content of 1.952 wt.% and sulfur concentration of 0.5 parts per million. The spherical beads having diameter of 3 mm had average strength of 38 kg.