TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: The step (b) is performed in the presence of hydrogen, and at 260-460 degrees C, or 300-380 degrees C. The step (d) is performed at 600-800 degrees C or 650-750 degrees C. The carbon dioxide is introduced into the first reaction chamber at a flow rate of 5-60 ml/minute. The reaction product is fed through water vapor during any one of steps (b), (c), or (d), or prior to the reaction product being transferred to the second reaction chamber. At least 80%, 90%, 95%, or nearly 100% of the carbon dioxide used in step (b) was converted to the reaction product comprising multiple wall carbon nanotubes. Preferred Components: The reducing agent is hydrogen gas. The nickel containing catalyst is supported by a metal oxide or oxide carrier. The metal oxide is silicon dioxide, aluminum oxide, a rare earth metal oxide, and/or a modified aluminum oxide. The oxide carrier is magnesium oxide, calcium oxide, other alkali-earth oxide, zinc oxide, zirconium oxide and/or titanium oxide. The group VIII metal containing catalyst is a nickel, cobalt, or iron containing catalyst or their composite. The reaction product comprises methane, and further comprises water, carbon dioxide, hydrogen, or carbon monoxide. The majority of the carbon nanotubes have closed tube ends. The outer diameter of the carbon nanotubes is 19-21 nm. The thickness of the carbon nanotube walls is 4-7 nm. The inner diameter of the carbon nanotubes is 7-10 nm or 3-5 nm. The water vapor pressure is 1-10 kPa or 1-5 kPa. The amount of water present within the reaction product after the product is fed through the water vapor is 1-10% or 1-5% by molar volume of the reaction product. At least part of the carbon nanotubes has open tube ends. The carbon-based carbon nanotubes yield was at least greater than or equal to 20% (preferably greater than or equal to 40%) from the carbon of the inlet carbon dioxide utilized in step (b). The carbon dioxide in step (b) is the only carbon source that is used to produce the carbon nanotubes. EXAMPLE - No suitable example given.