NOVELTY - Making carbon nanotubes comprises: (a) reducing a nickel containing catalyst with a reducing agent in a first reaction chamber; (b) contacting the nickel containing catalyst with carbon dioxide under conditions to produce a reaction product; (c) transferring the reaction product to a second reaction chamber that comprises a group VIII metal containing catalyst; and (d) contacting the group VIII metal containing catalyst with the reaction product under conditions to produce carbon nanotubes, where the first and second reaction chambers are in flow connection during the step (c).    USE - The method is useful for making carbon nanotubes, which are multi-wall and/or single-wall carbon nanotubes (all claimed), and are used in: nanotechnology, electronics, optics and other fields of materials science and technology; and products including nanotube-based transistors, circuits, cables, wires, batteries, solar cells, baseball bats, golf clubs and car parts.    ADVANTAGE - The method: provides carbon nanotubes by at least 20%, nearly 100% conversion of carbon dioxide (claimed); and utilizes water vapor, thus increasing the yield of the carbon nanotubes.    DETAILED DESCRIPTION - Making carbon nanotubes comprises: (a) reducing a nickel containing catalyst with a reducing agent in a first reaction chamber; (b) contacting the nickel containing catalyst with carbon dioxide under conditions to produce a reaction product; (c) transferring the reaction product to a second reaction chamber, where the second reaction chamber comprises a group VIII metal containing catalyst; and (d) contacting the group VIII metal containing catalyst with the reaction product under conditions to produce carbon nanotubes, where the first and second reaction chambers are in flow connection during the step (c), the only source of carbon used to form the carbon nanotubes is from the carbon dioxide used in step (b), and at least 20% of the carbon from the carbon dioxide used in step (b) is converted into carbon nanotubes. An INDEPENDENT CLAIM is also included for a carbon nanotube produced by the method.