Abstract: A process for the production of a carbon nanotube product comprises: introducing sequentially or concurrently a metal catalyst precursor, a source of carbon and a sulphur-containing additive into a continuous flow of a hydrogen-containing carrier gas in a temperature-controlled flow-through reactor; exposing the metal catalyst precursor in the flow of the carrier gas to a first temperature zone sufficient to generate particulate metal catalyst; exposing the catalyst, the source of carbon and the sulphur-containing additive to a second temperature zone downstream from the first temperature zone that can produce a carbon nanotube aggregate; discharging the aggregate as a continuous discharge through a discharge outlet of the reactor; collecting the continuous discharge in the form of a carbon nanotube product; and recycling continuously an exhaust stream of hydrogen by-product exhausted from the outlet to progressively replace the continuous flow.