A process for forming carbon nanofibers by means of pyrolyzation with plasma in a reactor is disclosed. The process includes the steps of: providing, in a reactor, a first catalyst in the form of solid catalytic particles; applying a vacuum to the reactor to create a reduced pressure in the reactor; feeding a first mixture of gases including a carbon-based gas into the reactor; forming, from the carbon-based gas, a plasma containing carbon free-radical species; and forming, in the presence of the catalytic particles, carbon nanofibers.