The catalytic growth of carbon nanotubes was investigated from the point of view of reaction mechanism. A great variety of catalyst supports (silica gel, zeotype materials, alumina, etc.) with different pore diameter was tested in acetylene decomposition at 1000 K. Quality and existence of carbon deposit was followed by transmission electron microscopy and the state of catalyst was investigated by in situ X-ray photoelectron spectroscopy measurements. It was proved that only catalyst particles deposited on the external surfaces of porous support could take part in the catalytic carbon nanotube formation.