NOVELTY - Catalyst system for the selective conversion of hydrocarbons into multi-walled carbon nanotubes and hydrogen, comprises nickel, cobalt, iron and aluminum oxide complex (I)    USE - The catalyst system is useful for the selective conversion of hydrocarbons into multi-walled carbon nanotubes and hydrogen (claimed). The carbon nanotubes are useful in artificial muscle, biosensors, composite materials, conductive plastics, flat panel display, microelectronic devices, extra strong fibers, electron field emissions, gas storage, technical textile, protection against flame and antistatic.    ADVANTAGE - The process for producing carbon nanotubes using the catalyst system: involves further optimization in selectivity and productivity without the formation of other types of carbon species (e.g. carbon fibers and amorphous carbon); does not require many purification steps; and is cost effective.    DETAILED DESCRIPTION - Catalyst system for the selective conversion of hydrocarbons into multi-walled carbon nanotubes and hydrogen, comprises nickel cobalt iron and aluminum oxide compound of formula (Ni, Co) FeyOz (Al2O3)w (I), where y represents the molar fraction of iron relative to cobalt and nickel.    y = 0.11-9 (preferably 2);    z = 1.12-14.5 (preferably 4); and    w = 1.5-64 (preferably 4.5-32).    INDEPENDENT CLAIMS are also included for:    (1) a process for synthesizing hydroxide precursor of formula (Ni, Co) Fey(OH)p(Al(OH)3)q (II) comprising reacting cobalt/nickel, iron and aluminum compounds using process such as impregnation, co-precipitation (both preferred), or sol-gel and citrate complexation; and    (2) a process for the selective conversion of hydrocarbons into multi-walled carbon nanotubes and hydrogen comprising: providing (II); activating (II) by drying and/or calcination; contacting the activated catalyst with a carbon source under multi-walled carbon nanotube production conditions of a reaction temperature and a reaction space time; and extracting multi-walled nanotubes.