The supported Ni co-catalyst surface of the thermocatalytic cracking (TCC) hybrid catalyst produces very active hydrogen species. Such species, once transferred (spilt-over) onto the surface of the main catalyst component (cracking sites), interact with the adsorbed reaction intermediates, resulting in a decreased formation of coke precursors (polynuclear aromatics) and the dearomatization/ring-opening of some heavy compounds of the feed. Simultaneously, there is a significant increase in the product yields of light olefins, particularly ethylene and propylene. Analysis of reaction products after 10 h of continuous reaction shows the very significant effects of these co-catalysts on heavy feedstocks such as vacuum gas oils, although the amounts of these (spilt-over) hydrogen species are very small, in comparison to the molecular hydrogen produced by the cracking reactions.