Alkanes, with the general formula CnH2n+2 , are liquid at room temperature when n is 5-17 & solid when n=18 or above. Therefore, cracking (whether thermal or catalytic) may involve solid or liquid high alkanes in many cases. As you know, the temperatures of both cracking processes are high enough to cause initial vaporization of the alkanes with simultaneous or subsequent bond breaking (the mechanism is still obscure). I think that all these reactions & the last 3 reactions (in the question) are better called (heterogeneously-catalyzed gas-phase reactions).   

No, Cracking is used to decompose VOC into smaller hydrocarbons CH4, C2H6 etc and PAH. you can't use it for gas phase reactions.

No. It cannot be used as gas phase reaction.