PetroStreet

What exactly is the reaction within Fisher-Tropsch reactor, and the associated beneficial products?

Fischer–Tropsch synthesis converts syngas into long-chain hydrocarbons.
FT is not one reaction, it’s a polymerization process on a metal surface.
Step-by-step:
CO adsorbs on catalyst (Co or Fe)
CO dissociates - C + O
Carbon atoms hydrogenate
CHx species chain-grow
Chains terminate - hydrocarbons leave surface

FT does not directly make “diesel” or “jet fuel”.
So what you get is methane, LPG, Naphtha, Diesel range, wax.

Syngas to long-chain hydrocarbons, and where exactly this reaction is used? I mean what are the major industrial units utilizing this reaction?

See this reaction is being used by Sasol Shell, Chevron to convert the NG to Syn Gas and then through Fischer-Tropsch to fuels including synthetic fuel, naphtha, FT wax, LPG, Jet fuel, and lubricants. Can also be used to have speciality chemicals... all too may end products, long chain hydrocarbons...

Thanks jeem.