The kinetics of reactions of D atoms with ethyl iodide adsorbed on Pt(111), H covered Pt(111), and monolayer C covered Pt(111) surfaces were studied using direct product detection. Ethane, C2H5D, was observed as gaseous product formed through ethyl abstraction from the halide. On C/Pt(111) substrates the reaction kinetics are compatible with the operation of Eley-Rideal mechanisms. At annealed halide submonolayers on C/Pt(111) ethane forms in one step; at three-dimensional halide islands a two-step reaction was observed, probably with a C2H5 radical as intermediate. The measured kinetics could be very well reproduced by a sequence of two Eley-Rideal reaction steps with cross-sections in line with expectations. On Pt(111) and H/Pt(111) substrates the abstraction kinetics of ethyl from the adsorbed halide is controlled by hot-atom mechanisms. Coadsorbed H leads to simultaneous abstraction of H from the surface towards HD and H-2, as well as to a gaseous C2H6 product. The ethyl abstraction cross-sections are in the range 0.5 to 1 Angstrom(2), in line with direct processes. The results provide further evidence that the substrate, nonmetallic or metallic, is instrumental in controlling the operating Eley-Rideal or hot-atom mechanisms of atom-adsorbate reactions.