A mechanistic reaction model of the pyrolysis of vaporized n-heptane in the presence of steam (P-H2O approximate to 18-32 kPa) is developed based on overall first-order decomposition kinetics, which satisfactorily describes the experimental data. The mechanistic model predicted that calcined, naturally occurring and readily available mineral rocks, Swedish quarried calcium oxide (quicklime) and Norwegian (Norsk Hydro) magnesium oxide (dolomitic magnesium oxide) applied as the catalytic materials increase the conversion of the vaporized feedstock (Pn-C7H16 = 2.9-4.7 kPa) without changing the distribution of light alpha-olefins (i.e., C2H4, C3+, C4H8), compared to pyrolysis in an empty reactor viz. thermal steam-cracking. The simulation calls attention to the fact that the endothermic pyrolysis reaction of the alkane n-heptane is proceeding not only in the homogeneous gas-phase but also on the mineral particles (catalytic cracking) with the same mechanism.