The catalyzed steam cracking of n-heptane was carried out using a fixed-bed reactor and different, commercially available limestone [CaCO3], dolomites [CaMg(CO3)(2)], and NiMo/gamma-Al2O3 as the catalysts. The steam cracking of n-heptane was investigated by variation of water and n-heptane partial pressure and by the additions of hydrogen and carbon dioxide to the water vapor at a total pressure of 101.3 kPa. In the presence of calcined dolomite (1073 K), the partial pressure of water vapor (P-H2O = 9.1-34.2 kPa) enchances cracking efficiency, whereas hydrogen (p(H2) approximate to 33 kPa) and carbon dioxide (CO2 = 39 vol %), when added to the cracking mixture (973 K), do suppress conversion of n-heptane.