Tar elimination and hot-gas conditioning in thermochemical conversion processes, i.e. thermal gasification, pyrolysis of heterogeneous materials involved two main classes of catalysts and/or additives: metallic and mineral oxides. This communication focused on the experimental kinetic data on catalytic steam cracking of vaporized toluene (PC7H8 = 0.93-1.15 kPa, H2O/C7H8 = 2.67 mol/mol, space-time tau = 0.067-0.127 kg h (Nm(3))(-1)) as a tar-derived species and/or Volatile Organic Compound (VOC). Toluene (C7H8) has been chosen as a model formula for reactive tar-derived one-ring species determined from tar constituents. Gaseous product distribution data were obtained at atmospheric pressure (101.3 kPa). steam pyrolysis temperature range of 923-1223 K and GHSV 1200-2300 Nm(3) (m(3)h)(-1). The overall catalytic pyrolysis of toluene over a commercial available metal based catalyst NiMo/gamma-Al2O3 was compared to the pyrolysis in presence of basic non-metallic mineral additives. i.e. Norwegian (Norsk Hydro) dolomitic magnesium oxide [MgO], Swedish low surface quicklime [CaO]. and calcined dolomite [CaM2(O)(2)]. The operational conditions were applied without internal or external mass-transfer limitations. Kinetics for the pyrolysis could be described by first-order reactions for all the studied additives. The influence of hydrogen gas (30 vol%, tau = 0.150 kg h (Nm)(-1)) and water vapor (P-H2O = 4.51-21.41 kPa, tau = 0.092-0.270 kg h (Nm(3))(-1)) in vaporized toluene cracking runs over low surface quicklime [CaO] was determined. A mechanistic model of the Langmuir-Hinshelwood type describing toluene decomposition was also developed. (C) 2003 Elsevier Ltd. All rights reserved.