Kinetic Model of the Partial Oxidation of Methane to Synthesis Gas Over Ru/TiO Catalyst 2 Costas Elmasides, Theophilos Ioannides, and Xenophon E. Verykios Dept. of Chemical Engineering, University of Patras, GR-265 00 Patras, Greece The kinetic beha®ior of the Ru r TiO catalyst in the partial oxidation of methane to 2 synthesis gas was in®estigated as a function of temperature and partial pressures of CH 4 and O . It was found that the catalyst promotes, to a large extent the direct formation of 2 CO and H from the reaction of methane and oxygen, while the reforming and 2 water  gas shift reactions are negligible under these conditions. A kinetic model, based on formation of CO and H as primary products and of CO and H O as secondary 2 2 2 oxidation products, describes satisfactorily the obser ®ed kinetic beha®ior. Values of model parameters satisfy thermodynamic constraints and agree well with data deri®ed from surface science techniques and kinetic studies of elementary surface processes that are in the literature. Introduction Formation of synthesis gas via catalytic partial oxidation of methane has received significant attention during the past several years. A review of the process and its comparison with existing technologies for syngas production has been pub- Ž . lished Pena et al., 1996 . Concerning the reaction pathway of the partial oxidation of methane to synthesis gas, two main reaction schemes have been proposed: one is the sequence of total oxidation fol- Ž . lowed by reforming reactions indirect scheme, Eqs. 2  4 , and the other is the direct conversion of methane to synthesis gas without the formation of CO and H O as reaction interme- 2 2 Ž . diates direct scheme, Eq. 1 . 1 o CH q O ™2H qCO  H sy35 kJ r mol 1 Ž. 4 2 2 298 2 CH q2O ™CO q2H O  H o sy801 kJ r mol 4 2 2 2 298 2 Ž. CH qCO ™2CO q2H  H o sq247 kJ r mol 3 Ž. 4 2 2 298 CH qHO ™CO q3H  H o sq206 kJ r mol 4 Ž. 4 2 2 298 Correspondence concerning this article should be addressed to X. E. Verykios. Present address of T. Ioannides: Foundation for Research and TechnologyHel- Ž . las FORTH , Institute of Chemical Engineering and High Temperature Chemical Ž . Processes ICErHT , P.O. Box 1414, GR-265 00 Patras, Greece. The indirect scheme is supported by experimental findings of several investigators, who have shown that a considerable hot spot develops at the entrance of the catalytic bed. This is indicative of the occurrence of the exothermic methane com- bustion. In this case, CO and H selectivity are practically 2 Ž . zero at low methane conversions 25% , where oxygen is Ž . not fully consumed Dissanayake et al., 1991 . It is generally accepted that the direct scheme is followed in the case of Rh and Pt catalysts under conditions of high temperature Ž . 1,000°C and very short contact times, as Schmidt and Ž . coworkers have shown Hickman and Schmidt, 1993a and Ž . Fathi et al. 1998 . Most catalysts seem to favor the indirect scheme at inter- Ž . mediate temperatures 700  800°C . A notable exception has been found to be the catalytic systems based on RurTiO 2 Ž . Boucouvalas et al., 1996a,b . More specifically, it has been found that, in the absence of significant mass- and heat- Ž . transfer resistances, high selectivity to synthesis gas 60% is obtained over RurTiO catalysts in the low methane con- 2 Ž . version range oxygen conversion 100% , at temperatures as low as 600  700°C. On the other hand, very low selectivity to synthesis gas is obtained when oxygen conversion is less Ž than 100%, over supported metal catalysts Ni, Rh, Pd, and . Ir , as well as Ru catalysts supported on carriers other than Ž . TiO Boucouvalas et al., 1996b . The extent of the direct 2 scheme was also found to be sensitive to modifications of the June 2000 Vol. 46, No. 6 AIChE Journal 1260