Transient response of catalyst bed temperature in the pulsed reaction of partial oxidation of methane to synthesis gas over supported group VIII metal catalysts

Mechanisms of partial oxidation of methane to synthesis gas were studied using a pulsed reaction technique and temperature jump measurement. Catalyst bed temperatures were directly measured by introducing 1 and 3 ml pulses of a mixture of CH4 and O-2 (2/1). With Ir, Pt and Ni/TiO2 catalysts, a sudden temperature increase at the front edge of the catalyst bed was observed upon introduction of the pulse. The synthesis gas production basically proceeded via two-step paths consisting of highly exothermic complete methane oxidation to give H2O and CO2 followed by the endothermic reforming of methane with H2O and CO2. In contrast, with the Rh and Pd/TiO2 catalysts, the temperature at the front edge of the catalyst bed decreased upon introduction of the CH4/O-2 (2/1) pulse and a small increase in the temperature at the rear end was observed, Initially, the endothermic decomposition of CH4 to H-2 and deposited carbon or CHx probably took place at the front edge of the catalyst bed, after which the deposited carbon or generated CHx species would be oxidized into COx. When the Ru/TiO2 catalyst was used, a temperature increase at the front edge of the catalyst bed was observed upon introduction of the 3 mi pulse of CH4/O-2, In contrast, the temperature drop at the front edge of the catalyst bed was observed for a 1 ml pulse of CH4/O-2. These results seemed to exhibit two possibilities for a synthesis gas formation route over the Ru/TiO2 catalyst, The reaction pathway of the partial oxidation of methane with group VIII metal-loaded catalysts depended strongly upon the metal species and reaction conditions. (C) 2001 Elsevier Science B.V. All rights reserved.