Transient response of catalyst bed temperature in the pulsed reaction of partial oxidation of methane to synthesis gas over supported rhodium and iridium catalysts

Mechanisms of partial oxidation of methane were studied using a pulsed reaction technique and temperature jump measurement. Catalyst bed temperatures were directly measured by introducing a pulse of a mixture of methane and oxygen (2/1), With Ir/TiO2 catalyst, a sudden temperature increase at the front edge of the catalyst bed was observed upon introduction of the pulse, but the temperature of the rear end of the catalyst bed increased only slightly. The synthesis gas production basically proceeded via a two-step path consisting of highly exothermic methane complete oxidation to give H2O and CO2, followed by the endothermic reforming of methane with H2O and CO2 over Ir/TiO2 catalyst. However, with Rh/TiO2 and Rh/Al2O3 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. At first, endothermic decomposition of CH4 to H-2 and deposited carbon or CHx probably took place at the front edge of the catalyst bed and then deposited carbon or generated CHx species would be oxidized into COx. However, on Rh/SiO2, synthesis gas was produced via a two-step path similar to the case of Ir/TiO2 catalyst. The reaction pathway of partial oxidation of methane with Rh-loaded catalysts depended strongly on the support materials. (C) 1999 Academic Press.