In situ time-resolved FTIR and in situ microprobe Raman spectroscopies were used to follow the primary products as well as the surface and gas phase species formed during the reaction of partial oxidation of methane (POM) to synthesis gas over Ir/SiO₂ catalyst. The results suggested that direct oxidation of CH₄ to CO is the dominant pathway of POM reaction over the freshly reduced Ir/SiO₂ catalyst, while the dominant schemes of CO formation over the catalyst under the steady state reaction condition are probably via the reactions of CO₂ and H₂O with the deposited carbon species (CH_x) and/or CH₄. The mechanistic difference between the POM to synthesis gas over freshly reduced Ir/SiO₂ catalyst and the catalyst under the steady state reaction may have resulted from the formation of significant amount of deposited carbon species in the latter system.

Key words: partial oxidation of methane(POM), synthesis gas, iridium catalyst, reaction mechanism