Abstract. In situ microprobe Raman and XRD techniques were used to follow the oxidation state of Rh/Al2O3 and Ru/Al2O3 catalysts during the catalytic ignition process of the partial oxidation of methane (POM) to synthesis gas. It was found that the catalyst was in the fully oxidized state before ignition of the POM reaction, and abruptly changed its oxidation state at the temperature at whi…