Methane oxidation – effect of support, precursor and pretreatment conditions – in situ reaction XPS and DRIFT

The methane combustion was studied on Pd supported catalysts searching for explanation of the effects of support, pretreatment and induction periods on the activity of the Pd/alumina, Pd/zirconia, Pd/niobia and Pd/niobia/alumina catalysts. Characterization of methane oxidation in XPS and DRIFTS chambers indicated that an induction period of at least 6 h is necessary to form Pd in a higher oxidation state Pd2+δ coexisting with PdO as the surface active phases. Similarly, DRIFTS measurements showed distinct species at the surface during the oxidation of methane after 6 h, indicating formate species on Pd/Alumina and CHx-species and O2− adsorption on the Pd/zirconia catalyst, suggesting different reaction mechanisms. The reverse pathway depends on the surface modification due to the temperature and induction time. The activity of the Pd/niobia/alumina was better than of the Pd/niobia. The effect of the precursor was observed, indicating that palladium nitrate precursor allows to lower dispersion but better performance on methane oxidation. The stability was studied and shows that the Pd/zirconia catalyst was stable and is regenerated, while the Pd/alumina catalyst deactivates very fast and is not regenerated. The effect of pretreatment of the catalysts on the methane oxidation showed different behavior depending of the support.