Effect of TiO₂ on Pd/La₂O₃-CeO₂-Al₂O₃ Systems during Catalytic Oxidation of Methane in the Presence of H₂O and SO₂

New results on the effect of TiO₂ on Pd/La₂O₃-CeO₂-Al₂O₃ systems for catalytic oxidation of methane in the presence of H₂O and SO₂ have been received. Low-temperature N₂-adsorption, XRD, SEM, HRTEM, XPS, EPR and FTIR techniques were used to characterize the catalyst. The presence of Ce³⁺ on the catalytic surface and in the volume near the lantana was revealed by EPR and XPS. After aging, the following changes are observed: (i) agglomeration of the Pd-clusters (from 8 nm to 12 nm); (ii) transformation of part of the TiO₂ from anatase to larger particles of rutile; and (iii)-the increase in PdO/Pd-ratio above its optimum. The modification by Ti of the La₂O₃-CeO₂-Al₂O₃ system leads to higher resistance towards the presence of SO₂ most likely due to the prevailing formation of unstable surface sulfites instead of thermally stable sulfates. Based on kinetic model calculations, the reaction pathway over the Pd/La₂O₃-CeO₂-TiO₂-Al₂O₃ catalyst follows the Mars-van Krevelen mechanism. For evaluation of the possible practical application of the obtained material, a sample of Pd/La₂O₃-CeO₂-TiO₂-Al₂O₃, supported on rolled aluminum-containing stainless steel (Aluchrom VDM^®), was prepared and tested. Methane oxidation in an industrial-scale monolithic reactor was simulated using a two-dimensional heterogeneous reactor model.