The Impact of CeO2 Loading on the Activity and Stability of PdO/γ-AlOOH/γ-Al2O3 Monolith Catalysts for CH4 Oxidation

This study reports on the activity and stability of PdO/γ-AlOOH/γ-Al 2O 3 monolith catalysts, promoted with varying amounts of CeO 2, for CH 4 oxidation. Although the beneficial effects of CeO 2 have been reported for powdered catalysts, this study used a cordierite (2MgO.2Al 2O 3.5SiO 2) mini-monolith (400 cells per square inch, 1 cm diameter × 2.5 cm length; ~52 cells), washcoated with a suspension of γ-Al 2O 3 combined with boehmite (γ-AlOOH), followed by sequential deposition of Ce and Pd (0.5 wt.%) by wetness impregnation. The monolith catalysts’ CH 4 oxidation activity and stability were assessed in the presence of CO, CO 2, H 2O and SO 2 at low temperature (≤550 °C), relevant to emission control from lean-burn natural gas vehicles (NGVs). The CeO 2 loading (0 to 4 wt.%) did not significantly impact the adhesion and thermal stability of the washcoat, but CeO 2 reduced the inhibition of CH 4 oxidation by H 2O and SO 2. The catalyst activity, measured by temperature-programmed methane oxidation (TPO) in a dry feed gas with 0.07 vol.% CH 4, showed that adding CeO 2 to the γ-AlOOH/γ-Al 2O 3 washcoat suppressed the activity of the catalysts; whereas, CeO 2 improved the catalyst activity when H 2O (2 and 5 vol.%) was present in the feed gas. Moreover, adding CeO 2 decreased catalyst deactivation that occurred in the presence of 10 vol.% H 2O and 5 ppmv SO 2 at 500 °C, measured over a 25 h time-on-stream (TOS) period. The highest catalyst activity and stability for CH 4 oxidation in the presence of H 2O was obtained by adding 2 wt.% CeO 2 to the washcoat. View Full-Tex