Pd loading threshold for an efficient noble metal use in Pd/CeO2 methane oxidation catalysts

The influence of the noble metal-support interaction on the performance, activation behavior and stability of Pd/CeO2 catalysts for total methane oxidation was systematically investigated. A series of samples with 1–3 wt% Pd loading supported on CeO2 with surface areas varying between 30 and 120 m2/g were tested as-prepared and after different reductive treatments. Distinct Pd structural states were identified, which influence the catalytic performance depending on the pre-treatment and the theoretical monolayer Pd coverage of CeO2. Although reductive treatments improved the catalytic activity, the stability strongly depended on the Pd coverage on ceria and the type of reducing agent. A threshold of Pd concentration on the ceria surface was identified that ensures optimal noble metal efficiency, activity and long-term durability. Below this threshold, rapid catalyst deactivation occurs due to redispersion on the strongly interacting support whereas above this threshold Pd is prone to sintering irrespective of the atmosphere.