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/CeO$_2$ 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 CeO$_2$. 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.