Study of Ag/CexNd1-xO2 nanocubes as soot oxidation catalysts for gasoline particulate filters: Balancing catalyst activity and stability by Nd doping

- Nd doping decreases the activity of Ag/CeO2 but enhances its thermal stability.
- Nd brings forth surface oxygen vacancies (VO-s) but reduces the bulk ones (VO-b).
- Both inadequate VO-b and excessive VO-s hinder the ceria bulk oxygen availability.
- Excessive VO-s induces the formation of O2− instead of highly active Ox−.
- VO-s and mesopores generated by Nd doping inhibit Ag sintering effectively.

Three nanocubic Ag/CexNd1-xO2 catalysts were synthesized to evaluate the influence of Nd doping on catalyst practicability. It was observed that Nd doping generated excessive ceria surface oxygen vacancies, but reduced the bulk oxygen vacancies. These variations in oxygen vacancies suppress the utilization of ceria bulk oxygen, and induce the formation of less active O2− species instead of O2−, resulting in a low soot oxidation activity. However, the introduction of Nd can inhibit Ag sintering and thus enhance the catalysts' thermal stability effectively. As a consequence, Ag/Ce0.95Nd0.05O2 nanocubes make a good balance between the catalyst activity and stability. Moreover, it was observed that catalyst deactivation during soot oxidation becomes more obvious when the catalysts and soot are not in close contact.

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