Epitaxial Domain of Pd Oxide with a Superperiodic Structure Formed on Sr3Ti2O7: A Promising Environmental Catalyst for Exhaust Gas Purification

The epitaxial growth of heterogeneous catalysts needs highly crystalline metal oxide-based ceramics as a catalyst support. However, the inherently low surface area of these ceramic materials poses a significant limitation to their catalytic application. Against this background, this study reveals that loading a very small amount of Pd species onto Sr3Ti2O7, which is a ceramic material synthesized by calcination at 1273 K, leads to the epitaxial bonding of Pd oxide based on the space group of Fm3m to the ab surface of Sr3Ti2O7. Interestingly, the Pd oxide particle with particle sizes in the range of 2–5 nm has a superperiodic structure, where ordered and disordered Pd atoms are cyclically repeated in the a-axial direction of Sr3Ti2O7. Density functional theory calculations suggest that the charge transfer from Sr3Ti2O7 to Pd oxide facilitates the formation of an epitaxial junction and causes structural fluctuations in Pd oxide. The Pd/Sr3Ti2O7 catalyst with a unique heterojunction exhibits excellent catalytic activity for the purification of automotive exhaust gases. In addition, the Pd/Sr3Ti2O7 catalyst is more active than the benchmark Pd/Al2O3 catalyst despite its low surface area of only 2 m2 g-1. This study demonstrates that metal oxide-based ceramics can be used as catalyst materials by precisely designing their heterojunctions.