Investigation of Local Structure and Enhanced Thermal Stability of Ir-Doped PdRu Nanoparticles for Three-Way Catalytic Applications

Abstract

The local structure and thermal stability of newly synthesized PdRuIr and PdRu alloy nanoparticles (NPs) were studied using X-ray absorption fine structure spectroscopy (XAFS) and compared with those of Ru NPs. Pd K-edge XAFS reveals that a significant fraction of Pd segregates, forming metal NP clusters. In the PdRuIr NPs, a small fraction of Pd forms an alloy with Ir, whereas a majority phase is Ru–Ir alloy having the novel face-centered cubic structure. Apart from the distinct local surroundings, XAFS analysis revealed the presence of an anharmonic disorder in the PdRu and PdRuIr NPs. The previously observed enhanced thermal stability with Pd and Ir doping was investigated using temperature-dependent in situ XAFS. In the Ru NPs, an abrupt change in the near-edge features was observed at 673 K, which was gradually suppressed for PdRu and PdRuIr NPs. At this temperature, the dynamical fluctuations were more pronounced in the pure Ru NPs, helping to convert surface-adsorbed O2 into the volatile RuO4 phase, thereby leading to earlier evaporation of Ru. Dynamical fluctuation suppresses with alloying elements or gets extended to a higher temperature, helping to delay the RuO4 formation process and enhancing the thermal stability of the PdRu and PdRuIr NPs in increasing order.