Non-FCC rich Au crystallites exhibiting unusual catalytic activity

Bipyramidal Au microcrystallites have been synthesized by thermalizing a Au-organic complex in the presence of Ag（I） ions, the latter acting as a shape- directing agent. With a highly corrugated morphology leading to strain-induced non-face-centered cubic （non-FCC） Au phases, the non-FCC portion can be tuned by varying the Ag/Au ratio, as verified by diffraction measurements. For a Ag/Au ratio of 0.34, the non-FCC Au portion was as high as 85%. X-ray microdiffraction and electron diffraction measurements reveal that the non-FCC contribution comes primarily from bipyramids, while other microcrystallites, namely, tetrahexahedrons and hexagrams, host non-FCC phases only at the edges and, to an even lesser extent, at the comers. When used as a catalyst for p-nitrophenol reduction, the non-FCC microcrystallites exhibit a significantly enhanced activity compared to FCC Au, which shows only negligible activity. These results are in accordance with trends in the values of two descriptors of reactivity calculated from first principles： The effective coordination number is found to decrease and the d-band center is found to increase in energy going from the FCC to the non-FCC phases of Au. Our findings contradict the general notion that Au is catalytically active only in nanodimensions and is otherwise inert; in this system, its activity arises from the non-FCC phases.

High-temperature elemental segregation induced structure degradation in high-entropy fluorite oxide

Fluorite-structured oxides constitute an important category of oxides with a wide range of high-temperature applications.Following the concept of high entropy,high-entropy fluorite oxides(HEFOs)have showcased intriguing high-temperature application potential.However,unlocking this potential necessitates an assessment of their long-term stability under high-temperature conditions.In this study,we conducted a prolonged heat treatment at 1000℃on typical HEFO,specifically(CeHfZrGdLa)O_(x).After 100 h,high-intensity X-ray diffraction(XRD)revealed a transition from a single-phase fluorite to a multi-phase configuration.Further investigation by analytical electron microscoy(AEM)demonstrated that this degradation resulted from facilitated element diffusion and consequent escalating chemical fluctuation at high temperatures,leading to spontaneous segregation and separation of Ce and La elements,forming Ce-rich,La-poor,and La-rich phases.Notably,the La-rich phase spontaneously transformed from a fluorite structure(space group Fm3m)to a bixbyite structure(space group Ia3)at elevated temperatures,resulting in the appearance of superstructure reflection in XRD profiles and electron diffraction patterns.Despite the intricate phase decomposition,the energy band gap showed minimal variation,suggesting potential property stability of(CeHfZrGdLa)O_(x)across a broad range of compositions.These findings offer valuable insights into the future applications of HEFOs.