Non-FCC rich Au crystallites exhibiting unusual catalytic activity  

作　　者：Gangaiah Mettela Nisha Mammen Joydip Joardar Shobhana Narasimhan Giridhar U. Kulkarni 

机构地区：[1]Thematic Unit of Excellence on Nanochemistry and Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore 560 064, India [2]Theoretical Sciences Unit, Jawaharlal Nehru Centre forAdvanced Scientific Research, Jakkur, Bangalore 560 064, India [3]IntemationalAdvanced Research Centre for Powder Metallurgy & New Materials, Balapur, Hyderabad 500 005, India [4]Centre for Nano and Soft Matter Sciences, Jalahalli, Bangalore 560 013, India

出　　处：《Nano Research》2017年第7期2271-2279,共9页纳米研究（英文版）

摘　　要：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.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.

关 键 词：Au microcrystallites non-face-centered cubic（non-FCC） phases microbeam X-raydiffraction （XRD） catalysis effective coordinationnumber 

分 类 号：O643.36[理学—物理化学] TQ546.5[理学—化学]