Abstract
To probe the nature of metal-catalysed processes and to design better metal-based catalysts, atomic scale understanding of catalytic processes is highly desirable. Here we use aberration-corrected environmental transmission electron microscopy to investigate the atomic scale processes of silver-based nanoparticles, which catalyse the oxidation of multi-wall carbon nanotubes. A direct semi-quantitative estimate of the oxidized carbon atoms by silver-based nanoparticles is achieved. A mechanism similar to the Mars–van Krevelen process is invoked to explain the catalytic oxidation process. Theoretical calculations, together with the experimental data, suggest that the oxygen molecules dissociate on the surface of silver nanoparticles and diffuse through the silver nanoparticles to reach the silver/carbon interfaces and subsequently oxidize the carbon. The lattice distortion caused by oxygen concentration gradient within the silver nanoparticles provides the direct evidence for oxygen diffusion. Such direct observation of atomic scale dynamics provides an important general methodology for investigations of catalytic processes.
Highlights
To probe the nature of metal-catalysed processes and to design better metal-based catalysts, atomic scale understanding of catalytic processes is highly desirable
How do the oxygen molecules dissociate and how do they transport to the Carbon nanotube (CNT)? It is important to understand the relationships among the atomic structures of Ag NPs, the atomic scale dynamics and the catalytic oxidation processes in order to develop better supported metal catalysts for desired catalytic properties
Many rounds of experiments confirmed that such a treatment does not oxidize the multi-wall CNTs (Supplementary Fig. 1 and Supplementary Note 1) and the contaminants were removed from the surfaces of the CNTs
Summary
To probe the nature of metal-catalysed processes and to design better metal-based catalysts, atomic scale understanding of catalytic processes is highly desirable. It is important to understand the relationships among the atomic structures of Ag NPs, the atomic scale dynamics and the catalytic oxidation processes in order to develop better supported metal catalysts for desired catalytic properties In this communication, an aberration-corrected environmental transmission electron microscopy (AC-ETEM) is used to directly record the processes of silver-based NPs catalysed oxidation of multi-wall CNTs (MW-CNTs). To the best of our knowledge, this is the first atomic scale observation of the oxidation of carbon materials by metal NPs. On the basis of the experimental observation, we propose that the oxygen molecules dissociate at the particle surfaces and the dissociated oxygen atoms diffuse through the NPs to reach the Ag/CNT interfaces and subsequently oxidize the CNTs. It is expected that such an approach to study catalytic reactions is general and may be extended to investigations of other important catalytic reactions
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