On the Effect of Atomic Structure on the Activity and Deactivation of Catalytic Gold Nanoparticles

We present studies of the structure and stability of catalytic gold nanoparticles through insitu aberration-corrected electron microscopy to investigate the effect of heating on the nature of the identified atomic active sites. Low coordination surface atoms are replaced by atomically clean surface facets through local rearrangements to minimise surface energy. The associated movement of surface atoms is proposed to directly precede Ostwald ripening. Expansive surface strain resulting from inherently strained structures, such as the decahedra, is shown to diminish with increasing particle size and the associated elastic energy is reduced through a shifting of the disclination axis towards the particle surface. At elevated temperatures a reduction in surface energy anisotropy may lead to energetically favourable morphologies with minimal intrinsic strain. Such processes will act as structural deactivation mechanisms, resulting in a loss of active sites without any necessary associated loss of surface area or change in particle size through traditional sintering mechanisms. Considerations of the active site stability and the particle size according to the reaction conditions are described.