Atomic Scale Observation of the Structural Dynamics of Supported Gold Nanocatalysts under 1,3-Butadiene by in situ Environmental Transmission Electron Microscopy

Supported gold catalysts have been reported to exhibit exceptional selectivity towards the desirable product, an alkene, in chemoselective hydrogenation of highly unsaturated alkynes and alkadienes. However, insights on the interactions between the gold nanoparticles and the 1,3-butadiene adsorbates are lacking. In this work, using atomic scale in situ ETEM with the support of DFT-based calculations, the reactivity of TiO2 supported gold nanoparticles below 7 nm towards 1,3-butadiene is investigated by monitoring their structure and dynamics under 10(5) Pa of 0.46 % C4H6/He during cooling at 300 & DEG;C and 200 & DEG;C. For sizes larger than 5 nm, the initial truncated octahedron morphology of gold nanoparticles is found to evolve towards a rounded morphology, with the growth of more open (110) surfaces and higher index facets at the expense of the initially present (100) and (111) facets, reflecting the adsorption of butadiene on low coordination sites at 300 & DEG;C. The morphology changes are shown to be accompanied by nucleation and glide of dislocations. At 200 & DEG;C, 1,3-butadiene adsorption is shown to predominateon (111) facets, with the nanoparticles reverting to a faceted morphology while maintaining their fcc structure. For smaller particle size, Au fcc structure is also maintained under 1,3-butadiene.