Growth of encapsulating carbon on supported Pt nanoparticles studied by in situ TEM

• Encapsulating coke formation on Pt/MgO model catalyst studied by in situ TEM.
• Time-resolved TEM images show formation of multiple partial layers simultaneously.
• Steps on Pt surface form spontaneously during nucleation and growth of carbon.

Carbon deposition on MgO-supported Pt nanoparticles from ethylene decomposition was studied by in situ transmission electron microscopy (TEM) at the atomic level. An imaging strategy was established for controlling beam-gas-sample interactions that minimizes beam-induced changes of the reaction. Using this strategy, it was possible to observe how carbon encapsulation occurs on Pt nanoparticles and the role of the Pt surface morphology. The evidence suggests that multiple partial layers grew simultaneously prior to full encapsulation of the nanoparticle. The growth of carbon on Pt nanoparticles was found to induce significant changes in the nanoparticle shape, resulting in particles becoming rounder as coking progressed. Closer examination of the surface structure revealed that in some cases carbon growth induced step formation.

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