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.
In situ ETEM experiment revealed interaction between beam-gas-sample where carbon coatings formed over MgO-supported Pt particles. HRTEM imaging at high temperature showed layer-by-layer formation of carbon layer while the particle shape underwent changes. Effect of e-beam dose rate on carbon layer formation was also investigated.