Operando Electron Microscopy Study of Cobalt-based Fischer-Tropsch Nanocatalysts

Thanks to their stability and selectivity for long-chains hydrocarbons, supported Co nanoparticles are the most commonly used catalysts in the Fischer-Tropsch synthesis reaction. We report here on the use of in situ transmission electron microscopy (TEM) to address the real-time evolution of cobalt-based catalysts during their reduction under relevant industrial activation condition (10(5) Pa, 430 degrees C), and their operation in syngas (H-2/CO=2, 10(5) Pa, 220 degrees C). To do so, we chose Co3O4-Pt nanoparticles supported on silica or alumina that can be directly compared to some industrial catalysts. By analysing the real space information contained in the TEM images, we have monitored the fragmentation of cobalt aggregates, the disappearance of cavities within the particles, their shape changes, the particle diffusion and coalescence processes, as well as the effect of the support (silica or alumina) on the behaviour of the Co phase. An easier reduction of cobalt catalysts supported on silica as compared to the same catalyst supported on alumina was also observed. During the catalyst operation under syngas, we have noticed the stability of the general shape of the particles. Simultaneously, using a residual gas analyser connected to the TEM holder, the main gas products of the Fischer-Tropsch reaction were systematically analysed. Our findings underline the benefit of the operando TEM to study the dynamical evolution of catalysts, at the nanoparticle level, under operation conditions.