Abstract
Using a MEMS nanoreactor in combination with a specially designed in situ Transmission Electron Microscope (TEM) holder and gas supply system, we imaged the formation of multiple layers of graphene encapsulating a cobalt nanoparticle, at 1 bar CO : N2 (1 : 1) and 500 °C. The cobalt nanoparticle was imaged live in a TEM during the Boudouard reaction. The in situ/operando TEM studies give insight into the behaviour of the catalyst at the nanometer-scale, under industrially relevant conditions. When switching from Fischer-Tropsch syngas conditions (CO : H2 : N2 1 : 2 : 3 at 1 bar) to CO-rich conditions (CO : N2 1 : 1 at 1 bar), we observed the formation of multi-layered graphene on Co nanoparticles at 500 °C. Due to the high temperature, the surface of the Co nanoparticles facilitated the Boudouard reaction, causing CO dissociation and the formation of layers of graphene. After the formation of the first patches of graphene at the surface of the nanoparticle, more and more layers grew over the course of about 40 minutes. In its final state, around 10 layers of carbon capped the nanoparticle. During this process, the carbon shell caused mechanical stress in the nanoparticle, inducing permanent deformation.
Highlights
Novel techniques and equipment to allow in situ and operando research on catalytic samples are currently under development
To investigate the behaviour of FT catalysts at elevated pressures and temperatures in a Transmission Electron Microscope (TEM), we used a combination of a MEMS nanoreactor loaded with Co nanoparticles, inserted in a specially designed in situ TEM sample holder
We have shown the in situ formation of layers of graphitic carbon on free-standing cobalt nanoparticles, at 500 C and 1 bar CO : N2 (1 : 1)
Summary
Paper possible to investigate a catalyst under industrially relevant working conditions: high temperatures and high gas pressures. The so-called temperature and pressure gaps between traditional catalysis research and the industrial applications are thereby bridged, improving the relevance of the results obtained via in situ research. Several research groups have used in situ techniques to explore the FT syngas reaction on cobalt, e.g. scanning tunnelling microscopy (STM),[3,4,5] X-ray diffraction (XRD),[6] and X-ray absorption spectroscopy (XAS),[7,8] yielding meaningful insight into the working state of the catalyst surface under industrially relevant conditions. To investigate the behaviour of FT catalysts at elevated pressures and temperatures in a TEM, we used a combination of a MEMS nanoreactor loaded with Co nanoparticles, inserted in a specially designed in situ TEM sample holder. A residual gas analyser (RGA) monitored the product gas stream leaving the outlet of the nanoreactor
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