As gas–solid heterogeneous catalytic reactions are molecular in nature, a full mechanistic understanding of the process requires atomicâ€scale characterization under realistic operating conditions. Although atomic resolution imaging has become routine in modern highâ€vacuum (scanning) transmission electron microscopy ((S)TEM), both image quality and resolution nominally degrade on introduction of the reaction gases. In this work, we systematically assess the effects of different gases at various pressures on the quality and resolution of images obtained at room temperature in the annular dark field STEM imaging mode by using a differentially pumped (DP) gas cell. This imaging mode is largely free from inelastic scattering effects induced by the presence of gases and retains good imaging properties over a wide range of gas mass/pressures. We demonstrate the application of ESTEM with atomic resolution images for a complex oxide alkane oxidation catalyst MoVNbTeOx (M1) immersed in light and heavy gas environments.
