Date

Friday 26 Sep 2025

Time

13:15 - 13:45

Location

BW017

Supervisor

Irene Groot

Jury

Rik Mom

Hydrodesulfurization (HDS) remains an essential chemical process to ensure only trace amounts of sulfur end up in fuels, yet its atomic-scale chemistry is difficult to access because industrial conditions (∼450-700 K, 16-150 bar) lie far beyond what cryogenic, ultra high vacuum (UHV) scanning tunneling microscopy (STM) allows. This review article looks into recent developments in the field of STM in order to bridge this so-called ”pressure gap”: Highpressure STM (HP-STM), ReactorSTM, and the combined ReactorAFM/STM. UHV STM, as a baseline, delivers atomically sharp images of MoS2 and CoMos model catalysts, but is very restrictive in the environmental conditions. Using ReactorSTM, near-ambient pressure HDS imaging (0.3 bar, 510 K) shows three distinctive features on Co-substituted S-edges (Types I-III), with type-III corresponding to the C-S bond cleavage. On higher pressures (1 bar), increased catalytic activity (turnover frequency of ∼ 10−2 s−1 per active site) results in blurred imaging and time-averaged protrusions. Nevertheless, edge assignments remain possible, with Mo-terminated edges remaining stabilized in equilibrium, whereas Co-substituted S-edges are ”reaction-rate governed” and show dynamic restructuring under HDS. These various regimes work complementarily in imaging and allow for a demonstration of how STM connects two-dimensional smooth model surfaces to near-industrial behavior. In addition, development is currently active on a combined ReactorAFM/STM, which extends imaging to non-conductive oxide-supported catalysts, bridging not only the pressure gap, but also the materials gap. Collectively, these advances are all steady steps in closing the pressure gap for HDS and will allow for greater understanding relevant to industrial catalyst design.