Visualizing hydrogen-induced reshaping and edge activation in MoS₂ and Co-promoted MoS₂ catalyst clusters

Area of Science:

• Catalysis
• Materials Science
• Surface Chemistry

Background:

• Hydrodesulfurization (HDS) catalysis is crucial for fossil fuel purification, meeting strict sulfur emission regulations.
• Increasingly heavy crude oil feedstocks necessitate advanced HDS catalyst performance.
• Understanding the active sites of sulfided CoMo catalysts is key to improving HDS efficiency.

Purpose of the Study:

• To directly visualize and quantify structural changes in MoS2 and CoMoS catalysts under reducing conditions.
• To identify the nature of active sites on sulfided hydrodesulfurization catalysts.
• To correlate experimental observations with theoretical predictions of catalyst structure.

Main Methods:

• Scanning Tunneling Microscopy (STM) for direct visualization of catalyst morphology.
• Use of a molecular marker to probe catalytically relevant surface groups.
• Theoretical calculations to predict catalyst structures.

Main Results:

• Reducing conditions transform MoS2 and CoMoS catalyst clusters, altering shapes and edge terminations.
• Active catalyst sites exhibit fractional sulfur coverage.
• Evidence of catalytically relevant S-H groups on Co-promoted edges was observed using a molecular probe.

Conclusions:

• The experimentally observed catalyst structure under reducing conditions matches theoretical predictions for the active state.
• Direct visualization confirms fractional sulfur termination as representative of the active state in HDS catalysts.
• This work provides fundamental insights into the structure-activity relationship of CoMoS hydrodesulfurization catalysts.