Substoichiometric Molybdenum Sulfide Phases with Catalytically Active Basal Planes

Area of Science:

• Materials Science
• Catalysis
• Surface Chemistry

Background:

• Molybdenum sulfide (MoS₂) exhibits catalytic activity primarily at crystal edges.
• Defects on MoS₂ basal planes can enhance catalysis, but model systems are scarce.
• Understanding metal-centered catalysis on basal planes is crucial for new applications.

Purpose of the Study:

• Synthesize a novel substoichiometric molybdenum sulfide (s-MoS_x) phase.
• Investigate the catalytic potential of Mo-rich sites on the basal plane of s-MoS_x.
• Explore surface-directed Ullmann coupling reactions on s-MoS_x nanosheets.

Main Methods:

• Synthesis of substoichiometric molybdenum sulfide (s-MoS_x) on a copper substrate.
• Hydrogen-transfer catalysis studies involving dynamic adsorption/desorption processes.
• Scanning tunneling microscopy (STM) to observe Ullmann coupling reactions.

Main Results:

• A new phase of substoichiometric molybdenum sulfide (s-MoS_x) was successfully synthesized.
• The basal plane of s-MoS_x features reactive Mo-rich sites active in hydrogen-transfer catalysis.
• STM revealed that 4-fold symmetric sites on s-MoS_x direct Ullmann coupling to form cyclic tetramers with high selectivity.

Conclusions:

• Substoichiometric molybdenum sulfide (s-MoS_x) offers a model system for basal plane catalysis.
• The material demonstrates significant potential for hydrogen-transfer and selective C-C coupling reactions.
• This work expands the understanding of defect engineering in MoS₂ for enhanced catalytic performance.