Approaching Molecular Definition on Oxide-Supported Single-Atom Catalysts.

Area of Science:

• Heterogeneous catalysis
• Materials science
• Surface chemistry

Background:

• Single-atom catalysts (SACs) offer superior metal utilization and unique active sites compared to nanoparticle catalysts.
• However, ill-defined active sites in many supported SACs hinder structure-activity correlations and fundamental understanding.
• Complexity in traditional heterogeneous catalysts obscures intrinsic catalytic behaviors.

Purpose of the Study:

• To present strategies for simplifying supported single-atom catalysts (SACs) to enable detailed mechanistic studies.
• To highlight the use of well-defined oxide supports, such as polyoxometalates (POMs), for creating model SACs.
• To demonstrate how these defined systems can elucidate fundamental catalytic phenomena.

Main Methods:

• Utilizing molecularly defined polyoxometalates (POMs) as supports for atomically dispersed metals (Pt, Pd, Rh).
• Synthesizing polyoxometalate-supported single-atom catalysts (POM-SACs) with uniform active sites.
• Employing in situ spectroscopy, soluble POM-SAC analogues, and electrospray ionization mass spectrometry (ESI-MS) for mechanistic investigations.

Main Results:

• POM-SACs provide identical single-atom sites, ideal for in situ spectroscopic studies of catalytic reactions.
• Tunable redox properties of POM supports allow modification of catalytic behavior while maintaining active site geometry.
• ESI-MS successfully identified catalytic intermediates and resolved questions regarding hydrogen spillover.

Conclusions:

• Well-defined POM-SACs are powerful model systems for fundamental catalysis research.
• These systems overcome the limitations of complex heterogeneous catalysts, enabling clear structure-activity relationships.
• The developed methodologies offer broad utility for investigating catalytic mechanisms and resolving long-standing questions.