Interaction between Single Metal Atoms and UiO-66 Framework Revealed by Low-Dose Imaging

Area of Science:

• Materials Science
• Catalysis
• Nanotechnology

Background:

• Atomically dispersed metals within metal-organic frameworks (MOFs) are crucial for catalysis and energy applications.
• Amino groups have been hypothesized to promote single atom catalyst (SAC) formation due to strong metal-linker interactions.

Purpose of the Study:

• To investigate the precise atomic adsorption sites of platinum (Pt) and palladium (Pd) single atoms in UiO-66 based MOFs.
• To elucidate the role of amino groups in the formation and stability of single atom catalysts (SACs) within MOFs.

Main Methods:

• Low-dose integrated differential phase contrast scanning transmission electron microscopy (iDPC-STEM) was employed to visualize atomic structures.
• Density functional theory (DFT) calculations were performed to understand metal-MOF binding strengths.

Main Results:

• Single Pt atoms were observed on the benzene rings of p-benzenedicarboxylic acid (BDC) linkers in Pt@UiO-66.
• Single Pd atoms were found to be adsorbed by amino groups in Pd@UiO-66-NH2.
• Clustering of Pt and Pd atoms occurred in Pt@UiO-66-NH2 and Pd@UiO-66, respectively, indicating amino groups do not universally favor SACs.

Conclusions:

• The presence and location of amino groups significantly influence the dispersion of single metal atoms in MOFs.
• A moderate binding strength between metal atoms and MOFs is optimal for forming stable single atom catalysts.
• These findings provide direct atomic-level insights into metal-MOF interactions, guiding the design of advanced SACs.