Quantifying Microenvironment Effect on Metal Electronic Structure With Experimentally Accessible Descriptor: Examples of MOF-Incorporated Pt Catalysts.

The chemical microenvironment surrounding metal nanoparticles (NPs) plays crucial roles in regulating their electronic structures. However, due to the lack of quantitative descriptor, such effect has been understood largely in a qualitative manner. To address this issue, a series of reticular metal-organic frameworks (MOFs) with diverse functional groups (MIP-206-X, X = OH, OCH3, H, Cl, and F) were synthesized, and Pt NPs with similar sizes and loadings were incorporated to afford Pt@MIP-206-X for ammonia borane methanolysis. X-ray absorption near edge structure (XANES) was adopted to determine the d-orbital occupancy of Pt, and the electronic contribution from MOFs was quantified as the descriptor Δe, which was demonstrated to accurately describe the Pt-methanol adsorption strength (quantified by activation entropy and methanol desorption temperature) and exhibit an excellent linear correlation with catalytic activity. Isotopic analyses and DFT calculations revealed that a larger Δe strengthens methanol adsorption on Pt, promotes O─H bond cleavage as the rate-determining step (RDS), and leads to enhanced activity.