Interplay of Electronic and Steric Effects to Yield Low-Temperature CO Oxidation at Metal Single Sites in...

In contrast to catalytically active metal single atoms deposited on oxide nanoparticles, the crystalline nature of metal-organic frameworks (MOFs) allows for a thorough characterization of reaction mechanisms. Using defect-free HKUST-1 MOF thin films, we demonstrate that Cu⁺ /Cu²⁺ dimer defects, created in a controlled fashion by reducing the pristine Cu²⁺ /Cu²⁺ pairs of the intact framework, account for the high catalytic activity in low-temperature CO oxidation. Combining advanced IR spectroscopy and density functional theory we propose a new reaction mechanism where the key intermediate is an uncharged O₂ species, weakly bound to Cu⁺ /Cu²⁺ . Our results reveal a complex interplay between electronic and steric effects at defect sites in MOFs and provide important guidelines for tailoring and exploiting the catalytic activity of single metal atom sites.