Deciphering structural evolution of adsorbed ˙OH species on Zr-oxo nodes of UiO-66 to modulate methane hydroxylation

Abstract

Direct selective oxidation of methane (DSOM) to oxygenates under mild conditions is garnering increasing interest. UiO-66-H MOFs are effective for this reaction, while the active configuration of Zr-oxo nodes with adsorbed ˙OH species need further clarification from the atomic/molecular viewpoint. Here, we detect the evolution of the geometric and electronic structures of adsorbed oxygenic species on Zr-oxo nodes of UiO-66-H via the controlled ˙OH species. DFT calculations reveal a volcano-like curve relationship between the quantity of ˙OH species and the DSOM performance, which is further corroborated by experimental tests. Zr_oxo-˙OH is the main active configuration on Zr-oxo nodes of UiO-66-H at low ˙OH concentration, while it evolves to other oxygenic species (˙OOH, O₂, and H₂O) due to the self-reaction with the increase of ˙OH concentration, which leads to performance decrease. Furthermore, a critical descriptor of the p-band centers of O atoms in these oxygenic species on the Zr-oxo nodes is established, which can well represent the catalytic activity for the DSOM reaction.