Anisotropic node distortions in amorphous MOFs: Low-valent Zr sites as catalytic hotspots
Till Schertenleib, Mehrdad Asgari, Beatriz Mouriño, Vikram V. Karve, Timo M.O. Felder, Dragos Stoian, Volodymyr Bon, Jian Hao, Andres Ortega‐Guerrero, Emad Oveisi, Kumar Varoon Agrawal, Berend Smit, Stefan Kaskel, Simon J. L. Billinge, Wendy L. Queen
Abstract
We introduce a new approach to defect engineering in Zr-based metal-organic frameworks (Zr-MOFs), aiming to reduce Zr site valency while preserving high node connectivity. Using a rapid heat treatment (RHT) in humid air, oxygen vacancies (O-vacancies) were created in Dresden University of Technology (DUT)-67 through cluster dehydration. Unlike conventional defect engineering, aimed at creating missing-linker defects, this method breaks intra-cluster Zr- μ 3 O–Zr bonds, generating coordinatively unsaturated Zr (Zr cus ) sites. Pair distribution function (PDF) analysis, X-ray absorption spectroscopy (XAS), and density functional theory (DFT) calculations reveal that the O-vacancies lead to symmetry breaking, irreversible node distortions, and framework amorphization. This treatment converts 50% of metal sites to Zr cus sites, nearly doubling the catalytic activity of DUT-67 in glyoxal conversion to glycolic acid. DFT modeling and in situ PDF analysis highlight the dynamic behavior of Zr clusters under reaction conditions, suggesting a new avenue for defect engineering in Zr-MOFs to enhance catalytic performance.