In this work, we present a rapid heat treatment RHT method under humid airflow, which effectively induces O-vacancies in a Zr-MOF, DUT-67 (DUT = Dresden University of Technology). As a proof of concept, we test the catalytic performance of pristine and treated samples for the catalytic conversion of glyoxal (GO) to glycolic acid (GA), an important monomer for biopolymers. This model reaction was selected because both Brønsted-and Lewis acids have been shown to catalyze the conversion. We hypothesized that a synergy between missing linker defects (terminal OH/OH 2 groups that act as Brønsted acids) and Zr cus sites acting as open Lewis acid sites could catalyze this reaction more efficiently through optimized reaction pathways. Using a combination of x-ray absorption spectroscopy (XAS), pair distribution function (PDF) analysis, and density functional theory (DFT) calculations, we demonstrate how O-vacancies form in the {Zr 6 } nodes of DUT-67, creating low-symmetry Zr cus sites and leading to framework amorphization. Interestingly, we find that the local structure of the amorphous phase (aDUT-67) resembles that of m-ZrO 2 . Such node distortions in Zr-MOFs have been previously reported, and have been ascribed to cluster dehydration, the conversion of µ 3 -OH to µ 2 OH groups, or to missing linker defects. The range of explanations provided in the literature highlights the complexity of the problem. A systematic study considering missing-linker defects, O-vacancies, and a combination of both to establish a correlation between different defect modes and the role of low-symmetry {Zr 6 } clusters in catalysis has not been established until now.