DUT-67 consists of hexamer Zr 6 O 4 (OH) 4 clusters connected to 8 linking 2,5-thiophene dicarboxylate (tdc 2-) ligands and 4 non-linking acetate (CH 3 COO -) ligands yielding the framework composition [Zr 6 O 6 (OH) 2 (CH 3 COO) 2 (tdc) 4 ]. Firstly, we investigated the impact of RHT at 300 • C for varying durations (30, 60, 180, 600 seconds, and 6 hours) on the catalytic conversion of glyoxal (GO) to glycolic acid (GA), using nano-powdered (<100 nm) m-ZrO 2 as a reference. The yields are shown in Figure . Samples treated for 30 and 60 seconds showed GA yields similar to the untreated MOF. However, a significant increase was observed after 180 seconds of treatment. Prolonged exposure (600 seconds and 6 hours) resulted in reduced yields. PXRD analysis (Figure ) revealed that the heat treatment initially leads to a contraction of lattice parameters in DUT-67, as shown by the shift of Bragg peaks to higher angles in the 30-second and 60-second samples. This is the first indication of the creation of Zr cus sites since reduced valency means shorter Zr-O bonds, leading to lattice contractions. On the other hand, thermogravimetric analysis (TGA) profiles (Figure ) reveal that the composition of the as-synthesized MOF and the 30-and 60-second samples are essentially the same. This implies that the samples taken at 30 and 60 seconds have negligible defect densities if any exist. After 180 seconds of RHT, the disappearance of the {Zr 6 } dehydration step at ∼ 280 • C is observed, accompanied by a notable reduction in organic content (weight loss at ∼ 450 • C). From this, we estimated that the 180-second sample exhibited mostly dehydrated clusters and approximately 3% missing linker defects, as detailed in the supplementary information. N 2 adsorption isotherm measurements (Figure , S2, and Table ) confirmed that this sample remained porous with a Brunauer-Emmett-Teller surface area (S BET ) of 391 m 2 /g, indicating most tdc ligands remained intact. After 600 seconds, ∼ 53% of the ligands were removed, causing pore collapse and reducing porosity (S BET = 39 m 2 /g), explaining the performance decline.