Sulfate-modified MOF-808 as a superacid catalyst: a performance evaluation of Zr(iv) and Hf(iv) analogues in acetalization reactions

Abstract

In this study, we report the synthesis and characterization of MOF-808-SO₄-M (M = Zr(IV), Hf(IV)), derived from MOF-808-M precursors. The introduction of sulfate groups enhances the Brønsted acidity of these materials, significantly improving their catalytic performance in the benzaldehyde acetalization reaction. The materials were characterized using powder X-ray diffraction (PXRD), Fourier-transform infrared spectroscopy (FT-IR), nitrogen adsorption–desorption analysis, thermogravimetric analysis (TGA), energy-dispersive spectroscopy (EDS), and Hammett indicator tests. Catalytic evaluation revealed that MOF-808-SO₄-Zr exhibited significantly higher conversion compared to its Hf-based analogue, a difference attributed to its greater density of acid sites, as confirmed by temperature-programmed surface reaction (TPSR) analysis. These experimental results were further supported by density functional theory (DFT) calculations, which provided insights into the acidic properties and catalytic behavior of the materials.