Solvent-free synthesis and characterization of Ca²⁺-doped UiO-66(Zr) as heterogeneous catalyst for esterification of oleic acid with methanol: a joint experimental and computational study

The direct synthesis of metal-organic frameworks (MOFs) with multi-metal centers has been of great importance for the construction of multi-functional sites. In this work, we report the first time direct synthesis of Ca²⁺-doped UiO-66(Zr) under solvent-free conditions. The obtained materials were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), N₂ adsorption-desorption isotherm, Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and temperature-programmed desorption (TPD) analysis of NH₃ and CO₂. The results indicate that the incorporation of Ca²⁺ could greatly enhance the catalytic performance of UiO-66(Zr) in the esterification of oleic acid with methanol. Additionally, the kinetic behaviors on such materials are systematically investigated and density functional theory simulations are conducted using cluster and periodic models to investigate the effect of Ca²⁺ incorporation on the structure and reactivity of UiO-66(Zr).