Selective Oxidation of Alkenes over Uranyl-Anchored Mesoporous MCM-41 Molecular Sieves

Abstract

Uranyl-anchored MCM-41 (UO(2)(2+)/MCM-41) catalysts were prepared hydrothermally and systematically characterized,employing various analytical and spectroscopic techniques: namely, X-ray diffraction (XRD), nitrogen sorption isotherms, transmission electron microscopy (TEM), electron diffraction (ED), and thermogravimetry-differential thermal analysis, inductively coupled plasma-atomic emission spectroscopy, diffuse reflectance ultraviolet-visible (DRUV-vis) spectroscopy and fluorescence spectroscopy, and Fourier transform-intrared (FT-IR) spectroscopy. XRD confirms the incorporation of uranyl ions into the silicate matrix and that TEM and ED investigations corroborate the highly ordered structure of uranyl-incorporated MCM-41. Further, these findings were well supported by DRUV-vis, fluorescence, and FT-IR spectra, indicating the nature of uranyl ion species as well as their interaction with the silicate framework. Well-characterized, high-quality UO(2)(2+)/MCM-41 catalysts were employed for the liquid-phase allylic oxidation of a-pinene, beta-pinene, and cyclohexene under moderate reaction conditions using various solvents and oxidants. Under the optimized experimental conditions, the catalysts showed high substrate conversion and excellent product selectivity. In addition, the influence of various other parameters (viz., temperature, time, recyclability, uranium content, etc.) were also performed.