Template-Less and Surfactant-Less Synthesis of CeO2 Nanostructures for Catalytic Application in Ipso-hydroxylation of Aryl Boronic Acids and the aza-Michael Reaction.

Abstract

Due to its excellent physicochemical properties, CeO2 has found great importance as an electrochemical and in electronics, photocatalysis, sensing, and heterogeneous catalysis. Herein, we report the surfactant-less and template-less synthesis of CeO2 nanostructures by the hydrothermal method. The synthesized CeO2 nanostructures have been characterized in detail by electron microscopy, spectroscopy, diffractometry, and other analytical methods. The XRD studies revealed the formation of pure crystalline CeO2, possessing a cubic fluorite structure with an average crystallite size of 15.6 to 16.4 nm. Electron microscopy studies reveal the formation of cube-shaped CeO2 nanostructures with sizes below 25 nm. The cube-shaped CeO2 nanostructures exhibited a higher BET surface area compared to their bulk counterparts. The XPS analysis has confirmed the existence of Ce in the mixed oxidation states of +3 and +4, while O is present as O2- in the sample. The as-synthesized CeO2 nanostructures exhibit excellent catalytic activity in both the ipso-hydroxylation of aryl boronic acids and the aza-Michael reaction. The analysis of the used catalyst has confirmed its stability under the reported reaction conditions. The catalysts retain their catalytic activity up to the fifth run in both types of reactions, which is economically beneficial for industrial application.