Ce@STANPs/ZrO₂ as Nanocatalyst for Multicomponent Synthesis of Isatin-Derived Imidazoles under Green Reaction Conditions

A highly efficient and recyclable catalyst, cerium-immobilized silicotungstic acid nanoparticle-impregnated zirconia (Ce@STANPs/ZrO2), has been synthesized. The catalytic activity of Ce@STANPs/ZrO2 was investigated for the first time in multicomponent synthesis of isatin-based imidazoles under microwave irradiation in water. Ce@STANPs/ZrO2 was used for CO bond activation in overall reaction to synthesize isatin-based imidazoles. The structure of catalyst was confirmed by characterization techniques, such as Fourier transform infrared (FTIR), scanning electron microscopy (SEM)/energy dispersive X-ray, elemental mapping, transmission electron microscopy, ζ-potential and diffraction light scattering, X-ray diffraction (XRD), thermogravimetric analysis, temperature-programmed desorption-NH3, electron paramagnetic resonance (EPR), and inductively coupled plasma atomic emission spectroscopy (ICP-AES) analyses. The recovered catalyst was found to be efficient up to seventh cycle and was confirmed by FTIR, SEM, XRD, EPR, and ICP-AES analyses. The advantages of the present protocol are recyclability of catalyst, green reaction conditions, excellent yield (94%) of the products, shorter reaction time period (5–7 min), and clean reaction profile