CO2 adsorption and conversion of epoxides catalyzed by inexpensive and active mesoporous structured mixed-phase (anatase/brookite) TiO2

An efficient adsorption of CO2 and the conversion of epoxides into valuable products by inexpensive and active catalysts are of great interests and are really daunting challenge. Herein, we report the synthesis of propylene carbonate (PC) with excellent yield (100%) from the cycloaddition of CO2 and propylene oxide (PO) (fixation or adsorption of CO2) catalysed by NiO-modified-TiO2 (designated as NiO/TiO2) nanoparticles (NPs) with tetrabutylammonium iodide (nBu4NI) used as co-catalyst under solvent free conditions. For this purpose, mesoporous structured mixed-phase (anatase/brookite) TiO2 and NiO/TiO2 NPs were synthesized by an eco-friendly and simple sol-gel method. Synthesized NiO/TiO2 NPs catalyst was thoroughly characterized by various analytical techniques such as Fourier-Transform Infrared (FTIR) Spectroscopy, Energy Dispersive X-Ray (EDX) analysis, Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES), X-Ray Diffraction (XRD), X-Ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET) method, Scanning Electron Microscopy (SEM), and High-Resolution Transmission Electron Microscopy (HRTEM). To broaden the scope of cycloaddition of CO2, several other epoxides as substrates were also examined using NiO/TiO2 NPs catalyst and the cyclic carbonates products (86.9–100%) were accomplished. Moreover, the enhanced adsorption studies of CO2 with solid mixed oxides catalysts are also remarked. Furthermore, NiO/TiO2 NPs catalyst was simply recovered, reused for four successive runs without significant loss of its original activity, and regenerated for further use.