Dimethyl Carbonate Synthesis via Transesterification of Propylene Carbonate Using an Efficient Reduced Graphene Oxide-Supported ZnO Nanocatalyst

Abstract

In the present study, reduced graphene oxide-supported zinc oxide nanocatalysts (rGO/ZnO) with varying graphene contents (1, 2, 5, and 10%) were synthesized and employed for the production of dimethyl carbonate by transesterification of CH3OH and propylene carbonate (PC). Graphene oxide sheets were synthesized using an electrochemical method coupled with an oxidation process, and ZnO nanoparticles were synthesized using the chemical coprecipitation method, and the reduced graphene oxide-supported ZnO nanocatalysts (rGO/ZnO) were obtained by simple mixing liquid ammonia as the reducing agent. Synthesized nanocatalysts were characterized using various sophisticated techniques such as field-emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The bifunctional characteristic of the catalysts was investigated by NH3- and CO2-temperature programmed desorption (TPD). Surface properties such as surface area, desorption average pore diameter, and cumulative pore volume of the nanocatalyst were quantified using the Brunauer–Emmett–Teller method. 5% rGO/ZnO (named 5G/Z) gave the best results owing to the high concentration of acidic–basic sites along with the large surface area. The reaction conditions (450 rpm, 453 K, 3% of catalyst dose with respect to PC, and 4 h) were optimized using the 5G/Z nanocatalyst at which a maximum yield of 74% was obtained. The values of ΔrHmo and ΔrGmo as calculated using a nonideal thermodynamic approach were found to be 117 and −58 kJ/mol, respectively. Recyclability and reusability studies were successfully conducted up to four consecutive cycles using the 5G/Z nanocatalyst.