Direct Dimethyl Carbonates Synthesis over CeO2 and Evaluation of Catalyst Morphology Role in Catalytic Performance

Abstract

In recent years, direct synthesis of dimethyl carbonate (DMC) from carbon dioxide (CO2) has received considerable attention due to green and sustainable technology. Here, we report a production of DMC from major greenhouse gases and CO2 using various morphologies of cerium oxide (CeO2). Time-dependent synthesis of CeO2, with controlled morphology having various shapes including sphere, nanorods and spindle shape, along with its formation mechanism is proposed. The experimental results indicate the morphology of CeO2 was mostly dependent on the reaction time where crystal growth occurred through Ostwald ripening. The morphology, size and shape of CeO2 were observed using transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM).The crystallographic analysis using X-ray diffraction (XRD) shows cubic fluorite phase of CeO2 with crystallite size ~72.0 nm using the Debye–Scherrer equation. The nitrogen adsorption desorption technique suggested the formation of the highly mesoporous framework of CeO2 and the excellent surface area around 104.5 m2/g obtained for CeO2 spindles by Brunauer–Emmett–Teller (BET) method. The DMC synthesis reactions were studied over CeO2 catalyst with different morphologies. The results of catalytic reactions specify that the morphology of catalyst plays an important role in their catalytic performances, where spindle shape CeO2 was the most active catalyst producing of up to13.04 mmol of DMC. Furthermore, various dehydrating agents were used to improve the DMC production at optimized reaction parameters. The overall results reveal that the higher surface area and spindle shape of CeO2 makes it a useful, reusable catalyst for one-pot DMC synthesis.