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 Δ
r
H
m
o and Δ
r
G
m
o 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.