High anthropogenic CO2 emissions are among
the main
causes of climate change. Herein, we investigate the use of CO2 for the synthesis of organic cyclic carbonates on metal-free
nitrogen-doped carbon catalysts obtained from chitosan, chitin, and
shrimp shell wastes, both in batch and in continuous flow (CF). The
catalysts were characterized by N2 physisorption, CO2-temperature-programmed desorption, X-ray photoelectron spectroscopy,
scanning electron microscopy, and CNHS elemental analysis, and all
reactivity tests were run in the absence of solvents. Under batch
conditions, the catalyst obtained by calcination of chitin exhibited
excellent performance in the conversion of epichlorohydrin (selected
as a model epoxide), resulting in the corresponding cyclic carbonate
with 96% selectivity at complete conversion, at 150 °C and 30
bar CO2, for 4 h. On the other hand, in a CF regime, a
quantitative conversion and a carbonate selectivity >99% were achieved
at 150 °C, by using the catalyst obtained from shrimp waste.
Remarkably, the material displayed an outstanding stability over a
reaction run time of 180 min. The robustness of the synthetized catalysts
was confirmed by their good operational stability and reusability:
ca. (75 ± 3)% of the initial conversion was achieved/retained
by all systems, after six recycles. Also, additional batch experiments
proved that the catalysts were successful on different terminal and
internal epoxides.