CeO2-catalyzed synthesis of 5-membered cyclic carbonates from CO2 and diols

All the environmental issues related to greenhouse gases have led to a huge improvement of the research about CO2 capture and utilization over the last decades. Carbon dioxide, due to the wide availability and the non-toxicity, is a suitable feedstock material for producing chemicals and its non-reductive conversion allows the synthesis of different organic compounds like methane, methanol, urea and carbonates. The latter class has many applications in chemical industry, such as solvents in liquid-liquid extractions or electrolytes for secondary batteries. A new eco-friendly process is the synthesis of cyclic carbonates from CO2 and diols using cerium oxide, or ceria, as catalyst. The equilibrium limitation given by the formation of water as product can be avoided exploiting a dehydrating agent, like 2-cyanopyridine. In this work, the synthesis of two different 5-membered cyclic carbonates, styrene and 1,2-butylene carbonates, starting from styrene glycol and 1,2-butanediol respectively, was detected. At first, reactions with different conditions were performed in order to study the influence of time and temperature. Results for the former substrate did not show yields high enough to justify a pursuing of the research. As regards the latter, instead, great conversions can be achieved even for low temperatures. Afterwards, two different parameters were investigated for the butylene carbonate synthesis: the amount of dehydrating agent and the CO2 pressure. An excess of dehydrant is required for obtaining good yields, but a ratio of 2:1 compared to diol is a sufficient trade-off. The study also showed that a decrease of the pressure leads to an improvement of the process. Overall, while the synthesis of styrene carbonate is not a suitable option at the moment, butylene carbonate has a great potential due to the opportunity of obtaining remarkably high conversions also for short reaction times and relatively low temperatures.