Abstract:

Direct polymerization of CO₂ with diols for synthesis of carbonates represents a sustainable and efficient approach for CO₂ utilization, in which CeO₂ exhibits favorable catalytic properties in the reaction system. In this study, nanometer-sized CeO₂ catalysts were synthesized via a hydrothermal method utilizing NaOH as precipitating agent. The effects of sintering temperatures (500, 600, and 700 ℃) and surfactants (cationic, anionic, and nonionic) on structural and physicochemical properties of CeO₂ were thoroughly investigated. When the sintering temperature was 600 ℃, CeO₂ displayed an optimal crystallinity and a higher concentration of defect sites compared to the other temperatures. The surfactants significantly increased oxygen vacancy concentration on the surface of CeO₂, leading to a maximum CO₂ uptake of 0.532 mmol/g at 25 ℃. Building upon these findings, a series of synthesized CeO₂ catalysts were applied in the one-step synthesis of polycarbonate from CO₂ and diol, resulting in significant improvements in both conversion and selectivity within the reaction system. The results demonstrated that catalytic activities of CeO₂ prepared at various sintering temperatures with different surfactants displayed notable differences. Notably, the CeO₂ catalyst sintered with cetyltrimethylammonium bromide (CTAB) as the surfactant at 600 ℃ exhibited the highest catalytic activity and selectivity, achieving a conversion of 91.0% for 1,6-hexanediol and a selectivity of 76.6% for poly(6-hydroxyhexyl) carbonate. The outstanding catalytic performance of CeO₂ with the high yield can be primarily attributed to its favorable structural characteristics, abundant defect sites, and high CO₂ uptake capacity.

Key words: CeO₂ nanoparticle, defect site, surfactant, CO₂ conversion, diol, polycarbonate