Multivariate optimization of CO2 conversion on Ce/Tb oxides by chemical looping

Abstract

The catalytic conversion of CO₂ into valuable chemicals, such as CO, offers a promising solution to mitigate greenhouse gas emissions and promote sustainable energy cycles. In this study, cerium-terbium oxides were optimized for CO production through thermochemical cycles, utilizing a response surface methodology. Optimization was performed for both the first cycle and the average of three cycles to identify key parameters, including calcination temperature, terbium concentration, reduction time, oxidation time, and cycle temperature. The cubic response surface model demonstrated strong predictive capabilities (R² > 0.99) and highlighted significant interactions between key variables. These findings underscore the potential of cerium-terbium oxides as robust, tunable materials for thermochemical CO₂ conversion, offering insights for industrial application in energy-efficient processes. For the first cycle and the average over three cycles, the optimal terbium concentration (0.22–0.23 mol) was consistent, while reaction times and temperatures significantly impacted CO production, with oxidation time being a critical factor for achieving high conversion in shorter times. An alternative optimization approach minimized operational energy by reducing reaction temperatures and times. Additionally, electron paramagnetic resonance analysis revealed the presence of paramagnetic centers associated with oxygen vacancies, confirming the defect-rich nature of the reduced cerium-terbium oxide and its potential relevance for CO₂ activation.