Exploring the capture and catalytic properties of sodium manganates: Bifunctional ceramics for CO/CO2 chemisorption and CO oxidation

Sodium manganate-based materials (α-NaMnO₂ and Na₂Mn₃O₇) were prepared using different synthesis procedures and precursors. Obtained samples were characterized by XRD, ATR-FTIR, N₂ adsorption-desorption and SEM, while their CO_x capture and catalytic properties were evaluated using thermogravimetric and mass spectrometer techniques. Overall, significant differences in CO/CO₂ chemisorption and CO oxidation processes were observed, indicating that preparation procedures strongly influence performance; co-precipitated manganate sample exhibited a maximum CO₂ uptake of 9.5 wt% at 800 °C and 100% CO conversion at 450 °C. Specifically, an optimal α-NaMnO₂:Na₂Mn₃O₇ weight ratio of 0.78:0.22 was found to exhibit the best bifunctional performance. Kinetic analysis of CO₂ capture using the Avrami-Erofeev model revealed a mechanism transition dependence from surface chemisorption to bulk diffusion. Simultaneously, CO oxidation process was found to follow a Mars-van Krevelen pathway. Na₂Mn₃O₇ phase facilitates low-temperature activation, while the α-NaMnO₂ phase is responsible for the higher capture yield.