Effect of the Support on Cerium–Praseodymium Mixed Oxide for CO ₂ -to-CO Conversion via Reverse Water–Gas Shift Chemical Looping

Praseodymium-doped ceria (Ce0.75Pr0.25O2-δ) was synthesized via a modified Pechini method and supported on three different oxides: SiO2, γ-Al2O3, and ZrO2. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), BET area, transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), and Raman spectroscopy. XRD confirmed the formation of a cubic fluorite-type structure for all samples, with additional peaks corresponding to the supports; ZrO2 was found to coexist in monoclinic and tetragonal phases. Elemental mapping revealed that the interaction between γ-Al2O3 and nanostructured ZrO2 promoted a homogeneous distribution of Ce and Pr, suggesting stronger interfacial bonding. Redox performance was evaluated through thermogravimetric cycling under H2/CO2 atmospheres. The γ-Al2O3-supported sample exhibited the highest CO production at 500 °C, followed by the amorphous SiO2-supported material, whereas crystalline SiO2 and commercial ZrO2 showed lower activity. However, when nanostructured ZrO2 synthesized at 300 °C was used as support-showing a significantly higher BET surface area─the redox performance improved to levels comparable with γ-Al2O3. Gas-phase FTIR analysis during the oxidation step confirmed CO as the only carbon-containing product, with no detectable CH4 formation, evidencing high RWGS selectivity. Long-term cycling tests at 600 °C (72 cycles, equivalent to 24 h of continuous operation) demonstrated stable CO production and structural retention for the γ-Al2O3-supported system. These findings highlight the critical role of the support’s textural and interfacial properties in governing redox activity and confirm Ce0.75Pr0.25O2-δ/γ-Al2O3 as a robust and efficient material for thermochemical CO2 splitting.