Novel binary Ti-Zr, Ti-Ce, and Zr-Ce oxides as dual-function adsorbents and reaction accelerators for CO₂ capture and ethylene urea synthesis

Carbon capture and utilization are promising for addressing climate change, reducing CO₂ emissions and converting captured CO₂ into valuable chemicals. In this study, we explored Ti-Zr, Ti-Ce, and Zr-Ce oxides as CO₂ adsorbents and reaction accelerators for ethylene urea (EU) synthesis, aiming to develop a cost-effective CO₂ capture and transformation method. Binary metal oxides (TiₓZr₍₁₋ₓ₎O₂, TiₓCe₍₁₋ₓ₎O₂, and ZrₓCe₍₁₋ₓ₎O₂,) were synthesized via sol-gel and solvothermal methods, with X-ray diffraction revealing amorphous TiₓZr₍₁₋ₓ₎O₂, distinct TiO₂ and CeO₂ peaks for TiₓCe₍₁₋ₓ₎O₂, and intermediate crystallinity for ZrₓCe₍₁₋ₓ₎O₂. BET analysis indicated that TiₓZr₍₁₋ₓ₎O₂ had the highest surface area (~ 150 m2/g), which contributed to its high CO₂ adsorption (0.85 mmol/g) at 30 °C and 100 kPa pressure, almost double that of TiO₂ (0.42 mmol/g). CO₂ adsorption followed the Langmuir and Freundlich models (R2 > 0.98). Upon heating the CO₂-loaded oxides at 160 ℃ for 24 h, CeO₂ and ZrO₂ enhanced EU production, with CeO₂ showing superior selectivity. The reaction mechanism involved CO₂ desorption and dehydration. Ti₀.₃Zr₀.₇O₂ yielded 12.2 × 10⁻4 mmol/m2 EU, owing to its high CO₂ adsorption and higher zirconium content. Conversely, TiₓCe₍₁₋ₓ₎O₂ produced less EU (6.99 × 10⁻4 mmol/m2) due to lower CO₂ availability. These findings highlight TiₓZr₍₁₋ₓ₎O₂, especially Ti₀.₃Zr₀.₇O₂, as a promising catalyst for CO₂ utilization and EU synthesis.