Integrated CO ₂ capture and reverse water–gas shift reaction over CeO ₂ -CaO dual functional materials

Abstract

Achieving carbon neutrality is one of the most important tasks to meet the environmental challenges due to excessive CO₂ emissions. Integrated CO₂ capture and utilization (ICCU) represents an effective process for direct utilization of CO₂-contained exhaust gas (e.g. flue gas), in which converting the captured CO₂ into CO via reverse water-gas shift (RWGS) reaction is a promising route. The dual functional materials (DFMs), containing CO₂ adsorbents and catalysts, are widely applied to achieve ICCU. The conventional active metals (Ni, Fe, etc.)-based DFMs and non-transition metal DFMs (e.g. CaO) are restricted by low CO selectivity, catalytic efficiency or CO generation in the CO₂ capture step. To address the above obstructs in the application of DFMs, the metal oxides-based DFMs, MO_x-CaO (M = Al, Ce, Ti or Zr), are synthesized and evaluated. The CeO₂-CaO outperformed the other metal oxides-based DFMs and possessed significantly improved catalytic performance. It is found that 33% CeO₂-CaO DFM displayed approximately 49% CO₂ conversion and approximately 100% CO selectivity in integrated CO₂ capture and reverse water-gas shift reaction (ICCU-RWGS) at 650°C, while CaO-alone only achieved approximately 20% CO₂ conversion at the same condition. The surface basicity of CeO₂ is revealed to contribute to the improved catalytic performance by enhancing CO₂ chemisorption and activation in the hydrogenation step. Furthermore, CeO₂-CaO material possessed excellent cycle stability in 20 cycles ICCU-RWGS, achieving a sustainable and high-efficient performance in CO₂ conversion and CO selectivity.