Integrated CO2 capture and reverse water-gas shift reaction over CeO2-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, MOx-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.