Active metal-free CaO-based dual-function materials for integrated CO2 capture and reverse water–gas shift

Abstract

Integrated CO2 capture and conversion into CO via the reverse water–gas shift reaction (ICCC-RWGS) using CaO-based dual-function materials (DFMs) offers an attractive avenue for mitigating anthropogenic CO2 emissions. Active metal-free CaO-based DFMs have advantages such as no CO formation at the CO2 capture stage and high CO selectivity across a broad temperature range at the CO2 conversion stage, yet they face challenges with low CO yield. Herein, we report the enhanced performance of CaO-based DFMs co-doped with gallium (Ga) and zirconium (Zr) oxides in the ICCC-RWGS process. This improvement can be attributed to the synergistic interaction among Ca, Ga and Zr oxides, resulting in reduced CaO crystallites, enhanced surface basicity, and increased concentration of oxygen vacancies. The most promising DFM consists of 90 wt% CaO, 4.5 wt% Ca3Ga4O9 and 5.5 wt% CaZrO3 (with a Ga/Zr molar ratio of 1). When exposed to a simulated flue gas (5 % O2, 10 % H2O, 15 % CO2, and 70 % N2), this DFM exhibits a stable CO2 capture capacity of 11.90 mmol/gDFM over 20 consecutive isothermal ICCC-RWGS cycles at 650 °C. Meanwhile, its CO2 conversion and CO yield are maintained at 83.4 % and 10.26 mmol/gDFM, respectively. This study highlights the significance of a multi-metal oxide synergistic strategy in CaO-based DFMs to achieve superior performance in the ICCC-RWGS process.