Gallium-Promoted CeO2 Intensifies CO Production during CaCO3 Hydrogenation

Abstract The thermal decomposition of limestone (primarily CaCO3) in the cement industry is highly energy-intensive and generates substantial CO2 emissions. Carbonate hydrogenation, i.e., carbonate decomposition in a H2 atmosphere, has recently emerged as a promising strategy to accelerate decomposition while enabling in situ CO2 conversion to CO. However, direct CaCO3 hydrogenation is intrinsically constrained by a trade-off between the decomposition rate and CO selectivity. Herein, this limitation is addressed by introducing gallium-promoted CeO2 catalysts into the CaCO3 hydrogenation system. A series of Ga/CeO2 catalysts with varying Ga loadings were synthesized via an impregnation method on oxygen-vacancy-rich CeO2, resulting in highly dispersed Ga species. The catalytic performance was systematically evaluated under different Ga loadings, reaction temperatures, catalyst-to-CaCO3 mass ratios, H2 concentrations, and gas hourly space velocities. Among the catalysts tested, 3%Ga/CeO2 exhibited the best performance, delivering approximately 80% CO selectivity at 700 °C, while simultaneously accelerating CaCO3 decomposition by reducing the reaction time from 16.3 to 10.8 min compared to direct CaCO3 hydrogenation. Furthermore, in situ infrared spectroscopy combined with density functional theory (DFT) calculations was employed to elucidate the underlying promotional mechanism. The results demonstrate that electron-rich Ga−CeO2 interfacial sites serve as the key active centers. In the absence of a catalyst, H2 activation is hindered by a high dissociation energy barrier on CaO, limiting the efficiency of CaCO3 hydrogenation. In contrast, the Ga−CeO2 interface provides low-barrier pathways for H2 activation, generating abundant reactive H species that readily react with adsorbed CO2 or CaCO3. This interfacial synergy effectively modulates the reaction pathway during CaCO3 hydrogenation and intensifies CO formation.