CO2 reutilization for methane production via a catalytic process promoted by hydrides

Abstract

CO₂ emissions have been continuously increasing during the last half of the century with a relevant impact on the planet and are the main contributor to the greenhouse effect and global warming. The development of new technologies to mitigate these emissions poses a challenge. Herein, the recycling of CO₂ to produce CH₄ selectively by using Mg₂FeH₆ and Mg₂NiH₄ complex hydrides as dual conversion promoters and hydrogen sources has been demonstrated. Magnesium-based metal hydrides containing Fe and Ni catalyzed the hydrogenation of CO₂ and their total conversion was obtained at 400 °C after 5 h and 10 h, respectively. The complete hydrogenation of CO₂ depended on the complex hydride, H₂ : CO₂ mol ratio, and experimental conditions: temperature and time. For both hydrides, the activation of CO₂ on the metal surface and its subsequent capture resulted in the formation of MgO. Investigations on the Mg₂FeH₆–CO₂ system indicated that the main process occurs via the reversed water–gas shift reaction (WGSR), followed by the methanation of CO in the presence of steam. In contrast, the reduction of CO₂ by the Mg-based hydride in the Mg₂NiH₄–CO₂ system has a strong contribution to the global process. Complex metal hydrides are promising dual promoter-hydrogen sources for CO₂ recycling and conversion into valuable fuels such as CH₄.