MgH₂/Cu_xO Hydrogen Storage Composite with Defect-Rich Surfaces for Carbon Dioxide Hydrogenation

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Abstract

Thermal conversion of CO₂ to value-added chemicals is challenging due to the extreme inertness of the CO₂ molecule and the low selectivity of products. We reported a defect-rich MgH₂/Cu_xO hydrogen storage composite from mechanochemical ball-milling for the catalytic hydrogenation of CO₂ to lower olefins. The defect-rich MgH₂/Cu_xO hydrogen storage composite achieves a C₂=-C₄= selectivity of 54.8% and a CO₂ conversion of 20.7% at 350 °C under a low H₂/CO₂ ratio of 1:5, which increases the efficiency of H₂ utilization by offering lattice H- species for hydrogenation. Density functional theory calculations show that the defective structure of MgH₂/Cu_xO can promote CO₂ molecule adsorption and activation, while the electronic structure of MgH₂ is beneficial for offering lattice H- for CO₂ molecule hydrogenation. The lattice H- can combine the C site of CO₂ molecule to promote the formation of Mg formate, which can be further hydrogenated to lower olefins under a low H- concentration. This work for CO₂ conversion by a defect-rich MgH₂/Cu_xO hydrogen storage composite can inspire the catalysts design for the hydrogenation of CO₂ to lower olefins.

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