Can CO₂ and steam react in the absence of electrolysis at high temperatures?

The fundamental question of whether CO₂ can react with steam at high temperatures in the absence of electrolysis or high pressures is answered. These two gases are commonly co-present as industrial wastes. Herein, a simple experiment by flowing CO₂ and steam through a CaCl₂ matrix at 500–1000 °C and atmospheric pressure was designed. Comprehensive characterizations and density functional theory calculations were conducted. Meanwhile, this study aims to recover HCl from CaCl₂ via a low-emission oxy-pyrohydrolysis process. As confirmed, CO₂ and steam interact strongly on the CaCl₂ surface, leading to an explicit formation of CaCO₃/CaO and a nearly complete release of HCl. This is mainly contributed to a halved energy required for the splitting of H₂O, resulting from the formation of a bicarbonate-like structure to replace Cl⁻ out of CaCl₂, an otherwise industrial waste, whilst an important dopant for carbon capture, utilization and storage, and medium for electrochemical synthesis.