Alkali and Alkaline Earth Metal Hydrides Driven Thermochemical Reduction of CO ₂ to CH ₃ OH at Ambient Pressure

The reduction of carbon dioxide (CO₂) to methanol (CH₃OH), is presently constrained by energy-intensive processes requiring high temperatures and pressures to overcome kinetic and thermodynamic limitations. This work unveils for the first time a reaction pathway for alkali and alkaline earth metal hydrides (LiH, NaH, KH, MgH₂, CaH₂, and BaH₂), enabling the activation and selective reduction of CO₂ to methanol under ambient pressure. This finding represents a significant departure from the established paradigm, which exclusively produced methane at moderate pressures (0.1-1 MPa). Temperature-programmed reaction studies reveal that these metal hydrides function synergistically as both hydrogen sources and promoters for CO₂ reduction, exhibiting hydrocarbon production within specific temperature windows. Systematic screening identifies lithium hydride (LiH) as the most effective material, with a maximum production rate of 0.182 μmol_MeOH·mol_metal ^-1·h^-1 at 245 °C under ambient pressure, highlighting a structure-activity relationship governed by metal-formate stability. Through mechanistic investigation, we elucidate a formate (HCOO*)-mediated pathway wherein the hydride ion serves as a potent nucleophile, directly reducing CO₂ without the need for high H₂ partial pressures. This discovery provides a transformative framework for the sustainable synthesis of CH₃OH and lays the groundwork for the development of next-generation materials incorporating reactive ionic hydrides for the conversion of CO₂ under mild conditions.