Alkali and Alkaline Earth Metal Hydrides Driven Thermochemical Reduction of CO2 to CH3OH 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 μmolMeOH·molmetal -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.