Hydrothermal Reduction of CO2 with Compounds Containing Nitrogen

Reduction of CO₂ into value-added chemicals is an attractive means of reducing greenhouse gas emissions and a possible approach toward renewable synthetic fuels. The conventional reductant for CO₂ hydrogenation is gaseous hydrogen from high-pressure cylinder, which solves storage and transportation problems. Moreover, the elaborately prepared and noble metal–involved catalysts are commonly required. Thus, safe and facile hydrogen sources are needed urgently. Some inorganic and organic compounds having nitrogen that possess reductive amine groups exhibit satisfied reductive ability under hydrothermal conditions. More importantly, these compounds are actually considered nonflammable when being transported, whereas hydrogen burns with an invisible flame. Therefore, these compounds containing amine groups are promising safe reducing agents. Hydrous hydrazine (N₂H₄•H₂O), which possesses high hydrogen capacity (7.9%), is a typical liquid hydrogen storage material. Herein, hydrous hydrazine was employed as an in situ hydrogen source for the reduction of CO₂ with general Ni and ZnO powders. More than 60% yield of formic acid with 99% selectivity was obtained. The proposed method is simple and safe because it requires neither elaborately prepared catalysts nor high-purity hydrogen and hydrogen storage.