Impact of grain size and reactant ratio on reduction of CO2 to CH4 by alkali metal hydride

This paper aims to investigate the influence of the grain size and the alkali metal hydride (AH, where A = lithium (Li), sodium (Na) or potassium (K))/carbon dioxide (CO₂) mole ratio on carbon dioxide reduction-conversion to methane (CH₄) through alkali metal hydrides at an intermediate temperature. The result of this investigation shows that the grain size and AH (A = Li, Na or K)/carbon dioxide mole ratio have a considerable effect on the methane mole percentage and output. Compared with the original sample, when the lithium or potassium hydride sample is milled for 2 h, the mole percentage and output of methane increase. When the time for which the lithium or potassium hydride sample is milled is increased from 2 to 48 h, the mole percentage and output of methane change very little. For the sodium hydride and carbon dioxide system, the grain size of the sample has little effect on the methane mole percentage and output. In brief, alkali metal hydride milled for 2 h is enough for the methanation reaction. In consideration of the AH/carbon dioxide mole ratio, the effects on different reaction systems are not consistent. Activated alkali metal hydrides can effectively convert carbon dioxide to methane under various AH/carbon dioxide mole ratios, and the higher the mole ratio of AH/carbon dioxide, the better the methanation of alkali metal hydride with carbon dioxide.