Mechanochemical CO2 methanation over LaNi-based alloys

Abstract We report that CH4 production occurs, when LaNi-based alloy powders are mechanically ball-milled in a mixture CO2 and H2 gases for several hours. In Gas Chromatography (GC) analysis after the milling, the CO2 peak disappeared and the CH4 peak emerged. Activated LaNi5 powder demonstrated even higher catalytic activity than pristine LaNi5 or Ni powder. Energy Dispersive X-Ray (EDX) analysis of these powders revealed Fe and Cr present in the powder, suggesting an alloying of the sample powders with elements from the ball-milling media occurred during the milling. Atom probe tomography (APT) analysis unveiled that the resulting microstructure mainly consists of disproportionated metallic La/Ni, and nanometer scale oxides of La, Fe, Cr and Ni. Moreover, LaFe-carboxides and a trace of hydrocarboxylic compounds were detected. Ball-milling of a similar compound, LaNi4.6Al0.4, under CO2 atmosphere resulted in complete disappearance of CO2 in the milling vial. Subsequent milling of this powder in H2 atmosphere generated CH4. The results obtained in this study suggest that finely dispersed carboxides of Fe and La could be intermediates to lead to mechanochemically activated CO2 methanation.