Thermal Reduction of CO2 with Activated Alkali Metal Aluminum Hydrides for Selective Methanation

In this work, the thermochemical methanation reaction of the activated alkali metal aluminum hydride AAlH4 (A = Li or Na) with carbon dioxide was methodically investigated. It was pointed out that the transformation of carbon dioxide to methane employing the as-milled alkali metal aluminum hydride is highly selective and rapid. After the reaction is performed for 1 h, methane is the only hydrocarbon and its output reached 42.0%. The output of methane and molar fraction in products mainly depend on the operating temperature, thermostatic time, the pressure of carbon dioxide, and the AAlH4 (A = Li or Na)/CO2 molar ratio. The CH4 output of the NaAlH4–CO2 system is higher than that of the LiAlH4–CO2 system conducted under the same reaction conditions. By various characterizations, we know that aluminum, alkali hydride, amorphous carbon, alkali aluminate, and hydrogen are formed during the reaction, and the interaction between amorphous carbon and hydrogen results in CH4 formation.