Investigations of the conversion of inorganic carbonates to methane

Abstract

Inorganic carbonates, which occur abundantly on earth, constitute an inexpensive natural source of carbon. Therefore, the direct conversion of these carbonates into methane is of considerable importance. Thermal decomposition of transition metal carbonates with the composition MCa(CO₃)₂ (where M=Co, Ni, or Fe, and M/Ca is 1:1) and M¹M²Ca(CO₃)₃ (where M¹M²=CoNi, NiFe, or FeCo, and M¹/M²/Ca is 1:1:2) shows that the reduced transition metals in combination with metal oxide nanoparticles (e.g., Co/CoO/CaO) act as catalysts for the conversion of CO₂ (produced from the carbonates) into methane. The favorable decomposition conditions include heating at 550°C in an H₂ atmosphere for 5-6 h. These catalysts are found to be excellent for the methanation of CaCO₃, exhibiting high efficiency in the utilization of H₂ with 100 % conversion and 100 % selectivity. The best catalyst for conversion of CaCO₃ into CH₄ is Co/CoO/CaO. There are also indications that similar catalysts based on Fe may yield higher hydrocarbons.