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(CO(3))(2) (where M=Co, Ni, or Fe, and M/Ca is 1:1) and M(1)M(2)Ca(CO(3))(3) (where M(1)M(2)=CoNi, NiFe, or FeCo, and M(1)/M(2)/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 CO(2) (produced from the carbonates) into methane. The favorable decomposition conditions include heating at 550 degrees C in an H(2) atmosphere for 5-6 h. These catalysts are found to be excellent for the methanation of CaCO(3), exhibiting high efficiency in the utilization of H(2) with 100 % conversion and 100 % selectivity. The best catalyst for conversion of CaCO(3) into CH(4) is Co/CoO/CaO. There are also indications that similar catalysts based on Fe may yield higher hydrocarbons.

Abiotic Methane on Earth

“…This process is quite interesting because it produces CH 4 through one step, directly from the solid carbonate, without mediation of gaseous CO 2 (as typically happens in the catalytic hydrogenation or FTT reaction, discussed below). The occurrence of reactions (7a–7c) was confirmed by laboratory experiments: very rapidly (instantaneously) at 250°C in H 2 atmosphere with mixed alkaline‐Earth metal/transition metal carbonates including Mg, Ca, Co, Ni, and Cu [ Reller et al ., ]; with similar metal carbonates at 550°C, in five hours [ Jagadeesan et al ., ]; and at 300–400°C with Ir‐Pd catalysts, in 100 min time scale [ Yoshida et al ., ]. There are currently no studies to our knowledge at lower temperatures and over longer time scales.…”

Hydrogenation of Inorganic Metal Carbonates: A Review on Its Potential for Carbon Dioxide Utilization and Emission Reduction

“…from the Jawaharlal Nehru Centre for Advanced Scientific Research, India, investigated CaCO 3 and mixed‐metal/CaCO 3 hydrogenation promoted with catalytically active metallic nanoparticles in a continuous‐flow, packed‐bed, stainless‐steel reactor and managed to directly convert the inorganic carbonates into C 1 –C 3 hydrocarbons 13, 52…”

“…extensively studied hydrocarbon formation from various mixed inorganic carbonates and made remarkable conclusions about hydrocarbon selectivity for C 1 –C 3 chain lengths 13, 52. In the first study, Jagadeesan et al.…”

“…In the first study, Jagadeesan et al. examined methane formation from mixed alkaline‐earth‐metal/transition‐metal carbonates at 823 K 52. The operating pressure was not stated and the assumption could thus be made that the work was carried out at atmospheric pressure.…”

Highly Selective Room‐Temperature Catalyst‐Free Reduction of Alkaline Carbonates to Methane by Metal Hydrides

“…Recently, the direct conversion of metal carbonates (alkali carbonates) to hydrocarbons by high‐temperature catalytic hydrogenation (as opposed to the separation of CO 2 from flue gas for catalytic hydrogenation) has attracted increased attention due to the ready availability and ease of handling of these species. Thus, Sommerbauer et al found that magnesite is converted to magnesium oxide, methane, carbon dioxide, and carbon monoxide under a high pressure of hydrogen at 748–778 K in the absence of catalysts, whereas Jagadeesan et al reported the direct conversion of transition metal carbonates to methane in a hydrogen atmosphere at 550 °C catalyzed by metal nanoparticles such as Co/CoO/CaO . Jagadeesan et al also examined the direct transition metal ion‐assisted conversion of inorganic carbonates to C 1 —C 3 hydrocarbons in a hydrogen atmosphere at 673 K .…”