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

Abstract

The realization of effective CO2 conversion into valuable hydrocarbons is a promising way of addressing the current environmental and energy issues. A convenient, highly selective, and efficient method of CO2 methanation and the synthesis of COx‐free hydrogen/methane fuel mixtures by ball milling‐induced reactions of alkaline carbonates with metal hydrides (MHs) is reported. The natural resources of MgCO3/CaCO3 and MgH2/CaH2 are used as carbon and hydrogen sources, respectively. Mechanochemical investigations of the room‐temperature reactions indicate that some alkaline carbonates can be reduced by MHs under catalyst‐free conditions to selectively afford CH4 as the sole hydrocarbon product in yields of up to 73%. Moreover, the contents of methane in the gaseous products and its yield are shown, which mainly depend on the nature of metal carbonates/hydrides, rate and duration of ball milling, and reaction mixture composition. Thus, this study opens new ways to achieve the CO2 utilization and synthesize of COx‐free hydrogen and methane fuel mixtures.

Selective methanation of carbonate@carbon composite formed by the reaction of carbon dioxide with alkali metals

“…The Raman spectrum of the solid product is shown in Figure 2C, where it is possible to recognize the main D and G‐band characteristics of carbon. The first peak at 1339 cm −1 is the D‐band, and the second peak at the 1593 cm −1 is the G‐band, which is consistent with the literature 47,48 . The chemical environment of carbon and oxygen in the solid products was probed by XPS.…”

“…The first peak at 1339 cm −1 is the D-band, and the second peak at the 1593 cm −1 is the G-band, which is consistent with the literature. 47,48 The chemical environment of carbon and oxygen in the solid products was probed by XPS. C 1 second peaks of elemental carbon and carbonate are observed at 284.5 and 290.0 eV, respectively, further confirming the existence of F I G U R E 2 XRD (A), FTIR (B), Raman (C), and XPS (D) spectra of the solid product (Li 2 CO 3 @C, Na 2 CO 3 @C, K 2 CO 3 @C) after the reaction of alkali metal (Li, Na, K) with CO 2 [Colour figure can be viewed at wileyonlinelibrary.com] carbon in the solid products ( Figure 2D).…”

Alkaline Earth Metal-Induced Hydrogenation of the CaO-Captured CO2 to Methane at Room Temperature

“…We propose that the increment of Ca content and H 2 pressure is beneficial to the formation of CaH 2 , promoting the efficiency of hydrogenating CaCO 3 to CH 4 . Our group has reported that the methane yields for the reaction of CaCO 3 with CaH 2 at 550 rpm for 48 h equaled 67.6%, which is higher than that (45.77%) in the Ca-induced hydrogenation of CaCO 3 under the similar experimental condition.…”

CO2 storage and conversion to CH4 by wet mechanochemical activation of olivine at room temperature

“…In these conditions, maximum CH 4 formation is only possible by transformation of some carbonaceous solid species present in the solid state in H 2 environment. Previous investigations have shown that CH 4 can be formed during milling of carbonate phases [47] or inorganic carbon [48] inH 2 rich atmosphere. The experimental evidence collected is not enough to clarify the main mechanism operating, but the reduction of MgCO 3 to CH 4 in H 2 environment is highly possible.…”