Contents lists available at ScienceDirect Journal of CO 2 Utilization journal homepage: www.elsevier.com/locate/jcou Methane production by mechanochemical processing of MgH 2 -Li 2 CO 3 as sources of H 2 and CO 2 at room temperature María L. Grasso a,b, *, Luisa Fernández Albanesi a,c , Sebastiano Garroni d , Gabriele Mulas d , Fabiana C. Gennari a,c,e a Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), R8402AGP, S. C. de, Bariloche, Río Negro, Argentina b Universidad Nacional de Cuyo (UNCuyo), Facultad de Ciencias Exactas y Naturales, M5502JMA, Ciudad de Mendoza, Mendoza, Argentina c Centro Atómico Bariloche (CAB-CNEA), R8402AGP, S.C. de, Bariloche, Río Negro, Argentina d Dipartimento di Chimica e Farmacia and INSTM, Università degli Studi di Sassari, 07100, Sassari, Italy e Universidad Nacional de Cuyo (UNCuyo), Instituto Balseiro, Av. Bustillo 9500, R8402AGP, Bariloche, Río Negro, Argentina ARTICLE INFO Keywords: CO 2 conversion Alkaline carbonates Light metal hydrides Methane Hydrogen ABSTRACT The reutilization of CO 2 to produce valuable chemical fuels is an attractive approach to reduce the greenhouse effect and global warming. In this work, the room temperature production of CH 4 /H 2 fuel mixtures via me- chanochemical activation of Li 2 CO 3 -MgH 2 system was explored. The CH 4 /H 2 fuel mixtures were obtained by a free-catalyst reaction, with high selectivity and using Li 2 CO 3 and MgH 2 as solid portable sources of CO 2 and H 2 , respectively. The effect of processing parameters on both the evolution of the solid phases and the production of CH 4 /H 2 fuel mixtures was studied using X-ray diffraction, spectroscopic techniques, electron scanning micro- scopy and gas chromatography. Thermodynamic calculations predict the complete CO 2 reduction to CH 4 , with simultaneous formation of MgO and Li 2 O. Experimental evidence supports the progressive formation of MgO and the appearance of Li 2 O. The presence of H 2 simultaneously with CH 4 in the gas phase was due to kinetic re- strictions. Based on experimental results and equilibrium composition calculations, the reaction mechanism was proposed. The kinetic analysis reveals that the rate limiting CH 4 production is the nucleation of MgO/Li 2 O in the surroundings of Li 2 CO 3 , while the H 2 release is controlled by the reaction interface between MgH 2 /Mg or MgH 2 / MgO. 1. Introduction Carbon dioxide gas (CO 2 ) is considered one of the main contributors to global warming and climate change because of its role in the greenhouse effect. Human activities, such as combustion of fossil ma- terials (coal, oil, natural gas), industrial processes, changes in land use and deforestation, are considered to be the main responsible for the growing CO 2 atmospheric concentration, from 280 ppm in the pre-in- dustrial era to 415 ppm in 2019 [1], with an increase of 0.8 °C in global planet temperature. Intergovernmental Panel on Climate Change (IPCC) has estimated that by the end of the century, CO 2 concentration would reach 700 ppm and the average temperature would increase up to 5 °C, with devastating and irreversible climate changes [2]. For these rea- sons, a current and urgent challenge is to find a sustainable way to reduce CO 2 concentration in the atmosphere. Unfortunately, the con- tinuous increase in energy demand due to a growing population and life-style quality implies more CO 2 atmospheric emissions [3]. Carbon dioxide capture and utilization (CCU) is a very promising strategy to mitigate CO 2 emissions, having at the same time a benefit related to the production of value-added products. Here, CO 2 acts as a carbon source to synthesize products such as alcohols, polymers and synthetic fuels. Also, there are direct applications of the captured CO 2 : in carbonated drinks, as dry-ice, in fire extinguishers or in algae farms for photosynthesis [3,4]. Among synthetic fuels to be produced from CO 2 , methane is the hydrocarbon with the highest hydrogen to carbon ratio. Its gravimetric heat is greater (55.5 MJ/kg) than butane (49.5 MJ/kg), diesel (44.8 MJ/kg) and methanol (22.7 MJ/kg) [5]. In addition, CH 4 is compatible with our current storage and distribution network. Based on its good properties, methane is considered an at- tractive and alternative fuel. Interestingly, the addition of H 2 to CH 4 produces a fuel-gas mixture with improved properties for its use in stationary applications like heaters, boilers and turbines or in mobile https://doi.org/10.1016/j.jcou.2020.101209 Received 7 May 2020; Received in revised form 29 May 2020; Accepted 6 June 2020 ⁎ Corresponding author at: Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Universidad Nacional de Cuyo (UNCuyo), Facultad de Ciencias Exactas y Naturales, Av. Bustillo 9500, R8402AGP, Bariloche, Río Negro, Argentina. E-mail address: maria.grasso@cab.cnea.gov.ar (M.L. Grasso). Journal of CO₂ Utilization 40 (2020) 101209 2212-9820/ © 2020 Elsevier Ltd. All rights reserved. T