CO2 hydrogenation to synthetic natural gas with light hydrocarbons on Mn-promoted mesoporous Co3O4-Al2O3 metal oxides

Direct CO2 conversion into synthetic natural gas (SNG, CH4) with simultaneous small production of light paraffinic C2-C4 hydrocarbons to enhance a heating value of SNG was investigated with ordered mesoporous CoMnAl mixed metal oxides (denoted as m-CoMnAl). CO2 hydrogenation activity to form hydrocarbons with small CO byproduct formed by a reverse water gas shift reaction (RWGS) was strongly affected by the MnO2 promoter content in the ordered Co3O4-Al2O3 mesoporous structures. The m-CoMnAl structures with proper amount of Mn promoter were found to be effective to enhance CO2 conversion to methane with small amount of light hydrocarbons formation, which were mainly attributed to the presence of abundant oxygen vacant sites with a stable preservation of the partially oxidized cobalt nanoparticles in the ordered mesoporous Co3O4-Al2O3 structures even under a reductive hydrogenation condition. Selective methanation of CO2 was found to be more favorable on the highly reduced metallic cobalt nanoparticles formed with smaller amount of Mn promoter (m-CoMnAl(0.05)), however, excessive Mn content such as Mn/Co ratio > 1 (m-CoMnAl(1.0)) revealed less structural stability of ordered mesoporous structures with lower CO2 conversion with relatively higher CO selectivity of 1.4 % with lower olefin selectivity through severe phase segregations of the Co-Mn-Al mixed metal oxides with selective formations of MnCO3 phases.