HYDRIDE FORMING MATERIALS FOR CO2 CONVERSION:CO2 METHANATION USING MGH2 AS A PORTABLE HYDROGEN MEDIUM

GUILLERMINA AMICA; FABIANA GENNARI

Congreso; XXIX INTERNATIONAL MATERIALS RESEARCH CONGRESS C. MATERIALS FOR ENERGY CONVERSION, STORAGE, AND HARVESTING; 2021

In this work, for the first time, the feasibility of the reduction of CO2 to CH4 using MgH2 in the presence and absence of cobalt as a catalyst was investigated. It was demonstratedthat the methanation mechanism depends on the presence of a catalyst and its nature and other factors such as the grade of microstructural refinement, molar ratio H2:CO2, reactiontime and temperature are crucial and non-independent factors for the process effectiveness. Without a catalyst the process is favored employing a molar ratio MgH2:CO2 of 2:1. Under this condition, a methane yield of 44.6% was obtained after 24 h of thermal treatment at 400oC. As predicted from thermodynamic calculations, the gas phase was a mixture of CH4and H2. The experiments also showed the presence of small amounts of CO2, CO and superior hydrocarbons in the gas phase, whereas the solid product contained Mg, MgO, andC with little MgCO3. The global mechanism for the un-catalyzed MgH2 involves the direct reduction of CO2 and the generation of CH4 via C as an intermediary. When either thetemperature or the reaction time is lowered, the performance values drop sharply because while equilibrium is not reached, CO2 is not totally reduced to C, but it is partially reducedto CO. Otherwise, it was shown that the use of catalysts allows the accuracy of a different methanation mechanism. The best methane yield (78%) was obtained for the MgH2?10 wt%Co sample per treatment under CO2 for 48 hours at 350 oC considering a molar ratio MgH2:CO2 of 4:1. The global mechanism responds to a Sabatier process favored by Co asan active catalyst and it also involves the reverse water gas shift reaction followed by methanation of CO in the presence of steam. The catalyzed process is more selective, asthere was no evidence of the formation of superior hydrocarbons. As the use of catalysts allows lowering the operational temperature without reducing the methane yield, this research provides interesting insight into a thermochemical method for CO2 reduction to CH4 employing a solid hydrogen storage medium as an H2 source.