Novel application of Ru-based catalysts on MgAl oxides alkaline adsorbents for cyclic CO2 methanation
Andrea Rizzetto, Enrico Sartoretti, Marco Piumetti, Raffaele Pirone, Samir Bensaid
Abstract
• Ru-based catalysts on MgO and MgAl oxides are effective for cyclic CO 2 methanation. • Doping MgAl with K 2 CO 3 enhances surface alkalinity and CO 2 capture performance. • Cyclic methanation tests were performed, with dry and wet adsorption stages. • Ru/MgAl and Ru-K/MgAl catalysts are effective and selective for methane production. • Operando FTIR deeply investigates transient species on catalyst surfaces. This study explores the performances of Ru-based catalysts with a low metal content (2 wt%) supported on MgO and Mg-Al Oxides (MgAl) for cyclic CO 2 adsorption and methanation at atmospheric pressure. Adsorption and desorption tests demonstrated that MgAl-based catalysts are more promising for CO 2 capture due to their larger surface area and better distribution of active sites (Mg 2+ –O 2- ). Moreover, doping the MgAl support with K 2 CO 3 further improves surface alkalinity and, consequently, capture performance. During cyclic operations, all the catalysts proved effective and selective for methane production. To simulate realistic conditions, both dry and wet CO 2 adsorptions were conducted before the methanation stage. The presence of moisture positively influenced gas carbonation for all catalysts, increasing the overall amount of CO 2 captured. Specifically, Ru/MgAl exhibited the best performance in terms of adsorption and conversion to methane (approximately 85 % after dry adsorption and 79 % after wet adsorption), with a maximum methane production of 183 and 220 μmol CH4 g −1 , respectively. The reaction yield was further enhanced with Ru-K/MgAl, achieving 327 μmol CH4 g −1 after dry adsorption and 333 μmol CH4 g −1 after wet adsorption. However, this catalyst displays different conversion kinetics, attributed to slowed carbonate migration, low Ru dispersion, limited specific surface area, and excessive carbonation strength. Operando FTIR tests revealed differences in reaction intermediates between Ru/MgAl and Ru-K/MgAl, by going deeper into the kinetic differences observed. The study concludes that Ru/MgAl materials are highly promising catalysts for CO 2 adsorption and methane production, supporting the development of technologies for CO 2 abatement and renewable energy utilisation.