Study of ceria-composite materials for high-temperature CO2 capture and their ruthenium functionalization for methane production

A set of Dual Function Materials (DFMs) was prepared to seize the CO2 from a rich feed gas and to in-situ convert it to methane (synthetic natural gas). Specifically, ruthenium-ceria composite materials were synthesized through successive impregnation depositions on two high surface area supports, namely Al2O3 and ZSM-5. Cerium oxide has both the roles of CO2 adsorbent and promoter support for ruthenium, which represents the active component for methanation. Three different quantities of ceria (10, 20, and 30 wt%) were dispersed onto the solid supports, and the adsorption capacities of the ceria-based materials were studied at different temper-atures (150, 200, and 250 degrees C) at atmospheric pressure. The samples exhibiting the best results in terms of CO2 adsorption (30 wt% CeO2/Al2O3 and 30 wt% CeO2/ZSM-5) were subsequently impregnated to obtain ruthenium-loaded catalysts (2 wt% Ru). These functionalized materials were characterized by XRD, N2 physisorption at -196 degrees C, TPDRO, ICP-MS, XPS, FESEM, HRTEM, and FT-IR. Then, cyclic experiments of CO2 adsorption and methanation were performed, simulating a real use of the catalysts at 250 degrees C and atmospheric pressure. The deposition of ruthenium-ceria on a high surface area support was found to be crucial for maintaining the methanation activity of this catalytic system under cyclic CO2 adsorption-hydrogenation conditions. The Al2O3- supported ruthenium-ceria catalyst adsorbed a lower amount of CO2 (ca. 200 mu mol g-1 per each cycle) with respect to the zeolite-supported sample (ca. 300 mu mol g-1); nevertheless, the former material presented the best methanation performances, thanks to an intermediate ruthenium-ceria interaction, yielding a maximum of 51% of CO2 converted and producing up to 111 mu mol g-1 of CH4.