Cyclic operation of CO2 capture and conversion into methane on Ni-hydrotalcite based dual function materials (DFMs)
A. Catarina Faria, Raquel Trujillano, V. Rives, Carlos V. Miguel, Alírio E. Rodrigues, Luı́s M. Madeira
Abstract
Ni-hydrotalcite-based dual function materials (DFMs) have been prepared and applied for the combined CO2 capture and methanation in a single reactor. The materials have been synthesized with different chemical properties (by partial substitutions of Mg with Ni, by changing the M2+/M3+ molar ratio – i.e., the (Ni2++Mg2+)/Al3+ ratio, and by impregnation with Cs (≈10 wt%)) and the effect of reduction temperature on their cyclic performance was studied. After calcination, the materials were reduced at increasing temperatures, from 400° to 600°C. The cyclic operation started with the capture of CO2 from a 15% CO2/N2 stream (feeding for 20 min), followed by the methanation stage with pure H2. The Cs-promoted sample reduced at 450 °C featured a CO2 sorption capacity of 0.48 molCO2·kgcDFM-1 and produced ca. 0.33 molCH4·kgcDFM-1. Its good performance was associated to a higher number of medium and strong basic sites. The sample containing the highest M2+/M3+ molar ratio (≈3) exhibited the highest selectivity towards methane (≈ 100%) and fastest methanation kinetics.