In-situ hydrogenation of dual function material for integrated CO2 capture and methanation with the presence of steam

Abstract

The impacts of steam on hydrogenation of dual function materials (DFM) for Integrated CO₂ Capture and in-situ methanation (ICCM) is a new area requiring detailed investigations prior to industrialization. This work investigated impacts from steams on hydrogenation of Ru-Na₂CO₃/γ-Al₂O₃ DFM for ICCM that containing Na₂O adsorbent, Ru sites, and γ-Al₂O₃ support. DFM performance was examined in cyclic reactions as introducing external steam during hydrogenation, and the behaviors of adsorbed CO₂ species during hydrogenation were characterized by in-situ DRIFTS and H₂-TPSR. CH₄ selectivity decreased sharply from 84.3 % to 1.2 % as increasing external steam concentrations to 20 vol.%, and the conversion of adsorbent component decreased from 298.5 μmol g^-1 to 167.1 μmol g^-1. b-CO₃^2- and m-CO₃^2- formed at Na₂CO₃/γ-Al₂O₃ interface were the carbonate species that could be hydrogenated into CH₄, some of which were desorbed into CO₂ due to moisture-driven desorption effects. With the presence of external steam in H₂ reactants, the conversion of carbonate species is a competing process between hydrogenation and moisture-driven desorption. In ICCM reaction with external steam present, b-CO₃^2- was preferred to be desorbed into CO₂; while for m-CO₃^2-, desorption into CO₂ by steam and hydrogenation into CH₄ proceeded in parallel. Strong moisture-driven desorption effects from steam product were demonstrated in a fixed-bed reactor, which also led to rapid decrease of localized selectivity of CH₄ along bed height.