Internal CO2 utilization in methane to hydrogen fuel processor

CO2 adsorption and methanation are particularly effective in achieving near-zero carbon emissions through carbon capture and utilization (CCU) in methane-to-hydrogen fuel processors (FP), especially when the adsorbent and catalyst are precisely tailored to the specific operating conditions of the FP. This study aims to design and develop efficient CO2 adsorbents and CO2 methanation catalysts that operate effectively under conditions mimicking those of an FP. The selective CO2 adsorption of the prepared activated carbon (AC)-based adsorbents was assessed via Ideal Adsorbed Solution Theory (IAST) selectivity. The IAST selectivity of AC3-based adsorbents, initially treated with HNO3, was further enhanced by H2SO4 treatment, achieving a maximum IAST selectivity of 198 in the AC3-9M-L adsorbent. The superior performance of AC3 samples was linked to their abundance of specific surface groups, especially carboxyl and lactone species, as detected by TPSGD. Further improvement in sulfur-treated AC3 adsorbents was associated with their sulfur content, measured by the S/Si ratio from XRF analysis. CO2 methanation was conducted over Ni-La/γ-Al2O3 catalysts using a Box-Behnken design to evaluate factors such as reaction temperature, H2/CO2 feed ratio, La promoter loading, and feed flow-to-catalyst weight (F/W) ratio. Among these, the H2/CO2 feed ratio had the most significant positive impact on CO2 methanation, within a range of 0.5-1.5. Higher temperatures slightly increased CO2 conversion, with notable exceptions, but decreased CH4 selectivity. Elevated La loading modestly enhanced CO2 methanation performance, while higher F/W ratios generally reduced it, except at low temperatures. Operando FTIR-DRIFTS-MS studies on Ni-La/γ-Al2O3 under a low H2/CO2 feed ratio of 1:1 suggested that the CO2 methanation reaction likely proceeded via H-assisted CO2 dissociation, with weakly bridged CO species correlating to CH4 production, as evaluated qualitatively and quantitatively. Therefore, a CCU unit integrating novel adsorbents and catalysts can be developed within the FP-PEMFC to minimize carbon emissions per energy unit produced and enhance overall efficiency.