Abstract
Dual function materials (DFMs) for CO₂ capture and conversion couple the endothermic CO₂ desorption step of a traditional adsorbent with the exothermic hydrogenation of CO₂ over a catalyst in a unique way; a single reactor operating at an isothermal temperature (320 °C) and pressure (1atm) can capture CO₂ from flue gas, and release it as methane upon exposure to renewable hydrogen. This combined CO₂ capture and utilization eliminates the energy intensive CO₂ desorption step associated with conventional CO₂ capture systems as well as avoiding the problem of transporting concentrated CO₂ to another site for storage or utilization. Here DFMs containing Rh and dispersed CaO have been developed (˃1% Rh 10% CaO/γ-Al₂O₃) which have improved performance compared to the 5% Ru 10% CaO/γ-Al₂O₃ DFM (0.50 g-mol CH₄/kg DFM) developed previously. Ruthenium remains the catalyst of choice due to its lower price and excellent low temperature performance. The role of CO₂ adsorption capacity on the final methanation capacity of the DFM has also been investigated by testing several new sorbents. Two novel DFM compositions are reported here (5% Ru 10% K₂CO₃/Al₂O₃ and 5% Ru 10% Na₂CO₃/Al₂O₃) both of which have much greater methanation capacities (0.91 and 1.05 g-mol CH₄/kg DFM) compared to the previous 5% Ru 10% CaO/γ-Al₂O₃ DFM.