Dual function materials for CO₂ capture and conversion using renewable H₂

The accumulation of CO₂ emissions in the atmosphere due to industrialization is being held responsible for climate change with increasing certainty by the scientific community. In order to prevent its further accumulation in the atmosphere, CO₂ must be captured for storage or converted to useful products. Current materials and processes for CO₂ capture are energy intensive. We report a feasibility study of dual function materials (DFM), which capture CO₂ from an emission source and at the same temperature (320 °C) in the same reactor convert it to synthetic natural gas, requiring no additional heat input. The DFM consists of Ru as methanation catalyst and nano dispersed CaO as CO₂ adsorbent, both supported on a porous γ-Al₂O₃ carrier. A spillover process drives CO₂ from the sorbent to the Ru sites where methanation occurs using stored H₂ from excess renewable power. This approach utilizes flue gas sensible heat and eliminates the current energy intensive and corrosive capture and storage processes without having to transport captured CO₂ or add external heat

In situ CO2 capture using CaO/γ-Al₂O₃ washcoated monoliths for sorption enhanced water gas shift reaction

In situ capture of CO₂ allows the thermodynamically constrained water gas shift (WGS) process to operate at higher temperatures (i.e., 350 C) where reaction kinetics are more favorable. Dispersed CaO/γ-Al₂O₃ was investigated as a sorbent for in situ CO₂ capture for an enhanced water gas shift application. The CO₂ adsorbent (CaO/γ-Al₂O₃) and WGS catalyst (Pt/γ-Al₂O₃) were integrated as multiple layers of washcoats on a monolith structure. CO₂ capture experiments were performed using thermal gravimetric analysis (TGA) and a bench scale flow through reactor. Enhancement of the water gas shift (EWGS) reaction was demonstrated using monoliths (400 cells/in.2) washcoated with separate layers of dispersed CaO/γ-Al₂O₃ and Pt/γ-Al₂O₃ in a flow reactor. Capture experiments in a reactor using monoliths coated with CaO/γ-Al₂O₃ indicated that increased concentrations of steam in the reactant mixture increase the capture capacity of the CO₂ adsorbent as well as the extent of regeneration. A maximum capture capacity of 0.63 mol of CO₂/kg of sorbent (for 8.4% CaO on γ-Al₂O₃ washcoated with a loading of 3.45 g/in.3 on monolith) was observed at 350 C for a reactant mixture consisting of 10% CO₂, 28% steam, and balance N₂. Hydrogen production was enhanced in the presence of monoliths coated with a layer of 1% Pt/γ-Al2O₃ and a separate layer of 9.4% CaO/γ-Al₂O₃. A greater volume of hydrogen compared to the baseline WGS case was produced over a fixed amount of time for multiple cycles of EWGS. The CO conversion was enhanced beyond equilibrium during the period of rapid CO₂ capture by the nanodispersed adsorbent. Following saturation of the adsorbent, the monoliths were regenerated (CO₂ was released) in situ, at temperatures far below the temperature required for decomposition of bulk CaCO₃. It was demonstrated that the water gas shift reaction could be enhanced for at least nine cycles with in situ regeneration of adsorbent between cycles. Isothermal regeneration with only steam was shown to be a feasible method for developing a process

Kinetics of CO₂ methanation over Ru/γ-Al₂O₃ and implications for renewable energy storage applications

Kinetics of CO₂ hydrogenation over a 10% Ru/γ-Al₂O₃ catalyst were investigated using thermogravimetric analysis and a differential reactor approach at atmospheric pressure and 230–245 °C. The data is consistent with an Eley–Rideal mechanism where H2 gas reacts with adsorbed CO₂ species. Activation energy, pre-exponential factor and reaction orders with respect to CO₂, H₂, CH₄, and H₂O were determined to develop an empirical rate equation. Methane was the only hydrocarbon product observed during CO₂ hydrogenation. The activation energy was found to be 66.1 kJ/g-mole CH₄. The reaction order for H₂ was 0.88 and for CO₂ 0.34. Product reaction orders were essentially zero. This work is part of a larger study related to capture and conversion of CO₂ to synthetic natural gas

CO₂ utilization with a novel dual function material (DFM) for capture and catalytic conversion to synthetic natural gas: An update

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