Enhanced Activity of Integrated CO₂ Capture and Reduction to CH₄ under Pressurized Conditions toward Atmospheric CO₂ Utilization

Abstract

Direct conversion of dilute CO2 contained in power plant or industrial exhaust gas and the atmosphere into high-concentration hydrocarbons without a need of separate CO2 capture and purification processes is one of the awaited technologies in envisioned low-carbon societies. In this study, we investigated the performance of integrated CO2 capture and reduction to CH4 over Nibased dual functional catalysts promoted with Na, K and Ca. Ni/Na-γ-Al2O3 exhibited the highest activity for integrated CO2 (5% CO2) capture and reduction, achieving high CO2 conversion (>96%) and CH4 selectivity (>93%). In addition, very low concentration CO2 (100 ppm CO2) was successfully converted to 11.5% CH4 at the peak point (>1000 times higher concentration than that of the supplied CO2) over Ni/Na-γ-Al2O3. The Ni-based dual functional catalyst exhibited a high CO2 conversion exceeding 90%, even when 20%O2 was present during CO2 capture. Furthermore, an increased operation pressure had positive impacts on both CO2 capture and CH4 formation, and these advantageous effects were also observed when CO2 concentration was at the level of atmospheric CO2 (100-400 ppm). As pressure increased from 0.1 to 0.9 MPa, CH4 production capacity with 400 ppm CO2 was enhanced from 111 to 160 µmol gcat -1 . The approach in combination with the efficient catalyst shows encouraging promises for CO2 utilization, enabling direct air capture-conversion to value-added chemicals.CH4 productivity increased from 188 to 266 μmol gcat −1 . In addition, the effect of pressure on catalyst performance was also investigated at very low CO2 levels of 100 and 400 ppm, and high pressure was found to positively affect both CO2 capture and CH4 formation. These results suggest that high pressure enhances the CO2 absorption and CH4 formation capacities of dual-functional catalysts and allows for efficient integrated CO2 capture and reduction into CH4 even at atmospheric levels of CO2. The approach, in combination with the efficient catalyst, is promising for CO2 utilization, thus enabling direct air capture-conversion to value-added chemicals.

Direct air capture: process technology, techno-economic and socio-political challenges

“…A similar process using a Ni/Na-g-Al 2 O 3 dual-function material has also been proposed; 100 ppm CO 2 feeds were converted to 11.5% CH 4 in a cyclic sorption and hydrogenation process. 349 Opportunities for passive contacting with CO 2 in the air, and leveraging existing civil and industrial infrastructure. 'Passive' contactors have been proposed as novel DAC technologies suitable for specific applications.…”

Recent advances in direct air capture by adsorption

“…73 Recent progress in dual-function materials, which are active for both CO 2 capture and utilization, offers a new perspective on system design. [74][75][76] DAC and reduction take place in sequence so that regeneration can be avoided. In practice, the sorbent particle size, packing surface area, and height/diameter ratios of contactors, among others, should be assessed.…”

“…83 Because a DAC facility can provide on-site CO 2 generation anywhere, its application is advantageous in addition to its environmental benefits. Recently, the potential application of adsorption-based DAC in indoor air removal, 115,191,193,208,209 CO 2 fertilization, 178,210 biomass production, [211][212][213][214][215] fuel production (CH 4 , 68,70,75,[216][217][218][219][220][221][222] methanol, 71,[223][224][225][226] aviation fuel, 73,[227][228][229][230][231][232] hydrocarbons 233 ), chemicals (Fischer-Tropsch process, 234,235 carbon nanotubes, 236 dimethyl carbonate, 237 syngas 238,239 ), mineralization, [240][241][242][243][244] storage, 245,246 enhanced oil recovery (EOR), …”

Direct air capture by membranes

“…For example, there are some reports on the chemical conversion of CO 2 by using low-concentration CO 2 . [11][12][13] Very recently, CO 2 conversion to CH 4 with low CO 2 concentration gas (100-400 ppm) was successfully achieved, though it requires rather high temperature and pressurized condition.…”