Directly capturing CO2 from the air and using it to produce solar fuel in a flow-through process is an innovative approach to reducing atmospheric CO2 levels. Traditional methods of storing CO2 have uncertain long-term consequences, so this study represents dual flow reactor for collecting and utilizing carbon directly from the airThe reactor converts the captured CO2 into synthesis gas (syngas), a mixture of CO and H2, using light, without the need for high temperatures or pressure.

Key aspects and findings of the study:

• DACCU technology: Integrated system for direct air carbon capture and utilization (DACCU). The system consists of two main parts:
• CO2 collection: Solid silica gel adsorbent with polyamine (SBA-15|PEI). The adsorbent selectively captures CO2 from the air during darkness (night operation), while other gases, such as N2 and O2, pass through.
• CO2 release: The captured CO2 is released by photothermal heating using concentrated sunlight during the day. A parabolic solar concentrator heats the adsorbent to 80-100°C, allowing for efficient CO2 release.
• CO2 utilization: The released CO2 is photochemically converted into synthesis gas using a hybrid material based on alumina/silica-titanium and cobalt bis(terpyridine) (Al2O3/SiO2|TiO2|CotpyP). Ethylene glycol (EG) obtained from depolymerized polyethylene terephthalate (PET) is used as the reducing agent.
• Operating principle: The system is designed for diurnal operation, where CO2 is captured at night and converted to syngas during the day.
• Materials and methods:
• Adsorbent synthesis: Polyamine (PEI) is impregnated onto a porous support made of mesoporous silica gel (SBA-15).
• Catalyst synthesis: The cobalt molecular catalyst (CotpyP) is immobilized on TiO2 nanoparticles, which are dispersed on a high surface area support (SiO2 or Al2O3).
• DACCU reactor testing: A two-bed reactor is filled with SBA-15|PEI adsorbent and γ-Al2O3|TiO2|CotpyP composite. Humid air is passed through the collection layer for 12 hours in the dark. Then the flow is switched to N2, the CO2U layer is humidified with EG and the solar simulator is turned on.
• Results and discussion:
• CO2 collection: The SBA-15|PEI adsorbent effectively removes CO2 from the air for 9 hours. The total collection capacity is approximately 87 mg CO2 per gram of adsorbent.
• CO2 release: Concentrated sunlight combined with an infrared absorption layer enables efficient CO2 release at a temperature of around 100°C. The CO2 concentration in the outlet stream reaches 30 ppm (v/v) within 30 minutes of the start of sunlight.
• CO2 utilization: The hybrid material Al2O3/SiO2|TiO2|CotpyP catalyzes the gas-phase photoreduction of CO2 to synthesis gas. The use of EG as a reducing agent increases the rate of CO2 reduction and enables the utilization of waste streams.
• DACCU integration: The system successfully captures, concentrates and converts CO2 from the air into synthesis gas using simulated sunlight.
• System flexibility: The system allows unreacted CO2 to be recaptured and redirected to the reaction unit, increasing CO2 conversion.
• Additional information:
• Product analysis: The main products of EG oxidation are formate and glycolaldehyde dimer.
• Isotopic labeling: The use of 13CO2 confirms that CO is a product of CO2 reduction.
• Material support: The use of alumina as a catalyst support leads to higher CO production.
• Reaction conditions: The optimal temperature for CO2 conversion is 25 °C.
• Advantages:
• Use of solar energy: Reduces the energy intensity of the process.
• Use of waste materials: EG from recycled PET plastic as a reducing agent.
• Time separation of collection and conversion: Solves the problems of low CO2 concentration and the presence of O2 in the air.
• Potential applications:
• Production of renewable fuels and chemicals.
• Reducing greenhouse gas emissions.
• Utilization of CO2 directly at the point of its creation.

In conclusion, this study demonstrates an integrated and sustainable system for the direct capture and utilization of CO2 from the air, which has the potential to contribute to the reduction of greenhouse gas emissions and the production of renewable fuels. Spring

Glossary of key terms

• DACCU (Direct Air Carbon Capture and Utilization): Direct capture of CO2 from the air and its use for the production of valuable products.
• Syngas (Synthesis gas): A mixture of carbon monoxide (CO) and hydrogen (H2) that is used as a precursor for the production of fuels and chemicals.
• Photothermal Heating: Heating a material by absorbing light (most often infrared), which is converted into heat.
• Photocatalyst: A material that accelerates a chemical reaction in the presence of light.
• PEI (Polyethyleneimine): Polymer used as an active chemical for CO2 capture.
• SBA-15: A mesoporous silicate that serves as a solid support for PEI in CO2 capture.
• CotpyP (Cobalt bis(terpyridine)): A cobalt-containing molecular catalyst used for CO2 reduction.
• TiO2 (Titanium oxide): Titanium dioxide, used as a photoactive semiconductor in a catalyst for CO2U.
• EG (Ethylene glycol): Alcohol used as a reducing agent (electron source) in the photocatalytic reduction of CO2.
• TON (Turnover Number): The number of product molecules formed per catalyst molecule.
• TOF (Turnover Frequency): The rate at which a catalyst converts reactants into products (TON per unit time).