International research team including Khalifa University paves way towards the design of new simple and efficient photocatalysts made from covalent organic frameworks (COFs) to reduce captured CO2 into useful products

As the world continues to pump carbon into the atmosphere, it is increasingly important to not only reduce emissions but also find ways to capture and use carbon dioxide. Carbon capture and storage technologies are noble approaches, but don’t tend to make much money. Instead, attention turns to economically viable and valuable approaches to turn carbon dioxide into something useful.

Dr. Dinesh Shetty, Assistant Professor of Chemistry, and Dr. Abdul Khayum Mohammed, Postdoctoral Researcher, collaborated with an international team to develop a new photocatalyst to efficiently and sustainably transform carbon dioxide into useful products. The research team comprised members from New York University Abu Dhabi, American University of Beirut, Instituto de Ciencia de Materiales de Madrid, Spain, University of Strasbourg, France, and University of Nova Gorica, Slovenia. The team’s results were published in

“Excessive anthropogenic emissions of carbon dioxide into the atmosphere have led to global warming,” Dr. Shetty explained. “At the same time, CO2 is a nontoxic, inexpensive, abundant, and renewable source of carbon. Converting it into high value-added products would be a viable and economic use of the carbon dioxide around us.”

Numerous processes already exist to transform CO2 emissions into various chemicals valuable for industry, and among these processes, photocatalytic reduction of CO2 has been noted as particularly promising. There’s little wonder why: this is photosynthesis. Green plants convert carbon dioxide and water into carbohydrates, performing this reaction under ambient conditions using just sunlight, which is an inexhaustible and environmentally-friendly energy source. Even better, photocatalytic CO2 reduction doesn’t create any secondary pollution.

“Carbon dioxide can be reduced into many forms, with carbon monoxide and formate the most common reduction products,” Dr. Shetty said. “Formate is preferred as it is the simplest oxygenated species produced, and an intermediate in the formation of methanol and other higher-order hydrocarbons, which can be used in plastics, paints, organic solvents, and fuel cells.”

Photocatalytic reduction of CO2 is not new—many semiconductor and molecular-based systems have been studied. However, their limited conversion efficiency, low binding affinity for CO2, unfavorable active-site architecture, and rapid charge recombination limit their overall performance. Covalent organic frameworks (COFs), such as that developed by the research team, have the potential to address many of these issues.

COFs are a class of materials that form two- or three-dimensional structures through reactions between their organic components, resulting in strong, covalent bonds that create porous, crystalline materials. They are uniquely tunable, with well-defined structures and good chemical stability and plenty of pores for adsorption applications.

Capturing the CO2 is the first step. A sorbent material is needed to selectively grab the carbon dioxide and allow it to collect in the pores in the material. And COFs for CO2 reduction already exist, but the majority produce carbon monoxide as their product, which is the less desirable of the two common products. Those that do produce formate often involve expensive noble metals or even enzymes.

The research team synthesized a novel COF using two different building units known as porphyrins and isoindigo to ensure the captured carbon dioxide reduces into formate, not carbon monoxide. Their PI-COF has a square layered structure and an improved affinity for carbon dioxide adsorption. Even without expensive rare materials or special catalysts, the research team’s PI-COF reduced carbon dioxide into formate with yields comparable to more complex systems.

“Our system performs similarly to others but requires much less power, making it a much more environmentally-friendly system,” Dr. Shetty said. “We expect this to pave the way towards more sustainable yet equally efficient photocatalytic systems for CO2 reduction.” Currently, Dr. Shetty’s team at KU is working on economically viable COF-based photoconducting materials for CO2 conversion.

Dr. Shetty is also a member of the Center for Catalysis and Separation (CeCaS), one of the research centers at KU.

Jade Sterling
Science Writer
4 February 2022

The post A Unique Photocatalyst Could Turn the CO2 in the Atmosphere into Useful and Valuable Products appeared first on Khalifa University.

With myriad materials to choose from, simulations help speed up the process of selecting the right materials for the job. 

.

With most of the world still relying on fossil fuel-driven power plants for their energy, carbon dioxide emissions remain a global concern. Reducing greenhouse gas emissions, particularly carbon dioxide, is paramount in combating climate change.

One way to do this is to capture the carbon dioxide (CO₂) emissions directly from the smokestacks of the power plants before they enter the atmosphere.

Dr. Lourdes Vega, Director of the Khalifa University Research and Innovation Center on CO₂ and Hydrogen (RICH) and Professor of Chemical Engineering, is leading a collaborative research team that is analyzing different types of materials to determine their potential for post-combustion carbon dioxide capture and separation.

The team includes Dr. Daniel Bahamon, Research Scientist, and, Assistant Professor of Chemical Engineering, both from Khalifa University, along with Dr. Santiago Builes from EAFIT University, Colombia, and Wei Anlu from China University of Petroleum, a student who spent six months at the RICH Center at Khalifa University for performing part of this study. They published their work in January in the journal.

“Mitigation strategies such as carbon capture, utilization and storage (CCUS) play an import role in limiting the contribution of CO₂ emissions to global climate change. One key approach to this is capturing post-combustion CO₂ from flue gas at power stations and chemical manufacturing plants,” explained Dr. Vega.

Flue gas is the by-product gas that leaves a fossil fuel power station or plant via a chimney known as a flue. While its composition depends on what is being burned, it mostly comprises nitrogen, carbon dioxide, water vapor and a number of pollutants such as particulate matter, carbon monoxide, nitrogen oxides and sulfur oxides. The ‘smoke’ seen pouring from these flues is not smoke at all, but the water vapor in the gas forming a cloud as it meets cooler air.

Carbon dioxide is the second largest component of flue gas at around 4 to 25 percent, depending on the source. Although there are technologies available now to capture this carbon dioxide before it can wreak havoc on the atmosphere, they have several disadvantages.

Currently, aqueous amine solutions, which are solutions containing water and amines, organic compounds derived from ammonia and containing a nitrogen atom attached to hydrogen and carbon atoms, are used to capture CO₂ in large-scale applications. Amine solutions are excellent at trapping the CO₂, making them the most popular and developed carbon capture technology. However, the disadvantage to this technology is that in order to separate the trapped CO₂ from the amine solution, it has to be heated, requiring additional energy, and some of the amines are lost in this high energy process.

To overcome the shortcomings of amine solutions, solid sorbent materials are a viable alternative. Solid sorbents can selectively adsorb CO₂, however some solid sorbent materials perform better than others, and finding the most optimal carbon capturing material was the focus of Dr. Vega’s investigation.

A good adsorbent is a highly porous material with a large internal surface, full of holes to collect the CO₂. Metal-organic frameworks (MOF) materials possess enhanced stability, greater CO₂ cycling capacities and lower regeneration energies, making MOFs a material of choice for solid sorbent-based carbon capture.

However, MOFs alone are not enough to adsorb the CO₂ from flue gas at low pressures, especially since water vapor in the gas can compete with the carbon dioxide for adsorption. To counter this, attention has turned to amine-functionalized MOFs, where amines are grafted onto the open metal sites to increase CO₂ adsorption selectivity and capacity. These materials combine the benefits of both the MOFs and the amines, avoiding the disadvantages of the need for heating the solvent for removing the CO2 or the evaporation of the amines.

There are multiple types of amines, each of which has different characteristics relevant to CO₂ capture. Finding the optimal amine for each real-world application can be a time-consuming endeavor.

“Molecular simulations can allow the systematic and precise study of the various relevant variables of a system,” explained Dr. Vega. “We can isolate and quantify the effect of each functionalized MOF on the performance of the system, making simulation an excellent tool for the rational design of materials.”

The research team used molecular simulations to explore the relationship between the structure of different kinds of amine-grafted MOFs and their CO₂ adsorption performance.

A series of amine-grafted MOFs were screened, establishing the most promising materials for adsorbing low-concentration CO₂, while considering their regeneration performance, or how many cycles the MOFs could operate before degrading.

“Our work offers a molecular understanding of how functionalization takes place on MOFs and how it affects their final performance, providing guidance on the design of the best material/amine combination for optimal post-combustion CO₂ capture,” said Dr. Vega.  Once the best material is found with this procedure, it will be synthesized and tested in a reactor at the conditions required for CO2 capture from different sources.

Dr. Vega’s team’s work is a significant contribution to the development of efficient and sustainable carbon capture utilization and storage solutions, as part of the RICH Center effort to find optimal materials to produce clean energy. 

Jade Sterling
Science Writer
15 April 2021

The post KU Team Develops Simulations to Find Materials for Capturing Carbon from Carbon Dioxide Emissions appeared first on Khalifa University.

By Dr. Ludovic �ٳܳ�é��

Dr. Ludovic �ٳܳ�é�� , Assistant Professor of Chemical Engineering at Khalifa University, outlines the strategies and technologies that could be deployed to turn CO2 emissions into a resilient circular economy.

Read Arabic story .

The continuous emission of carbon dioxide into the atmosphere is the leading cause of climate change and subsequent extreme weather events.

In 2015, the international community adopted the Paris Climate Agreement, agreeing to limit the global average rise in temperature to less than 2° C, compared to pre-industrial levels, but with ambitions to limit the rise to less than 1.5° C. Along with a paradigm shift from fossil fuels to renewable energy sources, deployment of carbon capture and storage technologies was proposed as a core strategy to actively and significantly reduce greenhouse gas emissions. This is in addition to the clear economic benefit that could be derived from using CO2 as a feedstock material for chemical products in a resilient circular economy.

While research into CO2 capture technologies is gaining traction, research into integrated capture and conversion strategies – which involves capturing CO2 at its source and effectively transforming the CO2 into value-added chemicals within the same chemical process – has received significantly less attention.

With my colleagues from Deakin University in Australia, including Dr. James Maina, Prof. Jennifer Pringle and Prof. Joselito Razal, and Dr. Suzana Nunes from King Abdullah University of Science and Technology in Saudi Arabia, Dr. Fausto Gallucci from Eindhoven University of Technology in Netherlands, and Dr. Lourdes Vega, Director of Khalifa University’s Research and Innovation Center on CO2 and Hydrogen (RICH), we published a review paper in the journal to assess recent advances in the integrated capture and conversion of CO2 from industry gases and atmospheric air.

Carbon capture and storage technologies (CSS) have been demonstrated across a number of pilot operations globally and typically include capturing CO2 from emission sources such as power plants, followed by compression prior to transportation to long-term storage sites. Although CSS technologies are viable for the capture of CO2 from large sources at high concentration levels, such as fossil fuel power plants or cement factories, they are not practical for small and distributed sources, such as transportation and residential heating, which cumulatively account for around half of all CO2 emissions.

For these cases, technologies that can extract CO2 directly from the atmosphere are needed if the associated carbon emissions are to be mitigated. These are direct air capture technologies (DAC) and they have some distinct advantages over traditional carbon capture technologies, including not needing to be located close to emission sources, which makes them deployable to any location around the world. However, since there is a much lower concentration of CO2 in the atmosphere compared to that available in the by-product gas from industrial plants, DAC is much more costly and energy intensive.

Associated with carbon capture and storage is carbon capture and utilization (CCU) where the CO2 captured from various sources is put back to work as a raw material. While CCU is most often associated with Enhanced Oil Recovery, CO2 can also produce valuable chemicals and fuels, which may be marketed to generate revenue and offset the expenses associated with the capture process. With a suitable catalyst, CO2 can be converted into a wide variety of products, including acids, monomers and carbon nanomaterials.

The potential for developing profitable businesses from products generated from CO2 is evidenced by the large number of recent start-up companies. The annual methanol market, for example, is expected to reach US$91.5 billion by 2026 and since methanol can be made from hydrogen and CO2, this represents a significant opportunity.

However, to further minimize energy requirements and eliminate the risk of secondary CO2 emissions, new, sustainable and energy efficient materials and processes that capture and convert CO2 emissions from the air directly need to be developed.

In our paper, we recommend that conversion reactions be carried out using renewable energy and that any chemicals and catalyst materials be produced using sustainable methods. Otherwise, CO2 derived products won’t have a low carbon footprint compared to fossil-fuel derived products. To highlight this, the generation of methanol from a reaction between CO2 and hydrogen generated by reforming of natural gas was found to release three times more CO2 than the conventional industrial production technique. But when the same reaction was carried out with hydrogen generated from wind power, there was a 58 percent reduction in emissions.

There is great potential in the scale-up and commercialization of capture and conversion technologies, but there are also key technological challenges hindering the advancement of this field that research can help overcome. Research and development carried out in the RICH Center at Khalifa University is tackling some of these challenges from a different angle. 

Dr. Ludovic �ٳܳ�é�� is an Assistant Professor of Chemical Engineering at Khalifa University and a faculty member of the Research and Innovation Center on CO2 and Hydrogen (RICH). 

The post Carbon Capture and Conversion Technologies Could Clean the Atmosphere and Turn CO2 into Commercial Opportunities appeared first on Khalifa University.