It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
An innovative project designed to validate hydrogen combustion engines for ocean-going vessels and lay the foundation to scale up the technology is set to proceed in March 2025 aboard a cargo ship operated by Carisbrooke Shipping. The partnership led by Carnot Engines and funded as part of the UK government’s initiatives in decarbonization has secured a source for hydrogen from biomass to power the 40-day sea trials.
Waste-to-hydrogen producer Compact Syngas Solutions has joined the effort and will supply 200 kg of hydrogen for the trials. Based in Wales, the company has developed an advanced gasification process that generates electricity, heat, and hydrogen gas from waste products. It employs materials including waste wood and other selected non-recyclable resources in its process. Compact Syngas Solutions was the recipient of a UK grant for £4 million to develop its biomass and waste-to-hydrogen plants including the addition of carbon capture to its hydrogen production.
“Sourcing hydrogen for our trial has proven harder than we expected, and we’re massively grateful to Compact Syngas Solutions for helping out,” said Jeremy Howard-Knight, head of business development at Carnot. “It’s incredible to think that these huge ocean-going vessels are being powered by waste wood that could have ended its days by rotting on a tip.”
Carnot was awarded £2.3 million in February 2023 to deploy a 50kW hydrogen auxiliary engine demonstrator working with Carisbrooke Shipping, Brunel University, and the Manufacturing Technology Centre while involving Bureau Veritas and the UK’s Maritime and Coastguard Agency for regulatory compliance.
The project is based on the assertion that smaller vessels running shorter ranges would be able to consider electrification or fuel cells, but for long-distance ocean-going cargo vessels this would not be viable. They assert that the cost, weight, and practicalities become prohibitive but their concept for a hydrogen combustion engine would be a compelling solution.
Carnot reports by pioneering the use of technical ceramics in combustion engines, it has eliminated major limiting factors to engine efficiency. It reports its engines have a break thermal efficiency of 70 percent, nearly double what is achieved by modern state-of-the-art engines. Carnot said the engines will massively reduce fuel consumption and costs. It highlights that above a certain air-to-fuel ratio, hydrogen combustion emits zero emissions with negligible levels of CO2, NOx, and PM.
The demonstration calls for testing of the engine at Brunel University and then it will be placed aboard one of Carisbrooke Shipping’s K-class cargo ships. Built in 2010 in China, the vessels are 6,800 dwt and have a length of 106 meters (348 feet). They operate at speeds of up to 11 knots with a MAK main engine and a Sandfirden diesel auxiliary engine.
The trial will run for 40 days in the Irish Sea starting in March 2025. The vessel will be operating between Bristol and Belfast. Carnot says the 50kW engine will be a precursor to 200 to 400kW auxiliary engines. Eventually, they expect to produce a 1 to 10MW main engine based on this technology.
China’s top miner to spend $24 billion on coal-to-oil project
Bloomberg News | October 10, 2024 | Credit: cbpix/Adobe Stock China’s biggest coal miner announced the construction this week of another massive project to supply feedstock for petrochemicals makers and help clear a prospective surplus of the fossil fuel. China Energy Investment Corp. said it will spend 170 billion yuan ($24 billion) to build an integrated plant in the northwestern region of Xinjiang that will turn coal into oil products. As is expected of all such projects, the facility will be powered by renewable energy — although its inputs and outputs will be anything but clean. The first phase is slated to come online in 2027.
The facility in Hami city is just the latest in a series of coal-to-oil developments greenlit in recent years in the mining hubs of Xinjiang, Shaanxi, Ningxia and Inner Mongolia. Hami alone has indicated it will approve 300 billion yuan’s worth of such projects in its five-year plan through 2025, which could consume 152 million tons of coal by the end of the decade.
For all of its rapid deployment of clean energy, China remains by far the world’s largest coal producer and continues to push output to record levels, which hit 4.7 billion tons last year. But the fuel’s main usage in generating electricity has reached a turning point, after being surpassed for the first time by solar and wind installations. Moreover, President Xi Jinping has said consumption needs to start falling from 2026 to meet the nation’s climate goals, which has led coal miners to seek other avenues for their product.
One problem is that China’s petrochemicals industry is in a funk, the victim of its own breakneck expansion just as consumption has faltered due to a weak economy. Coal-to-oil profits slumped 53% last year, according to the China Petroleum and Chemical Industrial Federation.
Another is that healthy margins rely on a wide spread between the price of coal, which China has been successful in suppressing, and the price of oil, which has suffered as Chinese imports have slowed. Beijing’s wider efforts to decarbonize the economy continue to weigh heavily on oil processing generally, and Chinese consumption of products like diesel and gasoline may already have peaked.
The Hami facility, which will be capable of yielding 4 million tons of oil products a year for processing into materials like polyester, is more likely to prosper because CEIC’s scale allows it to mine coal particularly cheaply. It’s liquefaction technology has also been touted as state of the art.
But the timing nevertheless represents a risk. China’s coal-to-oil capacity rose 24% to 11 million tons in 2023 compared to 2019. That means the new plant will account for a significant chunk of Chinese output at a time when its customers aren’t in great shape and pressure is mounting on industry to reduce rather than add to national carbon emissions.
The commercialization of CO2 utilization technology to produce formic acid is imminent
Development of a CCU process for formic acid production with both economic and environmental viability. Expected to expedite the commercialization of CCU through the world's largest-scale demonstration.
NATIONAL RESEARCH COUNCIL OF SCIENCE & TECHNOLOGY
IMAGE:
FLOWCHART OF THE PROCESS (ABOVE) FOR PRODUCING FORMIC ACID THROUGH THE CONVERSION OF NEWLY DEVELOPED CARBON DIOXIDE (CO2) USING CARBON CAPTURE & UTILIZATION (CCU), AND PILOT-SCALE PROCESS VERIFICATION DATA (BELOW).
CCU (Carbon Capture & Utilization), which captures CO2 and converts it into useful compounds, is crucial for rapidly transitioning to a carbon-neutral society. While CCS (Carbon Capture & Storage), which only involves CO2 storage, has entered the initial commercialization stage due to its relatively simple process and low operational costs, CCU has only been explored at the research level due to the complexity of conversion processes and high production costs of compounds.
Dr. Lee Ung's team at the Clean Energy Research Center of the Korea Institute of Science and Technology (KIST, Director Oh Sang Rok) announced the development of a novel CCU process that converts CO2 into formic acid. Formic acid, an organic acid, is a high-value compound used in various industries such as leather, food, and pharmaceuticals. Currently formic acid retains a large market consuming around one million tons annually, which is expected to grow in the future owing to its potential use as a hydrogen carrier. Moreover, it has a higher production efficiency compared to other CCU-based chemicals, as it can be produced from a single CO2 molecule.
The research team selected 1-methylpyrrolidine, which exhibited the highest CO2 conversion rate among various amines mediating formic acid production reactions, and optimized the operating temperature and pressure of the reactor containing a ruthenium (Ru)-based catalyst, thereby increasing the CO2 conversion rate to over twice the current level of 38%. Furthermore, to address the excessive energy consumption and formic acid decomposition issues during CO2 separation from air or exhaust gases and formic acid purification, the team developed a simultaneous capture-conversion process that directly converts CO2 captured within the amine without separating it. As a result, they significantly reduced the formic acid production cost from around $790 per ton to $490 per ton while mitigating CO2 emissions, compared to conventional formic acid production.
To evaluate the commercialization potential of the developed formic acid production process, the research team constructed the world's largest pilot plant capable of producing 10 kg of formic acid per day. Previous CCU studies were conducted on a small scale in laboratories and did not consider the product purification process required for large-scale production. However, the research team developed processes and materials to minimize corrosion and formic acid decomposition, and optimized operating conditions that led to successful production of formic acid with a purity exceeding 92%.
The team plans to complete a 100 kg per day pilot plant by 2025 and conduct process verification, aiming for commercialization by 2030. Success in process verification with the 100 kg pilot plant is expected to enable transportation and sales to demand companies.
Dr. Lee Ung stated, "Through this research, we have confirmed the commercialization potential of our process that converts CO2 to formic acid, which is a huge breakthrough considering that most CCU technologies are being conducted at lab-scale." He further expressed his intention to contribute to achieving the country's carbon neutrality goal by accelerating the commercialization of CCU. .
A depiction of the pilot-scale demonstration process in operation. It consists of a reaction section, separation section, recycling, and vacuum systems, enabling stable continuous operation and enhancing commercialization potential.
CREDIT
Korea Institute of Science and Technology
KIST was established in 1966 as the first government-funded research institute in Korea. KIST now strives to solve national and social challenges and secure growth engines through leading and innovative research. For more information, please visit KIST’s website at https://eng.kist.re.kr/
This research was supported by the Ministry of Science and ICT (Minister Lee Jong-Ho) as part of KIST's major projects and the Carbon-to-X project(2020M3H7A1098271). The research results were published in the latest issue of the international journal "Joule" (IF 39.8, JCR top 0.9%).
Accelerating the net-zero economy with CO2-hydrogenated formic acid production: Process development and pilot plant demonstration
Nanoparticle catalysts convert carbon dioxide to carbon monoxide to make useful compounds
NEWS RELEASE
TSINGHUA UNIVERSITY PRESS
IMAGE:
THE IMAGE TO THE LEFT DEPICTS Β-MO2C NANOPARTICLES SUPPORTED ON SIO2 (Β-MO2C/SIO2). THE GRAPH ON THE RIGHT REPRESENTS THE INCREASED CATALYTIC ACTIVITY OF Β-MO2C/SIO2 IN CO PRODUCTION RATE IN THE RWGS REACTION COMPARED TO BULK Β-MO2C, REPRESENTED BY THE BLACK BAR. EACH BAR REPRESENTS A DIFFERENT PERCENTAGE OF MO2C LOADING WEIGHT BASED ON THE MASS OF THE SIO2 SUPPORT. CATALYTIC ACTIVITY FOR THIS DATA WAS MEASURED AT 400°C.
As a greenhouse gas, carbon dioxide (CO2) contributes to climate change as it accumulates in the atmosphere. One way to reduce the amount of unwanted CO2 in the atmosphere is to convert the gas into a useful carbon product that can be used to generate valuable compounds. A recent study attached nanoparticle of beta phase molybdenum carbide (β-Mo2C) catalysts on a silicon dioxide (SiO2) support to speed the conversion of CO2 into more useful carbon monoxide (CO) gas.
CO2 is a very stable molecule, which makes conversion of the greenhouse gas into other molecules challenging. Catalysts can be used in chemical reactions to lower the amount of energy required to form or break chemical bonds and are used in the reverse water gas shift (RWGS) reaction to convert CO2 and hydrogen gas (H2) into CO and water (H2O). Importantly, the CO gas produced by the reaction is called syngas, or synthesis gas, when combined with H2 and can be used as a carbon source to create other important compounds.
Traditional catalysts in the RWGS reaction are made from precious metals, including platinum (Pt), palladium (Pd) and gold (Au), limiting the cost efficiency of the reaction. Because of this, new catalyst materials and formation methods are developed to increase the practicality of the RWGS reaction as a means of lowering atmospheric CO2 and generating syngas.
In order to address the cost issues of traditional RWGS catalysts, a team of researchers from the University of Illinois in Urbana-Champaign studied the formation and catalytic activity of cheaper nanoparticle β-Mo2C catalysts on a SiO2 support to determine if the lower-cost catalyst could enhance activity levels of β-Mo2C with a silica oxide support in the RWGS reaction.
The team published their study in Carbon Futureon April 30.
“Society is moving towards a carbon-neutral economy. Carbon dioxide is a greenhouse gas, thus any technology that can break down the carbon-oxide bond in this molecule and turn carbon into a value-added chemical could be of great interest. One important C1 chemical is carbon monoxide, which is an essential feedstock to produce a range of products, such as synthetic fuels and vitamin A,” said Hong Yang, Alkire chair professor in the Department of Chemical and Biomolecular Engineering at the University of Illinois at Urbana-Champaign and senior author of the paper.
Specifically, the researchers synthesized β-Mo2C nanoparticle catalysts absorbed onto a SiO2 support (β-Mo2C/SiO2). The amorphous structure of the SiO2 support was critical for nanoparticle formation, activity and stability of the β-Mo2C/SiO2 catalyst. The team additionally tested cesium (Ce), magnesium (Mg), titanium (Ti) and aluminum (Al) oxides as potential supports, but catalyst on SiO2 produced the best catalyst formation at the temperature of 650°C.
“It appears the disordered nature of amorphous silica, which behaves like glue to catalyst nanoparticles, is a key factor of our success in achieving high metal loading and the corresponding high activity,” said Siying Yu, graduate student in the Department of Chemical and Biomolecular Engineering at the University of Illinois at Urbana-Champaign and co-author of the paper.
Importantly, the SiO2 catalyst support structure improves the catalytic activity of β-Mo2C 8-fold compared to bulk β-Mo2C. Even with improved catalytic activity, the β-Mo2C/SiO2 catalyst demonstrated high CO conversion and increased stability compared to bulk β-Mo2C in RWGS reactions.
“A major discovery of our work is a new process for producing high metal-loading catalysts made of molybdenum carbide nanoparticles. Such metal carbide catalysts are developed for converting carbon dioxide into carbon oxide at high production rate and selectivity,” said Andrew Kuhn, former graduate student in the Department of Chemical and Biomolecular Engineering at the University of Illinois at Urbana-Champaign and first author of the paper.
The researchers performed their study under reaction conditions that favored conversion to CO gas, with a H2:CO2 ratio equal to 1:1. This ratio differs from the more commonly tested ratio of less than 3:1. Reactions were also performed at temperatures between 300 to 600°C. Under these conditions, the team produced more concentrated CO, which is more efficient for downstream compound synthesis.
The team sees this research as a launching point for other catalysts that leverage support structures to increase activity. “Our ability to synthesize phase-pure metal carbide nanomaterials at high loading opens the door for the development of new catalysts for the process of CO2 utilization,” said Yang. “I hope through in-depth study of the synthesis-structure-property relationship of this catalyst we will soon be able to uncover new important applications for value-added conversion of CO2 and the sustainable development of our economy.”
Other contributors include Rachel Park, Di Gao and Cheng Zhang from the Department of Chemical and Biomolecular Engineering at the University of Illinois at Urbana-Champaign in Urbana, Illinois; and Yuanhui Zhang from the Department of Agricultural and Biological Engineering at the University of Illinois at Urbana-Champaign.
This research was supported by the University of Illinois, Urbana-Champaign start-up fund.
Carbon Future is an open access, peer-reviewed and international interdisciplinary journal, published by Tsinghua University Press and exclusively available via SciOpen. Carbon Future reports carbon-related materials and processes, including catalysis, energy conversion and storage, as well as low carbon emission process and engineering. Carbon Future will publish Research Articles, Reviews, Minireviews, Highlights, Perspectives, and News and Views from all aspects concerned with carbon. Carbon Future will publish articles that focus on, but not limited to, the following areas: carbon-related or -derived materials, carbon-related catalysis and fundamentals, low carbon-related energy conversion and storage, low carbon emission chemical processes.
SciOpen is a professional open access resource for discovery of scientific and technical content published by the Tsinghua University Press and its publishing partners, providing the scholarly publishing community with innovative technology and market-leading capabilities. SciOpen provides end-to-end services across manuscript submission, peer review, content hosting, analytics, and identity management and expert advice to ensure each journal’s development by offering a range of options across all functions as Journal Layout, Production Services, Editorial Services, Marketing and Promotions, Online Functionality, etc. By digitalizing the publishing process, SciOpen widens the reach, deepens the impact, and accelerates the exchange of ideas.
Starting a new year, many people pledge to enact self-care routines that improve their appearance. And facial sheet masks soaked in skin care ingredients provide an easy way to do this. However, these wet masks and their waterproof packaging often contain plastics and preservatives. Now, a study in ACS Applied Materials & Interfaces reports a dry-packaged hydrating facial mask that is made of biobased and sustainable materials.
Consumers in the beauty industry are increasingly concerned about the sustainability and sourcing of personal care items, in terms of both products’ ingredients and packaging. Facial sheet masks are popular cosmetic products advertised to benefit and enhance the skin. But they are typically made with plastic backing fabrics and are packaged with wet ingredients, requiring preservatives and disposable water-tight pouches. A more environmentally friendly option would be to package the facial masks dry. So, Jinlain Hu and coworkers aimed to design a facial sheet mask with biobased materials that could be enveloped in paper and later activated to deliver moisture and nutrients.
The researchers developed a facial mask with a sheet of plant-based polylactic acid (PLA), which could repel water, and they coated it in a layer of gelatin mixed with hyaluronic acid and green tea extract. They deposited the top layer as either tiny fibers or microspheres, using electrospinning or electrospray, respectively, and tested how well the masks could transfer moisture. They found:
Water droplets did not pass through the masks without skin contact, regardless of which side a water droplet was placed on.
Contact with skin initiated one-way water transport from PLA to gelatin to skin, but only for masks coated with gelatin-based microspheres.
Placing the mask on moistened, rather than dry, skin improved water delivery through the mask.
Finally, the team investigated how its mask’s ingredients impacted mouse cells as a proxy for reactions on skin. Fewer cells showed signals of aging when grown on the mask compared with cells grown in control conditions; the researchers attribute this to the antioxidant properties of the green tea extracts. The team says the beneficial properties of the natural ingredients and the one-way moisture-delivery design make this mask a promising alternative with a lesser environmental impact compared to traditional, wet-packed products.
The authors acknowledge funding from the City University of Hong Kong, the National Natural Science Foundation of China, and Shenzhen-Hong Kong-Macau Science & Technology Fund.
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The American Chemical Society (ACS) is a nonprofit organization chartered by the U.S. Congress. ACS’ mission is to advance the broader chemistry enterprise and its practitioners for the benefit of Earth and all its people. The Society is a global leader in promoting excellence in science education and providing access to chemistry-related information and research through its multiple research solutions, peer-reviewed journals, scientific conferences, eBooks and weekly news periodical Chemical & Engineering News. ACS journals are among the most cited, most trusted and most read within the scientific literature; however, ACS itself does not conduct chemical research. As a leader in scientific information solutions, its CAS division partners with global innovators to accelerate breakthroughs by curating, connecting and analyzing the world’s scientific knowledge. ACS’ main offices are in Washington, D.C., and Columbus, Ohio.
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Note: ACS does not conduct research, but publishes and publicizes peer-reviewed scientific studies.
Electrosprayed Environment-Friendly Dry Triode-Like Facial Masks for Skincare
Lithuanian researchers recycle surgical masks for hydrogen-rich gas production
Lithuanian researchers investigate the possibilities of plasma gasification as an eco-friendly technique to convert used surgical masks into clean energy.
During the COVID-19 pandemic, thousands of tons of used surgical masks were dumped every month without a real vision to manage them. Although the world has successfully passed the critical period, a serious industrial eco-solution must be developed to deal with this waste.
Researchers from Kaunas University of Technology (KTU) and Lithuanian Energy Institute, aiming to design a solution for surgical mask waste management are investigating the possibilities of plasma gasification as an eco-friendly technique to convert surgical mask waste into clean energy products.
After conducting a series of experiments, they obtained synthetic gas (aka syngas) with a high abundance of hydrogen.
“There are two ways of converting waste to energy – by transforming solid waste into liquid product, or gases. Gasification allows converting huge amounts of waste to syngas, which is similar to natural and is a composition of several gases (such as hydrogen, carbon dioxide, carbon monoxide, and methane). During our experiments, we played with the composition of this synthetic gas and increased its concentration of hydrogen, and, in turn, its heating value,” says Samy Yousef, a chief researcher at Kaunas University of Technology, Lithuania.
For the conversion of surgical masks, the researchers applied plasma gasification on defective FFP2 face masks, which were shredded beforehand into a uniform particle size, and then converted to granules that could be easily controlled during treatment.
The highest yield of hydrogen was obtained at an S/C (steam-to-carbon ratio) of 1.45. Overall, the obtained syngas showed a 42% higher heating value than that produced from biomass.
Traditional waste management technique was improved
Yousef’s research team, composed of scientists from two Lithuanian research institutions, KTU and Lithuanian Energy Institute, are working on the topics of recycling and waste management, and are always looking for waste, which is present in huge amounts and has a unique structure. In their work, they have conducted pyrolysis experiments on cigarette butts, used wind turbine blades, and textile waste, which have all shown promising results for upscaling and commercialization. Yet, this time, for the recycling of surgical masks, a different method was applied.
“Gasification is a traditional waste management technique. Differently from pyrolysis, which is still a new and developing method we don’t need much investment in developing infrastructure. Arc plasma gasification, which we have applied for the decomposition of surgical masks, means that under high temperatures generated by arc plasma, we can decompose face masks to gas within a few seconds. In pyrolysis, it takes up to an hour to get the final product. In advanced gasification, the process is almost instantaneous,” explains Yousef.
He says that advanced gasification techniques, such as plasma gasification, are more efficient in obtaining a better concentration of hydrogen (up to 50%) within synthetic gas production. Moreover, plasma gasification decreases the amount of tar in the syngas, which makes its quality higher.
Hydrogen-rich gas has better heating values
According to Yousef, plasma gasification is one of the best methods to obtain synthetic gas, which is rich in hydrogen.
“Hydrogen increases the heating value of the synthetic gas,” explains Yousef and continues describing the different types of hydrogen: grey is obtained from natural gas or methane, green – from green sources (e.g., electrolysis), blue – from steam reforming.
“Maybe we could call our black hydrogen, as it’s made from waste?” he says half-jokingly.
The yield of syngas was around 95% of the total amount of feedstock. The remaining products were soot and tar. The analysis revealed that benzene, toluene, naphthalene and acenaphthylene were the main compounds in collected tar. According to the researchers, it can be used as a clean fuel in different industries with low carbon emissions.
The soot was formulated in the last stage of plasma gasification. Its main component is black carbon, which can have numerous applications related to energy, wastewater treatment, and agriculture, or can be used as a filler material in composites.
The researchers believe that their proposed method for surgical mask waste recycling has a high potential to be commercialized. According to Yousef, a researcher from KTU, their main aim was to obtain synthetic gas, which is rich in hydrogen. Although hydrogen can be separated from the obtained syngas, it can also be used as a mixture of gases. As such, it already has half a higher heating value than that produced from biomass.
JOURNAL
International Journal of Hydrogen Energy
METHOD OF RESEARCH
Experimental study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Plasma steam gasification of surgical mask waste for hydrogen-rich syngas production
Friday, January 12, 2024
Catalytic combo converts CO2 to solid carbon nanofibers
Tandem electrocatalytic-thermocatalytic conversion could help offset emissions of potent greenhouse gas by locking carbon away in a useful material
SCIENTISTS HAVE DEVISED A STRATEGY FOR CONVERTING CARBON DIOXIDE (CO2) FROM THE ATMOSPHERE INTO VALUABLE CARBON NANOFIBERS. THE PROCESS USES TANDEM ELECTROCATALYTIC (BLUE RING) AND THERMOCATALYTIC (ORANGE RING) REACTIONS TO CONVERT THE CO2 (TEAL AND SILVER MOLECULES) PLUS WATER (PURPLE AND TEAL) INTO "FIXED" CARBON NANOFIBERS (SILVER), PRODUCING HYDROGEN GAS (H2, PURPLE) AS A BENEFICIAL BYPRODUCT. THE CARBON NANOFIBERS COULD BE USED TO STRENGTHEN BUILDING MATERIALS SUCH AS CEMENT AND LOCK AWAY CARBON FOR DECADES.
CREDIT: (ZHENHUA XIE/BROOKHAVEN NATIONAL LABORATORY AND COLUMBIA UNIVERSITY; ERWEI HUANG/BROOKHAVEN NATIONAL LABORATORY)
UPTON, NY—Scientists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory and Columbia University have developed a way to convert carbon dioxide (CO2), a potent greenhouse gas, into carbon nanofibers, materials with a wide range of unique properties and many potential long-term uses. Their strategy uses tandem electrochemical and thermochemical reactions run at relatively low temperatures and ambient pressure. As the scientists describe in the journal Nature Catalysis, this approach could successfully lock carbon away in a useful solid form to offset or even achieve negative carbon emissions.
“You can put the carbon nanofibers into cement to strengthen the cement,” said Jingguang Chen, a professor of chemical engineering at Columbia with a joint appointment at Brookhaven Lab who led the research. “That would lock the carbon away in concrete for at least 50 years, potentially longer. By then, the world should be shifted to primarily renewable energy sources that don’t emit carbon.”
As a bonus, the process also produces hydrogen gas (H2), a promising alternative fuel that, when used, creates zero emissions.
Capturing or converting carbon
The idea of capturing CO2 or converting it to other materials to combat climate change is not new. But simply storing CO2 gas can lead to leaks. And many CO2 conversions produce carbon-based chemicals or fuels that are used right away, which releases CO2 right back into the atmosphere.
“The novelty of this work is that we are trying to convert CO2 into something that is value-added but in a solid, useful form,” Chen said.
Such solid carbon materials—including carbon nanotubes and nanofibers with dimensions measuring billionths of a meter—have many appealing properties, including strength and thermal and electrical conductivity. But it’s no simple matter to extract carbon from carbon dioxide and get it to assemble into these fine-scale structures. One direct, heat-driven process requires temperatures in excess of 1,000 degrees Celsius.
“It’s very unrealistic for large-scale CO2 mitigation,” Chen said. “In contrast, we found a process that can occur at about 400 degrees Celsius, which is a much more practical, industrially achievable temperature.”
The tandem two-step
The trick was to break the reaction into stages and to use two different types of catalysts—materials that make it easier for molecules to come together and react.
“If you decouple the reaction into several sub-reaction steps you can consider using different kinds of energy input and catalysts to make each part of the reaction work,” said Brookhaven Lab and Columbia research scientist Zhenhua Xie, lead author on the paper.
The scientists started by realizing that carbon monoxide (CO) is a much better starting material than CO2 for making carbon nanofibers (CNF). Then they backtracked to find the most efficient way to generate CO from CO2.
Earlier work from their group steered them to use a commercially available electrocatalyst made of palladium supported on carbon. Electrocatalysts drive chemical reactions using an electric current. In the presence of flowing electrons and protons, the catalyst splits both CO2 and water (H2O) into CO and H2.
For the second step, the scientists turned to a heat-activated thermocatalyst made of an iron-cobalt alloy. It operates at temperatures around 400 degrees Celsius, significantly milder than a direct CO2-to-CNF conversion would require. They also discovered that adding a bit of extra metallic cobalt greatly enhances the formation of the carbon nanofibers.
“By coupling electrocatalysis and thermocatalysis, we are using this tandem process to achieve things that cannot be achieved by either process alone,” Chen said.
On the modeling front, the scientists used “density functional theory” (DFT) calculations to analyze the atomic arrangements and other characteristics of the catalysts when interacting with the active chemical environment.
“We are looking at the structures to determine what are the stable phases of the catalyst under reaction conditions,” explained study co-author Ping Liu of Brookhaven’s Chemistry Division who led these calculations. “We are looking at active sites and how these sites are bonding with the reaction intermediates. By determining the barriers, or transition states, from one step to another, we learn exactly how the catalyst is functioning during the reaction.”
X-ray diffraction and x-ray absorption experiments at NSLS-II tracked how the catalysts change physically and chemically during the reactions. For example, synchrotron x-rays revealed how the presence of electric current transforms metallic palladium in the catalyst into palladium hydride, a metal that is key to producing both H2 and CO in the first reaction stage.
For the second stage, “We wanted to know what’s the structure of the iron-cobalt system under reaction conditions and how to optimize the iron-cobalt catalyst,” Xie said. The x-ray experiments confirmed that both an alloy of iron and cobalt plus some extra metallic cobalt are present and needed to convert CO to carbon nanofibers.
“The two work together sequentially,” said Liu, whose DFT calculations helped explain the process.
“According to our study, the cobalt-iron sites in the alloy help to break the C-O bonds of carbon monoxide. That makes atomic carbon available to serve as the source for building carbon nanofibers. Then the extra cobalt is there to facilitate the formation of the C-C bonds that link up the carbon atoms,” she explained.
Recycle-ready, carbon-negative
“Transmission electron microscopy (TEM) analysis conducted at CFN revealed the morphologies, crystal structures, and elemental distributions within the carbon nanofibers both with and without catalysts,” said CFN scientist and study co-author Sooyeon Hwang.
The images show that, as the carbon nanofibers grow, the catalyst gets pushed up and away from the surface. That makes it easy to recycle the catalytic metal, Chen said.
“We use acid to leach the metal out without destroying the carbon nanofiber so we can concentrate the metals and recycle them to be used as a catalyst again,” he said.
This ease of catalyst recycling, commercial availability of the catalysts, and relatively mild reaction conditions for the second reaction all contribute to a favorable assessment of the energy and other costs associated with the process, the researchers said.
“For practical applications, both are really important—the CO2 footprint analysis and the recyclability of the catalyst,” said Chen. “Our technical results and these other analyses show that this tandem strategy opens a door for decarbonizing CO2 into valuable solid carbon products while producing renewable H2.”
If these processes are driven by renewable energy, the results would be truly carbon-negative, opening new opportunities for CO2 mitigation.
Brookhaven National Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit science.energy.gov.
The electrocatalytic-thermocatalytic tandem strategy for CNF production circumvents thermodynamic constraints by combining the co-electrolysis of CO2 and water into syngas (CO and H2) with a subsequent thermochemical process under mild conditions (370-450 °C, ambient pressure). This yields a high CNF production rate. The optimal synergy of iron-cobalt (FeCo) alloy and extra metallic Co enhanced the dissociative activation of syngas, promoting carbon-carbon bond formation for CNF production.
CREDIT
(Zhenhua Xie/Brookhaven National Laboratory and Columbia University)
microscopic images of carbon nanofibers
CAPTION
High-resolution transmission electron microscopy (TEM) shows the tip of the resulting carbon nanofiber (left) on the iron-cobalt/cerium oxide (FeCo/CeO2) thermocatalyst. Scientists mapped the structure and chemical composition of newly formed carbon nanofibers (right) using scanning transmission electron microscopy (STEM), high-angle annular dark field (HAADF) imaging, and energy-dispersive x-ray spectroscopy (EDS) (scale bar represents 8 nanometers). The images show that the nanofibers are made of carbon (C), and reveal that the catalytic metals, iron (Fe) and cobalt (Co), are pushed away from the catalytic surface and accumulate at the tip of the nanofiber.
CREDIT
(Center for Functional Nanomaterials/Brookhaven National Laboratory)
