Carbon dioxide conversion process may be adapted for biofuel synthesis
Using a novel approach involving a key enzyme that helps regulate global nitrogen, University of California, Irvine molecular biologists have discovered an effective way to convert carbon dioxide (CO2) to carbon monoxide (CO) that can be adapted for commercial applications like biofuel synthesis.
Led by Yilin Hu, UCI assistant professor of molecular biology & biochemistry at the Ayala School of Biological Sciences, the researchers found that they could successfully express the reductase component of the nitrogenase enzyme alone in the bacterium Azotobacter vinelandii and directly use this bacterium to convert CO2 to CO. The intracellular environment of the bacterium was shown to favor the conversion of CO2 in a way that would be more applicable to the future development of strategies for large-scale production of CO. The findings were surprising to the group, as nitrogenase was only previously believed to convert nitrogen (N2) to ammonia (NH3) within the bacterium under similar conditions. The full study can be found online in Nature Chemical Biology.
Hu and her colleagues knew that the intracellular environment of the bacterium Azotobacter vinelandii favors other reduction reactions, due in part to its well-known oxygen protection mechanisms and presence of physiological electron donors. But they were unsure if the intracellular environment would support the conversion of CO2 to CO.
They were excited to discover that the bacterium could reduce CO2 and release CO as a product, which makes it an attractive whole-cell system that could be explored further for new ways of recycling atmospheric CO2 into biofuels and other commercial chemical products. These findings of Hu’s group establish the nitrogenase enzyme as a fascinating template for developing approaches to energy-efficient and environmentally-friendly fuel production.
“Our observation that a bacterium can convert CO2 to CO opens up new avenues for biotechnological adaptation of this reaction into a process that effectively recycles the greenhouse gas into the starting material for biofuel synthesis that will help us simultaneously combat two major challenges we face nowadays: global warming and energy shortages,” Hu said.
Graphene quantum dots may offer a simple way to recycle waste carbon dioxide into valuable fuel rather than release it into the atmosphere or bury it underground, according to Rice University scientists.
Nitrogen-doped graphene quantum dots (NGQDs) are an efficient electrocatalyst to make complex hydrocarbons from carbon dioxide, according to the research team led by Rice materials scientist Pulickel Ajayan. Using electrocatalysis, his lab has demonstrated the conversion of the greenhouse gas into small batches of ethylene and ethanol.
The research is detailed this week in Nature Communications.
Though they don’t entirely understand the mechanism, the researchers found NGQDs worked nearly as efficiently as copper, which is also being tested as a catalyst to reduce carbon dioxide into liquid fuels and chemicals. And NGQDs keep their catalytic activity for a long time, they reported.
“It is surprising because people have tried all different kinds of catalysts. And there are only a few real choices such as copper,” Ajayan said. “I think what we found is fundamentally interesting, because it provides an efficient pathway to screen new types of catalysts to convert carbon dioxide to higher-value products.”
Those problems are hardly a secret. Atmospheric carbon dioxide rose above 400 parts per million earlier this year, the highest it’s been in at least 800,000 years, as measured through ice-core analysis.
“If we can convert a sizable fraction of the carbon dioxide that is emitted, we could curb the rising levels of atmospheric carbon dioxide levels, which have been linked to climate change,” said co-author Paul Kenis of the University of Illinois.
In lab tests, NGQDs proved able to reduce carbon dioxide by up to 90 percent and convert 45 percent into either ethylene or alcohol, comparable to copper electrocatalysts.
Graphene quantum dots are atom-thick sheets of carbon atoms that have been split into particles about a nanometer thick and just a few nanometers wide. The addition of nitrogen atoms to the dots enables varying chemical reactions when an electric current is applied and a feedstock like carbon dioxide is introduced.
“Carbon is typically not a catalyst,” Ajayan said. “One of our questions is why this doping is so effective. When nitrogen is inserted into the hexagonal graphitic lattice, there are multiple positions it can take. Each of these positions, depending on where nitrogen sits, should have different catalytic activity. So it’s been a puzzle, and though people have written a lot of papers in the last five to 10 years on doped and defective carbon being catalytic, the puzzle is not really solved.”
“Our findings suggest that the pyridinic nitrogen (a basic organic compound) sitting at the edge of graphene quantum dots leads the catalytic conversion of carbon dioxide to hydrocarbons,” said Rice postdoctoral researcher Jingjie Wu, co-lead author of the paper. “The next task is further increasing nitrogen concentration to help increase the yield of hydrocarbons.”
Ajayan noted that while electrocatalysis is effective at lab scales for now, industry relies on scalable thermal catalysis to produce fuels and chemicals. “For that reason, companies probably won’t use it any time soon for large-scale production. But electrocatalysis can be easily done in the lab, and we showed it will be useful in the development of new catalysts.”
Learn more: Carbon dots dash toward ‘green’ recycling role
Researchers have successfully turned carbon dioxide into solid rock by injecting it into ancient lava flows
For the first time, scientists have injected carbon dioxide into ancient lava flows and watched it solidify, demonstrating that capturing carbon dioxide from the atmosphere or a power plant smokestack and safely storing it underground may be a realistic way to help reduce greenhouse gas emissions to tackle climate change, according to research published Friday.
Scientists working at the Wallula Basalt Pilot Project in Washington State turned liquefied carbon dioxide into solid rock by injecting the gas into basalt formations. Over a span of about two years, the carbon dioxide solidified into a mineral called ankerite, according to the study conducted by Pacific Northwest National Laboratory researchers. The research was published in the journal Environmental Science and Technology.
“This study further supports the idea that one of the major rock types on the planet—basalts—can be used to store carbon dioxide permanently and safely,” said study lead author Pete McGrail, a carbon dioxide and climate change researcher at PNNL.
Carbon capture and storage may be critical to helping prevent global warming from exceeding 2°C (3.6°F), either by capturing emissions from their source or by directly removing carbon dioxide from the atmosphere, according to the Intergovernmental Panel on Climate Change.
But scientists worry that storing captured carbon underground as a liquid or a gas may not be safe because stored carbon dioxide could explosively leak into the atmosphere through fissures in the earth or be exposed to terrorism risk, creating a climate catastrophe.
To solve that problem, researchers have been studying ways to store carbon dioxide underground as a solid, especially in basalt formations.
Basalt is a volcanic rock that makes up roughly 70 percent of the earth’s surface. When it is exposed to carbon dioxide and water, a chemical reaction occurs, converting the gas to a chalk-like solid material. Scientists previously thought the chemical reaction would take thousands of years to occur, but new research shows it can happen within a few years.
“Basalt storage is unique in the geologic sequestration of carbon dioxide because the principal trapping mechanism is a chemical reaction that locks the carbon dioxide away as a carbonate mineral that can never leak or return to the atmosphere,” McGrail said.
Earlier this year, researchers at the CarbFix project in Iceland were able to pump a geothermal power plant’s carbon dioxide-rich volcanic gases into deep underground but recently formed basalt formations and chemically solidify them in about two years.
In a new twist to waste-to-fuel technology, scientists at the Department of Energy’s Oak Ridge National Laboratory have developed an electrochemical process that uses tiny spikes of carbon and copper to turn carbon dioxide, a greenhouse gas, into ethanol. Their finding, which involves nanofabrication and catalysis science, was serendipitous.
“We discovered somewhat by accident that this material worked,” said ORNL’s Adam Rondinone, lead author of the team’s study published in ChemistrySelect. “We were trying to study the first step of a proposed reaction when we realized that the catalyst was doing the entire reaction on its own.”
The team used a catalyst made of carbon, copper and nitrogen and applied voltage to trigger a complicated chemical reaction that essentially reverses the combustion process. With the help of the nanotechnology-based catalyst which contains multiple reaction sites, the solution of carbon dioxide dissolved in water turned into ethanol with a yield of 63 percent. Typically, this type of electrochemical reaction results in a mix of several different products in small amounts.
“We’re taking carbon dioxide, a waste product of combustion, and we’re pushing that combustion reaction backwards with very high selectivity to a useful fuel,” Rondinone said. “Ethanol was a surprise — it’s extremely difficult to go straight from carbon dioxide to ethanol with a single catalyst.”
The catalyst’s novelty lies in its nanoscale structure, consisting of copper nanoparticles embedded in carbon spikes. This nano-texturing approach avoids the use of expensive or rare metals such as platinum that limit the economic viability of many catalysts.
“By using common materials, but arranging them with nanotechnology, we figured out how to limit the side reactions and end up with the one thing that we want,” Rondinone said.
The researchers’ initial analysis suggests that the spiky textured surface of the catalysts provides ample reactive sites to facilitate the carbon dioxide-to-ethanol conversion.
“They are like 50-nanometer lightning rods that concentrate electrochemical reactivity at the tip of the spike,” Rondinone said.
Given the technique’s reliance on low-cost materials and an ability to operate at room temperature in water, the researchers believe the approach could be scaled up for industrially relevant applications. For instance, the process could be used to store excess electricity generated from variable power sources such as wind and solar.
“A process like this would allow you to consume extra electricity when it’s available to make and store as ethanol,” Rondinone said. “This could help to balance a grid supplied by intermittent renewable sources.”
The researchers plan to refine their approach to improve the overall production rate and further study the catalyst’s properties and behavior.
Weizmann Institute scientists engineer bacteria to create sugar from the greenhouse gas carbon dioxide
All life on the planet relies, in one way or another, on a process called carbon fixation: the ability of plants, algae and certain bacteria to “pump” carbon dioxide (CO2) from the environment, add solar or other energy and turn it into the sugars that are the required starting point needed for life processes. At the top of the food chain are different organisms (some of which think, mistakenly, that they are “more advanced”) that use the opposite means of survival: they eat sugars (made by photosynthetic plants and microorganisms) and then release carbon dioxide into the atmosphere. This means of growth is called “heterotrophism.” Humans are, of course, heterotrophs in the biological sense because the food they consume originates from the carbon fixation processes of nonhuman producers.
Is it possible to “reprogram” an organism that is found higher in the food chain, which consumes sugar and releases carbon dioxide, so that it will consume carbon dioxide from the environment and produce the sugars it needs to build its body mass? That is just what a group of Weizmann Institute of Science researchers recently did. Dr. Niv Antonovsky, who led this research in Prof. Ron Milo’s lab at the Institute’s Plant and Environmental Sciences Department, says that the ability to improve carbon fixation is crucial for our ability to cope with future challenges, such as the need to supply food to a growing population on shrinking land resources while using less fossil fuel.
The new building material could transform polluting emissions into a valuable resource
Imagine a world with little or no concrete. Would that even be possible? After all, concrete is everywhere — on our roads, our driveways, in our homes, bridges and buildings. For the past 200 years, it’s been the very foundation of much of our planet.
But the production of cement, which when mixed with water forms the binding agent in concrete, is also one of the biggest contributors to greenhouse gas emissions. In fact, about 5 percent of the planet’s greenhouse gas emissions comes from concrete.
An even larger source of carbon dioxide emissions is flue gas emitted from smokestacks at power plants around the world. Carbon emissions from those plants are the largest source of harmful global greenhouse gas in the world.
A team of interdisciplinary researchers at UCLA has been working on a unique solution that may help eliminate these sources of greenhouse gases. Their plan would be to create a closed-loop process: capturing carbon from power plant smokestacks and using it to create a new building material — CO2NCRETE — that would be fabricated using 3D printers. That’s “upcycling.”
“What this technology does is take something that we have viewed as a nuisance — carbon dioxide that’s emitted from smokestacks — and turn it into something valuable,” said J.R. DeShazo, professor of public policy at the UCLA Luskin School of Public Affairs and director of the UCLA Luskin Center for Innovation.
“I decided to get involved in this project because it could be a game-changer for climate policy,” DeShazo said. “This technology tackles global climate change, which is one of the biggest challenges that society faces now and will face over the next century.”
DeShazo has provided the public policy and economic guidance for this research. The scientific contributions have been led by Gaurav Sant, associate professor and Henry Samueli Fellow in Civil and Environmental Engineering; Richard Kaner, distinguished professor in chemistry and biochemistry, and materials science and engineering; Laurent Pilon, professor in mechanical and aerospace engineering and bioengineering; and Matthieu Bauchy, assistant professor in civil and environmental engineering.
This isn’t the first attempt to capture carbon emissions from power plants. It’s been done before, but the challenge has been what to do with the carbon dioxide once it’s captured.
“We hope to not only capture more gas,” DeShazo said, “but we’re going to take that gas and, instead of storing it, which is the current approach, we’re going to try to use it to create a new kind of building material that will replace cement.”
“The approach we are trying to propose is you look at carbon dioxide as a resource — a resource you can reutilize,” Sant said. “While cement production results in carbon dioxide, just as the production of coal or the production of natural gas does, if we can reutilize CO2 to make a building material which would be a new kind of cement, that’s an opportunity.”
The researchers are excited about the possibility of reducing greenhouse gas in the U.S., especially in regions where coal-fired power plants are abundant. “But even more so is the promise to reduce the emissions in China and India,” DeShazo said. “China is currently the largest greenhouse gas producer in the world, and India will soon be number two, surpassing us.”
Thus far, the new construction material has been produced only at a lab scale, using 3-D printers to shape it into tiny cones. “We have proof of concept that we can do this,” DeShazo said. “But we need to begin the process of increasing the volume of material and then think about how to pilot it commercially. It’s one thing to prove these technologies in the laboratory. It’s another to take them out into the field and see how they work under real-world conditions.”
“We can demonstrate a process where we take lime and combine it with carbon dioxide to produce a cement-like material,” Sant said. “The big challenge we foresee with this is we’re not just trying to develop a building material. We’re trying to develop a process solution, an integrated technology which goes right from CO2 to a finished product.
“3-D printing has been done for some time in the biomedical world,” Sant said, “but when you do it in a biomedical setting, you’re interested in resolution. You’re interested in precision. In construction, all of these things are important but not at the same scale. There is a scale challenge, because rather than print something that’s 5 centimeters long, we want to be able to print a beam that’s 5 meters long. The size scalability is a really important part.”
Another challenge is convincing stakeholders that a cosmic shift like the researchers are proposing is beneficial — not just for the planet, but for them, too.
“This technology could change the economic incentives associated with these power plants in their operations and turn the smokestack flue gas into a resource countries can use, to build up their cities, extend their road systems,” DeShazo said. “It takes what was a problem and turns it into a benefit in products and services that are going to be very much needed and valued in places like India and China.”
A molecular system that holds great promise for the capture and storage of carbon dioxide has been modified so that it now also holds great promise as a catalyst for converting captured carbon dioxide into valuable chemical products.
The sponge-like quality of a COF’s vast internal surface area enables the system to absorb and store enormous quantities of targeted molecules, such as carbon dioxide.
Researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) have incorporated molecules of carbon dioxide reduction catalysts into the sponge-like crystals of covalent organic frameworks (COFs). This creates a molecular system that not only absorbs carbon dioxide, but also selectively reduces it to carbon monoxide, which serves as a primary building block for a wide range of chemical products including fuels, pharmaceuticals and plastics.
An increase in human-made carbon dioxide in the atmosphere could initiate a chain reaction between plants and microorganisms that would unsettle one of the largest carbon reservoirs on the planet — soil.
Researchers based at Princeton University report in the journal Nature Climate Change that the carbon in soil — which contains twice the amount of carbon in all plants and Earth’s atmosphere combined — could become increasingly volatile as people add more carbon dioxide to the atmosphere, largely because of increased plant growth. The researchers developed the first computer model to show at a global scale the complex interaction between carbon, plants and soil, which includes numerous bacteria, fungi, minerals and carbon compounds that respond in complex ways to temperature, moisture and the carbon that plants contribute to soil.
Although a greenhouse gas and pollutant, carbon dioxide also supports plant growth. As trees and other vegetation flourish in a carbon dioxide-rich future, their roots could stimulate microbial activity in soil that in turn accelerates the decomposition of soil carbon and its release into the atmosphere as carbon dioxide, the researchers found.
This effect counters current key projections regarding Earth’s future carbon cycle, particularly that greater plant growth could offset carbon dioxide emissions as flora take up more of the gas, said first author Benjamin Sulman, who conducted the modeling work as a postdoctoral researcher at the Princeton Environmental Institute.
“You should not count on getting more carbon storage in the soil just because tree growth is increasing,” said Sulman, who is now a postdoctoral researcher at Indiana University.
It could be the key to large-scale implementation of carbon capture
Carbon capture is a process by which waste carbon dioxide (CO2) released by factories and power plants is collected and stored away, in order to reduce global carbon emissions. There are two major ways of carbon capture today, one using powder-like solid materials which “stick” to CO2, and one using liquids that absorb it. Despite their potential environmental and energy benefits, current carbon capture strategies are prohibitive because of engineering demands, cost and overall energy-efficiency. Collaborating scientists from EPFL, UC Berkley and Beijing have combined carbon-capturing solids and liquids to develop a “slurry” that offers the best of both worlds: as a liquid it is relatively simple to implement on a large scale, while it maintains the lower costs and energy efficiency of a solid carbon-capturing material. The breakthrough method is published in Nature Communications.
The most common approach to carbon capture uses liquid amine solutions, which can absorb CO2 from the atmosphere. On a large scale, the system uses two columns, one for capturing CO2 and the other for releasing it from the liquid, in a process referred to as “regeneration”. For amine solutions, regeneration is the most energy-consuming part because the CO2 is so strongly bound to the amine molecules that it is necessary to actually boil them in order to separate them.
An alternative to liquids is to use solid materials known as “metal-organic frameworks” (MOFs). These are fine powders whose particles are made up of metal atoms that are connected into a 3D structure with organic linkers. Their surface is covered with nano-size pores that collect CO2 molecules. But despite its lower cost, as this method involves transporting solids it is very demanding in terms of engineering. Berend Smit, Director of the Energy Center at EPFL, explains: “Imagine trying to walk with a plateful of baby powder. It’s going to go everywhere, and it’s very difficult to control.”
Working with scientists from Beijing and UC Berkeley, Smit is a lead author on a breakthrough carbon-capture innovation that uses a mixture of solid and liquid in solution called a “slurry”. The solid part of the slurry is a MOF called ZIF-8, which is suspended in a 2-methylimidazole glycol liquid mixture.
“Why a slurry?” says Smit. “Because in the materials that are currently used for adsorption the pores are too large and the surrounding liquid would fill them, and not let them capture CO2 molecules. So here we looked at a material – ZIF-8 – whose pores are too small for the glycol’s molecules to fit, but big enough for capturing the CO2 molecules from flue gas.”
ZIF-8 is a good material for carbon-capturing slurries, because it displays excellent solution, chemical and thermal stability, which is important for repeated regeneration cycles. ZIF-8 crystals have narrow pores (3.4 Å in diameter) that are smaller than the diameter of glycol molecules (4.5 Å), preventing them from entering. Even though other liquids were tested in the design of the slurry, including ethanol, hexane, methylbenzene and tetrachloromethane, their molecules are small enough to enter the ZIF-8 pores and reduce its carbon capturing efficiency. In this respect, glycerol has so far been shown to be an ideal liquid.