Tag Archives: #methane

Scientists Turn Methane Into Methanol At Room Temperature (Chemistry)

A “tantalizing” principle borrowed from nature turns harmful methane into useful methanol at room temperature. A team of researchers from Stanford University and the University of Leuven in Belgium has further elucidated the process in a new study in the current edition of Science.

The discovery may be an important step toward a methanol fuel economy with abundant methane as the feedstock, an advance that could fundamentally change how the world uses natural gas. Methanol – the simplest alcohol ­­– is used to make various products, like paints and plastics, and as an additive to gasoline. Rich in hydrogen, methanol can drive new-age fuel cells that could yield significant environmental benefits.

If natural gas, of which methane is the primary component, could be converted economically into methanol, the resulting liquid fuel would be much more easily stored and transported than natural gas and pure hydrogen. That also would greatly reduce the emissions of methane from natural gas processing plants and pipelines. Today, escaped methane, a greenhouse gas many times more potent than carbon dioxide, nearly negates the environmental advantages of natural gas over oil and coal. The team’s new study is their latest to advance a low-energy way to produce methanol from methane.

Professor Edward Solomon and PhD alumnus Benjamin Snyder seated at desk.
Benjamin Snyder (right) and his former PhD adviser, Edward Solomon, a professor of chemistry at Stanford and of photon science at SLAC. (Image credit: Linda A. Cicero)

“This process uses common crystals known as iron zeolites that are known to convert natural gas to methanol at room temperature,” explains Benjamin Snyder, who earned his doctorate at Stanford studying catalysts to address key facets of this challenge. “But, this is extremely challenging chemistry to achieve on a practical level, as methane is stubbornly chemically inert.”

When methane is infused into porous iron zeolites, methanol is rapidly produced at room temperature with no additional heat or energy required. By comparison, the conventional industrial process for making methanol from methane requires temperatures of 1000°C (1832°F) and extreme high pressure.

“That’s an economically tantalizing process, but it’s not that easy. Significant barriers prevent scaling up this process to industrial levels,” said Edward Solomon, Stanford professor of chemistry and of photon science at SLAC National Accelerator Laboratory. Solomon is the senior author of the new study.

Keeping the zeolites on

Doctoral student Hannah Rhoda with resonance Raman equipment
Hannah Rhoda with the resonance Raman spectroscopy equipment, which shoots a laser into a sample to obtain vibrational information from the exact site being studied. Researchers in the current study used this technique to help assign the Fe(III)-OH and the Fe(III)OCH3 poisoned sites, which illuminated the mechanism. (Image credit: Casey O’Sullivan)

Unfortunately, most iron zeolites deactivate quickly. Unable to process more methane, the process peters out. Scientists have been keen to study ways to improve iron zeolite performance. The new study, co-authored by Hannah Rhoda, a Stanford doctoral candidate in inorganic chemistry, uses advanced spectroscopy to explore the physical structure of the most promising zeolites for methane-to-methanol production.

“A key question here is how to get the methanol out without destroying the catalyst,” Rhoda said.

Choosing two attractive iron zeolites, the team studied the physical structure of the lattices around the iron. They discovered that the reactivity varies dramatically according to the size of the pores in the surrounding crystal structure. The team refers to it as the “cage effect,” as encapsulating lattice resembles a cage.

If the pores in the cages are too big, the active site deactivates after just one reaction cycle and never reactivates again.  When the pore apertures are smaller, however, they coordinate a precise molecular dance between the reactants and the iron active sites – one that directly produces methanol and regenerates the active site. Leveraging this so-called ‘cage effect,’ the team was able to reactivate 40 percent of the deactivated sites repeatedly – a significant conceptual advance toward an industrial-scale catalytic process.

An illustration of the cage structures of two iron-based zeolites used in the study
An illustration of the cage structures of two iron-based zeolites used in the study. The red and gold spheres (representing oxygen and iron, respectively) make up the active site. The cage structure, in gray, is formed of silicon, aluminum and oxygen. The blue sphere quantifies the size of the largest molecule that can diffuse freely in and out of the active site cage (methane diameter is ~4.2 Å). (Credit: Benjamin Snyder)

“Catalytic cycling – the continual reactivation of regenerated sites – could someday lead to continual, economical methanol production from natural gas,” said Snyder, now a postdoctoral fellow at UC-Berkeley in the Department of Chemistry under Jeffrey R. Long.

This fundamental step forward in basic science will help elucidate for chemists and chemical engineers the process iron zeolites use to produce methanol at room temperature, but much work remains before such a process might be industrialized.

Next up on Snyder’s list: tackling achieving the process not only at room temperature but using ambient air rather than some other source of oxygen, such as the nitrous oxide used in these experiments. Dealing with a powerful oxidizing agent like oxygen, which is notoriously hard to control in chemical reactions, will be another considerable hurdle along the path.

For now, Snyder was both pleased and amazed by the illustrative powers of the sophisticated spectroscopic instrumentation in the Solomon labs that were leveraged for this study. These were invaluable to his understanding of the chemistry and the chemical structures involved in the methane-to-methanol process.

“It’s cool how you can get some very powerful atomic-level insight, like the cage effect, from these tools that weren’t available to previous generations of chemists,” Snyder said.

University of Leuven researchers on this study were Max Bols, Dieter Plessers, Robert  Schoonheydt and, Bert F. Sels. This research was funded by the U.S. National Science Foundation, a Stanford Graduate Fellowship, Stanford Woods Institute for the Environment and the Research Foundation–Flanders (FWO).

Reference: Benjamin E. R. Snyder, Max L. Bols, Hannah M. Rhoda, Dieter Plessers, Robert A. Schoonheydt, Bert F. Sels, Edward I. Solomon, “Cage effects control the mechanism of methane hydroxylation in zeolites”, Science  16 Jul 2021: Vol. 373, Issue 6552, pp. 327-331 DOI: https://doi.org/10.1126/science.abd5803

Provided by Stanford University

Methane in the Plumes Of Saturn’s Moon Enceladus: Possible Signs of Life? (Planetary Science)

A study published in Nature Astronomy concludes that known geochemical processes can’t explain the levels of methane measured by the Cassini spacecraft on Saturn’s icy moon

An unknown methane-producing process is likely at work in the hidden ocean beneath the icy shell of Saturn’s moon Enceladus, suggests a new study published in Nature Astronomy by scientists at the University of Arizona and Paris Sciences & Lettres University.

Giant water plumes erupting from Enceladus have long fascinated scientists and the public alike, inspiring research and speculation about the vast ocean that is believed to be sandwiched between the moon’s rocky core and its icy shell. Flying through the plumes and sampling their chemical makeup, the Cassini spacecraft detected a relatively high concentration of certain molecules associated with hydrothermal vents on the bottom of Earth’s oceans, specifically dihydrogen, methane and carbon dioxide. The amount of methane found in the plumes was particularly unexpected.

“We wanted to know: Could Earthlike microbes that ‘eat’ the dihydrogen and produce methane explain the surprisingly large amount of methane detected by Cassini?” said Regis Ferriere, an associate professor in the University of Arizona Department of Ecology and Evolutionary Biology and one of the study’s two lead authors. “Searching for such microbes, known as methanogens, at Enceladus’ seafloor would require extremely challenging deep-dive missions that are not in sight for several decades.”

Ferriere and his team took a different, easier route: They constructed mathematical models to calculate the probability that different processes, including biological methanogenesis, might explain the Cassini data.

This cutaway view of Saturn’s moon Enceladus is an artist’s rendering that depicts possible hydrothermal activity that may be taking place on and under the seafloor of the moon’s subsurface ocean, based on results from NASA’s Cassini mission. © NASA/JPL-Caltech

The authors applied new mathematical models that combine geochemistry and microbial ecology to analyze Cassini plume data and model the possible processes that would best explain the observations. They conclude that Cassini’s data are consistent either with microbial hydrothermal vent activity, or with processes that don’t involve life forms but are different from the ones known to occur on Earth.

On Earth, hydrothermal activity occurs when cold seawater seeps into the ocean floor, circulates through the underlying rock and passes close by a heat source, such as a magma chamber, before spewing out into the water again through hydrothermal vents. On Earth, methane can be produced through hydrothermal activity, but at a slow rate. Most of the production is due to microorganisms that harness the chemical disequilibrium of hydrothermally produced dihydrogen as a source of energy, and produce methane from carbon dioxide in a process called methanogenesis.

The team looked at Enceladus’ plume composition as the end result of several chemical and physical processes taking place in the moon’s interior. First, the researchers assessed what hydrothermal production of dihydrogen would best fit Cassini’s observations, and whether this production could provide enough “food” to sustain a population of Earthlike hydrogenotrophic methanogens. To do that, they developed a model for the population dynamics of a hypothetical hydrogenotrophic methanogen, whose thermal and energetic niche was modeled after known strains from Earth.

The authors then ran the model to see whether a given set of chemical conditions, such as the dihydrogen concentration in the hydrothermal fluid, and temperature would provide a suitable environment for these microbes to grow. They also looked at what effect a hypothetical microbe population would have on its environment – for example, on the escape rates of dihydrogen and methane in the plume.

“In summary, not only could we evaluate whether Cassini’s observations are compatible with an environment habitable for life, but we could also make quantitative predictions about observations to be expected, should methanogenesis actually occur at Enceladus’ seafloor,” Ferriere explained.

The results suggest that even the highest possible estimate of abiotic methane production – or methane production without biological aid – based on known hydrothermal chemistry is far from sufficient to explain the methane concentration measured in the plumes. Adding biological methanogenesis to the mix, however, could produce enough methane to match Cassini’s observations.

“Obviously, we are not concluding that life exists in Enceladus’ ocean,” Ferriere said. “Rather, we wanted to understand how likely it would be that Enceladus’ hydrothermal vents could be habitable to Earthlike microorganisms. Very likely, the Cassini data tell us, according to our models.

“And biological methanogenesis appears to be compatible with the data. In other words, we can’t discard the ‘life hypothesis’ as highly improbable. To reject the life hypothesis, we need more data from future missions,” he added.

The authors hope their paper provides guidance for studies aimed at better understanding the observations made by Cassini and that it encourages research to elucidate the abiotic processes that could produce enough methane to explain the data.

For example, methane could come from the chemical breakdown of primordial organic matter that may be present in Enceladus’ core and that could be partially turned into dihydrogen, methane and carbon dioxide through the hydrothermal process. This hypothesis is very plausible if it turns out that Enceladus formed through the accretion of organic-rich material supplied by comets, Ferriere explained.

“It partly boils down to how probable we believe different hypotheses are to begin with,” he said. “For example, if we deem the probability of life in Enceladus to be extremely low, then such alternative abiotic mechanisms become much more likely, even if they are very alien compared to what we know here on Earth.”

According to the authors, a very promising advance of the paper lies in its methodology, as it is not limited to specific systems such as interior oceans of icy moons and paves the way to deal with chemical data from planets outside the solar system as they become available in the coming decades.

A full list of authors and funding information can be found in the paper, “Bayesian analysis of Enceladus’s plume data to assess methanogenesis,” in the July 7 issue of Nature Astronomy.

Featured image: This artist’s impression depicts NASA’s Cassini spacecraft flying through a plume of presumed water erupting from the surface of Saturn’s moon Enceladus. © NASA

Provided by University of Arizona

Novel Photocatalyst Effectively Turns Carbon Dioxide into Methane Fuel With Light (Chemistry)

Carbon dioxide (CO2) is one of the major greenhouse gases causing global warming. If the carbon dioxide could be converted into energy, it would be killing two birds with one stone in addressing the environmental issues. A joint research team led by City University of Hong Kong (CityU) has developed a new photocatalyst which can produce methane fuel (CH4) selectively and effectively from carbon dioxide using sunlight. According to their research, the quantity of methane produced was almost doubled in the first 8 hours of the reaction process.

The research was led by Dr Ng Yun-hau, Associate Professor in the School of Energy and Environment (SEE), in collaboration with researchers from Australia, Malaysia and the United Kingdom. Their findings have been recently published in the scientific journal Angewandte Chemie, titled “Metal-Organic Frameworks Decorated Cuprous Oxide Nanowires for Long-lived Charges Applied in Selective Photocatalytic CO2 Reduction to CH4”.

Nature-inspired photocatalysis

“Inspired by the photosynthesis in nature, carbon dioxide can now be converted effectively into methane fuel by our newly designed solar-powered catalyst, which will lower carbon emission. Furthermore, this new catalyst is made from copper-based materials, which is abundant and hence affordable,” said Dr Ng.   

He explained that it is thermodynamically challenging to convert carbon dioxide into methane using a photocatalyst because the chemical reduction process involves a simultaneous transfer of eight electrons. Carbon monoxide, which is harmful to human, is more commonly produced in the process because it requires the transfer of two electrons only.

He pointed out that cuprous oxide (Cu2O), a semiconducting material, has been applied as both photocatalyst and electrocatalyst to reduce carbon dioxide into other chemical products like carbon monoxide and methane in different studies. However, it faces several limitations in the reduction process, including its inferior stability and the non-selective reduction which causes the formation of an array of various products. Separation and purification of these products from the mixture can be highly challenging and this imposes technological barrier for large scale application. Furthermore, cuprous oxide can easily corrode after brief illumination and evolve into metallic copper or copper oxide.

Selective production of pure methane 

To overcome these challenges, Dr Ng and his team synthesised a novel photocatalyst by enwrapping cuprous oxide with copper-based metal-organic frameworks (MOFs). Using this new catalyst, the team could manipulate the transfer of electrons and selectively produce pure methane gas.

With the MOF shell, the new catalyst’s maximum carbon dioxide uptake is almost seven times of the bare cuprous oxide. (Photo source: DOI number: 10.1002/anie.202015735)

They discovered that when compared with cuprous oxide without MOF shell, cuprous oxide with MOF shell reduced carbon dioxide into methane stably under visible-light irradiation with an almost doubled yield. Also, cuprous oxide with MOF shell was more durable and the maximum carbon dioxide uptake was almost seven times of the bare cuprous oxide.

Carbon dioxide uptake increased

The team encapsulated the one-dimensional (1-D) cuprous oxide nanowires (with a diameter of about 400nm) with the copper-based MOF outer shell of about 300nm in thickness. This conformal coating of MOF on cuprous oxide would not block light-harvesting of the catalyst. Besides, MOF is a good carbon dioxide adsorbent. It provided considerable surface areas for carbon dioxide adsorption and reduction. As it was closely attached to the cuprous oxide, it brought a higher concentration of carbon dioxide adsorbed at locations near the catalytic active sites, strengthening the interaction between carbon dioxide and the catalyst.

Figure a shows the images of copper wires, cuprous oxide nanowires and cuprous oxide with MOF shell. Figure b, c and d are their scanning electron microscope images respectively. (Photo source: DOI number: 10.1002/anie.202015735)
In contrast to the bare cuprous oxide sample, which lost its intrinsic activity in the fifth run, cuprous oxide with MOF shell retained 69.2% of its original efficiency for methane production after five runs. (Photo source: DOI number: 10.1002/anie.202015735)

Moreover, the team discovered that the cuprous oxide was stabilised by the conformal coating of MOF. The excited charges in cuprous oxide upon illumination could efficiently migrate to the MOF. In this way, excessive accumulation of excited charges within the catalyst which could lead to self-corrosion was avoided, hence extended the catalyst’s lifetime.   

Electrons stayed in MOF with higher chance of having chemical reactions 

Dr Wu Hao, the first author of the paper who is also from SEE, pointed out one of the highlights of this research and said: “By using the advanced time-resolved photoluminescence spectroscopy, we observed that once the electrons were excited to the conduction band of the cuprous oxide, they would be directly transferred to the lowest unoccupied molecular orbital (LUMO) of the MOF and stayed there, but did not return quickly to their valence band, which is of lower energy. This created a long-lived charge separated state. Therefore, electrons that stayed in the MOF would have a higher chance to undergo chemical reactions.”

Extends the understanding of relationships between MOFs and metal oxides

Previously, it was generally believed that the improved photocatalytic activities were merely induced by MOF’s reactant concentration effect and MOF only served as a reactant adsorbent. However, Dr Ng’s team unveiled how the excited charges migrate between cuprous oxide and MOF in this research. “MOF is proven to play a more significant role in shaping the reaction mechanism as it changes the electron pathway,” he said. He pointed out that this discovery has extended the understanding of relationships between MOFs and metal oxides beyond their conventional physical/chemical adsorption type of interactions to facilitating charge separation.

The team has spent more than two years to develop this effective strategy in converting carbon dioxide. Their next step will be to further increase the methane production rate and explore ways to scale up both the synthesis of the catalyst and the reactor systems. “In the entire process of converting carbon dioxide to methane, the only energy input we have used was sunlight. We hope in the future, carbon dioxide emitted from factories and transportation can be ‘recycled’ to produce green fuels,” concluded Dr Ng.

Dr Ng Yun-hau is an expert in photocatalysis. He researches on developing photocatalyst materials and the mechanism of charge separation induced by light. (Photo source: City University of Hong Kong)
Dr Wu Hao, the first author of the paper. (Photo source: City University of Hong Kong)

Dr Ng is the corresponding author of the paper and the first author is Dr Wu Hao. Other collaborating researchers are from University College London, University of New South Wales, Monash University in Malaysia, and the Swinburne University of Technology. 

The research was funded by CityU, Hong Kong Research Grant Council and the Australian Research Council.

Featured image: Dr Ng and his team synthesised a new photocatalyst by enwrapping cuprous oxide with copper-based metal-organic frameworks. (Photo source: City University of Hong Kong)

Reference: Wu, H., Kong, X.Y., Wen, X., Chai, S., Lovell, E..C., Tang, J. and Ng, Y.H. (2021), Metal‐Organic Frameworks Decorated Cuprous Oxide Nanowires for Long‐lived Charges Applied in Selective Photocatalytic CO2 Reduction to CH4. Angew. Chem. Int. Ed.. Accepted Author Manuscript. https://doi.org/10.1002/anie.202015735 DOI: 10.1002/anie.202015735

Provided by CityU

The Moon Controls the Release of Methane in Arctic Ocean (Planetary Science)

High tides may even counter the potential threat of submarine methane release from the warming Arctic.

It may not be very well known, but the Arctic Ocean leaks enormous amounts of the potent greenhouse gas methane. These leaks have been ongoing for thousands of years but could be intensified by a future warmer ocean. The potential for this gas to escape the ocean, and contribute to the greenhouse gas budget in the atmosphere, is an important mystery that scientists are trying to solve.

Full moon in Tromsø, Norway. Photo: Maja Sojtaric ©Maja Sojtaric

The total amount of methane in the atmosphere has increased immensely over the past decades, and while some of the increase can be ascribed to human activity, other sources are not very well constrained.

A recent paper in Nature Communications even implies that the moon has a role to play.

Small pressure changes affect methane release

The moon controls one of the most formidable forces in nature – the tides that shape our coastlines. Tides, in turn, significantly affect the intensity of methane emissions from the Arctic Ocean seafloor.

“We noticed that gas accumulations, which are in the sediments within a meter from the seafloor, are vulnerable to even slight pressure changes in the water column. Low tide means less of such hydrostatic pressure and higher intensity of methane release. High tide equals high pressure and lower intensity of the release” says co-author of the paper Andreia Plaza Faverola.

“It is the first time that this observation has been made in the Arctic Ocean. It means that slight pressure changes can release significant amounts of methane. This is a game-changer and the highest impact of the study.” Says another co-author, Jochen Knies.

New methods reveal unknown release sites

Plaza Faverola points out that the observations were made by placing a tool called a piezometer in the sediments and leaving it there for four days.

Retrieving the pressure tool, piezometer, which was monitoring the methane release from the ocean floor sediments. Photo: Screenshot from video. P.Domel.

It measured the pressure and temperature of the water inside the pores of the sediment. Hourly changes in the measured pressure and temperature revealed the presence of gas close to the seafloor that ascends and descends as the tides change. The measurements were made in an area of the Arctic Ocean where no methane release has previously been observed but where massive gas hydrate concentrations have been sampled.

“This tells us that gas release from the seafloor is more widespread than we can see using traditional sonar surveys. We saw no bubbles or columns of gas in the water. Gas burps that have a periodicity of several hours won’t be identified unless there is a permanent monitoring tool in place, such as the piezometer.” Says Plaza Faverola.

Methane release can be seen as flares rising from the ocean floor. But the release is not always visible using the usual methods. Screenshot from data visualization by Andreia Plaza Faverola.

These observations imply that the quantification of present-day gas emissions in the Arctic may be underestimated. High tides, however, seem to influence gas emissions by reducing their height and volume.

“What we found was unexpected and the implications are big. This is a deep-water site. Small changes in pressure can increase the gas emissions but the methane will still stay in the ocean due to the water depth. But what happens in shallower sites? This approach needs to be done in shallow Arctic waters as well, over a longer period. In shallow water, the possibility that methane will reach the atmosphere is greater.” Says Knies.

May counteract the temperature effects

High sea-level seems thus to influence gas emissions by potentially reducing their height and volume. The question remains whether sea-level rise due to global warming might partially counterbalance the effect of temperature on submarine methane emissions.

“Earth systems are interconnected in ways that we are still deciphering, and our study reveals one of such interconnections in the Arctic: The moon causes tidal forces, the tides generate pressure changes, and bottom currents that in turn shape the seafloor and impact submarine methane emissions. Fascinating!” says Andreia Plaza Faverola.

The paper is the result of a collaboration between CAGE and Ifremer under the project SEAMSTRESS – Tectonic Stress Effects on Arctic Methane Seepage.

Reference: Sultan, N., Plaza-Faverola, A., Vadakkepuliyambatta, S. et al. Impact of tides and sea-level on deep-sea Arctic methane emissions. Nat Commun 11, 5087 (2020). https://www.nature.com/articles/s41467-020-18899-3 https://doi.org/10.1038/s41467-020-18899-3

Provided by UIT Arctic University of Norway

Study Reveals How to Improve Natural Gas Production In Shale (Engineering)

Molecular-dynamics simulations and high-pressure small-angle neutron scattering help team discover optimal methane-releasing pressure range.

A new hydrocarbon study contradicts conventional wisdom about how methane is trapped in rock, revealing a new strategy to more easily access the valuable energy resource.

A Los Alamos study reveals how production pressures can be optimized to efficiently recover natural gas. ©stock image

“The most challenging issue facing the shale energy industry is the very low hydrocarbon recovery rates: less than 10 percent for oil and 20 percent for gas. Our study yielded new insights into the fundamental mechanisms governing hydrocarbon transport within shale nanopores,” said Hongwu Xu, an author from Los Alamos National Laboratory’s Earth and Environmental Sciences Division. “The results will ultimately help develop better pressure management strategies for enhancing unconventional hydrocarbon recovery.”

Most of U.S. natural gas is hidden deep within shale reservoirs. Low shale porosity and permeability make recovering natural gas in tight reservoirs challenging, especially in the late stage of well life. The pores are miniscule–typically less than five nanometers–and poorly understood. Understanding the hydrocarbon retention mechanisms deep underground is critical to increase methane recovering efficiency. Pressure management is a cheap and effective tool available to control production efficiency that can be readily adjusted during well operation–but the study’s multi-institution research team discovered a trade-off.

This team, including the lead author, Chelsea Neil, also of Los Alamos, integrated molecular dynamics simulations with novel in situ high-pressure small-angle neutron scattering (SANS) to examine methane behavior in Marcellus shale in the Appalachian basin, the nation’s largest natural gas field, to better understand gas transport and recovery as pressure is modified to extract the gas. The investigation focused on interactions between methane and the organic content (kerogen) in rock that stores a majority of hydrocarbons.

The study’s findings indicate that while high pressures are beneficial for methane recovery from larger pores, dense gas is trapped in smaller, common shale nanopores due to kerogen deformation. For the first time, they present experimental evidence that this deformation exists and proposed a methane-releasing pressure range that significantly impacts methane recovery. These insights help optimize strategies to boost natural gas production as well as better understand fluid mechanics.

Methane behavior was compared during two pressure cycles with peak pressures of 3000 psi and 6000 psi, as it was previously believed that increasing pressure from injected fluids into fractures would increase gas recovery. The team discovered that unexpected methane behavior occurrs in very small but prevalent nanopores in the kerogen: the pore uptake of methane was elastic up to the lower peak pressure, but became plastic and irreversible at 6,000 psi, trapping dense methane clusters that developed in the sub-2 nanometer pore, which encompass 90 percent of the measured shale porosity.

Led by Los Alamos, the multi-institution study was published in Nature’s new Communications Earth & Environment journal this week. Partners include the New Mexico Consortium, University of Maryland, and the National Institute of Standards and Technology Center for Neutron Research.

References : “Reduced methane recovery at high pressure due to methane trapping in shale nanopores”; Chelsea W. Neil, Mohamed Mehana, Rex P. Hjelm, Marilyn E. Hawley, Erik B. Watkins, Yimin Mao, Hari Viswanathan, Qinjun Kang, and Hongwu Xu;
Communications Earth & Environment; DOI: https://doi.org/10.1038/s43247-020-00047-w

Provided by Los Alamos National Laboratory

In The Beginning, There Was Sugar (Chemistry / Planetary Science)

Organic molecules formed the basis for the evolution of life. But how could inorganic precursors have given rise to them? LMU chemist Oliver Trapp now reports a reaction pathway in which minerals catalyze the formation of sugars in the absence of water.

Prebiotic organic molecules could have been formed in such a setting at the dawn of life: Yellowstone Parc, USA. Photo: Oliver Trapp

More than 4 billion years ago, the Earth was very far from being the Blue Planet it would later become. At that point it had just begun to cool and, in the course of that process, the concentric structural zones that lie ever deeper beneath our feet were formed. The early Earth was dominated by volcanism, and the atmosphere was made up of carbon dioxide, nitrogen, methane, ammonia, hydrogen sulfide and water vapor. In this decidedly inhospitable environment the building blocks of life were formed. How then might this have come about?

Researchers have puzzled over the question for decades. The first breakthrough was made in 1953 by two chemists, named Stanley Miller and Harold C. Urey, at the University of Chicago. In their experiments, they simulated the atmosphere of the primordial Earth in a closed reaction system that contained the gases mentioned above. A miniature ‘ocean’ was heated to provide water vapor, and electrical discharges were passed through the system to mimic the effects of lightning. When they analyzed the chemicals produced under these conditions, Miller and Urey detected amino acids – the basic constituents of proteins – as well as a number of other organic acids.

It is now known that the conditions employed in these experiments did not reflect those that prevailed on the early Earth. Nevertheless, the Miller-Urey experiment initiated the field of prebiotic chemical evolution. However, it not throw much light on how other classes of molecules found in all biological cells – such as sugars, fats and nucleic acids – might have been generated. These compounds are however indispensable ingredients of the process that led to the first bacteria and subsequently to photosynthetic cyanobacteria that produced oxygen. This is why Oliver Trapp, Professor of Organic Chemistry at LMU, decided to focus his research on the prebiotic synthesis of these substances.

From formaldehyde to sugar

The story of synthetic routes from smaller precursors to sugars goes back almost a century prior to the Miller-Urey experiment. In 1861, the Russian chemist Alexander Butlerov showed that formaldehyde could give rise to various sugars via what became known as the formose reaction. Miller und Urey in fact found formic acid in their experiments, and it can be readily reduced to yield formaldehyde. Butlerov also discovered that the formose reaction is promoted by a number of metal oxides and hydroxides, including those of calcium, barium, thallium and lead. Notably calcium is abundantly available on and below the Earth’s surface.

However, the hypothesis that sugars could have been produced via the formose reaction runs into two difficulties. The ‘classical’ formose reaction produces a diverse mixture of compounds, and it takes place only in aqueous media. These requirements are at odds with the fact that sugars have been detected in meteorites.

Together with colleagues at LMU and the Max Planck Institute for Astronomy in Heidelberg, Trapp therefore decided to explore whether formaldehyde could give rise to sugars in a solid-phase system. With a view to simulating the kinds of mechanical forces to which solid minerals would have been subjected, all the reaction components were combined in a ball mill – in the absence of solvents, but adding enough formaldehyde to saturate the powdered solids

And indeed, the formose reaction was observed and several different minerals were found to catalyze it. The formaldehyde was adsorbed onto the solid particles, and the interaction resulted in the formation of the formaldehyde dimer (glycolaldehyde) – and ribose, the 5-carbon sugar that is an essential constituent of ribonucleic acid (RNA). RNA is thought to have merged prior to DNA, and it serves as the repository of genetic information in many viruses, as well as providing the templates for protein synthesis in all cellular organisms. More complex sugars were also obtained in the experiments, together with a few byproducts, such as lactic acid and methanol.

“Our results provide a plausible explanation for the formation of sugars in the solid phase, even under extraterrestrial settings in the absence of water,” says Trapp. They also prompt new questions that may point to new and unexpected prebiotic routes to the basic components of life as we know it, as Trapp affirms. “We are convinced that these new insights will open up entirely new perspectives for research on prebiotic, chemical evolution,” he says.

References: Haas, M., Lamour, S., Christ, S.B. et al. Mineral-mediated carbohydrate synthesis by mechanical forces in a primordial geochemical setting. Commun Chem 3, 140 (2020). https://doi.org/10.1038/s42004-020-00387-w

Provided by LMU Munich

Pluto’s Ice Caps Made of Methane, Turns Earth’s Process Upside Down (Planetary Science)

The mountains discovered on Pluto during the New Horizons spacecraft’s flyby of the dwarf planet in 2015 are covered by a blanket of methane ice, creating bright deposits strikingly like the snow-capped mountain chains found on Earth.

Pluto as seen from data taken by New Horizon’s flyby in 2015 of the dwarf planet, with a close-up view of the Pigafetta Montes mountain range. The colorization on the right indicates the concentrations of methane ice, with the highest concentrations at higher elevations in red, decreasing downslope to the lowest concentrations in blue. Credits: NASA/JHUAPL/SwRI and Ames Research Center/Daniel Rutter

New research conducted by an international team of scientists, including researchers at NASA’s Ames Research Center in California’s Silicon Valley, analyzed New Horizons data from Pluto’s atmosphere and surface, using numerical simulations of Pluto’s climate to reveal that these ice caps are created through an entirely different process than they are on Earth.

“It is particularly remarkable to see that two very similar landscapes on Earth and Pluto can be created by two very dissimilar processes,” said Tanguy Bertrand, a postdoctoral researcher at Ames and lead author on the paper detailing these results, which was published in Nature Communications. “Though theoretically objects like Neptune’s moon Triton could have a similar process, nowhere else in our solar system has ice-capped mountains like this besides Earth.”

On our planet, atmospheric temperatures decrease with altitude, mostly because of the cooling induced by the expansion of the air in upward motions. The cool atmosphere in turn cools temperatures at the surface. When a moist wind approaches a mountain on Earth, its water vapor cools and condenses, forming clouds and then the snow seen on mountain tops. But on Pluto, the opposite occurs. The dwarf planet’s atmosphere actually gets warmer as altitude increases because the methane gas that’s more concentrated higher up absorbs solar radiation. However, the atmosphere is too thin to impact the surface temperatures, which remain constant. And unlike Earth’s upward winds, on Pluto, winds that travel down mountain slopes dominate.

To understand how the same landscape could be produced with different materials and under different conditions, the researchers developed a 3D model of Pluto’s climate at the Laboratoire de Météorologie in Paris, France, simulating the atmosphere and surface over time. They found that Pluto’s atmosphere has more gaseous methane at its warmer, higher altitudes, allowing for that gas to saturate, condense, and then freeze directly on the mountain peaks without any clouds forming. At lower altitudes, there’s no methane frost because there’s less of this gaseous methane, making it impossible for condensation to occur.

This process not only creates the methane ice caps on Pluto’s mountains, but also similar features on its crater rims as well. The mysterious bladed terrain that can be found in the Tartarus Dorsa region around Pluto’s equator is also explained by this cycle.

“Pluto really is one of the best natural laboratories we have to explore the physical and dynamic processes involved when compounds that regularly transition between solid and gas states interact with a planetary surface,” said Bertrand. “The New Horizons flyby revealed astonishing glacial landscapes we continue to learn from.”

References: Bertrand, T., Forget, F., Schmitt, B. et al. Equatorial mountains on Pluto are covered by methane frosts resulting from a unique atmospheric process. Nat Commun 11, 5056 (2020). https://doi.org/10.1038/s41467-020-18845-3

Provided by NASA

Scientists Find Efficient Way to Convert Carbon Dioxide into Ethylene (Chemistry)

Electrochemical CO2 reduction to value-added chemical feedstocks is of considerable interest for renewable energy storage and renewable source generation while mitigating CO2 emissions from human activity. Copper represents an effective catalyst in reducing CO2 to hydrocarbons or oxygenates, but it is often plagued by a low product selectivity and limited long-term stability. Now Choi and colleagues reported that copper nanowires with rich surface steps to catalyze a chemical reaction that reduces carbon dioxide (CO2) emissions while generating ethylene (C2H4), an important chemical used to produce plastics, solvents, cosmetics and other important products globally.

Copper represents an effective catalyst in reducing carbon dioxide to hydrocarbons or oxygenates, but it is often plagued by a low product selectivity and limited long-term stability. Choi et al report that copper nanowires with rich surface steps exhibit a remarkably high Faradaic efficiency for ethylene that can be maintained for over 200 hours. Image credit: Choi et al, doi: 10.1038/s41929-020-00504-x.

Using copper to kick start the carbon dioxide reduction into ethylene reaction has suffered two strikes against it.

First, the initial chemical reaction also produced hydrogen and methane — both undesirable in industrial production.

Second, previous attempts that resulted in ethylene production did not last long, with conversion efficiency tailing off as the system continued to run.

To overcome these two hurdles, Professor Goddard III and colleagues focused on the design of the copper nanowires with highly active steps — similar to a set of stairs arranged at atomic scale.

One intriguing finding of this collaborative study is that this step pattern across the nanowires’ surfaces remained stable under the reaction conditions, contrary to general belief that these high energy features would smooth out.

This is the key to both the system’s durability and selectivity in producing ethylene, instead of other end products.

The scientists demonstrated a carbon dioxide-to-ethylene conversion rate of greater than 70%, much more efficient than previous designs, which yielded at least 10% less under the same conditions.

The new system ran for 200 hours, with little change in conversion efficiency, a major advance for copper-based catalysts.

In addition, the comprehensive understanding of the structure-function relation illustrated a new perspective to design highly active and durable carbon dioxide reduction catalyst in action.

References: Choi, C., Kwon, S., Cheng, T. et al. Highly active and stable stepped Cu surface for enhanced electrochemical CO2 reduction to C2H4. Nat Catal (2020). https://doi.org/10.1038/s41929-020-00504-x link: https://www.nature.com/articles/s41929-020-00504-x