Category Archives: Chemistry

Scientists Discover New Mechanisms of Activity Improvement On Bimetallic Catalysts For Hydrogen Generation & Fuel Cells (Chemistry)

A group of researchers at the Hong Kong University of Science and Technology (HKUST) and Xiamen University has revealed new understandings of how surface ruthenium atoms can improve the hydrogen evolution and oxidation activities of platinum. This discovery opens a new venue for rational design of more advanced catalysts for electrolyzer and fuel cell applications. 

Hydrogen is a clean energy carrier that does not contain carbon. It is believed to play an essential role in our future sustainable society. Hydrogen can be produced from water via the hydrogen evolution reaction (HER) in an electrolyzer by using renewable energies, and consumed via a hydrogen oxidation reaction (HOR) in a fuel cell to generate electricity. Unfortunately, these two reactions are well-known kinetically sluggish in alkaline media, even on the most active platinum catalysts. The slow reaction rates limit the efficiencies of these two electrochemical devices and hinder their wide adoption. It has been known that the reaction rates of HER/HOR on platinum can be improved by surface modification or alloying with ruthenium. However, the mechanisms for this promotion have been under debate for over decades. Part of the reasons is a lack of direct observation of behaviors of hydrogen atoms on the surfaces of catalysts.

To reveal the enigma of high HER/HOR activities on platinum-ruthenium bimetallic catalysts, a research team led by Prof. Minhua ShaoDepartment of Chemical and Biological Engineering and Energy Institute at HKUST, recently applied the powerful surface-enhanced infrared absorption spectroscopy (SEIRAS) to directly monitor the binding strength of the important reaction intermediate, hydrogen atoms on various surfaces. Through the combined electrochemical, spectroscopic, and theoretical studies they confirmed the surface ruthenium atoms interacted with the sub-surface platinum is one order of magnitude more active than platinum, i.e., the ruthenium rather than platinum atoms are main active sites in this system. 

“Previous works mainly used conventional electrochemical and characterization techniques, which cannot directly monitor the adsorption behavior of hydrogen reaction intermediates. In this work, we use the powerful surface-enhanced infrared absorption spectroscopy, which is among the very few techniques that can directly “see” surface hydrogen atoms, and provides us more straightforward information on how ruthenium improves the activity” said Prof. Shao. “This work rules out the most widespread theory that the bifunctional effect on the interface between platinum and ruthenium is the cause of increased activities, and opens new directions on future design of more advanced HER/HOR catalysts, which can consequently reduce the usage of precious metals in both water electrolyzers and hydrogen fuel cells.”

This work is part of the newly founded Collaborative Research Fund project led by Prof. Shao “Development of high-performance and long-life alkaline membrane fuel cells”, and constitutes an important subsection of fundamental research to this whole project. Following works on the development of practical and high-performance bimetallic platinum-ruthenium electrocatalysts based on these findings is in progress.

This study was recently published in Nature Catalysis entitled “The Role of Ruthenium in Improving the Kinetics of Hydrogen Oxidation and Evolution Reactions of Platinum”.

Featured image: Ruthenium atoms supported on platinum are extremely active to produce hydrogen © HKUST


Provided by HKUST

New Solvents To Break Down Plant Cellulose For Bioethanol (Chemistry)

Kanazawa University researchers experimented with different combinations of zwitterionic molecules to produce a solvent that is liquid below 100°C and very effective at breaking down cellulose. This research may lead to much more cost-effective and safe production of biofuels, such as ethanol from switchgrass or plant husks.

Scientists from the Institute of Science and Engineering at Kanazawa University have developed new solvent mixtures to break down the tough structure of plant cellulose for the production of bioethanol. These new solvents work under mild conditions, have reduced toxicity and are more environmentally friendly compared with currently available solvents. This work may lead to improved technologies for the conversion of currently unused biomass to fuel.

Biofuels, such as ethanol produced from switchgrass or sugarcane, may allow us to reduce our reliance on nonrenewable fossil fuels. However, the process of making biofuels usually requires breaking down the cellulose from plants, which consists of long polymer chains, into smaller sugar molecules. This is not a simple task, as illustrated by how unappetizing tree bark or grass stalks look to us humans. Cellulose has a complex hydrogen bonding network, which makes it extremely chemical resistant. Current methods for processing cellulose rely on harsh reaction conditions and toxic chemicals.

Now, scientists from Kanazawa University have used a special class of molecules called “zwitterions” to create novel solvents with the ability to dissolve cellulose. Zwitterions are special in that they have both a positive and negative charge, but at different locations on the molecule so they cannot neutralize each other. These charges are highly effective at disrupting the hydrogen bonds keeping the cellulose from being broken down. “Because almost all zwitterions are solid under normal reaction conditions, our experiments used eutectic mixtures,” first author Gyanendra Sharma explains. A eutectic system is a mixture of substances with a melting point lower than that of its constituent parts. This is accomplished by using molecules with different structures, so that regular crystals are harder to form.

In these experiments, the team mixed four different zwitterions at various ratios. They found 22 combinations that were liquid below 100°C. Of these, two mixtures were also highly effective at dissolving cellulose. “Our work shows that it is possible to replace many of the toxic chemicals used today with more environmentally friendly alternatives as we move towards a more renewable energy ecosystem,” senior author Kosuke Kuroda says. This research demonstrates the potential of using combinations of zwitterions to create mixtures with properties not possessed by any molecule individually.

Suitable solvents are needed to produce ethanol from cellulosic plant biomass. We have found that liquid zwitterions are suitable for it, but it has been difficult to liquefy zwitterions and the species have been strictly limited. Therefore, the solid zwitterions were liquefied through making deep eutectic solvents, which are liquids from solid-solid mixtures. The liquefied zwitterionic solvent was able to dissolve the cellulose. © Kanazawa University

Suitable solvents are needed to produce ethanol from cellulosic plant biomass. We have found that liquid zwitterions are suitable for it, but it has been difficult to liquefy zwitterions and the species have been strictly limited. Therefore, the solid zwitterions were liquefied through making deep eutectic solvents, which are liquids from solid-solid mixtures. The liquefied zwitterionic solvent was able to dissolve the cellulose.

[Funder]
This study was partly supported by KAKENHI (18K14281 from the Japan Society for the Promotion of Science), and the Leading Initiative for Excellent Young Researchers (from Ministry of Education, Culture, Sports, Science and Technology-Japan). This research was also partly supported by the COI program “Construction of next-generation infrastructure using innovative materials–Realization of a safe and secure society that can coexist with the Earth for centuries”, which is supported by Ministry of Education, Culture, Sports, Science and Technology-Japan and Japan Science and Technology Agency and Kanazawa University Sakigake project 2020.”

[Article]


Provided by Kanazawa University

Researchers Report A Fast, Efficient Method For Synthesizing Glycoproteins (Chemistry)

Many processes in the body are regulated by the functions of proteins. For example, almost all molecules—such as DNA, proteins, oligosaccharides, and small bioactive molecules—are generated by enzymes. However, changes in protein functions in response to abnormal conditions cause critical diseases. Researchers from Osaka University have demonstrated a rapid, robust chemical method for preparing the highly pure (homogeneous) glycoproteins needed to investigate these changes. Their findings were published in the Journal of the American Chemical Society.

The efficacy of enzymes and functional proteins is regulated by protein modifications. A typical protein modification is glycosylation—adding sugar chains called glycans to proteins to give glycoproteins. Glycoproteins are found on the cell surface and in body fluids and play important roles in many biological processes. However, the glycoproteins formed can have many different glycan structures. Therefore, studying which glycan structures are essential for individual biological events is challenging.

The production of glycoproteins such as biologics—therapeutics produced from, or containing components of, living organisms—uses mammalian cell expression methods, but it is not possible to regulate the structure of the glycan added to the protein. Chemical synthesis is therefore the best way to make homogeneous glycoproteins that are appropriate for basic biological experiments. However, chemical methods require over 100 chemical conversion steps and are time-consuming.

The Osaka researchers identified an unprecedented and efficient amide bond formation reaction between glycan-amino acid and two peptides: diacyl disulfide coupling and thioacid capture ligation. They demonstrated that glycosyl asparagine thioacid exhibited excellent chemoselective coupling with peptides, and the conditions used could generate glycosyl polypeptide within a few chemical conversion steps.

“We essentially used the glycosyl asparagine to form a junction between two functional peptides, giving a glycoprotein,” explains study first author Kota Nomura. “We achieved this in just a few steps, making it a highly efficient approach with little waste of valuable glycan materials.”

The team demonstrated the feasibility of their technique by synthesizing two cytokine glycoproteins. Cytokines are important bioactive molecules that are involved in inflammation and immune responses. Reliably producing them therefore provided important proof of the utility of the new synthetic route.

“We have demonstrated a reliable means of synthesizing glycoproteins that will allow the thorough study of glycan biological function, as well as the generation of biologics,” study corresponding author Yasuhiro Kajihara explains.

The article, “Glycoprotein semisynthesis by chemical insertion of glycosyl asparagine using a bifunctional thioacid-mediated strategy,” was published in the Journal of the American Chemical Society at DOI: https://doi.org/10.1021/jacs.1c02601

Featured image: Glycoprotein synthesis by chemical insertion using a thioacid-mediated strategy: the method assembles a full glycoprotein segment in two steps. © Osaka University


Provided by Osaka University

Green Hydrogen: Why Do Certain Catalysts Improve In Operation? (Chemistry)

As a rule, most catalyst materials deteriorate during repeated catalytic cycles – they age. But there are also compounds that increase their performance over the course of catalysis. One example is the mineral erythrite, a mineral compound comprising cobalt and arsenic oxides with a molecular formula of (Co3(AsO4)2∙8H2O). The mineral stands out because of its purple colour. Erythrite lends itself to accelerating oxygen generation at the anode during electrolytic splitting of water into hydrogen and oxygen.

Samples from Costa Rica

The young investigator group headed by Dr. Marcel Risch at the HZB together with groups from Costa Rica has now analysed these catalysing mineral materials in detail at BESSY II and made an interesting discovery.

Schematic of the electrochemical restructuring of erythrite. The fine needle-like structure melts during the conversion from a crystalline material to an amorphous one, which is porous like a Swiss cheese. © HZB

Using samples produced by colleagues in Costa Rica consisting of tiny erythrite crystals in powder form, Javier Villalobos, a doctoral student in Risch’s group at the HZB, coated the electrodes with this powder. He then examined them before, during, and after hundreds of electrolysis cycles in four different pH-neutral electrolytes, including ordinary soda water (carbonated water).

Loss of original structure

Over time, the surface of each catalytically active layer exhibited clear changes in all the electrolytes. The original crystalline structure was lost, as shown by images from the scanning electron microscope, and more cobalt ions changed their oxidation number due to the applied voltage, which was determined electrochemically. Increased oxygen yield was also demonstrated over time in soda water (carbonated water), though only in that electrolyte. The catalyst clearly improved.

Observations at BESSY II

With analyses at BESSY II, the researchers are now able to explain why this was the case: using X-ray absorption spectroscopy, they scanned the atomic and chemical environment around the cobalt ions. The more active samples lost their original erythrite crystal structure and were transformed into a less ordered structure that can be described as platelets just two atoms thick. The larger these platelets became, the more active the sample was. The data over the course of the catalysis cycles showed that the oxidation number of the cobalt in these platelets increased the most in soda water, from 2.0 to 2.8. Since oxides with an oxidation number of 3 are known to be very good catalysts, this explains the improvement relative to the catalysts that formed in the other electrolytes.

Oxygen yield doubled

In soda water, the oxygen yield per cobalt ion decreased by a factor of 28 over 800 cycles, but at the same time 56 times as many cobalt atoms changed their oxidation number electrochemically. Macroscopically, the electrical current generation and thus the oxygen yield of the electrode doubled.

From needles to swiss cheese

In a nutshell, Risch explains: “Over time, the material becomes like Swiss cheese with many holes and a larger surface area where many more reactions can take place. Even if the individual catalytically active centres become somewhat weaker over time, the larger surface area means that many more potential catalytically active centres come into contact with the electrolyte and increase the yield.”

Risch suggests that such mechanisms can also be found in many other classes of materials consisting of non-toxic compounds, which can be developed into suitable catalysts.


Featured image:Crystalline cobalt arsenide is a catalyst that generates oxygen during electrolytic water splitting in the production of hydrogen. The material is considered to be a model system for an important group of catalysts whose performance increases under certain conditions in the course of electrolysis. Now a HZB-team headed by Marcel Risch has observed at BESSY II how two simultaneous mechanisms are responsible for this. The catalytic activity of the individual catalysis centres decreases in the course of electrolysis, but at the same time the morphology of the catalyst layer also changes. Under favourable conditions, considerably more catalysis centres come into contact with the electrolyte as a result, so that the overall performance of the catalyst increases.© CC BY 3.0, via Wikimedia Commons


Reference: Javier Villalobos, Diego González‐Flores, Roberto Urcuyo, Mavis L. Montero, Götz Schuck, Paul Beyer, Marcel Risch. Requirements for Beneficial Electrochemical Restructuring: A Model Study on a Cobalt Oxide in Selected Electrolytes. Advanced Energy Materials, 2021; 2101737 DOI: 10.1002/aenm.202101737


Produced by Helmholtz Zentrum Berlin

Chemists Produced An Unusual Organic Pigment, Which is “Switched On” By An Electrical Charge (Chemistry)

In photosynthesis and organic photovoltaics, pigment molecules convert light into electrical charge. A team of chemists have now produced an unusual organic pigment, which is “switched on” by an electrical charge to become a potent dye that absorbs light in the near-infrared range. The team’s study, published in the journal Angewandte Chemie, suggests potential applications in systems for electrophysical materials research, photovoltaics, and sensor technology.

Charged pigments with intense colors have been predominantly metal based. One well-known example is iron-based Berlin blue or Prussian blue, which is a rich, deep blue. In terms of their chemistry, dyes and pigments of this kind are symmetrical molecules, with one side having a higher charge than the other. The sides exchange electrons, and the molecule absorbs light that is at the same wavelength as this energy exchange.

Purely organic pigments with similarly intense colors are rare. Nonetheless, Francis D’Souza’s team from the University of North Texas, and colleagues, have now developed a modular organic molecular system precisely to meet this brief. Compared to metals, organic materials have the advantage of being easy to modify. The team chose to target modular construction of the dye molecules, to give customizable molecules that could potentially be given a wide variety of different properties.

The core of the new molecule was made of a red fluorescent dye molecule. The researchers then attached a two-part “push–pull”, or “donor–acceptor”, molecular system to both sides of this core. These systems were able to stabilize electrical charges under specific conditions.

In the uncharged state, the pigment was just a blue-colored dye molecule. But when an electronic charge was applied, it demonstrated its full capabilities. The team observed a new, intense absorption band, but not in the visible-light range. The new dye absorbed in the near-infrared range, i.e., in the transitional region between visible light and heat radiation on the electromagnetic spectrum.

It was only when the two donor–acceptor units resonated with each other that absorption became possible: “The additional, free electron shuffles between the two chemically equivalent entities revealing a new charge-transfer peak in the near-infrared region,” state the authors. The molecule had become a mixed valence compound, with similar properties to metal-based dye compounds.

These electronically switchable organic pigments could be excellent model substances for basic research, says D’Souza. They could be used to help better understand electron transfer, as found in photosynthesis, for example. In addition to their potential as research aids, they could be used as efficient electron-transporting material in photonic devices and are also suitable as markers for analyzing electron transitions.


Reference: Faizal Khan et al, Photoinduced Charge Separation Prompted Intervalence Charge Transfer in a Bis(thienyl)diketopyrrolopyrrole Bridged Donor‐TCBD Push‐Pull System, Angewandte Chemie International Edition (2021). DOI: 10.1002/anie.202108293


Provided by Wiley

Proteins Communicating Through the DNA Molecule Constitute A Newly Discovered Genetic “Switch” (Chemistry)

Proteins can communicate through DNA, conducting a long-distance dialogue that serves as a kind of genetic “switch,” according to Weizmann Institute of Science researchers. They found that the binding of proteins to one site of a DNA molecule can physically affect another binding site at a distant location, and that this “peer effect” activates certain genes. This effect had previously been observed in artificial systems, but the Weizmann study is the first to show it takes place in the DNA of living organisms.

A team headed by Dr. Hagen Hofmann of the Chemical and Structural Biology Department made this discovery while studying a peculiar phenomenon in the soil bacteria Bacillus subtilis. A small minority of these bacteria demonstrate a unique skill: an ability to enrich their genomes by taking up bacterial gene segments scattered in the soil around them. This ability depends on a protein called ComK, a transcription factor, which binds to the DNA to activate the genes that make the scavenging possible. However, it was unknown how exactly this activation works.

(l-r) Dr. Nadav Elad, Dr. Haim Rozenberg, Dr. Gabriel Rosenblum, Jakub Jungwirth and Dr. Hagen Hofmann. Twisting a rope from one end © Weizmann Institute of Science

Staff Scientist Dr. Gabriel Rosenblum led this study, in which the researchers explored the bacterial DNA using advanced biophysical tools – single-molecule FRET and cryogenic electron microscopy. In particular, they focused on the two sites on the DNA molecule to which ComK proteins bind.

They found that when two ComK molecules bind to one of the sites, it sets off a signal that facilitates the binding of two additional ComK molecules at the second site. The signal can travel between the sites because physical changes triggered by the original proteins’ binding create tension that is transmitted along the DNA, something like twisting a rope from one end. Once all four molecules are bound to the DNA, a threshold is passed, switching on the bacterium’s gene scavenging ability.

“We were surprised to discover that DNA, in addition to containing the genetic code, acts like a communication cable, transmitting information over a relatively long distance from one protein binding site to another,” Rosenblum says.

By manipulating the bacterial DNA and monitoring the effects of these manipulations, the scientists clarified the details of the long-distance communication within the DNA. They found that for communication – or cooperation – between two sites to occur, these sites must be located at a particular distance from one another, and they must face the same direction on the DNA helix. Any deviation from these two conditions – for example, increasing the distance – weakened the communication. The sequence of genetic letters running between the two sites was found to have little effect on this communication, whereas a break in the DNA interrupted it completely, providing further evidence that this communication occurs through a physical connection.

A 3D reconstruction from single particles of bacterial DNA (gray) and ComK proteins (red), imaged by cryogenic electron microscopy, viewed from the front (left) and at a 90 degrees rotation. ComK molecules bound to two sites communicate through the DNA segment between them © Weizmann Institute of Science

Knowing these details may help design molecular switches of desired strengths for a variety of applications. The latter may include genetically engineering bacteria to clean up environmental pollution or synthesizing enzymes to be used as drugs.

“Long-distance communication within a DNA molecule is a new type of regulatory mechanism – one that opens up previously unavailable methods for designing the genetic circuits of the future,” Hofmann says.

The research team included Dr. Nadav Elad of Weizmann’s Chemical Research Support Department; Dr. Haim Rozenberg and Dr. Felix Wiggers of the Chemical and Structural Biology Department; and Jakub Jungwirth of the Chemical and Biological Physics Department.


Reference: Rosenblum, G., Elad, N., Rozenberg, H. et al. Allostery through DNA drives phenotype switching. Nat Commun 12, 2967 (2021). https://doi.org/10.1038/s41467-021-23148-2


Provided by Weizmann Institute of Science

3D Ordered Channel Enhances Electrocatalysis (Chemistry)

A team led by Prof. YU Shuhong and Prof. HOU Zhonghuai from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences developed a theory-guided microchemical engineering (MCE) approach to manipulate the reaction kinetics and thus optimize the electrocatalytic performance of methanol oxidation reaction (MOR) in 3D ordered and crossed-linked channel (3DOC). The study was published in Journal of the American Chemical Society.

In the micro-nanoscale chemical engineering, two primary factors generally affect electrocatalytic kinetics at the electrode-electrolyte interface, i.e., the reaction on the electrode surface and mass transfer from the electrolyte to the near-surface and within the diffusion layer.

The surface reaction can be optimized by designing catalysts to nanoscale and increasing porosity to increase the active sites, as well as by adjusting the electronic structure and binding energy to increase the intrinsic activity of active sites. For macrocatalyst-involved electrocatalysis, the mass transfer from the bulk electrolyte to the catalyst surface is fast enough due to the negligible characteristic length of the diffusion layer compared to the catalyst size.

However, as the catalyst downsizes to the nanoscale, the mass transfer deviates greatly from the prediction by traditional theory owing to the comparable diffusion layer length. Therefore, a novel methodology of optimizing the kinetics of given catalysts remains urgent to maximize the electrocatalytic performances.

In this study, the researchers proposed a MCE approach involving catalyst process optimization. 

They selected platinum nanotubes (Pt NTs) as the model catalyst, employed air-liquid interface assembly and in-situ electrochemical etching to construct an ideal 3D ordered and crossed-linked channel, and used MOR as the model reaction to test the electrocatalytic performance of 3DOC. The measurement results indicated that there is an optimal channel size of 3DOC for MOR. 

Besides, based on the free energy density function of the electrode surface, the researchers established a comprehensive kinetic model coupling the surface reaction and mass transfer to accurately regulate the kinetics and optimize the MOR performance. The results showed that increasing the channel size of 3DOC promoted the mass transfer from the bulk electrolyte onto the catalyst surface, and weakened the vertical electron flow of the reaction in 3DOC. 

This competition between the mass transfer and surface reaction led to the best MOR performance on 3DOC with a specific size. Under the optimized channel size, mass transfer and surface reaction in the channeled microreactor were both well regulated. 

This structural optimization, different from the traditionally thermodynamic catalyst design, ensures a significant increase in heterogeneous electrocatalytic performance. Using proposed MCE coupling mass transfer and surface reaction, the kinetic optimization in electrocatalysis can be realized. This MCE strategy will bring about a leap forward in structured catalyst design and kinetic modulation.


Provided by Chinese Academy of Sciences

Scientists Show A Single Catalyst Can Perform The First Step of Turning CO2 Into Fuel in Two Very Different Ways (Chemistry)

Their work aims to bridge two approaches to driving the reaction – one powered by heat, the other by electricity – with the goal of discovering more efficient and sustainable ways to convert carbon dioxide into useful products.

Virtually all chemical and fuel production relies on catalysts, which accelerate chemical reactions without being consumed in the process. Most of these reactions take place in huge reactor vessels and may require high temperatures and pressures.

Scientists have been working on alternative ways to drive these reactions with electricity, rather than heat. This could potentially allow cheap, efficient, distributed manufacturing powered by renewable sources of electricity.

But researchers who specialize in these two approaches – heat versus electricity – tend to work independently, developing different types of catalysts tailored to their specific reaction environments.

A new line of research aims to change that. Scientists at Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory reported today that they have made a new catalyst that works with either heat or electricity. Based on nickel atoms, the catalyst accelerates a reaction for turning carbon dioxide into carbon monoxide – the first step in making fuels and useful chemicals from CO2.

The results represent an important step toward unifying the understanding of catalytic reactions in these two very different conditions with distinct driving forces at play, said Thomas Jaramillo, professor at SLAC and Stanford and director of the SUNCAT Institute for Interface Science and Catalysis, where the research took place.

“This is a rarity in our field,” he said. “The fact that we could bring it together in one framework to look at the same material is what makes this work special, and it opens up a whole new avenue to look at catalysts in a much broader way.”

The results also explain how the new catalyst drives this key reaction faster when used in an electrochemical reactor, the research team said. Their report appeared in the print edition of Angewandte Chemie this week.

Toward a sustainable chemistry future

Finding ways to transform CO2 into chemicals, fuels, and other products, from methanol to plastics and synthetic natural gas, is a major focus of SUNCAT research. If done on a large scale using renewable energy, it could create market incentives for recycling the greenhouse gas. This will require a new generation of catalysts and processes to carry out these transformations cheaply and efficiently on an industrial scale – and making those discoveries will require new ideas.

In search of some new directions, SUNCAT formed a team of PhD students involving three research groups in the chemical engineering department at Stanford: Sindhu Nathan from Professor Stacey Bent’s group, whose research focuses on heat-driven catalytic reactions, and David Koshy, who is co-advised by Jaramillo and Professor Zhenan Bao and has been focusing on electrochemical reactions.

Nathan’s work has been aimed at understanding heat-driven catalytic reactions at a fundamental, atomic level.

“Heat-driven reactions are what’s commonly used in industry now,” she said. “And for some reactions, a heat-driven process would be challenging to implement because it may require very high temperatures ­­and pressures to get the desired reaction to proceed.”

Driving reactions with electricity could make some transformations more efficient, Koshy said,  “because you don’t have to heat things up, and you can also make reactors and other components smaller, cheaper and more modular ­– plus it’s a good way to take advantage of renewable resources.”

Scientists who study these two types of reactions work in parallel and rarely interact, so they don’t have many opportunities to gain insights from each other that might help them design more effective catalysts.

But if the two camps could work on the same catalyst, it would establish a basis for unifying their understanding of reaction mechanisms in both environments, Jaramillo said. “We had theoretical reasons to think that the same catalyst would work in both sets of reaction conditions,” he said, “but this idea had not been tested.”

A new avenue for catalyst discovery

For their experiments, the team chose a catalyst Koshy recently synthesized called NiPACN. The active parts of the catalyst – the places where it grabs passing molecules, gets them to react and releases the products – consist of individual nickel atoms bonded to nitrogen atoms that are scattered throughout the carbon material. Koshy’s research had already determined that NiPACN can drive certain electrochemical reactions with high efficiency. Could it do the same under thermal conditions?

A ball-and-stick illustration of a single nickel atom (green) bonded to nitrogen atoms (blue) on the surface of a carbon material. The arrangement allows the nickel atoms to catalyze two types of reactions involved in making fuel from CO2.
This illustration shows one of the active sites of a new catalyst that accelerates the first step in making fuels and useful chemicals from carbon dioxide. The active sites consist of nickel atoms (green) bonded to nitrogen atoms (blue) and scattered throughout a carbon material (gray). SLAC and Stanford researchers discovered that this catalyst, called NiPACN, works in reactions driven by heat or electricity – an important step toward unifying the understanding of catalytic reactions in these two very different reaction environments. (Greg Stewart/SLAC National Accelerator Laboratory)

To answer this question, the team took the powdered catalyst to SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL). They worked with Distinguished Staff Scientist Simon Bare to develop a tiny reactor where the catalyst could expedite a reaction between hydrogen and carbon dioxide at high temperatures and pressure. The setup allowed them to shine X-rays into the reaction through a window and watch the reaction proceed.

In particular, they wanted to see if the harsh conditions inside the reactor changed the catalyst as it facilitated the reaction between hydrogen and CO2.

“People might say, how do you know the atomic structure didn’t change, making this a slightly different catalyst than the one we had previously tested in electrochemical reactions?” Koshy said. “We had to show that the nickel reaction centers still look the same when the reaction is finished.”

That’s exactly what they found when they examined the catalyst in atomic detail before and after the reaction with X-rays and transmission electron microscopy.

Going forward, the research team wrote, studies like this one will be essential for unifying the study of catalytic phenomena across reaction environments, which will ultimately bolster efforts to discover new catalysts for transforming the fuel and chemical industries.

Parts of this study were carried out at the Stanford Nano Shared Facilities, the Canadian Center for Electron Microscopy and the Center for Nanophase Materials Sciences (CNMS) at DOE’s Oak Ridge National Laboratory. CNMS and SSRL are DOE Office of Science user facilities. Major funding came from the DOE Office of Science, including support from the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub.

Citation: David M. Koshy et al., Angewandte Chemie, 06 April 2021 (10.1002/anie.202101326)


Provided by SLAC Stanford

Researchers Develop Dynamic Trimer Catalyst for Efficient Hydrogenations (Chemistry)

A team led by Prof. LU Junling and Prof. WEI Shiqiang from University of Science and Technology of China (USTC) of the Chinese Academy of Sciences (CAS) developed a dynamic trimer catalyst for highly efficient hydrogenations by synergizing metal-support interactions and spatial confinement. This catalyst showed good activity, selectivity and stability in selective hydrogenation of acetylene and 1,3 butadiene in olefin rich atmosphere. The study was published in Nature Nanotechnology.

Supported atomic dispersion catalysts (SADCs) have attracted extensive attention due to their high atomic utilization efficiency and unique catalytic performance. Compared with those of traditional metal nanoparticle catalysts, the active sites of SADCs are isolated from each other. They have uniform structures, which makes these catalysts show high selectivity and good anti-carbon deposition performance in hydrocarbon selective hydrogenation.

However, due to the rapid increase in surface free energy, it is a great challenge to obtain catalysts with high loading and high stability under reaction conditions. Among the two standard methods, strong metal-support interactions (MSIs) may lead to a significant reduction in reaction activity, while microporous confined active metals may affect the mass transfer of the reaction. Therefore, the rational design of high loading, high stability and high activity SADCs is in urgent.

The research team led by Prof. LU prepared high loading Ni1Cu2 trimer catalyst on g-C3N4 support, utilizing the strong metal-support interaction between Cu, Ni and rich nitrogen on g-C3N4 support, as well as the confinement of pre-deposited Cu to Ni atoms. The loading of Ni and Cu were 3.1 wt.% and 8.1 wt.% respectively.

In the selective hydrogenation of acetylene in ethylene rich atmosphere, the prepared Ni1Cu2 trimer structure catalyst showed excellent catalytic performance in activity, selectivity and stability. The catalyst realized the complete conversion of acetylene at about 170 ℃, maintains 90% ethylene selectivity, and can maintain stability for more than 350 hours.

The excellent carbon deposition resistance of the above catalyst was further proved by in situ synchrotron radiation technology. Prof. WEI revealed the coordination structure information of Ni in hydrogen and acetylene hydrogenation atmosphere with the help of in-situ X-ray absorption spectroscopy (XAFS).

In-situ synchrotron radiation vacuum ultraviolet photoionization mass spectrometry and in-situ thermogravimetry showed that there was no carbon deposition in the reaction process. These characterizations indicated that the possible structure of the catalyst is Cu-OH-Ni-OH-Cu. In-situ diffuse reflectance infrared Fourier transform spectroscopy (DIRTFS) of acetylene hydrogenation reaction showed that OH groups were directly involved in the catalytic reaction.

Furthermore, a team led by Prof. LI Weixue from Dalian Institute of Chemical Physics of CAS determined the spatial configuration of Cu-OH-Ni-OH-Cu structure through theoretical calculation. They revealed that the covalent bond interaction between the three atoms of Ni1Cu2 and the support, and the confinement of Cu atoms on both sides to the intermediate active Ni atom, are the internal reasons for the high stability of the catalyst, and the isolated active Ni site limits the co-adsorption of acetylene and ethylene, making it have excellent carbon deposition resistance.

The coordination of metal-support interaction and atomic confinement brings new insights into dynamic structural changes in the catalytic process, which can not only improve the adsorption of reaction molecules and catalytic activity, but also maintain high stability. The single Ni site makes the catalyst show high selectivity and high carbon deposition resistance.

Featured image: Structural characterization: A representative HAADF-STEM image of Ni1Cu2/g-C3N4 with atomic resolution, where isolated atoms, triangular trimers and linear trimers are highlighted by dashed yellow circles, red triangles and green rectangles, respectively. © Authors


Reference: Gu, J., Jian, M., Huang, L. et al. Synergizing metal–support interactions and spatial confinement boosts dynamics of atomic nickel for hydrogenations. Nat. Nanotechnol. (2021). https://doi.org/10.1038/s41565-021-00951-y


Provided by Chinese Academy of Sciences