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Версия для печати | Главная > Центр > Научные советы > Научный совет по катализу > ... > 2016 год >  № 78

№78

 

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  • Валентин Николаевич Пармон
    Лауреат премии «Глобальная энергия»
  • Владимир Борисович Казанский
    К 85-летию со дня рождения
  • Усеин Меметович Джемилев
    К 70-летию со дня рождения
  • II Научно-технологический симпозиум
    «Нефтепереработка: катализаторы и гидропроцессы»
  • 4-я Международная школа-конференция
    «Каталитический дизайн. От исследований на молекулярном уровне к практической реализации»
  • За рубежом
  • Приглашения на конференции



Валентин Николаевич Пармон
Лауреат премии «Глобальная энергия»

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Владимир Борисович Казанский
К 85-летию со дня рождения

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Усеин Меметович Джемилев
К 70-летию со дня рождения

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II Научно-технологический симпозиум
«Нефтепереработка: катализаторы и гидропроцессы»

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4-я Международная школа-конференция
«Каталитический дизайн. От исследований на молекулярном уровне к практической реализации»

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Chemists announce the end of the innocence
for cyclopentadienyl

Supposedly unreactive ligand caught in the act of protonation, suggesting new opportunities in catalyst design

Discovery of the rhodium Cp*H intermediate has revealed a new type of metal-ligand cooperation that could benefit catalyst design.

Sometimes chemists set themselves up for a surprise. Following sets of experiments in which something doesn’t happen and doesn’t seem likely to happen, they soon believe it never will. Until it does.

Two research groups have independently uncovered one of these surprises involving the popular transition-metal ligand pentamethylcyclopentadienyl, or Cp*.

Chemists have traditionally thought of cyclopentadienyl ligands as being “innocent,” which means they offer electronic support to a metal catalyst but generally don’t do anything chemically. The two groups were studying reactions involving Cp*Rh(bipyridine), often used in hydrogenation reactions and in hydrogen-forming reactions, when they found that the expected metal hydride intermediate was followed by formation of an unexpected intermediate in which the hydrogen had migrated to one of the carbon atoms in the Cp* ring.

“These two reports showing that the seemingly innocent Cp* ligand can reversibly form a C–H bond by proton transfer from rhodium hydride are remarkable,” comments chemistry professor David Milstein of the Weizmann Institute of Science, who was not involved in the research. “Considering the ubiquity of cyclopentadienyl metal complexes in homogeneous catalysis, this pathway should be seriously considered in the design and understanding of reactions in which proton/hydride transfer may be involved.”

Alexander J. M. Miller of the University of North Carolina, Chapel Hill, who led one of the teams, says chemists had previously worked out mechanisms involving hydride intermediates that made sense and thought the story ended there. But they did not exercise due diligence and poke around enough to see that a protonated Cp* intermediate, denoted Cp*H, could be involved as well. “What’s more surprising,” Miller points out, “the Cp*H complex is not a dead end. This diene complex is still an active catalyst.”

Miller’s group came across the Cp*H intermediate while investigating hydride transfer reactions with the cellular enzyme cofactor nicotinamide adenine dinucleotide (NAD+) to form the reduced product NADH (Chem. Commun. 2016, DOI: 10.1039/c6cc00575f).

Meanwhile, a team led by Harry B. Gray and Jay R. Winkler at Caltech and James D. Blakemore at the University of Kansas discovered the Cp*H intermediate while investigating the coupling of protons to form H2 when treating Cp*Rh(bipyridine) with acid (Proc. Natl. Acad. Sci. USA 2016, DOI: 10.1073/pnas.1606018113).

“These discoveries illustrate the versatility of mechanisms by which protons and hydrides can be delivered to and from metals,” comments Morris Bullock, director of the Center for Molecular Electrocatalysis at Pacific Northwest National Laboratory. “While these examples are for rhodium, the prevalence of cyclopentadienyl ligands in organometallic catalysts raises the possibility that similar reactivity could be widespread and involve other metals, and may be intentionally exploited in the design of new catalysts.”

 

Proposed names for new periodic table elements announced by IUPAC

Elements 113, 115, 117, and 118 are likely to become nihonium, moscovium, tennessine, and oganesson

Nihonium, moscovium, tennessine, and oganesson are the recommended names for elements 113, 115, 117, and 118, the International Union of Pure & Applied Chemistry (IUPAC) announced today.

IUPAC officially added the elements to the periodic table at the end of 2015. Those credited with discovering the elements get the rights to propose permanent names and symbols. The names will be finalized after public review and formal approval by the IUPAC Council.

The proposed names for elements 113, 115, 117, and 118 are nihonium, moscovium, tennessine, and oganesson.

According to recommendations published by IUPAC in April, elements can be named after a mythological concept, a mineral, a place or country, a property, or a scientist (Pure Appl. Chem.2016, DOI: 10.1515/pac-2015-0802). Element names should also “have an ending that reflects and maintains historical and chemical consistency,” the recommendations say. “This would be in general ‘-ium’ for elements belonging to groups 1–16, i.e. including the f-block elements, ‘-ine’ for elements of group 17 and ‘-on’ for elements of group 18.”

Japan’s RIKEN research institution was credited with discovering element 113. Nihonium (Nh) comes from Nihon, which is one of two ways to say “Japan” in Japanese. It is the first element discovered in and named after an Asian country.

The discoveries of the other three elements were credited to European-American collaborations involving Russia’s Joint Institute for Nuclear Research and the U.S. Lawrence Livermore and Oak Ridge national laboratories.

Moscovium (Mc) recognizes Moscow and its surrounding area “and honors the ancient Russian land that is the home of the Joint Institute for Nuclear Research,” says an IUPAC press release.

Tennessine (Ts) “is in recognition of the contribution of the Tennessee region, including Oak Ridge National Laboratory, Vanderbilt University, and the University of Tennessee at Knoxville, to superheavy element research, including the production and chemical separation of unique actinide target materials for superheavy element synthesis,” the release also says.

Oganesson (Og) honors Russian nuclear physicist Yuri T. Oganessian, who leads the Flerov Laboratory of Nuclear Reactions at the Joint Institute for Nuclear Research. He joins his countrymen Vasili Samarsky-Bykhovets (samarium), Dmitri Mendeleev (mendelevium), and Georgy Flerov (flerovium) in having a namesake element.

In April, Nature Chemistry published element name predictions by freelance writer Philip Ball, Worcester Polytechnic Institute chemistry professor Shawn Burdette, chemistry writer and blogger Kat Day, UCLA lecturer and author Eric Scerri, and Stockholm University chemistry researcher Brett Thornton (Nat. Chem. 2016, DOI: 10.1038/nchem.2482).

Burdette came closest to the proposed names, suggesting nipponium (Nippon is the other way to say “Japan” in Japanese), moscovium, tennessine, and oganesson. “After my element prediction success, I’m retiring from chemistry,” he joked on Twitter. “I can’t see my career going any higher.”

 

Iron-sulfur gel provides possible green route to ammonia

Chalcogel catalyst reduces dinitrogen in water under ambient temperature and pressure

To produce the large quantities of fertilizer needed to sustain global food production, industry relies on the Haber-Bosch process to split dinitrogen from the air to synthesize ammonia. But to generate the high temperatures and pressures needed for the reaction, ammonia plants consume fossil fuels and, as a result, contribute significantly to greenhouse gas emissions.

This chalcogel, a network of Fe4S4 clusters linked with [Sn2S6]4– anions, uses visible light to convert N2 to NH3.

Researchers want to develop a green alternative to the Haber-Bosch process. In a new effort, Mercouri G. Kanatzidis and George C. Schatz of Northwestern University and coworkers used iron-sulfur (Fe4S4) clusters, found naturally in the nitrogenase enzymes bacteria use to split dinitrogen, to make a light-driven catalyst that converts N2 to NH3 in water at ambient temperature and pressure (Proc. Natl. Acad. Sci. USA 2016, DOI: 10.1073/pnas.1605512113).

After synthesizing the Fe4S4 clusters, the researchers link them with [Sn2S6]4– anions and form the complex into a chalcogel, a foamy gel containing the chalcogen element sulfur. The black material absorbs visible light and uses that energy to break the N≡N triple bond, one of the strongest in chemistry. The nitrogen atoms then combine with water-derived hydrogen to make NH3.

Other researchers have developed transition metal-N2 complexes that convert N2 to NH3, but those systems typically require organic solvents, low temperatures, and/or high pressures. Some previously developed light-based systems also can reduce N2, but the chalcogel is 10 times as efficient.

Hybrid synthetic-biological approaches, such as a nanorod-nitrogenase system (Science 2016, DOI: 10.1126/science.aaf2091, C&EN, April 25, page 9), are much more efficient than the chalcogel system. But the hybrid approach has limitations: Obtaining nitrogenase from organisms is difficult, and the enzymes are not stable for more than a few hours after isolation, Kanatzidis says.

The chalcogel is orders of magnitude less efficient than the Haber-Bosch process. But unlike the Haber-Bosch process or metal-N2 complexes, the chalcogel catalyst can fix N2 under quite mild conditions using light as the only driving force, comments photocatalysis specialist Lizhi Zhang of Central China Normal University. Understanding of the chalcogel mechanism remains fragmentary at this point, he says, so further study is still needed to find ways to optimize the catalyst.

Catalysis expert Patrick Holland of Yale University says it isn’t fair to compare the efficiency of the chalcogel to the Haber-Bosch method because the industrial process has been optimized for more than a century. “The chalcogel already makes reasonable amounts of ammonia, so it’s a valid first step toward using light to drive N2 reduction,” he says. “The catalyst is very modifiable, so it could in principle be improved a lot in the long run.”

 

Harry Kroto’s last words on carbyne

Simulations suggest that carbon’s one-dimensional allotrope remains a theory

Sixteen days before his death, Nobel Laureate Harold W. Kroto published a study with colleagues at Arizona State University that ends thusly: “The bottom line is that carbyne, the linear carbon allotrope, remains as elusive and theoretical as ever.”

A crystal structure of gold-stabilized carbon chains proposed by Kroto, Buseck, and Tarakeshwar. The box shows the unit cell of the “pseudocarbyne.”

The team, led by Peter R. Buseck and Pilarisetty Tarakeshwar of Arizona State, used density functional theory to perform simulations that suggest a recent report of carbyne creation overlooks an important element, namely gold.

Last October, Guowei Yang of Sun Yat-sen University and coworkers reported that they had made carbyne crystals with the help of gold (Sci. Adv. 2015, DOI: 10.1126/sciadv.1500857). Firing a laser at a gold target in ethanol forms a small plasma above the target where carbyne can form, the team said.

Although transmission electron microscopy revealed that gold nanoparticles rested on the exterior of the crystal structures, further analyses, including Raman spectroscopy, led Yang’s team to conclude that gold was not integrated into the crystals. In other words, the substance was carbyne, a string of carbon atoms bonded together with alternating single and triple bonds.

The Arizona State researchers and Kroto contested the report with a letter to Science Advancesin January and now have data from simulations that indicate that the material is composed of carbon chains stabilized by gold nanoparticles (J. Phys. Chem. Lett. 2016, DOI: 10.1021/acs.jpclett.6b00671). The misidentification of gold-stabilized pseudocarbyne as pure carbyne can be chalked up to misinterpreted data, Buseck says.

For example, Yang’s team stated that a peak in an experimental Raman spectrum corresponded to carbon-carbon single bonds in carbyne. Yet the simulations did not reproduce this peak unless linear carbon chains were attached to gold particles. The appearance of this peak is likely due to the same plasmonic effect that metals provide in surface-enhanced Raman spectroscopy, Tarakeshwar says.

Yang stands by his team’s initial assessment, however. Different metal targets, such as palladium, produced crystals that yielded identical spectra, he says, although this was not shown in the October study. Different metals would have different spectra were they part of the crystal. Yang says the computational work is “just a theoretical simulation, not supported by any experimental observations.”

Experimental measurements do exist, but all the data were collected by Yang’s team, Buseck states. He adds that he has unsuccessfully tried to obtain samples from Yang to analyze. Although metal-stabilized carbon chains are not carbyne, they could be an interesting new class of materials, but that’s just speculation until there is more experimental evidence, Buseck says.

Rik R. Tykwinski, who studies long carbon chains at Friedrich Alexander University, Erlangen-Nuremberg, says he fully believes the work done by Kroto, Buseck, and Tarakeshwar. “Kroto often provided the voice of common sense in this field, sometimes quietly and sometimes quite vocally,” Tykwinski says. With this last publication, he adds, “Kroto’s legacy lives on.”

 

Carbon dioxide hydrogenated to methanol on large scale

Supported indium oxide catalyst could boost lab-scale process to an industrial level


Vacancies on the surface of a ZrO2-supported In2O3  catalyst play a key role in converting CO2 to CH3OH.

Manufacturers generally produce methanol, a key chemical building block and fuel, from petroleum-derived syngas, a mixture of carbon monoxide and hydrogen. Direct hydrogenation of the greenhouse gas carbon dioxide would be a more efficient and environmentally sustainable route to methanol. But practical catalysts capable of making this reaction happen on an industrial scale have been unavailable.

Scientists had shown earlier that indium oxide catalyzes the direct hydrogenation of CO2 to CH3OH on a lab scale. Javier Pérez-Ramírez of ETH Zurich and coworkers now demonstrate that zirconium oxide-supported In2O3 catalyzes the process under conditions similar to those required for industrial production (Angew. Chem. Int. Ed. 2016, DOI: 10.1002/anie.201600943).

The supported catalyst can convert CO2 and H2 to CH3OH over at least 1,000 hours of continuous use and outperforms most other hydrogenation catalysts. The researchers proved experimentally that oxygen vacancies on the catalyst surface make the reaction possible—a mechanism predicted by theoretical calculations from a team led by Qingfeng Ge of Southern Illinois University and Tianjin University (ACS Catal. 2013, DOI: 10.1021/cs400132a).

The ETH Zurich group optimized the reaction by adding CO to the starting materials and varying the temperature, both of which tuned the number of vacancies. The technique is “a long-sought breakthrough with the potential to realize continuous CO2 conversion to methanol on a commercial scale,” Ge says.

Pérez-Ramírez and coworkers have filed patent applications on the technology in collaboration with French energy firm Total, which has started pilot studies of the process.

Chemical & Engineering News


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