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Версия для печати | Главная > Центр > Научные советы > Научный совет по катализу > ... > 2013 год > № 66

№ 66

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  1. Валентин Николаевич Пармон —
    к 65-летию со дня рождения
  2. 55 лет Институту катализа им. Г.К. Борескова СО РАН
  3. 15-й Международный Конгресс по катализу
  4. XX Международная конференция
    по химическим реакторам ХИМРЕАКТОР-20
  5. За рубежом
  6. Приглашения на конференции
  7. Новый электронный журнал
    «Технологии добычи и использования углеводородов»



Валентин Николаевич Пармон — к 65-летию со дня рождения

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55 лет Институту катализа им. Г.К. Борескова СО РАН

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15-й Международный Конгресс по катализу

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XX Международная конференция по химическим реакторам ХИМРЕАКТОР-20

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За рубежом

Fluoride’s Unexpected Role In Photocatalysis

Materials: Acid’s surface residue, not just the catalyst, should get credit

By Mitch Jacoby

Titanium dioxide’s knack for mediating chemical reactions upon exposure to light has made the material a popular photocatalyst for various applications, such as sterilizing glass and other surfaces and splitting water to make hydrogen.

Researchers reported a few years ago that using hydrofluoric acid to synthesize nanocrystalline TiO2 significantly boosts its catalytic activity by exposing the material’s most active crystal faces. But a study just published in ACS Catalysis indicates the enhanced activity is mainly due to residual HF, not any particulars of crystal faceting (2013, DOI: 10.1021/cs400216a).

A crystal’s faces may be identical chemically, but structural and electronic differences can lead to differences in surface energy and catalytic activity. TiO2s so-called (001) face, for example, is known to be more active than other TiO2 faces. For that reason, researchers commonly use HF to synthesize TiO2 because the acid yields a large fraction of (001)-faceted crystals.

Liqiang Jing of Heilongjiang University in China and coworkers confirmed via X-ray diffraction that increasing HF concentration during synthesis increases the fraction of crystals exhibiting (001) facets. And in degradation tests using acetaldehyde and phenol as model pollutants, the team confirmed that the most active TiO2 catalysts are indeed the ones with primarily exposed (001) faces. However, when the group removed surface fluoride—confirmed by surface analyses—catalytic activity plummeted despite the large fraction of (001) facets. The group proposes that surface-bound HF greatly enhances adsorption of O2 molecules, which capture electrons liberated by light and are thereby stimulated to react.

Can Li, a research director at China’s Dalian Institute of Chemical Physics and an expert in this area, says the work is convincing. And Baibiao Huang of Shandong University in China notes that the finding may be applicable to other oxide semiconductor photocatalysts with high-energy surfaces. “For that reason, it is of great significance,” he says.

Ethanol-To-Butanol Conversion A Biofuel Plus

ACS Meeting News: Catalytic process creates butanol as a better biofuel option for gasoline

By Stephen K. Ritter

Ethanol derived from corn and sugarcane has been a blessing when it comes to transportation fuels. The millions of gallons of ethanol added to gasoline in the U.S. each year help oxygenate the fuel to limit pollution and stretch petroleum supplies. One draw-back is that ethanol reduces the energy content of gasoline, resulting in fewer miles per gallon when you are on the road.

Chemists and chemical engineers who are at work to find improved biofuels have decided that butanol is a better option than ethanol. The researchers are now trying to settle on the best way to mass produce butanol to start replacing ethanol.

One solution offered by Duncan F. Wass and his research team at the University of Bristol, in England, is a new family of ruthenium catalysts that readily convert ethanol to butanol. Wass presented his group’s latest results during a session in the Division of Catalysis Science & Technology at the American Chemical Society national meeting this week in New Orleans.

Butanol with two additional carbons has about 30% higher energy content per gallon than ethanol, Wass explained. He noted that efforts are under way in the Midwest to retrofit some ethanol facilities to butanol production. But with his group’s new catalysts, ethanol facilities wouldn’t need to be altered—the ethanol produced in the facilities could simply be upgraded to butanol in an additional condensation reaction step.

“Our technology is an indirect path to butanol,” Wass told C&EN. “But it’s flexible because it can upgrade ethanol made from either petroleum or biomass.” The ruthenium catalysts are very efficient, he added, producing butanol with 95% selectivity and ethanol conversion of better than 40%.

The ethanol-to-butanol catalytic process is complementary to the fermentation of sugars directly into butanol using engineered microbes, which is being developed by other scientists, Wass noted. But fermentation to butanol has a few limitations, including low conversion of around 4 to 5% because of the inherent toxicity of butanol to the microorganisms.

The Bristol catalytic process has been patented, and Wass is working with scientists at BP Biofuels to develop the technology. “The new catalysts, while at an early stage, have much in common with modern petrochemical processing,” commented Ian Dobson of Butamax Advanced Biofuels, a joint venture created by BP and DuPont, and technology adviser to BP Biofuels. “The catalysts hold the prospect of being able to convert ethanol to butanol in high yield and at large scale.”

Titanium Dioxide Coating Improves Efficiency Of Graphene-Based Solar Cells

Solar Energy: The antireflective layer could lead to efficient, low-cost devices

By Prachi Patel

Adding a layer of graphene to silicon solar cells cuts the devices’ potential costs. Such graphene-silicon cells, though, convert light to electricity with low efficiencies. A team of researchers now has boosted this efficiency by giving the solar cells an antireflective veneer (Nano Lett., DOI: 10.1021/nl400353f).

Commercially available silicon solar cells convert about 15% of incoming light energy into electrical energy. But the cells are expensive to fabricate in part because of the costs of adding a thin, charge-carrying silicon layer on top, a process that requires high temperatures. The devices are also capped with a grid of thin silver wires that serve as an electrode.

Blue Hue
A 65-nm-thick titanium dioxide layer coats a graphene-silicon solar cell. The cell appears blue, because the coating has reduced visible light reflection from the silicon surface.

Researchers led by Anyuan Cao of Peking University, in China, recently found that a graphene film can replace this charge-carrying layer, as well as serve as electrodes for the devices. Creating such films is a relatively inexpensive process. However, those graphene-silicon devices have efficiencies that top out around 8.6%, less than the 10% considered viable for commercial cells.

So Cao and his colleagues, including Hongbian Li of the National Center for Nanoscience and Technology, in Beijing, and Hongwei Zhu, of Tsinghua University, turned to an old trick used to improve the efficiency of silicon solar cells. They coated the graphene-silicon structure with a 65-nm-thick layer of titanium dioxide. This coating decreased the amount of visible light reflected from the silicon surface from over 30% to less than 10%. Less re-flected light meant the device absorbed more light to convert to electricity, and the efficiency of the cells jumped to 14.6%.

The researchers currently grow the graphene layer on copper foil using chemical vapor deposition, which requires relatively high temperatures, and then transfer it to the top of a silicon wafer. Cao points out that they could further lower costs for the cells by painting or spaying a graphene solution onto the silicon wafers to produce the graphene film.

The graphene-silicon cells are several square millimeters in area. To be more practical, the devices need to be larger, Cao says, which presents another hurdle his team must face. As the area of a graphene film increases, so does its resistance, making the solar cells less efficient.

The researchers also need to make the devices more stable, says Yongsheng Chen, a chemistry professor at Nankai University, in China: The device efficiency drops after sitting in the air for 20 days. Nevertheless, he says that the work is significant for its use of two abundant materials—silicon and graphene—to make solar cells without the need for high-temperature processing. “This, combined with the high power-conversion efficiency, makes it potentially attractive for next-generation solar cell technology.”

Bold Territory For Polymers

Materials Science: Chemists push the bounds of what’s structurally possible in polymer architectures

By Stephen K. Ritter

Polymer structures have traditionally been relatively simple, usually a linear chain made from a single type of monomer or perhaps a copolymer chain made from two or three types of monomers. Sometimes chemists might graft a side chain onto the polymer or cross-link the chains to form polymer networks.

But that old simplicity is falling by the wayside. Advances in polymer synthetic techniques that allow better control over the size and shape of polymers are allowing researchers to think more like architects to dream up exotic new polymer designs. One goal of the work is to create macromolecules with functional properties for drug delivery, catalysis, chemical sensing, and other applications.

Several polymer science experts have now pooled their talents to find out how far they can push the limits of polymer architecture (J. Am. Chem. Soc., DOI: 10.1021/ja400890v).

The research team is led by E. W. (Bert) Meijer of Eindhoven University of Technology, in the Netherlands; Krzysztof Matyjaszewski of Carnegie Mellon University; and Sergei S. Sheiko of the University of North Carolina, Chapel Hill. As a first test, the researchers set out to make a mega-sized copolymer consisting of a bottlebrush polymer with a collapsible tail, combining two of the recently developed advanced structural features in macromolecules.

Bottlebrush polymers are cylindrical in shape and have densely spaced side chains that resemble bristles on a brush. As for the polymer tail, chemists have created polymers with hydrogen-bonding capabilities that reversibly crumple into nanoparticles, a process similar to protein folding.

The team built the copolymer in four steps from methacrylate-based monomers. The process included grafting side chains onto the polymer and a postpolymerization step in which they added a hydrogen-bonding segment to a tail-like side chain. When the researchers shine ultraviolet light on the polymer, the tail sheds a protecting group to expose the hydrogen-bonding units. The end result is an unprecedented bottlebrush polymer with appended nanoparticles.

“This is an amazing example of how precision polymer synthesis techniques can be applied to the preparation of remarkably complex and functional macromolecular architectures,” says Marc A. Hillmyer, director of the University of Minnesota’s Center for Sustainable Polymers. “Combining controlled radical polymerizations, block copolymers, postpolymerization modifications, and triggered hydrogen-bonding interactions certainly pushes the limits of polymer synthesis.”

“A major challenge with synthetic polymers is that they are not as smart as well-defined natural systems, such as proteins,” says Craig J. Hawker, director of the Materials Research Laboratory at the University of California, Santa Barbara. “They do not fold in controllable ways or give unique molecular objects based on their synthetic design. I am convinced this work will spur other researchers to further push the frontiers of polymer synthesis, the ultimate goal being to design synthetic materials with many of the capabilities and properties of natural materials.”

Chemical & Engineering News


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