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Here comes the sun – visible light promoted MOF catalysts

Posted on behalf of Tien Nguyen

Tien Nguyen is working towards her PhD in David Nicewicz’s research group at the University of North Carolina at Chapel Hill, USA. Her current area of research focuses on anti-Markovnikov hydroamination of alkenes using photoredox catalysis.


To satisfy the energy demands of an ever-increasing population, it is critical to develop renewable energy sources. Photocatalytic hydrogen production from water stands out among the alternatives as this process yields a clean energy source and relies on visible light, which has exciting implications for harnessing the power of the sun.

In this article, Matsuoka and co-workers report efficient hydrogen production employing a Pt-deposited amino-functionalized Ti metal organic framework catalyst (Pt/Ti-MOF-NH2) in aqueous triethanolamine (TEOA) and visible light. The organic linker serves to absorb the light and donate electrons to the titanium-oxo cluster with TEOA present as a sacrificial electron donor. An optimal loading of 1.5 wt% was found for the Pt cocatalyst, which is proposed to trap the photogenerated electrons and suppress unproductive electron-hole recombination.

The authors also successfully extended this system to the reduction of nitrobenzene, providing an environmentally benign alternative to existing methods. They found that the photocatalyst could be reused at least three times with no appreciable loss in activity. These findings hold promise for the development of highly efficient photocatalysts promoted by naturally abundant sunlight.

Read the full article here:

Efficient hydrogen production and photocatalytic reduction of nitrobenzene over a visible-light-responsive metal–organic framework photocatalyst
Takashi Toyao, Masakazu Saito, Yu Horiuchi, Katsunori Mochizuki, Masatoshi Iwata, Hideyuki Higashimura and Masaya Matsuoka

Catal. Sci. Technol., 2013, DOI: 10.1039/c3cy00211j

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This one is “just right” – Nanoparticle size effects in CO methanation

Posted on behalf of Tien Nguyen, web-writer for Catalysis Science & Technology

Tien Nguyen is working towards her PhD in David Nicewicz’s research group at the University of North Carolina at Chapel Hill, USA. Her current area of research focuses on anti-Markovnikov hydroamination of alkenes using photoredox catalysis

On May 8th 2013, the NOAA’s (National Oceanic & Atmospheric Administration) Mauna Loa observatory recorded a daily mean concentration of CO2 in excess of 400 ppm, a record high since mankind’s appearance on the planet. As carbon dioxide levels continue to increase at an alarming rate, many laboratories are engaging in alternative energy research to mitigate this problem. 

One such solution involves the methanation reaction, which converts syngas (CO + H2) to synthetic natural gas (CH4). This reaction is highly sought after given that energy from burning natural gas releases approximately 30-45% less carbon dioxide than fossil fuels. 

In this article, researchers evaluated a series of α-Al2O3-supported Ni catalysts of various Ni particle size (5-10, 10-20 and 20-35 nm) for their catalytic efficiency in the methanation reaction. At high temperatures (300-600 °C), ambient pressure and high WHSV (weight hourly space velocity of 240,000 mL/g/h), Ni particles sized 10-20 nm exhibited the highest CO conversion, CH4 yield and turnover frequency, as well as the lowest carbon deposition. 

 

They hypothesized that the smaller Ni particles exhibit more carbon deposition because they have more exposed step edges, which are more susceptible to such formations. They also proposed that Ni particles that are too large may lead to the undesirable growth of carbon nanofibers. Having identified the optimal Ni particle size, the next advancement for the CO methanation reaction lies in improving the stability of these catalysts. 

Read the article here: 

Effect of nickel nanoparticle size in Ni/α-Al2O3 on CO methanation reaction for the production of synthetic natural gas
Jiajian Gao, Chunmiao Jia, Meiju Zhang, Fangna Gu, Guangwen Xua and Fabing Su

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A Green Cocktail for the Industrial Synthesis of Lactic acid

Posted on behalf of Shreesha Bhat

Lactic acid is a versatile chemical having wide applications in food, cosmetics and chemical industry. They are generally prepared by acid catalyzed reactions of hexoses and trioses, and one such triose i.e. glycerol has been found to be produced in surplus amounts as byproducts in production of biodiesel. Glycerol offers great potential to be used as a renewable feedstock for the production of various value-added products like lactic acid.

So far, base catalysts have not been explored for this purpose, except for the hydrothermal conversion of glycerol to lactic acid using alkali metal catalysts like NaOH/KOH. This method presents several drawbacks for the industrial synthesis like harsh reaction conditions (excess temperature, excess amount of strong base, etc.) and cost-intensive isolation of soluble alkali metal lactates (excess catalysts) which is highly uneconomical. As a solution to this problem, scientists at Graz University of Technology, Austria have come up with a “green” method for the industrial synthesis of lactic acid by mixing a cocktail of dihydroxyacetone and calcium hydroxide.

Glycerol to lactic acid

The sparingly soluble calcium hydroxide facilitates the easy removal of excess catalyst by simple mechanical filtration making this a highly economical and industrial friendly method. Another component of the cocktail Dihydroxyacetone- is easily obtained by the microbial oxidation of glycerol in high yields, thus reducing the glycerol burden in the biodiesel industry.

The present paper discusses the catalytic effects of various earth metal hydroxides like barium hydroxide, calcium hydroxide and magnesium hydroxide on the lactic acid formation from dihydroxyacetone. The screening studies indicate that calcium hydroxide is highly selective towards formation of lactic acid owing to its chelation properties. The intriguing mechanism of lactic acid formation by alkali earth metal catalysis was investigated by the means of mechanistic and kinetic studies which suggested two major pathways for lactate synthesis. It was found that the temperature differences play an important role in the preference of the reaction to proceed via either pathway. Various other studies like the effect of concentration of catalyst, feed concentration, temperature variations provide a detailed insight into the synthesis of lactic acid from dihydroxyacetone.

The extensive studies done by the Austrian scientists, has not only provided a potential solution to the enigmatic problem of industrial synthesis of lactic acid, but has also provided a way to recycle the surplus glycerol into a high value product like lactic acid.

To know how the green cocktail made its way to become an industrially feasible method for the synthesis of lactic acid, read the article:

Synthesis of lactic acid from dihydroxyacetone: use of alkaline earth-metal hydroxides
Susanne Lux and Matthäus Siebenhofer
Catal. Sci. Technol., 2013, DOI: 10.1039/c3cy20859a

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Tannins help in biphasic catalysis

There are pros and cons to both homogeneous and heterogeneous catalytic strategies. One way to get the best of both worlds is to use aqueous-organic biphasic catalysis. This approach hasn’t been widely utilised so far due to interfacial resistance between the phases which causes a low catalytic activity.

Researchers in China have overcome this by using tannins from Black Wattle (an acacia tree species). The tannins “amphiphilicly” stabilise catalytic palladium nanoparticles enabling them to catalyse reactions in the organic phase whilst remaining in the aqueous phase for subsequent re-use, without loss of activity.

Read the full article here:

Using plant tannin as natural amphiphilic stabilizer to construct aqueous-organic biphasic system for highly active and selective hydrogenation of quinoline
Hui Mao, Jun Ma, Yang Liao, Shilin Zhao and Xuepin Liao
Catal. Sci. Technol., 2013, DOI:10.1039/C3CY00108C

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Catalytic self-cleaning oven glass

Researchers from Belgium have developed a self-cleaning coating for oven windows. Of the available self-cleaning coatings, only a couple are optically transparent at working domestic oven temperatures and these require at least 3 hours of heating. Using manganese and manganese-ceria oxide coatings, the team of researchers discovered that an organic lipid contaminant could be oxidised within one hour to leave transparent, contaminant-free glass.

self-cleaning oven glass

Read the full article below:

Catalytic self-cleaning coatings for thermal oxidation of organic deposits on glass
Julie E. Verhelst, Daniel Decroupet and Dirk E. De Vos

Catal. Sci. Technol., 2013, DOI: 10.1039/C3CY20874E

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Non-canonical amino-acids: An emerging ploy to assist lipases in tackling hostile environments

Posted on behalf of Shreesha Bhat

ncAAs to Lipase:” Here I come comrade, to help you combat hostile environment”

“A friend in need is a friend indeed”. This proverb was justified in an area of chemical research where a group of German scientists devised a new strategy for assisting lipases in hostile environments. Lipases have an important role in organic chemistry as biocatalysts, but have stability issues in organic solvents and other hostile environments making them industrially non-feasible. Among the various approaches used to improve the stability of enzymes, an alternative strategy involving the incorporation of non-canonical amino acids (ncAAs) into the enzymes was adopted by the researchers, which not only resulted in improved stability but also enhanced activity and efficiency.

The subject of study was a lipase obtained from the thermostable bacterium Thermoanaerobacter thermohydrosulfuricus (TTL), from which various ncAAs-containing congeners (mainly analogues of tryptophan, proline, tyrosine, methionine and phenylalanine) were prepared and screened against various organic solvents. They were also evaluated against a set of hostile environments such as metal cations, surfactants, protein reducing, alkylating and denaturing agents, etc. Some congeners conferred stability against pyridine (an important co-solvent for lipase catalyzed polymer synthesis) while some against tert-butanol (solvent for biodiesel production) which is very likely to have a positive influence in the industrial arena.

The present Communication not only demonstrates the potential advantages of using ncAAs in hostile environments but also highlights the challenges that lay ahead in selective biocatalytic transformations.

Find out more about the potential of non-canonical amino acids by reading :

Non-canonical amino acids as a useful synthetic biological tool for lipase-catalysed reactions in hostile environments
Carlos G. Acevedo-Rocha, Michael G. Hoesl, Sebastian Nehring, Marina Royter, Christina Wolschner, Birgit Wiltschi, Garabed Antranikian and Nediljko Budisa
Catal. Sci. Technol., 2013, DOI: 10.1039/C3CY20712A

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Noble metal brings activity to tin oxide

Posted on behalf of Sara Coles, Web-writer

James Wiswall and his colleagues, working with Professor Margaret Wooldridge at the University of Michigan, USA, have been studying catalytic propane combustion. This reaction has important implications for areas such as power generation (for example, integration of catalysts directly into the internal combustion engine combustion chamber) and removal of volatile organic compounds (VOCs) from emissions.

The group used a stagnation-point flow reactor to study the catalytic activity of platinum, palladium, tin dioxide and 90 wt% SnO2–10 wt% Pt for the combustion of propane under a variety of reaction conditions. Preliminary results suggest that the 90 wt% SnO2–10 wt% Pt catalyst provides significant activity and has similar trends in activity as a function of stagnation-plane temperature to those of Pt and Pd, whereas pure SnO2 shows no activity.

The researchers are optimistic that even better activity could be obtained if optimisation studies are carried out.

This development shows potential for Pt/SnO2 to be used as a fuel oxidation catalyst. For more detail, read the full article:

An experimental investigation of catalytic oxidation of propane using temperature controlled Pt, Pd, SnO2, and 90% SnO2–10% Pt catalysts
J. T. Wiswall, M. S. Wooldridge and H. G. Im
Catal. Sci. Technol., 2013, 3, 618–625

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Industrial-scale enzyme catalysis a step closer

Many biocatalysts require expensive co-factors when they are used in the production of industrially relevant compounds, but a team of UK chemists has replaced one such co-factor – nicotinamide adenine dinucleotide phosphate (NADPH) – with a smaller, more practical molecule: methyl viologen.

The production of cyclohexanone has been successfully catalysed using this method, combining methyl viologen with a biocatalyst enzyme in an electrochemical microfluidic set-up.

The work, published in Catalysis Science & Technology, represents the first time such enzyme-catalysed chemistry has been carried out without a co-factor, and presents a practical and economic route to its use in large-scale synthesis.

Read the article…

Electro-enzymatic viologen-mediated substrate reduction using pentaerythritol tetranitrate reductase and a parallel, segmented fluid flow system
Karl Fisher, Stephan Mohr, David Mansell, Nicholas J. Goddard, Peter R. Fielden and Nigel S. Scrutton

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Nano gold boosts the Ullmann reaction

Researchers from the Indian Institute of Chemical Technology have extended the repertoire of C-C bond forming reactions catalysed by gold nanoparticles to include that of the Ullmann reaction.

The Ullmann reaction is an old favourite for synthesising biaryls – it proceeds by coupling together two aryl halides using a transition metal catalyst (traditionally copper).

The heterogeneous catalytic system employed by the authors makes use of gold nanoparticles stabilised on commercially-available nanocrystalline magnesium oxide.

Read more about this work by downloading the article now:

Ullmann coupling of aryl iodides catalyzed by gold nanoparticles stabilized on nanocrystalline magnesium oxide
Keya Layek, H. Maheswaran and M. Lakshmi Kantam

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Calling all budding science writers…

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Do you fancy yourself as a blogger extraordinaire?

We are currently looking for a web-writer for the Catalysis Science & Technology blog. The writer will cover our latest research, interview leading researchers in the field and will keep the community updated with upcoming conferences and events.

If you’re interested and would like to be considered, please contact the Catalysis Science & Technology Editorial Office. We will ask you to submit a sample writing piece.

We hope you’ll agree that this is a great opportunity to develop those science-writing skills as well as gaining experience in publishing and journalism. We look forward to hearing from you soon!

Be sure to contact us before 4th March 2013

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