Archive for the ‘Homogeneous catalysis’ Category

15th National Youth Catalysis Conference – China

Catalysis Science & Technology is proud to announce that it awarded poster prizes at the 15th National Youth Catalysis Conference, “Multidisciplinary and multi-scale catalytic science and technology”, in China. The conference was held on 19th July 2015, at the University of Science and Technology of China (USTC), in Hefei. Plenary lectures were given by Professor Qingbai Xu (Tsinghua University), Professor Ye Wang (Xiamen University), Professor Wenjie Shen (Dalian Insitute of Chemical Physics, CAS), Professor Jiaguo Yu (Wuhan University of Technology) and Professor Baoning Zong (SINOPEC research institute of petroleum processing). Professors Wang, Shen and Yu are pictured below (left-right), together with the prize winners, Professor Weixin Huang (USTC, the local Chair) and Catalysis Science & Technology Associate Editor, Professor Ding Ma (Peking University).

The Winners:

Di Xin (Dalian University of Technolgy)

Ding Liangbing (University of Science and Technology of China)

Song Xiaojing   (Jilin University)

Han Lupeng (East China Normal University)

Su Xiaojuan (Ningxia University)

Chen Lang (Hunan University)

Su Diefeng (Zhejing University)

Wei Mingming (Dalian Institute of Chemical Physics, CAS)

Wang Dandan   (Xiamen University)

Gu Jing (Nanjing University)

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Nature leads the way: A Biomimetic Tricopper complex as a catalyst for selective oxidation of smaller alkanes

2014 has arrived and with it a new batches of Hot Articles, one of which from January deserves special attention. Professor Sunny Chan‘s group at Academia Sinica,  Taiwan have achieved the distinction of being the first group to devise a molecular catalyst for the selective oxidation of methane to methanol. This reaction faces a formidable challenge in the form of inertness of the methane C–H bond which makes O-atom insertion into the molecule almost impossible in ambient conditions.  Even if this problem is solved, the product, methanol, is highly susceptible to over-oxidation leading to formation of other undesired products. For of these reasons, most of the researchers have failed to scale this gargantuan mountain of difficulties.

Time and again when scientists have found it difficult to get answers to tough and challenging problems they have turned to nature for inspiration. In this case, the solution lay in a particular class of enzymes called methane monoxygenases (MMO) found in the methanotrophic bacteria. These MMOs have metallic clusters at their centres, which catalyse this difficult reaction with ease. In order to emulate these catalytic centres, the researchers developed some biomimetic models containing tricopper clusters, one of which, [CuICuICuI(7-N-Etppz)][ClO4], successfully mediated the selective oxidation of methane without any over-oxidation. This tricopper complex, when activated by dioxygen (O2), harnesses a “singlet oxene”, the strongest oxidant that could be used for a facile O-atom insertion across the C-H bond.

Biomimetic Tricopper complex as a catalyst for selective oxidation of methane to methanol

The catalyst also gave selectivity in the cases of ethane and propane, but not with higher alkanes. The reason being is the design of the tricopper catalyst, which has a small hydrophobic binding pocket at the base and forms a transient complex with the alkane and carries out the oxene transfer to oxidize the substrate. This pocket is not big enough to accommodate the product methanol (as well as the other small alcohols), so it releases the product as soon as it is formed. This removes over-oxidation from the equation, giving profound selectivity in cases of smaller alkanes. The authors have further studied the catalytic cycles and analysed the factors affecting the catalytic turnovers and efficiency.

This work presents a move towards a more efficient flow system which, in the future, would help in increasing the yields of the products. One issue with the current system is the solubility of the catalyst in solvents which can dissolve CH4 gas which may be put to rest by some modification in the design of the catalyst, leaving brighter prospects for the future.

To find out more about this nature-inspired discovery, read the full article now for more details.

Developing an efficient catalyst for controlled oxidation of small alkanes under ambient conditions
Penumaka Nagababu, Steve S.-F. Yu, Suman Maji, Ravirala Ramu and Sunney I. Chan
Catal. Sci. Technol., 2014, DOI: 10.1039/C3CY00884C


Shreesha Bhat, Web Writer Shreesha Bhat is a M.S.(Pharm.) in Medicinal Chemistry from National Institute  of  Pharmaceutical Education and Research,  India. He has recently joined the research group of  Dr. Pallavi Sharma as a PhD student at the  University of Lincoln, UK. His project involves  the design and synthesis of Helicase-primase inhibitors for Herpes Simplex virus and development of useful synthetic methodologies.

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Doubts put to rest: On a Quest for the real intermediates in Iron based Water Oxidation at low pH

It gives an absolute delight to the grey matter to imagine power generated from simple tap water. Power which could be supplied to our home and cars and thus put an end to the incessant use of fossil fuels. Yes friends, after the Bronze and Iron age, now it’s time for the Hydrogen age. The term “Hydrogen Economy” is gaining momentum and has the potential to do for the energy revolution what the computer and the Internet have done for the information revolution.

Among the various methods available for hydrogen production, water-splitting is one of the most promising approaches. Earlier, water oxidation catalysis have been performed efficiently with expensive, toxic and earth-scarce transition metals, but 3d metal-based catalysts are much less established. Fillol and Costas in their Nature Chemistry paper explored the use of environmentally benign and easily available iron coordination complexes for water oxidation with evident success. Their observation suggested that the iron complexes, when combined with Ce(IV) gets decomposed to iron oxides, which are, in fact, the main active catalysts for the water oxidation.

Substantial work by Tai-Chu Lau and group indicated that the actual catalysts for water oxidation are different at low and high pH values. It has been confirmed through various studies that at high pH, Fe2O3 is indeed the active metal catalyst, but researchers are still mystified as to what would be the intermediate at low pH. It has been speculated that the water oxidation at low pH goes through a molecular oxo-Fe active intermediate, as no evidence for Fe oxide formation has been obtained till date. The reason for this was given by Fillol and Costas, who proved that Fe (III) does not oxidize water in acidic conditions nor does it convert to Fe oxide. Another possibility that has been looming in the minds of the scientists is that FeO42- ions being strong oxidants can oxidize water in acidic conditions. But, scientists have shown that Ce(IV) is not capable of oxidizing Fe(III) to  FeO42. So, It has been a matter of debate as to which is the real catalyst for low pH water oxidation: Is it FeO42- indeed? Or an oxo-Fe intermediate?

Water oxidation by iron complexes in presence of Ce(IV)

In this communication, a group of Iranian scientists have tried to answer this question and included it in their quest for a more effective iron-based water oxidation catalyst. Their work has substantial basis in the work done by Fillol and Costas whose one observation was the inability of Fe(III) oxohydroxo 2µ-(O,OH) diferric dimer to catalyze water oxidation. So, a question was posed by Mohammad Mahdi Najafpour and group if an Fe(III) complex with only one bridge (oxo {O} or hydroxo {OH}) can be a water oxidizing catalyst? And if FeO42- has any role in the whole process?

To answer the above two important questions, they synthesized an Fe(III) oxo diferric dimer with tris(2-pyridylmethyl)amine (tpa) ligand with only one µ-O bridge, and tested the dimer for water oxidation in presence of  Ce(IV), and found it to be 6 times more active (measured in terms of TOF)  than the monomer reported by Fillol, Costas and workers. This provided a new insight into the mechanism, suggesting that a monomer might be just a precursor to the active catalyst which might be a di- or a multinuclear iron compound. The experiments prove that even if Fe ions convert to FeO42- in the presence Ce(IV), FeO42- cannot oxidize water catalytically, thus putting an end to the long lasting debate of FeO42- being an intermediate in these reactions.

Read more at:

A dinuclear iron complex with a single oxo bridge as an efficient water-oxidizing catalyst in the presence of cerium (IV) ammonium nitrate: New findings and current controversies
Mohammad Mahdi Najafpour, Atefeh Nemati Moghaddam, Davood Jafarian Sedigh and Malgorzata Holynska
Catal. Sci. Technol.,2013, Accepted Manuscript
DOI:
10.1039/C3CY00644A


Shreesha Bhat, Web Writer Shreesha Bhat is a M.S.(Pharm.) in Medicinal Chemistry from National Institute  of  Pharmaceutical Education and Research,  India. He has recently joined the research group of Dr. Pallavi Sharma as a PhD student at the  University of Lincoln, UK. His area of interests  include  chemical  synthesis of biologically important molecules  and developing newer methods for organic synthesis using novel catalysts.

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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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Copper NHCs in catalysis

The first N-heterocyclic carbene-ligated coppper complex was made in the 90’s and no more than a decade later, their potential as catalysts was uncovered. As the number of Cu NHC complexes continues to grow, so does the number of catalytic possibilities.

In their Catalysis Science & Technology Mini Review, Researchers, Egbert, Cazin and Nolan from the University of St Andrews have outlined the reactions which benefit from this neat little complex; from hydrosilylations to allylic substitutions and click chemistry.

Download the article now…

Copper N-heterocyclic carbene complexes in catalysis
Jonathan D. Egbert, Catherine S. J. Cazin and Steven P. Nolan

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Olefin epoxidation – which catalyst to choose?

Simone Hauser, Mirza Cokoja and Fritz Kühn explore recent developments in homogeneous epoxidation catalysts in this hot Catalysis Science & Technology Perspective.  They look at the different catalysts used for different olefins as well as thinking about the context in which the catalysts would be used.

The manuscript is currently free so download it now, it might help you decide which catalyst to use….

Epoxidation of olefins with homogeneous catalysts – quo vadis?
Simone A. Hauser, Mirza Cokoja and Fritz E. Kühn
Catal. Sci. Technol., 2013
DOI: 10.1039/C2CY20595E

The epoxidation of olefins catalyzed by molecular transition metal compounds is a research field, which has been extensively studied over the past forty years.

Other Catalysis Science & Technology articles by the same author are:

Xylyltrioxorhenium – the first arylrhenium(VII) oxide applicable as an olefin epoxidation catalyst

Stefan Huber, Mirza Cokoja, Markus Drees, János Mínk and Fritz E. Kühn
Catal. Sci. Technol., 2013
DOI: 10.1039/C2CY20371E, Paper

PtO2 as a “self-dosing” hydrosilylation catalyst
Sophie Putzien, Eckhart Louis, Oskar Nuyken and Fritz E. Kühn
Catal. Sci. Technol., 2012, 2, 725-729
DOI: 10.1039/C2CY00367H

Methyltrioxorhenium-catalysed oxidation of pseudocumene in the presence of amphiphiles for the synthesis of vitamin E
Mónica Carril, Philipp Altmann, Werner Bonrath, Thomas Netscher, Jan Schütz and Fritz E. Kühn
Catal. Sci. Technol., 2012, 2, 722-724
DOI: 10.1039/C1CY00313E

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Hydroformylation for the higher alkenes

Hydroformylation (or the oxo process) is an important industrial procedure which combines alkenes with carbon monoxide and hydrogen to produce aldehydes, which are easily hydrogenated to alcohols and then plasticizers or detergents. Hydroformylation is used to produce around 9 million tons of aldehyde per year world-wide and is one of the largest industrial applications of homogeneous catalysis.

Alternative approaches for the aqueous–organic biphasic hydroformylation of higher alkenes

Catalyst recycling is highly desirable to reduce costs and was effectively implemented for short chain alkenes with the development of the aqueous biphasic Ruhrchemie/Rhone-Poulenc (RCH/RP) process, however due to mass-transfer limitations the application of this process is constrained to the short chain hydrocarbons. This Hot Perspective by Lorenz Obrecht, Paul C. J. Kamer and Wouter Laan details some of the alternative approaches which have been developed for the aqueous–organic biphasic hydroformylation for higher alkenes.

Alternative approaches for the aqueous–organic biphasic hydroformylation of higher alkenes
Lorenz Obrecht, Paul C. J. Kamer and Wouter Laan
Catal. Sci. Technol., 2013, Advance Article

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Catalysis in industry themed issue now online

This month’s Catalysis Science & Technology issue is the devoted to Homogeneous and Heterogeneous Catalysis in Industry.

The themed issue which is guest edited by Professors Hans de Vries (DSM and University of Groningen) and David Jackson (University of Glasgow) comprises a selection of articles that illustrate the research necessary for moving a reaction off the lab bench and into the industrial plant. Unsurprisingly, catalytic research is often key to this journey.

Catalysis in industry front coverSelect the links below to read the Editorial and review articles. The full issue can be accessed here.

Editorial
Homogeneous and Heterogeneous Catalysis in Industry; Johannes G. de Vries and S. David Jackson

Perspective
First-principles kinetic modeling in heterogeneous catalysis: an industrial perspective on best-practice, gaps and needs; Maarten K. Sabbe, Marie-Françoise Reyniers and Karsten Reuter

Mini Review
Advances in conversion of hemicellulosic biomass to furfural and upgrading to biofuels; Saikat Dutta, Sudipta De, Basudeb Saha and Md. Imteyaz Alam

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Organometallics in catalysis: an article collection

Perhaps the most well-known applications of organometallics in catalysis are the Ziegler–Natta catalysts which are used to generate polymers, the catalysts are made up of mixtures of transition metal halides and organo-aluminium complexes. Karl Ziegler and Giulio Natta were awarded the 1963 Nobel Prize in Chemistry for their discovery and development of the catalysts, which today are the most commonly used for the manufacture of polythene.

The esteemed history of organometallics are not to be under-estimated and include Grignard’s reagents, the Heck reaction, Schrock catalysts, Grubbs’ catalysts and the Suzuki Coupling to name just a few. Organometallic compounds have revolutionised science and industry and to keep you up to date with the latest break-through research being made across all areas of organometallics in catalysis, we have made this cross-journal article collection free until the 26th September.

Click here for the full list of free articles

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Ring opening of biomass-derived furan rings

Fuel conversion from biomass to liquid hydrocarbons is a fast moving area of research and presents an opportunity to decrease our dependence on fossil fuels and move towards a more carbon neutral fuel economy. For use in transportation there are currently a range of strategies being considered to create liquid fuel from different biomass feedstocks (see Catalytic routes for the conversion of biomass into liquid hydrocarbon transportation fuels).

John C. Gordon, L. A. ‘‘Pete’’ Silks and colleagues have recently investigated a method of opening biomass-derived furan rings, under mild conditions, using homogeneous Bronsted acid catalysis.

The products observed during acid catalyzed ring opening of furan containing biomass-derived substrates are strongly influenced by furan substituents.

When generating fuel from non-food biomass there are many chemical hurdles to overcome, including the breakdown of lignocellulose and subsequent deoxygenation and hydrogenation of the resulting products. Gasification followed by Fischer–Tropsch reaction is a promising route to biomass conversion, but requires high temperatures and initial oxidation of the biomass.

An important challenge is the opening of ring structures.

While cellulose based biofuel precursors can be hydrolyzed under mild conditions, subsequent dehydration of these sugars leads to the generation of furans and aldehydes. In their Hot Article John C. Gordon et al. have investigated experimentally and theoretically the ring opening mechanism of furans on molecules derived from biomass, using acid catalysis <100oC. This important study gives insight into the ring opening process which is necessary to create linear alkane chains for use as liquid fuels.

Download their article for free to find out more

Functional group dependence of the acid catalyzed ring opening of biomass derived furan rings: an experimental and theoretical study
Christopher R. Waidmann, Aaron W. Pierpont, Enrique R. Batista, John C. Gordon, Richard L. Martin, L. A. “Pete” Silks, Ryan M. West and Ruilian Wu
DOI: 10.1039/C2CY20395B

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