Archive for the ‘Catalysis’ Category

Copper A3 Coupling using a Switchable Homogeneous/Heterogeneous Catalyst

A MOC, I learned this week, is a metal-organic cage. I was familiar with MOMs, MOFs and MOBs, but MOCs were a new one. A MOM (metal-organic material) is a coordination-driven assembly constructed from metal nodes linked by organic ligands. MOMs encompass both MOFs (metal-organic frameworks) and MOCs (metal-organic cages). A MOF is an extended network with the potential for inner porosity, and a MOC is a discrete metal-ligand cluster. And that’s just about as far down the nomenclature rabbit hole I’m willing to go. If you’re keeping up you’ll realise that I forgot one! A MOB is a crowd of graduate students competing for free coffee at the public seminar.

Dong and co-workers at Shandong Normal University designed and prepared a MOM catalyst constructed from copper(II) nodes and a tripodal ligand consisting of a phenylic wheel functionalised with diketones. In chloroform these two components arrange into discrete MOC assemblies containing two tripodal ligands and three copper ions. The copper ions in the cluster are each coordinated to two diketone moieties (in a acetylacetonate-like fashion) in a quasi-square planar arrangement.

Synthesis of the tripodal ligand functionalised with diketone coordinating moieties.

Synthesis of the tripodal ligand functionalised with diketone coordinating moieties.

An interesting property of the material is that it can switch between the MOC form, soluble in halogenated solvents, and an insoluble MOF that assembles upon addition of 1,4-dioxane. 1,4-Dioxane is both an anti-solvent and a ligand; coordination between copper and 1,4-dioxane binds the discrete MOC cages to each other, arranging them into the extended MOF structure. This behaviour can be exploited to prepare a practical catalyst that combines the benefits of both homogeneous and heterogeneous catalysis, namely that homogeneous catalysts are generally more efficient, selective and easier to study, but heterogeneous catalysis are easier to recover and recycle. What better way to solve this problem than with a catalyst that is homogeneous during the reaction conditions, but heterogeneous when it comes to product separation?

Reversible metal-organic cage MOC(top left)-MOF(top right) metal-organic framework transition mediated by the addition of 1,4-dioxane. Coordination bonds between 1,4-dioxane shown (bottom image).

Reversible MOC(top left)-MOF(top right) transition mediated by the addition of 1,4-dioxane. Coordination bonds between 1,4-dioxane shown (bottom image).

The authors used the A3 coupling reaction to demonstrate this concept in a catalytic reaction. The A3 reaction is a transition metal-catalysed, multi-component coupling reaction between aldehydes, alkynes and amines. The products are propargylamines, practical synthetic intermediates for the synthesis of nitrogen heterocycles. The A3 reaction has been extensively studied and can be effected by a wide range of transition metal catalysts. Its versatility makes it a popular choice as a model catalytic reaction to demonstrate innovative ideas in catalytic design – as the authors have done here.

Coordination-driven assemblies have a unique potential for the synthesis of differentially soluble materials, used by the authors for novel catalytic design. Whether this particular metal-ligand combination can be applied to other copper catalysed reactions remains to be seen, nevertheless the principle offers an innovative approach that augments the range of methods striving to bridge the gap between homogeneous and heterogeneous catalysis.

To find out more please read:

Cu3L2 metal-organic cages for A3-coupling reactions: reversible coordination interaction triggered homogeneous catalysis and heterogeneous recovery

Gong-Jun Chen, Chao-Qun Chen, Xue-Tian Li, Hui-Chao Ma and Yu-Bin Dong.
Chem. Commun., 2018, 54, 11550-11553
DOI: 10.1039/c8cc07208f

About the author

Zoë Hearne is a PhD candidate in chemistry at McGill University in Montréal, Canada, under the supervision of Professor Chao-Jun Li. She hails from Canberra, Australia, where she completed her undergraduate degree. Her current research focuses on transition metal catalysis to effect novel transformations, and out of the lab she is an enthusiastic chemistry tutor and science communicator.

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)

Ruthenium Currency for a Hydrogen Fuel Economy

A group of researchers at the Chinese Academy of Sciences and Southwest University want us to kick the fossil fuels habit. Their research comes to us from China, a country using roughly one quarter of the world’s yearly energy consumption, and where the finite nature of fossil fuels is a very real threat to energy supply security. Leading in energy use, China also leads the world in electricity production from renewable sources and investment in clean energy projects.

Hydrogen is considered a viable alternative to fossil fuels as it is energy rich, more so than petrol or ethanol at 39 kWh/kg (petrol: 13 kWh/kg, ethanol: 8.2 kWh/kg), and upon combustion emits only water vapour. However, hydrogen is often obtained from fossil fuels, and it will only be a practical option for the world’s future energy needs if it can be produced from a renewable source.

Preparation of the Ru2P/reduced graphene oxide electrocatalyst for the hydrogen evolution reaction

Preparation of the Ru2P/reduced graphene oxide catalyst

To this end, water splitting offers a solution. In a water electrolysis cell, hydrogen is produced at the cathode via the hydrogen evolution reaction (HER, 2H+ + 2e –> H2), and molecular oxygen is produced at the anode (2H2O –> O2 + 4H+ + 4e). It is ideal in theory, but high energy efficiencies are required to make water splitting viable, and this relies on the development of catalytic electrodes to minimize overpotentials required to drive the reaction. Currently, state of the art HER electrocatalysts use platinum, which is expensive and rare. Furthermore, platinum catalysts are most efficient in an acidic electrolyte and proceed 2-3 times slower in alkaline solutions. On the other hand, the best oxygen evolution catalysts perform better in alkaline environments. Using an alkaline electrolyte has overall advantages as it is less corrosive, thus increasing the stability and lifetime of the electrolytic cell.

The authors have developed a HER catalyst, using ruthenium, with overpotentials and current densities superior to Pt/C in both alkaline and acidic conditions.

DFT calculation to probe the hydrogen adsorption energies on the active catalytic surface of the Ru2P on reduced graphene oxide catalyst.

DFT calculation to probe the hydrogen adsorption energies on the active catalytic surface of the Ru2P catalyst. a) and b) front and side views of the calculated Ru2P/reduced graphene oxide surface. c) free energy diagram for the HER with different catalysts.

The electrocatalyst is comprised of small, uniform Ru2P nanoparticles (~2-4 nm) evenly distributed on reduced graphene oxide sheets. The activity of the prepared catalyst (1.0 mg cm-2) for the HER was measured in an acidic medium (0.5 M H2SO4) and the overpotential to achieve a current density of -10 mA cm-2 was -22 mV, superior to Pt/C (-27 mV). In an alkaline environment (1.0 M KOH) catalyst performance was enhanced, with an overpotential of -13 mV (29 mV lower than Pt/C). High Faradaic efficiencies of more than 98% were measured in both acidic and alkaline solutions. Additionally, analysis was undertaken to further understand how the structure and composition of the catalyst influences its activity. Double layer capacitance measurements gave clues about the catalyst surface, while theoretical DFT calculations were used to study H-adsorption energies.

There is no way to avoid the reality that ruthenium is also a rare and costly metal, and for this reason may not hold the key to solving our energy woes. However, of real value are the insights gained from probing the structure function relationship of this highly active catalyst, which may guide the synthesis of rationally-designed catalysts using inexpensive and abundant materials.

To find out more please read:

Ultrasmall Ru2P nanoparticles on graphene: a highly efficient hydrogen evolution reaction electrocatalyst in both acidic and alkaline media

Tingting Liu, Shuo Wang, Qiuju Zhang, Liang Chen, Weihua Hu, Chang Ming Li.
Chem. Commun., 2018, 54, 3343-3346
DOI: 10.1039/c8cc01166d

About the author:

Zoë Hearne is a PhD candidate in chemistry at McGill University in Montréal, Canada, under the supervision of Professor Chao-Jun Li. She hails from Canberra, Australia, where she completed her undergraduate degree. Her current research focuses on transition metal catalysis to effect novel transformations, and out of the lab she is an enthusiastic chemistry tutor and science communicator.

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)

An Organometallic Toolbox for the Study and Synthesis of Unique N-Heterocyclic Carbenes

N-heterocyclic carbenes (NHCs) are an interesting example of chemical curiosity turned commonplace. NHCs are stable singlet carbenes located within an N-heterocycle, in which the carbon centre bears an sp2 hybridised pair of electrons. As early as 1835 chemists were thinking about carbenes, with Dumas’ optimistic (if unsuccessful) attempt to synthesise the methylene carbene by dehydrating methanol. For many years the intentional study of carbenes was considered too demanding because of their instability, and so they remained in relative obscurity. A number of seminal papers changed this preconception; in particular, a report by Wanzlick in 1968 reporting the synthesis of the first NHC-metal complex using mercury and the first synthesis of a stable and isolable NHC by Arduengo in 1991.

Intensification in research and interest in NHCs over the past thirty years may have originated with these seminal reports, but it continues because of the success of NHCs in catalysis: both as strongly σ-donating metal ligands and nucleophilic organocatalysts. One of the most valuable features of NHCs is the ability to tailor their steric and electronic properties by altering the heterocyclic ring and N-bound substituents. Accordingly, the study of NHC reactivity and the development of methods to functionalise NHCs are essential for continued innovation in this field.

Drs Marina Uzelac and Eva Hevia at the University of Strathclyde, Scotland, have written a review article summarising organometallic methods to metallate N-heterocyclic carbenes. The work summarises metallation of all three components of the NHC: the carbenic carbon, the heterocyclic backbone and the N-bound substituents.

The lithiated complex (1), synthesised by treatment of the N-heterocyclic carbene NHC with nBuLi, can be transmetallated at the C4 position by a number of main group elements to give a variety of bimetallic complexes (2). These complexes can be selectively quenched to generate NHC complexes with unconventional regiochemistry (3).

The lithiated complex (1) can be transmetallated at the C4 position by a number of main group elements to give a variety of bimetallic complexes (2). These complexes can be selectively quenched to generate NHC complexes with unconventional regiochemistry (3).

To exemplify the breadth of research discussed; beginning with 2,6-diisopropylphenyl (dipp) substituted imidazole-2-ylidenes, the reactivity of the NHC can be unlocked by initial addition of an alkali metal such as lithium, sodium or potassium (see figure). Metallation at the C4 position occurs by deprotonation of the vinyl protons in the NHC backbone, while a second metal coordinates to the carbene electron pair at the C2 position. From this species (1) it is possible to transmetallate the C4 position with a less-polar metal such as zinc, aluminium, gallium, boron or iron to furnish a bi-metallic NHC (2). Interestingly, addition of an electrophilic methyl or proton source to this species exclusively quenches the C2 position, generating a suite of unconventional complexes (3) with the carbene electron pair positioned on the C4 carbon.

Lithiation of NHC complexes: a) deprotonation of the backbone of NHC-borane complex; b) co-complexation of NHC-zinc complex with alkyllithium affording lithium zincate; c) deprotonation of the abnormal carbene complex.

Reactivity of main-group NHC complexes towards lithiation.

Further studies investigate how different reagents influence the regioselectively and extent of metallation, how metallated NHCs can activate small-molecules such as carbon dioxide, conditions which can lead to the metallation of N-dipp substitutents, as well as products and speciation following treatment of NHCs with a variety of bimetallic reagents.

In addition to expanding the knowledge of NHC reactivity, the work summarised in this review provides a reference and inspiration to researchers seeking to tailor NHCs for unique applications in synthesis and catalysis.

To find out more please read:

Polar organometallic strategies for regioselective C-H metallation of N-heterocyclic carbenes

Marina Uzelac and Eva Hevia.
Chem. Commun., 2018, Advance Article
DOI: 10.1039/c8cc00049b

About the author:

Zoë Hearne is a PhD candidate in chemistry at McGill University in Montréal, Canada, under the supervision of Professor Chao-Jun Li. She hails from Canberra, Australia, where she completed her undergraduate degree. Her current research focuses on transition metal catalysis to effect novel transformations, and out of the lab she is an enthusiastic chemistry tutor and science communicator.

 

 

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)

Hiding Carbon Dioxide in Oxazolidinones

Sometimes it feels as though the pinnacle of synthetic achievement is represented by 20 step total syntheses (with 10 contiguous stereocentres and 5 fused rings…). The level of chemical complexity that can be fashioned from simple building blocks is undoubtedly impressive, but amid such feats it is important not to lose sight of the elegance and worth of simple chemistry, especially when it aims to play a part in resolving profound challenges. One such challenge, which will increasingly confront future generations, is how to reduce the load of carbon dioxide in the atmosphere. One solution is to ‘fix’ carbon dioxide by integrating it into chemical building blocks of added complexity in a sustainable way.

The porosity and high surface area of metal organic frameworks (MOFs), a class of three-dimensional coordination networks, proffers them as ideal materials for capture and storage of carbon dioxide. A team of researchers have designed a MOF which consumes carbon dioxide in a different way: by transformation into value-added chemicals. The group have developed a catalytic MOF embedded with lewis-acidic copper centres capable of converting aziridines to oxazolidinones by the addition of carbon dioxide. Oxazolidinones are used as auxiliaries in chiral synthesis, and are structural components of some antibiotics.

The MOF, termed MMPF-10, is a metal-metalloporphyrin framework constructed from a copper-bound porphyrin ring chemically modified to incorporate 8 benzoic acid moieties, generating an octatopic ligand. These carboxylic acids groups form a second complex with copper in situ, termed a ‘paddlewheel’ for its appearance, with the formula [Cu2(CO2)4]. The resulting network contains hexagonal channels measuring 25.6 x 15.6 Å flanked by four of each of the two copper complexes. With 0.625 % of the catalyst at room temperature, 1 bar CO2 pressure, and in a solvent free environment, MMPF-10 catalyses the transformation of 1-methyl-2-phenylaziridine to yield 63% of the product.

metal-metalloporphyrin MOF catalyses catalyzes carbon dioxide fixation aziridines to oxazolidinones

Topology of MMPF-10 showing hexagonal channels in a) and c), and pentagonal cavities in b). Turquoise: copper, red: oxygen, grey: carbon, blue: nitrogen.

This work, a simple reaction to prepare oxazolidinones, shows that carbon dioxide can be fixed in specialised synthetic building blocks in a sustainable way. This is the way the first paragraph ended, ‘in a sustainable way’, because the challenge of developing such a reaction is two-fold: it must use carbon dioxide, and the reaction conditions must be sustainable. There will be no beneficial offset if the reaction uses a lot of energy, requires many resources, or generates larges quantities of waste. In this reaction the researchers have remained mindful of developing a mild, solvent-free reaction with low catalyst loading employing an earth abundant metal, reflecting an earnest aim to develop practical and sustainable chemistry.

To find out more please read:

A metal-metalloporphyrin framework based on an octatopic porphyrin ligand for chemical fixation of CO2 with aziridines

Xun Wang, Wen-Yang Gao, Zheng Niu, Lukasz Wojtas, Jason A. Perman, Yu-Sheng Chen, Zhong Li, Briana Aguila and Shengqian Ma
Chem. Commun., 2018, Advance Article
DOI: 10.1039/c7cc08844b

About the Author

Zoë Hearne is a PhD candidate in chemistry at McGill University in Montréal, Canada, under the supervision of Professor Chao-Jun Li. She hails from Canberra, Australia, where she completed her undergraduate degree. Her current research focuses on transition metal catalysis to effect novel transformations, and out of the lab she is an enthusiastic chemistry tutor and science communicator.

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)

Coordinating nature and photochemistry to create hydrogen

When we look to our future energy resources, the need to realise new means of renewable energy is immediately obvious. Much research is being carried out around the world into the development of systems that can generate energy – from H2 to biofuels to solar fuels – all of which place great importance on high efficiency and sustainability.

Looking at the world around us for inspiration, the obvious candidate is the photosynthetic process, where visible light is employed to convert CO2 and H2O into chemical energy. This process involves the transport of electrons through a complex series of intricately aligned porphyrin-related and protein biomolecules. We can explore the development of a system that mimics the behaviour of natural systems, with respect to the relay of electrons along a series of molecules, or, alternatively, we can take the components in these systems and exploit their properties in combination with other electronically-active but non-natural molecules.

Upon photoexcitation of [Ru(bpy)3]2+, electron transfer through a ferredoxin scaffold to a cobaloxime catalyst facilitates the production of hydrogen.It is the latter approach which Lisa Utschig and her team from Argonne National Laboratory, near Chicago in the US, employed to generate a molecular system capable of photocatalysing the production of hydrogen. In their biohybrid system, the photosensitiser ruthenium(II) tris(bipyridine), ferredoxin (a water-soluble electron transfer protein), and cobaloxime (a cobalt(II)-based catalyst), were combined to generate a miniature reaction center that mimics those which occur in biological systems. However, the Utschig group’s system has a smaller molecular weight, which allows for characterisation of the electronic processes that occur in the system.

Lisa and her colleagues found that the presence of ferredoxin in the catalytic system acted as a scaffold to stabilise the charge-separated state necessary for electron transfer and the desired production of H2. They also observed that the catalytic behaviour of the Ru(II)–Co(II) pair was only possible in the presence of ferredoxin, which acted to extend the lifetime of the otherwise transient Co(I), allowing the desired reaction to occur.

In order to fully understand and enhance the properties of the molecular systems developed to fulfil the increasing need for energy alternatives, we need to be able to probe the structure and processes that occur in the molecule; the use of smaller analogs to those that exist in nature offers a means by which to achieve this goal. The photoactivated catalyst discussed in this work is an important step forward in the development of an optimized system for use in solar fuel production.

Read this hot ChemComm article in full:
Aqueous light driven hydrogen production by a Ru–ferredoxin–Co biohybrid
S. R. Soltau, J. Niklas, P. D. Dahlberg, O. G. Poluektov, D. M. Tiede, K. L. Lulfort and L. M. Utschig
Chem. Commun., 2015, 51, 10628–10631
DOI: 10.1039/C5CC03006D

Biography

Anthea Blackburn is a guest web writer for Chemical Science. She hails originally from New Zealand, and is a recent graduate student of Northwestern University in the US, where she studied under the tutelage of Prof. Fraser Stoddart (a Scot. There, she exploited supramolecular chemistry to develop multidimensional systems and study the emergent properties that arise in these superstructures. When time and money allow, she is ambitiously attempting to visit all 50 US states.

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)

Improvements to a selective hydrogenation process using ionic liquids

In this ChemComm communication, Peter Claus and co-workers describe an interesting application of room temperature ionic liquids to the selective hydrogenation of 2-hexyne. Unlike many reports in the literature, where an ionic liquid acting as a solvent may enhance a particular reaction, this report outlines a solid supported catalyst system modified with an ionic liquid layer.

Such materials, known as SCILLS, (solid catalyst with an ionic liquid layer) have been investigated in a variety of hydrogenation reactions. In this work the desired reaction is the reduction of 2-hexyne to cis-2-hexene. The catalyst is 1 wt% palladium on silica, modified with various loadings of 3 common ionic liquids: BMIM hexafluorophosphate, BMIM bis(triflouoromethanesulfonyl)imide and N-butyl-N-methylpyrrolidinium dicyanamide ([BMPL][DCA]). The performance of the unmodified catalyst was compared with the yield and selectivity afforded by the SCILL systems. The best results were reported with the dicyanamide ionic liquid SCILL, ([BMPL][DCA]) at 30 wt% ionic liquid loading.

In such a process, there are several reactions that must be suppressed. As the product is an olefin, isomerisation to the trans product must be controlled, as must further hydrogenation to the fully reduced material, hexane. For a number of reasons, based on the nature and amount of chemisorbed hydrogen, and favourable dicyanamide anion interactions with palladium, the dicyanamide SCILL system is particularly effective.

Notably, this system gives improved performance in terms of selectivity and yield over the two best performing commercial catalysts for this task. For example, Lindlar´s catalyst, palladium on calcium carbonate, deactivated with lead, cannot match its performance. In this work, the authors give an example of how ionic liquids can add value to a commercial process, while also offering considerable process improvements, in terms of toxicity and arguably, simplicity. The group’s focus now turns to SCILL activity and stability in a continuous hydrogenation process.

Read this RSC Chemical Communication today!

ionic-liquid layer
Frederick Schwab, Natascha Weidler, Martin Lucas and Peter Claus
Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)

Printable Nanoscale Catalysts with Controlled Nano-morphologies

Nanoscale metal rings and dots could find potential use in a wide range of applications including catalysis. However, the impact the morphology differences have must be unambiguously ascertained before they can be used in practical applications. For this to be achieved there needs to be a simple and efficient fabrication process that can create arrays of nanoscale metal rings or dots for study.

Won Bae Kim and team, from the School of Materials Science and Engineering at the Gwangju Institute of Science and Technology, report such a method in their new ChemComm paper. They make use of the powerful transfer printing technique, but importantly have created suitable stamps that can generate ring or dot arrays. These stamps use one dimensional carbon nanostructures that are supported within the hexagonal pores of anodic aluminium oxide, the tip shapes being controlled by ion milling conditions. After loading with a suitable catalytic metal they are then used in transfer printing onto indium tin oxide substrates.

SEM images of nanoring and nanodot stamps showing the supported one dimensional carbon structures within the AAO pores.


The team demonstrate the catalytic ability of the printed metal ring and dot arrays by studying methanol oxidation in acidic solution with platinum structures and carbon monoxide electrooxidation in alkaline solution with gold structures. With this approach they were able to study the effect of morphology on the catalytic activity – to find out which was better, rings or dots, you will have to read the ChemComm article today!

To read the details for free* check out the Chem Comm article in full:

Transfer printing of metal nanoring and nanodot arrays for use in catalytic reactions

Sang Ho Lee, Sung Mook Choi, Seungha Yoon, Huisu Jeong, Gun Young Jung, Beong Ki Cho and Won Bae Kim

DOI: 10.1039/C4CC02939A

*Access is free untill Friday 4th July through a registered RSC account – click here to register

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)

The chemists’ enzyme

The title of this post was taken from the website of Barry Trost, one of the world’s leading scientists and author of an astonishing 924 papers. Describing his work, he states:

One major activity in designing new reactions and reagents involves the development of “chemists’ enzymes” – non-peptidic transition metal based catalysts that can perform chemo-, regio-, diastereo-, and especially enantioselective reactions.

Chemists have, for a long time, sought to reproduce the incredible feats of nature. Natural biology has evolved over many years to achieve the efficiency and reactivity that most lab-based chemists could only dream of. Nature achieves this by employing incredibly sophisticated enzymes which are, sadly, almost impossible to replicate by a synthetic chemist due to their complexity. An alternative idea is to use these enzymes as inspiration for new catalysts and try to focus on the general reasons why they work rather than trying to create direct copies.

Supramolecular catalysts for decarboxylative hydroformylation and aldehyde reduction.

Dr Bernhard Breit, Lisa Diab and Urs Gellrich at Albert-Ludwigs-Univertat in Germany have shown in a HOT ChemComm article that a highly selective catalyst can be created when combining a metal catalyst with a directing ligand to control the reaction. In this Communication, they report excellent results using  rhodium, the classic metal of choice for hydroformylation, and a functional group for recognition of the substrate. The net effect of these features combined is that the substrate is held in a specific way at the catalytic site. As a result, the reaction which follows can only occur in a specific way. This is similar to how enzymes control the chirality.

The concept behind this catalyst is one which could be applied to a great number of different reactions – no doubt we can look forward to reading about these in the near future.

Read this HOT ChemComm article today!

Tandem decarboxylative hydroformylation–hydrogenation reaction of α,β-unsaturated carboxylic acids toward aliphatic alcohols under mild conditions employing a supramolecular catalyst system
Lisa Diab, Urs Gellrich and Bernhard Breit
Chem. Commun., 2013, Advance Article
DOI: 10.1039/C3CC45547E, Communication

Ruaraidh McIntosh is a guest web-writer for ChemComm.  His research interests include supramolecular chemistry and catalysis.  When not working as a Research Fellow at Heriot-Watt University, Ruaraidh can usually be found in the kitchen where he has found a secondary application for his redoubtable skills in burning and profanity.

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)

A cloak of many carbons

Catalysts can be exceedingly useful in the real world, from treating our car’s exhaust fumes to creating fertilisers.  There are many ways to make catalysts and even multiple ways to make the same catalyst.  The path that you choose to a catalyst can have a significant impact on the quality of the end product.

Eloy del Rio and team from the Structure and Chemistry of Nanomaterials group at the University of Cadiz in Spain have investigated ceria-based oxide-supported gold catalysts for carbon monoxide oxidation.  The routine for depositing the metal phase onto the oxide support and the subsequent catalyst activation step can ultimately affect the activity of the catalyst.  Catalysts prepared by deposition-precipitation with urea followed by activation under oxidising conditions result in significantly more activity than those prepared under reducing conditions.

Variation in catalyst activity under oxidising and reducing activation protocols.

This had previously been observed by others, but the reason for the difference was never discussed.  The authors set out to find out why the activity differed.  They used a suite of nano-analytical and nano-structural techniques to probe the catalysts, finding that the catalyst prepared under reducing conditions had a coat of amorphous carbon which severely hampered the catalyst activity.  This could be removed by a re-oxidation treatment that burnt away the carbon layer and produced an active catalyst similar to the one produced under oxidising conditions.

The precipitating agent used in the synthesis can also influence the resulting activities of catalysts prepared via the deposition-precipitation method.  No difference between oxidising and reducing activations is observed when sodium carbonate is used in place of urea.

To read the details, check out the ChemComm article in full:

Dramatic effect of redox pre-treatments on the CO oxidation activity of Au/Ce0.50Tb0.12Zr0.38O2-x catalysts prepared by deposition-precipitation with urea: a nano-analytical and nano-structural study
E. del Rio, M. López-Haro, J.M. Cies, J.J. Delgado, J.J. Calvino, S. Trasobares, G. Blanco, M.A. Cauqui and S. Bernal
Chem. Commun., 2013, 49, Accepted Manuscript
DOI: 10.1039/C3CC42051e

Iain Larmour is a guest web writer for ChemComm.  He has researched a wide variety of topics during his years in the lab including nanostructured surfaces for water repellency and developing nanoparticle systems for bioanalysis by surface enhanced optical spectroscopies.  He currently works in science management with a focus on responses to climate change.  In his spare time he enjoys reading, photography and art.

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)