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Printable Nanoscale Catalysts with Controlled Nano-morphologies

05 Jun 2014

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

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The chemists’ enzyme

27 Sep 2013

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.

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A cloak of many carbons

28 Jun 2013

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/Ce_0.50Tb_0.12Zr_0.38O_2-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.

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