Department of Chemsitry

Professor SC Edman Tsang

Inorganic Chemistry

edman.tsang@chem.ox.ac.uk

Telephone: 44 (0) 1865 282 610

Research Group Website

Research

Our research interests are mainly on both fundamental and applied aspects in Solid State Chemistry and Heterogeneous Catalysis. Research work involves synthesis, testing and characterisation of novel solid state materials for a wide range of applications. The highlights below are some of the current projects taking place in our group, which should give you an overview of our research directions. As the Head of Wolfson Catalysis Laboratory I am more than happy to provide you further information if required, please contact me using the details above.

Development of Novel Nano-materials for Catalysis, Sensor and Bio-medical applications

Recent developments in nano-science have opened up new directions in chemistry to allow the synthesis of new nano-materials which could not be obtained by conventional means. The current research shows that they exhibit many fascinating size dependent properties. The use of well-defined, well-characterised pre-formed nanomaterials as building blocks for the synthesis of functional materials is a new direction for many exciting applications.

We are developing novel core-shell nanoparticles of controllable composition, size and morphology (see diagrams below). Some of them show exceptional catalytic activity and selectivity towards desired products. A new class of silica coated nano-magnet of controlled dimensions to host biocatalysts with the unique advantage of facilitating separation is also described by our group. By using simple nano-chemistry skills, we show that Pt nanocrystals with tailored sizes can be decorated with Co atoms in a controlled manner. The blockage of unselective Pt corner sites by Co and its electronic influence to the Pt surface can dramatically improve the catalytic performance of Pt for the selective hydrogenation of α,β-unsaturated aldehydes.

Nanosize magnet (4nm core) coated with catalyst/enzyme as magnetic separable catalysts

A model showing Co atoms decorating on corner sites of Pt nanocrystal as an ultraselective nanocatalyst for hydrogenation of α,β-unsaturated aldehydes to corresponding alcohols

In nano-sensor and biomedical areas, our interests include using hollow carbon nanotube as nano-scale test tube for catalysis, separation, storage, magnetic, electronic applications. Research on attachment, testing and characterization of enzymes and DNA in opened carbon nanotubes at Oxford are underway. These studies open up promising lines allowing developments of biosensors or drug or gene-delivery/storage methods as well as nano-surgerical devices. Also, we are working on new synthesis of materials (magnetic, radionuclides) encapsulated in nano-carbon onions. By teaming up with Manchester hospital important applications of these encapsulated radioisotopes in onions for medical diagnosis are being developed.

Opening and filling of carbon nanotubes

Filling Nano-size Carbon Onions with Radioisotope (99mTc) as new lungs imaging and medical bio-tracers

A TEM micrograph shows an assembly of 33 nm SiO2@FePt particles with size distribution <5% in form of a high quality colloid crystal as a molecular filter

Corresponding electron diffraction patterns (and with simulated patterns-left hand corner) indicative of a hcp packing

Solid State Sensors

Solid state chemical sensors represent an exciting and innovative research area which has developed rapidly in the past 10 years. The key to the design of an ultra selective chemical sensor requires the recognition of an organic or inorganic substrate by an immobilized receptor molecule generating a surface host-guest product. There will be a signal transduction upon the molecular recognition converting the chemical/physical process into measurable parameters.

At Oxford, we are interested in developing new but ultra-selective nano-sensors for detection of gaseous hydrocarbons, inorganic metal ions or complex organic molecules such as DNA molecule, etc and elucidating their sensing mechanisms.

The diagram shows adsorbed oxygen species on the semiconductor oxide surface in air causes the formation of the depletion layer (charge separation). The reaction of the hydrocarbon with the oxide material surface upon exposure (via metal dopant) leads to the re-injection of electrons into the oxide bulk. The change in resistance gives rise to an electrical signal as one typical sensing mechanism for the detection of hydrocarbon.

Heterogeneous Catalysis and Cleaner Energy Provisions

Heterogeneous catalysis plays a vital role in energy provisions and environment, which relates to both wealth and welfare of mankind. Particularly, carbon dioxide (CO2) issue has recently become the focus of global attention because of the position of CO2 as the primary greenhouse gas and the implication of its emissions on the problem of climate change. Burning non-renewable fuels releases the CO2 stored millions of years ago. Deforestation releases the carbon stored in trees and also results for more CO2 in the atmosphere.

Thus, we work in the areas of carbon dioxide activation, capture, storage and subsequent conversion into useful chemicals/materials (reduction in carbon loading in atmosphere) and the development of alternative renewable energy sources (carbon neutral catalytic processes) in collaboration with a number of UK universities through EPSRC funded consortia (Formic acid economy and C-cycle: CO2 capture ,activation and utilisation) and industrial companies (Johnson Matthey, Thomas Swan and Aramco, etc) in order to take the long term vision of reducing the carbon emission to the atmosphere. Current projects concerning hydrogen storage, development of fuel cell catalysts, cleaner catalytic combustion, green chemistry (oil, gas and coal ultilization), energy efficiency chemical processes (on-board reforming), catalytic processes for energy productions (i.e. photocatalysis, reforming of bio-fuels) are ongoing.

Heterogeneous Catalysis and Fine Chemical Production (Green Chemistry)

Today tremendous pressure is currently exerted on chemical manufacturing industry to develop new synthetic methods that are environmentally more acceptable. For example, oxidation is an important industrial reaction but the current industrial practise is to use stoichiometric oxidants (manganates, chromates, etc) that generate a large quantity of inorganic pollutants. Our research is to seek cleaner alternative catalytic oxidation processes. We are working on a number of new approaches including the use of supported aqueous phase catalyst (SAPC) which concerns the creation of a thin water film carrying a homogeneous oxidation catalyst on a high surface area solid support in bulk organic solvent. SAPC substantially increase the interfacial surface area and provide an elegant way of heterogenising biphasic catalysts. Their main advantages concern easy catalyst recovery and increased activity. Selective oxidation of alcohols in supercritical carbon dioxide supercritical fluids (SCFs) is also under our intense investigation. We have recently shown that aerobic oxidation of alcohols to carbonyl compounds in scCO2 is an attractive, environmentally friendly alternative to the well-known aqueous phase oxidation on supported platinum metal catalysts. Mechanistic elucidation indicates that the favourable oxidative dehydrogenation of alcohol combined with readily desorption of lesser hydrophilic intermediates i.e. aldehyde prevent the alcohol from over-oxidation to acids with no detectable catalyst deactivation and no metal leaching (see Scheme 1) in supercritical fluid phase. Modify the hydrophobicity/hydrophilicity of the catalyst relative to the CO2 can also lead to significantly increase in conversion and catalyst stability.

Scheme 1. Catalytic oxidative dehydrogenation of an alcohol to form an acid.

Similarly, inorganic hydrides are conventionally employed for a wide range of important organic syntheses and many of them have proved to be excellent stoichiometric hydrogenation reagents. However, the preparation and regeneration of the highly toxic hydrides give separation and waste issues and so they are deemed unsuitable for the pharmaceutical and cosmetic industries in modern plants. Our approach is to carry out fundamental research to underpin the development of new but cleaner heterogeneous hydrogenation catalysts for their replacement.


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