Induction heating of nanoparticle catalysts for synthetic chemistry

Lead Research Organisation: University of Leeds
Department Name: Sch of Chemistry

Abstract

Context of research: Catalysis is the centrepiece of modern synthetic science, with application in both academic research and industrial manufacturing. A current key challenge in this field of research is achieving higher catalytic activity, efficiency and product throughput, i.e. intensification, while avoiding undesirable products. Intensification of catalytic processes often involves higher temperature which speeds up reactions, including side reactions. Many of these side reactions are not related to the catalyst, but are inherent to the starting materials and reaction conditions.

This project will explore the use of induction heating to selectively heat up ferromagnetic nanoparticles as catalysts in solution. This will enable direct energy transfer to the catalyst and catalyst-substrate complexes, circumventing non-catalysed side reactions which are associated with high temperature.

Aims and objectives: The objectives of the project are listed below.
(i) Development of suitable induction heating batch and flow reactors.
(ii) Development of ferromagnetic nanoparticles of iron, iron oxide and iron alloys with other metals which can replace traditional precious metal organometallic catalysts.
(iii) Evaluation of these catalysts and reactors and benchmarking against traditional heating processes.

Potential applications and benefits:
The project has potential applications across the whole field of catalysis, from synthetic processes to bulk and specialty chemicals manufacturing processes. The developed ferromagnetic nanoparticles are potential IPs which will be commercialised as appropriate.

The student will benefit from training in inorganic chemistry, nanoparticle science and techniques, and catalytic research. He will also benefit from an interdisciplinary seminar programme at the Institute of Process Research & Development, University of Leeds. Presentations and knowledge transfer to industry in the High Value Chemical Manufacture sector, through our biannaual Industrial Days, and at postgraduate conferences will be part of his training.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509681/1 01/10/2016 30/09/2021
1799248 Studentship EP/N509681/1 01/10/2016 31/03/2020 Joseph Kyle Sheppard
 
Description Induction heating, pertaining to the activation of magnetically susceptible nanometre-sized catalysts, was found to be an extremely challenging research route. A variety of iron-based nanoparticle catalysts were synthesised: Iron oxide nanoparticles and Iron/Copper bimetallic nanoparticles with varying ratios of iron and copper. These were found to display chemical reactivity under conventional reaction conditions (heating applied via an external source of heat, e.g. a hot plate) but failed to yield any reactivity under induction heating conditions. Two induction heating reactors were trailed, one placed the reaction directly between the induction coils of the apparatus but was limited at supplying 150 Watts of power; the other was capable of supplying between 200-2000 Watts (though this was only utilised at a maximum of 600 Watts due to safety concerns) however the reaction occurred outside the induction coils but still within the generated magnetic field. In both cases no statistically relevant increase in solution temperature or development of reaction product was observed. The conclusion thus reached was that a catalytic quantity (1-10 mol%) of magnetic material was too low for induction heating to have an impact. Examples from the literature of induction heating being used to drive chemical reactions typically focus on using a packed-bed reactor full of ferromagnetic material, around which the induction coils are placed. The reaction mixture is then flowed through this packed bed. Whilst effective, this represents an increase in ferromagnetic material loading of several orders of magnitude. It is also quite typical for the ferromagnetic material in the packed-bed reactors to be chemically inert, there to simply provide the reaction a source of energy.

Focus was then drawn towards exploring the use of bimetallic nanoparticles as catalysts in challenging reactions under conventional conditions. The reaction chosen to study was Decarboxylative Cross Coupling (DCC). DCC is important as it forms aryl-aryl bonds, a very useful synthetic tool that enables the production of a wide variety of products, from medicine to agricultural chemicals. However, the literature surrounding the reaction typically reports the need for high reaction temperatures, high catalyst loadings and long reaction times. Using modified techniques developed during the induction heating work, a series of Palladium/Copper bimetallic nanoparticles were synthesised (varying ratios of palladium and copper, various capping agents) and characterised (Atomic Absorption Spectroscopy for metal content, Transition Electron Microscopy for size/shape distributions). A clear synergistic effect between the alloyed metals was observed, with palladium rich bimetallic nanoparticles outperforming both copper rich bimetallics and pure palladium nanoparticles. The palladium rich bimetallic nanoparticles were found to be competitive with respect to the homogeneous catalyst systems reported in the literature, and in some cases were found to outperform, with the lead catalyst able to reach 100% reaction completion in less than 1 hour under conditions 30oC cooler than typical literature procedures - a significant improvement. Research in this area is still ongoing as this approach is tested for robustness.
Exploitation Route Whilst induction heating, pertaining to this research project, was eventually identified as a research path too challenging given the scope of work required to make headway, this does present opportunities for future work. A key issue, one which could likely form the basis of an entire body of research, is in reactor design. As a chemist I tried my best in this regard, but someone with knowledge of chemical engineering would likely find some success here - specifically in designing a powerful reactor that can be operated safely. Also, during this project, several approaches have been developed for the synthesis of mono- and bimetallic nanoparticles, including ferromagnetic materials (iron, iron/copper, nickel, nickel/copper) which could be used as potential catalysts in a well-designed induction heating reactor.

There are also several other avenues of research that have been opened during this project. Ferromagnetic nanoparticle catalysts can be investigated as high-surface area heterogeneous catalysts that can be easily recovered and reused via the use of an external magnet (a rich and active field of research as of the submission of this report). During this project evidence has been gathered that suggests that the mechanism of decarboxylative cross coupling (DCC) is dependent on initial conditions such as solvent choice, this has not been reported in the literature and further investigations could form the basis of a paper. Finally, the bimetallic nanoparticles synthesised during this project all show an activity towards decarboxylation (different from DCC), as such there is scope to continue investigations in that direction, potentially exploring the use of palladium/silver and palladium/gold alloys (of which the project has briefly investigated).
Sectors Agriculture, Food and Drink,Chemicals,Environment,Pharmaceuticals and Medical Biotechnology