Seeing the Light with Manganese - Unveiling Catalysis by an Earth Abundant Metal

Catalysts play a vital role in modern chemistry. Fundamentally, they increase the speed of a chemical reaction as well as its selectivity, resulting in fewer unwanted byproducts. As this increases the efficiency of a process, it is not surprising that the chemical industry relies heavily on catalysts to prepare the pharmaceuticals, agrochemicals and plastics (to name but a few applications) which underpin our modern lives. The selection of the most active catalyst for a given reaction is therefore extremely important if a process is to operate at peak efficiency.

However, the selection of the most active catalyst is incredibly difficult. It is impossible to predict without detailed experimentation which exact combination of chemical structures and conditions will have the most desirable properties. Armed with a detailed understanding of how the catalyst operates (the mechanism) and in particular how chemical bond activation and formation occurs provides important insight for the chemist to determine how the different reactants interact with the catalyst. With a comprehensive view of mechanism, detailed and informed predictions can then be made on the reaction protocol and how to improve the structure of the catalyst.

This programme of research focuses on employing a new method to study the mechanisms which underpin processes catalysed by metals that are abundant in the Earth's crust. We have discovered a new method to study catalytic reactions which has the potential to revolutionise how mechanistic insight is obtained. Using a system based on the transition metal manganese, we have shown how a catalyst that is normally activated by strong heating can be activated by light. We have coupled this insight with time-resolved infra-red spectroscopy, in which the light that activates the catalyst is provided by a laser pulse. A second laser pulse, which follows a short time later (the so-called pump-probe delay), then examines the catalyst structure as it reacts during the chemical reaction. As the process of using light is highly selective we generate high concentrations of the chemical species which are actually responsible for the reaction and so can study their behaviour.

Our studies so far have been performed at the Central Laser Facility at the Rutherford Appleton Laboratory where pump-probe delays from a picosecond (a trillionth of a second) to a millisecond (a hundredth of a second). This gives unprecedented insight into the chemical process which underpin catalysis by manganese. This proposal aims to build on this unique insight in two ways:

Firstly, we will develop facilities in York which provide complementary methods to examine the reactions occurring from a nanosecond (a billionth of a second) to several hours. By combining the data from the different experimental methods we will be able to study the processes which underpin catalysis over 16 orders of magnitude in time. To give an analogy, if we imagined our shortest time measurement was one second, then our longest would be 1.4 billion years later!

Secondly, we will develop new methods using light to activate a host of different catalytic reactions at different stages in the chemical reactions. By relying on advancements in a related field that have shown how light can be used as a trigger to selectively activate acids and related groups, we will be able to initiate a host of important catalytic processes and then study their behaviour over the same wide range of timescales.

Finally, we will integrate state-of-the-art robotic experimentation to accelerate our discovery process.

This programme will result in new insight into reactions, providing unique information about the behaviour of catalysts which cannot be obtained by other means. This will, in turn, permit the catalyst structure and reaction conditions to improved in an informed manner so that the most efficient systems are used.