Substances that accelerate chemical reactions, known as catalysts, are key tools in chemical engineering with a range of important uses worldwide.

Catalysts are substances that accelerate chemical reactions without undergoing any permeant changes themselves and are fundamental tools for chemical engineers.

In the Department of Chemical Engineering at Imperial College London, catalysts are used in a variety of projects, from energy and environmental engineering to biomedical applications and manufacturing.

So, what are they and how do they work?

A tool for optimising processes

Simply put, a catalyst is a substance that increases the rate of a reaction without altering the products of the reaction and is unchanged chemically throughout the process.

They speed up the rate of a reaction by providing an alternative energy pathway that has a lower activation energy – or the minimum quantity of energy required for the reaction to take place. This means that more particles have the activation energy required for the reaction, which increases the speed of the reaction.

By using a catalyst and therefore lowering the amount of energy needed for a reaction to take place, industrial processes can reduce costs and energy required in a range of processes. 

Tricked into producing more low-carbon hydrogen

In the face of climate change, low-carbon hydrogen is a promising alternative to fossil fuels to help enable the decarbonisation of industrial sectors. In 2020, global demand for hydrogen was approximately 90 million tonnes with important applications in fertilisers, oil refining and petrochemicals, transportation, steel production and electricity generation.

Hydrogen (H₂) is currently manufactured by combining water and carbon monoxide which creates hydrogen and a by-product of carbon dioxide. This reaction is called the water-gas shift process.

A concept known as sorption-enhanced water-gas shift (SEWGS) is regaining popularity as a way to increase hydrogen production, while simultaneously capturing carbon dioxide. Sorption is a physical and chemical process which includes both adsorption (where molecules from a liquid or gas adhere to the surface of a solid) and absorption (where molecules from a liquid or gas become incorporated into a solid).

Sorption-enhanced processes involve combining a sorbent with a catalyst so that the carbon dioxide is selectively taken up by the sorbent. This subsequently tricks the chemical reaction into producing more hydrogen.

According to Research Associate Dr David Danaci: “The concept of sorption-enhanced water-gas shift reactions (SEWGS) has been around for some time now, but recently, as there is growing interest for low-carbon hydrogen, it has remerged as a way to increase H₂ production while simultaneously capturing CO₂. This could result in an overall cheaper process for low-carbon hydrogen production.”

He added: “Improving the performance of the catalyst-sorbent combination is key to maximising performance and reducing costs, as this will result in smaller equipment and less energy input to produce a given amount of product.”

Dr Danaci’s work investigates different parts of the SEWGS process including producing new catalyst/sorbent combinations for better performance, investigating the impact of impurities in the feed gas on catalyst/sorbent performance and techno-economic analyses of the process.

Using sunlight to speed up reactions

Photocatalysis is a novel, sustainable process involving a catalyst that works by absorbing light.

Associate Researcher Dr Giulia Tarantino investigates the use of solid photocatalysts to produce fluorinated compounds. Fluorinated compounds are chemicals containing the element fluorine, with uses including agrochemicals, pharmaceuticals, polymers, Positron Emission Tomography (PET) imaging scans used to monitor metabolic processes, and as a detector for cancers.

Despite their widespread uses in the chemical industry, current methods for producing these molecules are still affected by poor sustainability and the high amounts of waste produced. One way to increase the sustainability of this chemical process is to use a catalyst that can be easily removed from the reaction mixture.

Dr Tarantino said: “My work demonstrates that solid photo-catalysts can be employed to efficiently synthesise these fluorinated compounds, representing a breakthrough toward the sustainable synthesis of fluorinated compounds.” 

Generating catalysts from unusual sources

Catalysts are most commonly based on metals, particularly precious metals like palladium or platinum. However, these can cause supply issues or be toxic in nature so are often problematic for human-related uses.

Therefore, finding alternative catalysts made from more abundant metals such as less toxic and costly iron and manganese is imperative.

Research Fellow Alain Li’s work focuses on the possibility of using waste material from the meat industry to create useful catalysts instead of metal mineral sources. Every year in the UK, around nine million tons of blood waste is produced which naturally contains iron, carbon and nitrogen that can be used to make catalysts.

These iron-based catalysts hold immense potential for chemical processes due to their inexpensive nature.

According to Li: “This research has the potential to allow sourcing metal-based catalysts from industrial waste, providing opportunities for a more sustainable and resilient chemical industry.” 

Paving the way for innovative solutions

The work of these researchers exemplifies the novel and innovative ways in which catalysts are being developed and used across the globe.

Together, chemical engineers like Dr Danaci, Dr Tarantino and Li use these unique and important chemical tools to help optimise industrial processes, tackling some of societies biggest challenges from climate change and improving healthcare, to catering for a growing population.