New process points to cheaper way to clean up car exhaust

Catalytic converters could become smaller, cheaper and more fuel-efficient thanks to a new manufacturing process developed at Imperial College London.

Conventional converters use a catalyst typically made from precious metals to convert toxic pollutants from car exhaust fumes into less harmful gases.

Engineers at Imperial have produced a new converter design, made possible by a novel manufacturing process, that cuts the amount of expensive catalyst needed and could also reduce how much energy is used to pass the exhaust through the converter.

Dr Ben Kingsbury, who invented the new converter, said he estimated the design would cut the size of the hollow ceramic block that forms the substrate for the catalyst by around half.

‘In modern cars space really is at a premium and if you can reduce the size of the substrate that is very interesting,’ he told The Engineer.

The catalyst is spread over the internal surface of a number of hollow tubes inside the ceramic block. Using a method in which the ceramic molecules self-assemble into a novel structure, the researchers were able to effectively create micro channels along the inside of the tubes, simultaneously increasing their surface area and reducing the thickness of the catalyst layer.

They claim this reduces the amount of catalyst needed by up to 80 per cent and increases the amount of exhaust that can be detoxified at any one time – meaning the overall size of the device can be reduced.

The structure’s greater surface area also means the tubes themselves can be larger, reducing the pressure within the converter and so cutting the amount of energy it drains from the engine.

Kingsbury said the new design could reduce the pressure by 40 to 70 per cent compared to existing models, leading to a fuel saving of 2 to 3 per cent.

The manufacturing process was developed from a system created by Kingsbury’s colleagues at Imperial originally design to produce polymer membranes but that has also been used to create novel fuel-cell structures.

Described as a ‘phase inversion and sintering process’, the manufacturing technique involves mixing the ceramic material with a solvent and a polymer binder to create a suspension liquid.

This is extruded into a water bath, causing the polymer to precipitate out of the suspension and leaving behind a solid ceramic material whose molecules self-assemble into the desired structure.

The challenge for the researchers was quantifying how the different parameters of the process affected the final product in order to be able to design specific structures.

They have now created a spinout firm, Microtech Ceramics, and plan to scale up the technology in order to license it to automotive manufacturers, helped by an Enterprise Fellowship grant from the Royal Academy of Engineering.

This will involve demonstrating the durability of the new design and how it can be integrated with the rest of the exhaust system.