Ethylene is the first organic compound produced worldwide –about 100 million tonnes per year– and is the basis for many commonly used chemicals, such as polyethylene. Bags, toys or kitchen cling film are made of polyethylene. To obtain it, ethylene needs to be purified using a catalyst.

Purified ethylene is essential to prepare the compounds that follow it in the chemical value chain, such as polyethylene, the second most produced plastic in the world. This purification requires a catalyst to support the process, as raw ethylene contains 1% acetylene, which prevents polymerisation and must therefore be hydrogenated to ethylene. For this reason, the reaction must be kept in a very strict temperature range to avoid an unexpected temperature increase.

Ethylene purification is the world's second largest volume reaction in organic chemistry. Bags of all kinds, packaging, pipes are objects made of polyethylene, which accounts for about 15% of the nearly 400 million tonnes of plastics produced in 2021.

Thus, this project has developed a well-defined palladium catalyst, inserted in a solid metal-organic framework (MOF), which allows much better control of the temperature range of the reaction and stops any secondary reaction, allowing the reaction to be carried out under industrial conditions in a safer and more efficient way, avoiding the safety and cost problems associated with the current industrial process.

The new catalyst performs the entire purification process on a single palladium atom bonded to a single gold atom, which modifies the activity of the palladium to make it more efficient and selective and thus able to work in a temperature range of almost 100 degrees Celsius, compared to 50 degrees Celsius for current catalysts. In addition, due to the small pore size of the MOF, unwanted acetylene polymerisation processes are controlled.

According to the team, the new catalyst could be used in industrial plants for ethylene purification once the scale-up of the synthesis of the material is developed.

The work, recently published in the journal Nature Catalysis, involves the Institute for Molecular Science (ICMOL) of the UV, the Institute for Chemical Technology (ITQ), the University of Cádiz, the CELLS-ALBA synchrotron and the University of Calabria (Italy).

The new catalyst, which has been patented, describes the synthesis of the new MOF material and its excellent catalytic activity in the reaction of acetylene hydrogenation in ethylene streams. The co-ownership of this patent corresponds to the Universitat de València, the CSIC and the UPV, in an example of collaboration between different research institutions.

Reference:

Ballesteros-Soberanas, J., Martín, N., Bacic, M., Tiburcio, E., Mon, M., Hernandez-Garrido, J. C., Marini, C., Boronat, M., Ferrando-Soria, J., Armentano, D., Pardo, E. & Leyva-Pérez A. A MOF-supported Pd1-Au1 dimer catalyses the semi-hydrogenation reaction of acetylene in ethylene with a nearly barrier-less activation energy. Nature Catalysis. https://www.nature.com/articles/s41929-024-01130-7

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