Dissolved metals make effective catalysts

Liquid metals could be the long-awaited solution to ‘greening’ the chemical industry, according to researchers who have tested a new technique they hope can replace energy-intensive chemical engineering processes that hark back to the early 20th century.

Chemical production accounts for approximately 10–15% of total greenhouse gas emissions, while more than 10% of the world’s total energy is used in chemical factories.

Now, in a paper in Nature Nanotechnology, an Australian research team reports a much-needed innovation that moves away from old, energy-intensive catalysts made from solid materials. The research is led by Kourosh Kalantar-Zadeh, head of the University of Sydney’s School of Chemical and Biomolecular Engineering, and Junma Tang, who works jointly at the University of Sydney and UNSW.

A catalyst is a substance that makes chemical reactions occur faster and more easily without participating in the reaction. Solid catalysts – typically solid metals or solid compounds of metals – are commonly used in the chemical industry to make plastics, fertilizers, fuels and feedstock. But chemical production using solid catalysts is highly energy intensive, requiring temperatures of up to a 1000°C.

The new process instead uses liquid metals to dissolve tin and nickel, giving them unique mobility and allowing them to migrate to the surface of the liquid metals and react with input molecules such as canola oil. This results in the rotation, fragmentation and reassembly of the canola oil molecules into smaller organic chains, including propylene, a high-energy fuel crucial for many industries.

“Our method offers an unparalleled possibility to the chemical industry for reducing energy consumption and greening chemical reactions,” said Kalantar-Zadeh. “It’s expected that the chemical sector will account for more than 20% of emissions by 2050. But chemical manufacturing is much less visible than other sectors – a paradigm shift is vital.”

Atoms in liquid metals are more randomly arranged and have greater freedom of movement than in solids, making it easier form them to come into contact with chemical compounds and participate in chemical reactions. “Theoretically, they can catalyze chemicals at much lower temperatures – meaning they require far less energy,” explained Kalantar-Zadeh.

In their study, the researchers dissolved high-melting-point nickel and tin in a gallium-based liquid metal that has a melting point of just 30°C.

“By dissolving nickel in liquid gallium, we gained access to liquid nickel at very low temperatures – acting as a ‘super catalyst’,” said Tang. “In comparison, solid nickel’s melting point is 1455°C. The same effect, to a lesser degree, is also experienced for tin metal in liquid gallium.”

The metals were dispersed in liquid metal solvents at the atomic level. “So we have access to single atom catalysts,” said Arifur Rahim, a fellow in the University of Syndey’s School of Chemical and Biomolecular Engineering. “Single atom is the highest surface area accessibility for catalysis, which offer a remarkable advantage to the chemical industry.”

The researchers said their approach could also be used for other chemical reactions by mixing metals using the low-temperature process. “It requires such low temperature to catalyze that we could even theoretically do it in the kitchen with the gas cooktop – but don’t try that at home,” Tang said.

This story is adapted from material from the University of Sydney, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.