Scientists have discovered how to make platinum more affordable as a catalyst: turning it into a liquid at low temperature.
It has been known for centuries that noble metals such as platinum, gold, ruthenium and palladium are excellent catalysts for chemical reactions, because they help to break the chemical bonds between atoms more efficiently than other metals.
But noble metals are rare and expensive, so large-scale industrial manufacturers often opt for cheaper and less effective alternatives such as iron. (Iron is used as a catalyst in the mass production of fertilizers, for example).
The disadvantage of using lower quality catalysts is that the chemical reactions have to be heated to high temperatures, which increases the carbon footprint of many industrial processes.
In a record achievement, researchers at UNSW Sydney and RMIT in Australia dissolved platinum into liquid gallium, splitting the platinum atoms so that there was more catalytic potential in a smaller amount of platinum.
Platinum typically has a melting point of 1,700 ° C (3,092 Fahrenheit), which means that it is usually a solid when used as a catalyst.
By infusing platinum into a gallium matrix, it adopts the melting point of gallium, a soft, silvery, non-toxic metal that basically melts at an ambient temperature of 29.8 ° C. A useful feature of liquid gallium is that it dissolves metals (such as water dissolves salt and sugar) by separating the individual atoms of each molecule.
According to researchers, the invention has the potential to save energy costs and reduce emissions in industrial manufacturing.
“A number of important chemical reactions could be performed at a relatively low temperature with the use of a more efficient catalyst such as liquid platinum,” lead author and chemical engineer Md told ScienceAlert. Arifur Rahim of UNSW Sydney.
Scientists have been trying to make expensive noble metal catalysts more affordable through a process of “miniaturization” since 2011, Rahim explains.
When metals are solid, only the atoms on the outside can be used in the reactions, so there is a lot of waste. If you break down this solid into smaller and smaller groups (think of nanoparticles), you will get a more efficient reaction, as more metal atoms can be muscles: many hands do a light job.
The most efficient and small system would make each individual atom available to do the work of a catalyst.
“When you miniaturize the system, you maximize the surface-to-volume ratio and efficiency of use of the atom so that your overall catalyst consumption is lower over time, and this can possibly make your product affordable.” , says Rahim.
“Theoretically, you get the most efficiency out of this catalytic metal when it’s on an atomic scale, because you can’t go any further.”
In single-atom catalysts, the bonds that hold the catalyst together are split and each atom is individually anchored in a substance called a matrix.
Therefore, Rahim and his colleagues tested the gallium as a matrix. Once dissolved in gallium, they found that all the platinum atoms split from all the other platinum atoms, making it a perfect miniature catalyst.
“When dissolved, platinum atoms disperse spatially into the liquid gallium matrix without atomic clusters (i.e., the absence of a platinum-platinum bond) that can drive different catalytic reactions with remarkable mass activity. “, write the researchers in their article.
Platinum is mobile when in a liquid matrix, and much less prone to the problem of firing, where solid catalysts are covered in carbon and must be cleaned before they can be reused.
Gallium is not as cheap as iron. But it can be used over and over again for the same reactions. This is because, like platinum, gallium is not deactivated or degraded during the reaction.
The process of dissolving platinum in gallium requires raising the temperature to about 400 ° C for a few hours. But it is a unique energy investment that saves more temperature rises later in the chemical manufacturing process, the researchers say.
The team expects their technique to lead to much cleaner, cheaper products, from fertilizers to green fuel cells.
The study was published in the journal Nature Chemistry.