Scientists have discovered a way to reduce the cost of platinum as a catalyst by converting it to a low-temperature liquid.
Noble metals such as platinum, gold, ruthenium, and palladium have long been recognized to be effective catalysts for chemical processes because they break chemical bonds between atoms more efficiently than other metals.
Due to the rarity and high cost of noble metals, large-scale industrial firms typically choose for less expensive, less effective alternatives such as iron. (For example, iron is utilized as a catalyst in the bulk manufacture of fertilizer.)
Chemical reactions must be heated to high temperatures when utilizing lower-quality catalysts, which increases the carbon footprint of many industrial operations.
Researchers from UNSW Sydney and RMIT in Australia have broken a world record by dissolving platinum in liquid gallium and dividing the platinum atoms apart, resulting in higher catalytic potential in a smaller amount of platinum.
Platinum has a melting temperature of 1,700 degrees Celsius (3,092 degrees Fahrenheit), hence it is generally a solid when employed as a catalyst.
It adapts the melting point of gallium – a soft, silvery, non-toxic metal that melts essentially at ambient temperature of 29.8 °C – by infusing platinum into a gallium matrix. One important property of liquid gallium is that it dissolves metals by separating the constituent atoms in each molecule, similar to how water dissolves salt and sugar.
According to the researchers, the concept has the potential to reduce energy expenditures and emissions in industrial manufacturing.
"A range of important chemical reactions could be performed at relatively low temperature with the use of a more efficient catalyst like liquid platinum," lead author and chemical engineer Md. Arifur Rahim of UNSW Sydney told.
Since 2011, scientists have been attempting to reduce the cost of pricey noble metal catalysts using a method known as "miniaturization," according to Rahim.
Only the atoms on the exterior of metals may be employed in reactions when they are solid, therefore there is a lot of waste. You obtain a more efficient reaction if you break this solid down into smaller and smaller clumps (think nanoparticles) because more metal atoms can muscle in — many hands make light work.
Each every atom would be accessible to conduct the task of a catalyst in the most efficient and tiny system.
"When you miniaturize the system, you're maximizing the surface-to-volume ratio and the atom utilization efficiency so that your overall consumption of the catalyst is smaller over time, and that can possibly make your product affordable," Rahim explains.
"Theoretically, you get the maximum efficiency of that catalytic metal when it is at the atomic scale, because you cannot go beyond that."
The bonds that keep the catalyst together are broken in single-atom catalysts, and each atom is separately anchored in a material called a matrix.
As a result, Rahim and his colleagues experimented using gallium as a matrix. They discovered that when platinum was dissolved in gallium, every platinum atom was divided from every other platinum atom, resulting in a perfect tiny catalyst.
"When dissolved, platinum atoms are spatially dispersed in the liquid gallium matrix without atomic clustering (i.e., the absence of platinum-platinum bonding) that can drive different catalytic reactions with remarkable mass activity," the researchers write in their publication.
When platinum is in a liquid matrix, it is far less prone to the problem of coking, which occurs when solid catalysts become coated with carbon and must be cleaned before being reused.
Gallium is more expensive than iron. It can, however, be used again for the same effects. Gallium, like platinum, does not get deactivated or degraded during the process.
The temperature must be raised to around 400 °C for a few hours to dissolve platinum in gallium. However, the researchers claim that it is a one-time energy input that prevents future temperature rises later in the chemical synthesis process.
From fertilizer to green fuel cells, the team thinks that their method will lead to considerably cleaner and cheaper products.
