An interesting article has just come out on a liquid metal platinum/gallium solution catalyst composition showing substantially greater activity. The article reference is: Rahim, M.A., Tang, J., Christofferson, A.J. et al. Low-temperature liquid platinum catalyst. Nat. Chem. (2022). https://doi.org/10.1038/s41557-022-00965-6. The publisher charges for a download of the article. I didn’t shell out $32 for a copy so all I’ve seen is the abstract.

Being in chemical manufacturing, I can say that Platinum Group Metal (PGM) catalysts can represent a significant raw material cost in manufacturing even though it is used in “catalytic quantities”. Low catalyst loading is always desirable because of cost, but the trade-off is longer reaction time and/or higher pressure and temperature. Production scale high pressure vessels may not be available at organizations that do little high pressure work. At some point catalyst cost savings are canceled out by extended production time or more severe conditions. Fishing out catalyst from filter cake and preparing it for reuse can be time consuming and costly and may not be worthwhile.

Some PGM catalysts can even ignite a combustible atmosphere and also provide a dust hazard to workers. Extra handling is problematic. Most bulk suppliers take PGM waste back from their customers for recycle.

What has captured everyone’s attention about this gallium/platinum composition is the enhanced reaction rates reported for the electrochemical oxidation of methanol. Rahim et al. report a rate enhancement of “three orders of magnitude” over solid platinum catalysts at temperatures between 318 – 343 Kelvin.

The authors state that the Ga/Pt liquid catalyst mixture contains atomically dispersed Pt atoms within the gallium matrix. The mixture is prepared by simply contacting solid platinum pellets with liquid gallium to make a solution. Ideally, solid catalyst particles should be as small as possible to minimize the unfavorable surface to volume ratio. Solid platinum or other PGM catalysts are only active at the surface. The Pt/Ga mixture provides highly active atomic platinum at the liquid surface where presumably the chemistry happens.

In my experience with gallium, I’ve noticed that the metal will wet some surfaces like glass and plastic. Perhaps the gallium film on glass I saw is only an oxide layer- I don’t know. But it would seem that maximizing the availability of platinum atoms over a larger surface would be a good next step for even better efficiency.