Single-atom catalysts gained a toehold

Studies showed isolated atoms on solids can serve as stable active catalysts

Mitch Jacoby

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When exposed to high temperature in air, platinum desorbs from nanocrystals as PtO2 (gray and red), and can be trapped on CeO2 (gold and red).
Credit: Abhaya Datye/U of New Mexico

Mediating chemical reactions with a single catalytically active atom on a solid surface has seemed like a good idea, albeit a fanciful one, for some time. This singular approach to catalysis gained traction this year as researchers in several countries demonstrated that such reactions are indeed feasible.

Tiny particles of a catalytic material—often a noble metal such as platinum—dispersed on a metal oxide or other solid support material are workhorses for industrial-scale chemical processes, including converting crude oil to valuable products such as gasoline. Compared with these conventional multiatom catalysts, single-atom versions would greatly reduce the consumption of costly and scarce precious metals. In addition, the atomic-scale uniformity would minimize unwanted reactions and by-products and simplify researchers’ efforts to deduce reaction mechanisms, a key step in making better catalysts.

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In another example of single-atom catalysis from 2011, single platinum atoms (yellow balls and three bright spots in background TEM image) on iron oxide (purple and gray) mediate conversion of CO to CO2.
Credit: Jun Li/Tsinghau U.

In one example this year, Abhaya K. Datye of the University of New Mexico and coworkers showed that exposing platinum nanoparticles to hot oxidizing conditions causes the metal to form volatile PtO2, which desorbs from the nanoparticles. The researchers trapped that mobile supply of platinum atoms on a nearby cerium oxide surface, forming a catalyst for CO oxidation, a key reaction in engine emission cleanup (Science 2016, DOI: 10.1126/science.aaf8800).

In another success, a group led by Tao Zhang, director of China’s Dalian Institute of Chemical Physics, developed a wet chemistry method for making single-atom cobalt catalysts. These catalysts, which avoid precious metals, can mediate hydrogenations and other reactions. But before now, detailed knowledge of the active sites in these catalysts has remained elusive, hampering their development. Zhang’s group determined that the active site in its catalyst consists of a cobalt atom bonded to four pyridinic nitrogen atoms in a graphitelike layer and capped with O2 molecules (Chem. Sci. 2016, DOI: 10.1039/c6sc02105k).

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