Better Platinum Reactivity Beckons

Figure 1. Professor Yong Wang and other researchers determined a way to keep platinum stable at high temperatures. Source: WSU

In effort to find ways to use less platinum in chemical reactions, a team of researchers at the University of New Mexico (UNM), Albuquerque, N.M., and Washington State University (WSU), Pullman, Wash., have developed a unique approach to trap platinum atoms. Their method improves reactivity and selectivity, as well as the efficiency and stability of reactions at high temperatures. It has many applications for clean energy systems that use the precious metal, they say.

Currently, at high temperatures, platinum atoms become mobile and fly together into clumps, which reduces catalyst efficiency and performance. The researchers devised a method to capture platinum atoms that keeps them stable and lets them continue catalysis.

“Precious metals are widely used in emission control, but there are always the issues of how to best utilize them and keep them stable,’’ says Yong Wang, professor at WSU’s school of chemical engineering and bioengineering. “You want to use as little as possible to achieve your objectives, but it’s normally hard to keep the atoms highly dispersed under working conditions.”

The team created a tiny, nanoscale trap using cerium oxide shaped into nanometer-sized rods and polyhedrons to capture the platinum atoms.

“When mixed with a platinum/aluminum oxide catalyst and aged in air at 800°C, the platinum transferred to the ceria and was trapped. Polyhedral ceria and nanorods were more effective than ceria cubes at anchoring the platinum. Performing synthesis at high temperatures ensures that only the most-stable binding sites are occupied, yielding a sinter-resistant, atomically dispersed catalyst,” the researchers wrote in an article published in Science.

“The atom-trapping technique should be broadly applicable for preparing single-atom catalysts,” notes Abhaya Datye, a professor of chemical and biological engineering at UNM who led the study. “It is remarkable that simply combining the ceria with a platinum catalyst was sufficient to allow trapping of the atoms and retaining the performance of the catalyst.

“Even more surprising is that the process of trapping occurs by heating the catalyst to high temperatures — precisely the conditions used for accelerated aging of these catalysts,” he adds.

The researcher say adding cerium oxide requires no exotic precursors and is a straightforward process.

“This work provides the guiding principles, so that industry can design catalysts to better utilize precious metals and keep them much more stable,’’ says Wang.

Wang isn’t sure when the catalyst will be available for commercial use. Commercial catalysts already use the same compositions, but not the supports with sufficiently large number of defect sites, he notes.

The team will address the challenge of scalable synthesis of support, as well as studying the catalyst’s susceptibility to poisoning in future work. “This is still [in] a fundamental research [stage]. The purpose is to provide the knowledge in designing the catalyst.”