Research Highlights

An AIMR-led research team has combined the use of an organic modifier with supercritical hydrothermal treatment techniques to design a strategy for regenerating facetted nanocatalysts¹. The team demonstrates this strategy by regenerating degraded cubic ceria (CeO₂) nanoparticles back to their original cubic shape.

All heterogeneous catalysts degrade over time: poisoned by chemicals, fouled by carbon deposits, sintered by heat and pressure, or eroded by wear and tear. For this reason, the design of new catalysts often includes catalyst regeneration, aiming for regeneration methods that are clean, easy, and cheap.

However, while conventional regeneration approaches can ameliorate the above degradation mechanisms, they cannot address a mechanism particular to nanocatalysts—degradation through changes in surface facets.

Here, the AIMR research team designs a regeneration approach aimed at reorienting active surface facets through partial dissolution-reprecipitation with a facet-selective organic modifier under supercritical hydrothermal conditions.

“CeO₂ nanoparticles are unique in that their shapes, exposed facets, and size distributions are controlled using carboxylic acids,” says Takaaki Tomai, first author of the research. “To regenerate the (100) facet of the nanocatalyst, we use the decanoic acid surface modifier to control the exposed facet, and the formation of a Ce organometallic complex to promote dissolution in supercritical water.”

Monitoring the particle size, shape, and catalytic activity by transmission-electron microscopy (TEM) and by oxygen storage capacity measurements, the team uses non-cubic CeO₂ nanoparticles to determine the optimum conditions for cubic-nanoparticle regeneration. The team then demonstrate the approach by degrading pristine cubic CeO₂ nanoparticles in air and restoring the cubic shapes to these same particles.

“Because our design involves complex particle-to-modifier interactions through partial dissolution and re-precipitation, none of us were sure whether it was going to work,” says Tomai. “We were very excited to see the cubic shapes on the first TEM images of the regenerated nanoparticles.”

Future directions will develop this simple nanocatalyst recycling approach to target several of the United Nations’ 17 Sustainable Development Goals², including clean water and sanitation, affordable and clean energy, responsible consumption and production, and conservation of life below water.

(Author: Patrick Han)