Platinum (Pt) nanoparticles can change shape while catalyzing a reaction, and the surface beneath them helps determine how that transformation unfolds.

A research team, led by Professor Kwangjin An of the School of Energy and Chemical Engineering at UNIST, together with Professor Jeong Woo Han's group at Seoul National University, found that different crystal facets of titanium dioxide (TiO₂) produce distinct Pt structures before and during carbon monoxide oxidation. The resulting differences at the Pt–TiO₂ interface have a pronounced effect on catalytic activity.

Pt is widely used in catalysts for applications ranging from emissions control to fuel cells. Because the metal is expensive, it is typically dispersed as nanoparticles on a support, whose surface structure can influence both particle shape and reactivity. 

The researchers examined Pt nanoparticles about 1.8 nanometers across on two facets of anatase TiO₂, known as (001) and (101). Despite their similar size, the particles took on markedly different shapes. On the (001) surface, Pt spread across the TiO₂ to form a relatively flat, hemispherical structure with a broad interface. On the (101) surface, it remained more compact and faceted.

The difference persisted as CO oxidation began. Pt on TiO₂(001) extensive retained contact with the support as its surface restructured during the reaction. On TiO₂(101), the particles developed a more ordered, cuboctahedral shape and maintained a more limited interface with the support.

The two structures also showed substantially different catalytic behavior. Under the conditions tested, the apparent activation energy for CO oxidation was 58.1 ± 0.3 kJ mol⁻¹ on the predominantly (001)-faceted catalyst, compared with 109.1 ± 1.5 kJ mol⁻¹ on its (101)-dominated counterpart.

The difference became more pronounced after the first reaction cycle. Across subsequent reaction cycles, its apparent activation energy fell by 22.7% to 25.6% relative to the first run, while the (101)-based catalyst changed little. The researchers traced this behavior to the interface that developed between Pt and TiO₂ during the reaction.

At that interface, oxygen from the TiO₂ lattice participates directly in converting CO to CO₂, leaving oxygen vacuums that must then be replenished. The broader interface formed on TiO₂(001) allows this oxygen cycle to proceed more readily. Calculations likewise found lower energy barriers for oxygen activation on the (001) surface throughout the reaction pathway.

To follow these changes, the researchers combined electron microscopy and X-ray spectroscopy with computational modeling. The experiments captured differences in Pt structure before and after reaction, while simulations reproduced the distinct particle shapes favored by the two TiO₂ facets. Density functional theory calculations then connected those structures to differences in reaction energetics.

“A catalyst may not be consumed by a reaction, but that does not mean its structure remains unchanged while it is working,” said Professor An. “Our results show that the surface supporting a metal nanoparticle can determine not only its initial structure, but also how that structure evolves during the reaction. Understanding these changes could help guide the design of catalysts that make more effective use of costly metals, such as platinum.”

Jihun Kim of UNIST and Yunkyung Kim of Seoul National University contributed equally as first authors. Sinmyung Yoon, Jeong Woo Han, and Kwangjin An served as corresponding authors. The study was published in August 2026 issue of Nature Communications , with support from the Ministry of Science and ICT (MSIT) and the National Research Foundation of Korea (NRF). 

Journal Reference

Jihun Kim, Yunkyung Kim, Daewon Oh,   et al. ,“TiO2-facet-dependent reconstruction of Pt nanoparticles during CO oxidation,”   Nat., Commun.,  (2026).